AS3.2
Orals: Tue, 25 Apr | Room F2
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, 24–28 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, 24–28 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 (kchem) overestimates as compared to kHTDMA though the assumption of external mixing of aerosols improved the values of predicted k. CCN derived hygroscopicity (kccn) underestimates as compared to hygroscopicity derived from HTDMA measurements. Both kchem and kccn are found to follow the similar diurnal variation of kHTDMA. Thus, the kchem and can be used as a proxy of in the absence of direct HTDMA measurements. Using kchem 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 Apr 2023, EGU23-11022, https://doi.org/10.5194/egusphere-egu23-11022, 2023.
Food and economic safety in West Africa rely heavily on rainfed agriculture and are threatened by climate change and demographic growth. Accurate rainfall information is therefore crucial to ensure safety against these challenges. However, existing rainfall models fail to accurately represent the highly variable and sparsely monitored West African rainfall distribution. Satellite rainfall products show a poor correlation with ground-based rainfall measurements and literature suggests that atmospheric aerosols are partly to blame for this poor performance.
West Africa presents higher airborne aerosol concentrations than other regions of the world, mainly originating from dust outbreaks in the Sahara Desert and biomass burning across the Atlantic Ocean in South and Central Africa. Furthermore, climate in West Africa is modulated by the movement of the Intertropical Convergence Zone (ITCZ), that separates a hot, dry and dusty air mass from the Sahara Desert from a cold and humid air mass from the Atlantic Ocean. The ITCZ marks the transition between the dry and the rainy season in the reigon.
In this work we study the relationship between atmospheric dust during the dry and the rainy season and precipitation in West Africa using Google Earth Engine. We employ IMERG precipitation data for West Africa and aerosol data from the TROPOMI instrument on-board Sentinel 5P over the whole of Africa between 2018 and 2022, to capture the largest sources of airborne aerosols reaching West Africa throughout the year. We investigate precipitation on a 0.5 degree resolution grid covering West Africa and part of the adjacent Atlantic Ocean and spanning over all West African climatic regions, from the Sahara in the North to the Guinean and Guinean-Congolian regions in the South. We analyze regional and remote aerosol-precipitation connections at different temporal and spatial scales and for the different climatic regions.
The aim of this research is to further the knowledge about the relationship between African dust and West African rainfall so we can better account for and reproduce these processes in satellite rainfall retrieval models.
How to cite: Estebanez Camarena, M., ten Veldhuis, M.-C., and van de Giesen, N.: Evaluating the influence of African dust in West African rainfall through Earth observation, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13118, https://doi.org/10.5194/egusphere-egu23-13118, 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 Apr 2023, EGU23-3152, https://doi.org/10.5194/egusphere-egu23-3152, 2023.
Evidence from model simulations has suggested that anthropogenic aerosols may have forced multidecadal variability in a range of North Atlantic variables including sea surface temperatures, ocean circulation, and sea ice. However, many questions remain concerning the importance of anthropogenic aerosols in driving past changes in the North Atlantic climate system. The pathways via which changes in aerosol and aerosol precursor emissions, and oxidant levels, influence climate are complex. They involve both chemical and physical processes, and likely include changes in clouds, radiation, surface temperatures, atmospheric and oceanic circulation, and Arctic sea ice. This complexity is an important factor in the large uncertainty surrounding the role of anthropogenic aerosol in North Atlantic climate change, and was one of the major motivations for the UK’s North Atlantic Climate System Integrated Study (ACSIS). ACSIS was a multidisciplinary research programme conducted over the period 2016-2022, delivered by a consortium of seven UK institutions. This presentation draws together findings from the programme to provide an overall synthesis of what was learned in ACSIS about the role of anthropogenic aerosol in North Atlantic climate change. Remaining uncertainties, the potential for observational constraints, and opportunities for future work will also be discussed.
ACSIS made extensive use of simulations conducted for CMIP6, particularly historical simulations, and attribution experiments included in AerChemMIP and DAMIP. Additional sensitivity experiments with HadGEM3-GC3.1 and UKESM1 were used to quantify the effects of uncertainty in aerosol forcing in the absence of the additional uncertainty associated with model differences, to decompose the aerosol forcing, and to better illustrate the role of aerosol in recent changes.
As aerosol emissions increased (1850-1985), North Atlantic CDNC increased. Emissions of ozone precursors, and resulting changes in OH, contributed to this trend. This led to downwelling surface shortwave decreases across the North Atlantic, which drove colder surface temperatures, increased sea ice extent, and increased mean sea level pressure. In contrast, the eastern subpolar gyre warmed, likely due to increased ocean heat convergence due to the increase in the AMOC.
As local aerosol emissions fell (1986-2014) much of the reverse occurred. Downwelling surface shortwave increased across the North Atlantic, predominantly over land, driving warmer surface temperatures and reduced sea ice extent. The eastern subpolar gyre cooled. However, the role of aerosol in this later period is less clear due to a dominance of temperature-mediated cloud feedbacks over aerosol forcing, AMOC related feedbacks, and a changing aerosol forcing pattern.
How to cite: Wilcox, L., Sutton, R., Robson, J., Dong, B., Griffiths, P., Grosvenor, D., Hodson, D., Keeble, J., Rumbold, S., Archibald, A., Carslaw, K., Dittus, A., Harvey, B., and Sinha, B.: The Role of Anthropogenic Aerosols in Recent North Atlantic Climate Change: A Synthesis of Findings from the UK ACSIS Programme, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15360, https://doi.org/10.5194/egusphere-egu23-15360, 2023.
Orals: Wed, 26 Apr | Room F2
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, 24–28 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, 24–28 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, 24–28 Apr 2023, EGU23-6535, https://doi.org/10.5194/egusphere-egu23-6535, 2023.
With global storm-resolving models (SRMs) a new type of global high-resolution models is now becoming available that explicitly resolves the main drivers of the atmospheric flow of matter and energy on the kilometer scale. In these models, arguably two poorly constrained physical processes remain unresolved - microphysics and turbulence - but are at least fundamentally linked to their controlling factors, i.e., the circulation. In this study, we use a global SRM with two different microphysical schemes and do several sensitivity runs, where we vary one parameter of the applied microphysics scheme in its range of uncertainty. We find that the two microphysics schemes have distinct signatures (e.g., in how condensate is partitioned in ice and snow) but their mean cloud cover and total condensate is rather robust. Perturbing single parameters of each scheme also affects the condensate distributions and causes several 10s W/m2 variations in radiative fluxes. Changes in radiative properties of cloudy points dominate changes in the radiative balance at the top of the atmosphere. Overall, microphysical sensitivities in global SRMs are substantial and resemble inter-model differences of a multi-model ensemble.
How to cite: Naumann, A. K.: Microphysical controls on condensate distributions and the tropical energy budget in global storm-resolving models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6739, https://doi.org/10.5194/egusphere-egu23-6739, 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 Apr 2023, EGU23-7634, https://doi.org/10.5194/egusphere-egu23-7634, 2023.
With the changing climate, the study of fog formation is essential and needs of the hour, as the nature of fog has changed due to impact of complexity of natural and anthropogenic aerosols. Chemical and physical properties of condensation nuclei (CN) influence the formation of fog and thus visibility over India. The presences of ample water vapor in the air, microphysical and thermodynamic property of CN are crucial for the occurrence and sustenance of fog. The visibility parameterization is depending on the number of cloud droplets. The aerosol particle and conversion of aerosol to fog droplet, which requires external nuclei for water vapor to condensation, is controlled by the processes of condensation or diffusional growth. The condensation process is controlled by solute effect (Raoult's effect) and the curvature effect (Kelvin effect) and may happen over a pre-existing Aitken aerosol particle. The growth of droplets is determined by the size of CN and a droplet will always try to maintain an equilibrium state if the equilibrium supersaturation is less than the amount of water vapor available in the atmosphere. The Köhler curve portrays the evaporation of droplets under the “curvature effect” and the “solute effect”. Droplets with higher solute concentration have lower critical supersaturation values. Thus, hygroscopicity (κ), which is highly related to the activation of aerosols to CN, takes into account the contribution of aerosol particles to fog droplet formation. The κ-Köhler theory combining the Kelvin's equation and Raoult's law are used for the activation of a deliquesced aerosol particle, which is forming an aqueous solution droplet into a smaller cloud droplet. Hygroscopicity is linked with the water activity and thus the thermodynamics of solution governs the aerosols liquid water and hence, better understanding of hygroscopicity is essential in numerical model for the fog and visibility prediction. The microphysical properties of fog are also regulated by aerosol, which is more strongly reliant on concentration aerosols and its chemistry (hygroscopicity and water activity). The saturation value needed for fog formation can be brought down by aerosol number concentration. It is concluded that the complexity in fog and visibility forecasting is found to be high due to multiple factors having a role at multiple levels. We may propose a revised visibility parameterization over Indian subcontinent.
