The diversity in particle composition within the atmospheric aerosol is well-documented in field observations, but usually grossly oversimplified in chemistry transport models or earth system model. This is for good reasons--- to save computational cost---but comes with the trade-off of introducing considerable and difficult-to-quantify structural uncertainty in our predictions of aerosol composition, and by extension, of aerosol interactions with clouds and radiation. This presentation will illustrate how targeted particle-resolved simulations can be used to quantify structural uncertainty in more approximate aerosol models (i.e., sectional or modal models). The particle-resolved approach resolves the aerosol using individual computational particles that evolve in size and composition during their simulated lifetime in the atmosphere. I will present our model development of WRF-PartMC, a stochastic particle-resolved model embedded into the Weather Research and Forecasting Model (WRF) for explicit simulation of aerosol mixing state on the regional scale. The novel computational methods developed for this purpose include a particle-resolved emission inventory and stochastic transport algorithms. With its fully-resolved aerosol mixing state representation, WRF-PartMC allows for direct inter-model comparisons with traditional aerosol schemes used in regional and climate models. We used this modeling approach to quantify the extent to which simplifying the diversity of aerosol composition introduces errors in our estimates of cloud condensation nuclei concentration and aerosol optical properties. I’ll conclude the presentation by demonstrating how machine learning can leverage particle-resolved simulation data to efficiently bridge to the global scale.

How to cite: Riemer, N., Curtis, J., Ching, J., Yao, Y., Zheng, Z., and West, M.: What is the aerosol state in the ambient atmosphere? Or: Multiscale modeling to tackle structural uncertainty in aerosol models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10839, https://doi.org/10.5194/egusphere-egu23-10839, 2023.

Biogenic volatile organic compounds (BVOCs) and their oxidation products are known to facilitate the formation and growth of secondary aerosol particles in the ambient atmosphere. Some originate from the ocean, emitted by plankton or bacteria, while others stem from vegetation over the continents. Both marine and continental processes leading to aerosol formation or growth has been researched extensively and described in numerous publications. Their interactions however are yet to be examined. We seek to understand how marine precursors such as dimethyl sulfide (DMS) affects new particle formation over the boreal forest, and how highly oxygenated organic molecules (HOM) originating from monoterpenes grows said particles into the cloud condensation nuclei (CCN) size range.

We have utilised the Lagrangian chemistry transport model ADCHEM in reproducing observations from the SMEARII station (61°51' N, 24°17' E) located
in Hyytiala, Finland, during the year of 2018. The model operates along trajectories generated by HYSPLIT, using meteorology data from GDAS and incorporating emission inputs from CAMS. The atmospheric cluster dynamics code (ACDC) is coupled to the model in order to consider ion mediated new particle formation from sulphuric acid and ammonia.

We demonstrate how ADCHEM captures the gas-phase concentrations of key species including sulfuric acid (SA), HOM monomers and HOM dimers along with new particle formation and growth as observed by CI-APi-TOF and SMPS instrumentation, respectively. By running the model without anthropogenic influence, we show how DMS-derived SA and ammonia emitted from the ocean is transported inland in quantities sufficient to initiate
NPF over the boreal forest. The newly formed particles grow by condensation of HOM to reach the CCN size range. Our model results also indicate gas-phase concentrations of iodic acid (IA) at approximately 10⁵ molecules cm^-3, originating from marine emissions of methyl iodide (MeI). While ADCHEM does not consider the effect of IA on NPF, studies have claimed that IA may be able to cluster is the presence of SA and ammonia. This could increase the marine impact on continental NPF and will become the focus of future work with ADCHEM.

We theorise that the interactive marine and continental aerosol formation may act as a key element in the hydrological cycle. Marine air masses not only transport water vapour inland from the ocean but also SA, ammonia and halogens that under the influence of HOM formed over the boreal forest initiates the formation and growth of aerosol particles (without anthropogenic influence) ultimately reaching the CCN size range. These particles in turn can influence the formation, lifetime and precipitation patterns of clouds.

Figure (1). Measured and modelled aerosol particle number concentrations at the SMEARII station. The bottom panel
illustrates ADCHEM model results without the influence of DMS.

How to cite: Wollesen de Jonge, R. and Roldin, P.: Maritime-continental air-mass exchanges of biogenic marine volatile compounds boost inorganic new particle formation and production of cloud condensation nuclei over the boreal forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12511, https://doi.org/10.5194/egusphere-egu23-12511, 2023.

Hygroscopicity of atmospheric aerosol primarily depends on the size and chemical composition of the particle and is important for estimating anthropogenic aerosol radiative forcing. Hygroscopicity is highly related to the activation of aerosols to Cloud Condensation Nuclei (CCN), and hence plays a crucial role in cloud formation and modulating its properties. However, due to limitations of measurement techniques, seasonal variation in size segregated aerosol hygroscopicity (k) is not available over the Indian region.  This study presents ‘k’ as derived from a Humidified Tandem Differential Mobility Analyzer (HTDMA) over the High Altitude Cloud Physics Laboratory (HACPL) in the Western Ghats, India for more than a year (from May 2019 to May 2020).  The average hygroscopicity values of aerosol particles of diameters 32, 50, 75, 110, 150, 210, and 260 nm at 90% RH conditions are 0.189, 0.177, 0.163, 0.170, 0.183, 0.199, 0.207 respectively during the entire observation period.  k was observed to decrease with an increase in size in the Aitken mode regime (32-75 nm) and an increase in the accumulation mode (110-260 nm).  Seasonal variation of hygroscopicity for a wide range of particle diameters is reported which is highly demanding as there is a change in the air mass flow pattern in each of the seasons.  The diurnal cycle of hygroscopicity showed a prominent peak during the midnight to early morning hours followed by a decrease in the forenoon hours and a secondary peak in the afternoon hours.  k is found to be higher in pre-monsoon as compared to the winter season as Chl is approximately 3% higher in pre-monsoon and NH₄Cl is highly hygroscopic among the assumed chemical composition.  Assuming the internal and external mixing of aerosols, the closure study yields chemically derived hygroscopicity (k_chem) overestimates as compared to k_HTDMA though the assumption of external mixing of aerosols improved the values of predicted k. CCN derived hygroscopicity (k_ccn) underestimates as compared to hygroscopicity derived from HTDMA measurements. Both k_chem and k_ccn are found to follow the similar diurnal variation of k_HTDMA. Thus, the k_chem and   can be used as a proxy of  in the absence of direct HTDMA measurements. Using k_chem and  in numerical models will propagate systematic bias in aerosol to CCN activation processes so a parameterization of hygroscopicity with dry diameter of sub-micron particles is developed and that could be used for a closer real-atmospheric value of hygroscopicity.

Keywords: Hygroscopicity, Parameterization, sub-micron aerosols

How to cite: Ray, A., Pandithurai, G., Mukherjee, S., Kumar, A. V., and Hazra, A.: Closure and parameterization of sub-micron aerosols’ hygroscopicity and it’s seasonal variability over the Western Ghats, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-396, https://doi.org/10.5194/egusphere-egu23-396, 2023.

The presence of anthropogenic organic compounds in aerosols can affect climate by altering the hygroscopicity of the aerosols and their behaviors as cloud condensation nuclei. Due to their importance, characteristics of atmospheric organic aerosols and their mixtures have been studied.

Among atmospheric organic aerosols, secondary organic aerosols (SOA) have not been well known. However, understanding on the chemical and photochemical properties of SOA is necessary to forecast the concentration of ultrafine particles more accurately. One of the important factors affecting the formation of SOA is the intensity of light. The stronger the intensity of light, the more the photochemical reactions, and thus the more the SOA formation. Thus, in this study, we examined how the formation of secondary organic aerosols can be changed under various UV light intensity.  

For this study, we used a smog chamber (1mm1.7m) with a Teflon or Tedlar bag used as a reactor. To provide ozone and clean air into the chamber, zero air generator (8301 LC, EcoTech, Australia) and gas dilution calibrator (Serinus CAL, EcoTech, Australia) were used. To detect ozone, NOx and particulate matters, ozone analyzer (Serinus 10, EcoTech, Australia), NOx analyzer (Serinus 40, EcoTech, Australia) and scanning mobility particle sizer (3938 Series, TSI, USA) were used, respectively. Input gas wasa mixture of NO, NO₂, ozone and toluene, and set temperature varies from 25 to 26 C. 22 lamps (Philps TL-40W) were used for UV light sources, and the intensity was set by controlling 22 lamps. 

According to our investigations, the concentration of SOA with the strongest UV lights was more than three times higher than that without UV lights. As a result of the SOA formation, the concentration of NOx was decreased while the concentration of ozone was increased. We also found that the ratio of NOx and toluene affects the concentrations of SOA in the chamber experiments.

Acknowledgments

This study was supported by the National Research Foundation of Korea (grant number NRF-2021R1C1C1013350).

How to cite: Lee, J. Y., Kim, H., Kim, J., and Jung, H. Y.: Formation of secondary organic aerosols under various UV light intensities in a smog chamber, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10250, https://doi.org/10.5194/egusphere-egu23-10250, 2023.

Carbonaceous soot particles are formed during incomplete combustion of fossil fuels, biofuels or biomass and are considered to be a significant proportion of aerosol emission, especially in polluted areas, and to contain light-absorbing carbon fractions. The light-absorbing carbon components make these particles exhibit positive radiative forcing and thus they contribute to atmospheric warming processes. The exact contribution to this process however still has significant uncertainties. One of the sources of uncertainty is related to the capacity to accurately describe soot spectral optical properties (MAC/MSC/MEC - mass absorption/scattering/extinction cross-sections in m²g^-1; CRI - complex refractive index), due to significant uncertainties for key measurements like the absorption coefficient or absorbing mass fraction. A second source is considered to be the change of the optical properties with the variable physico-chemical state of soot (e.g. chemical composition, morphology, primary particle size, aggregate size distribution, coating and mixing state) which depends on (i) the combustion conditions/sources  and is (ii) known to change during atmospheric lifetime due to ageing and mixing processes.

