AS3.10 | Clouds, Aerosol, Radiation and Precipitation interactions
Clouds, Aerosol, Radiation and Precipitation interactions
Co-organized by CL2
Convener: Edward Gryspeerdt | Co-conveners: Annica Ekman, Benjamin Heutte, Geeta Persad, Ruth Price, Anna Possner, Jennie L. Thomas
Orals
| Thu, 18 Apr, 08:30–12:25 (CEST), 14:00–15:40 (CEST)
 
Room F2
Posters on site
| Attendance Fri, 19 Apr, 10:45–12:30 (CEST) | Display Fri, 19 Apr, 08:30–12:30
 
Hall X5
Posters virtual
| Attendance Fri, 19 Apr, 14:00–15:45 (CEST) | Display Fri, 19 Apr, 08:30–18:00
 
vHall X5
Orals |
Thu, 08:30
Fri, 10:45
Fri, 14:00
Clouds and aerosols play a key role in climate and weather-related processes over a wide range of spatial and temporal scales. An initial forcing due to changes in the aerosol concentration and composition may also be enhanced or dampened by feedback processes such as modified cloud dynamics, surface exchange or atmospheric circulation patterns. This session aims to link research activities in observations and modelling of radiative, dynamical and microphysical processes of clouds, aerosols, and their interactions. Studies addressing several aspects of the aerosol-cloud-radiation-precipitation system are encouraged.

There are several other related sessions on aerosols, clouds, radiation and precipitation processes focused on specific themes (see links below)

Topics covered in this session include, but are not limited to:
- Cloud and aerosol macro- and microphysical properties, precipitation formation mechanisms and their role in the energy budget
- Observational constraints on aerosol-cloud interactions
- Use of observational simulators to constrain aerosols, clouds and their radiative effects in models
- Experimental cloud and aerosol studies
- High-resolution modelling, including large-eddy simulation and cloud-resolving models
- Parameterization of cloud and aerosol microphysics/dynamics/radiation processes

Orals: Thu, 18 Apr | Room F2

Chairpersons: Anna Possner, Edward Gryspeerdt
Radiation, Cloud and Aerosol Physics
08:30–08:40
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EGU24-18173
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On-site presentation
Chiel van Heerwaarden, Wouter Mol, Menno Veerman, Bart van Stratum, Mirjam Tijhuis, Bert Heusinkveld, Oscar Hartogensis, Jordi Vilà-Guerau de Arellano, and Mary-rose Mangan

This year marks the end of the Shedding Light On Cloud Shadows project (SLOCS, 2019-2024). SLOCS aims to understand temporal, spatial, and spectral variability in surface solar irradiance driven by individual clouds from field observations and 3D cloud-resolving large-eddy simulations. In this contribution, we would like to present the highlights of the project and the most important conclusions.

The reason for initiating SLOCS is that clouds trigger large fluctuations in solar surface irradiance, and therefore in surface heat fluxes, but there is still much to be learned about these fluctuations. The incoming radiation in shadows is almost an order of magnitude less than under clear sky, while peaks near clouds shadows can sometimes reach a 50% increase with respect to clear sky, due to scattering of sunlight on clouds. Performing cloud-resolving simulations with realistic surface solar irradiance patterns under broken clouds remains therefore a challenge, and current cloud-resolving models do not capture the radiation-cloud interactions well. 

The Shedding Light On Cloud Shadows (SLOCS) project addresses this challenge by i) performing spatial observations in a spatial grid fine enough (~50 m, 10 Hz) to capture individual clouds using a newly designed instrument, and ii) developing 3D radiative transfer models for cloud-resolving models with optimal balance between detail level and performance. The FESSTVaL, LIAISE, and CloudRoots campaigns provided unique opportunities to measure surface solar irradiance around cloud shadows in different climates. In the campaigns, we performed grid measurements of radiation, while benefiting from complementary boundary-layer and cloud observations.

The most important lessons learned from the field observations are:
1. Scales as small as meters and seconds contribute significantly to fluctuations in surface solar irradiance
2. All broken cloud patterns generate strong peaks, but the underlying mechanisms vary greatly amoung cloud types
3. Spectral variations (in colors of light) are mostly significant under cumulus clouds.

We used those observations to set up a series of cloud-resolving simulations with MicroHH and to evaluate two newly-developed radiative transfer solvers: i) a ray tracer fast enough to be coupled to our cloud-resolving model and ii) a solver that post-processes the outcome of a 1D two-stream solver to emulate 3D effects. Also, we studied the impact of periodic and open lateral boundary conditions. The most important conclusions are:

1. Capturing 3D interactions between clouds and radiation accurately leads to larger clouds with more liquid water compared to those in simulations with conventional 1D methods
2. Post-processing conventional 1D radiation computations allows for simulating surface solar irradiance fields with realistic probability density functions, but inaccurate cloud shadow shape and location.
3. Open lateral boundaries in large-eddy simulations are at least as important as correct radiation-cloud interactions in producing realistic cloud shadows in the range from hectometers to kilometers.

How to cite: van Heerwaarden, C., Mol, W., Veerman, M., van Stratum, B., Tijhuis, M., Heusinkveld, B., Hartogensis, O., Vilà-Guerau de Arellano, J., and Mangan, M.: The Shedding Light On Cloud Shadows project: measuring and simulating surface solar irradiance under broken clouds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18173, https://doi.org/10.5194/egusphere-egu24-18173, 2024.

08:40–08:50
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EGU24-5996
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ECS
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On-site presentation
Mirjam Tijhuis, Bart van Stratum, and Chiel van Heerwaarden

Most atmospheric models consider radiative transfer only in the vertical direction (1D), as 3D radiative transfer calculations are too costly. Thereby, horizontal transfer of radiation is omitted, resulting in incorrect surface radiation fields. Previous work on 3D radiative effects mainly used uncoupled 3D radiative transfer. In our current work, we study the impact of coupled 3D radiative transfer on the development of clouds, and the resulting impact on the domain average surface solar irradiance.

We performed a series of realistic Large-Eddy simulations with MicroHH. We developed the option to use aerosol data from the CAMS global reanalysis to include the interactions between aerosols and radiation in our LES simulations. This makes sure our simulated radiation is in line with observations. To investigate the impact of 3D radiative transfer, we selected 12 days on which shallow cumulus clouds formed over Cabauw, the Netherlands. For each day, we performed simulations with 1D radiative transfer and with a coupled ray-tracer. The simulations with the coupled ray-tracer also include the results of uncoupled 1D radiative transfer. This allows us to compare the differences between 1D and 3D radiative transfer when the clouds are the same.  

In general, our simulations with coupled 3D radiative transfer have a higher domain average liquid water path compared to our simulations with coupled 1D radiative transfer. The cloud cover is similar in both simulations, but the cloud size is increased in the simulations with coupled 3D radiative transfer. For the domain average radiation, we find that 3D radiative transfer in general decreases the direct radiation and increases the diffuse radiation, but the net effect is on average less than 1 W m-2. We can explain the differences in radiation when we look separately at the direct and diffuse radiation, the uncoupled 3D effects, and the impact of the change in the clouds. The uncoupled effect of 3D radiative transfer is an increase in global radiation, which is counteracted by a decrease is global radiation caused by the change in clouds.

How to cite: Tijhuis, M., van Stratum, B., and van Heerwaarden, C.: Coupled 3D radiation deepens cumulus clouds without changing the mean surface solar irradiance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5996, https://doi.org/10.5194/egusphere-egu24-5996, 2024.

08:50–09:00
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EGU24-17813
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ECS
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On-site presentation
Jonas Witthuhn, Hartwig Deneke, and Heike Kalesse-Los

Investigating solar radiation and its variability due to clouds and aerosol is critical for efficient and reliable solar energy systems. During broken cloud conditions, reflections at cloud edges and changing aerosol properties in the vicinity of clouds affect the surface solar radiation significantly. In these situations, the distinction between clouds and clear skies with aerosol is not always well defined[1]. As seen from the surface, this region exists around cloud core shadows and is called the transition zone. Here, a unique dataset of observations from a dense pyranometer network is used to detect and investigate signatures of shortwave broadband transmittance in the transition zone.

The TROPOS pyranometer network consists of up to 100 individual stations. Data of one campaign is used for this study: 60 stations were distributed over an area of about 6 km² during the S2VSR[2] measurement campaign in 2023 at the ARM Southern Great Planes (SGP) site in Oklahoma, USA. The surface solar irradiance is measured at each station with a time resolution of 10 Hz. The transition zone is detected and characterized by applying a modified clear sky detection algorithm[3] to the data. An additional component of our analysis is the determination of the cloud motion. This vector is determined using the Farneback optical flow algorithm[4] on a cloud shadow mask calculated from the “Clouds Optically Gridded by Stereo” (COGS) product[5].

The study aims to quantify the small-scale effects of the transition zone on surface solar irradiance and potential photo-voltaic yield. This information is valuable for photo-voltaic site planning and provides scientifically relevant insights into the interaction between clouds, aerosol and solar radiation.


[1] e.g., Calbó et al. 2017, https://doi.org/10.1016/j.atmosres.2017.06.010

[2] https://www.arm.gov/research/campaigns/sgp2023s2vsr

[3] Bright et al. 2020, https://doi.org/10.1016/j.rser.2020.109706

[4] Farneback 2000, https://doi.org/10.1109/ICPR.2000.905291.

[5] Romps & Oktem et al. 2018, https://doi.org/10.1175/bams-d-18-0029.1

How to cite: Witthuhn, J., Deneke, H., and Kalesse-Los, H.: Typical signatures of the transition zone of cumulus cloud shadows in solar radiation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17813, https://doi.org/10.5194/egusphere-egu24-17813, 2024.

09:00–09:10
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EGU24-288
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ECS
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Highlight
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On-site presentation
Goutam Choudhury and Tom Goren

The cloud radiative effect (CRE) of low-level marine clouds has traditionally been expressed primarily as a linear function of the cloud cover. However, recent studies have revealed a substantial change in CRE even at a constant cloud cover. This change is attributed to variations in cloud morphology governed by the horizontal and vertical distribution of cloud water. A unique feature of these morphologies, especially for low marine clouds, is the occurrence of distinct quantities of optically thin clouds. Understanding the impact of these thin clouds on low-level marine CRE is crucial for two reasons. First, spaceborne studies indicate a prevalent occurrence of thin clouds in areas characterized by peak low-level cloud cover. Second, the relationship between thin clouds and CRE may differ from that of their optically thicker counterparts due to their semitransparency to incoming shortwave and outgoing longwave radiations. This study investigates the influence of thin clouds on the CRE of low-level clouds over the Southeast Pacific Ocean using six years of concurrent measurements from MODIS and CERES spaceborne sensors. The results show a substantial influence of thin clouds on the shortwave and longwave components of CRE, as well as the balance them. The findings emphasize the need for a more comprehensive representation of thin clouds and, therefore, cloud morphology in climate models.

How to cite: Choudhury, G. and Goren, T.: Role of thin clouds in modulating the cloud radiative effect of marine low clouds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-288, https://doi.org/10.5194/egusphere-egu24-288, 2024.

09:10–09:20
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EGU24-2702
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ECS
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On-site presentation
Shri Vignesh, Ambedkar Sanket, Arya Narayanan Unni, Srikrishna Sahu, Sachin S. Gunthe, Swetaprovo Chaudhuri, Rama Govindarajan, and Raman I. Sujith

There has been significant progress in comprehending the role of characteristic properties of aerosol in cloud droplet formation over the past decade [1]; however, the growth of cloud droplets into rain droplets, initiating precipitation in warm clouds, is still not well understood [2]. Collision and coalescence among droplets are assumed to be responsible for the rapid growth of cloud droplets to rain droplets. Turbulence is believed to play a significant role in the growth of cloud droplets [2]. 

The influence of turbulence on droplet dynamics is nominally characterized by the Stokes number, which decides if the droplet either follows the streamlines or decorrelates from it. Due to their deviation from the streamlines, droplets can form clusters and caustics, thereby increasing the chance of collisions [3]. Thus, the size distribution of droplets can determine the influence of turbulence on droplet collisions. The cloud droplet size distribution depends on several parameters, such as the initial aerosol number concentration, aerosol properties, and the in-cloud supersaturation. Thus, investigating the influence of turbulence on a given droplet size distribution can facilitate a better scientific understanding of the onset of precipitation. 

In the present study, we experimentally investigated the influence of turbulence on different cloud droplet size distributions. We generated homogeneous isotropic turbulence of various intensities in a closed chamber and seeded it with droplets relevant to that observed in clouds originating under different environmental conditions. Using Phase Doppler particle analyzer (PDPA), we measured the droplet size distributions and analyzed the changes with turbulence intensity. Our experiments show significant growth for cloud droplet size distributions with a higher degree of polydispersity than slender droplet size distributions. We attribute this enhancement in collisions to the induced relative velocity between droplets of different Stokes numbers. We observed a positive trend between clustering and droplet size growth, thus indicating the role of clustering in enhancing collisions.