How to cite: Bhowmik, Dr. M., Hazra, Dr. A., and Ghude, Dr. S. D.: Is a more physical representation of aerosol activation needed for fog forecasting in perspective of climate change? , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10939, https://doi.org/10.5194/egusphere-egu23-10939, 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.
[1] https://cloudlab.ethz.ch/
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, 24–28 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, 24–28 Apr 2023, EGU23-5377, https://doi.org/10.5194/egusphere-egu23-5377, 2023.
Maritime shipping remains a large source of anthropogenic airborne pollutants, including exhaust particles that can act as cloud condensation nuclei (CCN). The International Maritime Organization (IMO) imposed global fuel sulfur content (FSC) limits on marine fuels in order to target ship exhaust sulfur oxides and particulate matter emissions, but has allowed competing pathways to regulatory compliance; i.e., low FSC fuels versus exhaust after-treatment. Laboratory experiments revealed that these compliance measures have secondary effects on physicochemical properties of exhaust particles, affecting their CCN activity (Santos et al., 2022a; 2022b). We observe that combustion of low FSC fuels results in emissions of highly hydrophobic particles, causing significant reductions in CCN emissions, whereas wet scrubbing leads to an increase in CCN activity.
One area of focus is the Arctic region, which has been shown to be particularly susceptible to the effects of climate warming. A steady decrease in observed sea ice cover amplifies the regional warming (Screen and Simmonds, 2010), but also opens the region to increased ship traffic which may result in further climate feedbacks (Stephenson et al., 2018). It is of particular interest to identify how increased ship exhaust particle emissions may affect cloud processes; for example, by facilitating liquid droplet formation and thus, potentially changing the radiative properties of the aerosol and clouds.
Here, we investigate how increased shipping activity potentially influences the properties of Arctic mixed-phase clouds. In our study the experimentally observed characteristics of marine particle emissions and their liquid droplet forming potential have been implemented in large eddy simulations. We use the MIMICA model (MISU/MIT Cloud-Aerosol model) (Savre et al., 2014) to simulate a stable stratiform mixed-phase cloud based on the Arctic Summer Cloud Ocean Study (ASCOS) (Tjernström et al., 2014). A range of input parameters for ship aerosol, including size distributions, number concentrations, vertical distributions and hygroscopicities, has been studied to assess the potential impact on cloud properties and regional climate.
Santos et al. (2022a). Environ. Sci.: Processes Impacts, 24:1769-1781
Santos et al. (2022b). Environ. Sci.: Atmos., Advance Article
Savre et al. (2014). J. Adv. Model. Earth Syst., 6:630-649
Screen and Simmonds (2010). Nature, 464(7293):1334–1337
Stephenson et al. (2018). Geophys. Res. Lett., 45:9898–9908
Tjernström et al. (2014). Atmos. Chem. Phys., 14:2823-2869
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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 Apr 2023, EGU23-1907, https://doi.org/10.5194/egusphere-egu23-1907, 2023.
How clouds respond to anthropogenic sulfate aerosols is one of the largest sources of uncertainty in the radiative forcing of climate over the industrial era. This uncertainty limits our ability to predict equilibrium climate sensitivity (ECS) – the equilibrium global warming following a doubling of atmospheric CO2. Here we use satellite observations to quantify relationships between sulfate aerosols and low-level clouds while carefully controlling for meteorology. We then combine the relationships with estimates of the change in sulfate concentration since about 1850 to constrain the associated radiative forcing. We estimate that the cloud-mediated radiative forcing from anthropogenic sulfate aerosols is −1.11 ± 0.43 W m-2 over the global ocean (95% confidence). This constraint implies that ECS is likely between 2.9 and 4.5 K (66% confidence). Our results indicate that aerosol forcing is less uncertain and ECS is probably larger than the ranges proposed by recent climate assessments.
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, 24–28 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, PM2.5 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 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, 24–28 Apr 2023, EGU23-5203, https://doi.org/10.5194/egusphere-egu23-5203, 2023.
Posters on site: Wed, 26 Apr, 16:15–18:00 | Hall X5
Southern Africa, and in particular its western part, Namibia, is considered a climate change hotspot by the IPCC and is at risk of severe temperature-related changes. As examples, models projections suggest by the end of the century: 1) Increase of surface temperature of +4 to +7°C; 2) destruction of the stratocumulus cloud deck along the western coast; and 3) decrease of the fog inland. The role of aerosols in this context is still not completely quantified, due to their high spatial and temporal variability, the many sources responsible for the complex mixture and the lack of continuous observations. Most of the past regional climate modelling (RCM) and intensive field campaigns focussed primarily on constraining the radiative effects of the seasonal biomass burning aerosols generally occurring in the end of the austral winter (August to October). However, the aerosol spectral optical properties, aerosol optical depth and the organic fractions are not studied enough to provide a firm understanding of regional aerosol load, interaction with radiation and interplays in relation to particle chemistry.
In this work, we present the first analysis of new long-term ground-based aerosol observations conducted since april 2022 at Gobabeb Namib Research Institue (23°33’40‘’S, 15°02’24’’E) in Namibia. Gobabeb is located in the hyperarid Namib desert and it is under the influence of different air masses, transporting maritime and biomass burning aerosols, amongst others. The measurements of optical and physical properties of the aerosol mixtures are analysed to provide with the aerosol single scattering albedo and mass absorption, scattering and extinction efficiencies which are needed to evaluate the first Africa-based Earth system model by the Global Change Institute at the University of Witwatersrand in South Africa. The in situ surface data are complemented by the analysis of pre-existing observations such as those from the AERONET sunphotometers.
How to cite: Hemeret, F., Formenti, P., Di-Biagio, C., Language, B., Chevaillier, S., Féron, A., Cazaunau, M., Torres-Sánchez, R., Piketh, S., Engelbrecht, F., Moolla, R., Bezuidenhoudt, U., Luyanda, B., Marais, E., and Maggs-Kölling, G.: New observations of climate-relevant properties of atmospheric aerosols in Namibia, southern Africa., EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-465, https://doi.org/10.5194/egusphere-egu23-465, 2023.
Condensation trails (contrails) are aircraft-induced line-shaped high clouds, which may persist and grow to form contrail cirrus in ice supersaturated regions. Contrail cirrus is the largest known component of aviation radiative forcing, with a large uncertainty associated with troposphere water budgets and contrail radiative properties. In addition, due to the limited number of climate models able to simulate contrail cirrus, the uncertainty in the global contrail cirrus radiative forcing cannot be estimated statistically.
The aim of this work is to implement a contrail cirrus parameterisation in the UK Earth System Model, therefore providing a new independent estimate of the contrail cirrus radiative forcing to be used in future assessments of aviation climate impacts. The new diagnostic scheme is based on the processes governing contrail formation (Schmidt-Appleman Criteria) and persistence (ice supersaturation). Persistent contrails are then added to the model cloud fields, where they interact with and evolve alongside natural clouds.
We use ensemble runs of both nudged and free running model experiments to estimate the contrail cirrus cover and effective radiative forcing. Comparisons with a similar contrail scheme implemented in the NCAR Community Atmospheric Model (CAM) indicate the importance of the host climate model via (i) the host’s cloud microphysics scheme (e.g. single vs. double moment) and (ii) its ability to simulate realistic ice supersaturated regions. By providing a new independent assessment of the contrail cirrus radiative forcing, our work contributes to improving our understanding of aviation climate impacts and therefore potential mitigation strategies for current and future generation aircraft.
How to cite: Zhang, W., Rap, A., Van Weverberg, K., Furtado, K., Feng, W., Morcrette, C., Forster, P., and Francis, T.: Understanding sources of contrail cirrus radiative forcing uncertainty using a new diagnostic contrail scheme for the UK Earth System Model, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1413, https://doi.org/10.5194/egusphere-egu23-1413, 2023.
Despite their small size, aerosols strongly influence Earth's climate. Aerosols scatter and absorb radiation referred to as aerosol-radiation interactions but also modify the properties of clouds, as cloud droplets form on aerosol particles, referred to as aerosol-cloud interactions. Kilometer-scale simulations allow us to examine long-standing questions related to these interactions. Such simulations resolve atmospheric motions on scales of a few kilometers and represent important atmospheric processes like convective updrafts that were parameterized previously. Regional simulations revealed significant effects of aerosols on convective clouds and provided insights into the underlying processes and drivers.
To examine these interactions with the climate model ICON, we developed the simple aerosol model HAMlite based on and fully traceable to the complex aerosol model HAM. HAMlite represents aerosols as an ensemble of log-normal modes. To reduce the computational and physical complexity, aerosol microphysics are discarded and aerosol sizes and compositions are prescribed. The selection of modes is flexible and can include the Aitken, accumulation, and coarse modes. The calculation of aerosol properties and thermodynamics remains fully consistent with HAM. HAMlite is linked to the atmospheric processes of ICON. Aerosols are transported as tracers in the dynamical core and coupled to the radiation, turbulence, and cloud microphysics schemes.