The present work aims at providing new measurements of soot spectral optical properties and investigating their dependence on particles’ physico-chemical state and the role of measurement uncertainties. For this, a set of original experiments was performed in the 4.3m³ CESAM atmospheric simulation chamber (https://cesam.cnrs.fr/) on soot aerosols generated by a commercial propane diffusion flame soot generator (miniCAST model 6204 TYPE C, JING). In these experiments, the variability of soot properties due to (i) generation and (ii) atmospheric ageing was explored. Different combustion conditions going from fuel–leaner to fuel-richer were set to produce soot aerosol with different effective densities, EC/TC-ratios ranging from 0.8 ± 0.1 to 0.0 ± 0.1 and size distributions with median diameters between 30 and 120 nm. Selected aerosols were subjected to ageing in a N₂/O₂ atmosphere under simulated atmospheric conditions (humid, with/without illumination, up to 26 hours lifetime). In these conditions, physical and chemical ageing, under the presence of different gaseous phases (O₃, SO₂) and addition of a second aerosol phase produced by photo-oxidation of SO₂ or the ozonolysis of α-pinene, led to changes in the physico-chemical properties of the soot.

State-of-the-art techniques were used to generate an extensive dataset of physico-chemical parameters (mass concentration, morphology, effective density, composition, size distribution) and spectral optical properties (absorption, scattering, extinction coefficients) for different soot aerosols and different ageing states of these. The absorption coefficient in particular was measured by both filter-based (AE - Aethalometer, MAAP - Multi-Angle Absorption Photometer, MWAA – Multi-Wavelength Absorbance Analyzer, PP_UniMI - Polar Photometer by University of Milano) and extinction minus scattering techniques. The MAC, MSC and MEC datasets, retrieved by combining these measurements, will be presented for the ensemble of chamber experiments and the variability of these parameters in link with variations in the particles’ physico-chemical properties will be discussed together with key relevant uncertainties.

How to cite: Heuser, J., Di Biagio, C., Renzi, L., Marinoni, A., Yon, J., Zanatta, M., Yu, C., Bergé, A., Cazaunau, M., Chevaillier, S., Laj, P., Massabo, D., Noyalet, G., Pangui, E., Prati, P., Temime-Roussell, B., Vecchi, R., Bernardoni, V., Vernocchi, V., and Doussin, J.-F.: Simulation chamber study of the spectral mass absorption, scattering, and extinction cross-sections (MAC, MSC, MEC) of fresh and aged combustion aerosols, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-462, https://doi.org/10.5194/egusphere-egu23-462, 2023.

This study presents part of the results of the CALISHTO campaign (Cloud-AerosoL InteractionS in the Helmos Background TropOsphere) that took place in autumn 2021 at the free-troposphere high-altitude Helmos station (2314 m a.s.l.). A Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM, Aerodyne) was deployed among other instruments (AE31, PVM-100, SMPS, EC/OC analyzer) in the framework of the campaign. The chemical characterization of the non-refractory PM₁ (NR-PM₁), the influence from the Boundary Layer / Free Troposphere, the origin of the incoming masses and the influence of clouds were studied. The sources of PM₁ including the non-refractory species of ACSM (organics and inorganics) combined with the equivalent black carbon were also investigated by applying the PMF model to the combined dataset. The results showed that there is a great variability of aerosol characteristics depending on the height of the PBL and the origin of the air masses. During September the station was exposed to PBL emissions, and thus displayed much higher mass concentrations of NR-PM₁ than October and November. Concerning the sources of PM₁, different types were identified with ammonium sulphate and oxygenated organics being predominant, as expected for aged aerosol with the degree of ageing investigated against air mass origin and microphysical parameters.  

How to cite: Eleftheriadis, K., Zografou, O., Gini, M., Fetfatzis, P., Granakis, K., Diapouli, E., Manousakas, M. I., Foskinis, R., Papayannis, A., and Nenes, A.: High-altitude aerosol characterization and PMF analysis of PM1 at the Helmos Mt station during the CALISHTO campaign, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16028, https://doi.org/10.5194/egusphere-egu23-16028, 2023.

The present study attempts to investigate the climatic impacts of PBAPs using the GISS-E2.1 Earth system model with the newly built PBAP emission model recently introduced to GISS-E2.1 to calculate the terrestrial and marine fluxes of PBAPs and estimate their transport and sinks. The current version of the PBAPs emission model accounts for different tracers of PBAPs including bacteria, fungal spores, and marine PBAPs (MPBAPs). The new PBAP tracers are allowed to interact with the radiation and to affect the liquid cloud droplet number concentration (CDNC).

Primary biological aerosol particles (PBAPs) can play a key role in cloud formation and phase regionally and locally by acting as cloud condensation nuclei (CCN), and ice nucleating particles (INP) at high sub-zero temperatures. Earlier studies suggested that the climatic impacts of PBAPs are negligible due to their globally small contribution to the total observed aerosol loads compared to other aerosols such as dust. However, PBAPs emissions are not yet well constrained. According to the IPCC AR5 report, the terrestrial emission flux of PBAPs was estimated in the range of 50-1000 Tg/yr, while AR6 neither updated the earlier estimates nor mentioned PBAPs at all. Recent observations proposed that the PBAPs' concentrations have likely been underestimated in earlier modelling studies. This suggests that PBAPs emission together with their climatic impacts and feedback remain highly uncertain, and thus, require a deeper investigation.

The study involves several scenarios where the emission fluxes of PBAPs were varied and different climatic diagnostics including, precipitation, cloud parameters, and direct and indirect radiative forcing resulting from these runs were compared with the ones from the control run of GISS-E2.1 with no PBAPs. We further investigated whether these differences were statistically significant. In this context, we present the results of the impact of changing the PBAPs' number fluxes on emission mass fluxes, burdens, number and mass concentrations, and atmospheric lifetime. For bacteria and when using the best estimate of number fluxes for bacteria cell diameter of 1 mm, the global average of emission, burden, and atmospheric lifetime was estimated to be 0.79 Tg/yr, 7.5 Gg, and 3.5 days, respectively. Those values are comparable with what has been reported by Burrows et al. (2009). For fungal spores, we estimated 2.55 Tg/yr, 19.5 Gg, and 2.8 days, which were comparable with Janssen et al. (2021). We further found that PBAPs have an overall negative/cooling direct forcing (NDF), however, the global average of the NDF was an order of magnitude smaller than the NDF of other aerosols, e.g., seasalt and OC. Nevertheless, regionally, the higher the emission of PBAPs (over vegetated surfaces), the cooling can be evidenced, which cannot be negligible (values up to ~ -0.4 W/m²). Moreover, adding PBAPs contributed to more global negative/cooling indirect forcing (NIF) (-28.8 w/m²) than the NIF from the control run (-27.1 W/m²).   

References

    Burrows, S. M. et al., ACP 2009, 9(23), 9281, doi: 10.5194/acp-9-9281-2009.

    Huang, S. et al., Environment International 2021, 146., doi: 10.1016/j.envint.2020.106197

    Janssen et al., ACP 2021, 21(6), 4381., doi: 10.5194/acp-21-4381-2021

How to cite: Sahyoun, M., Tsigaridis, K., and Im, U.: Predicting the Climatic impacts of Primary Biological Aerosol Particles; Sensitivity study using GISS-E2.1 Earth system model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17582, https://doi.org/10.5194/egusphere-egu23-17582, 2023.

Representing detailed atmospheric aerosol processes in global climate models has proven challenging from both a computational and a parameterization perspective. A recent study on different Earth System Models (ESM) responses to small changes in the precursors to new aerosol particle formation (NPF) showed that two different models can produce opposite radiative outcomes in response to the removal of isoprene emissions (atmospheric cooling versus warming; Sporre et al., 2020).

Here, we examine and test particle formation rate schemes and the sensitivity of the ESM EC-Earth3 applied in the work by Sporre et al. 2020. We have replaced the formation rate scheme based on Riccobono et al. (2014), derived exclusively from the relationship between organics vapors and sulfuric acid (H₂SO₄), with a more detailed molecular-model-based formation rate look-up table approach. This new scheme was created utilizing the Atmospheric Cluster Dynamics Code (ACDC) and currently applies tables of NPF from H₂SO₄ and ammonia. The tables include the effects of atmospheric H₂SO₄ and ammonia concentrations, temperature, ion-pair production, and cluster scavenging sink in the NPF process. We compare our model simulation results with ambient spring-time measurements of aerosol formation. We focus on boreal conditions and compare the performance of the new scheme to the previous model configuration to assess the simulations of local NPF events. For benchmarking, we also couple M7 with a one-dimensional high-resolution trajectory model ADCHEM with a more complex representation of aerosol chemistry. This enables us to compare observations of aerosol size distribution data from SMEAR II, a boreal measurement station in Finland (61.85°N, 24.28°E) with our ESM model results and with the detailed ADCHEM model results.

Keywords: global modeling, new particle formation, aerosols, clouds, radiative effects, EC-Earth.

Sporre, M. K., …, R., & Berntsen, T. K. (2020). Large difference in aerosol radiative effects from BVOC-SOA treatment in three Earth system models, Atmos. Chem. Phys., 20, 8953–8973. https://doi.org/10.5194/acp-20-8953-2020.

Riccobono F., Schobesberger S., Scott C. E., et al. (2014) Oxidation products of biogenic emissions contribute to nucleation of atmospheric particles. Science. 344, 717–721, doi:10.1126/science.1243527.

Session: AS3.2

Consent: The presenting author is acting on behalf and with the consent of all authors of this contribution.

How to cite: Svenhag, C., Sporre, M., Roldin, P., Nieradzik, L., Yazgi, D., and Olenius, T.: Modeling global radiative responses and aerosol composition changes in EC-Earth3 from detailed new-particle formation predictions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12466, https://doi.org/10.5194/egusphere-egu23-12466, 2023.