Acknowledgments: We thank Dr. Amit Kumar Patra and Dr. T. Narayana Rao for their valuable suggestions. We acknowledge the ISRO-IITM cell (No. SP/21-22/1197/AE/ISRO/002696) and  IoE initiative (SP22231222CPETWOCTSHOC) for funding this work. 

References:

[1] Gunthe, S.S., King, S.M., Rose, D., Chen, Q., Roldin, P., Farmer, D.K., Jimenez, J.L., Artaxo, P., Andreae, M.O., Martin, S.T. and Pöschl, U., 2009. Cloud condensation nuclei in pristine tropical rainforest air of Amazonia: size-resolved measurements and modeling of atmospheric aerosol composition and CCN activity. Atmospheric Chemistry and Physics, 9(19), pp.7551-7575.

[2] Devenish, B.J., Bartello, P., Brenguier, J.L., Collins, L.R., Grabowski, W.W., IJzermans, R.H.A., Malinowski, S.P., Reeks, M.W., Vassilicos, J.C., Wang, L.P. and Warhaft, Z., 2012. Droplet growth in warm turbulent clouds. Quarterly Journal of the Royal Meteorological Society, 138(667), pp.1401-1429.

[3] Ravichandran, S. and Govindarajan, R., 2015. Caustics and clustering in the vicinity of a vortex. Physics of Fluids, 27(3).

How to cite: Vignesh, S., Sanket, A., Narayanan Unni, A., Sahu, S., S. Gunthe, S., Chaudhuri, S., Govindarajan, R., and I. Sujith, R.: Exploring the Influence of Turbulence on Droplet Size Growth and Precipitation in Warm Clouds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2702, https://doi.org/10.5194/egusphere-egu24-2702, 2024.

09:20–09:30
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EGU24-8917
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On-site presentation
Ari Laaksonen, Linnea Mustonen, Ana A. Piedehierro, Yrjö Viisanen, and André Welti

A number of studies have reported experimental CCN activation properties of water insoluble particles, mainly various minerals and soots, during the past decade or so (e.g. Kumar et al., 2011; Lathem et al., 2011, Dalirian et al., 2018). A popular theoretical framework for interpreting the results is the FHH adsorption activation theory (Sorjamaa and Laaksonen, 2007), which is a combination of the two-parameter FHH adsorption isotherm model and the Kelvin equation. However, it has become clear that the FHH activation theory tends to overpredict critical supersaturations quite substantially when the FHH parameters are determined from experimental water adsorption isotherms (Laaksonen et al., 2016; Hatch et al., 2019). A possible reason for the discrepancy is surface roughness of the particles, not accounted for in the FHH adsorption activation theory (Laaksonen et al., 2016). One way to quantify the extent of the surface roughness is through the surface fractal dimension, which can be determined e.g. with the help of nitrogen adsorption measurements. We showed earlier (Laaksonen et al., 2016) that employing the surface fractal dimension within the FHH framework does seem to improve the theoretical predictions. However, our data for water and nitrogen adsorption measurements were obtained from literature sources, and therefore the surface properties of a given mineral species employed in the adsorption measurements and in the CCN experiments were not necessarily similar. Therefore, the uncertainty limits of the surface fractal dimension -corrected predictions were rather high. Here, we compare theoretical and experimental critical supersaturations for several metal oxide and mineral aerosols. The materials used in the water and nitrogen adsorption measurements are the same as those used in the CCN experiments, allowing us to improve the reliability of our conclusions regarding the quality of the theoretical predictions.   

Dalirian, M, Ylisirniö, A., Buchholz, A., Schlesinger, D., Ström, J., Virtanen, A. and Riipinen, I. (2018). Cloud droplet activation of black carbon particles coated with organic compounds of varying solubility.  Atmos. Chem. Phys. 18, 12477-12489.

Hatch, C.D., Tumminello, P.R., Cassingham, M.A., Greenaway, A.L., Meredith, R. and Christie, M.J. (2019). Technical note: Frenkel, Halsey and Hill analysis of water on clay minerals: toward closure between cloud condensation nuclei activity and water adsorption. Atmos. Chem. Phys. 19, 13581-13589.

Kumar, P, Sokolik, I.N. and A. Nenes, A (2011). Measurements of cloud condensation nuclei activity and droplet activation kinetics of fresh unprocessed regional dust samples and minerals. Atmos. Chem. Phys. 11, 3527–3541.

Laaksonen, A., Malila, J. and Nenes A (2016). Surface fractal dimension, water adsorption efficiency, and cloud nucleation activity of insoluble aerosol. Sci. Rep. 6, 25504.

Lathem, T., Kumar, P., Nenes, A., Dufek, J., Sokolik, I.N., Trail, M. and Russell, A. (2011). Hygroscopic properties of volcanic ash. Geophys. Res. Lett. 38, L11802.

Sorjamaa, R. and Laaksonen A. (2007). The effect of H2O adsorption on cloud drop activation of insoluble particles: a theoretical framework. Atmos. Chem. Phys. 7, 6175–6180.

How to cite: Laaksonen, A., Mustonen, L., Piedehierro, A. A., Viisanen, Y., and Welti, A.: Cloud drop activation of insoluble particles: impact of surface properties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8917, https://doi.org/10.5194/egusphere-egu24-8917, 2024.

09:30–09:40
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EGU24-1773
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ECS
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On-site presentation
Manuella El Haber, Corinne Ferronato, Ludovic Fine, Anne Girroir-Fendler, and Barbara Nozière

The surface tension of sub-micron aerosol particles is expected to affect their efficiency in becoming cloud droplets. Over the last years the role of surfactants in the activation of atmospheric aerosols into cloud droplets has received a growing interest. However, most of the investigations have focused on mixtures containing only one surfactant, while the composition of atmospheric aerosol is complex. Until now, there was little experimental information on the surface properties of mixtures of surfactants with other aerosol components. In this work pendant droplet tensiometry was used to determine the adsorption isotherms and cmc of aqueous mixtures of amphiphilic surfactants (SDS, Brij35, TritonX100, TritonX114, and CTAC) with inorganic salts (NaCl, (NH4)2SO4) and soluble organic acids (oxalic and glutaric acid). Interestingly, inorganic salts and organic acids systematically enhanced the efficiency of the surfactants by further lowering the surface tension and, in some cases, the CMC. Furthermore, all the mixtures studied were strongly non-ideal, some even displaying some synergism, thus demonstrating that the common assumption of ideality for aerosol mixtures is not valid. The molecular interactions between the mixture components were either in the bulk (salting out), in the mixed surface monolayer (synergy on the surface tension) or in the micelles (synergy on the CMC) and need to be included when describing such aerosol mixtures.

Figure 1: Evolution of the minimal surface tension for mixtures of amphiphilic surfactants and organic acids (left) and two amphiphilic surfactants (right).

How to cite: El Haber, M., Ferronato, C., Fine, L., Girroir-Fendler, A., and Nozière, B.: Salting out, non‑ideality and synergism enhance surfactant efficiency in atmospheric aerosols, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1773, https://doi.org/10.5194/egusphere-egu24-1773, 2024.

09:40–09:50
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EGU24-21392
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On-site presentation
Karoline Block, Mahnoosh Haghighatnasab, Daniel G. Partridge, Philip Stier, and Johannes Quaas

Determining number concentrations of cloud condensation nuclei (CCN) is one of the first steps in the chain in analysis of cloud droplet formation, the direct microphysical link between aerosols and cloud droplets, and a process key for aerosol-cloud interactions (ACI). 

Here, we present a new CCN dataset (https://doi.org/10.26050/WDCC/QUAERERE_CCNCAMS_v1) which combines aerosol modeling with observations to better explore magnitude, source, temporal and spatial distribution of CCN numbers. The dataset features 3-D CCN number concentrations of global coverage for various supersaturations and aerosol species covering the years from 2003 to 2021 with daily frequency.

CCN are derived based on aerosol mass mixing ratios from the latest Copernicus Atmosphere Monitoring Service reanalysis (CAMSRA) in a diagnostic model that uses CAMSRA aerosol properties and a simplified kappa-Köhler framework which are suitable for global models. The emitted aerosols in CAMSRA are not only based on input from emission inventories using aerosol observations, they also have a strong tie to satellite-retrieved aerosol optical depth (AOD) as this is assimilated as a constraining factor in the reanalysis. Thus, this dataset is one of its kind as it offers lots of opportunities to be used for evaluation in models and in ACI studies.

We will illustrate the distribution and variability of such derived CCN, evaluate them with observations and have a look at some specific features this dataset provides.

Data description paper (preprint): https://essd.copernicus.org/preprints/essd-2023-172/

How to cite: Block, K., Haghighatnasab, M., Partridge, D. G., Stier, P., and Quaas, J.: Cloud condensation nuclei concentrations derived from the CAMS reanalysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21392, https://doi.org/10.5194/egusphere-egu24-21392, 2024.

09:50–10:00
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EGU24-15938
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Highlight
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On-site presentation
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Laura Wilcox, Robert Allen, Bjørn Samset, Molly MacRae, Luke Fraser-Leach, Tsuyoshi Koshiro, Paul Kushner, Anna Lewinschal, Risto Makkonen, Joonas Merikanto, Declan O'Donnell, Naga Oshima, David Paynter, Steven Rumbold, Toshihiko Takemura, Kostas Tsigaridis, and Dan Westervelt

Anthropogenic aerosol emissions are expected to change rapidly over the coming decades, with complex geographical and seasonal patterns. This is expected to drive strong, spatially varying trends in temperature, hydroclimate, and extreme events, both near and far from emission sources. These changes are poorly constrained in current models, and very sparsely represented in climate risk assessments, partly because of a lack of dedicated emission pathways and multi-model investigations.

The Regional Aerosol Model Intercomparison Project (RAMIP) is designed to quantify and bound the role of regional aerosol emissions changes in near-term climate projections. RAMIP experiments are based on the SSPs commonly used in CMIP6 Endorsed MIPs, but are designed to explore sensitivities to aerosol type and location, and provide improved constraints on uncertainties driven by aerosol radiative forcing and the dynamical response to aerosol changes. The core experiments assess the effects of different aerosol emission pathways in East Asia, South Asia, Africa and the Middle East, and North America and Europe through 2051, using a multi-ensemble-member approach in a set of 10 Earth System Models.

Based on early output from a subset of participating RAMIP models, we highlight regions where current and future aerosol reductions may lead to changes in seasonal mean climate and the frequency and severity of extreme events. We will also show examples of how the near-future evolution of temperature and precipitation extremes in Europe and Asia may be influenced by local air quality policies, and those further afield.

How to cite: Wilcox, L., Allen, R., Samset, B., MacRae, M., Fraser-Leach, L., Koshiro, T., Kushner, P., Lewinschal, A., Makkonen, R., Merikanto, J., O'Donnell, D., Oshima, N., Paynter, D., Rumbold, S., Takemura, T., Tsigaridis, K., and Westervelt, D.: Climate responses to regional aerosol emissions: Early multi-model results from RAMIP, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15938, https://doi.org/10.5194/egusphere-egu24-15938, 2024.

10:00–10:10
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EGU24-1229
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ECS
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Highlight
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On-site presentation
Guy Dagan and Eshkol Eytan

Understanding the impact of anthropogenic aerosols on extreme precipitation is of both social and scientific significance. While anthropogenic absorbing aerosols are known to influence Earth's energy balance and atmospheric convection, their role in extreme events remains unclear. This study employs convective-resolving radiative-convective-equilibrium simulations to comprehensively investigate the impact of absorbing aerosols on extreme tropical precipitation. Our findings reveal an underappreciated mechanism whereby absorbing aerosols can, under certain conditions, significantly intensify extreme precipitation despite reducing the mean. Notably, we demonstrate that a mechanism previously observed in much warmer (hothouse) climates—where intense rainfall alternates with multi-day dry spells—can manifest under current realistic conditions due to the influence of absorbing aerosols. This mechanism operates when an aerosol perturbation shifts the lower tropospheric radiative heating rate to positive values, generating a strong inhibition layer. Our work underscores an additional potential effect of absorbing aerosols, with implications for climate change mitigation and disaster risk management.

How to cite: Dagan, G. and Eytan, E.: Absorbing aerosols can strongly enhance extrem precipitation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1229, https://doi.org/10.5194/egusphere-egu24-1229, 2024.

Coffee break
Chairpersons: Edward Gryspeerdt, Anna Possner
Aerosol-Cloud Interactions
10:45–10:55
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EGU24-21400
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solicited
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Highlight
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On-site presentation
Franziska Glassmeier and Benjamin Hernandez

The evolution of stratocumulus cloud decks is governed by three timescales: the large-scale evolution of the boundary layer, the mesoscale evolution of liquid water path and cloud fraction, and the microscale processes of cloud microphysics and aerosol-cloud interactions. Our quantitative understanding of aerosol-cloud-climate cooling is especially challenged by the mesoscale response of stratocumulus decks to aerosol perturbations. This response can on the one hand be muted because cloud adjustments partially compensate an initial effect, a feature known as buffering or resilience. On the other hand, stratocumulus may respond by drastic transitions between the closed- and open-cell morphologies or into the shallow-cumulus regime. We will conceptualize this behavior from the perspective of dynamical-systems theory. Our description can be visualized as a quasi-potential landscape. This landscape quantifies the resilience of mesoscale cloud states to perturbations and charts transition pathways. Building on this, we will explore implications for the quantification of adjustments, especially in cloud fraction.