We present first results from global simulations with ICON-HAMlite. The atmosphere is governed by non-hydrostatic conservation equations, the land is represented with the dynamic vegetation model JSBACH, and the sea surface temperature and sea ice are prescribed with the AMIP database. The horizontal resolution is about 5 km and time period is about 40 days. First, we evaluate the global distributions of the different aerosol modes. And second, we investigate how aerosols influence the diurnal cycle and deep convection in the tropics. In contrast to regional simulations, global simulations include the large-scale circulation and in particular the budgetary constraints on precipitation due to the conservation of water and energy.
How to cite: Weiss, P., Herbert, R., and Stier, P.: A reduced complexity aerosol model for km-scale climate models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2082, https://doi.org/10.5194/egusphere-egu23-2082, 2023.
Global warming potential (GWP) has been used as an indicator to compare with the greenhouse effect of different gases. Utilized gases, especially, in semiconductor and display manufacturing processes are greenhouse gas with high GWP values. Accordingly, countries and relevant companies are trying to synthesize the alternative gases expressed with low GWP values along with a lot of interest. But GWP values of these hasn’t been presented at any other thesis. Hence it is inevitable to measure GWP of newly gases to compare with climate effect between conventionally used gases and newly gases.
Therefore, this study proposes a measurement method of GWP based on various papers using instrument such as fourier-transform infrared spectroscopy (FT-IR), time of flight- mass spectroscopy (TOF-MS) equipped with the proton transfer reaction (PTR) as a detector and so on. Equation is used in IPCC fifth assessment report to calculate the GWP.
- Calculating absorbed cross-sectional area by measuring infrared absorption spectra using FT-IR and by applying to lambert-beer’s law
- Applying original pinnock curve (Pinnock et al., 1995) and final pinnock curve using the line-by-line model (Myhre et al., 2006) to calculate the radiative forcing by integrating the calculated absorbed cross-sectional area from first step
- Measuring the rate constant when they react with the hydroxyl radical using PTR-MS equipped with the PTR and calculating the atmospheric lifetime based on the constant and tropospheric lifetime of CH3CCl3 as a reference material proposed by WMO (2014)
- In accordance with the IPCC fifth assessment report (2013), calculating GWP using the radiative forcing and atmospheric lifetime induced by second and third step, respectively
Acknowledgment:
This work was supported by Korea Environment Industry & Technology Institute (KEITI) through Climate Change R&D Project for New Climate Regime Program, funded by Korea Ministry of Environment (MOE) ( 2022003560008 ).
How to cite: Lee, B. J. and Park, S. H.: The measurement method of global warming potential based on the infrared absorption spectra and rate constant with the hydroxyl radical, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2489, https://doi.org/10.5194/egusphere-egu23-2489, 2023.
Atmospheric aerosols and their interaction with clouds are the largest uncertainty in the human forcing of the climate system. Anthropogenic emissions have increased aerosol concentrations, increasing the concentration of cloud droplets and leading to reductions in droplet size and increases in cloud reflectivity (a negative radiative forcing). Central to this climate impact is the susceptibility of cloud droplet number to aerosol. This susceptibility varies widely with the method and data used to estimate it and within global climate models, explaining much of the variation in estimates of the radiative forcing from aerosol-cloud interactions (RFaci). Better constraints on the susceptibility have been a key target for recent observation-based constraints on the aerosol forcing.
Previous work has shown that the aerosol burden of the clean, pre-industrial atmosphere has been demonstrated as a key uncertainty for the aerosol forcing. Here we show that the behaviour of clouds under these clean conditions is of equal importance for understanding the spread in radiative forcing estimates between models and observations. This means that the uncertainty in the aerosol impact on clouds is, counterintuitively, driven by situations with little aerosol. Removing these clean conditions from observational estimates of the susceptibility produces a close agreement between different model and observational estimates of the cloud response to aerosol, but does not provide a strong constraint on the RFaci. If we are to produce tighter constraints on the radiative forcing from aerosol-cloud interactions, better constraints on the behaviour of cloud in keen conditions are vital.
How to cite: Gryspeerdt, E., Povey, A. C., Grainger, R. G., Hasekamp, O., Hsu, N. C., Mulcahy, J. P., Sayer, A. M., and Sorooshian, A.: Uncertainty in aerosol-cloud radiative forcing is driven by clean conditions, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-16589, https://doi.org/10.5194/egusphere-egu23-16589, 2023.
India as a hotspot for air pollution has heavy black carbon (BC) and dust (DU) loadings. BC has been identified to significantly impact the Indian climate. However, whether BC-climate interactions regulate Indian DU during the premonsoon season is unclear. Here, using long-term Reanalysis data, we show that Indian DU is positively correlated to northern Indian BC while negatively correlated to southern Indian BC. We further identify the mechanism of BC-dust-climate interactions revealed during COVID-19. BC reduction in northern India due to lockdown decreases solar heating in the atmosphere and increases surface albedo of the Tibetan Plateau (TP), inducing a descending atmospheric motion. Colder air from the TP together with warmer southern Indian air heated by biomass burning BC results in easterly wind anomalies, which reduces dust transport from the Middle East and Sahara and local dust emissions. The premonsoon aerosol-climate interactions delay the outbreak of the subsequent Indian summer monsoon.
How to cite: Wei, L., Wang, Y., Lu, Z., and Liu, X.: Black carbon-climate interactions regulate dust burdens over India revealed during COVID-19, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2490, https://doi.org/10.5194/egusphere-egu23-2490, 2023.
Black carbon (BC) aerosols in the atmosphere play a significant role in climate systems due to their strong ability to absorb solar radiation. The lifetime of BC depends on atmospheric transport, aging and consequently on wet scavenging processes (in-cloud and below-cloud scavenging). In this study, sequential rainwater samples in eight rainfall events collected in 2 mm interval were measured by a tandem system including a single particle soot photometer (SP2) and a nebulizer. The results showed that the volume-weighted average (VWA) mass concentrations of refractory black carbon (rBC) in each rainfall event varied, ranging from 10.8 to 78.9 μg/L. The highest rBC concentrations in the rainwater samples typically occurred in the first fraction from individual rainfall events. The geometric mean median mass-equivalent diameter (MMD) decreased under precipitation, indicating that r BC with larger sizes was relatively aged and preferentially removed by wet scavenging. A positive correlation ( R2 = 0.73) between the VWA mass concentrations of rBC in rainwater and that in ambient air suggested the important contribution of scavenging process. Additionally, the contributions of in-cloud and below-cloud scavenging were distinguished and accounted for 74% and 26% to wet scavenging, respectively. The scavenging ratio of rBC particles was estimated to be 0.06 on average. This study provides helpful information for better under-standing the mechanism of rBC wet scavenging and reducing the uncertainty of numerical simulations of the climate effects of rBC.
How to cite: Lei, S. and Pan, X.: Refractory black carbon aerosols in rainwater in the summer of 2019 in Beijing: Mass concentration, size distribution and wet scavenging ratio, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4962, https://doi.org/10.5194/egusphere-egu23-4962, 2023.
Charge accumulation on aerosol particles (including water droplets) plays a critical role in a variety of natural and industrial processes. It gives rise to lightning in thunder- and sandstorms, influences particle transport and interactions in the atmosphere and can lead to dangerous dust explosions during industrial processing [1]. Shavlov et al. [2] suggest that the hydroxide ions and protons formed by the dissociation of water molecules are sufficient to cause charging during evaporation and condensation of droplets or surface-adsorbed water on solid particles. This hypothesis is backed up by Moreira et al. [3] who find that liquid evaporation leads to charge buildup on dielectric surfaces.
By levitating individual aerosol particles in an optical trap we can characterize and manipulate the particle without losing information to ensemble averages or external interference from other particles or substrates [4, 5]. Our setup allows for trapping of various types of solid and liquid particles in the micrometer size range, like silica spheres, water droplets or droplets with solid nuclei inside. Figure 1 shows an illustration of the measurement principle. The particle’s charge is measured by applying a sinusoidal electric field and observing the resulting particle motion. The Mie scattering pattern of the particle furthermore gives information about the particle’s size and refractive index, both at equilibrium and during evaporation and condensation. The experiment allows us to control the relative humidity and air ion concentration around as well as air flow across the particle.
Ultimately we hope to contribute to a better understanding of the microphysical processes involved in thundercloud electrification and adjacent electrical phenomena in the atmosphere.
FIGURE 1. Optical tweezers (λ = 532 nm) holding a solid or liquid aerosol particle. A sinusoidal electric field is applied between the two electrodes and the resulting particle motion as well as the particle’s Mie scattering pattern are recorded.