Abstract: This work used the Multi-element observation data from the Station for Observing Regional Processes of the Earth System (SORPES) from November 27 to December 3, 2018. It quantitatively analyzed the influence of mixed air pollution conditions on the surface micrometeorological elements and energy balance characteristics under the combined effects of long-distance sand and dust and local emission pollution. On this basis, the response characteristics of surface meteorological elements and energy distribution under different pollution conditions in autumn and winter in Nanjing are compared by synthetic analysis. The results showed that the daytime temperature on polluted days was about 1°C lower than that on clean days, and the night temperature was about 2°C higher. Both downward/upward shortwave radiation flux decreased on polluted days, and the long-wave radiation flux at night increased. On clean days, the net radiation budget during the day was 45.6% higher than that of polluted days and the surface sensible heat flux was 75.5% higher than that of polluted days. The average Bowen ratio at night on polluted days was higher than that on clean days, indicating that the nighttime sensible heat exchange was stronger. The results help to deeply understand the influence process and mechanism of air pollution from different sources and different properties on surface energy balance and local meteorological elements in the urban agglomerations of the Yangtze River Delta, and the results also provide a verification basis for the interaction between air pollution and meteorological conditions, air quality prediction and corresponding countermeasures.

How to cite: Wang, J., Ling, X., Zhu, X., Guo, W., Zou, J., and Sun, J.: Influence of mixed air pollution on surface micro-meteorological characteristics in autumn and winter in Nanjing area, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3816, https://doi.org/10.5194/egusphere-egu23-3816, 2023.

Absorbing aerosols emitted from biomass burning play an essential role in affecting the radiation balance, cloudiness, and atmospheric circulation over tropical regions. Assessments of these impacts rely heavily on the modeled aerosol absorption from poorly constrained global models and thus exhibit large uncertainties. By combining the AeroCom global model ensemble with satellite and in situ observations, we provide new constraints on the aerosol absorption optical depth (AAOD) over the Amazon and Africa. Our approach enables identifying, for each model, error contributions from emission, lifetime, and MAC (mass absorption coefficient), with emission and MAC dominating the modeled AAOD errors. In addition to primary emissions, we quantify substantial formation of secondary organic aerosols over the Amazon but not over Africa, which potentially contributes to the modeled AAOD errors. Furthermore, we find that discrepancies in the direct aerosol radiative effects between models decrease by threefold after correcting for the identified errors. This demonstrates that our work can significantly reduce the uncertainty in aerosols, which are considered the most uncertain radiative forcing agent.

How to cite: Zhong, Q., Schutgens, N., and van der Werf, G. and the AeroCom modelers: Threefold reduction of modeled uncertainty in direct radiative effects by constraining absorbing aerosols over biomass burning regions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7097, https://doi.org/10.5194/egusphere-egu23-7097, 2023.

Near-cloud aerosols have distinct direct radiative effects (DRE) compared to aerosols far from clouds due to aerosol hygroscopic growth and cloud-related processes. Since near-cloud regions cover approximately 20-30% of the globe, DRE from these regions must be understood and better quantified. However, retrieving aerosol properties in the vicinity of clouds is challenging, mainly because the adjacent three-dimensional (3D) cloud radiative effects obscure aerosol scattering signals. In this paper, we will first introduce a new method for retrieving aerosol properties in the vicinity of clouds, capitalizing on machine-learning techniques that allow us to incorporate 3D radiative effects directly. Using this retrieval capability, we will show how DRE varies with cloud organizations such as Sugar, Fish, Gravel, and Flowers, which are commonly observed in the trade-wind regimes. More importantly, we will discuss the implications for near-cloud aerosol DRE under a warmer climate.

How to cite: Yang, C. K. and Chiu, J. C.: Investigating the Near-cloud Aerosol Direct Radiative Effects Under Cloud Organizations of Sugar, Fish, Gravel, and Flowers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11022, https://doi.org/10.5194/egusphere-egu23-11022, 2023.

The Tibetan Plateau (TP) is important for weather and climate. Relatively clean aerosol conditions over the Plateau makes the study on the aerosol-cloud-precipitation interactions in this region distinctive. A convective event with precipitation observed on 24 July 2014 in Naqu was selected to explore the influence of aerosols on the onset and intensity of precipitation. We use the Modern-Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) reanalysis to derive the cloud condensation nuclei (CCN), which can be regarded as the real-time background. These values are adopted to initialize the regional WRF 4.0 meteorological model and to simulate the onset of convective events and the formation of precipitation. Four sets of experiments were adopted for our simulations. A detailed analysis of microphysical processes shows that, with the increase in the aerosol number concentration, the conversion rate of cloud water to rain in clouds is enhanced at first. Under polluted situation, the conversion process of cloud water to rain is suppressed; however, the transformation of cloud water to graupel and the development of convective clouds are favored. As a result, the onset of the precipitation is delayed and cold-rain intensity increases.

How to cite: Jiang, M., Li, Y., Hu, W., Yang, Y., and Brasseur, G.: Model simulation of the aerosol perturbation on the Tibetan Plateau convective precipitation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3557, https://doi.org/10.5194/egusphere-egu23-3557, 2023.

The expectations of the public and policymakers for accurate climate projections have grown with improvements in climate models. Internal variability, however, poses an inherent limit on climate predictability and, thus, accurate future climate projections of temperature and precipitation. This challenge is further amplified at a regional scale where internal variability can even dominate over forced anthropogenic climate change.

In this study, we focused on the contribution of decadal climate variability and anthropogenic forcing (greenhouse gases and aerosols) on past precipitation changes over Australia since the 1970s. Using observational data, we find that the variance explained on decadal to multi-decadal timescales is comparable to that on sub-decadal scales across Australia, underlining the importance of examining Australian trends in the context of variability. While decadal and longer precipitation trends over Australia’s east coast are dominated by internal variability, significant drying trends in the austral winter (June to August) over southwest Western Australia and wettening trends in summer (December to February) over northwest Australia are evident. We further disentangle the influence of internal variability from that of different anthropogenic forcing agents on these trends using simulations from the CESM2 Large Ensemble and idealised anthropogenic aerosol simulations from PDRMIP (Precipitation Driver Response Model Intercomparison Project). Our findings provide additional evidence for the significant role of internal variability on regional climate change and also underline the importance of a focused dialogue between scientists, policymakers and the public to ensure realistic expectations for regional future climate projections.

How to cite: Fahrenbach, N., Bollasina, M., Samset, B., Cowan, T., and Ekman, A.: Past trends in Australian rainfall: internally generated or human-caused?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1448, https://doi.org/10.5194/egusphere-egu23-1448, 2023.

The observed variety of aerosol effects on precipitation at different spatial and time scales means that no simple answer to this question has so far been discovered.  However, although aerosol effects are many, it remains possible that there are universal constraints on the number of degrees of freedom needed to represent them.  We use convective-scale simulations to reveal a self-similar probability density function that underpins surface rainfall statistics. This function is independent of cloud-droplet number concentration and is unchanged by aerosol perturbations. It therefore represents an invariant property of our model with respect to cloud–aerosol interactions. For a given aerosol concentration, if at least one moment of the rainfall distribution on cloud-droplet number is a known input parameter, then this can be combined with the self-similar function to reconstruct the entire rainfall distribution to a useful degree of accuracy. We will demonstrate this using simulations from convective permitting, aerosol interacting simulations over China.

How to cite: Field, P. and Furtado, K.: Do aerosols increase or decrease precipitation?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6429, https://doi.org/10.5194/egusphere-egu23-6429, 2023.

Rainfall prediction is one of the most challenging and uncertain tasks in weather forecasting, which has a significant impact on human society. Detection of heavy rainfall trends may be masked or amplified by natural variability, and numerical weather prediction (NWP) models have difficulty to predict them accurately. Therefore, understanding of rainfall effects with the evolution of atmospheric parameters and seeking atmospheric precursors of rainfall for nowcasting or prediction become an urgent need.

To date, most related studies have analyzed only a limited number of rain events or lacked long-term observations. This is likely to have a weak robustness. A multi-instrument and multi-parameter atmospheric monitoring system to detect precipitation precursors can improve the existing nowcasting system. AGORA (Andalusian Global ObseRvatory of the Atmosphere) is an ACTRIS facility located in the southeast of the Iberian Peninsula which offers unique infrastructure for the study of aerosol, clouds and precipitation. AGORA consists of two stations, an urban station located in the city of Granada (680 m asl) and a high-mountain station located in the National Park of Sierra Nevada (2580 m asl), separated by a horizontal distance of 20 km only. This infrastructure comprises state-of-the-art instrumentation covering active and passive remote sensing and in-situ techniques, including lidars, cloud radars, microwave radiometer, and weather stations. These instruments can obtain multiple atmospheric parameters (atmospheric water, aerosol, temperature, wind, etc.), including their vertical profiles.

In this study, we investigate the potential of different atmospheric parameters from ground-based microwave radiometer, ceilometer, nephelometer, absorption photometer and weather stations for the nowcasting of rainfall. We use 694 rain events identified by microwave radiometer in the southeast of Iberian Peninsula to identify conditions favorable to trigger rainfall over 10 years, and to analyze how they are related to observed changes in water vapor and aerosol load and properties. The composite analysis is carried out in a long time interval of 8 hours before and 16 hours after rain, with the onset of rain serving as the time marker for this method. The aim of our study is to show the typical behavior of rainfall, to reveal the interaction of rainfall with atmospheric parameters, and to explore the precursors of rainfall.

How to cite: Navas Guzmán, F., Wang, W., Hocke, K., Nania, L., Cazorla, A., Titos, G., Matthey, R., and Alados Arboledas, L.: Investigation of rainfall precursors using in-situ and remote sensing techniques in the southeast of the Iberian Peninsula, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12641, https://doi.org/10.5194/egusphere-egu23-12641, 2023.