How to cite: Glassmeier, F. and Hernandez, B.: A dynamical-systems perspective on aerosol-stratocumulus interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21400, https://doi.org/10.5194/egusphere-egu24-21400, 2024.

10:55–11:05
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EGU24-11712
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ECS
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On-site presentation
Fani Alexandri, Felix Müller, Goutam Choudhury, Peggy Achtert, Torsten Seelig, and Matthias Tesche

Aerosol-cloud interactions are of central importance for understanding climate processes but remains the largest uncertainty associated with climate change. Hence, the effective radiative forcing (ERF) due to ACI and rapid adjustments (ERFaci) is still assessed only with medium confidence. An important part of this uncertainty originates from the difficulty of quantifying ACI using observations, especially for ice-containing clouds. In this study, we present a novel Cloud-by-Cloud (CxC) approach for studying ACI in satellite observations that merges properties of individual clouds that have been tracked from geostationary satellite observations with height-resolved concentrations of cloud condensation nuclei (nCCN) and ice nucleating particles (nINP) from polar-orbiting lidar data. This approach lays the foundations for better understanding of ACI through a thorough investigation of matched aerosol-cloud cases at cloud level. The methodology is applied to satellite observations over Central Europe and Northern Africa for several years, resulting in a bottom-up dataset of combining parameters that can be stratified accordingly for assessing the impact of changes in cloud-relevant aerosol concentrations on the surrounding quality assured liquid and ice-containing clouds. The first preliminary results of this novel CxC approach are promising and constitute a step forward in the quantification of ERFaci from space.

How to cite: Alexandri, F., Müller, F., Choudhury, G., Achtert, P., Seelig, T., and Tesche, M.: A cloud-by-cloud approach for studying aerosol-cloud interaction in satellite observations , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11712, https://doi.org/10.5194/egusphere-egu24-11712, 2024.

11:05–11:15
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EGU24-12779
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On-site presentation
Tom Goren, Odran Sourdeval, Jan Kretzschmar, and Johannes Quaas

The estimation of cloud radiative forcing (RFaci), arising from aerosol-cloud interactions (also known as the first indirect effect), relies on approximating cloud albedo susceptibility (β) to changes in droplet concentration. β depends on both cloud albedo and droplet concentration, which are observable through satellite observations. Typically, satellite data is spatially aggregated to coarser resolutions, such as 1 × 1° scenes. However, at these spatial scales, cloud albedo tends to be heterogeneous, while the β approximation assumes homogeneity. This study demonstrates that the common practice of aggregating satellite data and neglecting cloud albedo heterogeneity results in an average overestimation of 10% in previous RFaci estimates.

How to cite: Goren, T., Sourdeval, O., Kretzschmar, J., and Quaas, J.: Spatial Aggregation of Satellite Observations Leads to an Overestimation of the Radiative Forcing due to Aerosol-Cloud Interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12779, https://doi.org/10.5194/egusphere-egu24-12779, 2024.

11:15–11:25
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EGU24-21153
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Highlight
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On-site presentation
Hailing Jia, Johannes Quaas, and Otto Hasekamp

Aerosol–cloud interactions contribute substantially to uncertainties in anthropogenic forcing, in which the sensitivity of cloud droplet number concentration (Nd) to aerosol plays a central role. Here we use satellite observations to show that the aerosol–Nd relation (in log–log space) is not linear as commonly assumed. Instead, the Nd sensitivity decreases at large aerosol concentrations due to the transition from aerosol-limited to updraft-limited regime, making the widely used linear method problematic. The similar nonlinear behavior is also observed in weekly cycles; specifically, polluted conditions exhibit a reduced amplitude of weekly cycles in Nd compared to clean conditions with similar aerosol perturbations.  A sigmoidal transition is shown to adequately fit the data. When using this revised relationship, the additional warming that arises from air pollution mitigation is delayed by two to three decades in heavily polluted locations, compared to the linear relationship. This cloud-mediated climate penalty will manifest markedly starting around 2025 in China and 2050 in India after applying the strongest air quality policy, underlining the urgency of mitigating greenhouse gas emissions.

How to cite: Jia, H., Quaas, J., and Hasekamp, O.: Nonlinearity of the cloud response postpones climate penalty of mitigating air pollution in polluted regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21153, https://doi.org/10.5194/egusphere-egu24-21153, 2024.

11:25–11:35
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EGU24-12965
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Virtual presentation
Bastiaan van Diedenhoven, McKenna Stanford, Ann Frindlind, Andrew Ackerman, Qian Xiao, Jian Wang, Otto Hasekamp, Snorre Stamnes, Brian Cairns, Andrzej Wasilewski, and Mikhail Alexandrov

The evolution of cumulus congestus within tropical oceanic and maritime environments is modulated by the interaction of convective dynamics, liquid- and ice-phase microphysical processes, aerosol loading, and entrainment of ambient environmental air. Characterizing this evolution requires robust observational constraints of aerosol properties and cloud macrophysics and microphysics. The NASA Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) field campaign in 2019 targeted growing cumulus congestus clouds using airborne in situ and remote sensing platforms. In situ aircraft microphysical measurements and retrievals from the Research Scanning Polarimeter (RSP) both show that cloud droplet number concentrations decrease and effective radius increases with increasing cloud top height, with droplet size distributions (DSDs) that broaden with height. These observed components are responsive to an active collision-coalescence process that produce millimeter-sized drops, onsetting warm-rain formation. Here, we present an analysis of CAMP2Ex RSP data showing the evolution of droplet number concentrations and DSDs with height and its variation with RSP-retrieved aerosol number concentrations. For one case study (RF14, 9/25/2019), we perform large eddy simulations (LES) at 100-m horizontal grid spacing using bin and bulk microphysics schemes. Detailed multi-modal, vertically resolved aerosol measurements from the Fast Integrated Mobility Spectrometer (FIMS) are used as input. The relative ability of the bulk and bin schemes to produce the observed DSD evolution, from activation to warm-rain production, is evaluated. Sensitivity experiments are performed to assess the roles of height-varying aerosol concentrations, rain-forming collision-coalescence, and entrainment in realizing observed droplet number concentration and effective radius profiles. Additionally, we share the prospect of detailed aerosol properties, droplet number concentrations, and DSDs, similar to as acquired by RSP, becoming available from polarimeters on NASA’s PACE satellite mission, launched in early 2024.

How to cite: van Diedenhoven, B., Stanford, M., Frindlind, A., Ackerman, A., Xiao, Q., Wang, J., Hasekamp, O., Stamnes, S., Cairns, B., Wasilewski, A., and Alexandrov, M.: Evaluating Droplet Size Distribution Evolution in Aerosol-constrained Simulations of Tropical Cumulus Congestus against Airborne Polarimetry Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12965, https://doi.org/10.5194/egusphere-egu24-12965, 2024.

11:35–11:45
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EGU24-1828
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ECS
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On-site presentation
Moa K. Sporre, Linda Hartman, Shubham Singh, and Johan Friberg

Fog can substantially impact air traffic by inhibiting or aggravating take-off or landing. This can result in large economical costs and even loss of human lives. In this study we investigate how fog frequency has changed at Swedish airports over time. The large north-south extent of Sweden with strong gradients in aerosol concentrations makes it an interesting study area for aerosol impact on fog. We base the study on visibility data from 14 airports. Most visibility data from the airports start in the 1970s but some stations have data before this and some have measurements that start in the 1980s. The visibility measurements are combined with data on air temperature, wind speed, wind direction, and air pressure from the airports. In the study we also include measurements aerosol proxies, namely SO2 in the air from 4 stations and SO42- in rainwater from 10 stations in Sweden. Moreover, emission data of SO2 from Europe from 1970 to present day has been analysed. 
The analysis shows that the fog frequency changes in Sweden vary with location of the airport. At four airports in southern Sweden, the fog frequency show a statistically significant decrease when comparing the periods before and after 1995. The most prominent changes has occurred at the airports close to Malmö and Gothenburg. The annual fog frequency for these stations changes from 5-6 % in the 1980s to 3-4 % in the 2010s with higher changes during winter. For the airports located further north there is no decrease in fog frequency. Some airports in the northern part of Sweden show a statistically significant increase in fog frequency, though the fog frequencies are lower there than in southern Sweden. 
We find that the fog frequency changes in Southern Sweden correlate well with changes in air of SO2, rainwater SO42- concentrations, which both show strong decreases since the 1970 and 1980s in southern Sweden. The changes in these concentrations are much weaker further north in Sweden. The fog frequency changes in southern Sweden thus seems to be driven by changes in the load of hygroscopic aerosol. The fog changes in northern Sweden correlate well with temperature, which is increasing at all airports. The rising temperatures in the north could contribute with more favorable conditions for fog formation at these airports where it previously was to cold for fog formation during parts of the year. Out results indicate that the work on air pollution mitigation in Europe over the past 50 years has reduced fog impact on air traffic in southern Sweden.    

How to cite: Sporre, M. K., Hartman, L., Singh, S., and Friberg, J.: Long term changes in fog frequency at Swedish airports and its potential drivers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1828, https://doi.org/10.5194/egusphere-egu24-1828, 2024.

11:45–11:55
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EGU24-3278
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Highlight
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On-site presentation
brian soden and chanyoung park

Anthropogenic aerosols and their interactions with clouds play a crucial role in regulating the Earth's radiation balance and introduce significant uncertainties in climate change projection. The effective radiative forcing due to aerosol-cloud interactions (ERFaci) is particularly difficult to quantify, leading to uncertainties in model projections of cloud feedback and climate sensitivity. Analysis of CMIP6 model simulations indicate that models with a strongly-positive cloud feedback tend to be offset with strongly negative ACI, leading to similar projections of global mean temperatures during the historical period. However, because anthropogenic aerosol primarily occur in the Northern Hemisphere, the hemispheric asymmetry in warming (NH-SH) differs significantly between low and high ACI models, with observed trends being more consistent with low ACI (weak cloud feedback) models. However, recent satellite estimates of ERFaci based on cloud controlling factors (CCF) is more consistent with high ACI models.  We evaluate the CCF approach using a series of perfect model experiments. The magnitude of ERFaci depends on two factors: the amount of aerosol loading between the pre-industrial and present day, and the susceptibility of cloud albedo and cloud lifetime to that aerosol loading. By comparing observationally-constrained estimates of ERFaci with CMIP6 model simulations, we quantify the contributions of aerosol loading differences and cloud susceptibility to the inter-model spread. We find that explicitly accounting for the role of aerosol activation on cloud droplet formation is essential to obtaining accurate estimates of ERFaci, and when this is done, the satellite constrained estimates of ERFaci are more consistent with low ACI models.

How to cite: soden, B. and park, C.: Reconciling Top-Down and Bottom-Up Estimates of the Effective Radiative Forcing from Aerosol-Cloud Interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3278, https://doi.org/10.5194/egusphere-egu24-3278, 2024.

11:55–12:05
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EGU24-15150
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On-site presentation
Harri Kokkola, Muhammed Irfan, Antti Lipponen, Silvia Calderon, and Antti Arola

Determining the susceptibilities of cloud properties to perturbations in aerosols has been a persisting challenge in climate research. For example, satellite-retrieved susceptibility of cloud droplet number concentration (CDNC) to changes in cloud condensation nuclei (CCN) varies regionally, also having opposite correlations over land and ocean. Over the oceans, the correlation between CCN and CDNC is positive and in many cases, with a proper regression method, the dlogCDNC/dlogCCN exceeds 1. On the other hand, over land, many studies have found a negative correlation. As our preliminary global climate model simulations give qualitatively similar results to satellite retrievals, we have used the model together with reanalysis data of aerosol, meteorological properties, and cloud properties to interpret how other parameters such as cloud activation updrafts and vertical mixing of aerosol affect the satellite derived CCN vs CDNC correlations. In this study, we focus on ocean regions determining how these different atmospheric properties affect the derived slope between CCN and CDNC. Our results indicate that as satellite derived CCN is a columnar value, does not properly represent the true variability of cloud base CCN. Thus, the mixing of aerosol as well as cloud activation updrafts cause biases in the satellite determined CCN vs CDNC correlations.

How to cite: Kokkola, H., Irfan, M., Lipponen, A., Calderon, S., and Arola, A.: Using a global aerosol model to interpret satellite-derived aerosol-cloud interactions , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15150, https://doi.org/10.5194/egusphere-egu24-15150, 2024.

