The Arctic is experiencing a faster warming, known as the Arctic amplification, but climate projections are still uncertain due to the aerosol-cloud interactions (ACI). The impact of aerosols on glaciation temperature, acting as ice nucleating particles, is poorly understood, especially for aerosols from long-range transport. During transport, physico-chemical properties of aerosols evolve due to aging, complicating the quantification of their role.
This study considers satellite observations from POLDER and MODIS instruments with atmospheric chemistry model (GEOS-Chem) and reanalysis datasets (ERA5) to investigate the influence of aerosols on cloud properties and glaciation temperatures. Carbon monoxide (CO) is employed as a passive tracer to aerosols from combustion sources. GEOS-Chem is used to distinguish between biomass burning (BB) and anthropogenic (ANT) emissions and further identify the source regions of air parcels. Spatial and temporal co-localization of cloud, aerosol, and environmental parameter datasets is performed to assess the interplay between meteorological parameters and aerosol properties on cloud properties and on the glaciation process.
Our analysis reveals distinct impacts of aerosols from BB and ANT sources on the glaciation temperature. Preliminary results indicate that pollution plumes from BB are associated with an increase or decrease of about 1.7°C of the glaciation temperature depending on the source region, while ANT pollution plumes suggest an increase of the glaciation temperature between 1.5°C and 2.8°C depending on the transport of air parcels before interacting with the clouds. This work highlights the necessity of considering transport-induced changes in aerosol properties to improve our understanding of the ACI and Arctic climate dynamics.
How to cite: Coopman, Q. and Riedi, J.: Understanding the Impact of Aerosol Transport on the cloud glaciation temperature in the Arctic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9656, https://doi.org/10.5194/egusphere-egu25-9656, 2025.
For most regions of the world, the availability of mineral dust particles drives the production of primary ice in mixed-phase clouds. The mineral dust acts as an ice nucleating particle (INP), which facilitates the freezing of supercooled cloud droplets at higher temperatures than in its absence (~ -38C). Mixed-phase clouds are ubiquitous in the polar regions, but are far from the world’s primary sources of dust emissions in the tropics and subtropics. Secondary sources from high-latitude sources exist but do not fully explain observations of relatively high INP concentrations during the full annual cycle.
In this study we identify a previously overlooked source of low-latitude dust: those from long-lived dusts in smaller size modes that have been in the atmosphere for up to 5 months. Using simulations of the UK Earth System Model (UKESM), we find that although fresh dust contributes most of the dust mass in the polar regions, the INP contribution is weighted towards the older dust particles. In some regions, dust older than 90 days contributes over 50% of the total dust-sourced INP concentration. This occurs due to changes in the dust population size distribution, and has important implications. Close to primary dust sources, the INP concentration is dependent on the super-micron particles, whereas far from the source (i.e. the polar regions and remote oceans) the INP concentration is dependent on the smaller, older, sub-micron particles.
How to cite: Herbert, R., Arnold, S., Murray, B., and Carslaw, K.: Long lived dusts from low latitudes may dominate primary ice production in polar regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17097, https://doi.org/10.5194/egusphere-egu25-17097, 2025.
Low-level mixed-phase clouds (LLMPCs) containing both ice and supercooled liquid water are ubiquitous in the Arctic and play a crucial role for radiative fluxes. Mixed-phase clouds are inherently instable due to the competition over water between ice crystals and liquid droplets. The persistence of LLMPCs in the Arctic is challenging to reproduce in models, which affects predictions of the energy budget. These challenges stem from current uncertainties related to the complex web of interactions between aerosol particles, cloud microphysics, atmospheric (thermo-)dynamics and surface processes. These uncertainties can be partly attributed to the scarcity of detailed observations of aerosol characteristics and cloud microphysical properties as well as their interactions within clouds.
LLMPCs highly depend on the presence of aerosol particles acting as cloud condensation nuclei (CCN) or ice nucleating particles (INPs). In the Arctic, where aerosol concentrations can be very low, small changes in aerosol properties (e.g., size, chemical composition, hygroscopicity) can significantly impact the radiative properties and lifetime of LLMPCs. Accurate knowledge of aerosol characteristics at cloud level and their influence on cloud properties is crucial for improving the representation of clouds and their radiative behavior.
To address the need for more observations of aerosols and cloud properties at cloud level, a tethered-balloon equipped with the Modular Multiplatform Compatible Air Measurements System (MoMuCAMS) was deployed from the Swedish icebreaker Oden during the Atmospheric River and onset of sea ice melt (ARTofMELT) expedition. The expedition took place in the Fram Strait during the transition from spring to summer (May – June) in 2023. In total, 23 flights up to 645 m above mean sea level were performed, collecting unique and detailed measurements of aerosol and cloud droplet size distributions from 8 nm to 50 µm, below, inside and above LLMPCs. A key aspect addressed with the measurements is how boundary layer and free tropospheric aerosols contribute to the formation of clouds.
Results from of a case study examining the data collected from three consecutive flights through a single cloud layer located between roughly 150 and 350 meters above the surface will be presented. A combination of in situ vertical and surface-based measurements with remote sensing data and modeling studies is used to understand to what extent aerosols from below and above the cloud contribute to the formation of cloud droplets. Results indicate that the cloud is coupled to the surface and profiles of particle number size distributions show a homogenous distribution between the surface and the cloud. A comparison between estimated CCN concentrations below and above the cloud and observed cloud droplet number concentrations suggests however, that entrainment of aerosol from the free troposphere is needed to produce the amount of droplets observed.
These observations suggest that also when clouds are coupled to the surface, a different and significant source of CCN and INPs can feed the cloud from above, which is then not observable from surface-based measurements. This can have important implications for the representation of cloud microphysical and radiative properties based solely on surface-based observations.
How to cite: Pohorsky, R., Calmer, R., Dönmez, B., Brooks, I., Guy, H., Haberstock, L., Kojoj, J., Fauré, N., Murto, S., Mavis, C., Creamean, J., Tjernström, M., Zieger, P., and Schmale, J.: Influence of free tropospheric aerosols on the microphysical properties of a coupled low-level cloud in the central Arctic: a case study from the ARTofMELT expedition. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19436, https://doi.org/10.5194/egusphere-egu25-19436, 2025.
In recent years, there has been a breakthrough in the identification and description of various secondary ice production (SIP) mechanisms that affect mixed-phase clouds. However, SIP is in general not described well in climate and mesoscale models, which leads to notable biases in the representation of warm mixed-phase clouds in terms of ice content, ice number concentration and cloud structure. In this study, the Integrated Community Limited Area Modelling System (ICLAMS) has been utilized to examine the formation and evolution of wintertime orographic clouds over Mt. Helmos, Greece. ICLAMS is a special version of the Regional Atmospheric Modelling System (RAMS). In addition to the Hallett-Mossop process, already included in the model, two additional SIP mechanisms are implemented, a) collisional break-up of ice particles and b) droplet shattering. Model results are evaluated against in-situ and remote sensing observations collected during the CleanCloud CHOPIN campaign (https://go.epfl.ch/chopin-campaign) at Mt. Helmos in the Peloponnese, Greece during Fall 2024 to Spring 2025. Remote sensing (wind lidar and cloud radar) data are used to evaluate model performance, through the application of forward operators (cloud radar simulator) and comparison with radar reflectivity and turbulence parameters. The mesoscale model simulations indicate that SIP enhances aggregation and results in clouds with increased ice crystal number concentrations, aligning more closely with observed distributions. Among the SIP mechanisms, collisional break-up is identified as the dominant contributor to simulated SIP rates, underscoring its critical role in accurately representing orographic mixed-phase clouds.
How to cite: Chaniotis, I., Georgakaki, P., Patlakas, P., Foskinis, R., Clerx, N., Molina, C., Gini, M., Zieger, P., Eleftheriadis, K., Berne, A., Papayannis, A., Komppula, M., Flocas, H., and Nenes, A.: Investigating Secondary Ice Production effects on wintertime orographic clouds using the Regional Atmospheric Modelling System (RAMS), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17259, https://doi.org/10.5194/egusphere-egu25-17259, 2025.
The partitioning between liquid- and ice-phase cloud water content can have a substantial impact on the cloud’s radiative effect and on precipitation. This partitioning is expected to change on average with global warming due to warmer temperatures, more atmospheric moisture, and different cloud nucleating particle distributions, which then feed back into the changing climate. Changes in mixed phase clouds (MPCs) are difficult to predict due to the complexity of microphysical processes that determine cloud phase partitioning and the uncertainty of future aerosol emissions, both natural and anthropogenic. The characteristics of MPCs are particularly sensitive to the availability of ice-nucleating particles (INPs), which are generally few in number relative to overall aerosol concentrations. Primary bioaerosol emissions are understood to be important to INP availability, making these aerosols and the processes affecting them critical to understanding how clouds and precipitation might change with global warming and with different anthropogenic emissions.
The CleanCloud project under which this research is conducted targets these aerosols and MPCs in order to improve our understanding and climate predictions of a post-aerosol drawdown and warmer world with different natural aerosol sources. We present preliminary observations from the CleanCloud Helmos Orographic SIte Experiment (CHOPIN) campaign targeting primary bioaerosols at the Helmos Hellenic Atmospheric Aerosol Climate Change Station (HAC2) on Mount Helmos in the Peloponnese peninsula, southern Greece, carried out between October 2024 and April 2025. At an altitude of 2314 m, atmospheric conditions at HAC2 are at times within the planetary boundary layer and otherwise more representative of the free troposphere. During wintertime at this altitude, MPCs can be frequently observed at HAC2. We employed a ground-based counterflow virtual impactor (GCVI; Brechtel Industries) in order to sample clouds and observe cloud residuals using a multiparameter bioaerosol spectrometer (MBS; CAIR, University of Herefordshire), scanning electrical mobility spectrometer (SEMS; Brechtel Industries), and a portable ice nucleation experiment (PINE; EPFL). Samples were also taken for offline analysis with transmission electron microscopy (TEM; MRI-JMA).
We present a preliminary overview of fluorescent primary bioaerosol particle (fPBAP) measurements at HAC2 in both cloud residuals and whole air as part of the CHOPIN campaign. We relate these to observed INP concentrations measured by the PINE, and to cloud properties measured by a fog monitor (FM120; DMT, Inc.) and a ground-based fog and aerosol sensor (GFAS; DMT, Inc.).
How to cite: Jönsson, A., Zieger, P., Eleftheriadis, K., Gini, M., Kawana, K., Nenes, A., Molina, C., Fetfatzis, P., Foskinis, R., Asplund, J., Haberstock, L., and Adachi, K.: Fluorescent primary bioaerosol particle measurements in mixed phase cloud residuals at Mount Helmos, Greece, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19341, https://doi.org/10.5194/egusphere-egu25-19341, 2025.
Surface-active organics lower the aerosol surface tension (σs/a), leading to enhanced cloud condensation nuclei (CCN) activity and potentially exerting impacts on the climate. Quantification of σs/a is mainly limited to laboratory or modeling work for particles with selected sizes and known chemical compositions. Inferred values from ambient aerosol populations are deficient. In this study, we propose a new method to derive σs/a by combining field measurements made at an urban site in northern China with the κ-Köhler theory. The results present new evidence that organics remarkably lower the surface tension of aerosols in a polluted atmosphere. Particles sized around 40 nm have an averaged σs/a of 53.8 mN m-1, while particles sized up to 100 nm show σs/a values approaching that of pure water. The dependence curve of σs/a with the organic mass resembles the behavior of dicarboxylic acids, suggesting their critical role in reducing the surface tension. The study further reveals that neglecting the σs/a lowering effect would result in lowered ultrafine CCN (diameter < 100 nm) concentrations by 6.8% to 42.1% at a typical range of supersaturations in clouds, demonstrating the significant impact of surface tension on the CCN concentrations of urban aerosols.
How to cite: Fan, T., Ren, J., Liu, C., Li, Z., Liu, J., Sun, Y., Wang, Y., Jin, X., and Zhang, F.: Surface-tension lowering of aerosols by organics in urban atmospheres: implication to cloud condensation nuclei prediction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2203, https://doi.org/10.5194/egusphere-egu25-2203, 2025.
Surface solar irradiance variability is present under all broken clouds, but the patterns, magnitude of variability, and mechanisms behind it vary greatly with cloud type. Most radiative transfer models do not resolve the observed variability, primarily due to limiting radiative transport to two streams (up and down) to save computation time. From observations, we selected a diverse set of surface solar irradiance patterns under various cloud types and modelled these cloud types in combination with a Monte Carlo ray tracer for accurate 3D radiative transfer. Stratus, altocumulus, and cumulus growing into cumulonimbus are among the studied cloud types. The goal of these experiments is to understand through which mechanisms various cloud types generate observed patterns of irradiance variability.
The results show that we can capture the essence in four mechanisms. We find that for optically thin (optical thickness < 6) clouds, scattering in the forward direction dominates. In cloud fields with enough optically thin area, such as altocumulus, "forward escape" alone can drive areas of irradiance enhancement of over 50 % of clear-sky irradiance. For flat, optically thick clouds (optical thickness > 6), irradiance is instead scattered diffusely downward ("downward escape"), and (extreme) enhancements are thus found directly below the cloud rather than in the direction along the solar angle. For vertically structured clouds, "side escape" dominates domain-averaged diffuse irradiance enhancement until anvil clouds form and start shading the updraft. Lastly, under optically thick cloud cover, surface albedo enhances downward radiative fluxes due to multiple scattering between surface and cloud. This both brightens shadows and contributes 10 to 60 % of the total irradiance enhancement in sunlit areas for respectively low (0.2) to high (0.8) albedo.
With these four mechanisms, we provide a framework for understanding the vast diversity and complexity found in surface solar irradiance and cloudiness. Such a framework can guide the development of parameterizations that capture 3D solar irradiance effect at a fraction of the computational cost of 3D radiative transfer models, for example.
How to cite: Mol, W. and van Heerwaarden, C.: Mechanisms of surface solar irradiance variability under broken clouds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8614, https://doi.org/10.5194/egusphere-egu25-8614, 2025.
Accurately estimating cloud microphysics is crucial for reducing uncertainties in weather and climate models. A particular challenge is capturing the interactions between the cloud microphysics and turbulence. The pervasive shallow cumulus clouds over tropical oceans play a critical role in the Earth’s energy budget, making their study crucial for understanding atmospheric dynamics. In this context, the EUREC4A field campaign, conducted over the Atlantic Ocean close to Barbados from January to February 2020, gathered approximately 200 hours of unique observational data from these clouds [1]. The data was collected by two Max Planck CloudKites deployed from ships. A subset of this data includes Particle Image Velocimetry (PIV) and holographic measurements taken within clouds, providing unique insight into cloud dynamics. To our knowledge, our data represent the first application of airborne PIV in atmospheric clouds and provide an unprecedented opportunity to link cloud turbulence and microphysics.
In this study, we explore the feasibility and accuracy of estimating high-resolution turbulence energy dissipation rates within clouds based on the PIV data. We used the approximate 100k PIV image pairs from both precipitating and non-precipitating clouds collected during the EUREC4A campaign. We employed several established dissipation rate estimating methods, including the second-order structure function method [2] and the 2D gradient method used in the field of planar PIV [3, 4]. The turbulence energy dissipation rate across different cloud types (or flight segments) observed during the campaign is computed.
In addition, we have performed a detailed comparative analysis of the dissipation rate estimated with different techniques, including a 1- and 3-dimensional pitot tube. We also investigate the two-dimensional spatial distribution of cloud droplets and its correlation with turbulence features. We believe that these findings will improve our understanding of turbulence in shallow cumulus clouds and its impact on their formation and evolution.
References
[1] Bony, S., Stevens, B., Ament, F., Bigorre, S., Chazette, P., Crewell, S., ... & Wirth, M. EUREC 4 A: A field campaign to elucidate the couplings between clouds, convection and circulation., Surveys in Geophysics, 38, 1529–1568 (2017).
[2] Schröder, M., Bätge, T., Bodenschatz, E., Wilczek, M., & Bagheri, G. Estimating the turbulent kinetic energy dissipation rate from one-dimensional velocity measurements in time., Atmospheric Measurement Techniques, 17, 2, 627-657 (2024).
[3] Tanaka, T. & Eaton, J. K. A correction method for measuring turbulence kinetic energy dissipation rate by PIV: Validated by random Oseen vortices synthetic image test., Experiments in Fluids, 42, 6, 893-902 (2007).
[4] Verwey, C., & Birouk, M. Dissipation rate estimation in a highly turbulent isotropic flow using 2D-PIV. Flow., Turbulence and Combustion, 109, 3, 647-665 (2022).
How to cite: Kim, Y., Bodenschatz, E., and Bagheri, G.: Estimation of turbulence dissipation rate within shallow cumulus using airborne Particle Image Velocimetry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7034, https://doi.org/10.5194/egusphere-egu25-7034, 2025.
Cloud droplet temperature is an important parameter influencing cloud microphysical and radiative processes. The supercooled droplet temperature and lifetime impact cloud ice and precipitation formation via homogeneous freezing and activation of ice-nucleating particles through contact and immersion freezing. While most observational and modeling studies often assume droplet temperature to be almost equal to the ambient temperature (Ta), this assumption may not always be valid, particularly when droplets experience strong relative humidity (RH) gradients at cloud boundaries.
This study investigates the evolution of temperature and lifetime of evaporating, supercooled cloud droplets considering initial droplet radius (r0) and temperature (Tr0), and environmental relative humidity (RH), ambient temperature (Ta), and pressure (P). The time (tss) required by droplets to reach a lower steady-state temperature (Tss) after sudden introduction into a new subsaturated environment, the magnitude of ΔT = Ta - Tss, and droplet survival time (tst) at Tss are calculated. The temperature difference (ΔT) is found to increase with Ta, and decrease with RH and P. ΔT values are typically 1–5 K lower than Ta, with highest values (~10.3 K) for very low RH, low P, and Ta closer to 0°C. Results show that tss is < 0.5 s over the range of initial droplet and environmental conditions considered. Tss of the evaporating droplets can be approximated by the environmental thermodynamic wet-bulb temperature. Radiation was found to play a minor role in influencing droplet temperatures, except for larger droplets in environments close to saturation. The implications for ice nucleation in cloud-top generating cells and near cloud edges are discussed. Using Tss instead of Ta in widely used parameterization schemes could lead to enhanced number concentrations of activated ice-nucleating particles (INPs), by a typical factor of 2–30, with the greatest increases (>100) coincident with low RH, low P, and Ta closer to 0°C. The findings corroborate the hypothesized mechanism of potential enhancement of ice nucleation at cloud boundaries, such as cloud-top generating cells and for ambient temperatures close to 0°C. The importance of using accurate droplet temperatures to improve existing primary ice nucleation parameterization schemes, especially in sub-saturated environments, is highlighted.
The impacts of droplet evaporative cooling on droplet lifetimes are compared with Maxwellian pure diffusion-limited evaporation approach under similar conditions. For higher RH and larger droplets, droplet lifetimes can increase by more than 100 s compared to those with droplet cooling ignored. Larger droplets (r0 ~ 30–50 µm) can survive at Tss for about 5 s to over 10 min, depending on the subsaturation of the environment. The impacts of droplet evaporative cooling on evolution of drop size distributions, using high-resolution direct numerical simulations of moderately supercooled mixed-phase cloud boundaries, are discussed.
How to cite: Roy, P., Rauber, R. M., Di Girolamo, L., Chen, S., Xue, L., and Tessendorf, S. A.: Can evaporative cooling of water droplets play a role in enhancing ice formation at moderately supercooled cloud boundaries?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14843, https://doi.org/10.5194/egusphere-egu25-14843, 2025.