Atmospheric rivers (ARs) play an essential role in extreme precipitation phenomena. To predict
such events, a correct simulation of ARs becomes crucial. Since most of the regional climate models
do not take aerosols into account in an interactive way, the main objective pursued in this work was to
analyse the role of aerosols in the intensity and behaviour of ARs on the regional scale. The identifi-
cation of ARs has always been carried out in global climate simulations applying detection algorithms
that may not be suitable in regional climate models, due to the presence of boundaries in the spatial
domain.

This work presents a new ARs identification algorithm for regional climate simulations (AIRA).
The implemented algorithm has proved to be able to properly identify the vapour structures associated
with ARs. AIRA was applied to a set of hourly data from three regional simulations (BASE, ARI and
ARCI), covering a period of 20 years. In BASE, aerosols were prescribed, while the model incorporates
aerosols dynamically in both ARI and ARCI. In ARI, aerosols are only incorporated interactively in
aerosol-radiation interactions. In ARCI, they are also included in the microphysical processes.

AIRA has identified about 250 ARs in the three simulations. Spring and autumn ARs were the
most frequent, intense and long-lasting, while they were less frequent, shorter and weaker in summer.
The identified ARs explain up to a 30% of the total precipitation in some areas of the Iberian Penin-
sula. The differences between the three simulations are significant in the spatial distribution of the
precipitation and in the trajectory and intensity of some ARs. Although the number of detected ARs
is similar, the temporal steps with ARs common to the three simulations represent only a 37% of the
total BASE steps containing ARs. This indicates that the sensitivity to the inclusion of aerosols is
relevant. The common ARs events showed that the BASE and ARI simulations generally present sim-
ilar trajectoriesk. However, important differences appear regarding ARCI, specially
when ARs are not quite intense.

A cluster analysis of the thickness field between 1000 and 850 hPa in ARI identifies three main
patterns. The comparison between the centroids in ARI and ARCI, reveals that the differences between
ARs in both simulations are mainly related to the aerosols type and concentration. The main
mechanism behind this behaviour is related to the modification of the temperature field due
to aerosol-cloud interactions (indirect effect) while aerosol-radiation effects are less relevant. 

How to cite: Raluy-López, E., Segado-Moreno, L., Sánchez-Jiménez, F., García-Fernández, E., Jiménez-Guerrero, P., and Montávez, J. P.: Response of atmospheric rivers to aerosols treatment in regional climate simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14509, https://doi.org/10.5194/egusphere-egu23-14509, 2023.

How to cite: Samset, B. H., Wilcox, L. J., Lund, M. T., Iles, C., Stjern, C. W., and Nordling, K.: Near-term precipitation change highly sensitive to black carbon emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3152, https://doi.org/10.5194/egusphere-egu23-3152, 2023.

Since the release of the first CMIP6 simulations one of the most discussed topics is the higher effective climate sensitivity (ECS) of some of the models resulting in an increased range of ECS values in CMIP6 compared to previous CMIP phases. An important contribution to ECS is the cloud climate feedback. Although climate models have continuously been developed and improved over the last decades, a realistic representation of clouds remains challenging. As projected changes in cloud properties and cloud feedbacks also depend on the simulated present-day fields, this contributes to the large uncertainties in modelled ECS.

In this study, we investigate the representation of both, cloud physical and radiative properties from CMIP5 and CMIP6 models grouped by ECS. Model results from historical simulations are compared to observations and projected changes of cloud properties in future scenario simulations are analysed by ECS group. For consistent processing of all datasets, the Earth System Model Evaluation Tool (ESMValTool) is applied to CMIP5 and CMIP6 simulations alongside with satellite observations.

Our results show that there are significant differences in simulated cloud properties and cloud radiative effects among the low/medium/high ECS groups with the high ECS models typically showing a better agreement with observations than the two other groups. Further analysis also shows differences in the projected changes in cloud properties among the different ECS groups related to cloud cover, cloud ice and cloud liquid water content. For example, a decrease in TOA net cloud radiative effect with increasing temperature is found in the tropics in the high ECS models whereas there is an increase in TOA net cloud radiative effect in medium and low ECS models.

How to cite: Bock, L., Lauer, A., and Eyring, V.: Projected changes in cloud properties in low/medium/high ECS models from CMIP5 and CMIP6, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11310, https://doi.org/10.5194/egusphere-egu23-11310, 2023.

Marine low-level clouds play an important role in the Earth's energy budget. They reflect large amounts of incoming solar radiation that would otherwise heat the Earth's surface. Areas of persistent low-level stratocumulus clouds cover the subtropical eastern oceans where lower-tropospheric stability is high. Based on spaceborne lidar measurements, which allow to precisely identify clouds at different altitudes, we find that low-level cloud cover of Peruvian, Namibian, and Californian stratocumulus decreased by between 0.05 and 0.10 per decade between 2007 and 2021. A seasonally resolved analysis gives even stronger trends for those seasons in which low-level cloud cover is highest. No trend is found for Australian and Canarian stratocumulus. The decrease in low-level cloud cover is strongly tied to increasing sea-surface temperatures. Our analysis suggests statistical significant reductions in albedo for Namibian and Californian stratocumulus of 0.11 and 0.05, respectively, per 0.10 decrease in low-level cloud cover. Such changes will have a direct impact in the Earth's energy budget by reducing the cooling effect of major marine stratocumulus sheets.

How to cite: Tesche, M. and Bruder, S.: Trends in subtropical marine low-level cloud cover from 2007 to 2021, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5374, https://doi.org/10.5194/egusphere-egu23-5374, 2023.

Clouds are a key component of the hydrological cycle and play an important role in weather and climate. Feedbacks between clouds and climate have important implications for climate sensitivity and thus on amplitude and pace of future climate change. In this study, as part of the SPARC Reanalysis Intercomparison Project (S-RIP) phase 2, we compare the cloud parameters from different reanalysis datasets, including the most widely used reanalyses ERA5, MERRA2 and JRA-55, with satellite observations. The study focuses on tropospheric clouds on monthly to seasonal and multi-year time scales. Means and variability of cloud parameters from the reanalyses such as cloud fraction, cloud liquid and ice water content as well as cloud radiative effects are compared to satellite observations for specific cloud regimes and regions. In addition to evaluating the performance of the different reanalysis products, we investigate whether the multi-reanalysis mean is in closer agreement with the observations than the individual reanalyses.

The analyses are performed with the Earth System Model Evaluation Tool (ESMValTool), a community developed open-source software tool. The tool provides common operations such as interpolating data on the same grid, calculating multi-reanalysis means, common data masking, area extraction, and basic statistics such as seasonal means, annual means, area means, etc. which facilitates a fair comparison with observations. Uncertainties are estimated using multi-product observational reference datasets.

How to cite: Lauer, A., Bock, L., and Hassler, B.: Cloud parameters from reanalysis datasets – a comparison with satellite data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6535, https://doi.org/10.5194/egusphere-egu23-6535, 2023.

Increased aerosol potentially impacts the cloud droplet spectrum, which in turn affects the aerosol-cloud interaction (ACI), known as the dispersion effect (DE). To consider DE in general circulation models (GCMs), many parameterizations have been proposed, but there are relatively few quantitative and global evaluations due to lacking suitable data and methodology. Additionally, both observations and numerical simulations confirmed that DE has opposite effects on ACI in aerosol- and updraft-limited regimes, but whether this effect can be reproduced by parameterizations has no clear conclusion until now. In this study, we used a liquid water content (LWC) binning method and worldwide data (China, Canada, Brazil, and Chile) to evaluate six dispersion parameterizations, namely Martin94, RLiu03, PengL03, Liu08, LiuLi15, and Zhang22. The LWC binning method ensures the difference between ACI values calculated by the cloud droplet number concentration and the effective radius is mainly caused by DE, which makes the quantitative calculation of DE possible. The results show that 1). DE has a weakening effect on ACI in the aerosol-limited regime, but an enhanced effect in the updraft-limited regime; 2). empirical parameterizations (Martin94, RLiu03, PengL03, and Liu08) can only show the weakening effect of DE on ACI, leading to an underestimation (-29% ~ -42%) for calculated ACI, especially for the updraft-limited regime; 3). both LiuLi15 and Zhang22 can reproduce the opposite effects of DE on ACI in different regimes, so we recommend giving priority to the LiuLi15 and the Zhang22 schemes when calculating DE in GCMs.

How to cite: Wang, H., Peng, Y., Lu, C., and Quaas, J.: Evaluate parameterizations of cloud droplet spectral dispersion by using worldwide aircraft data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4331, https://doi.org/10.5194/egusphere-egu23-4331, 2023.

Earth's climate system is complex. Thus, trying to represent this system as the sum of its parts, climate models have grown increasingly complex as well (Shackley et al., 1998). However, this makes the model results and behaviour difficult to interpret, and increases simulations' computational costs.

Building onto Proske et al. (2022), who demonstrated the potential for simplification in the two moment cloud microphysics (CMP) scheme of the global aerosol climate model ECHAM-HAM, we implement such simplifications for the CMP and activation scheme in ECHAM-HAM. For the CMP the sensitivity of the model to a specific process determines whether it is simplifiable. For example, heterogeneous freezing and secondary ice production in their present implementation can be removed without strong deviations in results. Replacing the sublimation and self-collection of ice with a constant rate, or replacing melting of ice crystals with a climatology has similarly small effects. The deviations that simplifications of other processes such as riming produce are larger, but all simplifications are robust to changing climate states.
For aerosol activation into cloud condensation nuclei, using a climatology of CCN diagnosed from a previous run gives satisfactory results. From the perspective of the CMP this simplification eliminates the need for the whole aerosol module HAM, associated with large computational time savings (for aerosol optical effects, the representation of at least anthropogenic aerosols with a simplified climatology has already been demonstrated successfully (Stevens et al., 2017)).