12:05–12:15
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EGU24-9292
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ECS
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On-site presentation
Jianqi Zhao, Xiaoyan Ma, Johannes Quaas, and Hailing Jia

This study employed the WRF-Chem-SBM model which couples spectral-bin cloud microphysics (SBM) and online aerosol module (MOSAIC) to investigate aerosol-cloud interactions in liquid-phase clouds over eastern China and its adjacent oceans. The results indicate that with an increase in aerosol number concentration (Na), cloud droplet number concentration (Nd) exhibits a trend of initially increasing and then decreasing, both over land and ocean. The difference lies in the stronger convective and land surface effects over land, leading to more intense activation, while over the ocean, weaker supersaturation and richer water vapor content result in weaker activation but more favorable conditions for cloud droplet growth. Cloud processes over land are more intense than over the ocean, but the cloud liquid water content (CLWC) in both regions shows a similar trend with the variation of Nd. In precipitating clouds with richer water content and stronger intracloud processes, as Nd increases, the cloud droplet effective radius decreases, and CLWC exhibits a gradual increase followed by a rapid decrease. In non-precipitating clouds with lower water content and weaker intracloud processes, the increase in Nd leads to a more gradual growth of CLWC, and the subsequent decrease in CLWC is also more subtle. Furthermore, this study discusses the impact of meteorological and aerosol conditions on aerosol activation and cloud development. Environments with a moderate Na are more conducive to aerosol activation, while in environments with low to moderate Na, CLWC exhibits faster growth. Compared to humidification, cooling has a more significant effect on aerosol activation and CLWC growth.

How to cite: Zhao, J., Ma, X., Quaas, J., and Jia, H.: Exploring aerosol-cloud interactions in liquid-phase clouds over eastern China and its adjacent ocean using the WRF-Chem-SBM model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9292, https://doi.org/10.5194/egusphere-egu24-9292, 2024.

12:15–12:25
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EGU24-2062
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ECS
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On-site presentation
Wenhui Zhao, Yi Huang, Steven Siems, Michael Manton, and Daniel Harrison

The important role of warm clouds in regulating the regional energy balance and ocean temperature, that are directly linked to the thermal coral bleaching events, has been increasingly recognised over the Great Barrier Reef (GBR). These shallow clouds, however, are by their nature sensitive to perturbations in both their thermodynamic environment and microphysical background. In this study, we employ the Weather Research and Forecasting (WRF) model with a convection-permitting configuration at 1 km resolution to examine the interactions between the warm clouds and different local forcings over the GBR. A range of local forcings including local aerosol loading, coastal topography, and sea surface temperature (SST) is examined.

Our simulations show a strong response of cloud microphysical properties, including cloud droplet number concentration (CDNC), liquid water path (LWP), and precipitation to the changes in atmospheric aerosol population over the GBR. Higher CDNC and LWP correlated to increased aerosol number concentration leads to a rise in shortwave cloud radiative effect, though the magnitude is small, over both the mountains and upwind over the GBR. While cloud fraction shows little responses, a slight deepening of the simulated clouds is evident over the upwind region in correspondence to the increased aerosol number concentration. A downwind effect of aerosol loading on simulated cloud and precipitation properties is further noted. In consideration of the coastal topography, cloud fraction and accumulated precipitation are strongly sensitive to orographic forcing over the GBR. Orographic lifting and low-level convergence are found to be crucial in explaining the cloud and precipitation features over the coastal mountains downwind of the GBR. However, clouds over the upwind ocean are more strongly constrained by the trade wind inversion, whose properties are, in part, regulated by the coastal topography. Finally, on the scales considered in our study, the warm cloud fraction and the ensuant precipitation over the GBR show only a small response to the local SST forcing, with this response being tied to the simulated cloud type.

How to cite: Zhao, W., Huang, Y., Siems, S., Manton, M., and Harrison, D.: Interactions of warm cloud, precipitation, and local forcings over the Great Barrier Reef: Insights from convection-permitting simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2062, https://doi.org/10.5194/egusphere-egu24-2062, 2024.

Lunch break
Chairpersons: Benjamin Heutte, Ruth Price, Jennie L. Thomas
14:00–14:10
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EGU24-12164
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Highlight
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On-site presentation
Po-Lun Ma

The role of aerosol and aerosol-cloud interactions (ACI) in the Earth system is a major source of uncertainty in projections of Earth’s future climate and in interpreting how the climate has evolved in the past. The “Enabling Aerosol-cloud interactions at GLobal convection-permitting scalES (EAGLES)” project aims to achieve unprecedented realism in predictions of aerosol and ACI in the next-generation Earth system models. The effort includes improving the representation of aerosol and ACI processes with physics-based or data-driven methods, readying the parameterizations for kilometer-scale simulations, and constraining the model using process-oriented diagnostics based on both satellite and in-situ measurements. By combining process models, large-eddy simulations, and observational data from ARM, satellites, and other sources, stubborn model biases associated with resolution and physics have been addressed accordingly. We demonstrate that improved atmospheric simulations can be achieved with better physics, better integration with data, and better software. We also identify new opportunities for improvements.

How to cite: Ma, P.-L.: Enabling Aerosol-cloud interactions at GLobal convection-permitting scalES (EAGLES), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12164, https://doi.org/10.5194/egusphere-egu24-12164, 2024.

14:10–14:20
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EGU24-20572
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Highlight
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On-site presentation
Philip Stier, Philipp Weiss, Ross Herbert, and Maor Sela

Aerosol effects on convective clouds and climate mediated via radiative and microphysical perturbations remain highly uncertain. Microphysical perturbations are generally not included in current climate models due to the simplified representation of convective clouds in existing parameterisations. Progress has been made through regional cloud resolving modelling, however such simulations often neglect energy and water budget constraints and the coupling to larger scales.

The emergence of global km-scale climate models provides a significant opportunity to advance our understanding of aerosol-convection interactions. Here we present results from a hierarchy of global km-scale atmospheric model simulations using ICON, investigating aerosol effects on convective clouds. 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, provide fascinating insights into the physical processes underlying aerosol effects on convection and into the interaction of local perturbations with the larger scale dynamics – but neglect key aerosol-convection interactions. These simulations highlight the importance of the radiatively mediated pathway for tropical convective clouds, with significant impacts on the diurnal cycle of cloud properties and precipitation over the Amazon and the Congo basin – and interactions with the large-scale dynamics for perturbations over the Pacific warm pool region.

We contrast our results from idealised simulations with simulations including explicit aerosols, enabled by a novel reduced complexity aerosol scheme suitable for global km-scale models, HAM-Lite. Comparison of the idealised simulations with prescribed aerosol perturbations and the simulations with explicit aerosols, provides new insights into the complexity of aerosol-convection interactions. This study provides a testbed for a future global km-scale model intercomparison project focusing on aerosol effects as part of the GEWEX Aerosol Precipitation (GAP) initiative.

How to cite: Stier, P., Weiss, P., Herbert, R., and Sela, M.: Aerosol effects on convective clouds in global km-scale models – from idealised aerosol perturbations to explicit aerosol modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20572, https://doi.org/10.5194/egusphere-egu24-20572, 2024.

14:20–14:30
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EGU24-6816
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ECS
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On-site presentation
Huihui Wu, Nicholas Marsden, Paul Connolly, Michael Flynn, Paul Williams, Graeme Nott, Kezhen Hu, Declan Finney, Navaneeth Thamban, Keith Bower, Alan Blyth, Thomas Choularton, Martin Gallagher, and Hugh Coe

Aerosol particles can affect the formation and properties of clouds by acting as cloud condensation nuclei (CCN) and ice nucleating particles (INP). The accurate representation of aerosol size distribution and composition along with cloud nucleating properties play an important role in describing aerosol-cloud interactions. The Deep Convective Microphysics Experiment (DCMEX) is a project aimed at improving the representation of microphysical processes in deep convective clouds. The DCMEX campaign (July to Aug 2022) was conducted using the UK FAAM (Facility for Airborne Atmospheric Measurements) BAe-146 Atmospheric Research Aircraft and characterized the aerosol-cloud system over the isolated Magdalena Mountain region in New Mexico. The aircraft was equipped with a range of online instruments to measure aerosol chemical composition (i.e., Aerosol Mass Spectrometry, AMS; Laser Ablation Aerosol Particle Time of Flight mass spectrometry, LAAPToF) and aerosol size distributions, as well as cloud microphysics.

A 6-days backward dispersion analysis of this region shows that the air source flow transferred from Northwest (NW, California coast) to Southeast (SE, Gulf of Mexico) during the campaign period. This air mass source change coincided with changes in meteorological parameters including such as enhancement of convection available potential energy (CAPE), decreased cloud-base height, and increased boundary layer humidity. The aerosol size distribution and chemical composition in out-of-cloud runs also show variations under different air mass source conditions. Larger sulphate and lower organic contributions were observed in the sub-micron (<1 μm) aerosol mass fraction in the SE airflow when compared to flow from the NW, with the organic components more oxidized. The LAAPToF single particle measurements (0.5-2.5 μm) indicate more aged sea salt in number fraction within the SE ocean flow. The calculated kappa values suggest more hygroscopic aerosols with the source transfer. Number size distributions indicate enhanced Aiken-mode particles when the air mass source changed.

A bin-microphysics model was employed to simulate the warm cloud development in this convective system. The simulation results show that both the change of aerosol characteristics and cloud-base conditions affect the warm cloud development, which follow the trends seen in the cloud microphysics observations. Initial cloud base conditions (i.e., initial temperature and relative humidity) mainly affected cloud properties by altering the water mixing ratios while aerosol characteristics mainly affected the initial cloud droplet number concentrations.

Next, we will combine these online aerosol measurements with detailed cloud microphysical measurements and offline INP analysis, to investigate the contributory effect of aerosols on primary ice formation in this deep-convection system and their relationship to secondary ice production processes.

How to cite: Wu, H., Marsden, N., Connolly, P., Flynn, M., Williams, P., Nott, G., Hu, K., Finney, D., Thamban, N., Bower, K., Blyth, A., Choularton, T., Gallagher, M., and Coe, H.: Observations of ambient aerosol and warm cloud formation in a New Mexico summer deep-convection system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6816, https://doi.org/10.5194/egusphere-egu24-6816, 2024.

Polar aerosols and clouds
14:30–14:40
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EGU24-16865
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ECS
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On-site presentation
Julia Asplund, Annica ML Ekman, Gabriel Freitas, Mats A. Granskog, Benjamin Heutte, Remy Lapere, Morven Muilwijk, Tuomas Naakka, Julia Schmale, Jennie Thomas, and Paul Zieger

Aerosol-cloud interactions remain among the most uncertain key parameters in the fast-changing Arctic climate system. Arctic clouds often consist of both liquid droplets and ice crystals, the abundance of which is constrained by the availability of ice nucleating particles (INP). We present observations of fluorescent primary biological aerosol particles (fPBAP), shown to be potent INP, obtained during the Arctic Ocean 2018 expedition onboard the Swedish icebreaker Oden in August- September of 2018, at the North Pole. The fPBAP were recorded on a single-particle level using a Multiparameter Bioaerosol Spectrometer, as a part of a complete setup for measuring physical and chemical aerosol properties.  Potential sources of fPBAP during an extended period of high concentrations are investigated using a combination of auxiliary measurements, trajectory analysis, remote sensing data, ocean biogeochemistry reanalysis data, and model experiments with WRF-Chem. Our evidence suggests that the observed case of increased fPBAP concentration at the North Pole was caused by transport of fPBAP enriched marine aerosol from a source within the Arctic region, but in open water south of the pack ice. We also highlight how future interdisciplinary efforts can be used more efficiently to improve the source mapping of Arctic fPBAP, which is needed to assess their overall climate-relevance in the polar regions.

How to cite: Asplund, J., Ekman, A. M., Freitas, G., Granskog, M. A., Heutte, B., Lapere, R., Muilwijk, M., Naakka, T., Schmale, J., Thomas, J., and Zieger, P.: Observation of fluorescent primary biological particles at the North Pole: A case of inter-coupled system behaviour?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16865, https://doi.org/10.5194/egusphere-egu24-16865, 2024.

14:40–14:50
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EGU24-11095
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ECS
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On-site presentation
Tómas Zoëga, Trude Storelvmo, and Kirstin Krüger

Effusive volcanic eruptions are known to impact climate through the emission of sulphur dioxide and subsequent formation of sulphate aerosols. These aerosols affect radiative transfer in the atmosphere, both directly by scattering sunlight and indirectly through aerosol-cloud interactions. By scattering sunlight, the direct aerosol effect leads to surface cooling. Changes in cloud properties as a result aerosol-cloud interactions, on the other hand, lead to both reflection of sunlight and trapping of outgoing thermal emissions from the ground. Clouds, therefore, have the potential to either cause surface warming or cooling, depending on factors such as the cloud response to the volcanic aerosols and the availability of sunlight.

We perform a series of simulations using the Community Earth System Model with the Community Atmosphere Model (CESM2-CAM6) to simulate the climate impacts of northern hemisphere, high latitude, effusive volcanic eruptions. We construct a standard eruption scenario, using the 2014-15 Holuhraun eruption in Iceland as a reference. The Holuhraun eruption released up to 9.6 Tg SO2 over a period of six months, from September 2014 to February 2015, with the emission rate gradually decreasing over time. We apply several different magnitude scalings to this standard scenario and vary the timing of the eruption. This allows us to analyse the climate response as a function of both the eruption size and season.