Aerosol-cloud interactions remain one of the largest uncertainties in quantifying anthropogenic impacts on climate, particularly through their influence on cloud liquid water path (LWP), cloud droplet number concentration (CDNC), and cloud susceptibility to aerosol perturbations. This presentation synthesizes insights from satellite observations, large-eddy simulations, global climate models, long-term in-situ observations, and advanced statistical analyses to address biases and uncertainties in these interactions. Satellite-based studies often report a decreasing LWP with increasing CDNC, yet retrieval errors and natural spatial variability can mask positive LWP adjustments, leading to an underestimation of the cooling effects of aerosol-cloud interactions. Large-eddy simulations of marine stratocumulus clouds reveal that assumptions of adiabaticity and spatial variability in cloud properties contribute to biases in satellite-derived LWP-CDNC relationships. However, with careful case selection and well-defined meteorological conditions, satellite-based estimations can be improved. Building on these findings, global climate modeling and machine learning analyses highlight the importance of updraft velocity and aerosol size distributions in shaping the CCN-CDNC relationship. Advanced methods such as Elastic Net Regression isolate these confounding factors, refining susceptibility estimates and enhancing consistency with physical expectations. Further, long-term in-situ observations of aerosols and clouds at high-latitude locations reveal that the susceptibility of CDNC to CCN is significantly higher for low-level stratiform clouds than suggested by global oceanic satellite data. This implies stronger aerosol radiative forcing than current satellite-based estimates assume. Comparisons with Earth system models reveal large inter-model variability in susceptibility, driven by differences in sub-grid scale updraft velocities and aerosol size distributions. Even models with relatively accurate susceptibility values exhibit unrealistic underlying physics, highlighting areas for improvement in model representation. Lastly, combining satellite, reanalysis, and in-situ ACTRIS observations, we evaluate the roles of aerosol size distributions and updrafts in warm cloud formation, bridging gaps between microphysical processes and large-scale variability. This comprehensive approach emphasizes the need for integrating multi-platform observations with advanced modeling and statistical methods to reduce biases and improve the fidelity of aerosol-cloud interaction estimates. These advancements are crucial for more accurately quantifying aerosol radiative forcing and its implications for climate prediction.
How to cite: Kokkola, H., Romakkaniemi, S., Virtanan, A., Partridge, D., Blichner, S., Mielonen, T., Calderón, S., Irfan, M., Lipponen, A., Virtanen, T., Holopainen, E., Kolmonen, P., Raj Jallu, P., Moisseev, D., Mom, B., and Arola, A.: Reconciling aerosol-cloud interactions through multiscale observations, modeling, and statistical techniques, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16481, https://doi.org/10.5194/egusphere-egu25-16481, 2025.
Satellite sensors provide global monitoring of cloud properties, such as cloud effective radius and cloud optical thickness, which have been extensively used to quantify the radiative forcing due to aerosol-cloud interactions. These cloud properties are simultaneously retrieved from a pair of reflectance measurements using a bi-spectral retrieval algorithm. However, the algorithm’s solution space is limited, and retrievals often fail when observations fall outside this space. Upon analyzing five years of quality-constrained liquid-cloud pixels observed by MODIS aboard Aqua, we find that a significant 10% of cloudy pixels experience retrieval failure, primarily because the observations correspond to an effective radius exceeding MODIS’s upper retrieval limit of 30 µm. The omission of these cloudy pixels introduces a sampling bias in aggregated mean gridded cloud properties, affecting, among other things, radiative forcing calculations. To address this, we restore the failed cloud retrievals in MODIS using two reconstruction algorithms: (1) a conservative approach that assigns a fixed minimum effective radius to failed pixels, and (2) a realistic approach that uses extreme effective radius distributions from spaceborne radar measurements. Our findings reveal that MODIS-derived cloud droplet number concentration is positively biased, while liquid water path is negatively biased. Accounting for this bias increases the magnitude of cloud water adjustments, highlighting the crucial need to expand the solution space in MODIS and similar sensors.
How to cite: Choudhury, G. and Goren, T.: Sampling bias from satellite retrieval failure of cloud properties and its implications for aerosol-cloud interactions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9585, https://doi.org/10.5194/egusphere-egu25-9585, 2025.
The difficulty in establishing causality between stratocumulus cloud droplet number concentration (Nd) and liquid water path (LWP) is well established. Recent studies on the satellite observations of the development of clouds over short time scales to examine the role of Nd perturbations in LWP variations demonstrated that LWP evolved differently depending on the initial Nd. This highlighted the need to consider the temporal development rather than the instantaneous measurements.
Here we characterise the dependence of this short timescale behaviour on the local meteorological environment, with aerosol production, entrainment from the free troposphere and wet scavenging all acting to modify the Nd. Many of these effects act to further steepen the Nd–LWP relationship and obscure the causal Nd impact on LWP. The multi-dimensional process space to represent stratocumulus is reduced to the two-dimensional Nd-LWP state space. The role of different physical processes is investigated and process-level fingerprints are extracted in this space.
How to cite: Nair, V. and Gryspeerdt, E.: Short time-scale evolution of aerosol-cloud interactions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19417, https://doi.org/10.5194/egusphere-egu25-19417, 2025.
Relationships between variables derived from satellite observations can be interpreted as causal connections between explanatory and response variables. When physical processes support the observed relationship, it appears more likely to represent a true causal link. A notable example is the observed relationship between liquid water path and droplet number concentration in marine low clouds, which aligns with the physical mechanisms involved. However, a closer examination reveals that the observed relationships may actually be driven by co-variability between meteorological conditions and aerosol levels, reflecting the climatological evolution of stratocumulus clouds. We therefore suggest that the aerosol influence on marine low clouds should be separated into two pathways: (1) the influence of background aerosol levels on the clouds' climatology, which overlays the co-variability, and (2) the causal response, as seen in the case of ship tracks.
How to cite: Goren, T., Choudhury, G., Kretzschmar, J., and McCoy, I.: When Co-Variability Mimics Causal Aerosol-Cloud Interactions in Satellite Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10728, https://doi.org/10.5194/egusphere-egu25-10728, 2025.
Deep convective clouds (DCCs) are crucial in the Earth’s energy budget. Although the abundant DCC-generated ice-phase anvil and cirrus theoretically have a warming effect, the reported observations of their cloud radiative effect (CRE) by previous studies are unexpectedly negative. Here, based on five years of global satellite data analysis, we find that the apparent contradiction between theory and observations resulted from neglecting the radiative contribution of background underlying clouds based on active and passive satellite observations. The probability of underlying clouds vertically below the anvils is up to 2/3. They can contribute up to 70% of the observed total shortwave cooling effect when they fully overlap with anvils. After excluding the effect of underlying clouds, most of the anvil CRE changes sign from negative to positive, increasing by over +25 W/m2, especially over land. This revelation suggests a substantially underestimated warming effect of DCC anvils and cirrus in previous observations. Also, it may imply an underestimated aerosol-driven positive radiative forcing on DCC, which has been estimated as neutral previously.
How to cite: Pan, Z., Yin, J., Liu, F., Zang, L., Mao, F., and Rosenfeld, D.: Vertical Structure of Deep Convective Clouds and Their Large Radiative Warming Masked by Background Water Clouds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20156, https://doi.org/10.5194/egusphere-egu25-20156, 2025.
The Amazon rainforest plays an important role in global climate systems, particularly in regional precipitation patterns, atmospheric circulation, and Earth's energy balance. Convective systems in this region are intricately linked to these broader climatic processes. Through a combination of ground-based, satellite, and aircraft observations, we find that Amazonian convective clouds are particularly sensitive to aerosol concentrations, being highly aerosol-limited. This study explores the relationship between cloud droplet concentrations and ambient aerosol particles, both within the Amazon and in broader regions, evaluating various parameterizations commonly used in global climate models. Machine learning methods were used to capture the relationships between various aerosol, cloud, and meteorological parameters in the Amazon rainforest. To gain deeper insight into the microphysical processes within individual clouds, we examine the evolution of the cloud droplet effective radius (rₑ) as a function of cloud temperature (T), looking into the vertical structure of deep convective cumulus clouds.
How to cite: Pöhlker, M. L., Romshoo, B., Lauer, O., Maddali, J., Liznerski, P., Henkes, A., Quaas, J., Seifert, P., Gaudek, T., Meller, B., Raj, S., Machado, L., Cecchini, M., Albrecht, R., Atabakhsh, S., Artaxo, P., Yang, Y., Babu Suja, A., Kloft, M., and Pöhlker, C.: Convective clouds over the Amazon rainforest – aerosol dependence and microphysical features, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10796, https://doi.org/10.5194/egusphere-egu25-10796, 2025.
Last year, we presented the Cloud-by-Cloud (CxC) approach for studying aerosol-cloud interactions (ACI) through a combination of observations with polar-orbiting and geostationary satellites. Specifically, cloud-relevant aerosol concentrations at cloud level are matched to individual clouds that are observed throughout their life time.
The methodology has now been applied to 11 years of data from MSG-SEVIRI and the CALIPSO lidar over Europe and northern Africa. The resulting data set of several thousand matched aerosol-cloud cases provides a first satellite-based assessment of ACI in warm and cold clouds in which the aerosol component is expressed in actual number concentrations of cloud condensation nuclei (nCCN) and ice nucleating particles (nINP) at cloud level. We present findings of the aerosol impact on cloud droplet number concentration, effective radius, liquid water path and cloud phase for different aerosol types and discuss differences to the conventional data-aggregation approach in which aerosols are expressed through aerosol optical depth.
How to cite: Alexandri, F., Müller, F., Choudhury, G., Seelig, T., Tesche-Achtert, P., and Tesche, M.: Combining spaceborne observations of CCN, INP, and cloud development for assessing ACI in liquid and ice-containing clouds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18210, https://doi.org/10.5194/egusphere-egu25-18210, 2025.
The first indirect effect of aerosols on cloud reflectivity, primarily through changes in cloud droplet number concentration (Nd) or effective radius (Reff), remains one of the most uncertain components of anthropogenic radiative forcing. The strength of the first aerosol indirect effect (AIE) is quantified using relationships between aerosol proxies and Nd/Reff. For large-scale assessments, these relationships have historically been observed via satellites and serve as critical constraints for climate models calculating radiative forcing from aerosol-cloud interactions (ACIs). They have often relied on observations of aerosol optical depth or aerosol index, which are column-integrated proxies for Cloud Condensation Nuclei (CCN) concentration that may not be directly relevant for studying ACIs. Additionally, these proxies are influenced not only by particle concentration but also by size distribution, composition, and relative humidity. Since CCN represents only a fraction of the aerosol size distribution, there may not always be an obvious correlation between CCN and optical properties, introducing uncertainties in estimating indirect effects when using aerosol optical properties.
To address this issue, we developed a machine learning approach to estimate the vertical profile of CCN concentration at 0.4% supersaturation using airborne High Spectral Resolution Lidar Generation-2 (HSRL-2) data and collocated in situ CCN, the latter as truth to train a neural network model. Reanalysis data were used to enhance model performance. Our algorithm predicts vertically resolved CCN concentration within a mean relative uncertainty of 20% and is applicable to EarthCARE/ATLID measurements. Utilizing this new CCN product derived from the full suite of HSRL-2 extinction and backscatter measurements and reanalysis data of relative humidity and temperature in ACTIVATE (Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment) along with collocated cloud properties retrieved from Research Scanning Polarimeter data, we investigate the first AIE over the western North Atlantic Ocean. Our preliminary findings indicate that the new CCN product consistently constrains the relationships between CCN and Nd/Reff, for a wide range of cloud liquid water paths. The separation of indirect effects for different aerosol types indicates the expected differences in aerosol properties relevant for ACI. Overall, our approach using ML-derived CCN yields tighter constraints and physically more plausible insights into ACIs than vertically-resolved aerosol extinction, vertically-resolved aerosol index (extinction multiplied by Angstrom exponent), or column-integrated aerosol optical depth. We will conclude our presentation by illustrating that the aerosol vertical distribution and hygroscopic growth characteristics are the primary reasons why aerosol optical properties are inadequate for directly constraining the first AIE in the western North Atlantic Ocean.
How to cite: Redemann, J., Gao, L., Lenhardt, E., Burton, S., Crosbie, E., Fenn, M., Ferrare, R., Hair, J., Hostetler, C., Nehrir, A., Shingler, T., Cairns, B., and Sorooshian, A.: Machine Learning derived CCN concentrations provide better constraints on the first aerosol indirect effect than aerosol optical properties, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11812, https://doi.org/10.5194/egusphere-egu25-11812, 2025.
The vertical structures of precipitation serve as a direct link between clouds and surface precipitation, reflecting the processes of cloud and precipitation formation and development. However, their significance remains debatable, particularly concerning the aerosol effects on these structures. We utilize data from PM2.5 station measurements and the GPM 2A DPR to investigate the impact of aerosols on the vertical structure of precipitation and its microphysical characteristics.
Our findings show that the raindrop size in cold-topped (storm top height more than freezing level) precipitation exhibits three distinct trends from the storm top height to the surface: raindrop size decreases or shows no significant change in the upper layers, increases rapidly in the middle layers, and slightly decreases in the lower layers. Based on the observed turning points in raindrop size changes, we conducted a study on the influence of aerosols on the vertical structure of precipitation.
This study reveals phenomena different from previous views. Conventional wisdom suggests that higher and more extensive cloud development leads to greater surface precipitation intensity. However, our results indicate that for local cold-topped convective precipitation, the correlation between storm top height and precipitation rate at different altitudes decreases gradually with decreasing altitude. Absorbing aerosols are identified as a significant factor exacerbating the heterogeneity of precipitation vertical structures.
Within clouds, aerosols act as cloud condensation nuclei (CCN), influencing the growth of cloud droplets and ice crystals through microphysical effects. The competition between latent heat released and evaporative cooling initially increases storm top height but subsequently reduces it. Above the freezing level, precipitation rates and raindrop sizes remain highly consistent with storm top height. Below the freezing level, however, the vertical structure of precipitation is altered by evaporation. Larger raindrops and higher proportions of absorbing aerosols enhance evaporation, leading to a complex relationship where surface precipitation rates first decrease and then increase with increasing aerosol concentration. This response to aerosol is almost opposite to that observed above the freezing level.
This indicates that aerosols significantly exacerbate the heterogeneity of precipitation vertical structures through both microphysical and radiative effects.
How to cite: Sun, Y. and Zhao, C.: Aerosols exacerbating the heterogeneity of precipitation vertical structures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7763, https://doi.org/10.5194/egusphere-egu25-7763, 2025.
We present the findings from our in-situ holographic measurements conducted in shallow cumulus clouds, using the tethered aerostat Max Planck CloudKite (MPCK) during the EUREC4A campaign. The MPCK+ instrument is equipped with a holographic system sampling cloud droplets 8µm diameter or larger in a 10cm^3 three-dimensional volume every 12cm. This unprecedentedly small inter-sample spacing for holographic measurements is achieved by combining two variables: the high sampling frequency of our MPCK+ holographic setup, set at 75 Hz, and the low true airspeed of the aerostat.
The microphysical characteristics of clouds, such as droplet concentration, size distribution and liquid water content can be calculated with sub-meter spatial resolution. This allows us to obtain a detailed horizontal snapshot of a cloud's microphysics. The three-dimensional nature of holographic droplet data also allows a direct calculation of the radial distribution function (RDF), and the high measurement cadence of the MPCK+ data invites a spatially localized investigation of cloud droplet clustering.
We present an overview of our holographic data showcasing the structure of shallow cumulus clouds as well as an analysis of cloud droplet clustering in a short horizontal cloud snapshot.
How to cite: Thiede, B., Larsen, M. L., Schlenczek, O., Nordsiek, F., Bodenschatz, E., and Bagheri, G.: A Closer Look into Shallow Cumulus Clouds: Investigating Cloud Microphysics and Droplet Clustering Using the Max Planck Cloudkite+, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13932, https://doi.org/10.5194/egusphere-egu25-13932, 2025.
Earth system models struggle to accurately simulate aerosol’s interactions with weather and climate. This is largely attributed to structural uncertainty including insufficient process representation and model resolution due to limited computer power, and model tuning has become a low-cost remedy for improving performance. With unprecedented computational capability, improved understanding, modern software, and novel machine learning algorithms, high-resolution Earth system modeling with accurate and yet expensive process representations has become possible. In this study, we quantify the impacts of longstanding structural uncertainty on aerosol effective radiative forcing (ERF) by incorporating much more sophisticated process representations in U.S. Department of Energy’s Energy Exascale Earth System Model (E3SM). The ERF associated with aerosol-cloud interactions is further decomposed into the Twomey effect, liquid water path (LWP) adjustment, and cloud fraction adjustment using a satellite-based radiative kernel so that the impacts of each new process representation on aerosol ERF can be evaluated against observations. We find that while increasing model resolution to kilometer scale changes aerosol ERF by 30%, model physics representations (aerosol mixing assumption, condensational growth, secondary organic and sulfate aerosol formation, aerosol optics, aerosol activation, emission, giant aerosol, chemistry, warm rain process, and aerosol-turbulence coupling) contributes to a factor-of-two variation in aerosol ERF. As opposed to model tuning, this approach improves understanding and increases confidence in simulations as they are traceable to physics. Furthermore, even though the model’s total aerosol ERF or the Twomey effect alone can be brought to agree well with satellite estimate, significant biases in LWP and cloud fraction adjustments remain, highlighting the importance of improving aerosol interactions with cloud macrophysics in the model.
How to cite: Ma, P.-L., Hast, J., Geiss, A., Hassan Mozumder, M. T., Huang, M., Qin, Y., Wu, M., Zaveri, R., Zhang, K., Kang, L., Marchand, R., Larson, V., Morrison, H., Zhao, B., Wall, C., and Yao, Y.: Advancing understanding and predictability of aerosol effective radiative forcing due to structural uncertainty in an Earth system model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7303, https://doi.org/10.5194/egusphere-egu25-7303, 2025.
Aerosol-cloud interactions are a persistent source of uncertainty in climate research. This study presents findings from a model intercomparison project examining the impact of aerosols on clouds and climate in "cloud-resolving" Radiative-Convective Equilibrium (RCE) simulations. Specifically, 11 different models conducted RCE simulations under varying aerosol concentrations, domain configurations, and sea surface temperatures (SSTs). We analyze the response of domain-mean cloud and radiative properties to imposed aerosol concentrations across different SSTs. Additionally, we explore the potential impact of aerosols on convective aggregation and large-scale circulation in large-domain simulations.
The results reveal that the cloud and radiative responses to aerosols vary substantially across models. However, a common trend across models, SSTs, and domain configurations is that increased aerosol loading tends to suppress warm rain formation, enhance cloud water content in the mid-troposphere, and consequently increase mid-tropospheric humidity and upper-tropospheric temperature, impacting static stability. The warming of the upper troposphere can be attributed to reduced entrainment effects due to the higher environmental humidity in the mid-troposphere. However, examining high percentiles of vertical velocities at the mid troposphere do not demonstrate convective invigoration. In large-domain simulations, where convection tends to self-organize, aerosol loading does not influence self-organization but tends to reduce the intensity of large-scale circulation forming between convective clusters and dry regions. This reduction in circulation intensity can be explained by the increase in static stability.
How to cite: Dagan, G., van den Heever, S. C., Stier, P., Abbott, T. H., Barthlott, C., Chaboureau, J.-P., de Roode, S., Fan, J., Gasparini, B., Hoose, C., Jansson, F., Kulkarni, G., Leung, G., Prabhakaran, T., Romps, D. M., Shum, D., Tijhuis, M., van Heerwaarden, C. C., Wing, A., and Yunpeng, S.: RCEMIP-ACI: Aerosol-Cloud Interactions in a Multimodel Ensemble of Radiative-Convective Equilibrium Simulations , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9604, https://doi.org/10.5194/egusphere-egu25-9604, 2025.
Aerosol-cloud interactions remain a significant source of uncertainty in our understanding of climate change. Ship emissions provide a unique natural experiment, artificially brightening clouds through the injection of aerosols that act as cloud condensation nuclei. These "ship tracks" offer a valuable opportunity to evaluate the impacts of aerosols on clouds. Comparing satellite observations of aerosol-cloud interactions with model simulations is often challenging. Direct case studies of natural experiments, such as those involving ship tracks, allow for more precise investigation of the representation of physical processes in models, enabling a clearer assessment of where models succeed or fail. Such simulations are also critical for evaluating the potential of marine cloud brightening as a climate intervention strategy.