Of course, the value of simplifications and the evaluation standard for their results depends on one's modelling purpose (Parker, 2009). However, our results show that ECHAM-HAM contains redundancy in model detail and thus question the value of complexity in model representation as a normative principle (Shackley et al., 1998).

Parker, W. S. “Confirmation and Adequacy-for-Purpose in Climate Modelling.” Aristot. Soc. Suppl. Vol. 83, no. 1 (2009): 233–49. https://doi.org/10.1111/j.1467-8349.2009.00180.x.

Proske, U., S. Ferrachat, D. Neubauer, M. Staab, and U. Lohmann. “Assessing the Potential for Simplification in Global Climate Model Cloud Microphysics.” Atmos. Chem. Phys. 22, no. 7 (April 12, 2022): 4737–62. https://doi.org/10.5194/acp-22-4737-2022.

Shackley, S., P. Young, S. Parkinson, and B. Wynne. “Uncertainty, Complexity and Concepts of Good Science in Climate Change Modelling: Are GCMs the Best Tools?” Clim. Change 38, no. 2 (1998): 159–205. https://doi.org/10.1023/A:1005310109968.

Stevens, B., S. Fiedler, S. Kinne, K. Peters, S. Rast, J. Müsse, S. J. Smith, and T. Mauritsen. “MACv2-SP: A Parameterization of Anthropogenic Aerosol Optical Properties and an Associated Twomey Effect for Use in CMIP6.” Geosci. Model Dev. 10, no. 1 (2017): 433–52. https://doi.org/10.5194/gmd-10-433-2017.

How to cite: Proske, U., Ferrachat, S., and Lohmann, U.: Simplifying cloud microphysical process representation to reduce climate model complexity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1440, https://doi.org/10.5194/egusphere-egu23-1440, 2023.

The accurate representation of clouds and their phase is crucial to enable a correct representation of the Earth’s radiation balance. This has been demonstrated by large radiative errors in global models over the Southern Ocean mainly caused by an incorrect representation of supercooled liquid lowlevel clouds. In contrast to lowlevel clouds, midlevel clouds are rarely investigated. To fill this gap, this study investigates active satellite observations of midlevel clouds over the Southern Ocean and the Arctic Ocean from 2007 and 2008 with a comprehensive comparison to observations of lowlevel clouds. Midlevel and lowlevel clouds are distinguished by cloud base height. The DARDAR dataset provides a detailed phase categorization based on CloudSat and CALIPSO measurements. We have analyzed the cloud phase partitioning as a function of cloud top temperature, vertical cloud thickness, and the horizontal cloud extent. A local minimum in the mean liquid fraction within a cloud column can be observed for a cloud top temperature of -15 °C. An exception to this observation occurs for lowlevel clouds over the Arctic Ocean, which feature a plateau instead of a minimum. This hints at processes producing ice at these temperatures, which could be habit dependent vapor growth, secondary ice production, or a combination of both processes, as already discussed in other studies. Furthermore, daily sea ice concentrations from a passive microwave instrument are collocated to investigate their correlation with the cloud phase. At equal cloud top temperature, lowlevel clouds over the Southern Ocean and the Arctic Ocean have a higher liquid fraction, if they occur over sea ice. Midlevel clouds over the Southern Ocean show the same behaviour, while midlevel clouds over the Arctic Ocean show no significant phase dependence on the sea ice concentration. In addition, collocated CAMS reanalysis data are used to investigate the influence of different concentrations of various aerosol types such as sea salt, dust, black carbon, or organic matter on the cloud phase. Preliminary results show a stronger influence of the mixing ratio of sea salt on the phase of lowlevel clouds, but also the phase of midlevel clouds over the Southern Ocean seems to be influenced. Future work will further investigate the influence of different parameters, such as sea ice concentration, aerosol concentration, and cloud top temperature on the cloud phase by applying a machine learning model and exploring the relative importance of these parameters for the cloud phase, as well as their interactions and synergies.

How to cite: Dietel, B., Sourdeval, O., and Hoose, C.: The phase of midlevel and lowlevel clouds over the Southern Ocean and the Arctic Ocean and their dependence on cloud top temperature, sea ice, and aerosol concentrations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6713, https://doi.org/10.5194/egusphere-egu23-6713, 2023.

Aviation has been under increasing pressure in recent years to substantially cut its impact on climate. The International Air Transport Association (IATA) committed in October 2021 to achieve net-zero carbon emissions by 2050. Other similar ambitious targets have been set for aviation, all relying strongly on alternative fuel aircraft such as hydrogen combustion or fuel cells. A significant (i.e. 60%) proportion of the current aviation contribution to global warming is caused by non-CO₂ effects, with contrail cirrus the largest of these effects. Here we perform and analyse the first calculation of the contrail cirrus effective radiative forcing (ERF) for fuel cell powered aircraft and one of the first calculations for liquid hydrogen combustion aircraft, comparing them with estimates for kerosene and sustainable aviation fuel (SAF).

The exhaust mix of the hydrogen combustion in an aircraft gas turbine or hydrogen fuel cell aircraft is different to that of the current hydrocarbon fuels. This leads to a potential climate penalty due to the significant increase in associated water vapour emissions. We find that for liquid hydrogen combustion and fuel cell powered planes, the area of the globe covered by contrails is set to increase substantially (~70%) due to their additional water vapour emissions leading to more regions of the atmosphere becoming susceptible to contrail formation. However, the expected cleaner exhaust and corresponding increase in average contrail particle sizes lead to changes in contrail radiative properties. These changes result in a reduction in contrail cirrus ERF for liquid hydrogen combustion (~25%) and fuel cell (~20%) powered planes, compared to kerosene planes. SAF planes are expected to lead to a slight (~5%) increase in contrail cover, but a decrease (~20%) contrail cirrus ERF, compared to kerosene planes.

In general, our analysis finds that changes in contrail cirrus ERF are relatively modest between fuel types, compared to the overall uncertainty in the ERF estimate itself. Some of this uncertainty stems from our representation of physical processes in contrails and further work is needed to look at the effects of alternative fuels on contrail ice crystal sizes, contrail lifetimes and aerosol-cloud interactions. 

How to cite: Rap, A., Feng, W., Forster, P., Marsh, D., and Murray, B.: The climate impact of contrails from hydrogen combustion and fuel cell aircraft, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5520, https://doi.org/10.5194/egusphere-egu23-5520, 2023.

            Degraded meteorological conditions, including fog, limit the performance of optical sensors used in various fields of application (avionics, intelligent road vehicles, etc.). Cerema, the French research and expertise center under the supervision of the Ecological Transition Ministry, conducts evaluations of these sensors under artificial and controlled fog conditions in the dedicated PAVIN Fog&Rain platform.  In order to perform a digital twin of the platform, it is necessary to develop robust modeling of the propagation of electromagnetic waves in fog. Propagation is governed by the phenomena of scattering and absorption of photons in contact with fog droplets. The fog Droplet Size Distribution (DSD) is a key parameter of the propagation models.

In the present work, we investigate the DSD identification from spectral radiation measurements by inverting the stationary radiative transfer equation (RTE). This distribution together with Lorenz-Mie scattering theory allow to compute the optical properties (scattering coefficient, absorption coefficient, and phase function). First, we prove the well-posedness of the underlying inverse problem, then we perform some numerical experiments using synthetic data. The numerical results suggest that the method allows to identify the DSD.

We present some numerical results obtained by using various models describing
the particle size distribution (e.g. Shettle and Fenn models) and some experimental distribution measured in the Cerema platform. Afterwards, the identification of the DSDs is carried out using the radiative transfer equation with the collision term (multiple scattering) and by performing direct scattering and backscattering measurements. The robustness of the reconstruction was studied numerically by introducing several noise levels to the measurements.

How to cite: Krayem, A., Bernardin, F., and Munch, A.: Identification of fog Particle Size Distributions by inverting the radiative transfer equation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7634, https://doi.org/10.5194/egusphere-egu23-7634, 2023.

Wintertime stratus clouds over the Swiss Plateau can last for days.  They dissipate either due to airmass changes, absorption of solar radiation during the day, or after glaciation when a sufficiently large number of cloud droplets freezes. After formation, the ice crystals grow in an ice-supersaturated environment via vapor deposition until they are large enough to sediment from the cloud as drizzle or freezing drizzle.

To better understand how quickly ice crystals of various habits grow in real clouds with turbulence, we conduct glaciogenic seeding experiments in wintertime stratus clouds over the Swiss Plateau in our project CLOUDLAB[1]. During these experiments, a drone releases silver iodide (AgI) particles into the cloud, upwind of our measurement site, and we use various ground-based remote sensing and in-situ cloud and aerosol instruments to detect the microphysical changes induced by seeding. Preliminary results from the first CLOUDLAB field campaign proved that our method successfully allows us to detect the seeding signal in the cloud radar. In addition to our field measurements, we conduct numerical model simulations with ICON at different horizontal resolutions and different seeding particle concentrations to understand which seeding AgI concentration is theoretically needed for partial or full glaciation of the cloud, i.e. how fast the ice crystals grow at the expense of the evaporating cloud droplets due to the Wegener-Bergeron-Findeisen process.

First results will be presented in this talk.

How to cite: Lohmann, U., Henneberger, J., Ramelli, F., Spirig, R., Fuchs, C., Miller, A., Omanovic, N., Zhang, H., Bühl, J., Gaudek, T., Ohneiser, K., Radenz, M., Seifert, P., Baettig, P., Hervo, M., and Leuenberger, D.: Investigating ice crystal formation and growth in wintertime stratus clouds over the Swiss Plateau (CLOUDLAB project), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9124, https://doi.org/10.5194/egusphere-egu23-9124, 2023.