Acknowledgments
This project has received funding from the European Research Council (ERC) under the European Union’s Starting Grant (No. 949120).
References
- Zhang L., et al. (2016) Indoor Built Environ 25 (3) 437-440.
- Shavlov A. et al. (2018) J Aerosol Sci. 123 17-26.
- Moreira K. S., et al. (2020) Mater. Interfaces 7(18) 202000884.
- Reich O., et al. (2020) Phys. 3(1).
- Ricci F., et al. (2022) ACS Nano 6 (16) 8677–8683.
How to cite: Stoellner, A., Lenton, I., Muller, C., and Waitukaitis, S.: Measuring spontaneous charging of single aerosol particles , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6166, https://doi.org/10.5194/egusphere-egu23-6166, 2023.
One of the largest uncertainties in estimating the anthropogenic radiative forcing is related to the impact of atmospheric aerosols on cloud properties. This uncertainty originates mainly from the complicated nature of aerosol-cloud interaction as it is much stronger and more difficult to observe than the aerosol-radiation interaction. The estimates of radiative forcing due to changes in cloud properties vary significantly between different global climate models, highlighting the need for constraining this forcing by using observations. Moreover, it is challenging to determine the impact of aerosols on clouds from satellite observations only. In this study, we aim to improve that by combining the in-situ observations with satellite retrievals, in order to reduce uncertainties in the anthropogenic impact on clouds and the climate. The study is performed for the low-level liquid clouds over the Southern Great Plains (SGP), Oklahoma. The in-situ data on particle number concentration, large enough to act as cloud condensation nuclei (CCN), with diameter larger than 100 nm (N100) were collected for a 5-year period from the Atmospheric Radiation Measurement (ARM) observatory at SGP site. In this analysis, the level-2 collection-6 MODIS cloud property dataset (MYD06_L2) with a 1x1 km resolution was used, where only liquid, single-layer clouds with a cloud top warmer than 268 K were included. It was observed that both CER and COT increased with increasing CWP. However, at a same level of CWP, the CER was smaller, and COT was larger at high N100 concentrations, as compared to the lower N100 concentrations. This result is consistent with the hypothesis of enhanced aerosol load increasing the number concentration of CCN, which in turn leads to smaller cloud droplets.
How to cite: Taneja, K., Kokkola, H., Romakkaniemi, S., Arola, A., Chellappan, S., and Mielonen, T.: Effect of aerosols on the properties of low-level liquid clouds over the Southern Great Plains, USA, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7104, https://doi.org/10.5194/egusphere-egu23-7104, 2023.
Cirrus clouds have a net positive radiative forcing effect on the climate, leading to the suggestion of cirrus cloud thinning (CCT) as a means to ameliorate global warming. By deliberately thinning cirrus clouds, more longwave radiation is able to escape the Earth system into space, cooling the planet. CCT has been modelled as part of the Geoengineering Model Intercomparison project in the G7cirrus experiment. Given the complexities of cirrus cloud modeling, to obtain similar results across different models this experiment simulates CCT by increasing the fall seed of ice crystals in cirrus clouds. This is carried out against a SSP5-8.5 scenario background, beginning in 2020 and ending in 2100. So far, G7cirrus has been run in two Earth System Models: UKESM1 and IPSL. Here, we look at some preliminary results from this experiment, such as analysing the intervention’s effective radiative forcing and its impact on different climate variables such as air temperature and precipitation.
How to cite: Smith, W., Visioni, D., and Hunt, H.: Preliminary results from global modelling of Cirrus Cloud Thinning in the Geoengineering Model Intercomparison Project, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7402, https://doi.org/10.5194/egusphere-egu23-7402, 2023.
Aerosol particles play a key role on Earth’s radiation budget and indirectly affect climate due to aerosol-cloud interactions (ACI), by acting as ice nucleating particles (INP) during the phase change in mixed-phased clouds. The forcing associated with the modification of cloud optical properties due to aerosol is yet insufficiently understood and represents a large uncertainty in future climate projections. Spaceborne remote sensing is a promising technique for quantifying ACI at a global scale and improving the performance of climate models.
Height-resolved measurements of aerosol optical properties from the Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite are used to estimate the vertical distributions of INP concentrations. Individually tracked clouds from geostationary observations are then matched with the aforementioned concentrations in the vicinity of those clouds. Hence, a bottom-up data set of cold clouds is formed that can be stratified according to different aerosol and cloud properties to investigate the INP effects on ice-containing clouds.
How to cite: Alexandri, F., Mueller, F., Seelig, T., and Tesche, M.: Combining geostationary and polar-orbiting satellite observations for studying the effect of INP on cold clouds, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7846, https://doi.org/10.5194/egusphere-egu23-7846, 2023.
This study applies explainable machine learning to near-global daily satellite and reanalysis data. We quantify and analyse the sensitivities of cloud fraction (CLF) to aerosol changes and their dependence on meteorological parameters.
Aerosol-cloud interactions have prolonged influences on the Earth’s radiation budget but remain one of the most substantial uncertainties in the climate system. Marine boundary layer clouds (MBLCs) are particularly important since they cover a large portion of the Earth’s surface. One of the biggest challenges in quantifying aerosol-cloud interactions from observations lies in isolating the CLF adjustments due to aerosol perturbations from the covariability of local meteorology and quantifying the influences of meteorology on the aerosol-CLF relationship. In this study, 10 years (2011-2020) of near-global daily satellite cloud products are used in combination with reanalysis data of meteorological confounders. Using cloud droplet number concentration (CDNC) as a proxy for aerosol, MBLC CLF is predicted by region-specific gradient boosting machine learning models. By means of SHapley Additive exPlanation (SHAP) regression values, the predictions are explained by quantifying the sensitivities of CLF to the predictors. Furthermore, the meteorological influences on the CLF adjustments are analysed with SHAP interaction values to define an interaction index (IAI). Globally, the regional ML models are able to capture on average 32% and up to around 71% of the variability of CLF. Global patterns of CLF sensitivities show that CLF is positively associated with CDNC and lower tropospheric stability (LTS), strongest in low-cloud regions. Increased sea surface temperature (SST) on the other hand will lead to reduced CLF, probably by increasing the vertical moisture gradient. The CDNC-CLF sensitivities are especially strong in stratocumulus-to-cumulus transition regions. Negative CLF sensitivities to the u wind component at 700 hPa are found for most regions which may indicate an influence of facilitated turbulence at the cloud top. In terms of the interactive effects of meteorological parameters, a significant dependence of the CDNC-CLF relationship on LTS and SST is found in low-cloud regions, and the patterns coincide with sensitivities. Positive IAIs are shown globally for SST and LTS, indicating that the CDCN-CLF sensitivity is stronger with high SST/LTS values.
The ongoing work shows that CDNC-CLF sensitivity is positive globally after accounting for meteorological covariations. Globally, SST and LTS can influence the positive CDNC-CLF relationship significantly, which is especially the case in stratocumulus regions. Detailed investigations will be carried out for not only SST/LTS but also other predictors to dig out the physics and causality behind the statistics.
How to cite: Jia, Y., Andersen, H., and Cermak, J.: Constraints on cloud fraction adjustment to aerosols using explainable machine learning, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9516, https://doi.org/10.5194/egusphere-egu23-9516, 2023.
Suspended particles of mineral dust are known to have a strong impact on the evolution of clouds and precipitation from meteorological to climate timescales. The ability to understand and predict the impacts of dust outbreaks on storm development and evolution would strongly benefit water management, food security, agriculture, and flood early warning systems. This is especially true for the Eastern Mediterranean, being a region heavily impacted by climate extremes and events (drought, floods) and frequent dust transportation from the Saharan desert throughout the year. To investigate the impact of mineral dust on the characteristics of storm development in the E. Mediterranean, several cases studies were examined with the aid of the Integrated Community Limited Area Modeling System (ICLAMS), a version of the Regional Atmospheric Modeling System (RAMS) augmented to include various parameterizations and numerical schemes of the complex microphysical processes of the forementioned aerosol particles. All cases involved storms developed in frontal systems with considerable vertical development and potential for deep convective clouds characterized by strong wind gusts, high rainfall and hailfall rates. In the simulations, dust emissions were allowed to provide particles that act as cloud condensation nuclei (CCN) and ice nuclei (IN). From the simulations we investigate how different descriptions of primary ice formation may affect results regarding cloud and precipitation characteristics, as well as the potential role of ice multiplication processes and the impact of enhanced cloud glaciation on convective invigoration of the storm clouds. In all cases considered (without any effects of ice multiplication and enhanced glaciation from it), precipitation patterns were spatially shifted under the influence of dust, maximum cloud updrafts were significantly increased, and the extreme conditions of rain and hail rates were enhanced considerably (up to 45% and 100% respectively).