In this study, we simulate ship tracks using the UK Met Office Unified Model in km-scale resolution. By incorporating real ship locations and representing ships as moving aerosol sources within a two-moment cloud microphysics and coupled aerosol scheme, we successfully reproduce the cloud droplet number concentration of observed ship tracks for a specific day in a hindcast (relative to observations). Direct comparisons between these simulated tracks and MODIS satellite observations reveal differences in the model’s ability to represent the magnitude and timescales of cloud and precipitation processes, such as the LWP adjustments to aerosols and the width/depth of the resultant ship tracks. These comparisons shed light on the requirements for accurately simulating ship tracks.
To further investigate the representation of aerosol-cloud interactions within models, we examine the sensitivity of aerosol impacts to grid resolution. This analysis addresses a critical question for scaling high-resolution simulations to global climate models (GCMs): Can small-scale constraints (such as ship tracks) reliably constrain the parametrisations of large-scale models? We explore whether the scaling of aerosol effects from high resolution models to GCM resolutions are linear or if saturation and concentration effects must be considered. The findings from this study contribute to improving the representation of aerosol-cloud interactions in models and enhancing our understanding of their role in climate systems.
How to cite: Tippett, A., Gryspeerdt, E., and Field, P.: Simulating shipping impacts on clouds in a high-resolution weather model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18825, https://doi.org/10.5194/egusphere-egu25-18825, 2025.
Cloud-water adjustments are a part of aerosol-cloud interactions, affecting the ability of clouds to reflect shortwave radiation by processes altering the vertically integrated cloud water content L in response to changes in the droplet concentration N. In this study, we utilize a simple entrainment parameterization for mixed-layer models to determine entrainment-mediated cloud-water adjustments in non-precipitating stratocumulus. At lower N, L decreases due to an increase in entrainment in response to an increase in N suppressing the stabilizing effect of evaporating precipitation (virga) on boundary layer dynamics. At higher N, the cessation of cloud-droplet sedimentation sustains more liquid water at the cloud top, and hence stronger preconditioning of free-tropospheric air, which increases entrainment with N. Overall, cloud-water adjustments are found to weaken distinctly from dln(L)/dln(N) = -0.48 at N = 100 cm-3 to -0.03 at N = 1000 cm-3, indicating that a single value to describe cloud-water adjustments in non-precipitating clouds is insufficient. Based on these results, we speculate that cloud-water adjustments at lower N are associated with slow changes in boundary layer dynamics, while a faster response is associated with the preconditioning of free-tropospheric air at higher N.
How to cite: Hoffmann, F., Chen, Y.-S., and Feingold, G.: On the Processes Determining the Slope of Cloud-Water Adjustments in Non-Precipitating Stratocumulus, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3708, https://doi.org/10.5194/egusphere-egu25-3708, 2025.
An understanding of aerosol-cloud interactions is key to many areas of climate science due to the diversity of mechanisms by which clouds interact with the Earth’s climate. One such area of growing interest is Climate Intervention – deliberately altering the climate to counteract anthropogenic Climate Change. Many Climate Intervention techniques concern aerosol-cloud interactions in some way, Marine Cloud Brightening (MCB) – whereby aerosols are injected into the marine boundary layer to increase the albedo of low clouds – does in particular. Developing a comprehensive understanding of MCB requires modelling across all scales. The focus of this work is modelling with large-eddy simulations (LES) and parcel models, performing a variety of experiments such as step forcing and continuous injection of aerosols in different models of the same class. Most the LES experiments have been performed in MONC (Met Office NERC Cloud) and compared to DALES (Dutch Atmospheric LES). Model intercomparison is key to understanding MCB; thus far there is disagreement among LES models over some important details of MCB, such the impact of small injected aerosols on the entrainment of dry air. It is hoped that better comparison of models can address this.
How to cite: Smith, W. M.: Modelling marine cloud brightening in large-eddy simulation and parcel model intercomparison projects, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19507, https://doi.org/10.5194/egusphere-egu25-19507, 2025.
Aerosol-cloud interactions are complex processes that contribute significantly to uncertainties in predicting global climate. Cloud droplet formation is influenced by factors such as the hygroscopicity of soluble aerosol particles, aerosol processing within clouds, aerosol particle number concentration, and updraft velocity. Accurately understanding these factors is crucial for better representing cloud droplet numbers on a global scale. Updraft velocity is characterized by the probability density function (PDF) of the vertical velocity distribution. Earth system models (ESMs) typically assume a constant standard deviation (σw) for the vertical velocity PDF (van Noije et al. 2021; Mulcahy et al. 2020). However, this assumption may be inaccurate, as it has been shown that the σw exhibits significant diurnal variability (Bougiatioti et al. 2020). In this study, we implemented the turbulent kinetic energy (TKE) calculations to OpenIFS cycle 48r1 (OIFS48r1) following Bastak Duran et al. (2018). In addition, we implemented Morales and Nenes (2014) activation parameterization (M&N) to OIFS48r1 including the TKE to calculate the σw instead of using a constant σw for the vertical velocity PDF. OIFS48r1 is derived from the Integrated Forecasting System (IFS) developed by European Centre for Medium-Range Weather Forecasts (ECMWF) and it will be the main atmospheric model used in the newest version of European Community ESM (EC-Earth 4). First, we investigated the effects of using constant σw values of 0 and 0.8 m/s on the TKE-derived σw and their impact on column averaged cloud droplet number concentrations. The results showed that using σw of 0 m/s led to very low droplet numbers, as weaker updraft variability resulted in smaller supersaturations, causing fewer particles to activate. On the other hand, using σw of 0.8 m/s produced stronger activation, particularly in regions with high aerosol particle number concentrations. When using the TKE-derived σw, the differences in droplet numbers compared to the activation scheme with σw of 0.8 m/s were minimal. Next, we compared the monthly column-averaged and boundary-layer (BL) average number of activated particles obtained from the TKE-derived σw activation routine with the pre-existing Abdul-Razzak and Ghan (2000) activation parameterization (AR&G). The results showed that the AR&G scheme produced stronger activation than the M&N scheme, both in terms of the total column average and the BL-averaged regions. One of the reasons for this difference could be due to the activation calculations in the M&N scheme, which are only performed in areas where clouds are present, while in the AR&G scheme, activation is calculated for every gridbox.
How to cite: Holopainen, E. and Nenes, A.: Aerosol processes and activation in OpenIFS cycle 48r1 portable global aerosol-climate and weather prediction model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9397, https://doi.org/10.5194/egusphere-egu25-9397, 2025.
We have developed a double moment aerosol model appropriate for numerical weather prediction (NWP) within the Met Office’s Unified Model framework. Our aerosol model (Sol-Insol) is fully coupled to a double moment cloud microphysics model (CASIM) permitting aerosol-cloud interactions to be resolved at high-resolution. As a test we investigate how our setup performs against traditional ACI parametrizations used for NWP by comparing model results to observations from the Café-Brazil field campaign over the Amazon. Our simulations contribute to the CleanCloud model intercomparison project (MIP) aimed at improving aerosol-cloud interactions across timescales. As a case study, we use 14th January 2023, a date selected due to HALO aircraft observations being recorded alongside a pronounced mesoscale squall line.
The MIP protocol sets out 3 regional domains surrounding the ATTO site - a 6.6km resolution grid over the Northern part of South America into Central America, a 3.3km resolution grid inside this and then a 1.6km resolution grid covering the Amazon. Three model configurations were selected to isolate the impacts of aerosol on cloud and precipitation: a control run with no aerosol scheme, fixed cloud CDNC and a Cooper ICNC vs T relation (CONTROL); a coupled aerosol-cloud run with arbitrary initialised aerosols (ARB-AER); and a coupled aerosol-cloud run with aerosol initialised to CAMS reanalysis data (CAM-AER).
We constrain the simulated aerosol, cloud and radiation properties using a range of co-located satellite, surface (ATTO) and air (HALO) observations. Our results show that initialising the aerosol to CAMS reanalysis concentrations leads to slightly improved results relative to CONTROL while ARB-AER performs significantly worse when looking at observed top of the atmosphere radiation, highlighting the high sensitivity of cloud to ambient aerosol. Further experiments comparing ground and flight observations to model metrics help to support the conclusion that CAM-AER is performing better than ARB-AER and highlights potential improvements to NWP hydro-forecasts from using realistic aerosol properties.
How to cite: Carton-Kelly, J., Jones, A., and Field, P.: Investigating a double moment, fully coupled aerosol-cloud model over the Amazon, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3245, https://doi.org/10.5194/egusphere-egu25-3245, 2025.
A major uncertainty in the cloud-feedback to a warming climate can be attributed to shallow convection in the trades. With recent advances in observational and computational resources, the potential impact of the mesoscale organization of these clouds became apparent. While the processes leading to the mesoscale organization are not resolved in current climate models, observations of these features and more importantly their interaction with different scales became available through field campaigns like EUREC4A.
This study quantifies the ability of large-domain large-eddy simulations to represent the observed mesoscale variability in cloudiness. By using forward operators to mimic the observations, we show that the stratiform cloud amount and precipitation frequency remain challenging to simulate at hectometre resolutions. Despite these challenges, the simulations show a similar sensitivity in cloud distribution to environmental conditions.
By perturbing the 41 days simulation with a 13-fold increase in CCN concentration we quantify the sensitivity of the mesoscale cloud organisation to changes in precipitation and show the strong influence on the cold-pool driven cloud formations. We further emphasise the importance to correctly represent the mesoscale processes in climate simulations by showing that changes in cloud-radiative effects due to aerosol changes vary day-by-day with varying contributions from changes in cloud albedo and cloud fraction.
How to cite: Schulz, H., Wood, R., and Stevens, B.: Quantification of aerosol influence on day-to-day mesoscale variability of shallow convection, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18015, https://doi.org/10.5194/egusphere-egu25-18015, 2025.
Anthropogenic aerosol emissions have had a major influence on global climate over the industrial era, counteracting some of the warming and precipitation increases due to rising greenhouse gas concentrations. These greenhouse gas driven changes are now rapidly being unmasked, through a range of national and regional policies aimed at improving air quality. However, unlike greenhouse gases, aerosol emissions have strongly regional response patterns, and influence the climate both near to, and far from emission sources. These regional influences have to date not been quantified in a consistent, multi-model framework.
Here, we present results from the Regional Aerosol Model Intercomparison Project (RAMIP). Ten CMIP6 era models have performed 10- member ensemble simulations investigating the climate response to aerosol emissions, separately, from South Asia, East Asia, Africa and the Middle East, and Europe and North America. All RAMIP experiments are based on two CMIP6-era SSPs: SSP3-7.0 (strong GHG increases, minimal aerosol reductions) and a hybrid SSP370-126aer (anthropogenic emissions of SO2, organic carbon, and black carbon are rapidly reduced following SSP1-2.6, either globally or regionally).
We find a rapid surface warming in response to aerosol reductions, and strong precipitation increases, but with marked regional differences in the magnitude of the response. While there are many robust responses, strong inter-model differences in the pattern and strength of the responses in some regions highlights where aerosol related uncertainty is large in the near-future.
We discuss the linearity of the effective radiative forcing and climate responses from regional aerosol perturbations, and demonstrate that emission location is key to the amplitude and extent of the response. In particular, emission changes in East Asia and North America and Europe have a larger global temperature impact than those over South Asia due to their influence on Pacific clouds. This initial analysis demonstrates the need for aerosol awareness in the design of future scenario ensembles, and in climate risk and impact studies both near to and far from aerosol emission sources.
How to cite: Wilcox, L., Samset, B., Stjern, C., and Allen, R. and the RAMIP Team: Distinct climate responses to regional aerosol emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6015, https://doi.org/10.5194/egusphere-egu25-6015, 2025.
The rate of global warming has seemingly increased since around 2010, relative to the previous 30-year period, leading up to the recent strong records in global surface temperature anomalies set in 2023 and 2024. Concurrently, Chinese emissions of SO2 have dropped dramatically as a consequence of strong national air quality policies. This has, in turn, led to marked reductions in atmospheric sulphate aerosol loadings over, and downwind from, the Chinese mainland, as well as strong improvements in air quality. To date, the contribution of Chinese emissions reductions to the intensification of global warming, through unmasking of greenhouse gas driven climate change, has however not been quantified.
Here, we use simulations from the Regional Aerosol Model Intercomparison Project (RAMIP) to investigate the climate response to strong reductions in Chinese SO2 emissions, closely analogous to real-world changes since 2010. We use 10-member ensembles of fully coupled simulations from ten CMIP6 era Global Climate Models, to quantify the global and regional, seasonally resolved influences on temperature and precipitation in a total of 100 ensemble members.
Overall, we find a warming due to recent reductions in SO2 emissions from China of 0.07 ± 0.05 ºC. Assuming that this has happened since 2010 leads to a warming rate of 0.05 ºC / decade. Recent observations of global surface temperature anomalies indicate a warming rate increase of 0.07 ºC / decade, when filtered for the effects of interannual variability in sea surface temperature patterns. Hence, our results indicate a strong contribution of aerosol emissions reductions to this elevated warming rate. This conclusion is supported by the geographical pattern of elevated warming, as well as correspondence between modelled and observed top-of-atmosphere radiative imbalance changes.
How to cite: Samset, B. H., Wilcox, L. J., and Allen, R. J. and the RAMIP team: Strong contribution of SO2 emissions reductions from China to global warming intensification since 2010, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6060, https://doi.org/10.5194/egusphere-egu25-6060, 2025.
The quantification of aerosol-induced radiative forcing remains a significant challenge in climate modeling, primarily due to the complex interplay of aerosol and clouds in a warming world. Traditional approaches often rely on either bottom-up process-based models, difficult to constrain against present-day observations, or top-down methods that lack the ability to capture the underlying processes accurately.
Here, we present an approach that combines both bottom-up process-based constraints and top-down energetic constraints of aerosol forcing and cloud feedbacks simultaneously to achieve a more comprehensive understanding of aerosol impacts on clouds and the climate. We generate one million samples of parametric uncertainty of aerosol forcing and cloud feedback and estimate the historic temperatures they would have produced using an impulse-response model. Both the temperature trajectories and the associated microphysical properties (such as the hemispheric contrast in cloud droplet number concentration) can then be compared to observations simultaneously.
Applying the new method to the Community Atmosphere Model v6, we infer narrower parameter ranges for key process parameters, a reduced effective radiative forcing of -1.08 [-1.29 – -0.77] Wm-2, and hence 66% more precise future projections.
How to cite: Watson-Parris, D.: Integrating Bottom-Up Process-Based Constraints with Top-Down Energetic Constraints of Historic Warming for More Accurate Future Projections, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21790, https://doi.org/10.5194/egusphere-egu25-21790, 2025.
The western North Pacific Subtropical High (WNPSH) significantly influences East Asian weather. In the Northwest Pacific where sea‐salt aerosols (SSAs) are abundant and the large‐scale environment is dominated by the dry subsidence of the WNPSH during summer, inhomogeneous SSAs form as a product of the environment. However, the extent to which inhomogeneous SSAs affect the WNPSH remains unclear. This study investigates the radiative effects of SSAs through numerical simulations, revealing a novel mechanism for the strengthening of the WNPSH. The results demonstrate that inhomogeneous SSAs enhance the WNPSH by generating diabatic cooling in the upper troposphere and associated unstable subsidence motion. Further considering the radiative hysteresis effects of inhomogeneous SSAs, the WNPSH further strengthens under the combined dynamic and thermodynamic influences associated with upper‐level radiative cooling. Inhomogeneous SSAs not only enhance the WNPSH but also influence the location where the central area of high pressure intensifies.
How to cite: Shu, S.: Inhomogeneous Sea‐Salt Aerosols—A New StrengtheningMechanism for the Western North Pacific Subtropical High, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14328, https://doi.org/10.5194/egusphere-egu25-14328, 2025.
Anthropogenic aerosol emissions are projected to decline significantly by 2050, with major implications for regional climate. However, unlike greenhouse gases, aerosol impacts are spatially heterogeneous and can influence climate both near emission sources and through remote teleconnections. This is particularly important for the Indian monsoon system, where both local and remote aerosol changes can significantly affect precipitation patterns.
Using the Regional Aerosol Model Intercomparison Project (RAMIP) framework, we examine how local and remote aerosol emission changes influence Indian climate across both pre-monsoon and monsoon seasons. Our analysis employs 10-member ensembles from multiple CMIP6-era models to compare three experiments: Global, South Asian, and East Asian aerosol reductions relative to a high-emission baseline (SSP3-7.0). This experimental design allows us to isolate and quantify the distinct impacts of regional emission changes. Initial results reveal that global aerosol reductions lead to more widespread and intense precipitation changes compared to regional reductions alone, with South Asian aerosol reductions largely mirroring the global response pattern while East Asian emissions play an additional role in modulating monsoon circulation. The Western Ghats and Indo-Gangetic Plains show particularly strong responses. We find significant inter-model diversity in the spatial patterns and magnitudes of these changes, highlighting key areas of uncertainty in aerosol-monsoon interactions. Through detailed analysis of circulation patterns and moisture transport, we investigate the mechanisms driving these precipitation responses and their implications for future climate projections.
Our findings provide insights into the complex relationship between regional aerosol emissions and monsoon dynamics, with important implications for both climate prediction and air quality management in South Asia.
How to cite: Bhandekar, A., Lawrence, B., Abraham, L., O’Connor, F., and Maynard, C. and the RAMIP Team: Indian Summer Monsoon Response to Regional Aerosol Emission Changes: RAMIP insights, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4280, https://doi.org/10.5194/egusphere-egu25-4280, 2025.
Attributing variations in the Asian summer monsoon to aerosol forcing is crucial for reducing uncertainties in future regional water availability projections. This is essential for effective risk management and adaptation planning in this densely populated region. However, accurately simulating the monsoon remains a significant challenge for climate models due to persistent biases, which compromise their reliability in attributing anthropogenic influences. In this study, we analyze a set of climate model experiments to uncover the connection between these biases and the monsoon’s response to Asian aerosols, focusing on the underlying physical mechanisms, including large-scale circulation changes. The impact of aerosols on monsoon precipitation and circulation is strongly shaped by a model's ability to represent the spatio-temporal variability in climatological monsoon winds, clouds, and precipitation across Asia. This variability modulates the magnitude and efficacy of aerosol–cloud–precipitation interactions, a key component of the total aerosol response. Our findings reveal a strong interplay between South Asia and East Asia monsoon precipitation biases, with their relative dominance significantly influencing the overall monsoon response. Notably, there is a sharp contrast between aerosol-driven changes during early and late summer, which can be attributed to the opposing signs and seasonal evolution of biases in these two regions. Realistically simulating the progression of large-scale atmospheric circulation is essential to fully capture the aerosol impact across Asia. These insights have significant implications for improving the understanding and reducing inconsistencies in model responses to aerosol changes over Asia, both in historical simulations and future projections.
How to cite: Liu, Z., Bollasina, M., and Wilcox, L.: Impact of Asian aerosols on the summer monsoon strongly modulated by regional precipitation biases, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16348, https://doi.org/10.5194/egusphere-egu25-16348, 2025.
Rapid urbanization and industrialization lead to significant changes in land use and land cover (LULC), particularly in agricultural activities over the Indo-Gangetic Plain (IGP), which in turn impacts the distribution of aerosol loading. In the present study, climatological and spatio-temporal trends of aerosol optical depth (AOD) and aerosol sources are investigated over the IGP region from 2001 to 2022. Climatological analysis of the AOD over the upper, central, and lower IGP regions was conducted using satellite-based MODIS data. LULC analysis over the IGP region during the study period showed a significant increase in crop land and built-up area, mainly replacing the vegetation. It is hypothesized that changes in LULC patterns, especially the expansion of cropland and crop residue burning (CRB), are major drivers of aerosol trends. The results reveal significant AOD increases, particularly in the lower IGP, which experienced extensive vegetation loss replaced by cropland, intensifying CRB and aerosol emissions. In contrast, the upper IGP exhibited reduced CRB activity and even declining AOD trends during the second half of the study period (2012–2022), indicating improved air quality. The findings highlight a direct relationship between LULC changes, CRB, and AOD trends, emphasizing the need for sustainable agricultural practices and emission control measures to mitigate aerosol pollution and improve air quality across the IGP.
How to cite: Kumar Singh, R. and Satyanarayana, A. N. V.: Impact of Land Use Changes during Agricultural Cycles on AOD Trends over the Indo-Gangetic Plain during Last Two Decades, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2136, https://doi.org/10.5194/egusphere-egu25-2136, 2025.