The climate impacts of global aviation include CO₂ effects and their so-called non-CO₂ effects. Among
those non-CO₂ effects, the effects of aerosol-cirrus interactions are the least understood and the latest
assessment of aviation radiative forcing could not give a best estimate and an uncertainty range [1]. Previous
studies [2, 3] have shown that a perturbation to the ice crystal number leads to a change in cirrus lifetime
and ice water path. In this talk, we investigate whether aerosol perturbations to ice nucleation can produce
large perturbations to cirrus ice crystal number.
We study these interactions using the 3D Met-Office NERC Cloud model (MONC). MONC is a Large Eddy
Simulation model coupled to the cloud micro-physics scheme, CASIM. We simulate two types of cirrus namely
the Gravity Wave cirrus (GW) and the Warm Conveyor Belt cirrus (WCB). The GW cirrus is thicker with
a higher ice crystal number concentration (ICNC) compared to the WCB cirrus, which is consistent with
aircraft observations [4]. We find that perturbing the formation stage of the cirrus cloud by injecting soluble
aerosols leads to an increase in ice crystal number and a decrease in the initial crystal size. Furthermore,
the ice clouds created in the presence of the injected soluble aerosols tend to have a higher ice water content
and an increased lifetime. Both GW and WCB cirrus clouds behave similarly to perturbation by soluble
aerosols at the formation stage.
In contrast, perturbing a pre-existing cirrus with soluble and insoluble aerosols does not change the properties
of the ice cloud. Ice crystal growth by vapour deposition uses available water vapour during the lifetime of
the cirrus [5, 6], which we find comes at the expense of activating aerosols that would lead to an increase
in the ICNC. Hence, although cirrus clouds would be sensitive to a perturbation in their ice crystal number
concentration, it is difficult to obtain such perturbations by injecting aerosols at cloud level, for example from
commercial aircraft exhaust. Furthermore, even though these results do not completely preclude large cirrus
perturbations from aviation aerosols in specific cases, they suggest that the corresponding global radiative
forcing is small.

References
[1] Lee et al. Atmospheric Environment. (2021). 
[2] Verma & Burkhardt. Atmospheric Chemistry and Physics. (2022).
[3] Gilbert et al. In preparation. (2022).
[4] Li et al. Atmospheric Chemistry and Physics Discussions. (2022).
[5] Hill et al. Quarterly Journal of the Royal Meteorological Society. (2014).
[6] Lohmann & Feichter. Atmospheric Chemistry and Physics. (2005).

How to cite: Purseed, J. and Bellouin, N.: Large Eddy Simulations of aerosol-cirrus interactions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5377, https://doi.org/10.5194/egusphere-egu23-5377, 2023.

How to cite: Santos, L., Salo, K., Frostenberg, H., Kong, X., Noda, J., Kristensen, T., Ohigashi, T., Ekman, A., Ickes, L., and Thomson, E.: Changes in cloud activity of ship exhaust particles: Potential effects on Arctic mixed-phase clouds, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14906, https://doi.org/10.5194/egusphere-egu23-14906, 2023.

Living downwind of a cement-producing or a metallurgical plant could mean you get more snow, fewer clouds and more sunshine compared to nearby areas. We use satellite observations to reveal the glaciation of supercooled stratiform liquid-phase clouds by anthropogenic aerosols acting as ice-nucleating particles. There are strong indications that glaciation is caused by aerosols emitted from oil refineries, coal-fired power plants, cement, metal smelting and processing, chemical plants, and other anthropogenic air pollution sources in Europe, Asia, North America and Australia. Heavily polluted areas derived by simulating aerosol dispersion from strong anthropogenic aerosol point sources overlap with the areas of glaciation, snowfall, and decreased cloud cover strikingly well. Moreover, the polluted areas with decreased cloud cover are plume-shaped, with a distinctive head pointing towards the pollution source, similar to aerosol-polluted cloud tracks in liquid-water clouds (Toll et al 2019 Nature https://doi.org/10.1038/s41586-019-1423-9).

Glaciation-induced snowfall downwind of aerosol sources is observed using ground-based precipitation radars, and tracks of snow are also seen on the ground in satellite imagery. Aerosol-induced glaciation and snowfall lead to reduced cloud cover. At multiple aerosol sources, glaciation events are more frequent than polluted tracks in liquid-phase clouds. Thus, at least locally at some aerosol sources in the middle and high latitudes, the warming effect induced by aerosols acting as ice-nucleating particles likely exceeds the cooling effect induced by aerosols acting as cloud condensation nuclei. Further research is needed to quantify the global radiative forcing by anthropogenic ice nucleating particles.

How to cite: Toll, V., Rahu, J., Keernik, H., Trofimov, H., Voormansik, T., Manshausen, P., Hung, E., Michelson, D., Christensen, M., Post, P., Junninen, H., Lohmann, U., Watson-Parris, D., Stier, P., Donaldson, N., Storelvmo, T., Kulmala, M., and Bellouin, N.: Anthropogenic aerosols turn liquid cloud droplets into ice crystals, produce snow and eat holes in the clouds, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4129, https://doi.org/10.5194/egusphere-egu23-4129, 2023.

It is unclear to what extent the cooling effect of anthropogenic air pollution particles, known as aerosols, counteract the warming effect of greenhouse gases. In particular, it is uncertain how strong the cooling effect caused by aerosol-induced changes in cloud properties is. Clouds and precipitation can form in the Earth's atmosphere thanks to aerosols. However, cloud thickness, coverage, and lifetime may be perturbed when anthropogenic activities add additional aerosols to clouds, leading to the formation of more numerous, but smaller droplets. We show that it is possible to quantify these perturbations by comparing the properties of polluted clouds at air pollution hotspots with those of nearby unpolluted clouds. There are large-scale polluted cloud areas around the world that are hundreds of kilometres in size, yet surrounded by distinctively less polluted cloud areas. We show that such strong anthropogenic cloud perturbations occur intermittently and only under favourable meteorological conditions. We challenge the assumption of a unidirectional increase in cloud thickness in current climate models and show that, on average, cloud thickness does not increase in response to aerosols. This suggests that the cooling effect of anthropogenic aerosols on Earth's climate may not be as strong as previously thought. Our results will ultimately lead to more reliable climate projections.

How to cite: Trofimov, H. and Toll, V.: Polluted clouds at air pollution hot spots help to better understand anthropogenic impacts on Earth’s climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12707, https://doi.org/10.5194/egusphere-egu23-12707, 2023.

Aerosol-cloud interactions remain a large source of uncertainty in anthropogenic climate forcing. One of the reasons for this uncertainty is the confounding role of meteorology, influencing both aerosols and cloud properties. To untangle these variables, ship tracks, the clouds polluted by shipping emissions, have been widely studied. Recently, the use of shipping emissions locations and amounts, combined with reanalysis winds, has allowed us to study polluted clouds by following ship emissions to the locations they are advected to by the time of a satellite measurement of clouds. This is possible even when no visible tracks appear in satellite images. Here, we additionally use emission amounts data and investigate their effect on key cloud characteristics like droplet numbers and liquid water. This per-ship emissions data is valuable as it allows us to investigate cloud property changes stratified by region or meteorology. Between the ships with the lowest and highest emissions, droplet number anomalies increase by an order of magnitude from 0.25% to 2.5%, but the effect saturates at high emissions. We furthermore present evidence that increases of liquid water are insensitive to the amount of aerosol increases. Crossing data with a set of machine-learning detected ship tracks, we show that emissions amount has a similarly saturating effect on the formation of visible tracks as on droplet number, increasing roughly linearly for a large range of emissions before saturating (and even declining) at high emissions. The saturation of cloud responses at relatively high emissions could indicate that clouds react strongly to reductions in aerosol emissions.

How to cite: Manshausen, P., Watson-Parris, D., Christensen, M. W., Jalkanen, J.-P., and Stier, P.: Assessing cloud sensitivity to shipping aerosol across large emissions ranges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15921, https://doi.org/10.5194/egusphere-egu23-15921, 2023.

Aerosol-cloud-interactions remain a large climate uncertainty; especially uncertain is the liquid water path (LWP) adjustment to varying aerosol concentrations in stratocumulus (StCu). Large-eddy simulations (LES) have found that the LWP response of StCu to aerosol can be either positive or negative depending on the cloud regime, whereas climate models simulate uniformly positive correlations. Observations of the real-world evolution of LWP in varying aerosol environments are needed to resolve the nature of the correlation between LWP and aerosol. We address this by analyzing a large ensemble of parcel trajectories over the southeast Pacific within the GOES-16 field of regard. Preliminary results are consistent with LES, showing consistent regime dependent evolution of the LWP depending on the initial cloud state, with LWP generally decreasing with varying number concentrations (N). However, LWP generally increases at low N, potentially supporting LES conclusions showing a cloud-regime dependence. To investigate this further, we will further condition observations by MERRA-2 large-scale environmental variables (e.g. estimated inversion strength, moisture, and boundary-layer decoupling). We expect environmental differences will correlate with the differences between changes in LWP at low and high N.

How to cite: Smalley, K. and Lebsock, M.: A Geostationary View of a Liquid water Path Adjustment dependence on Cloud Regime, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-909, https://doi.org/10.5194/egusphere-egu23-909, 2023.

A large part of the uncertainty around future global warming is due to the cooling effect of aerosol-liquid cloud interactions, and in particular to the elusive sign of liquid water path (LWP) adjustments to aerosol perturbations. We quantify this adjustment with a novel causal approach that combines physical knowledge in the form of a causal graph with geostationary satellite observations of stratocumulus clouds. This allows us to remove confounding from large-scale meteorology and to disentangle counteracting physical processes such as cloud-top entrainment enhancement and precipitation suppression due to aerosol perturbations. The resulting LWP adjustment is time-dependent, with positive initial values due to fast precipitation suppression and negative values after entrainment enhancement has fully developed. We also use the causal framework as a diagnosis tool to detect potential issues with precipitation retrievals, which might cause precipitation-related influences on the LWP to be underestimated. These results suggest that time-aware causal analyses are key to reconcile conflicting studies concerning the sign of LWP adjustments across different data sources.