For eruptions starting in winter, we find significant surface warming in our simulations as a result of trapping of outgoing thermal emissions in the absence of sunlight. This warming is mainly confined to the Arctic but also appears over parts of northern Eurasia and North-America, albeit to a lesser extent. This is consistent with our previous work on the Holuhraun eruption where we found evidence for winter surface warming over the Greenland Sea as a result of that eruption, both in model simulations and observations.

Conversely, we find surface cooling during summertime eruptions. The spatial distribution of the cooling pattern is different from the winter warming as the cooling predominantly occurs over the Eurasian and North-American continents and is hardly visible in the Arctic. Furthermore, based on preliminary results, whereas the Arctic winter warming is mainly due to aerosol-cloud interactions, the continental summer cooling stems mostly from the direct aerosol effect. Our results indicate a non-linear relationship between the surface air temperature response and the eruption size.

How to cite: Zoëga, T., Storelvmo, T., and Krüger, K.: Surface climate response to the size and season of northern hemisphere, high latitude, effusive volcanic eruptions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11095, https://doi.org/10.5194/egusphere-egu24-11095, 2024.

14:50–15:00
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EGU24-19084
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ECS
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On-site presentation
Basudev Swain, Vountas Marco, Deroubaix Adrien, Lelli Luca, Gunthe Sachin S., Bösch Hartmut, and Burrows John P.

The Arctic is currently warming rapidly, at a rate four times higher than the global average. This warming has significant consequences, leading to increased precipitation in the Arctic. Aerosols play a crucial role in cloud formation, cloud condensation nuclei (CCNs) and ice-nucleating particles (INPs), influencing rain and snowfall. However, uncertainties remain in the modelling of aerosols and their impact on precipitation due to a lack of high-resolution spatio-temporal observations. This is particularly the case in the central Arctic cryosphere due to the presence of extensive cold, bright snow and ice surfaces coupled with widespread cloud cover.

This study addresses the observational data gap and provides an opportunity to refine model simulations at different spatio-temporal scales. We achieve this by using total aerosol optical depth (AOD) datasets generated by the AEROSNOW algorithm over the extensive central Arctic cryosphere. AEROSNOW retrieves AOD data using top-of-atmosphere reflectance measurements obtained through the Advanced Along-Track Scanning Radiometer (AATSR) aboard the ENVISAT satellite, spanning from 2003 to 2011. AEROSNOW integrates an aerosol retrieval algorithm with a rigorous cloud masking scheme and intro-
duces a novel quality flagging methodology tailored for the central Arctic region (≥ 72°N).

Using the AEROSNOW retrieved dataset for the central Arctic, we evaluate different models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). Our results show significant differences in the spatio-temporal aerosol load and its annual and seasonal variations with precipitation. In particular, there is a decrease in aerosol loading that coincides with increased precipitation along the northern periphery of Alaska and the Bering Sea.

Significant discrepancies and variations of up to 6.2 mm/day in precipitation are observed between models, with higher aerosol loading leading to lower precipitation and vice versa. Furthermore, the spatially averaged multi-model mean overestimates aerosol concentrations in spring and underestimates them in summer compared to satellite observations. The CMIP6 models do not reproduce the seasonal variations in aerosol distribution seen with AEROSNOW, particularly an increase in aerosol loading during the summer coinciding with the sea ice retreat cycle. These discrepancies may be due to the lack of advanced natural aerosol formation mechanisms in the models, as a consequence of Arctic warming, and exposure to open
ocean emissions.

In summary, our study has led us to speculate that as model sophistication increases, modelled aerosol processes become increasingly uncertain. Ultimately, this investigation has the potential to elucidate the critical link between aerosols and the prevailing rain-dominated Arctic conditions under ongoing Arctic warming in future CMIP projects.

How to cite: Swain, B., Marco, V., Adrien, D., Luca, L., Sachin S., G., Hartmut, B., and John P., B.: Assessing Model simulation for central Arctic aerosol load by usingAEROSNOW dataset: Relevance for precipitation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19084, https://doi.org/10.5194/egusphere-egu24-19084, 2024.

15:00–15:10
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EGU24-17179
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On-site presentation
Amélie Kirchgaessner, Markus Frey, Floor van den Heuvel, Tom Lachlan-Cope, Ananth Ranjithkumar, and Xin Yang

Arctic clouds are still poorly represented in climate models. An important reason for this is our lack of knowledge regarding the various sources of natural aerosol in the high Arctic. Recent field campaigns have provided evidence that over sea ice blowing snow can act as a source of sea salt aerosol (SSA). This source can account for the maximum in SSA that occurs in the Polar Regions during winter and spring. SSA can influence the regional climate through the indirect radiative effect, but also through the role it plays as nucleation particle in cloud formation. Its contribution to and potential as ice nucleating particle (INP) is still largely unknown though. 

 Here we will present offline samples of airborne aerosol taken in the Central Arctic during MOSAiC focussing on the transition period from winter to spring. The samples comprise of quasi-ciontinuous low-volume air filter samples taken in the British Antarctic Survey’s aerosol lab container on board of RV Polarstern, weekly snow samples from the ice floe, and filter samples taken by tethered balloon. These samples were analysed for their ice nucleating characteristics using a peltier cold stage and applying a machine learning algorithm to the images taken during the cooling process.

Initial results confirm an increased presence of INP in both the airborne and snow samples at the turn from winter to spring. 

How to cite: Kirchgaessner, A., Frey, M., van den Heuvel, F., Lachlan-Cope, T., Ranjithkumar, A., and Yang, X.: Ice nucleating properties of air filter and snow samples taken in the Central Arctic during MOSAiC, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17179, https://doi.org/10.5194/egusphere-egu24-17179, 2024.

15:10–15:20
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EGU24-4358
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ECS
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On-site presentation
Erin Raif, Sarah Barr, Mark Tarn, James McQuaid, Martin Daily, Steven Abel, Paul Barrett, Keith Bower, Paul Field, Kenneth Carslaw, and Benjamin Murray

Concentrations of ice-nucleating particles (INPs) were measured in springtime cold-air outbreaks over the Norwegian and Barents Seas using filter samples taken on board the FAAM BAe-146 aircraft. These measurements of INP concentrations were comparable to the highest INP concentrations previously observed in the Arctic and were similar to typical terrestrial midlatitude INP concentrations. This is important because shallow cloud systems such as those in mid- to high-latitude cold-air outbreaks are highly sensitive to INPs and are a highly uncertain contributor to cloud feedbacks. 

To investigate the types of aerosol responsible for this high INP concentration, we used aerosol-size data from underwing optical probes to derive an active site density of the INP samples. By comparing to laboratory derived active site densities of different aerosol types, this suggested that sea spray was unlikely to be a dominant INP type and that there were likely to be strong biological and dust components to the INP population. Scanning electron microscopy with energy-dispersive spectroscopy used on selected filters revealed that sub-micron particles were dominantly sulphates and carbonaceous, while super-micron particles were dominantly mineral dust.

Samples taken above the cloud decks had greater active site densities than those below, and back-trajectory analysis and meteorological conditions suggested a lack of obvious local INP sources. We hypothesise that the high INP concentration is most likely to be associated with aged aerosol that has accumulated over the Arctic (Arctic Haze).  These high INP concentrations imply that these clouds may have a more negative cloud-phase feedback than their Southern Ocean equivalents.

How to cite: Raif, E., Barr, S., Tarn, M., McQuaid, J., Daily, M., Abel, S., Barrett, P., Bower, K., Field, P., Carslaw, K., and Murray, B.: Ice-nucleating particles in springtime cold-air outbreaks associated with Arctic haze, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4358, https://doi.org/10.5194/egusphere-egu24-4358, 2024.

15:20–15:30
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EGU24-5460
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Highlight
|
On-site presentation
Julia Schmale, Athanasios Nenes, Iris Thurnherr, Silvia Henning, Christian Tatzelt, Andrea Baccarini, and Martin Gysel-Beer

The Southern Ocean is a key component of the climate system, where clouds especially matter. Therefore, it is important to correctly simulate clouds in climate models. Even though there has been substantial improvement, climate models still struggle in their representation of cloud microphysical properties.

In this study, based on data from the Antarctic Circumnavigation Expedition in 2026/17, we explore environmental factors, such as stable water isotopes in atmospheric water vapor, cyclones and boundary layer stability, that influence the abundance of aerosols and their size distribution, the most important variables for particles to act as cloud condensation nuclei (CCN), along a latitudinal gradient from 35°S to 75°S. Moreover, we use a cloud parcel model to estimate the cloud droplet number concentration and cloud maximum supersaturation (SS) based on the particles’ size distribution, hygroscopicity and measured updraft velocities.

Based on the latitudinal gradient of observed CCN, which features a distinct minimum around 60°S, and the carbon monoxide mixing ratios, which reach background levels south of 60°S indicating absence of anthropogenic influence, we compare aerosol properties north and south of this latitude. The northern aerosol population features two distinct Aitken modes, a nucleation mode and a mode with a Hoppel minimum around 60 nm. The presence of cyclones reduces the particle number concentrations over all diameters. We also observe a stronger Aitken mode presence in unstable boundary layer conditions, where downward mixing of freshly formed particles in the outflow of clouds in the free troposphere can occur. The southern population features only three modes, a nucleation mode and two distinct bimodal distributions with Hoppel minima around 70 nm. Only in stable boundary layer conditions an Aitken mode emerges in the 75th percentile that is larger in particle number than the accumulation mode, pointing towards a potential source of condensable vapors from the ocean surface that grow the Aitken mode, leading to observably higher kappa values. The Aitken mode is further associated with air masses with relatively less depletion in d18O, pointing towards a marine source further north.

The cloud droplet number concentration simulations feature the same latitudinal pattern as the measured CCN with the “dip” around 60°S. This is consistent with droplet observations from satellites. Interestingly, the simulated cloud maximum SS tends to increase with latitude, from roughly 0.27% at 40°S towards 0.43% at 75°S. To estimate the sensitivity of clouds towards available aerosol particles, we form the ratio of the particle number concentration larger than the observed Hoppel minimum over the simulated cloud droplet number concentrations. We find that clouds north and south of 60°S experience elevated sensitivity (ratio < 1) to aerosol concentrations in 23 % and 27 % of the time, respectively. This demonstrates that the Southern Ocean cloud regime is indeed sensitive to aerosol number and size distributions, which in turn are influenced by synoptic features (e.g., cyclones) and marine boundary layer stability. On the other hand, frequent occurrence of low SS, demonstrates that cloud formation is also often updraft limited.

How to cite: Schmale, J., Nenes, A., Thurnherr, I., Henning, S., Tatzelt, C., Baccarini, A., and Gysel-Beer, M.: Aerosol size distribution variability over the Southern Ocean: implications for cloud droplet number concentrations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5460, https://doi.org/10.5194/egusphere-egu24-5460, 2024.

15:30–15:40
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EGU24-17439
|
On-site presentation
Alexander Mangold, Karen De Causmaecker, Quentin Laffineur, Preben Van Overmeiren, Charlotte Deramaix, Christophe Walgraeve, Nadine Mattielli, and Andy Delcloo

Atmospheric composition plays an important role in present and near-future climate change. Airborne particles exert direct and indirect radiative impacts and can serve as cloud condensation and ice nuclei, having therefore a strong influence on cloud formation and precipitation. Furthermore, a detailed understanding of present-day atmospheric transport pathways of particles from source to deposition in Antarctica remains essential.

Since 2010, the aerosol total number and size distribution, aerosol absorption coefficient and mass concentration of light-absorbing aerosols and the aerosol total scattering coefficient have been monitored at the Belgian research station Princess Elisabeth Antarctica (PEA). The station is situated in Dronning Maud Land, East Antarctica (71.95° S, 23.35° E, 1390 m asl). Besides these instruments, a cloud condensation nuclei counter was operated during three austral summers. Meteorological data come from an automatic weather station. In this work, we investigate the climatology of the particle properties with respect to the air mass origin. To that end, we used the FLEXTRA trajectory model to investigate transport pathways into Antarctica. The model was driven with ECMWF ERA-5 meteorological fields. 10-days 3D backward trajectories, starting from PEA, were calculated for the period 01/01/2010 to 31/12/2020, in 3-hour-intervals. A k-means cluster analysis has been done based on latitude, longitude and altitude, resulting in four clusters of air mass origin.

We will present results for the climatology of particle properties and the air mass origin. In addition, the backward trajectories have been combined with measured atmospheric particle properties and parameters like potential vorticity and exposure to sunshine duration, showing the distribution of the measured atmospheric particle properties between and within the air mass origin clusters. Some distinct features could be seen in the air mass origin clustering. Source regions from South America, Southern Africa and Australia, New Zealand were limited and the Southern Ocean was a main source region, as was the Antarctic continent itself. For each season, the dominating cluster represented mainly air masses of Antarctic continental origin with a large influence of upper tropospheric air. We will show further results of our analysis on air mass origin and atmospheric and particle properties, with respect to differentiations between seasons, clusters, continental and maritime origin and source altitude compartments.