Precipitation changes over sub-Saharan Africa linked to remote aerosol emissions have severely impacted agriculture, ecosystems, and livelihoods historically in the region. Established links between aerosol emissions and precipitation responses impact future projections of sub-Saharan precipitation, which remain uncertain due to differences in model representations of aerosol, aerosol-precipitation interactions, and unclear future aerosol emission pathways. Ongoing large reductions in aerosol emissions from East Asia, combined with uncertainty in future aerosol emissions for India and Africa, indicate that aerosol changes are likely to play an important role in African climate in the near-term future.
In this presentation, we identify regional African precipitation responses to local and remote aerosol emission changes, and establish mechanisms behind them. We focus on responses in the East and West African monsoons, including changes to the intensity, timing, spatial pattern, and variability of rainfall. We also demonstrate the sensitivity of the responses to aerosol emission region, to determine whether local or remote emission changes dominate rainfall responses on seasonal timescales. Using the Regional Aerosol Model Intercomparison Project experiments, we quantify the role of regional aerosol emission changes in near-term African precipitation responses. This allows us to determine the aerosol emission regions which dominate the African precipitation responses, while also exploring sensitivities to absorbing and scattering species of aerosol emissions.
Current analysis has determined that reductions in global aerosol emissions cause West Africa to become significantly hotter and wetter, with a northward shift in precipitation found in some models; this change is strongest along the coastline in most models, though there is considerable diversity in the magnitude of modelled responses.
This work highlights the role of changing aerosol emissions on African precipitation patterns, providing essential information for near-term climate adaptation strategies.
How to cite: Toolan, C., Turner, A., and Adabouk Amooli, J. and the RAMIP Team: Sub-Saharan African Precipitation Responses to Aerosol Emission Changes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6953, https://doi.org/10.5194/egusphere-egu25-6953, 2025.
This study assessed Africa’s climate response to different injection materials for stratospheric aerosol geoengineering (SAG) using simulations from the SOCOLv4 model, which provides a set of SAG simulations following the G6sulfur experiment in the Geoengineering Multi-model Intercomparison Project (GeoMIP). We analysed four SAG experiments, which used four injection materials (sulfur, alumina, calcite, and diamond) referred to as G6sulfur, G6alumina, G6calcite, and G6diamond, respectively. The SAG experiments used a high-emission pathway (SSP5-8.5) as baseline in which each material was injected into the equatorial stratosphere to keep global warming levels similar to an intermediate emission pathway (SSP2-4.5). We assessed Africa’s climate response to these SAG materials by quantifying the end-of-century (2080-2099) mean changes in minimum and maximum temperatures and precipitation relative to SSP2-4.5. Our findings suggest that all injection materials show a cooling potential by keeping annual and seasonal minimum and maximum temperatures below SSP2-4.5 across most parts of the continent. Maximum and minimum temperatures could decrease the most between 10°S and 10°N, along the Guinean coast of west Africa and parts of Central Africa, by up to -2°C and -4°C, respectively. This SAG-induced cooling remains partial over north Africa where a residual warming of about 1°C could persist at the end of the century relative to the SSP2-4.5, irrespective of the injection material. On the other hand, the impact on precipitation is less linear and spatially heterogeneous. However, SAG could reverse the SSP5-8.5 projected mean continental and regional (especially over Central Africa) increases in annual and seasonal precipitation, inducing a dryer future under SAG across the continent, irrespective of the injection material. Our results further suggest that, relative to SSP2-4.5, G6alumina could cause the largest precipitation decrease and G6diamond the slightest decrease at the end of the century. In summary, our results show that irrespective of the injection material, SAG could significantly decrease temperatures across Africa, however lower warming and drying could still be achieved under SSP2-4.5, over parts of Africa.
How to cite: Odoulami, R. C., Patel, T. D., Sukhodolov, T., Egbebiyi, T. S., Vattioni, S., Chiodo, G., Lennard, C. J., Abiodun, B. J., and New, M. G.: Africa’s climate response to stratospheric aerosol injection materials, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13980, https://doi.org/10.5194/egusphere-egu25-13980, 2025.
Since the 1980s, the increase in greenhouse gases and the decrease in anthropogenic aerosols (AA) over Europe and the Mediterranean (MED), driven by air pollution control policies, along with anthropogenic land-use changes, have been linked to the enhanced regional warming trend in the MED, particularly during boreal summer (JJA). However, the effect of AA changes on the temperature trend over this region requires further investigation. This study examines temperature changes attributed to AA over the MED during the historical period (1850-2014) with respect to changes in effective radiative forcing (ERF) based on experiments from 11 CMIP6 Earth System Models. The transient shortwave ERF due to AA is assessed using the “histSST” and “histSST-piAer” experiments, which share the same historical forcings driven by prescribed sea surface temperatures and sea ice from the corresponding coupled models except that “histSST-piAer” uses pre-industrial aerosol precursor emissions from the year 1850. Shortwave ERFs due to aerosol-radiation interactions and aerosol-cloud interactions, as quantified by the approximate partial radiative perturbation (APRP) method, present a negative peak in 1965-1984 relative to 1850 over the MED region (multi-model means of -2.17±0.82 W m-2 and -3.08±1.85 W m-2, respectively), exhibiting trends towards less negative values in recent past (1995-2014) relative to the 1965-1984 period (changing by 0.94±0.37 W m-2 and 0.51±1.02 W m-2, respectively). Furthermore, we quantify the response in near-surface air temperature (monthly mean, and daily maximum and minimum) caused by AA on an annual and seasonal basis using the “historical” and “hist-piAer” experiments, which are driven by historical forcings except that “hist-piAer” uses fixed pre-industrial AA and aerosol precursor emissions. Consistent with the negative ERF changes, we find a surface cooling of -1.23±0.56 K in the 1965-1984 period relative to 1850 on an annual basis. During 1995-2014 there is an annual mean increase of 0.25±0.36 K relative to 1965-1984 pointing towards an amplification of warming due to AA reduction. The regional surface warming in 1995-214 relative to 1965-1984 is more prominent in JJA (0.26±0.34 K) than in boreal winter (0.18±0.57 K) as models show lower agreement on the sign of change during wintertime. Similar results are derived for maximum and minimum temperatures regarding the magnitude and the trend of changes over the MED region.
This work is implemented within the research project REINFORCE (impRovEments in the simulation of aerosol clImate liNkages in earth system models: From glObal to Regional sCalEs) in the framework of HFRI call “Basic Research Financing (Horizontal Support of all Sciences)” under the National Recovery and Resilience Plan “Greece 2.0” funded by the European Union – NextGenerationEU (HFRI; project no. 15155).
How to cite: Kalisoras, A., Georgoulias, A. K., Akritidis, D., Allen, R. J., Naik, V., and Zanis, P.: Anthropogenic aerosol-induced changes in radiative forcing and temperature over the Mediterranean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16293, https://doi.org/10.5194/egusphere-egu25-16293, 2025.
The freshwater resources of the Southwestern United States (SWUS) largely depend on wintertime precipitation, which has declined since 1980. During this period, the tropical Pacific sea surface temperature (SST) has exhibited a multi-decadal La Niña-like trend, inducing a teleconnection that reduces SWUS precipitation. However, the extent to which this SST trend is driven by internal variability (i.e., natural fluctuations) versus anthropogenic radiative forcings remains uncertain. This study explores two aspects of the impact of anthropogenic aerosols on the Pacific sector and their influence on the wintertime SWUS precipitation trend. First, we demonstrate that the La Niña-like SST trend is partially forced by anthropogenic aerosols, as evidenced by simulations from the Community Earth System Model version 2 (CESM2) large ensemble and its single-forcing large ensemble. This forced La Niña-like SST trend, in turn, drives a decline in SWUS precipitation through its teleconnection. Second, we show that the teleconnection pattern associated with internal Pacific decadal variability during the post-1980 period differs from the pre-industrial condition. Specifically, using a hierarchy of model simulations, we find that even under El Niño-like SST trends, there is a tendency toward a North Pacific anticyclonic circulation trend and reduced SWUS precipitation during post-1980 — contrary to the canonical El Niño teleconnection. This unintuitive yet robust circulation change arises from nonadditive responses to tropical mean warming and radiative effects from anthropogenic aerosols. As the forced SWUS precipitation decline combines with anthropogenic warming, the post-1980 period exhibits the most rapid SWUS soil moisture drying among past and future periods of similar length. Although future projected El Niño-like warming and aerosol emission reductions could potentially reverse the precipitation trend, these changes are unlikely to mitigate the currently projected drought risk in the region.
How to cite: Kuo, Y.-N., Lehner, F., Simpson, I., Deser, C., Phillips, A., Newman, M., Shin, S.-I., Wong, S., Arblaster, J., and Kim, H.: Evidence of Anthropogenic Aerosols Impacts on the Southwestern U.S. Droughts since 1980, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15483, https://doi.org/10.5194/egusphere-egu25-15483, 2025.
Wildfire activity in boreal regions is changing, due to climate change and other anthropogenic drivers. Given the high climate sensitivity of the Arctic and boreal regions, it is important to explore the impacts of these changes. There are also region-specific impacts of biomass burning particular to high latitude regions, such as black carbon (BC) deposition on snow. While many sources of atmospheric pollutions are being mitigated, fires are emerging as a growing contributor to poor air quality, both locally to the fire emissions source and across wider regions.
Here we investigate the climate and atmospheric impacts of several idealised biomass burning perturbations, focusing on aerosols. We present initial results from a new set of multi-model experiments (including CESM2, NorESM2 and EC-Earth), where biomass burning emissions are perturbed in several idealised experiments. The species concerned are: BC, SO4, organic carbon, SO2, DMS, and secondary organic aerosol precursors. We first perturb all boreal biomass burning emissions, and then smaller regions of interest individually (boreal North America, East Siberia and West Siberia). These experiments use 2005-2014 as a baseline period, and use the sum of this period as the perturbation, giving an approximately x10 perturbation in the regions of interest, in both fixed SST (30 years) and coupled (200 years) simulations. The strength and location of the aerosol changes studied here (when comparing aerosol optical depth) are comparable to the recent trends in aerosols between 2015-2024 and 2005-2014.
We will present the modelled atmospheric composition response both globally and in the focus regions described above, including teleconnections to other regions. This includes aerosol optical depth, aerosol absorption, and a breakdown by aerosol species. We will also highlight the climate response to the biomass burning perturbations, including effective radiative forcing (ERF) and fully-coupled climate response estimates.
How to cite: Staniaszek, Z., Samset, B., Lund, M. T., and Ekman, A.: Regional to global impacts of boreal biomass burning emissions changes: a multi-model study, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2559, https://doi.org/10.5194/egusphere-egu25-2559, 2025.
Posters on site: Tue, 29 Apr, 14:00–15:45 | Hall X5
Single-layer stratocumulus clouds (Sc), as the most common cloud system for stratiform clouds, plays an important role in global radiative balance due to their duration and extensive coverage. However, there are still substantial uncertainties in their formation and radiative forcing, creating significant challenges for accurately assessing cloud-climate feedbacks in climate models. In this paper, we use the Cloudsat 2B-CLDCLASS-LIDAR product to distinguish them from other cloud types, and investigate their formation causes and radiative effects with the ERA5 datasets and the 2B-FLXHR-LIDAR. The results show that (1) the single-layer Sc exhibits obvious seasonal variation in the spatial distribution, which is closely related to the distribution of whole-layer humidity (TCWV) and Lower Tropospheric Stability (LTS). Different aerosol concentrations alter the effects of TCWV and LTS. (2) the Cloud Fraction (CF) of the single-layer Sc showed an upward trend during January 2007-December 2010. It is believed that the CF interannual variations of the single-layer Sc are related to the monthly temperature and humidity anomalies in the middle and lower layers of the atmospheric troposphere. (3) CF has a larger impact on shortwave radiative forcing than on longwave, but its effect depends on the cloud geometric thickness (CGT). When the cloud layer is thin (61<CGT<941m), the CF enhances the cloud shortwave and longwave radiative forcing, resulting in a regional cooling effect (slope_CERnet=-1.2756); the thick cloud layer (941–1820m) will inhibit both radiation forcings, leading to a warming effect (slope_CERnet=3.0932). These findings will help improve the simulation of cloud radiative forcing, thereby reducing uncertainties in climate change assessments.
How to cite: Deng, X., Han, Y., Lu, C., Xie, X., Zhang, Y., Lu, T., Dong, L., and Zhou, Q.: Distributional characteristics and causes of single-layer stratiform clouds in the Southeastern Pacific Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-354, https://doi.org/10.5194/egusphere-egu25-354, 2025.
In recent years, the scientific community has placed growing emphasis on the impact of aerosols on the Indian Summer Monsoon (ISM) system. The ISM, the world’s strongest monsoon system, delivers approximately 80% of India’s annual rainfall from June to September, sustaining ecosystems, agriculture, and millions of livelihoods. The Indian subcontinent, with its diverse geography, dense population, and industrial zones, is a major source of aerosols through short-range and long-range transportation. Aerosols are instrumental in the process of cloud formation, functioning as cloud condensation nuclei (CCN) and ice nuclei (IN), which are vital for the formation and evolution of cloud hydrometers. Numerous possible mechanisms by how aerosols influence rainfall have been suggested by recent research on the direct radiative effects of aerosols. However, the microphysical impact of aerosols on monsoonal rainfall in the Indian Summer Monsoon Region (ISMR) remains largely unexplored. Indian summer monsoon rainfall is influenced by the large-scale circulation and different monsoon drivers. The large-scale driver modulates clouds and indicates the sign of seasonal mean ISM rainfall anomalies and the role of aerosols are secondary. Our current understanding of both the direction and magnitude of aerosol-cloud interaction (ACI), which induced changes in rainfall is insufficient. Furthermore, changes in thermodynamic and climatic circumstances, precipitation types, their vertical distribution in the atmosphere, cloud and dynamics all have a significant impact on the ACI and give feedback to ISM rainfall. In this context, we will carry out a comprehensive analysis of multi-satellite observations and numerical model simulations to examine the role of aerosol on cloud properties and precipitation susceptibility. The analysis of multi-satellite data reveals considerable spatial and vertical variability of dust aerosols over the ISM region. Increased dust activity can modify the monsoon cloud system, leading to significant changes in the microphysics of both the liquid and ice phases over the ISM region. The process analysis of ACI is crucial for accurately predicting monsoonal rainfall and will help resolve discrepancies in aerosol-cloud-rainfall interactions between models and observations. While more aerosols tend to reduce the cloud drop size and delay the warm rain, during the Indian summer monsoon, this is overcome by invigoration in higher moisture environments and cold-rain processes. The observational and modeling studies will be helpful for in depth understanding the role of aerosols and their interactions with clouds on the hydrological cycle by modifying the cloud properties and monsoon intraseasonal oscillations. The process studies must be beneficial for the realistic parameterization of cloud processes in the NWP model and can provide a pathway for increasing the grid point ISM rainfall skill through fundamental basic research on cloud microphysical processes.
How to cite: Vettikkattu Babu Nair, A., Bhowmik, M., Chowdhury, R., Hazra, A., and Rao, S. A.: Exploring the hidden role of aerosols in altering the Indian Summer Monsoon rainfall variability through cloud modification, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-387, https://doi.org/10.5194/egusphere-egu25-387, 2025.
Aerosol susceptibility (AS) is a parameter describing the sensitivity of cloud properties (such as increasing albedo and decreasing precipitation) to increasing aerosol concentrations. It has been shown that AS of shallow warm clouds decreases monotonically but remains positive with increasing condensation nuclei (CN) concentration. However, the presence of ice in the mixed-phase cloud may disrupt such susceptibility. We investigated the effect of ice-phase processes on AS by applying the WRF model with an aerosol-sensitive cloud microphysical scheme running in 1 km resolution. The type of low clouds investigated are the boundary-layer-topped clouds (BLTC) occurring frequently over the Northwest Pacific Ocean in winter. Aerosol sensitivity is examined by applying a wide range of CN concentration and ice nucleation rates, with the latter mimicking ice nuclei effects.
Our simulation results show that, with ice in the cloud, AS weakens and does not decrease monotonically with increasing CN concentration. The weakening of AS is due to the more efficient snow formation through the Wegener-Bergeron-Findeisen (WBF) process, which becomes stronger with more numerous cloud drops (increasing CN). Stronger snow production also enhanced graupel initiation. However, the riming growth of graupel tends to be inhibited under high CN conditions. Such a seesaw effect disrupted the monotonic trend of AS. We also found that CN and ice-phase processes can affect cloud coverage, which, in turn, gives feedback to the overall AS of all-sky albedo.
How to cite: Chen, J.-P. and Wu, C.-K.: Ice-Phase Influence on Aerosol Susceptibility in Wintertime Marine Boundary-Layer Clouds over Northwest Pacific Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1182, https://doi.org/10.5194/egusphere-egu25-1182, 2025.
How to cite: Zhao, Y., Li, J., Wen, D., Li, Y., Wang, Y., and Huang, J.: Distinct structure, radiative effects, and precipitation characteristics of deep convection systems in the Tibetan Plateau compared to the tropical Indian Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1291, https://doi.org/10.5194/egusphere-egu25-1291, 2025.
In this study, we investigated how submicron aerosol particles (APs) are scavenged by cloud droplets and raindrops, including the effects of ice nucleation on these particles. We used an original two-moment aerosol scheme, which contains the prognostic equations for the number and mass of APs in the air and in all types of hydrometeors. This scheme was integrated into a three-moment microphysics scheme within a three-dimensional, non-hydrostatic Advanced Regional Prediction System (ARPS) model (Vučković et al. 2022, 2023).
We analyzed the scavenging of APs through electroscavenging processes, which involve Coulomb interactions with raindrops and both Coulomb and image charge interactions with cloud droplets. We assumed a Boltzmann charge distribution of aerosols, while cloud droplets and raindrops can possess either positive or negative charges in an amount that depends on their surface area. The kernels calculated for discrete bins of APs and droplets/drops are incorporated into the bulk microphysical scheme.
Ice nucleation on the APs is also considered a scavenging mechanism. This approach allows us to analyse how these processes impact the number and mass of APs in the atmosphere, hydrometeors, and those washed out by precipitation. Our results indicate that electroscavenging is the dominant process for medium to large submicron APs, whereas Brownian diffusion primarily affects smaller particles. Nucleation scavenging caused by depositional nucleation on atmospheric particles (APs) is identified as the primary mechanism for nucleation scavenging involving APs. This process is especially significant for reducing mass, while it plays a lesser role in decreasing the number of APs in the atmosphere.
Electrostatic collection by cloud droplets and raindrops enhance the scavenging of APs regardless of their charge sign, and the presence of image charges on cloud droplets further increases this collection. Increasing the charge on hydrometeors correlates with a greater number and mass of aerosol particles removed. The sign of the charge is less significant: our findings show that even when droplets are uncharged, the collection efficiency is still high. Depositional nucleation scavenging is identified as the most important mechanism for reducing the mass of APs (Vučković et al. 2024).
This approach provides valuable insights into the redistribution of APs between the atmosphere, hydrometeors and precipitation. The results are applicable to issues related to air pollution, cloud modification, and climate modelling.
Acknowledgement: This research was supported by the Science Fund of the Republic of Serbia, No. 7389, Project Extreme weather events in Serbia - analysis, modelling and impacts” – EXTREMES
References
Vučković, V., D. Vujović, and A. Jovanović, 2022: Aerosol parameterisation in a three-moment microphysical scheme: Numerical simulation of submicron-sized aerosol scavenging. Atmos Res, 273, 106148, https://doi.org/10.1016/j.atmosres.2022.106148.
Vučković, V., D. Vujović, and D. Savić, 2023: Influence of electrostatic collection on scavenging of submicron-sized aerosols by cloud droplets and raindrops. Aerosol Science and Technology, 57, https://doi.org/10.1080/02786826.2023.2251551.
Vučković, V., D. Vujović, D. Savić, and L. Filipović, 2024: Impact of electro-collection and ice nucleation on aerosol scavenging. Aerosol Science and Technology, https://doi.org/10.1080/02786826.2024.2441289.
How to cite: Vučković, V., Vujović, D., Savić, D., and Filipović, L.: Submicron-size aerosol scavenging by electro-collection and ice nucleation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1885, https://doi.org/10.5194/egusphere-egu25-1885, 2025.