How to cite: Chaniotis, I., Nenes, A., and Flocas, H.: Dust impacts on storm development in the Eastern Mediterranean, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10174, https://doi.org/10.5194/egusphere-egu23-10174, 2023.
Understanding co-variability between particulate matter (PM) concentration and meteorological conditions could provide insight into how the former varies under given weather conditions and eventually improve its prediction skill. However, relatively short data length of observed PM2.5 is a challenging issue not limited to Korea. Therefore, in such an analysis PM10, which has reliable observation for more than 30 years, has been widely used as a proxy of fine particles. Also, there are two stations in Seoul, Korea have relatively long-term observed PM2.5 in the period of 2000-current. As a result, more reliable analysis on the daily variation of PM2.5 in comparison with PM10 and meteorological conditions is feasible. First, the winter-mean of both PM10 and PM2.5 showed significant decreasing trends in the period of 2000-2020. Interestingly, decreasing trends of these weakened in the last 10 years with a different rate, resulting in a nearly flat trend of PM2.5 yet a relatively consistent decreasing trend of PM10 in the period of 2010-2020, suggesting a potential discrepancy in the variability of PM2.5 and that of PM10. Second, unlike the previously noted difference in long-term trends of seasonal mean values, PM2.5 and PM10 shared significantly similar daily variabilities if Asian dust cases were removed. In other words, the aforementioned discrepancy in the long-term trend of seasonal mean values of PM2.5 and PM10 does not affect their daily variation. The covarying patterns of PM2.5 and meteorological conditions were denoted as a migratory synoptic system. In particular, a migratory anticyclone from northwest China had significant positive correlation patterns with PM2.5 from two days before and remained stagnant over Korea after two days due to blocking by low pressure over the Northern Pacific. Along with this system, warm temperature anomalies and weak northerlies in the low troposphere were present over Korea, which is a conducive condition for high PM2.5. On the contrary, Asian dust cases were accompanied by cyclone that extended from arid regions of northern China with corresponding negative temperature anomalies and strengthened northerlies. In short, a migratory synoptic system over Korea is tightly correlated with PM2.5 daily variations as well as PM10. But once again, Asian dust events could be an important mechanism to differentiate daily variations of PM2.5 and PM10.
How to cite: Jang, W. and Yoon, J.-H.: Daily variation of PM2.5 and covarying meteorological conditions during wintertime using long-term observation in Seoul, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10407, https://doi.org/10.5194/egusphere-egu23-10407, 2023.
Cirrus clouds provide a substantial amount of coverage in the earth’s atmosphere, resulting in a major impact on the global radiative budget. The extent of the radiative impact is determined by the aspherical ice crystal composition within the cirrus. Thus, a proper understanding of ice crystal single scattering properties is necessary for accurate climatological modeling and forecasting. One of the most relevant cirrus ice crystal habits is a polycrystalline bullet rosette, where individual bullets are radiating from the same nucleation point. Comprehensive studies on the dependencies of ice crystal habit formation have shown that bullet rosettes grow at a range of ice supersaturations with temperatures below -40 °C; environmental conditions frequently found within high altitude cirrus clouds. The Particle Habit Imaging Polar Scattering (PHIPS-HALO) probe is a unique aircraft mounted instrument which simultaneously acquires high-resolution stereo images and single scattering properties of individual cloud ice crystals. The ability to combine observed angular scattering functions with detailed images of their related crystals allows for in-depth analysis of the radiative effects of specific habits in critical atmospheric systems such as cirrus clouds. Here, a detailed explanation of the PHIPS-HALO performance and capabilities is provided with an investigation of single scattering properties of atmospheric bullet rosettes. Bullet rosette stereo-images were taken during a range of flights from the CIRRUS-HL campaign and were analyzed for their maximum dimensions as well as for crystal complexity and visually inspected for number of bullets per rosette, individual bullet aspect ratios and bullet hollowness. These bullet rosette microphysical properties were then associated with environmental conditions and with the simultaneously measured angular light scattering function and resulting asymmetry parameter. Angular scattering functions and asymmetry parameters are discussed for bullet rosettes grouped into subsets by complexity parameter. Results indicate that much lower asymmetry parameters represent real atmospheric bullet rosette crystals than what is expected by theoretical studies assuming smooth surfaces.
How to cite: Wagner, S., Schnaiter, M., Xu, G., Nehlert, F., and Järvinen, E.: PHIPS-HALO Radiative Measurement Applications to Atmospheric Bullet Rosette Ice Crystals , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10469, https://doi.org/10.5194/egusphere-egu23-10469, 2023.
Cloud-aerosol interactions constitute the largest source of uncertainty in predictions of the global climate. In this study we present WRF-PMCAMx, a powerful tool for detailed cloud-aerosol investigations. This consists of the Weather Research and Forecasting model (WRF; Skamarock et al., 2008) coupled with PMCAMx-UF (Patoulias et al. 2022). PMCAMx-UF is a three-dimensional chemical transport model with a high-resolution sectional bin aerosol approach. The aerosol fields predicted by PMCAMx-UF are used to update the cloud droplet and ice number predictions in the Morrison et al. (2005) microphysics scheme in the WRF atmospheric component. To evaluate the impact of this coupling, we compare the cloud, precipitation and radiation patterns predicted by WRF-PMCAMx over Europe to the diagnostic fields produced by the standard Morrison scheme in the open-source WRF code.
REFERENCES:
Morrison, H., Curry, J.A., and Khvorostyanov, V.I.: A New Double-Moment Microphysics Parameterization for Application in Cloud and Climate Models. Part I: Description, Atmos. Sci., 62, 3683-3704 62, 2005
Patoulias, D. and Pandis, S. N.: Simulation of the effects of low-volatility organic compounds on aerosol number concentrations in Europe. Atmos, Chem Phys., 22, 1689-1706, 2022.
Skamarock, W. C., Klemp, J. B., Dudhia, J., Gill, D. O., Barker, D., Duda, M. G., … Powers, J. G.: A Description of the Advanced Research WRF Version 3 (No. NCAR/TN-475+STR). University Corporation for Atmospheric Research. doi:10.5065/D68S4MVH, 2008
* This study is supported by the H2020-EU.1.3.- EXCELLENT SCIENCE - Marie-Skłodowska-Curie Actions project SIMPHAC (ID 8985685)
How to cite: Sotiropoulou, G., Patoulias, D., Pandis, S., and Nenes, A.: WRF-PMCAMx: a mesoscale model for cloud-aerosol interaction studies, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11682, https://doi.org/10.5194/egusphere-egu23-11682, 2023.
Observations and model results show an increase in extreme precipitation with global warming since the 1950s. During the last decades there have also been strong trends in anthropogenic aerosol concentration, aerosols that may affect cloud and precipitation processes that develop these extreme events. As human activities are the source of anthropogenic aerosols, they tend to be concentrated over highly populated regions where the potential cost and impact of extreme precipitation is high. In this study we investigate the link between extreme precipitation and aerosol particles in the atmosphere by using the cloud resolving WRF model. The model is set up with an aerosol-dependent cloud microphysics scheme that include processes such as; the increase in smaller droplets in aerosol rich clouds, the change in cloud reflective properties that can reduce surface evapotranspiration as well as a deepening of convective clouds and possible an increase in precipitation intensity. The model is run over several years in a stable climate to distinguish how these processes influence extreme precipitation separately from the extreme precipitation increase due to global warming.
How to cite: Steensen, B. and Alterskjær, K.: A model study on aerosol impact on extreme precipitation , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11727, https://doi.org/10.5194/egusphere-egu23-11727, 2023.
This contribution presents spatially distinct fog and low stratus (FLS) formation and dissipation regimes derived from satellite and reanalysis data and their sensitivities to meteorological and land surface conditions over central Europe.
FLS formation and dissipation processes are strongly governed by meteorological and land-surface conditions and vary geographically and across seasons. The timing of FLS formation and dissipation further has implications for traffic and solar energy production. While climatological analyses of FLS formation and dissipation exist, the influence of meteorological and land surface conditions on specific FLS formation and dissipation regimes is not clear yet.
In this study, satellite-derived fog and low stratus life cycle information is explicitly linked to land surface and meteorology in Europe. Pixel-based correlations of FLS formation and dissipation times with environmental conditions were analyzed in a hierarchical clustering approach. Spatially distinct regimes of FLS formation and dissipation can be identified, and a dependency on the background geography and climate is apparent. FLS formation and dissipation regimes are analyzed on multiple hierarchy levels, i.e. various cluster numbers are explored, to investigate the spatial division of larger regional regimes to smaller sub-regional and local regimes. Monthly mean sensitivities for selected sub-regional regimes suggest a dependency of those sensitivities on FLS type. A case study of a regime covering the Po valley in northern Italy is used to showcase the quantification of FLS drivers regionally using explainable machine learning. Future work will expand this approach to analyze and compare FLS drivers in regional regimes with different background geography and climate.