How to cite: Mangold, A., De Causmaecker, K., Laffineur, Q., Van Overmeiren, P., Deramaix, C., Walgraeve, C., Mattielli, N., and Delcloo, A.: Atmospheric aerosol characterization at Princess Elisabeth station, East Antarctica and identifying source regions using backward trajectory modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17439, https://doi.org/10.5194/egusphere-egu24-17439, 2024.

Posters on site: Fri, 19 Apr, 10:45–12:30 | Hall X5

Display time: Fri, 19 Apr, 08:30–Fri, 19 Apr, 12:30
Chairperson: Edward Gryspeerdt
X5.55
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EGU24-2107
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ECS
Darko Savic, Vladan Vuckovic, and Dragana Vujovic

In this work we have investigated the effect of aerosol particles (APs) scavenging by snow in a cumulonimbus cloud. It was shown that APs in the atmosphere have a major impact on cloud formation, development and its products, climate, environment, public health, etc. The scavenging coefficients for various snow scavenging processes were calculated, analyzed and implemented in a three-dimensional, three-moment microphysical model in which all the number concentrations and the mixing ratios, were explicitly calculated for all hydrometeor categories. Analyzing the AP scavenging coefficients we concluded that Brownian/turbulent diffusion is the dominant process for smaller diameter aerosols, up to a point, where inertial interception overpowers. Impaction scavenging is by far the most dominant process of APs scavenging by snow for particles larger than ~0.5 µm in diameter, therefore it was neglected because most of the APs injected into the cloud are of the diameter <0.2 µm. Scavenging coefficient of snow is comparable to that of raindrops or even cloud droplets, which means that APs scavenging with snow should be included in the model. Two sets of numerical experiments were conducted: (1) APs were scavenged only by cloud and rainwater and (2) APs were scavenged by cloud and rainwater and snow. No ice nucleation processes were included. The results of 3D numerical simulations showed that snow contributes more to mass than the number of AP washouts, as it collects larger particles more efficiently. As snowflakes melt into raindrops, scavenging by snow becomes a significant mechanism for removing APs from the atmosphere. Approximately 29.3% and 7.2% of the total number and mass of APs, respectively, get deposited on the ground through precipitation during a 3-hour simulation when snow does not actively collect APs. When snow collection is included in the model, the total number and mass of APs precipitated on the ground increase by 10.7% and 56.9%, giving a total of 32.4% and 11.3%, respectively.

How to cite: Savic, D., Vuckovic, V., and Vujovic, D.: The influence of submicron sized aerosol scavenging by snow in the Cb cloud, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2107, https://doi.org/10.5194/egusphere-egu24-2107, 2024.

X5.56
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EGU24-3659
Huan Guo and Songmiao Fan
We incorporated a temperature, dust, and sea spray aerosol-dependent ice nucleation parameterization in the recently developed GFDL AM4-MG2 framework, and refer to this new configuration as AM4-MG2-new. The major difference of the ice nucleation parameterizations in AM4-MG2-new and AM4-MG2 is the inclusion of sea spray aerosol as ice nucleating particles (INPs). Then we conducted AMIP (Atmospheric Model Intercomparison Project) mode simulation with AM4-MG2-new. It turns out that AM4-MG2-new produces mean model climate comparable to AM4-MG2, for example, similar cloud radiative and precipitation fields, but different cloud water phase partitioning or supercooled cloud fractions, especially over the mid-high latitudes where mixed-phase clouds (clouds that consist of both liquid and ice) are prevalent. The cloud-phase feedback could in turn impact the estimate of climate sensitivity. The results suggest that ice nucleation parameterizations, which have large uncertainties, have important impacts on climate sensitivity.

How to cite: Guo, H. and Fan, S.: The effects of ice nucleation parameterizations in GFDL climate model , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3659, https://doi.org/10.5194/egusphere-egu24-3659, 2024.

X5.57
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EGU24-3924
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ECS
Xiaoyan Zhang, Xiyan Xu*, Gensuo Jia, and Yue Liang

Numerical simulations mostly constrain the total amount of biomass burning aerosols but rarely prescribe the realistic emission variability. Ignoring high heterogeneity of emission variability may lead to uncertainties in climate projections. Based on the Community Earth System Model version 2 Large Ensemble Community Project (CESM2-LE), we investigated the impact of interannual variability of biomass burning emissions on tropical precipitation and extremes. Our results revealed that global carbonaceous aerosol emission was 180-320 Tg over the period 1990-2020. Tropical regions (30°S-30°N) had the largest emission flux and variability. Higher interannual variability triggered increasing precipitation and extremes in tropics where spatial heterogeneity of precipitation anomalies can be detected. More precipitation and northward ITCZ shift occurred in central and western Pacific Oceans, while precipitation reduction together with southward ITCZ rain-belt over eastern Pacific and Atlantic Basins. The asymmetries were attributable to weakened Walker circulation and its uplifting branch tilted toward the Southern hemisphere. Correspondingly, nonlinear aerosol-cloud interactions increased (reduced) the total and high cloud cover over the southern central-western Pacific (eastern Pacific and Atlantic) Oceans. Convective activities were then strengthened (weakened) due to lower (higher) outgoing longwave radiation at top of atmosphere, which drove the cross-equatorial heat transport variations, and ultimately led to southward (northward) shift of ITCZ. Our results revealed the synergistic mechanisms between biomass burning emission variability, radiation and cloud characteristics, and large-scale circulation modes, thereby gaining new insights into the tropical hydrological cycle.

How to cite: Zhang, X., Xu*, X., Jia, G., and Liang, Y.: Impact of biomass burning emission variability on precipitation over tropical oceans, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3924, https://doi.org/10.5194/egusphere-egu24-3924, 2024.

X5.58
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EGU24-4957
Jie Qiu and Chunsheng Zhao

Sea spray aerosols (SSA) play a crucial role as a primary aerosol source on a global scale, exerting significant influence on the Earth's radiative balance. Variations in sea water composition and concentrations across different regions can introduce disparities in sea spray aerosol properties. This study focuses on investigating and comparing the hygroscopicity of artificial sea salt particles and nascent sea spray aerosols from offshore waters and open sea areas within the Pacific Ocean. An aerosol optical tweezer (AOT) system is developed to measure the diameter hygroscopic growth factor (GF) and the hygroscopicity parameter (κ) of both artificial sea salt and natural sea spray aerosol particles. Our findings indicate that the hygroscopic properties of supermicron sea spray aerosols from offshore waters and open sea areas are remarkably similar and can be effectively represented by artificial sea salt particles. Furthermore, through the application of the theoretical Zdanovskii, Stokes, and Robinson (ZSR) mixing rule, the calculated κ values reinforce the validity of our aerosol optical tweezer measurements. Hence, we propose that, for modeling supermicron sea spray aerosol particles produced in either offshore waters or open sea areas, the properties of artificial sea salt particles, rather than NaCl particles, serve as robust proxies for natural sea spray aerosols. To be specific, we recommend utilizing a κ value of 1.20, for modeling sea spray aerosol properties at a relative humidity of 90% (RH=90%). This empirically derived κ value, rooted in our study, can enhance the accuracy of climate models and contribute to a more precise understanding of aerosol-climate interactions.

 

How to cite: Qiu, J. and Zhao, C.: Hygroscopic Behavior of Sea Spray Aerosols in Offshore Waters and Open Sea Areas Investigated with Aerosol Optical Tweezers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4957, https://doi.org/10.5194/egusphere-egu24-4957, 2024.

X5.59
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EGU24-5189
Moritz Schnelke, Maike Ahlgrimm, and Anna Possner

The Northeast Pacific stratocumulus deck is one of the well-known subtropical semipermanent stratocumulus decks that transitions into shallow cumuli along the sea surface temperature gradient away from the Californian coast line. In this study we use observational data from the Marine ARM GPCI Investigation of Clouds (MAGIC) ship campaign to evaluate stratocumulus to cumulus transitions (SCTs) in idealised large-eddy simulations (LESs) with the ICOsahedral Nonhydrostatic Model (ICON). The simulations are conducted with a horizontal resolution of 50 m and a vertical resolution of at most 10 m in the lowest 3 km of the atmosphere. 
From previous studies of SCTs, including MAGIC and in particular Leg15A, it is well known that entrainment processes drive an important, and likely dominant role in forcing the transition. However, recent studies have shown that microphysical effects like sedimentation or precipitation can significantly alter the course of the SCT. Suppressed precipitation through a higher number of cloud droplets often leads to a delayed SCT. On the other hand, this is counteracted by the associated increase in entrainment, which benefits the transition. This raises the question of the mechanism of this interaction and the overall strength of microphysical effects. 
Here we present the evaluation of ICON LES and the characterisation of nine selected transitions from the MAGIC campaign, including the well analysed Leg15A. 

How to cite: Schnelke, M., Ahlgrimm, M., and Possner, A.: Large-eddy simulations of the stratocumulus to cumulus transition in the Northeast Pacific using ICON, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5189, https://doi.org/10.5194/egusphere-egu24-5189, 2024.

X5.60
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EGU24-7092
Shuqi Guo and Chunsheng Zhao

The lifetime of clouds has an important influence on radiation balance, atmospheric matter cycling, and global precipitation patterns. However, current assessments of cloud lifetime rely on statistical methods, underscoring the need for effective observational techniques. Moreover, existing research predominantly centers on precipitation removal, neglecting the process of cloud dissipation.Utilizing optical tweezers-Raman spectroscopy technology and CCD real-time imaging, this study conducts experiments on the evaporation of individual suspended droplets with a series of concentration gradients. We establish a method for quantifying the evaporation time of microdroplets, and characterize their evaporation dynamics through the temporal variation of OH-stretching Raman peak. Our research reveals the substantial influence of droplet solute concentration on evaporation time, indicating that even minute variations in solute concentration within cloud droplets can induce profound disparities in their lifetime.Furthermore, alterations in environmental relative humidity also have an impact on the dissipation of cloud droplets. These findings hold critical scientific significance, enhancing our understanding of cloud lifetime and providing a scientific foundation for accurately simulating cloud generation and dissipation processes in numerical models.

How to cite: Guo, S. and Zhao, C.: Advancing Cloud Science: Exploring the Lifetime of Indiviual Cloud Droplets through Aerosol Optical Tweezers and Raman Spectroscopy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7092, https://doi.org/10.5194/egusphere-egu24-7092, 2024.

X5.61
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EGU24-9071
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ECS
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Highlight
Holographic Particle Tracking Velocimetry: Resolving cloud droplet dynamics
(withdrawn)
Birte Thiede, Freja Nordsiek, Oliver Schlenczek, Eberhard Bodenschatz, and Gholamhossein Bagheri
X5.62
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EGU24-9453
Mark D. Tarn, Polly B. Foster, Sam J. Clarke, James B. McQuaid, Joseph Robinson, Erin N. Raif, Sarah L. Barr, Katherine H. Bastin, Kathleen A. Thompson, Zongbo Shi, Richard Cotton, Paul R. Field, Keith N. Bower, Martin W. Gallagher, Thomas Choularton, and Benjamin J. Murray

As the Earth warms, it is important to understand how a change in the ice:water ratio in mixed-phase clouds influences the cloud-phase feedback; a cooling effect caused by the change in albedo of the cloud. Ice-nucleating particles (INPs), aerosols that can trigger the freezing of liquid cloud droplets via heterogeneous nucleation, may regulate this cooling process by maintaining the ice contents in clouds, hence it is necessary to identify the types, sources, and concentrations of INPs to determine their contribution and better represent this in models. We undertook ship and aircraft-based INP measurement campaign in the Labrador Sea region, which features clouds that are susceptible to the effect of INPs, in 2022: (i) a cruise on the RRS Discovery, as part of a joint SEANA/M-Phase project in May-June, and (ii) a flight campaign on the FAAM BAe-146 aircraft as part of the M-Phase project in October-November that focused on northwesterly cold air outbreak (CAO) cloud systems.

During the SEANA/M-Phase ship cruise, real-time measurements of INP concentrations were taken using a Portable Ice Nucleation Experiment (PINE) expansion chamber alongside offline filter-based measurements and bulk seawater measurements. Preliminary results suggest that high INP concentrations correlated with air masses that had passed over the exposed (i.e. not snow- or ice-covered) coastline of Greenland, while lower concentrations correlated with air masses that had passed over the sea ice. These results suggest a high-latitude source of INPs not currently accounted for in models, the study of which could be crucial in understanding their influence on clouds in a changing climate.