The efficiency of cloud seeding in enhancing precipitation is a subject of active debate within the scientific community. This work examines the impacts of cloud seeding in changing cloud properties and dynamics over Tom Green County in West Texas, USA, from 2015 to 2020. Several cloud categories including small, large, and type B are considered. The effect of cloud-seeding missions in changing clouds’ lifetime, area, volume, and precipitation mass is investigated. The results show that the average increase in the lifetime of small, large, and type B is 53.6, 27, and 3.5%, respectively, while the average area increased by 47.1, 27.5, and 5.0% respectively, and their average volume increased by 63.6, 33, and 5.6% respectively. A significant increase in the precipitation mass of the small, large, and type B clouds is observed after the seeding missions. From 2015 to 2020, the precipitation rates in seeded clouds are higher than the unseeded clouds. Comparing precipitation rates during the 2015–2020 cloud-seeding campaigns to the period from 2010 to 2014 before the campaigns shows no trend of increasing precipitation except during 2015 and 2016.
How to cite: Al Homoud, M., Logothetis, S.-A., SR Elnaggar, Y., and Farahat, A.: Assessment of the Cloud Seeding Efficiency over Tom Green County Texas, USA, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1987, https://doi.org/10.5194/egusphere-egu25-1987, 2025.
Shallow clouds significantly influence the Earth's radiative balance by modulating incoming and outgoing shortwave radiation. The formation and characteristics of shallow clouds are closely coupled with the land-atmosphere interactions and hence urbanization can have a distinct impact on the occurrence of shallow clouds. This study investigates the occurrence and radiative properties of shallow clouds using simultaneous observations of mini–Micro-Pulsed Lidar (MPL), pyranometers and a network of sky imager over Chennai. These observations span over four sites across Chennai, representing a mix of urban and semi-urban microenvironments, during the months of January and February. Largely, shallow clouds are having a mean cloud base height of 800-1000 m and a mean cloud thickness of 250-300 m. Mean cloud radiative forcing (CRF) of -200 W/m², confirms the strong cooling effect of shallow clouds. The diurnal variation of hourly averaged cloud fraction (CF) shows a peak of 0.3 around 10:00AM, followed by a gradual decline, consistent with the lifecycle of shallow clouds driven by local meteorological conditions, including temperature and humidity fluctuations. A strong negative correlation (r = -0.95) was observed between CF and CRF, highlighting enhanced cooling effects of shallow clouds with increasing CF. The detailed differences in CRF, CF and cloud albedo from the three additional sites spanning the urban to rural transect across the city will be discussed. Observational findings will provide valuable empirical data for refining cloud-climate interactions over urban environments in northeast monsoon region.
How to cite: Kumar Sarangi, S., Sarangi, C., Patel, N., Ali, S., Karimpuzha Ramadas, A., Hemanth, A., and Kumar Mehta, S.: Urban-Rural differences in characteristics for Shallow Clouds observed over Chennai, a tropical megacity in India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2046, https://doi.org/10.5194/egusphere-egu25-2046, 2025.
This study investigates the hydro-climatic changes in the Central-South Asia and Tibetan Plateau (CSATP) region under two future scenarios: high greenhouse gas emissions (SSP5-8.5) and the combined impact of greenhouse gases with stratospheric aerosol intervention (SAI). Using model simulations, we analyze key variables such as total water storage (TWS), temperature (TMP), precipitation (PCP), real evapotranspiration (RET), soil moisture (SM), and leaf area index (LAI) over the historical period (1985–2014) and the future period (2071–2100). The SSP5-8.5 scenario projects a significant increase in temperature, RET, precipitation extremes, and reductions in TWS, SM, and LAI, reflecting the adverse effects of unmitigated global warming. Conversely, the SSP5-8.5+SAI scenario demonstrates the potential to moderate these impacts. SAI reduces temperature anomalies and precipitation extremes while stabilizing RET, SM, and LAI levels. Results reveal region-specific responses; for instance, in the Tibetan Plateau, significant temperature and precipitation variability reductions are observed under SAI, highlighting its role in mitigating climate extremes. Similarly, soil moisture and TWS exhibit more stable trends under SAI than in the SSP-only scenario, underscoring its effectiveness in counteracting warming-induced drying trends. Overall, the findings underscore the critical role of SAI in alleviating the adverse hydro-climatic impacts of greenhouse gas emissions. While SAI does not entirely negate these impacts, it provides a viable pathway for reducing extremes and fostering climate stability in vulnerable regions. This study contributes to understanding the implications of climate engineering as a complementary strategy for climate adaptation in the CSATP region.
How to cite: Hussain, I., Hussain, A., and Rezaei, A.: Future hydro-climatic changes in Central-South Asia and Tibetan Plateau in response to global warming and stratospheric aerosol intervention scenarios, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2246, https://doi.org/10.5194/egusphere-egu25-2246, 2025.
There is a recognized urgent need for broadening and coordinating access to scientific information regarding Solar Radiation Modification (SRM) to support evidence-based decision making. To build such capacity, the research community has expressed the need for accessible and searchable metadata about modeling studies of SRM and associated impacts.
For this purpose, we have put together a prototype for a Repository, which is an extensive collection of peer-reviewed articles of Earth System Models (ESMs) simulations whose outputs have been used by impacts studies, and impacts studies that have used ESM data outputs. In its current version, the repository offers a list of peer-reviewed journal articles, with specific meta-data such as specific information on climate models, scenarios or impact targets used to simulate SRM, in order to enable users with the ability to identify the most relevant studies to their own research. The repository is accompanied by a Guide targeted at new entrants to the field, such as graduate students and established researchers conducting their first SRM studies. The Guide offers a narrative description of ESM experiments available for SRM impacts research today and reviews current limitations, uncertainties, and gaps that remain unaddressed. These resources will be freely available online.
How to cite: Kaufmann, S., Lamarque, J.-F., and Wong, A.: Resources on SRM Science for New Researchers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2298, https://doi.org/10.5194/egusphere-egu25-2298, 2025.
The 26th United Nations Climate Change Conference (COP26) proposes to limit global warming to <1.5 °C above pre-industrial levels until 2030 and aligns CO2 emissions with net-zero by 2050. To achieve this goal, it is crucial to replace fossil fuels with renewable and clean energy sources. Among the various renewable energy sources, solar energy undoubtedly stands out as an attractive option. Future meteorological conditions and emission reductions are expected to impact on solar energy potential. Consequently, the Weather Research and Forecasting model with chemistry (WRF-Chem) was applied to current (2016–2020) and future (2046–2050) under the shared socio-economic pathways (SSP) 2–4.5 scenario to investigate the impact of future meteorological conditions and emission reductions on solar energy potential. The evaluation of the WRF-Chem demonstrates satisfactory performance in capturing most meteorological and chemical variables at a climatological scale. However, the model underestimates 2 m temperature while overestimating 2 m specific humidity and 10 m wind speed, with mean bias (MB) of -0.1°C, 1.4 g kg-1, and 0.8 m s-1, respectively. Additionally, the WRF-Chem overestimates PM2.5, with normalized mean bias (NMB) of -20%. The model underestimates cloud fraction and precipitation caused by the limitation in the cloud microphysical parameterization. The model well reproduced the solar energy distribution in China, with R of 0.76 and NMB of -3%. Looking ahead, the future annual average solar energy increases by 2.2, 0.1, 2, 4.1, 1.9, and 2.9 W m-2 for China, Beijing-Tianjin-Hebei, Fenwei Plain, Yangtze River Delta, Pearl River Delta, and Sichuan Basin, respectively. The future annual average photovoltaic potential increase by 1–4% in these regions. This increase is primarily attributed to the increase in solar energy resulting from emission reductions (4.7, 5.1, 5.0, 4.7, 3.2, and 6.1 W m-2), which outweighs the decrease caused by meteorological conditions (2.5, 5.0, 2, 4.1, 1.9, and 2.9 W m-2). Hence, emission reduction plays a vital role in promoting solar energy utilization.
How to cite: Gao, Y., Zhang, Y., and Zhang, M.: Assessment of future solar energy potential changes under the shared socio-economic pathways scenario 2–4.5 with WRF-chem: The roles of meteorology and emission, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2412, https://doi.org/10.5194/egusphere-egu25-2412, 2025.
During the winter monsoon, a high-pressure ridge extends from Siberia to the northern South China Sea (SCS). This system brings northeasterly cold air, which rises over the warm sea surface of the SCS, causing atmospheric instability and frequent convection over the region. This continental cold-air outbreak also forms cloud streets over the northwestern Pacific. In this study, we investigated the effects of aerosol-cloud interactions over the upstream northwestern Pacific (e.g., the East China Sea) on convective activity in the downstream tropical area (e.g., the South China Sea). To achieve this, we selected two distinct cases associated with boundary layer clouds and conducted sensitivity experiments using different aerosol types—such as anthropogenic or continental, oceanic, and mixed aerosols—to simulate convection characteristics over the SCS. For our analysis, we employed the aerosol-sensitive National Taiwan University (NTU) multimoment microphysical scheme coupled with the Weather Research and Forecasting (WRF) model. Our results indicate that the thermal and moisture properties of the winter cold-air mass reaching the SCS and tropical oceans can be significantly influenced by anthropogenic aerosols produced over the East Asian continent. We also examined variations in orographic rainfall patterns over different regions, such as northeastern Taiwan and coastal Vietnam, in relation to these boundary layer clouds and their sensitivity to the choice of aerosol types. This study highlights the importance of using a multimoment microphysical scheme capable of accounting for diverse aerosol types to improve simulation accuracy with the WRF model.
Keywords: Aerosol-cloud interaction, South China Sea, Boundary layer clouds, WRF
How to cite: Dutta, U., Wu, C.-K., and Chen, J.-P.: Role of aerosols in modulating the convection over the South China Sea associated with boundary layer clouds during boreal winter, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2741, https://doi.org/10.5194/egusphere-egu25-2741, 2025.
Diurnal cloud pattern (DCP) determines total clouds’ impacts on Earth’s radiation balance in one day and is sensitive to climate change. Changes in DCP affect diurnal cycle of radiation and temperature, leading to obvious impacts on vegetation growth and human health, but with less attention and large projection spread. Here we show that future changes in cloud is significantly linked to present-day clouds’ climatology, reducing uncertainty by 60%-70% over typical regions. Under warming climate, various long-term trends in cloud fraction (CF) at different times determine the DCP changes. There are largely decreased noon and lightly changed night CF for most land, while distinct CF reduction at all times but more sever in the afternoon for ocean. Therefore, maritime (continental) area has enhanced (attenuate) amplitude, i.e., daily cloud variation rate, and more (less) shift of DCP. These DCP changes with significant CF deviation would reduce net cloud radiative (cooling) effect, amplifying surface warming. Especially, tremendous daily net radiative warming (exceeding 100 Wh/m2) occurs in extensive midlatitude ocean domain due to remarkable afternoon CF reduction.
How to cite: zhao, Y., Li, J., Wang, S., Wang, Y., and Wang, Y.: Constrained changes in future diurnal cloud pattern cause stronger ocean warming and radiation imbalance, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2980, https://doi.org/10.5194/egusphere-egu25-2980, 2025.
This study systematically evaluates clouds and their radiative impacts in the newly released U. S. Department of Energy (DOE)’s Energy Exascale Earth System Model (E3SM) version 3 using both satellite data and the DOE Atmospheric Radiation Measurement (ARM) program’s ground-based measurements. The comparison is done by utilizing the Cloud Feedback Model Intercomparison Project (CFMIP) Observation Simulator Package (COSP) and the ground-based lidar and radar simulator package, the Earth Model Column Collaboratory (EMC^2), to improve the model-observation cloud comparison. The use of detailed ARM cloud observations is to better diagnose the strengths and deficiencies of E3SM through process-level understanding. Compared to its earlier versions, E3SMv3 has significantly updated its atmospheric physical parameterizations including noticeable improvements in representing cloud and convective processes. These include the use of the Predicted Particle Properties (P3) scheme for stratiform clouds to improve the treatment of ice microphysical processes and aerosol-cloud interactions and a more sophisticated two-moment bulk cloud microphysics scheme for the Zhang-McFarlane (ZM) deep convection. In addition, mesoscale heating from organized convection is added on top of the ZM deep convective heating. The interactions of deep convection with its environment are enhanced. Several carefully defined sensitivity tests are conducted by tuning off each of the major changes relevant to clouds and convection to isolate their individual impacts on simulation of clouds. Detailed results will be presented in the meeting.
How to cite: Zhang, Y., Xie, S., Terai, R. C., Lin, W., Golaz, J.-C., Zhang, M., Qian, Y., and Tang, Q.: Towards Understanding Biases in Cloud Radiative Effects Simulated in E3SMv3, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3333, https://doi.org/10.5194/egusphere-egu25-3333, 2025.
Deep Convective Clouds (DCCs) are associated with severe weather, where ‘severity’ refers to the potential negative impact of weather systems on human safety and the economy. As a natural hazard, convective storms need to be incorporated into mitigation plans, which is particularly important for mid-latitudes. Additionally, in a warming climate, extreme events are expected to occur more frequently. Motivated by the lack of DCC-focused air mass studies, this work evaluates how changes in circulation (air mass location and transport) relate to DCC activity over Poland.
The two generations of Meteosat observations provide a unique data record for studying the atmosphere and climate variability over Europe since the 1980s. Meteosat data enable the detection and, in a basic form, the tracking of DCCs, but the monitoring is limited to the lifetime of DCCs. While Meteosat data allow for the tracking of DCCs to some extent, identifying and following the air mass associated with their formation is not feasible using Meteosat data alone. One approach to overcoming this obstacle is to track air parcel transport in the atmosphere—i.e., calculating air parcel trajectories.
In this research, we identify cases of Deep Convective Clouds over Poland using the bi-spectral threshold method for DCC detection, which assesses differences in Brightness Temperature (BT) between infrared and water vapor channels. Our analysis is based on Meteosat Visible Infra-Red Imager (MVIRI) and Spinning Enhanced Visible Infra-Red Imager (SEVIRI) retrievals from the summer season of 2005. Thereafter, for each observation time, we determine which cells of a 0.25°×0.25° grid over Poland can be classified as having DCCs present and calculate the backward trajectory of the air mass for the center of each grid cell. For tracking purposes, we use the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, a widely recognized tool developed by the National Oceanic and Atmospheric Administration (NOAA) Air Resources Laboratory. The study examines air mass patterns associated with deep convective clouds forming over Poland and addresses the question: What are the dominant air mass sources and transport pathways leading to the formation of DCCs over Poland?
This research was funded by the National Science Centre of Poland. Grant no. UMO-2023/49/N/ST10/00366.
How to cite: Wojciechowska, I. and Kotarba, A.: Air Mass Patterns for Deep Convective Clouds over Poland in the first and second generation Meteosat retrievals, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3346, https://doi.org/10.5194/egusphere-egu25-3346, 2025.
Atmospheric aerosols not only cause severe haze pollution, but also affect climate through changes in cloud properties. However, during the haze pollution, aerosol-cloud interactions are not well understood due to a lack of in-situ observations. In this study, we conducted simultaneous observations of cloud droplet and particle number size distribution, together with supporting atmospheric parameters, from ground to cloud base in East China using a high-payload tethered airship. We found that high concentrations of aerosols and cloud condensation nuclei were constrained below cloud, leading to the pronounced “Twomey effect” near the cloud base. The cloud inhibited the pollutants dispersion by reducing surface heat flux and thus deteriorated the near-surface haze pollution. Satellite retrievals matched well with the in-situ observations for low stratus clouds, while were insufficient to quantify aerosol-cloud interactions for other cases. Our results highlight the importance to combine in-situ vertical and satellite observations to quantify the aerosol-cloud interactions.
How to cite: Qi, X., Zhu, C., Chen, L., Chi, X., Wang, J., Niu, G., Lai, S., Nie, W., Zhu, Y., Huang, X., Kokkonen, T. V., Petäjä, T., Kerminen, V.-M., Kulmala, M., and Ding, A.: Aerosol-cloud interactions near cloud base deteriorating the haze pollution in East China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3965, https://doi.org/10.5194/egusphere-egu25-3965, 2025.
Droughts, prolonged periods of deficient precipitation and heightened evapotranspiration, pose severe threats to water resources, ecosystems, and socioeconomic well-being worldwide. While previous research has established that the continuous growth of greenhouse gas (GHG) emissions is a primary driver of global warming and the associated intensification of the hydrological cycle, the role of non-methane near-term climate forcers (NTCFs), including anthropogenic aerosols, in modulating drought risk remains less clearly understood. In particular, the complex interplay between aerosol-induced radiative cooling and greenhouse warming can produce non-linear drought responses at regional scales, notably in arid and semi-arid regions.
In this study, we employ seven Earth System Models (ESMs) participating in the Phase 6 of the Coupled Model Intercomparison Project (CMIP6) to investigate the specific contributions of NTCFs emission reduction to the evolution of drought characteristics (i.e., frequency, duration, and severity) under the SSP3-7.0 scenario. Droughts are identified by using the Standardized Precipitation Evapotranspiration Index (SPEI) at multiple timescales (3, 6, and 12 months).
Results reveal considerable spatial heterogeneity in the responses of drought metrics. Reductions in NTCFs generally lead to cooler temperatures and, in many tropical and mid-latitude regions, enhanced precipitation. For parts of southern Africa and South America, these changes translate into fewer and shorter droughts under the SSP3-7.0-lowNTCF scenario compared to SSP3-7.0. By contrast, arid and semi-arid regions such as the Sahara and West Asia exhibit a worsening of drought conditions—drought events become more frequent, severe, and prolonged. These outcomes indicate that aerosol-related cooling and its impact on atmospheric circulation may, in some regions, help maintain or strengthen rainfall, so that reducing aerosols can inadvertently diminish that effect and exacerbate water deficits. Indeed, our multi-model ensemble suggests heightened water stress in the Sahara and West Asia under the SSP3-7.0-lowNTCF scenario, underscoring how local feedbacks and large-scale circulation patterns can alter the hydrological response to emission mitigation.
Overall, our findings highlight the non-linear and regionally dependent effects of NTCF mitigation on drought risk. In many regions, curtailing aerosol and ozone-precursor emissions offers co-benefits for air quality and climate adaptation by decreasing drought likelihood; however, arid and semi-arid areas may face more severe drought outcomes.
How to cite: Zhou, T. and Bollasina, M.: Impacts of reductions in non-methane short-lived climate forcers on future droughts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4312, https://doi.org/10.5194/egusphere-egu25-4312, 2025.
Aerosol perturbations primarily affect albedo (Bellouin et al., 2019) by scattering a fraction of insolation back into space. Specifically, aerosol emissions enhance cloud formation and cloud cover, which directly increase albedo.
To investigate this effect, we analyze CMIP6 data from a set of experiments conducted using models with robust aerosol modules. Our focus is on variables such as cloud droplet number concentration, which reflect aerosol emissions, and cloud fraction, as well as their correlation with the shortwave radiative flux at the top of the atmosphere.
To achieve this, we apply a Random Forest Regression to the dataset, enabling a more precise quantification of the impact of aerosol-cloud interactions on the atmosphere’s radiative balance
How to cite: Clement, N.: Impact of aerosol-cloud interaction on aerosol effective radiative forcing revealed by a Random Forest Regression over CMIP6 data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5943, https://doi.org/10.5194/egusphere-egu25-5943, 2025.
In the Southern Hemisphere, regions in South America are recognized as significant sources of carbonaceous aerosols, which are produced by biomass burning. This type of burning typically occurs during the winter months, predominantly in the region known as the "Deforestation Arc," often associated with the expansion of agricultural and livestock production areas in Brazil. Given the limited number of observations in this region, numerical modeling becomes essential for analyzing and accurately representing biomass burning events. In this context, the purpose of this study is to discretize the atmospheric behavior during fire events across South America by utilizing the Weather Research and Forecasting with Chemistry (WRF-Chem) model, thereby assessing the impact of these carbonaceous aerosols on cloud microphysics throughout the region.