How to cite: Pauli, E., Cermak, J., and Andersen, H.: Identifying and analyzing fog and low stratus life cycle regimes over central Europe, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11754, https://doi.org/10.5194/egusphere-egu23-11754, 2023.
In this contribution, a statistical learning technique is used to quantify the response of cloud radiative effects to changes in a large number of environmental factors in spatial observation data.
Clouds play a key role for the Earth’s energy balance; however, their response to climatic and anthropogenic aerosol emission changes is not clear, yet. Here, 20 years of satellite observations of cloud radiative effects (CRE) are analysed together with reanalysis data sets in a (regularised) ridge regression framework to quantitatively link the variability of observed CREs to changes in environmental factors, or cloud-controlling factors (CCFs). In the literature the meteorological kernels of such CCF analyses are typically established in regime-specific regression frameworks based on a low (2-8) number of CCFs. In our data-driven approach, the capabilities of the regularised regression to deal with collinearities in a large number of predictors are exploited to establish a regime-independent CCF framework based on a large number of CCFs. Using a reference 7-CCF framework, we show that ridge regression produces nearly identical patterns of CCF sensitivities when compared to the traditional regression. In the data-driven framework, however, the traditional regression fails at producing consistent results due to overfitting. The data-driven analysis reveals distinct regional patterns of CCF importance for shortwave and longwave CRE:
- Sea surface temperatures and inversion strength are important for shortwave CRE in stratocumulus regions, in agreement with existing studies. However, zonal wind speeds in the free troposphere and surface fluxes are also shown to be important.
- Free tropospheric meridional winds are important drivers of CRE in the subtropical belts (20°-40°) in both hemispheres, likely capturing aspects of Rossby Wave-related CRE variability.
- Aerosols are shown to be most important for shortwave CRE in the regions of stratocumulus to cumulus transition.
While the multivariate method aims at limiting the influence of confounding factors on the estimated sensitivities, particularly the aerosol-CRE sensitivity may still be confounded to a degree. Future analyses of interactions between different CCFs and comparisons to global climate models are outlined.
How to cite: Andersen, H., Cermak, J., Douglas, A., Stier, P., and Wall, C.: Controls of cloud radiative effects: a data-driven observation-based quantification, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12131, https://doi.org/10.5194/egusphere-egu23-12131, 2023.
Aerosol particles, acting as condensation nuclei, affect the cloud microphysical and radiative properties as well as the precipitation processes. Aerosol-cloud interactions are not well understood and quantified yet. With the aim to contribute to their understanding, quantify the role of dust and marine aerosol in the cold and warm cloud formation, and for testing model parameterization, the MESSA-DIN (MEditerranean Sea Salt And Dust Ice Nuclei) measurement campaign was organized and carried out by the CNR-IMAA Atmospheric Observatory (CIAO), part of the Italian component of the European research infrastructure ACTRIS (Aerosol Clouds Trace gases Research InfraStructure). The measurements were performed at the coastal site of Soverato (10 m asl, 38.69◦ N, 16.54◦ E), on the South-Eastern coast of Italy, in the Central Mediterranean, from June to November 2021. Different types of remote sensing instruments were deployed and operated at the measurement site, including a polarization Raman lidar, a ceilometer, a Doppler lidar, a cloud Doppler radar, a microwave radiometer, a sun photometer and a sky-imager.
The synergy processing of the measurements from part of these instruments, using the ACTRIS algorithms, allows to distinguish between the aerosol and the different types of hydrometeors forming clouds and precipitations, as well as to retrieve aerosol geometrical and optical properties together with cloud geometrical and microphysical properties through the troposphere. The profiles of aerosol optical properties may allow to identify aerosol types and to retrieve their concentration profiles, using or adapting existing algorithms such as POLIPHON (Polarization Lidar Photometer Networking). Aerosol-type specific concentration profiles are used in models’ aerosol-type specific parameterizations for estimating cloud-relevant aerosol microphysical parameters, which are the concentration profiles of cloud condensation nuclei (CCN) and ice nucleating particles (INP). The above information and retrievals are investigated in synergy with air masses vertical and horizontal velocities through the troposphere, estimated from the Doppler lidar, and with column-integrated aerosol optical and microphysical properties, retrieved by the sun photometer using the AERONET (Aerosol Robotic Network) algorithms.
Case studies related to the formation of warm and cold clouds in presence of dust, marine aerosol and their mixture are discussed. Moreover, for cold clouds, the observational products are compared with the results of a DREAM-based aerosol transport model with included parameterizations for INP originating from both dust and marine aerosols, developed by the Republic Hydrometeorological Service of Serbia. Finally, correlations between clouds formation and properties and aerosol type and properties are also investigated, considering the role of vertical and horizontal wind profiles and other thermodynamic variables derived from observations or models.
How to cite: Rosoldi, M., Gandolfi, I., Summa, D., De Rosa, B., Cvetkovic, B., Nickovic, S., and Madonna, F.: Ground-based remote sensing observations of aerosols and clouds above a coastal site in the Central Mediterranean, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12715, https://doi.org/10.5194/egusphere-egu23-12715, 2023.
This contribution presents early results on the effects of biomass burning aerosols (BBA) on fog and low clouds (FLC) in the Namib, using data from multiple satellite platforms and station measurements.
Fog, which is the most relevant non-rainfall water source for plants and animals in the coastal parts of the Namib Desert, may become increasingly important for local ecosystems as regional climate simulations predict a warmer and drier climate for southern Africa in the future. Previous studies showed the role of BBA on cloud development over the ocean off the Namibian coast. The same processes are likely to influence Namib-region FLC formation and persistence as well. However, the potential effects of aerosols on FLC in the Namib Desert, a direct extension of the South-East Atlantic cloud system, have yet to be investigated.
A clear seasonal cycle of FLC dissipation is found in a satellite-based product of FLC formation and dissipation times, with longer FLC persistence during the BBA season. Using a BBA reanalysis product in combination with the satellite data, it is found that during this season, FLC dissipation times are positively correlated to BBA loading (higher aerosol loading coinciding with later FLC dissipation). It is assumed that semi-direct and indirect BBA effects contribute to this pattern, with further analyses aimed at isolating aerosol effects from possible confounders.
These findings are a first step in a better understanding of the Namib-region FLC system and will help in the development of a statistical model to quantify the sensitivities of FLC lifetime in the region in the next step of the project.
How to cite: Mass, A., Andersen, H., and Cermak, J.: An investigation of fog and low cloud life cycles and their interaction with biomass burning aerosols in the Namib, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13005, https://doi.org/10.5194/egusphere-egu23-13005, 2023.
Aerosols affect weather and climate by absorbing and scattering radiation. Such effects strongly depend on the optical properties of aerosols that are mainly controlled by their other characteristics like size distribution, morphology and chemical composition. Chemistry and aerosol microphysics constantly modify these characteristics causing a large spatial and temporal variability. Most atmospheric models cannot account for this variability as they rely on look-up table to treat aerosol optics. This simplification can lead to large errors in weather and climate models when it comes to aerosol radiative impacts.
This study presents a novel and computationally inexpensive machine learning approach for online representation of the aerosol optical properties. These properties are fully coupled with the chemical and microphysical variability of particles. Aerosol composition is considered with two ternary systems for solid (dust, soot and sea salt) and liquid (water, sulfate and organics) mixtures. Then Mie calculations are performed based on these aerosol compositions assuming core-shell and volume-average mixing states. The output of the Mie code is then used to train an artificial neural network. The results show that neural network model is able to predict the aerosol optical properties (extinction coefficient, single scattering albedo and asymmetry parameter) by R2 >0.90 and O(103 ) lower computational cost compared to Mie calculations. Potential applications of this approach for ICON-ART modeling system is discussed.
How to cite: Kumar, P. and Hoshyaripour, G. A.: Online calculation of aerosol optics in atmospheric models with machine learning, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13559, https://doi.org/10.5194/egusphere-egu23-13559, 2023.
We study the gravity-induced collisions of charged spheres of dielectric materials dispersed in a gaseous medium. When the gap thickness between the surfaces of two spheres is shorter than the mean free path of the surrounding fluid medium, continuum assumptions for the hydrodynamics interactions are no longer valid, and the non-continuum lubrication interactions result in surface-to-surface contact in finite time. Two like-charged dielectric spheres attract each other at close separations for a wide range of size and charge ratio values. We use trajectory analysis to calculate the collision rate and, thus, explore the role of electrostatic interactions on the collision dynamics of a pair of like-charged dielectric spheres. We present the modifications of pair trajectories due to electrostatic forces and show how collision efficiencies vary with the non-dimensional parameter capturing the relative strength of the electrostatic force to gravity as well as the charge ratio and size ratio.