How to cite: Fons, E., Runge, J., Neubauer, D., and Lohmann, U.: A causal approach to disentangle fast and slow stratocumulus adjustments to aerosol perturbations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1907, https://doi.org/10.5194/egusphere-egu23-1907, 2023.

How to cite: Wall, C., Norris, J., Possner, A., McCoy, D., McCoy, I., and Lutsko, N.: Assessing effective radiative forcing from aerosol-cloud interactions over the global ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1699, https://doi.org/10.5194/egusphere-egu23-1699, 2023.

Semi-volatile compounds (organics, nitrate, chloride) are ubiquitous in atmospheric aerosols and usually contribute over 50 % to particulate matter worldwide (Jimenez et al., 2009). Co-condensation of semi-volatiles and water vapour can enhance aerosol particle growth and facilitate their activation to cloud droplets, affecting cloud properties and thus the Earth's radiation balance.

Yet, the effect of co-condensation on aerosol hygroscopic growth is not well constrained as the loss of semi-volatiles during drying and heating in traditional aerosol sampling devices (e.g., by HTDMA, CCN counter) is poorly understood. Here, we developed a novel method to derive aerosol hygroscopic growth by considering the co-condensation effect, from open-access data including visibility, PM_2.5 mass concentration and meteorological parameters (Wang and Chen, 2019). By applying our visibility method and thermodynamic modelling in Delhi (India), we found that the co-condensation of HCl with water vapour can largely enhance aerosol hygroscopicity by doubling the light extinction coefficient of wetted particles and halving the critical supersaturation needed for cloud droplet activation (as shown in Fig. 1 a-b, Gunthe et al., 2021). Our recent results showed that the co-condensation effect in Chinese megacities (Beijing, Guangzhou, and Shanghai) is as significant as in Delhi, but acts via co-condensation of HNO₃.

The next question is how significant the co-condensation effect is globally and how much it can alter clouds and the radiation balance. Here, we combine novel field observation, a cloud parcel model, and an aerosol-climate model to disentangle this question. The particle and gas composition, particle size distribution, and air parcel cooling rate are essential factors for the co-condensation effect in a rising air parcel.

Our preliminary sensitivity study (doubling hygroscopicity) in a climate model showed that the co-condensation effect plays only a minor role in clouds formation globally, but significantly increases cloud droplet number concentration and liquid cloud cover in regions with large anthropogenic emissions, e.g. East/Southeast Asia, India, Europe, East US. Consistently, parcel model calculations confirm that for a given cooling rate, co-condensation increases the number of activated cloud nuclei. Our study will help to develop a parameterization for aerosol-climate models to include the co-condensation effect on cloud formation.

References

Gunthe, S. S., et al. (2021), Enhanced aerosol particle growth sustained by high continental chlorine emission in India, Nature Geoscience.

Jimenez, J. L., et al. (2009), Evolution of Organic Aerosols in the Atmosphere, Science, 326(5959), 1525-1529.

Wang, Y., and Y. Chen (2019), Significant Climate Impact of Highly Hygroscopic Atmospheric Aerosols in Delhi, India, Geophysical Research Letters, 46(10), 5535-5545.

How to cite: Wang, Y., Neubauer, D., Chen, Y., Liu, P., Luo, B., Proske, U., Ferrachat, S., Marcolli, C., and Lohmann, U.: By how much can co-condensation of semi-volatile compounds alter clouds?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2345, https://doi.org/10.5194/egusphere-egu23-2345, 2023.

There are two types of activation of aerosols to become cloud-droplets.   First, clouds with liquid have a base at the level of water saturation where the first cloud-droplets form during ascent.  In the first 10 m or so above the base, the supersaturation rises to a peak value and aerosols activate to become cloud-droplets (“cloud base activation”).  The supersaturation then relaxes to an equilibrium.  Second, if the supersaturation becomes high enough during ascent into the interior of the cloud aloft, then there can be “in-cloud activation” as an extra source of cloud droplets.  A possible cause of in-cloud activation is entrainment of aerosols from the environment that are large enough to activate.  Another cause can be an increase with height of the supersaturation, causing it to exceed the peak value at cloud-base.

In-cloud activation is often overlooked in cloud-microphysics schemes of atmospheric models and is challenging to represent.  In deep convective updrafts, simulations of storms have shown it can generate most of the droplets at subzero levels aloft.  In-cloud activation of aerosols to become droplets can even generate most of the ice crystals in the anvil cirriform anvils by their homogeneous freezing near -36 degC. 

This presentation provides a theoretical analysis of microphysical feedbacks controlling sustained in-cloud activation and precipitation production.  A parcel model with 3 evolution equations for cloud mass, precipitation mass and cloud-particle number is created, during ascent for a cloud of a single phase, liquid or ice.   The theory predicts how in-cloud activation is most likely to be triggered by the onset of precipitation during sufficient ascent, with the ascent only needing to approach almost twice the cloud-base updraft speed aloft.  The initial state of no precipitation is unstable with respect to a perturbation. In the 2D phase space of cloud mass and precipitation mass, a neutral line is elucidated. Unstable growth of precipitation mass occurs by a positive feedback, driving the microphysical system to cross the line into a regime of stability.  A stable equilibrium, namely an attractor, is approached where precipitation mass is balanced by accretion of cloud mass (source) and its fallout (sink).

The cloud-particle number concentration attains a stable equilibrium involving in-cloud activation.  A source of droplets from the inexorably increasing supersaturation, caused by the vertical acceleration, is balanced against losses from accretion of cloud droplets by precipitation. Formulae for novel dimensionless numbers, characterizing the microphysical equilibria and their stability, are derived analytically.  These include a ‘condensation–precipitation efficiency’ and an ‘in-cloud activation efficiency’.  

The theory explains the orders of magnitude of liquid water content commonly seen in convective and stratiform clouds.  Sensitivity tests are performed by altering the loading of cloud condensation nucleus (CCN) aerosols and the updraft speed.  Microphysical equilibria are sensitive to the assumed ascent but are insensitive to CCN aerosol concentrations.  Nevertheless, higher aerosol concentrations cause more extreme oscillations of the mass fields during the approach to equilibrium.   This theory of in-cloud activation applies to both ice-only and liquid-only cloud.   More details are available in a recent published paper.

How to cite: Phillips, V.: In-Cloud Activation of Aerosols and Microphysical Quasi-Equilibrium with Precipitation in Deep Cloudy Ascent: a New Theory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15789, https://doi.org/10.5194/egusphere-egu23-15789, 2023.

This study investigates the top of atmosphere (TOA) solar radiative forcing induced by the transport of the biomass burning (BB) absorbing aerosol from the African continent over the south-eastern Atlantic Stratocumulus (Sc) region during the longer fire seasons, i.e., the 4 months of June through September.

The evolution, since 2002, of the BB aerosol and the Sc cloud properties from MODIS satellite data, as well as the evolution of the TOA outgoing solar radiative flux in clear and all skies from CERES (Clouds and the Earth’s Radiant Energy System) satellite data are presented and discussed. In clear skies, CERES shows an increasing trend in TOA outgoing shortwave flux (negative TOA forcing) associated to an increasing trend in MODIS aerosol optical thickness (direct effect) over the southeastern Atlantic Sc region. While in the presence of clouds, CERES shows that the negative TOA forcing by BB aerosol in clear skies is converted into a positive forcing, consistent with previous studies.

Further statistical analyzes are performed to determine whether this positive TOA forcing is primarily attributed to the increase in BB aerosols above Sc clouds or to the negative trend in cloud cover and liquid water path observed by MODIS data.

How to cite: Jouan, C. and Myhre, G.: Investigating Solar Radiative Forcing by Biomass Burning Aerosols within Clouds Over Southwest Africa Using Satellite Data., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14888, https://doi.org/10.5194/egusphere-egu23-14888, 2023.

Aerosols interact with radiation and clouds and thereby disturb radiative budget and temperature structure in the atmosphere. To account for these effects, numerical weather prediction models rely on climatological mean concentrations. This simplification may lead to large errors in the forecasted cloud cover and radiative fluxes especially during major aerosol events. For example, Saharan dust events often coincide with significant errors in shortwave radiation and thus, day-ahead photovoltaic forecasts in Europe. In this study we investigate errors in the short-range forecasts during Saharan dust outbreaks in March 2021, analyze possible causes and explore the solutions. We use the data from pre-operational forecasts performed with the ICOsahedral Nonhydrostatic model with Aerosols and Reactive Trace gases (ICON-ART) based on two experiments: without dust effects and with direct dust effect only. We compare model data with the measurements from satellite and in-situ instruments. The results reveal that the inclusion of direct radiative effects from prognostic dust improves the forecast in surface radiation during clear-sky conditions. However, dusty Cirrus clouds are strongly underestimated, pointing to the importance of representing indirect effects. To fill this gap, we develop and test corresponding sub-grid parameterization for dusty Cirrus in the ICON-ART model. Only with help of this parameterization ICON-ART is able to simulate the formation of the dusty cirrus, which leads to substantial improvements in cloud cover and radiative fluxes compared to simulations without this parameterization. This study confirms that a reliable photovoltaic forecast requires explicit treatment of aerosol-cloud-radiation in numerical weather forecast systems.

How to cite: Hoshyaripour, G. A., Hermes, K., Seifert, A., Bachmann, V., Filipitsch, F., Foerstner, J., Grams, C., Hoose, C., Quinting, J., Rohde, A., Vogel, H., and Vogel, B.: Impacts of aerosol-cloud-radiation interactions on photovoltaic generation: case of Saharan dust outbreaks in March 2021, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14380, https://doi.org/10.5194/egusphere-egu23-14380, 2023.

In 2014/2015, the intense eruption of the Holuhraun/Bárðarbunga volcano in Iceland emitted extreme amounts of SO₂, far above the anthropogenic or natural background. This event had major impacts on cloud properties observed by satellite in the Northern Atlantic. Malavelle et al. (2017) showed that many climate models struggled to reproduce these observed impacts on clouds, indicating potential serious issues in the cloud-aerosol interaction frameworks currently used in models. These issues could explain part of the very large uncertainty remaining in current estimates of the radiative effect of aerosol-cloud interactions.