For this study, WRF-Chem version 4.3.1 was employed. The simulation began on September 28, 2007, and ended on October 3, 2007, using ERA5 fields to provide the initial and boundary conditions with a spatial resolution of 0.25°. The domain covered the South American region. Two simulations were conducted: the first, referred to as the control simulation (CTRL), had the coupling between aerosols, radiation, and cloud microphysics turned off, while the second, the fully coupled simulation (CPL), enabled both couplings. This approach facilitates a subsequent analysis to distinguish the role of aerosols on radiative properties and quantify the effects of coupling. For the analysis, precipitation fields, radiation components, and hydrometeor composition were evaluated in both simulations. This approach provides insights into the influence of biomass-burning aerosols on atmospheric processes and their role in modifying cloud microphysics and radiative balance.
How to cite: Lima de Bem, D., Anabor, V., Steffenel, L. A., Brenner, L., Morichetti, M., and Rizza, U.: Simulation of Biomass Burning Events and Their Atmospheric Effects: A Study with WRF-Chem, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6413, https://doi.org/10.5194/egusphere-egu25-6413, 2025.
Maritime stratocumulus clouds play a crucial role in Earth’s climate system by reflecting incoming solar radiation. The optical and microphysical properties of stratocumulus are determined by the droplet size distribution (DSD), commonly characterized by the mean droplet radius and relative dispersion. In this study, we identify distinct droplet evolution regimes within the stratocumulus-topped boundary layer (STBL) by tracking individual droplets in large-eddy simulations coupled with Lagrangian cloud microphysics. Two dominant regimes emerge: the adiabatic growth regime, dominated by droplet activation and condensation in the updraft, and the entrainment and descent regime. Droplets in the adiabatic growth regime follow consistent trajectories, with increasing mean droplet radius and decreasing relative dispersion. In the entrainment and descent regime, however, droplets follow diverse pathways: Droplets directly affected by entrainment and mixing at the cloud top show signs of inhomogeneous mixing, with some droplets completely evaporating, while droplets following the downdrafts without being directly affected by entrainment and mixing exhibit smoother changes in microphysical properties, resembling homogeneous mixing, indicating that such mixing-like signatures can arise from the large-scale STBL dynamics rather than mixing alone. This study underscores the complexity of droplet evolution within stratocumulus and highlights the need to distinguish between microphysical processes and large-scale dynamics when interpreting observed or simulated mixing-related microphysical properties.
How to cite: Lim, J.-S. and Hoffmann, F.: Regimes of Droplet Size Distribution Evolution in Stratocumulus: From Adiabatic Growth to Entrainment and Mixing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8044, https://doi.org/10.5194/egusphere-egu25-8044, 2025.
As the most populous and rapidly developing region, Asia has garnered significant attention regarding the anthropogenic influence on the atmospheric composition, climate, and hydrological cycle. Air pollution due to industrialization and urbanization is a local issue; however, its influence may go beyond regional scales due to large-scale atmospheric circulations along with the transport and evolution of particles. In this study, we investigated the impact of atmospheric circulation on regional air quality and its associated influence on regional precipitation. The datasets used for the analysis are the Cloud and the Earth’s Radiant Energy System (CERES – MODIS) and MERRA-2 Aerosol Optical Depth (AOD), Tropical Rainfall Measuring Mission (TRMM) rainfall and ERA-5 wind components for the years 2000 - 2019. The eastward drift of aerosol, along with the wind patterns, is observed. Also, the impacts of the long-range transport of natural and anthropogenic aerosols, as well as dust particles originating from the surrounding land masses, on the deepening of marine clouds and precipitation are evident over Southeast Asia. Moreover, the frequency and intensity of rain events exhibit modulation in response to the aerosol type and through their transport and interaction with clouds, and their vertical profile mainly by its impact on atmospheric heating. The Indian Ocean and Maritime Continent experience significant variability in both precipitation and AOD, reflecting the strong influence of the Madden-Julian Oscillation (MJO) in these regions. This highlights the importance of MJO in modulating aerosol distribution, which can further influence radiative forcing and local weather patterns. Understanding this coupling is critical for assessing regional air quality, hydrological cycles, and climate variability in tropical regions affected by the MJO.
How to cite: Joy, S., Avaronthan Veettil, S., and Vazhathottathil, M.: Wind-induced aerosol transport and associated precipitation enhancement over South - East Asia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8549, https://doi.org/10.5194/egusphere-egu25-8549, 2025.
High-resolution simulations such as direct numerical simulations (DNS) are imperative to resolve the metre-scale variability in the stratocumulus-topped boundary layer (STBL). Previous research has considered the liquid water path (LWP) as a proxy for the longwave radiative transfer, to simplify the expensive radiative transfer calculations. However, the contribution to the radiative fluxes from the absorptive gases is thereby neglected. Utilising the line-by-line radiative transfer model ARTS, we show that the cloud top radiative cooling is underestimated by 30% in earlier simulations that employed the LWP parametrisation. Moreover, we identify a layer warming at 2.5 K h-1 with thickness of merely about 5 m directly above the cloud top, which we call the cloud top inversional heating layer (CTIHL), the warming in which is attributed to the clear sky radiative effect. About the cloud top inversion, the absorptive gases, predominantly water vapour and carbon dioxide, exchange heat locally due to the strong temperature gradient. The clear sky radiative warming is compensated in the cloud layer by the cloud top radiative cooling due to the liquid water, resulting in the minimal thickness of the CTIHL, which poses challenge for observations. We investigate the environmental factors which modulate the strength of the CTIHL. It is determined that the warming magnitude of the CTIHL is sensitive to the strength of the inversion and water vapour content, but less to the concentration of carbon dioxide.
How to cite: Chan, K., Buehler, S. A., Mellado, J. P., and Brath, M.: Unveiling the hidden heating layer at the top of stratocumuli, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8619, https://doi.org/10.5194/egusphere-egu25-8619, 2025.
In this contribution, a statistical model built on observations (ERA5, SEVIRI) is used with climate model data from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to estimate the cloud-system responses to climate change in the Namib desert.
Fog, which is the most relevant non-rainfall water source for plants and animals in the coastal parts of the Namib Desert, may become increasingly important for local ecosystems as regional climate simulations predict a warmer and drier climate for southern Africa in the future. However, projecting changes in fog using global circulation models (GCMs) or even regional climate models (RCMs) is challenging because these numerical models often cannot resolve, or have yet to incorporate, many processes that drive fog development.
A statistical model is developed to predict fog and low cloud (FLC) occurrence in the Namib region by combining reanalysis products with satellite data. Assuming that the relationships learned by the statistical model in the current climate remain valid in the future, this model can utilize climate model outputs from CMIP6 as predictors to estimate changes in FLCs in the region.
It is found that under low-emission scenarios like SSP1-2.6, FLC cover remains mostly constant. In contrast, higher-emission scenarios such as SSP3-7.0 project a decrease in FLC cover by up to 10%, with this decline accelerating around 2050.
How to cite: Mass, A., Andersen, H., and Cermak, J.: How will climate change impact fog and low clouds in the Namib desert?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8750, https://doi.org/10.5194/egusphere-egu25-8750, 2025.
Key words: Cloud Radiative Effects (CRE), Three-Dimensional Radiative Transfer, ICON, MYSTIC, Low-Level Clouds, Cloud Microphysics
Abstract: The microphysical properties of low-level clouds play a critical role in influencing threedimensional (3D) cloud radiative effects (CRE), yet significant uncertainties and approximations persist in their parametrizations. Our research investigates how detailed microphysical parameterizations and high-resolution simulations can advance the representation of 3D CREs. We intend to establish a thorough framework for examining cloud-radiation interactions by integrating regional and local simulations with data from extensive observational campaigns. As a first step towards this objective, we present preliminary results from nested simulations of the ICON model at hectometer resolution, targeting specific low-level cloud regimes over the Lindenberg Observatory in Germany. Cloud microphysics is simulated with a two-moment microphysical scheme. The 3D cloud radiative effects are estimated from the application of the 3D radiative transfer model MYSTIC in offline mode. The resulting model data are extensively evaluated against observed ground-based radiation fluxes and cloud radar data. We discuss how spatial cloud heterogeneity and microphysical complexity significantly modulate the deviations between 1D and 3D CRE estimates. By integrating high-resolution simulations with advanced observational datasets, this work provides critical insights into the mechanisms driving cloud radiative effects and their representation in climate models. Ultimately, this project will lay the foundations for refining parameterizations of cloud feedbacks and enhancing the realism of atmospheric radiation schemes.
How to cite: Bellagente, I. E. and Senf, F.: How 3D cloud radiative effects are influenced by microphysics of low-level clouds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8938, https://doi.org/10.5194/egusphere-egu25-8938, 2025.
Aerosols from biomass burning significantly impact human health, climate and society. These particles can be both natural and human-induced sources. While wildfires are considered a natural source, seasonal burning of agricultural fields before planting is an example for anthropogenic sources. With increasing global temperatures, the frequency and intensity of wildfires are escalating. Despite their importance, our understanding of these aerosols and their accurate representation in global emission inventories remain inadequate. The current estimates of the global direct radiative forcing of these aerosols range from net cooling to net warming in climate models. This shows how little we know about these aerosols and the chemical transformation they undergo as they age when they are advected farther away from the source regions. The optical properties of these biomass burning aerosols depends on the type of vegetation that is burnt, the type of burning and the prevailing meteorological conditions. Hence, in this study, we attempt to evaluate their optical properties at the source and also, as they are transported away from their source and age.
Here, we use MODIS data to locate the fires in Africa and we chose those fires based on the percentage of area burnt and the fire intensity. A trajectory model, HYSPLIT, is run to get the trajectory of the fire plumes. These trajectories are then collocated with the CALIPSO tracks to estimate the optical properties of these aerosols as they age away from the source regions.
How to cite: Thomas, M. A., Devasthale, A., and Kahnert, M.: Insights into aging of biomass burning aerosols based on satellite observations and trajectory modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10008, https://doi.org/10.5194/egusphere-egu25-10008, 2025.
Clouds play an important role in the Earth’s climate through well-established mechanisms, such as their interactions with solar radiation and their role in precipitation. However, their influence on future climate projections remains highly uncertain. One of the key challenges is the understanding of aerosol-cloud interactions in studying clouds, as aerosols can serve as cloud condensation nuclei. Aerosols can have significant variability across both space and time. While in situ measurements provide precise data for a small atmospheric volume—just a few cubic centimetres—they may not accurately reflect the spatial (horizontal and vertical) variability of aerosol characteristics and therefore do not give accurate statistical information on the average cloud state and its variability.
Airborne observations offer the capability of sampling a larger volume of the atmosphere and therefore give a more comprehensive understanding of clouds.This study highlights UAV-based observations of particle size distributions both inside and outside clouds, conducted during the #CHOPIN (CleanCloud Helmos Orographic Site Experiment) campaign. As part of this campaign, the Unmanned Systems Research Laboratory (USRL) of the Cyprus Institute deployed light Unmanned Aircraft Systems at Mt. Helmos, Greece, from October 11 to November 1, 2024, providing valuable data for the study of clouds and their interactions with aerosols. This is one of the few times USRL/CYI reported observations aerosol-cloud interaction flights.
The #CHOPIN campaign, conducted in collaboration with NCSR Demokritos and FORTH/EPFL, was hosted at the Kalavryta Ski Center with a base altitude for the UAS takeoffs and landings of ~1.7 km ASL. The campaign aimed to improve the understanding of aerosol-cloud interactions and to evaluate remote sensing algorithms and models. Located in a rapidly changing "climate hotspot" at the intersection of various air masses, Mount Helmos is particularly sensitive to environmental changes, with interactions between wildfire smoke, pollution, sea salt, and Saharan dust. This unique setting provides an ideal location to study the dynamics of aerosol-cloud interactions.
During the campaign, several flights were performed inside and outside clouds operating in a horizontal area of approximately ~16km² and providing vertical profiles of particle size distribution from the ground up to 3.5 km ASL. We will focus on the cloud observations and the derivation of particle and droplet size distributions from UAV-based optical particle counters. These observations provide a good dataset for improving cloud-resolving models and for comparison with fixed station observations.
How to cite: Papetta, A., Voß, A., Goret, M., Håkansson, L., Michailidis, K., Bezantakos, S., Biskos, G., Kezoudi, M., Mihalopoulos, N., Sciare, J., and Marenco, F.: UAV-Based Insights into Cloud Particle Size Distributions from the CHOPIN Campaign, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13039, https://doi.org/10.5194/egusphere-egu25-13039, 2025.
Atmospheric aerosol particles are essential to Earth’s climate, serving as the nuclei for cloud droplet formation. The process of cloud droplet formation directly links aerosols and clouds, thereby influencing cloud properties (e.g., albedo and lifetime). Model estimates of effective radiative forcing suggest a net cooling effect from aerosol-cloud interactions (–0.84 W m‑2), but the wide range of values (–1.45 to –0.25 W m‑2) has hindered future climate projections (Masson-Delmotte et al., 2021).
Aerosol activation in general circulation models (GCMs) is parameterised, with the Abdul-Razzak & Ghan (2000; ARG) scheme used in the Unified Model for its efficiency, while the Morales Betancourt & Nenes (2014; MN) scheme represents a recent addition. These parameterisations are based on adiabatic cloud parcel model theory and estimate the maximum supersaturation (Smax) from which the cloud droplet number concentration (Nd) is derived. We will demonstrate that an improved GCM representation of cloud droplet formation is vital for constraining estimates of the climatic effect of aerosol-cloud interactions using a three-step holistic framework:
- Direct comparison of parameterisations against an efficient cloud parcel model
In this study the DiffeRential Evolution Adaptive Metropolis (DREAM) Markov Chain Monte Carlo algorithm (Vrugt et al., 2009) is used to compare predictions of Smax and Nd from the ARG and MN schemes with those from the Pseudo-Adiabatic bin-micRophySics university of Exeter Cloud parcel model (PARSEC), using model input parameters selected near-randomly from predefined prior ranges that reflect those used in GCMs. These comparisons show that ARG underestimates both Smax and Nd relative to PARSEC (both by up to ~60%), while MN, to a lesser extent, overpredicts both values. Crucially for future climate projections, we identify differences in model sensitivity to input parameters (e.g., updraft velocity), and parameter combinations, between the parameterisations and PARSEC.
- Offline evaluation against in-situ observations
The DREAM algorithm is applied within an inverse modelling framework to perform Nd closure experiments, using data from three marine aircraft campaigns that span updraft- and number-limited regimes. The results show that, compared to PARSEC, both ARG and MN often fail to match observed Nd, with ARG significantly underestimating Nd. Our framework reveals parameter sensitivities and correlations, offering insights for refining models and guiding future measurement campaigns.
- Online evaluation – exploring the Southern Ocean albedo bias
GCM predictions of cloud albedo in the Southern Ocean are significantly underestimated relative to observations (Mulcahy et al., 2018). Here, PARSEC has been integrated into the UK Met Office climate model, allowing the first online evaluation of existing aerosol activation parameterisations. Importantly, we quantify the impact of cloud droplet formation representation on the observed Southern Ocean albedo bias.
Finally, we will discuss the implications of our findings from (1-3) for the effectiveness of current aerosol activation parameterisations for geoengineering via marine cloud brightening.
(1) Masson-Delmotte, et al., 2021, DOI:10.1017/9781009157896.001, (2) Abdul-Razzak, H. and Ghan, S. J., 2000, DOI: 10.1029/1999JD901161, (3) Morales Betancourt, R. and Nenes, A, 2014, DOI: 10.5194/gmd-7-2345-2014, (4) Vrugt, J. A., et al., 2009, DOI:10.1515/IJNSNS.2009.10.3.273, (5) Mulcahy, J, P., et al., 2018, DOI: 10.1029/2018MS001464.
How to cite: Knight, J., Haslum, M., Bowen, P., Bearman, E., and Partridge, D.: A Holistic Investigation of Cloud Droplet Formation Representation in General Circulation Models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13393, https://doi.org/10.5194/egusphere-egu25-13393, 2025.
Sea Salt Aerosols (SSA) constitute a primary component of atmospheric aerosols over the ocean, playing an important role in Earth's radiation balance, cloud formation, and precipitation processes. These aerosols serve as significant cloud condensation nuclei for marine clouds, with their production influenced by wind speed, sea temperature, and salinity, and are directly emitted from the sea surface via sea spray. Their strong hygroscopic nature allows them to maintain water content even under unsaturated conditions, thereby impacting heat flux, atmospheric water vapor content, cloud droplet water content, and precipitation intensity. Current research either focuses on the effects of SSA emission fluxes on water vapor and heat flux under diverse marine meteorological conditions, often neglecting the microphysical processes of SSA as hydrometeors, or employs computationally intensive microphysical schemes that are not readily applicable in practice. This study calculates SSA emission fluxes based on sea surface temperature and wind speed, applying a computationally efficient bulk parameterization approach for SSA microphysical processes. The methodology is integrated with the WRF numerical model to examine the influence of SSA microphysical processes on the microphysics of tropical cyclones under idealized conditions, with a focus on cloud formation and precipitation processes.
How to cite: Liu, X., Chen, R., Xue, L., and Chen, S.: Effects of the Sea Salt Aerosol On an Idealized Tropical Cyclone Microphysics Using a Bulk Method, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14185, https://doi.org/10.5194/egusphere-egu25-14185, 2025.
The anthropogenic perturbation to cloud droplet number concentration (ΔlnNd) can be derived from the Nd-to-aerosol sensitivity in the present day (PD) (ßPD), and the anthropogenic perturbation to aerosol from the pre-industrial (PI) to PD. A key assumption in this process is that the PD aerosol-Nd relationship is indicative of the actual sensitivity of Nd to anthropogenic perturbation to aerosol, i.e., the PI-to-PD sensitivity (ßPI-PD). This assumption holds true only when using the cloud condensation nuclei at cloud base (CCNb) as the CCNb-Nd relationship is not dependent on aerosol regime. However, due to the difficulty in obtaining CCNb at a large scale, in practice one has to use proxies for the CCNb, which makes the above assumption less likely to hold. By combining multiple satellite observations, reanalysis, and AeroCom simulations, this study evaluates the performances of all existing proxies, and then constrain the radiative forcing from aerosol–cloud interactions (RFaci) by selecting ‘good’ proxies.
To assess whether a proxy-Nd relationship is aerosol-regime dependent, we propose a 'hemispheric contrast' approach, using the Northern and Southern Hemispheres to mimic the PD and PI aerosol environments, respectively. Under the same meteorological background, the hemispheric contrast in Nd at a certain aerosol amount serves as a measure of the aerosol-regime dependency. The results show that aerosol optical depth (AOD) exhibits the strongest dependency, followed sequentially by aerosol index (AI), sulfate burden (SO4C), surface sulfate mass (SO4S) and CCN burden (CCNc), and finally surface CCN (CCNS).
We further calculate the biases in RFaci caused by using ßPD instead of ßPI-PD in an ideal model world, based on the AeroCom model outputs. The results suggest that CCNS has the smallest bias (+3%), followed by AI, SO4S and CCNc with positive biases of ~+25%. The AOD and SO4C show the largest biases, with values of –60% and +80%, respectively. Assuming CCNs would give the true RFaci, the biases in observation-based RFaci can be thus inferred, which turn out to be of similar magnitude to those in the model world. This gives us the confidence that true RFaci is likely around –0.68 W m-2 (ocean only).
How to cite: Jia, H., Kroese, W., Quaas, J., van Diedenhoven, B., and Hasekamp, O.: Constraining aerosol–cloud radiative forcing using present-day observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15228, https://doi.org/10.5194/egusphere-egu25-15228, 2025.
Boreal forests are a significant natural source of aerosol particles. As anthropogenic emissions are expected to decline in the future, the relative contribution of boreal forest aerosols to cloud formation is likely to grow. Understanding the cloud-forming potential of these particles and accurately representing their effects in climate models is essential for assessing aerosol-cloud interactions. Previous research has highlighted the importance of aerosol particle number size distribution in predicting cloud condensation nuclei (CCN) concentrations, often outweighing uncertainties in overall aerosol composition. However, online measurement techniques typically provide data on total sub-micron particulate mass, without resolving chemical composition by size—a limitation that affects the accuracy of CCN predictions.