Offline filter-based INP measurements during the FAAM aircraft campaign showed highly reproducible INP concentrations during CAO events (0.05 INP L−1 at −15 °C), with both much higher and much lower concentrations during non-CAO days. Further analysis will include further processing of the campaign data, including aerosol size distributions together with real-time INP data taken from a new online continuous flow diffusion chamber (CFDC), the Met Office Ice Nuclei Counter (INC), aboard the aircraft, together with aerosol composition analysis via scanning electron microscopy of filters, which will allow the types and sources of INPs in the Labrador Sea region to be established.

The M-Phase campaigns in the Labrador Sea have shed some light on INP properties in the region, and further processing of the data will allow determination of INP sources, activity, and relationship with aerosol size distributions. Better representation of INPs in models based on these findings will allow for reduced uncertainty in the cloud-phase feedback and its impact on climate predictions.

How to cite: Tarn, M. D., Foster, P. B., Clarke, S. J., McQuaid, J. B., Robinson, J., Raif, E. N., Barr, S. L., Bastin, K. H., Thompson, K. A., Shi, Z., Cotton, R., Field, P. R., Bower, K. N., Gallagher, M. W., Choularton, T., and Murray, B. J.: Ice-nucleating particles over the Labrador Sea during the M-Phase campaigns, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9453, https://doi.org/10.5194/egusphere-egu24-9453, 2024.

X5.63
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EGU24-12304
Denghui Ji, Xiaoyu Sun, Mathias Palm, and Justus Notholt

A new pathway for Saharan dust transport to the Arctic is found recently[1,2], crossing the North Atlantic directly into the Arctic. In order to reveal the climatology features of this rapid pathway, Merra-2, ERA5 reanalysis data and Geos-Chem model simulations are used in this study. We started our analysis with a dust enhancement case study. From model simulations, on 14 March 2022, a Saharan dust event is transported northwards. This dust took only a few days to reach the Arctic along this pathway. In the following month, there were four dust enhancement events. Model results indicate that the Shahara Desert is the main source (~ 80%) of Arctic dust in spring. From Merra-2 reanalysis data (dust aerosol optical depth, AOD), this new pathway once opened from 2000 to 2015, and then closed until 2022. Combined with the North Atlantic Oscillation (NAO) index and the ERA5 reanalysis data (700 hPa wind field), we find that the opening of the rapid pathway tends to be in the weakly positive or negative phase of the NAO. It implies that the jet stream is more meandering, which is favorable for dust transport. Specifically, the opening of the rapid pathway requires the presence of cyclones in the residual circulation near Iceland and anticyclones in the mid-latitude Atlantic.

 

Reference

[1] Francis, D., Eayrs, C., Chaboureau, J.-P., Mote, T., & Holland, D. M. (2018). Polar jet associated circulation triggered a Saharan cyclone and derived the poleward transport of the African dust generated by the cyclone. Journal of Geophysical Research: Atmospheres, 123, 11,899–11,917. https://doi.org/10.1029/2018JD029095

[2] Francis, D., Mattingly, K. S., Lhermitte, S., Temimi, M., and Heil, P.: Atmospheric extremes caused high oceanward sea surface slope triggering the biggest calving event in more than 50 years at the Amery Ice Shelf, The Cryosphere, 15, 2147–2165, https://doi.org/10.5194/tc-15-2147-2021, 2021.

How to cite: Ji, D., Sun, X., Palm, M., and Notholt, J.: A Rapid Pathway for Saharan Dust Transport to the Arctic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12304, https://doi.org/10.5194/egusphere-egu24-12304, 2024.

X5.64
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EGU24-14768
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ECS
Aishwarya Singh, Kavyashree Kalkura, Rameshchand Ka, Ravikrishna Raghunathan, Ulrich Poschl, Hang Su, James Allan, Gordon Mcfiggans, Meinrat Andreae, Scot Martin, Hugh Coe, Pengfei Liu, and Sachin Gunthe

Aerosols, with their direct and indirect effects impacting the climate, have been established to significantly perturb Earth's radiative budget and hydrological cycle. The climate impact of aerosols is complex and multifaceted, with various factors influencing the combined net effect. The intricacies of aerosol effects, mainly through aerosol-cloud interactions, necessitate precise measurements to reduce the uncertainty in forecasting future climate fluctuations1. Studying their characteristics in pristine settings can provide an enhanced scientific understanding of aerosol impact in background conditions, as opposed to polluted ones2. With this motivation, we conducted a comprehensive field measurement campaign during the second phase of the COVID-induced lockdown in Munnar, a relatively clean high-altitude site in the Western Ghats of India. Munnar is surrounded by lush tea plantations and extensive forest reserves, and tea production and tourism are the major human activities in the area. However, suspended tourist activities due to the pandemic and frequent precipitation during monsoon enabled us to study the ambient aerosol characteristics in near-natural conditions3. This study presents results from the size-resolved Cloud Condensation Nuclei (SR-CCN) measurements conducted along with aerosol size distribution and chemical composition at the Natural Aerosol and Bioaerosol High Altitude Laboratory (NABHA; 10.09 N, 77.06 E; 1605m asl) during the Southwest Monsoon season between June-October 2021. The median number concentration for 10–450nm particles was observed to be 533cm-3, with 357cm-3and 908cm-3 as first and third quartiles, respectively, similar to other pristine locations, such as Amazonia during the wet season4. The average non-refractory particulate matter (NR-PM1) concentration was 2.28±1.81 µg/m3 (mean ± one standard deviation). The SR-CCN measurements were carried out for set supersaturations between 0.1% and 0.85% for particles ranging between 20-350 nm in diameter. The critical dry diameter varied from 60 to 150nm for highest to lowest supersaturation, similar to previously reported studies elsewhere4,5. During the campaign, the efficiency spectra of CCN often reached unity despite organic aerosols dominating the submicron aerosol composition.

Further, hygroscopicity, a particle size and composition function, was investigated using the kappa-Köhler theory. The hygroscopicity parameter, kappa, derived from SR-CCN measurements(kCCN) varied between 0.26 and 0.57. kCCN did not exhibit much variation in the Aitken mode regime (60-80nm) but increased in the accumulation mode (100-160nm), suggesting higher hygroscopic fraction in larger (aged) particles. Assuming a linear mixing of organic and inorganic aerosols, chemically derived hygroscopicity (kchem) was comparable to kCCN, following similar diurnal variation. Further details will be presented.

References:

1.Lohmann, U. & Ferrachat, S. Impact of parametric uncertainties on the present-day climate and on the anthropogenic aerosol effect. AtmosChemPhys (2010).

2.Andreae, M. O. Aerosols Before Pollution. Science (2007).

3.Navasakthi, S., Pandey, A., Bhari, J. S. & Sharma, A. Significant variation in air quality in South Indian cities during COVID-19 lockdown and unlock phases. EnvironMonitAssess (2023).

4.Gunthe, S. S. et al. Cloud condensation nuclei in pristine tropical rainforest air of Amazonia: size-resolved measurements and modeling of atmospheric aerosol composition and CCN activity. AtmosChemPhys (2009).

5.Singh, A. et al. Rapid growth and high cloud-forming potential of anthropogenic sulfate aerosol in a thermal power plant plume during COVID lockdown in India. NPJClimAtmosSci (2023).

How to cite: Singh, A., Kalkura, K., Ka, R., Raghunathan, R., Poschl, U., Su, H., Allan, J., Mcfiggans, G., Andreae, M., Martin, S., Coe, H., Liu, P., and Gunthe, S.: Cloud Condensation Nuclei (CCN) activity of sub-micron aerosols during the Southwest Monsoon over a pristine site in the Western Ghats, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14768, https://doi.org/10.5194/egusphere-egu24-14768, 2024.

X5.65
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EGU24-14993
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ECS
Sensitivity of cloud invigoration/suppression effects during Indian summer monsoon to model resolution in a global climate model
(withdrawn after no-show)
Puneet Sharma and Dilip Ganguly
X5.66
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EGU24-15271
Matteo Rinaldi, Marco Paglione, Marco Rapuano, Diego Fellin, Stefano Decesari, Niccolò Losi, Luca Ferrero, and Angelo Lupi

Remote from most human influences, the Southern Ocean (SO) is one of the most pristine regions on Earth and a window to preindustrial atmospheric conditions (Hamilton, 2015). Currently, many unknowns remain about atmospheric and oceanographic processes in this region and their relations. This is largely due to the poor understanding of aerosol sources and processes in this region.

Sub-micrometer aerosol samples were collected onboard the Italian RV Laura Bassi cruising the Southern Ocean and the Ross Sea, in the framework of the PNRA (Programma Nazionale di Ricerca in Antartide) project CAIAC (oCean Atmosphere Interactions in the Antarctic regions and Convergence latitude). The aim is to characterize the marine aerosol chemical composition in different ecoregions, with a particular interest for organic aerosols and their formation processes in relation with the patterns of oceanic biological activity.

Samples were collected by a high volume sampler (TECORA, ECHO-HIVOL, 500 LMP) from mid-January to mid-February 2023, deploying a wind direction selection system to avoid ship contaminations. A total of 9 samples were collected. The samples have been analysed for their water-soluble Carbon and Nitrogen content by a C-N elemental analyzer (Shimadzu) and for the ionic composition (including low molecular weight acids and amines) by ion chromatography (Dionex). The characterization of the water-soluble organic fraction in terms of tracers and functional group abundance was performed by 1H NMR (Proton Nuclear Magnetic Resonance) spectroscopy (Decesari et al, 2020).

The samples show variable contributions in terms of primary and secondary components, mostly depending on back trajectory origin and wind speed, with a general predominance of secondary species. Sulfate resulted generally the most abundant aerosol component, while water soluble organic matter (WSOM) showed a non-negligible contribution from 5 to 14% of the analysed mass. NMR spectra show the complexity of the WSOM composition, even though all the spectra were dominated by the MSA signal, which contribution in terms of carbon to WSOM spans from 8 to 64%.

Analysis of organic aerosol sources is in progress by back-trajectory analysis and statistical analysis of the NMR spectra.

 

Acknowledgements: CAIAC (oCean Atmosphere Interactions in the Antarctic regions and Convergence latitude) PNRA project.

 

Decesari, S. et al. (2020), Atmos. Chem. Phys., 20, 4193–4207, https://doi.org/10.5194/acp-20-4193-2020

Hamilton, D. S. Weather 2015, 70 (9), 264– 8, DOI: 10.1002/wea.2540

How to cite: Rinaldi, M., Paglione, M., Rapuano, M., Fellin, D., Decesari, S., Losi, N., Ferrero, L., and Lupi, A.: Chemical characterization of sub-micrometer marine aerosol around the Ross Sea during CAIAC (2022-23 Antarctic summer), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15271, https://doi.org/10.5194/egusphere-egu24-15271, 2024.

X5.67
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EGU24-16285
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ECS
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Highlight
Reducing the Impact of Aircraft-Induced Clouds on Climate –Development of the Contrail Avoidance Tool (CoAT)
(withdrawn)
Zane Dedekind, Alexei Korolev, and Jason A. Milbrandt
X5.68
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EGU24-16965
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ECS
Lukas Zipfel, Hendrik Andersen, Jan Cermak, and Daniel P. Grosvenor

In this work, a data set comprised of satellite observations and reanalysis data is used in explainable machine learning models to analyse the relationship between the cloud droplet number concentration (Nd), cloud liquid water path (LWP) and the fraction of precipitating clouds (PF) in 5 distinct marine stratocumulus (MSC) regions.

Aerosol--cloud--precipitation interactions (ACI) are a known major cause of uncertainties in simulations of the future climate. An improved understanding of the in-cloud feedback processes accompanying ACI could help in advancing their implementation in global climate models. This is especially the case for marine stratocumulus clouds which constitute the most common cloud type globally.

The machine learning framework applied here makes use of Shapley additive explanation (SHAP) values, allowing to isolate the impact of Nd from other confounding factors which proved to be very difficult in previous satellite based studies.

All examined MSC regions display a decrease of PF and an increase in LWP with increasing Nd, despite marked inter-regional differences in the distribution of Nd. The negative Nd-PF relationship is stronger in high LWP conditions, while the positive Nd-LWP relationship is amplified in precipitating clouds. While these results for the Nd-LWP relationship differ from the findings in recent satellite-based global analyses, they are consistent with previous studies using model simulations. The results presented here indicate that precipitation suppression plays an important role in MSC adjusting to aerosol-driven perturbations in Nd.

How to cite: Zipfel, L., Andersen, H., Cermak, J., and Grosvenor, D. P.: How cloud droplet number concentration impacts liquid water path and precipitation in marine stratocumulus clouds - a satellite-based analysis using explainable machine learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16965, https://doi.org/10.5194/egusphere-egu24-16965, 2024.

X5.69
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EGU24-17810
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ECS
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Alexandre Mass, Hendrik Andersen, Jan Cermak, and Eva Pauli

In this contribution, a statistical model and several satellite products (SEVIRI, CALIPSO) are used to study the potential semi-direct effects of biomass burning aerosols (BBA) on the persistence of fog and low clouds (FLC) in the Namib during the biomass burning season.

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 have yet to be investigated.