Here, we use MODIS observations of cloud properties during the eruption to evaluate 3 different cloud-aerosol interaction approaches of decreasing complexity in the WRF-Chem 4 regional atmospheric model: First, the default model setup, using the Abdul-Razzak and Ghan (2000) parameterization (AR2000), coupling MOSAIC-4bin aerosols to the Morrison-2-moment microphysics. Second, the Thompson & Eidhammer (2014) aerosol-aware microphysics (TE2014), coupled for this study to MOSAIC-4bin aerosols. Third, the default version of TE2014 in WRF 4 using forced offline aerosols, where we replaced the original static aerosol climatology with 3D time-varying aerosols during the eruption. This last simplified approach does not require simulating fully interactive aerosols, and could be used to investigate regional cloud-aerosol processes and radiative forcing at high resolutions and climate time scales at a lower computational cost.

In addition, we compare how these 3 cloud-aerosol approaches impact the detailed cloud response during the eruption in terms of cloud microphysical and optical properties, radiative fluxes, and precipitation.

How to cite: Marelle, L., raut, J.-C., Myhre, G., and Thomas, J.: Evaluating cloud-aerosol interaction parameterizations in the WRF-Chem model against cloud observations during a large volcanic eruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16289, https://doi.org/10.5194/egusphere-egu23-16289, 2023.

Aerosols act as cloud condensation nuclei (CCN) and ice nuclei (IN) within cloud droplets, therefore they influence the microphysical features of clouds. Although many numerical and observational studies have investigated aerosol-cloud interaction, the extent and quality of aerosol impact on cloud formation and precipitation processes are not clear yet. Volcanic eruptions, which are rich sources of various chemical compounds in the atmosphere, can help to improve the understanding of aerosol effects on clouds by providing natural laboratories with locally high aerosol conditions adjacent to an unperturbed environment.

In the present study, we selected two volcanoes that emitted different aerosols and trace gases into the atmosphere to investigate their impact on the cloud microphysical processes: the 2014 Holuhraun and the 2021 La Soufrière eruption. The first one is an Icelandic volcano that mostly emitted sulfur dioxide (SO2), which forms sulfate particles serving as CCN. The second one is located on the Caribbean island of Saint Vincent and is an ash-rich eruption, so it is an appropriate case to study heterogeneous ice nucleation since ash particles serve as IN.

We simulated the initial phases of these eruptions using the ICOsahedral Nonhydrostatic model with Aerosols and Reactive Trace gases (ICON-ART) and performed different sensitivity experiments. For each case, we conducted two different simulations, in one of which the volcanic emission is considered, while in the other one, it is not (termed ‘Plume’ and ‘No-plume’).  For more detailed analysis, we divided the simulated area into two areas inside and outside of the plume using these criteria, column abundance of SO2>1 DU for Holuhraun and mass concentration of ash>10^-4 gm^-3 for La Soufrière.

For the Holuhraun case, the results showed a pronounced effect of volcanic aerosols on the different hydrometeors and process rates. Furthermore, the range and distribution of the liquid water path (LWP) have a good agreement with MODIS-Aqua satellite retrievals. In the Plume simulation, an increase in the number of cloud droplets but with smaller sizes was observed while we saw a reduction of graupel mass concentration in this simulation. These results confirmed our expectations, since in the Plume case the aerosol number concentration increases, resulting in an enhancement of the cloud droplet number concentration but with a smaller droplet size. In addition, the riming rate which highly depends on the cloud droplet sizes was reduced in the Plume simulation and led to the reduction of graupel mass that is mostly created by riming.

For the La Soufrière case, we mostly concentrated on heterogeneous ice nucleation as this case was an ash-rich eruption. Our preliminary results showed that the enhancement of ash particles reduced the ice crystal number concentration although the number of heterogeneously nucleated particles increased. To explain this behavior, we refer to the fact that additional heterogeneous freezing suppresses homogeneous freezing so that the total number of ice crystals is reduced. 

Keywords: Aerosol, Cloud, ICON-ART Model, volcanic aerosols, aerosol-cloud interactions, Holuhraun eruption, La Soufrière eruption

How to cite: Zarei, F., Hoose, C., Bruckert, J., and Hoshyaripour, G. A.: Investigation of cloud response to the 2014 Holuhraun and the 2021 La Soufrière eruptions using the ICON-ART model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9212, https://doi.org/10.5194/egusphere-egu23-9212, 2023.

Aerosol effective radiative forcing (ERF) has persisted as the most uncertain aspect of anthropogenic forcing over the industrial period, limiting our ability to constrain estimates of climate sensitivity and the accuracy of climate projections. Aerosol-cloud interactions are the most uncertain component of aerosol ERF. The 2014 Holuhraun volcanic eruption acted as large source of sulfur dioxide, providing a natural experiment for testing aerosol-cloud interaction hypotheses at a climatically relevant scale. Our study builds on previous aerosol-cloud interaction analyses of the eruption. We evaluate the observed aerosol perturbation to cloud properties inside the volcanic plume in the weeks following the eruption. As expected, on most days, we find an in-plume shift to increased cloud droplet concentration and decreased effective radius. The sign and magnitude of an in-plume shift in liquid water path varies in the weeks following the eruption. We probe this variation in the observed in-plume cloud perturbations to elucidate the aerosol-cloud interaction mechanisms following the Holuhraun eruption.

How to cite: Peace, A., Haywood, J., Chen, Y., Jordan, G., Malavelle, F., Partridge, D., and Duncan, E.: Aerosol-cloud interactions derived from the 2014 Holuhraun volcanic eruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11374, https://doi.org/10.5194/egusphere-egu23-11374, 2023.

Earth sensors NIST Advanced Radiometer (NISTAR) and Earth Polychromatic Imaging Camera (EPIC) of the Deep Space Climate Observatory (DSCOVR) measure outgoing radiative fluxes of the entire sunlit Earth and key spectral characteristics at 10 km resolution, respectively.  The unique near backscatter angular perspective of DSCOVR is used to measure ozone, sulfur dioxide, aerosols, clouds, ocean surface photosynthetically available radiation (PAR), vegetation, sun glints, and to obtain UV radiation estimates.  In the presentation I will focus on clouds and aerosol EPIC products: cloud mask, cloud height and optical thickness, aerosol optical depth and aerosol height, single scattering albedo, their correlation and daytime variability.

How to cite: Marshak, A.: Cloud and aerosol observations from DSCOVR satellite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2765, https://doi.org/10.5194/egusphere-egu23-2765, 2023.

The determination of supercooled cloud fraction (SCF) based on satellite remote sensing is important for research fields including estimation of global radiative energy balance, artificial weather modification, and prevention of aircraft ice accretion. However, nearly all retrieval algorithms for passive instruments provide binary phase information - ice, supercooled or liquid - making it difficult to retrieve mixed-phase cloud properties and understand the transition from supercooled water droplets to ice crystals. Motivated by these questions, we proposed a method to evaluate the ice partitioning of single-layer thermodynamic cloud top phase, under the assumption of the shape of ice crystals.

In order to retrieve optical properties of SCF, we use a droxtal habit model to investigate the scattering properties of frozen supercooled water particles. We compare the single scattering phase functions between droxtals and spherical particles at different wavelengths. Furthermore, the difference of satellite observed radiance reflected by supercooled water clouds and ice clouds are discussed. The difference between cloud ice water path of these two categories of clouds and observations from the same satellite channel can be used to evaluate the SCF in single-layer cloud top mixed phase clouds. Taking the ice-to-liquid ratio in the GCM (global climate model)-Oriented CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) Cloud Product (CALIPSO-GOCCP) as the criteria to validate our retrieved SCF, the average deviation, root mean square error and correlation coefficient are 6.98%, 9.62%, and 0.78, respectively. As a future work, we plan to adjust ice particle habits regarding ambient temperature to represent frozen supercooled water particles.

Our method could be applied to the to be launched EarthCARE (Cloud, Aerosol and Radiation Explorer) satellite in 2023 as it boards one multi-spectral imager and one atmospheric lidar simultaneously. This study is also of interest for related researches on assessing the climate impacts of supercooled and mixed-phase clouds and validating the associated global model simulations.

How to cite: Wang, Z., Letu, H., Shang, H., Bugliaro, L., and Voigt, C.: The supercooled cloud fraction in the mixed-phase clouds from Himawari-8 observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8087, https://doi.org/10.5194/egusphere-egu23-8087, 2023.

Four decades of satellite-based observations of clouds are now available and there are currently four different global cloud climate data records (CDRs) available providing 35+ years of data from the passive imagers, namely CLARA-A3, ESA Cloud CCI, ISCCP and PATMOS-X. This contribution presents a comprehensive assessment of the latest versions of these four long-term cloud CDRs. Given the fact that clouds cover nearly 70% of our planet and exert strong control on the radiation budget through their effects on radiation, precipitation, circulation and through their susceptibility to aerosols, such a periodic observational assessment of their global state is necessary from the climate perspective. CLARA-A3, PATMOS-X and ISCCP have been improved considerably in the recent years, thanks mainly to improved calibration, better training, algorithm developments, and rigorous validations.

This contribution will focus on three main areas:

1) Presenting the state-of-the-art global climatologies of cloud properties from the said CDRs, while highlighting the agreements and disagreements among them.

2) Evaluating the decadal stability of cloudiness in these CDRs using CALIPSO and MODIS as the references in light of the stringent requirements set by the WMO Global Climate Observing Systems (GCOS).

3) Investigating the robust trends in global cloudiness and their commonalities across the CDRs.

How to cite: Devasthale, A. and Karlsson, K.-G.: A recent assessment of the state of global cloudiness in the satellite-based climate data records, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5203, https://doi.org/10.5194/egusphere-egu23-5203, 2023.