To address this limitation, we applied k-Köhler theory to evaluate how well observed and predicted CCN concentrations align, while simultaneously estimating size-resolved chemical composition. This approach leveraged an extensive dataset from the Hyytiälä research station in southern Finland, encompassing aerosol size distribution, CCN concentrations, and sub-micron aerosol composition derived from the Aerosol Chemical Speciation Monitor (ACSM) and an aethalometer. By exploring combinations of Aitken and accumulation mode compositions—expressed as mass fractions of organics, ammonium sulfate, and black carbon—we identified the composition that minimized prediction errors, achieving what we term "inverse CCN closure."
Our analysis of five years of data revealed distinct patterns in aerosol composition: inorganic compounds were enriched in the accumulation mode, while organics dominated the Aitken mode. This finding underscores the critical role of low-volatility organics in enabling the growth of newly-formed particles to CCN-relevant sizes, alongside the influence of aged aerosols from distant industrial sources and cloud-processed sulfate in the accumulation mode. Moreover, Aitken-mode particles were shown to contribute, sometimes substantially, to CCN concentrations in this boreal forest environment. These results highlight the necessity of investigating compositional differences between Aitken and accumulation mode particles to refine CCN predictions further. The uncertainty in the estimated modal aerosol chemical composition, stemming from measurement errors, will be quantified and presented.
This work was supported by the European Union’s Horizon 2020 research and innovation programme through the project FORCeS (grant agreement No. 821205) and the INTEGRATE project, funded by the European Research Council Consolidator Grant (No. 865799). Göran Gustafsson foundation is also gratefully acknowledged for financial support. Additional support for the SMEAR II station was provided by the University of Helsinki through ACTRIS-HY.
How to cite: Ranjan, R., Heikkinen, L., Dewey, M., Ekman, A. M. L., Partridge, D., Ahonen, L., Petäjä, T., Aalto, P. P., Luoma, K., and Riipinen, I.: Predicting Modal Aerosol Chemical Composition for Improved CCN Closure: A Boreal Forest Case Study, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15271, https://doi.org/10.5194/egusphere-egu25-15271, 2025.
Clouds have, by introducing the liquid phase as a chemical reaction chamber, the ability to change the aerosol size distribution. In as short as 40 minutes, the mass of an aerosol particle can increase by an order of magnitude due to chemical processing, with commensurate impacts on the precipitation efficiency and cloud optical properties. To study the chemical processing of aerosols in clouds, we developed the Chemical Mechanism Integrator (Cminor), a new, open-source, stand-alone Fortran environment for particle-based simulation of chemical multiphase mechanisms. Cminor employs advanced mathematical techniques tailored to heavily exploit the structure of chemical kinetic systems, multiple aqueous phases, and efficient evaluation of rate constants. Cminor uses the idea of Lagrangian cloud microphysics, i.e., computational particles, each representing a multitude of identical particles (e.g., aerosol particles of specific chemical composition). In addition to chemistry, Cminor predicts the activation of aerosol particles to cloud droplets and their subsequent growth by condensation, which enables us to directly investigate some impacts of the processed aerosol size distribution on cloud microphysics. While Cminor is currently applied in an adiabatic parcel framework, in which the influence of chemical processing on the aerosol size distribution is reliably captured, it will be coupled to a three-dimensional large-eddy simulation model shortly, which allows us to investigate the interactions of atmospheric chemistry, dynamics, and cloud physics with an unprecedented degree of detail.
How to cite: Rug, L., Schimmel, W., Hoffmann, F., and Knoth, O.: Clouds' Clout on the Aerosol Size Distribution - Modelling Detailed Chemical Processing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15296, https://doi.org/10.5194/egusphere-egu25-15296, 2025.
One of the main uncertainties in future climate projections is the cloud and aerosol contribution to the Earth’s radiative budget. The imprecise distinction between these aggregates of particles in suspension, combined with the transition zone within the cloud-aerosol continuum, further complicate the study of their radiative and climatic effects. Despite their importance, observations of the cloud-aerosol transition zone (TZ), particularly its vertical distribution, remain limited.
This study addresses this gap using a Vaisala CL31 ceilometer located at Girona (Spain), and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on the CALIPSO satellite. For the ceilometer, we conducted a sensitivity analysis of backscatter and signal-to-noise ratio thresholds used for cloud detection in the Cloudnetpy algorithm from ACTRIS Cloudnet and considered as TZ all those cases where varying those thresholds (from relaxed to a strict situation) changed cloud detection. The CALIOP data was processed by applying several filters to avoid artifacts, and identifying the TZ as the atmospheric layers within the no-confidence range (NCR) of the CAD score, as well as the Cirrus fringes (CAD = 106). Such methodologies enabled the assessment of the vertical distribution and frequency of clouds, aerosols, and the TZ.
Overall, results indicate a gradual transition in backscatter retrievals from cloud to cloud-free, where suspended particles detected near cloud boundaries induced higher backscatter values than those found further away. From the local perspective, we observed a 9.3% (with an uncertainty range of 5.4─20%) variation in cloud occurrence attributed to TZ conditions. When analyzing the whole backscatter profile, we found as many TZ conditions as cloudy values, remarking the importance of TZ vertical frequency. Furthermore, the analysis of TZ occurrence in height and time in Girona revealed that these conditions tend to concentrate below 800 m during night periods. However, annual height-hour distributions showed remarkable seasonal variability. From the global perspective, TZ layers’ optical characteristics showed three main TZ groups: 1. Cluster 1, layers with properties between high-altitude ice clouds and aerosols (e.g. wispy cloud fragments); 2. Cluster 2, layers with properties between water clouds and aerosols at lower altitudes (e.g. hydrated aerosols); 3. Layers classified as Cirrus fringes. The TZ conditions were found worldwide, appearing in 9.5% of all profiles and comprising 6.4% of the filtered layers. The Cluster 1 and Cirrus fringes layers predominate near the ITCZ and in mid-latitudes. In contrast, Cluster 2 is more frequent over the oceans in the central West African and East Asian coasts where elevated smoke and dusty marine aerosols are common. Both ground-based and satellite approaches highlight the significant ubiquity and vertical frequency of the TZ.
How to cite: Ruiz de Morales, J., Calbó, J., González, J.-A., Andersen, H., Cermak, J., Fuchs, J., and Sola, Y.: The Cloud-Aerosol Transition Zone from Satellite and Ground-Based Lidar Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16380, https://doi.org/10.5194/egusphere-egu25-16380, 2025.
This research attempts to reassess, using observation and latest literature studies, the importance of anthropogenic aerosol changes over the past 6000 years to present on regional and global climate forcings and its strong impact on the rate of climate change. Recent research studies (Hansen et al. 2023 & 2025) reveals that a better assimilation of higher aerosol forcing can help to explain the Holocene (temperature) conundrum (a stable Holocene climate, while greenhouse concentrations increased). Such an aerosol forcing has strong impact on paleo- and present climate change.
To this day, pre-industrial anthropogenic aerosol forcing sources remain, including harmful slash and burn agriculture and biomass cooking. But regulations and technologies for aerosol mitigation are present and in the pipeline.
This contributes to regional and global forcing changes, combined with mitigation from industrial aerosol sources like coal plant desulphurisation and notably, since the implementation of stringent sulphur regulations by the International Maritime Organization (IMO) in 2015 and 2020, mitigation of aerosols and aerosol cloud interactions over the dark (low albedo), relatively cold oceans, which act as the primary planetary heat sink of Earth’s Energy Imbalance. More strict regional sulphur regulations will soon come into effect.
Recent forcing estimates from IMO regulations vary widely, from only 0.08 W/m² based on a simple climate model (Hausfather & Forster 2023 using FaIR) to up to 0.50 W/m² based on observations (Hansen et al. 2025). Our analysis, based on NASA CERES satellite data, reveals that the active shipping region of the North Atlantic (20-60N) has experienced a 4-year averaged increase in Absorbed Solar Radiation of 3.0 W/m² and a regional Net flux increase of 1.4 W/m² since 2014, with estimated impacts on regional warming, extreme weather and on the Atlantic Meridional Overturning Circulation (AMOC).
These rapid reductions in aerosol (precursor) emissions combined with a high greenhouse gas (GHG) forcing (currently about +4 W/m² above 1750) may lead to regional, and potentially global, aerosol termination shocks, whereby the reduction of aerosols in absence of GHG reductions increases the rate of warming by >0.2°C/dec. And latest observations are already signalling a potential earlier than anticipated approach to climate tipping points (incl. coral reef die-off; AMOC slow down; and reducing Amazon rainforest and boreal forest carbon sinks), with underestimated climate sensitivities.
Because strong scientific uncertainties remain, we highlight the necessity, from a precautionary principle perspective, to urgently re-evaluation of regional and global climate models to better acknowledge and incorporate these aerosol changes and for policymakers to prepare for scenarios where previously considered 'safe' pathways might accelerate towards dangerous climate thresholds.
For mitigation, we advocate for policies that consider the full lifecycle impacts of emissions, including the unintended consequences of pollution control measures.
How to cite: Simons, L. and Dufournet, Y.: The Case for a Pre-industrial Aerosol Forcing and Impacts of Cleaner Air on Regional Climate Change: Urgent Call for Precautionary Mitigation and Adaptation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17621, https://doi.org/10.5194/egusphere-egu25-17621, 2025.
Aerosol-Cloud Interactions (ACI) play an important role in the hydrological cycle and are strong modulators of cloud radiative forcing and climate. Nevertheless, they remain poorly understood and constrained despite decades of research, because many processes and feedbacks are highly uncertain and are challenging to describe in regional and global climate models. Even less understood is the role of natural aerosol and ACI in a post-fossil future, where anthropogenic emissions is vastly reduced but emerging “natural” aerosol sources modulated by anthropogenic climate change (biomass burning, bioaerosols, dust) will dominate. The CleanCloud project aims to address these uncertainties and as part of its activities carries out major observational field campaigns at climate hot spots (Arctic, Mediterranean) to better constrain ACI processes, and, evaluate, improve and develop new remote sensing algorithms for studying aerosols, clouds and ACI.
The first CleanCloud campaign was based at the Villum Research Station (81.6° N, 16.6° W) in North Greenland, with in-situ and remote sensing measurements, and consisted of two phases, one during the spring (16 March – 13 April) and one during summer (16 July – 13 August) of 2024, in collaboration with the NASA ARCSIX aircraft mission. The second campaign, named “Cleancloud Helmos OrograPhic site experimeNt (CHOPIN)”, is ongoing and is anticipated to last for 6 months, starting from 1 October at Mt.Helmos (38.0o N, 22.2o E) in the Peloponnese, Greece. A series of in situ and remote sensing measurements were distributed at 6 sites along the lee side of Mt. Helmos, 4 at the Kalavrita ski Center’s parking lot (altitude ~ 1690 m), 1 at the foothills (altitude ~ 1747 m) and the Helmos Hellenic Atmospheric Aerosol and Climate Change station ((HAC)2) at the mountaintop (altitude ~ 2314 m) constrain almost every aspect of the aerosols, clouds and their interaction in the region – and especially in the orographic clouds that form at the (HAC)2 station.
Here, we present results from these two campaigns to examine the cloud (e.g., droplet number concentration & size) and aerosol microphysical characteristics (size distribution, CCN concentrations, chemical composition, bioaerosol number concentration and type) and cloud-scale dynamical forcing (vertical velocity) to understand their contribution to ACI processes. Radiosondes to derive the vertical structure of the atmosphere, Lidar systems and sun photometers were used to determine the presence of aerosol amount, their altitude and type (bioaerosol, dust, pollution, biomass burning) as well as the aerosol optical and columnar microphysical properties, Doppler lidars for turbulence and cloud-scale dynamics, radars to obtain the microphysical properties of the clouds, and finally satellites to retrieve the spatio-temporal evolution of the clouds. Additionally, in the case of CHOPIN campaign, cloud probes and cloud samplers were used to perform in-cloud sampling and to obtain the cloud microphysical properties. Thus, the use of this synergistic approach enables us to perform closure studies and to improve our current retrievals to predict cloud properties. These extensive field campaigns will aid in developing new ACI-related retrieval algorithms, development/improvement of parameterizations, and the ESA EarthCARE calibration/validation activities.
How to cite: Foskinis, R., Clerx, N., Molina, C., Mitsios, C., Kawana, K., Gidarakou, M., Fetfatzis, P., Gini, . I., Zografou, ., Granakis, ., Decesari, ., Paglione, M., Zieger, P., Jönsson, A., Violaki, K., Billault-Roux, A.-C. M., Zhang, L., Kumar, V., Podvin, T., Dubois, G., Komppula, M., Sørensen, L. L., Jensen, B., Christoffersen, C., Henning, S., Gryning, S.-E., Massling, A., Skov, H., Im, U., Eleftheriadis, K., Papayannis, A., Berne, A., and Nenes, A.: Retrieving Microphysical Properties of Arctic and Mediterranean clouds using a synergy of remote sensing and in situ instrumentation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18206, https://doi.org/10.5194/egusphere-egu25-18206, 2025.
Multiple methods using in situ observations exist to evaluate cloud microphysical characteristics associated with entrainment-mixing. These include comparing average drop sizes with drop concentrations, comparing these quantities weighted by their adiabatically derived values, as well as computing theoretically derived mixing parameters (e.g., Damköhler number [Dimotakis 2005] and transition length scale [Lehmann et al. 2009]). Although multiple methods exist to quantify entrainment-mixing, observational studies often incorporate a number of these methods due to a wide range of variability in the methods’ output. Further, multiple uncertainties exist when computing these parameters, ranging from required assumptions for determining adiabatic values to sampling limitations preventing the diagnosis of the entrained air’s humidity. For these reasons, most observational studies only evaluate a select number of flight legs due to the diligent analysis required case-by-case.
To compensate for such discrepancies, we introduce a novel method to diagnose the presence of entrainment by using the variance of drop concentrations on the order of ~100 m as a proxy variable. Drop concentrations are acquired using a commonly deployed cloud droplet probe (CDP) at ~10 m spatial resolutions. These basic factors allow for the dissemination of entrainment-mixing characteristics amongst hundreds of hours of cloud measurements acquired during numerous field campaigns.
Findings using this proxy variable suggest that the greatest ice crystal sizes in low-level mixed-phase clouds over the Southern Ocean are found in cloud samples associated with relatively weak entrainment (D’Alessandro and McFarquhar 2023). The methodology is further developed to evaluate how drop size distributions evolve in the presence of entrainment-mixing, revealing greater frequencies of inhomogeneous (homogeneous) mixing associated with high (low) aerosol environments and non-precipitating (precipitating) clouds in subtropical marine environments (D’Alessandro et al. submitted). Occurrence frequencies of inhomogeneous and homogenous mixing are approximately similar amongst four field campaigns, which sampled cloud regimes ranging from low-level warm and mixed-phase marine clouds to terrestrial, convective clouds. Additionally, the methodology in conjunction with measurements from the HOLODEC probe suggest the potential of droplet growth in the “bottleneck” size range (diameters ~25–50 µm) in the presence of entrainment.
Bibliography
D’Alessandro, J. J., and G. M. McFarquhar, 2023: Impacts of Drop Clustering and Entrainment-Mixing on Mixed Phase Shallow Cloud Properties Over the Southern Ocean: Results From SOCRATES. Journal of Geophysical Research: Atmospheres, 128, e2023JD038622, https://doi.org/10.1029/2023JD038622.
D’Alessandro, J. J., R. Wood, and P. N. Blossey, submitted: Evaluating entrainment-mixing characteristics through direct comparisons of drop size distributions using in situ observations from ACE-ENA. J. Atmos. Sci.
Dimotakis, P. E., 2005: TURBULENT MIXING. Annual Review of Fluid Mechanics, 37, 329–356, https://doi.org/10.1146/annurev.fluid.36.050802.122015.
Lehmann, K., H. Siebert, and R. A. Shaw, 2009: Homogeneous and inhomogeneous mixing in cumulus clouds: Dependence on local turbulence structure. Journal of the Atmospheric Sciences, 66, 3641–3659, https://doi.org/10.1175/2009JAS3012.1.
How to cite: Dalessandro, J., Wood, R., Blossey, P., and McFarquhar, G.: Novel measures for diagnosing and evaluating entrainment-mixing in warm and mixed-phase clouds using airborne, in situ measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18274, https://doi.org/10.5194/egusphere-egu25-18274, 2025.
This study utilizes the results of the Cyprus Cloud Aerosol and Radiation Experiment (CyCARE) campaign that took place in Limassol, Cyprus, during the period October 2016 - March 2018. The cloudnet target classification scheme was followed for the retrieval of cloud geometrical and microphysical properties and a climatological statistical analysis was applied for the investigation of cloud seasonal variability and characteristics. Of the total number of 1,338,785 available vertical profiles 440,377 (33%) were found to contain hydrometeors. The applied statistical analysis revealed that, in the presence of clouds, ice phase has appeared in 86% of the cases, mixed phase was identified in 43% of the cases, and liquid phase was observed in 42% of the cases. Precipitation (drizzle or rain) occurred in 28% of the cases. The seasonal analysis showed that clouds over Limassol during the study period are more frequent during the winter season (60%) followed by spring (22%) and autumn (17%). The most frequent cloud type is mixed phased clouds (354,440 profiles), followed by pure ice clouds (251,402) and liquid phase clouds (125,838). Concerning the cloud geometrical characteristics, cloud base height ranged from a median value of 1478 m for liquid precipitable clouds during winter to 9803 m for ice clouds during summer. Cloud top height varied from a median value of 1977 m for liquid precipitable clouds during winter to 10271 m for ice clouds during summer. Cloud vertical thickness ranged from a median of 249 m for liquid clouds during spring to 5519 m for mixed phase precipitable clouds during spring. Since June 2024 a new permanent ground-based remote sensing station, namely Cyprus Aerosol Remote sensing Observatory (CARO), has been established in Limassol and the continuous observations will be used in future aerosol-cloud interaction relevant studies in the region of eastern Mediterranean.
Acknowledgements
The authors acknowledge the ‘EXCELSIOR’: ERATOSTHENES: EΧcellence Research Centre for Earth Surveillance and Space-Based Monitoring of the Environment H2020 Widespread Teaming project (www.excelsior2020.eu). The ‘EXCELSIOR’ project has received funding from he European Union’s Horizon 2020 research and innovation programme under Grant Agreement No 857510, from the Government of the Republic of Cyprus through the Directorate General for the European Programmes, Coordination and Development and the Cyprus University of Technology. This study was supported by the ATARRI Horizon Europe Widespread Twinning Project. ATARRI receives funding from the European Union’s Horizon Europe Twinning Call (HORIZON-WIDERA-2023-ACCESS-02) under the grant agreement No 101160258.
How to cite: Kotsias, G., Mamouri, R.-E., Nisantzi, A., and Seifert, P.: Cloud observations over Limassol, Cyprus using CLOUDNET facilities, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18461, https://doi.org/10.5194/egusphere-egu25-18461, 2025.
Aerosol effects on convective clouds and precipitation mediated via radiative and microphysical perturbations remain highly uncertain. Microphysical perturbations are generally not included in current climate models due to the simplified representation of convective clouds in existing parameterisations. Progress has been made through regional cloud resolving modelling; however, such simulations often neglect energy and water budget constraints and the coupling to larger scales. The emergence of global km-scale climate models provides a significant opportunity to advance our understanding of aerosol-convection interactions, but the inclusion of prognostic aerosols has been limited previously by their high computational demands.
Here we present results from global km-scale atmospheric model simulations using ICON coupled to HAM-lite, a new reduced complexity aerosol model derived from the microphysical aerosol scheme HAM, suitable for global km-scale simulations [Weiss et al., GMD Discussions, 2024]. Performing aerosol perturbation experiments with pre-industrial and present-day aerosol emissions allows us to isolate anthropogenic aerosol effects on convective clouds and precipitation globally. As a first step, we compare simulated perturbations in terms of radiative (aerosol optical depth) and microphysical (cloud droplet number concentrations) against a set of observationally constrained idealised perturbations [Herbert et al., ACP Discussions, 2024]. This will allow us to put simulated cloud and precipitation responses in the simulations in the context of the perturbation strength.