How to cite: Patra, P. and Roy, A.: Collision efficiency of poly-dispersed charged spheres settling in a quiescent environment, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14021, https://doi.org/10.5194/egusphere-egu23-14021, 2023.
Volcanic eruptions provide invaluable natural experiments to evaluate the transport, evolution, and potential impact of sulphate aerosol on clouds in global climate models (GCMs). The 2014 fissure eruption in Holuhraun, Iceland had an emission rate greater than a third of daily global sulphur dioxide emissions at its peak, resulting in significant perturbations to cloud radiative properties across vast swathes on the North Atlantic. Probing the GCM representation of aerosol lifecycle during transport in the volcanic plume, offers a unique insight to improve aerosol source and sink process understanding, which is essential to reducing one of the largest sources of uncertainty in climate modelling - aerosol-cloud-interactions.
Using rural aerosol measurement sites with climatologically relevant time series, we first perform a Eulerian evaluation of the UK Met Office Earth System Model (UKESM1) simulation of the volcanic eruption. Both in-situ observations and UKESM1 demonstrate a significant increase in aerosol concentration during the volcanic eruption compared to the climatology (2008-2013). However, the ‘standard’ version of the model fails to replicate the significant growth events associated with new particle formation seen in the observations during the volcanic eruption. A second simulation of UKESM1 with the addition of boundary layer nucleation, which is not included in the standard configuration, accurately reproduces the timing of nucleation events seen during the eruption period. Finally, we utilise a Lagrangian framework, in which HYSPLIT trajectories are calculated for both GCMs and reanalysis data, to analyse the relevant aerosol source and sink processes during transport that drive the differences between modelled and observed aerosol at the measurement sites.
How to cite: Duncan, E., Jordan, G., Malavelle, F., Kim, P., Jones, A., Watson-Parris, D., Sellar, A., Haywood, J., Peace, A., Teixeira, J., Kipling, Z., and Partridge, D.: Following the Plume: Evaluation of UKESM1 simulation of 2014 Holuhraun eruption in a Lagrangian Framework. , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14608, https://doi.org/10.5194/egusphere-egu23-14608, 2023.
Near surface air temperature is a primary variable to track global climate change. While mean temperature is often used to quantify global warming, the diurnal temperature range (DTR) - defined as the difference of daily minimum and maximum temperature - can provide additional information on changes to the diurnal cycle and temperature extrema, which is important for impacts of climate change. Different to increasing global mean temperature, observations have shown a decrease of global mean DTR over recent decades. This trend has been attributed to human emissions of greenhouse gases (GHG) which increase daily minimum temperature (Tmin), usually measured at night, more than daily maximum temperature (Tmax), observed during the day, by trapping outgoing longwave radiation. Aerosol radiative forcing has been associated with absorbing and scattering incoming (solar) shortwave radiation; thus, aerosols are assumed to reduce Tmax more than Tmin, decreasing the DTR. However, historical single and ALL forcing simulations from models that are part of phase 6 of the Coupled Model Intercomparison Project (CMIP6) model a decrease of the DTR for GHG and ALL forcings but show an increase in the DTR for anthropogenic aerosols due to a larger reduction of Tmin than Tmax.
We investigate this discrepancy in aerosol contributions to changes in the DTR by applying causal inference methods to quantify the impact aerosols have on the DTR in Europe. To address the various effects aerosols have on the climate system, by interacting with both radiation and clouds, we include Tmin, Tmax, aerosol optical depth (AOD), cloud cover, cloud height, incoming shortwave radiation (SW) and outgoing longwave radiation using observational satellite and gridded station data for the past decade in our analysis. First results agree with the cooling effect of aerosols on Tmax by reducing SW radiation and show a positive effect of AOD on low cloud cover. They further suggest that a decrease of Tmax causes a decrease in Tmin, possibly explaining the CMIP6 model results.
How to cite: Roesch, C., Ballinger, A., Runge, J., and Hegerl, G.: Using causal inference to investigate anthropogenic aerosol impacts on the diurnal temperature range , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15030, https://doi.org/10.5194/egusphere-egu23-15030, 2023.
The Earth Clouds Aerosol and Radiation Explorer (JAXA/ESA) will be observing clouds, aerosols and vertical air motions with a high-sensitivity W-band Doppler Cloud Profiling Radar (CPR) and a 355 nm high spectral resolution Atmospheric Lidar (ATLID). The standard and research algorithms for cloud- precipitation and validation methodologies using ground observations have been developed and improved to make the most of the new observation capabilities of the satellite. This paper presents an overview of the active sensor-based algorithms prepared for the EarthCARE satellite mission, and the applications of the methodologies to understand the physical processes associated with clouds, precipitation and air-motion.
How to cite: Sato, K. and Okamoto, H.: Revealing cloud-precipitation processes from Spaceborne Doppler Cloud Radar, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15482, https://doi.org/10.5194/egusphere-egu23-15482, 2023.
Clouds, aerosols and vertical air motions are essential components to control climate systems. We need better Earth observing systems that can provide aerosol-, cloud- and precipitation microphysics, their radiation properties and in-cloud air motions to reduce uncertainties in climate change predictions. The Earth Clouds Aerosol and Radiation Explorer (EarthCARE) is a joint mission by Japan Aerospace Exploration Agency (JAXA) and the European Space Agency (ESA). It will carry Doppler cloud profiling radar (CPR), atmospheric high spectral resolution lidar (ATLID), multi-le spectral imager (MSI) and broad band radiometer (BBR). JAXA EarthCARE algorithms have been developed. Doppler capability of CPR is expected to provide terminal velocity of cloud and precipitation particles and vertical air motion inside clouds. High spectral resolution and polarization functions of ATLID provides true backscattering coefficient, extinction coefficient and depolarization ratio. Theoretical studies indicated that the two-dimensional diagram of lidar ratio and depolarization ratio is essential for discriminating among cloud particle shapes and orientations (Okamoto et al., 2019, Okamoto et al., 2020) in addition to aerosol types. Recently developed physical model (Sato et al., 2018) and vectorized physical model (Sato et al., 2019) can be used to take lidar multiple scattering into account for the interpretation of active sensor signals of optically thick clouds. Synergy of new observations with the theoretical improvements enables better cloud microphysics retrievals, leading to better estimation of radiative properties of cloud and precipitation particles and aerosol-cloud interactions. Synergetic ground-based observation systems are developed to evaluate the EarthCARE algorithms for space-borne active sensors. The systems consist of Multi-Field-of-view Multiple Scattering Polarization Lidar (Okamoto et al., 2016, Nishizawa et al., 2021), high spectral resolution lidar using a scanning Michelson interferometer (Jin et al., 2020), Direct detection Doppler lidar (Ishii et al., 2022) and 94 GHz cloud radar. The systems are designed to capture the characteristics of CloudSat, CALIPSO, and EarthCARE, leading to bridge the gap of these satellite data sets.
How to cite: Okamoto, H., Sato, K., and Nishizawa, T.: EarthCARE algorithms for retrieval of clouds, aerosols and vertical air motions , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15652, https://doi.org/10.5194/egusphere-egu23-15652, 2023.
Aerosol-cloud interactions are one of the key uncertainties in understanding future climate change. A commonly used method for constraining these interactions is using ship tracks. Aerosol-containing plumes from ships can develop into linearly shaped clouds identifiable in satellite images, isolating the aerosol impact on clouds. Previous studies have shown that ship tracks form more commonly in clean conditions, but even accounting for this, many ships that might be expected to form ship tracks do not. This leads to uncertainties in aerosol-cloud interactions and their climate impact.
Ship track formation depends on the aerosol-containing plumes from the ship being sufficiently concentrated upon reaching the cloud. The cloud must also be sensitive to aerosol. In focus are updraft-limited clouds: smaller updrafts promote slower cooling as a cloud parcel rises, higher critical supersaturation values and lower aerosol activation fractions. It is not clear which of these are more important, but it is vital to understand them if we are using ship tracks to retrieve cloud sensitivity to aerosol.
We develop a plume-parcel model to address these issues to estimate cloud droplet enhancements in ship tracks. Ship aerosol concentrations at the cloud height were modelled as plumes, simulating the shorter timescales of injection. Droplet number concentration enhancements were estimated using Köhler theory for over one hundred thousand ships off the coast of California.
Using a constant updraft, the model was able to achieve reasonable enhancements (r2 ranging between (0.32, 0.4)). These enhancements were shown to be significantly sensitive to the choice of the updraft. In order to examine the hypothetical updraft values required for activation, an optimisation algorithm was developed to fit updrafts to cloud enhancement observations; a 1-1 correlation was achieved between observed and parameterised enhancements. Updrafts consistent with Köhler theory are considerably smaller than cloud-top radiative cooling-based estimates, suggesting that these clouds are less sensitive to aerosol than current estimates suggest.