Comparison of our global km-scale simulations with prognostic aerosols with idealised simulations with prescribed aerosols [Herbert et al., 2024] provides a first insight into the effect of simulating global aerosols at the km-scale. Ultimately, this work offers a new way to study anthropogenic aerosol effects on convective clouds and precipitation globally, including microphysical and radiative perturbations, the diurnal cycle of convection, the coupling to the global circulation and regional climate.
How to cite: Stier, P., Weiss, P., De, S., Sela, M., and Jones, W.: Anthropogenic aerosol effects on convective clouds and precipitation in global km-scale simulations with ICON-HAM-lite , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18479, https://doi.org/10.5194/egusphere-egu25-18479, 2025.
We present the first results from the Max Planck CloudKite (MPCK) measurements conducted during the EUREC4A campaign in 2020, targeting shallow cumulus clouds in the trade wind regions near Barbados. The MPCK is a 250 m³ tethered balloon stabilized with a kite, capable of carrying up to 100 kg of scientific payload in no-wind conditions or heavier payloads in windy conditions, reaching altitudes of up to 2 km above ground level. During EUREC4A, we performed airborne measurements of cloud microphysics and turbulence using the MPCK+ instrument box, which combines fast inline holography with Particle Image Velocimetry (PIV) to resolve micrometer-scale features. The low true airspeed of the tethered balloon, combined with the high sampling frequencies of our imaging setups—15 Hz for PIV and 75 Hz for holography—provided unprecedented detail into the dynamics of shallow cumulus clouds. To date, we have analyzed over 300,000 holograms and 100,000 PIV images acquired during the campaign. Our analysis spans the structure of these clouds from their edges to their cores. We present results on droplet clustering, void formations, the influence of turbulence, and the mechanisms of entrainment and mixing. As clouds remain a major source of uncertainty in climate and weather models, we believe these findings represent a significant step forward in understanding cloud dynamics and their broader implications for atmospheric processes.
How to cite: Bagheri, G., Nordsiek, F., Schlenczek, O., Thiede, B., Kim, Y., Chavezmedina@ds.mpg.de, V., Larsen, M., Schroeder, M., and Bodenschatz, E.: High-Resolution Insights from the Max Planck CloudKite During EUREC4A, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18569, https://doi.org/10.5194/egusphere-egu25-18569, 2025.
Ice formation in mixed-phase clouds is a critical component of their evolution and impacts on the hydrological cycle and climate. Nevertheless, their quantification and link to different aerosol sources (dust, biological particles) and impact of atmospheric aging leads to considerable uncertainty in their description in atmospheric models. Observations at high altitude mountaintop sites can provide a way to alleviate this uncertainty, as observations can be carried out for extensive periods of time, and can sample both free tropospheric and boundary layer air from a variety of sources and over different seasons – and their associated INP levels.
Motivated by the above, we conducted the long-term observation at the top of the Mount Helmos (2314 m above sea level) for 6 months during the Cleancloud Helmos OrograPhic sIte experimeNt (CHOPIN) champaign, as part of the CleanCloud project. The INP concentrations were observed using a Portable Ice Nucleation Experiment (PINE) at -15°C and -25°C. We will discuss the characterization and drivers of INP changes between -15°C and -25°C, as well as cloud events and seasonal variations during fall, winter, and early spring. Additionally, we will discuss the controlling factors for INP activation in combination with other concurrent observations such as aerosol size distribution, fluorescent particle concentrations and shape, biological particle concentrations and speciation (e.g., flow cytometry) and laser remote sensing (elastic-Raman-fluorescence lidar), backtrajectory analysis, and in-situ aerosol chemical composition. We will evaluate the ability of existing parameterizations to capture the INP levels – and their link to aerosol type and origin – and examine whether aged INP (characterized by their airmass type, and acidity levels) tend to exhibit different INP activity compared to more freshly emitted particles.
How to cite: Kawana, K., Foskinis, R., Jönsson, A., Gidarakou, M., Molina, C., Mitsios, C., Gini, M., Fetfatzis, P., Papayannis, A., Zieger, P., Eleftheridadis, K., and Nenes, A.: Multiseasonal measurements of ice-nucleating particle (INPs) levels and their drivers in the Easter Mediterranean during the CHOPIN field campaign, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20598, https://doi.org/10.5194/egusphere-egu25-20598, 2025.
Posters virtual: Wed, 30 Apr, 14:00–15:45 | vPoster spot 5
EGU25-886 | ECS | Posters virtual | VPS3
Sensitivity of Cloud Invigoration and Suppression Effects to Major Aerosol species During the Indian Summer Monsoon in a Global Climate ModelWed, 30 Apr, 14:00–15:45 (CEST) vPoster spot 5 | vP5.4
Tropical deep convective clouds (DCCs) play a pivotal role in Earth's hydrological cycle, with their dynamics strongly influenced by aerosols. Depending on their properties, aerosols can either invigorate or suppress cloud formation and development. Previous observational studies and cloud-resolving model simulations have shown that aerosols such as black carbon (BC) and sulfates modify cloud microphysics, affecting droplet size distribution, latent heat release, and precipitation patterns. However, the use of global climate models (GCMs) to study these aerosol-cloud interactions remain limited, despite their ability to capture large-scale circulation patterns and associated non-linear feedback. This study investigates the sensitivity of aerosol-induced cloud invigoration and suppression (AIVe) to major aerosol species during the Indian summer monsoon (ISM) season using the Community Earth System Model, specifically its atmospheric component, the Community Atmosphere Model version 5 (CESM-CAM5). The analysis focuses on DCCs over central India during the monsoon months of June–September (JJAS) for the period 2005–2008. Aerosol and cloud parameters from CESM-CAM5 simulations, conducted at 0.5-degree horizontal resolution, are compared with satellite observations. Five Atmospheric Model Intercomparison Project (AMIP)-style simulations were performed: one with aerosols at pre-industrial level (PI) levels, another at present-day (PD) levels, and three additional simulations perturbing specific aerosol species (dust, BC, and sulfate) under PD conditions to isolate their individual effects on AIVe. The findings highlight that aerosol physico-chemical properties critically influence DCC behavior. Black carbon near the boundary layer increases cloud condensation nuclei (CCN) concentrations, delaying precipitation, enhancing warm-phase invigoration, and strengthening updrafts. In the upper troposphere, BC absorbs solar radiation, causing atmospheric warming that promotes cloud deepening and cold-phase processes. Additionally, BC intensifies both shortwave and longwave heating, prolonging cloud lifetimes and supporting deeper convection. Sulfate aerosols primarily enhance warm-phase invigoration through increased CCN concentrations at lower altitudes. However, their weaker vertical transport limits their impact on cold phase processes and deep convection compared to BC and dust. Dust aerosols with high concentrations in the mid-troposphere, act as efficient ice-nucleating particles (INPs), enhancing cold phase invigoration. However, suppressed updrafts in the upper troposphere reduce their overall effect on deep convective systems, emphasizing the importance of aerosol size, number concentration, and properties in shaping AIVe. This study underscores the complex interplay between aerosol characteristics and their vertical distribution in influencing cloud dynamics during the ISM. Detailed results and further implications will be presented.
How to cite: Sharma, P., Ganguly, D., and Kant, S.: Sensitivity of Cloud Invigoration and Suppression Effects to Major Aerosol species During the Indian Summer Monsoon in a Global Climate Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-886, https://doi.org/10.5194/egusphere-egu25-886, 2025.
EGU25-1370 | ECS | Posters virtual | VPS3
Evaluating WRF-Chem for simulating fog episodes: A Case Study from The National Capital Region Delhi, IndiaWed, 30 Apr, 14:00–15:45 (CEST) | vP5.5
During winter, dense fog occurrences in the Indo-Gangetic Plain pose severe risks to visibility, air quality, and public health, emphasizing the need for improved fog forecasting in India. This study employs a high-resolution WRF-Chem model (2 km × 2 km) to identify optimal configurations for simulating fog in the region and investigate the impact of urbanization-induced UHI/UDI (Urban Heat Island/Urban Dry Island) and elevated emissions on the fog life cycle in and around the megacity of Delhi.
A comprehensive sensitivity analysis explores model configurations across microphysics, planetary boundary layer (PBL), land surface models (LSM), radiation schemes, chemistry, and emission inputs. Simulations of surface and vertical meteorology are evaluated against data from weather stations and radiosonde profiles, while modeled chemistry is compared with ground-based measurements. Results demonstrate that specific combinations of microphysics, PBL, and LSM schemes coupled with chemistry effectively simulate Liquid Water Content (LWC), a critical fog proxy. Modeled relative humidity, particulate matter concentrations, and fog life cycles show strong agreement with observations. We then utilize this optimized model configuration to quantitatively analyze individual and combined effects of urbanization and aerosols on fog formation.
How to cite: K Lal, A., Kunchala, R. K., and Mohan, M.: Evaluating WRF-Chem for simulating fog episodes: A Case Study from The National Capital Region Delhi, India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1370, https://doi.org/10.5194/egusphere-egu25-1370, 2025.
EGU25-4697 | ECS | Posters virtual | VPS3
Direct and indirect effects of biomass burning and dust aerosols under various synoptic processes during the April 2020 pollution case in UkraineWed, 30 Apr, 14:00–15:45 (CEST) | vP5.6
Wildfires and dust storms significantly contribute to air pollution, causing adverse health impacts and intensifying various aerosol-meteorology feedbacks in the atmosphere through direct and indirect aerosol effects. These effects, however, are highly variable and depend on prevailing synoptic conditions. In April 2020, Ukraine experienced one of its most severe air pollution episodes, which had a profoundly negative impact on the Kyiv metropolitan area. This event was triggered by wildfires in the abandoned exclusion zone around the Chornobyl Nuclear Power Plant (northern Ukraine) and a dust storm that swept across the entire territory of Ukraine from the west to the east. Despite similar aerosol emissions – characterized by elevated levels of dust, organic carbon (OC), and black carbon (BC) – the atmospheric effects varied significantly under different synoptic processes during April 2020. This study presents seamless modeling results that analyze the meteorological response to direct (DAE) and indirect aerosol effects (IDAE) under varying synoptic conditions during this pollution episode in Ukraine.
Using the Environment – HIgh-Resolution Limited Area Model (Enviro-HIRLAM) at a 1.5 km horizontal resolution, four simulations/runs were conducted to investigate the role of aerosols: DAE run, IDAE run, combined aerosol effects (COMB run), and a reference (REF run) representing a standard Numerical Weather Prediction configuration without aerosol effects. The uniform and continuous effects of biomass burning and dust aerosols were primarily observed in radiation parameters, leading to a reduction in downwelling global and net short-wave radiation by 25-40 W/m². A clear correspondence between aerosol distribution and changes in the spatial patterns of other meteorological parameters was evident during the atmospheric fronts and the dust storm episode. Notably, the movement of a warm front caused near-surface air temperature to decrease and specific humidity to increase ahead of the front, with the opposite effects observed behind it. Compared to the REF run, these parameters exhibited local variations ranging from -2.6°C to +1.0°C for air temperature and from -1.5 g/kg to +1.0 g/kg for specific humidity. Aerosol effects during the stationary cold front led to an increase in air temperature and cloud liquid water content. However, transported sulfur aerosols significantly influenced these effects against the background of OC and BC emissions. In contrast, the subsequent dust storm and cold front had the opposite effect on air temperature, also impacting changes in turbulent kinetic energy. Most of these effects were associated with areas in model domain affected by elevated concentrations of dust, BC, and OC in their coarse and accumulation modes.
We acknowledge support through the grant HPC-Europa3 Transnational Access Programme for projects “Integrated modelling for assessment of potential pollution regional atmospheric transport as result of accidental wildfires”; projects Horizon Europe programme under Grant Agreement No 101137680 CERTAINTY (Cloud-aERosol inTeractions & their impActs IN The earth sYstem); project No 101036245 RI-URBANS (Research Infrastructures Services Reinforcing Air Quality Monitoring Capacities in European Urban & Industrial AreaS) and No 101056783 European Union via FOCI-project (Non-CO2 Forcers And Their Climate, Weather, Air Quality And Health Impacts).
How to cite: Savenets, M., Mahura, A., Nuterman, R., and Petäjä, T.: Direct and indirect effects of biomass burning and dust aerosols under various synoptic processes during the April 2020 pollution case in Ukraine, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4697, https://doi.org/10.5194/egusphere-egu25-4697, 2025.
EGU25-5362 | ECS | Posters virtual | VPS3
Turbulence-induced Non-Monotonic Influence of Aerosols on Cloud Droplet Size DistributionWed, 30 Apr, 14:00–15:45 (CEST) | vP5.7
Cloud droplet size distribution is essential for quantifying the role of clouds in earth system, including cloud albedo, precipitation formation, and cloud lifetime. The response of cloud droplet spectral relative dispersion (ε) to aerosol number concentration (Na) is highly uncertain, and the role of turbulence in ε–Na relationships is yet puzzling. This study uses large eddy simulation to examine the ε–Na relationship and derives an expression for ε from a minimal model to elucidate this relationship. Our findings indicate that as Na increases, ε initially decreases due to the aerosol’s effect on weakening the intensity of turbulence-induced broadening greater than its effect on weakening the intensity of condensational narrowing. However, as Na continues to increase, ε increases due to the aerosol’s effect on weakening the intensity of condensational narrowing more significant than its effect on weakening the intensity of turbulence-induced broadening. These findings improve the understanding of the aerosol effects on cloud droplet size distribution and address the challenge of quantifying aerosol indirect effects considering turbulence, potentially leading to new cloud microphysics parameterizations.
How to cite: Chen, Y., Chen, J., and Lu, C.: Turbulence-induced Non-Monotonic Influence of Aerosols on Cloud Droplet Size Distribution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5362, https://doi.org/10.5194/egusphere-egu25-5362, 2025.
EGU25-14891 | ECS | Posters virtual | VPS3
Impacts of anthropogenic emissions on monsoon precipitation over western India: Insights from high-resolution regional modelingWed, 30 Apr, 14:00–15:45 (CEST) | vP5.8
Air quality and climate over the western Indian region have been shown to be strongly influenced by trans-regional anthropogenic emissions originated from the Indo-Gangetic Plain (IGP) and central India, besides the local and regional processes. Nevertheless, the relative roles of local versus remote anthropogenic processes in changing precipitation over western India have remained unclear. In this regard, numerical simulations have been conducted using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to quantify regional versus trans-regional anthropogenic effects on cloud droplet number concentration (CDNC) and precipitation during monsoon (August 2019). WRF-Chem simulations show a good agreement with the ERA5 reanalysis for cloud fraction (CF) (r = 0.88, MB = 0.08 mm/day) and accumulated monthly precipitation (AMP) (r = 0.84, MB = -0.14 mm/day). Sensitivity simulations reveal that regional plus trans-regional anthropogenic emissions enhance CDNC by up to 5.1×106 number/cm2 (~121% of the average CDNC over WI) but significantly reduce the precipitation by up to 45 mm (~15% of the average precipitation). The findings also revealed that the impact of trans-regional emissions in perturbing CDNC and precipitation is higher than that of regional emissions. Our results suggest that anthropogenic emissions can substantially lower water resources in this already stressed arid region in India. The study also highlights that policies need to aim emission reductions ubiquitously and not only over western India for mitigating pollution impacts on regional precipitation.
How to cite: Dhaka, S., Lakshmi, S., Vaishya, A., Ojha, N., Pozzer, A., Ansari, T., and Sharma, A.: Impacts of anthropogenic emissions on monsoon precipitation over western India: Insights from high-resolution regional modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14891, https://doi.org/10.5194/egusphere-egu25-14891, 2025.
EGU25-15895 | Posters virtual | VPS3
Tracing Black Carbon's Historical Impact on Regional PrecipitationWed, 30 Apr, 14:00–15:45 (CEST) | vP5.9
Black carbon (BC) aerosols, strong absorbers of solar radiation, induce atmospheric heating, altering vertical profiles of temperature, water vapor, and clouds. These impacts can lead to localized precipitation changes, and may also initiate changes to atmospheric circulation, with potentially far-reaching impacts on precipitation patterns.
While prior studies suggest BC's significant influence on precipitation, its role in both local and remote precipitation change remains insufficiently quantified. To address this gap, we explore the extent to which historical BC emissions have shaped regional precipitation. Specifically, we ask: how much could future BC changes influence regional precipitation, based on insights from the historical period?
Using the Community Earth System Model version 2 (CESM2), we have generated a 20-member ensemble of simulations of 1950–2014 with anthropogenic BC emissions fixed at 1950 levels. By comparing these to standard historical simulations with evolving emissions, we isolate the impacts of BC emission trends from 1950 to 2014 on global and regional climates.
Our results reveal that BC emissions have caused localized drying in regions of high emissions, notably over Europe during the 1980s–1990s and Eastern China in the early 21st century. Furthermore, we find indications that BC exerts a dampening effect on the most extreme precipitation events, highlighting its historical role in modulating climate extremes.
How to cite: Stjern, C. W., Samset, B. H., Alterskjaer, K., and Johansen, A. N.: Tracing Black Carbon's Historical Impact on Regional Precipitation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15895, https://doi.org/10.5194/egusphere-egu25-15895, 2025.
EGU25-16951 | ECS | Posters virtual | VPS3
Satellite-Based Analysis of Size-Segregated Aerosols and Their Effects on Warm Cloud Properties over the Northern Indian OceanWed, 30 Apr, 14:00–15:45 (CEST) | vP5.10
Aerosol-cloud interactions contribute to 75–80% of the total radiative effect of aerosols and remain a major source of uncertainty in predicting future climate. Aerosols significantly influence the warm cloud properties by serving as cloud condensation nuclei (CCN). An increase in CCN leads to the formation of more numerous and smaller cloud droplets, suppresses warm rain by reducing the efficiency of collision and coalescence processes, and extends the cloud lifetime, and liquid water path (LWP) and/or cloud fraction (CF). The activation of a CCN into a cloud droplet is strongly influenced by its size and chemical composition, which subsequently affects the size distribution of cloud droplets and other cloud properties. Although the physical processes of nucleation are well documented for individual particles, the impact of aerosol size on cloud properties is often underestimated because both fine and coarse aerosols co-exist together. To bridge this gap, this study aims to address the impact of size-differentiated aerosols on warm cloud properties over the Northern Indian Ocean (NIO) by utilizing ~20 years of multi-satellite observation data.
The Arabian Sea (AS) and the Bay of Bengal (BoB) in the NIO were chosen in this study as these regions experience a continuous load of aerosols from natural and anthropogenic sources with high seasonal variations. Comparative analysis of size-segregated aerosol optical depth (AOD) revealed the dominance of coarse mode particles (c-AOD) over AS, and fine mode (f-AOD) over BoB. However, a significant increasing trend in the mean f-AOD, particularly during the post-monsoon (ON) and winter (DJF) seasons, is observed over both the AS (0.05/decade) and BoB (0.045/decade) from 2000 to 2021, primarily driven by rising anthropogenic emissions. Further, a climatological analysis of warm cloud CF during these seasons reveals a corresponding increasing trend over the AS (0.07/decade) and BoB (0.05/decade). A correlation analysis of c-AOD and f-AOD with warm CF was conducted, which revealed a stronger annual positive correlation of warm CF with c-AOD (AS: r = 0.56, BOB: r = 0.41) compared to f-AOD (AS: r = 0.37, BOB: r = 0.27). To further investigate the impact of f-AOD and c-AOD on cloud effective radius (CER) for a fixed LWP, an additional correlation analysis was performed. For low LWP (up to 70 gm-2), an increase in CER was observed with both c-AOD and f-AOD, with a more pronounced increase in CER associated with c-AOD over both the AS and BoB regions. However, as LWP increased, f-AOD exhibited a faster decrease in CER over the BoB compared to the AS. In contrast, c-AOD consistently showed an increasing CER with rising LWP, indicating a contrasting effect relative to f-AOD. These results indicate the dominant radiative effect of fine mode aerosols on cloud formation against the classical microphysical effect of coarse mode aerosols. Further analysis, incorporating meteorological parameters such as relative humidity and atmospheric stability, is essential to better understand these relationships and enhance the robustness of this study.
How to cite: Bangar, V. and Mishra, A. K.: Satellite-Based Analysis of Size-Segregated Aerosols and Their Effects on Warm Cloud Properties over the Northern Indian Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16951, https://doi.org/10.5194/egusphere-egu25-16951, 2025.