How to cite: Quilelli Correa Rocha Ribeiro, R., Gryspeerdt, E., and Van Reeuwijk, M.: Retrieving cloud sensitivity to aerosol using ship emissions, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-16095, https://doi.org/10.5194/egusphere-egu23-16095, 2023.
Aerosol effects on precipitation can be broadly categorized into radiatively and microphysically mediated effects – all of which remain highly uncertain. Their assessment in atmospheric models generally relies on the simulation of a complex chain of microphysical process growing aerosols into radiatively active size ranges and into size ranges suitable to act as cloud condensation nuclei, subsequently perturbing radiative fluxes, diabatic heating, cloud microphysical processes and ultimately precipitation formation. The associated uncertainties along each step in these complex process chains remain significant and make it difficult to disentangle uncertainties in aerosol and cloud processes.
Here we present results from a hierarchy of highly idealised model simulations in which aerosols are prescribed as fixed plumes of radiative properties, with an optional associated semi-empirical scaling of droplet number perturbations. These idealised simulations provide fascinating insights into the physical processes underlying aerosol effects on precipitation and into the interaction of local perturbations with the larger scale dynamics.
Idealised aqua-planet general circulation model simulations reveal that the response of regional precipitation to idealised and realistic aerosol radiative perturbations can be well explained in an energetic framework (because associated changes in the net diabatic heating needs to be balanced by latent heat release, surface or top-of-atmosphere fluxes or compensated for by energy divergence/convergence). Extending this framework by adding land and realistic sea surface temperatures in an AMIP setup, we probe the regional sensitivity of precipitation changes to absorbing aerosol perturbations across the globe. Our results confirm the findings from the aqua-planet studies that that the local precipitation response to aerosol absorption is opposite in sign between the tropics and the extratropics and we show that this contrasting response can be understood in terms of different mechanisms by which the large-scale circulation responds to heating in the extratropics and in the tropics. Finally, we apply our framework in cloud resolving km-scale model simulations regionally and globally, which highlights the importance of radiative perturbations as well as a complex interplay of aerosol effects with the diurnal cycle of precipitation.
How to cite: Stier, P., Williams, A., Herbert, R., Weiss, P., Dagan, G., and Watson-Parris, D.: Idealised studies of aerosol effects on precipitation – from aqua-planets to global km-scale models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-17581, https://doi.org/10.5194/egusphere-egu23-17581, 2023.
Posters virtual: Wed, 26 Apr, 16:15–18:00 | vHall AS
Clouds play a significant role in the dynamics and thermodynamics of the atmosphere. To understand the impact of clouds on climate and for better representation of these in the global models, accurate information about the temporal, spatial and vertical distribution of cloud properties such as microphysical, morphological and types are essential. In the present work, vertical structure and microphysics of clouds during southwest (SW) monsoon has been studied from a high altitude site (Mahabaleshwar (17.92°N, 73.66°E, and 1348 m above mean sea level (MSL)) and within ± 0.1 degrees) over Western Ghats, India. Vertical structure of the clouds has been detailed using radiosonde observations. Warm cloud microphysics was investigated using in-situ ground and aircraft cloud measurements. Radiosonde profiles showed the presence of single and multi-layered clouds over the observational site. Higher occurrence frequency for cloud layers below 2 km and above 6 km altitude compared to mid-level clouds (2 to 6 km) during SW monsoon were noticed. Higher occurrences of single layer clouds during June and September (transition period) were noticed whereas frequency of two-layer was higher in July and August (core period). Low (~30%) and high-level (~60%) clouds were dominantly seen compared to mid-level clouds over the observational site during SW monsoon. Warm cloud microphysics was investigated using collocated ground and airborne in situ measurements. Cloud microphysical properties such as cloud droplet number concentration (CDNC), liquid water content (LWC), droplet effective diameter (ED), droplet mean radius (Rm) respectively were analyzed. The cloud liquid water content and the effective droplet diameter showed increase with altitude. Analyzed cloud droplet size distribution (DSD) showed a steep decrease in number concentration of droplets above 25 µm diameters at altitudes above 1800 m, suggesting active collision-coalescence. This is the first such report combining in situ observations from two different platforms to study the vertical structure of monsoon clouds over a complex terrain like the Western Ghats in India.
How to cite: Leena, P. P., Varghese, M., .S.Kumar, J., Kumar, V. A., Pandithurai, G., .D.Patil, R., Resmi, E. A., and .V.Prabha, T.: A study on morphology and microphysics of clouds during southwest monsoon over Western Ghats, India, using multi-platform observations, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1946, https://doi.org/10.5194/egusphere-egu23-1946, 2023.
The aerosol particles that become condensation nuclei affect the formation and evolution of clouds, their cycle lifetime, and their optical properties, having thus a major impact on the atmosphere, the radiative balance and leading therefore to climate changes. The aim of the study is to investigate the second indirect aerosol effect and the relationship between cloud droplet effective radius and cloud albedo for cleaner and polluted clouds over two sites in Romania (Bucharest and Cluj-Napoca), using satellite data collected from March 2000 to March 2022. Present study is the first one over sites in Romania. A series of physical parameters (albedo, cloud cover fraction, cloud optical depth, liquid water path and cloud water radius) were extracted from the Clouds and the Earth's Radiant Energy System (CERES) database for Bucharest, as a high polluted city, and for Cluj - Napoca, as a cleaner city in Romania. The time series for albedo and low cloud characteristics contained 193.584 hourly profiles. In addition, based on the optical depth from CERES, we calculated low cloud albedo using a parameterization currently used in the climate models. The study was also focused on the life cycle of the low clouds and on the cloud cover fraction over the two sites. The annual and seasonal variations of the cloud physical parameters were investigated and compared for both sites. We highlight how the cloud droplet effective radius modifies differently the cloud albedo for polluted clouds over Bucharest (presence of more and smaller cloud droplets and thus, a higher cloud albedo and less drizzle size drops) than for the cleaner clouds over Cluj-Napoca (presence of fewer and larger cloud droplets, and therefore a lower cloud albedo). The results also shows comparatively the frecqueny of occurence of this type of clouds over both sites and the temporal trend of analyzed physical characteristics. Modifications and variations of cloud characteristics at a city scale help us to better understand the second indirect aerosol effect, life cycle and the climatology of low clouds.
Acknowledgment
GLSG, SS and GI acknowledge the support from NO Grants 2014-2021, under contract no 31/01.09.2020, Project EEA-RO-NO-2019-0423. GLSG work was also supported by the University of Bucharest, PhD research grant and by the Romanian Nucleu Programme.
How to cite: Saftoiu Golea, G. L., Stefan, S., Antonescu, B., and Iorga, G.: Changes in low clouds optical characteristics in the atmosphere of two different urban sites in Romania, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4266, https://doi.org/10.5194/egusphere-egu23-4266, 2023.
Aerosols play a critical role in climate change over the polar regions. The impacts of aerosol on Arctic Amplification is not well understood. In this talk, satellite observations from different instruments are used to understand the spatial and temporal changes of aerosol properties in the troposphere over the ocean in the Arctic in the past four decades. The model simulations are also used to identify the change of aerosol components. The change of Arctic haze due to anthropogenic source is well identified from both satellite observations and model simulations. However, the change of marine aerosol source in the Arctic, especially for the period with strong sea ice melting, is only being observed from satellite observations.
How to cite: Mei, L., Burrows, J., Vountas, M., and Bösch, H.: Change of tropospheric aerosol over the ocean in the Arctic observed from space, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11909, https://doi.org/10.5194/egusphere-egu23-11909, 2023.
Dust storm as one of severe natural disasters occur frequently in central Australia. Ground-based networks with visibility and PM observation instruments are more often used for dust storm monitoring and research. With the development of satellite remote sensing and general circulation models (GCM), dust storm research has been with larger spatial coverage, especially where ground-based stations cannot be installed. The Deepblue (DB) aerosol product from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) provide long-term aerosol records over 20 years from 2000 to the present. In this study, a dust AOD dataset was produced using MODIS DB and MERRA-2 aerosol reanalysis. The comparison of the dust AOD with AERONET data shows that 71% of collocated data points are within an EE of . The dust AOD dataset was then used to study seasonal dust distribution in Australia. Results show that dust storms occur more frequently in eastern Australia than the western part. In the northern part of eastern Australia, dust storm intensity reached the peak in the spring while in the southern part dust storm occur more frequently in the summer. Additionally, dust storms obtained from MODIS differs from those from traditional site observations, which reveals that our understanding on dust storm over regions without observations might be with large uncertainty.
How to cite: Che, Y., Yu, B., and Parsons, K.: Seasonal dust aerosol optical depth patterns using MODIS Deepblue aerosol product and MERRA-2 aerosol reanalysis, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-16295, https://doi.org/10.5194/egusphere-egu23-16295, 2023.