Using reanalysis products in combination with satellite data, a statistical model is built to predict FLC dissipation times in high and low BBA loading days. It is found that during this season, FLC dissipation times are positively correlated to BBA loading (higher aerosol loading coinciding with later FLC dissipation). By analyzing the contribution of the different predictors to the output of the statistical model, it is found that the positive correlation is mostly explained by the synoptic scale meteorology. Nevertheless, the synoptic scale circulation and aerosol loading are highly correlated in the region, thus some of the results could still be attributed to aerosol semi-direct effects. To definitively contrast aerosol effects from meteorology, modeling of aerosol-cloud interactions in the region could be promising.

How to cite: Mass, A., Andersen, H., Cermak, J., and Pauli, E.: An investigation of fog and low cloud life cycles and their interaction with biomass burning aerosols in the Namib, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17810, https://doi.org/10.5194/egusphere-egu24-17810, 2024.

X5.70
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EGU24-17218
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ECS
Rebecca Murray-Watson and Ed Gryspeerdt

The development of clouds during marine cold-air outbreaks (MCAOs) represent a complex phenomenon, transitioning from stratocumulus decks near ice edges to cumuliform fields downwind. This change cloud morphology changes the radiative properties of the cloud, and therefore is of importance to the surface energy budget. Therefore, it is crucial to understand the factors which may drive transition to a broken cloud field. Previous in situ and modelling studies suggest the formation of ice may enhance precipitation and therefore accelerate break-up. However, little is known about the development of mixed-phase clouds in MCAOs. 

This study uses pseudo-Lagrangian trajectories and satellite data to analyze this mixed-phase cloud development. We observe a rapid transition from liquid to ice phases in MCAO clouds, contrasting with similar cloud formations outside MCAO conditions. These mixed-phase clouds initially form at temperatures below -20°C near ice edges but can dominate even at -13°C further into outbreaks. This temperature shift suggests a significant role for biological ice nucleating particles (INPs), which increase in prevalence as air masses age over marine environments. The study also notes the influence of the air mass's history over snow- and ice-covered surfaces, which may be low in INPs, on cloud evolution. This link helps explain seasonal variations in Arctic cloud development, both during and outside of MCAOs. Our findings emphasize the importance of understanding local marine aerosol sources and the broader INP distribution in the Arctic for accurate cloud phase modeling in the region. 

How to cite: Murray-Watson, R. and Gryspeerdt, E.: Air mass history linked to the development of Arctic mixed-phase clouds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17218, https://doi.org/10.5194/egusphere-egu24-17218, 2024.

X5.71
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EGU24-12184
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ECS
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Highlight
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Adrian Hamel, Massimo del Guasta, Emma Järvinen, and Martin Schnaiter

In-situ measurements of small atmospheric ice crystals (< 100 µm) on the Antarctic plateau are rare. Yet, small ice crystals are abundant in a region that often reaches cirrus temperatures even in the warmest season. The Particle Phase Discriminator (PPD-2K) was deployed on DOME-C, Antarctica during austral summer 2023/2024. It was used to characterize the microphysical and optical properties of individual ice fog and diamond dust ice crystals having sizes between approximately 10 and 100 µm. These properties included particle concentration, size distribution and spatial light scattering patterns in the forward direction that allow the analysis of the particle sphericity (particle phase), shape and crystal complexity.
The atmospheric ice crystals on the Antarctic plateau commonly appear in form of ice fogs that have an effect on the radiative budget. In this presentation an ice fog event occurring between 26.11.2023 and 27.11.2023 is analyzed in detail using additional data from LIDAR, temperature and humidity sensors operated at DOME-C. The results are compared to previous findings in Antarctica and to ice fog measurements with the same instrument in a polluted environment at Fairbanks, Alaska.

How to cite: Hamel, A., del Guasta, M., Järvinen, E., and Schnaiter, M.: In-situ optical characterization of ice fog and diamond dust events at DOME-C, Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12184, https://doi.org/10.5194/egusphere-egu24-12184, 2024.

X5.72
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EGU24-19429
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ECS
Joanna Dyson, Nora Bergner, Lionel Favre, Benjamin Heutte, Julian Weng, Patrik Winiger, Athanasios Nenes, Kalliopi Violaki, and Julia Schmale

The Arctic is warming up to four times faster than the global average with fragile fjord ecosystems in the relatively warm Southern Greenland being especially sensitive to changes across various facets of the environment. With longer and warmer summer melt periods leading to increased glacial melt with marine and land-terminating glaciers slowly receding, the potential of sediments from newly exposed glacial outwash plains to be aerosolized increases. At the same time biological productivity in the ocean is changing. Hence, the composition and sources of atmospheric aerosols responsible for the formation of clouds in this region are evolving and we expect this to influence both the cloud condensation nuclei (CCN) and Ice Nucleating Particle (INP) populations. Given the complex terrain and mixture of ice, ocean and land in fjord systems, the dispersion of aerosols and gases originating at the surface is subject to lower atmosphere stability and dynamics before they can reach cloud level. 

In this presentation, we will show results from a comprehensive and extensive field campaign in the Kullajeq province of Southern Greenland in June-August 2023. We will present vertical aerosol size distributions, particle number concentrations and absorption measurements taken using a tethered balloon in addition to complementary ground based online aerosol measurements. Two key sources of aerosols will be discussed: near-daily local new particle formation (NPF), and long-range transported Canadian wildfire plumes. We will explore the following questions: Are aerosols from fjords and increased biological productivity the source of the frequent NPF observed in Narsaq, and how do aerosols from distant sources such as Canadian biomass burning effect the aerosol population in Southern Greenland?

How to cite: Dyson, J., Bergner, N., Favre, L., Heutte, B., Weng, J., Winiger, P., Nenes, A., Violaki, K., and Schmale, J.: Local and long-range transported sources of natural aerosols in southern Greenlandic fjord systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19429, https://doi.org/10.5194/egusphere-egu24-19429, 2024.

X5.73
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EGU24-15384
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ECS
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Eemeli Holopainen, Paraskevi Georgakaki, David Patoulias, Georgia Sotiropoulou, Romanos Foskinis, Spyros Pandis, and Athanasios Nenes

The interaction between aerosols and clouds is a complex process and it causes large uncertainties in predicting the global climate. This interaction has been studied using chemical transport models (CTMs) as they simulate the distribution and composition of atmospheric aerosols. In this study, we developed a coupled version of the Weather Research and Forecasting (WRF) model with the PMCAMx-UF CTM (Skamarock et al., 2008; Patoulias et al. 2022). We did this by using prognostic cloud droplet number in the Morrison et al. 2009 cloud microphysics scheme of the WRF model. We calculated the prognostic cloud droplet number from the predicted aerosol fields of PMCAMx-UF using the Morales and Nenes 2014 activation scheme. In addition, we investigated the effects of prognostic cloud droplets to secondary ice production (SIP) in the WRF model. This involved the incorporation of various SIP processes, including Hallett-Mossop (HM), collisional fracturing and breakup (BR), droplet freezing and shattering (DS), and sublimational breakup of snow (SBS) and graupel (SBG), following the approaches outlined in Georgakaki et al. 2023. First we evaluated the impact of coupled WRF-PMCAMx-UF model with prognostic droplets to the same model with prescribed droplet number as well as the SEVIRI satellite observations. Secondly we evaluated the effects of adding SIP processes and prognostic droplets to non-SIP and prescribed droplet case and satellite observations. The results showed that using the combined model with prognostic droplets decreased the cloud droplet number concentration (CDNC) and liquid water content (LWC) when compared to the prescribed droplet simulation. This caused a more positive surface radiative forcing and thus a warming effect. In addition, the number of small particles decreased and large particle numbers increased when switching to prognostic droplets. Further, comparing to satellite observations, the prognostic droplet simulation performed better in terms of CDNC than the prescribed droplet simulation. Adding the SIP processes to the model increased the ice crystal number concentration (ICNC) as well as LWC in some areas. Compared to satellite observations, introducing SIP and prognostic droplets into the model performed slightly better in terms of CDNC as well as ice water path (IWP) than the non-SIP and prescribed droplet cases. Thus, a more realistic representation of CDNC as well as incorporation of SIP processes in the coupled model allows a more precise capture of evolving aerosol-cloud interactions in the atmosphere.

How to cite: Holopainen, E., Georgakaki, P., Patoulias, D., Sotiropoulou, G., Foskinis, R., Pandis, S., and Nenes, A.: A mesoscale model for aerosol-cloud interaction studies WRF-PMCAMx-UF with insights to secondary ice production, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15384, https://doi.org/10.5194/egusphere-egu24-15384, 2024.

X5.74
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EGU24-17504
Kaori Kawana, Romanos Foskinis, Eemeli Holopainen, Alexandros Papayannis, Andreas Aktypis, Christos Kaltsonoudis, David Patoulias, Angeliki Matrali, Christina Vasilakopoulou, Evangelia Kostenidou, Kalliopi Florou, Nikos Kalivitis, Konstantinos Eleftheriadis, Constantini Samara, Mihalis Lazaridis, Nikolaos Mihalopoulos, Spyros Pandis, and Athanasios Nenes and the Observation Team

    Aerosol particles affect the climate system by directly absorbing and scattering solar radiation or by acting as cloud condensation nuclei (CCN) and modulating cloud radiative properties. Cloud particle activation is at the heart of these aerosol-cloud interactions, but it is important to quantify the degree to which aerosol (size distribution and composition) or dynamical aspects (vertical velocity) contribute to cloud droplet number concentration, as they determine in the end the cloud sensitivity to aerosol variations.

    In this study, we use a comprehensive dataset of number-size distributions and meteorological data observed at 11 sites throughout the E. Mediterranean (Greece) during the summers of 2020 and 2021 and use them as input into a state-of-the-art cloud activation parameterization to determine the potential activated cloud droplet number and maximum supersaturation. Remote sensing retrievals of droplet number complement the analysis and are used to evaluate the droplet number calculations carried out with the parameterization. We then examine the droplet formation characteristics of each region (urban, rural, remote, and mountain), determine when clouds are velocity- and aerosol-limited, link them to airmass origin, and discuss the implications for cloud formation in the region.

How to cite: Kawana, K., Foskinis, R., Holopainen, E., Papayannis, A., Aktypis, A., Kaltsonoudis, C., Patoulias, D., Matrali, A., Vasilakopoulou, C., Kostenidou, E., Florou, K., Kalivitis, N., Eleftheriadis, K., Samara, C., Lazaridis, M., Mihalopoulos, N., Pandis, S., and Nenes, A. and the Observation Team: Cloud droplet formation characteristics at eleven locations throughout Greece during summer 2020 and 2021, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17504, https://doi.org/10.5194/egusphere-egu24-17504, 2024.

X5.75
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EGU24-907
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ECS
Kamran Ansari and Ramachandran Srikanthan

Aerosols continue to contribute the largest uncertainty in quantifying Earth’s climate change. The uncertainty associated with aerosol radiative forcing is found to be higher over Asia. The simulation and future projection of aerosol impact on climate may not be highly accurate over Asia due to rapid changes in aerosol emissions, limitations in simulating the observed aerosol trends, and the non-availability of regional distribution of columnar aerosol parameters based on high-quality observational datasets on a seasonal scale. For the first time, this comprehensive study examines the spatial and regional variations of aerosol columnar optical and physical properties (aerosol optical depth (AOD), fine mode fraction (FMF), and single scattering albedo (SSA)) and their associated radiative effects (aerosol radiative forcing (ARF) and heating rate (HR)) using high-quality Aerosol Robotic Network (AERONET) datasets on seasonal and annual scales over Asia. This study is performed over a total of 44 selected AERONET observational sites covering different regions of Asia, e.g., Central, South, South-East, and East Asia. AOD, ARF at the surface and in the atmosphere, and aerosol-induced atmospheric HR are observed to be the highest over South Asia, followed by South-East, East, and Central Asia in each season. SSA is found to be lower over South and Central Asia compared to South-East and East Asia. The combined influence of both fine anthropogenic aerosol emissions (e.g., carbonaceous aerosols) from biomass burning and fossil fuel combustion, and coarse mode dust aerosols from seasonal transport lead to higher AOD (0.6) and lower SSA (0.90), which overall result in higher ARF (~−70 Wm-2 at surface and 40 Wm-2 in atmosphere) and HR (0.80 Kday-1) over South Asia. South-East and East Asia are dominated by fine aerosols (higher FMF) due to higher contributions from forest fire and anthropogenic emissions, respectively, and relatively less dominance of dust aerosols compared to Central and South Asia. In addition, the seasonal aerosol optical and radiative parameters over Asia are also compared and contrasted with other regions of the globe, e.g., North America, South America, Europe, Africa, and Australia, where aerosol emissions are significantly different and mostly lower than in Asia. These findings provide observational constraints that are crucial for the improvement in model simulations for accurately assessing the radiative and climatic impacts of aerosols over a global aerosol hotspot region, Asia, where the uncertainty associated with aerosol radiative forcing is found to be higher. Details of the spatiotemporal variations in aerosol characteristics over Asia will be presented, compared and contrasted with the rest of the world, and inferences will be drawn. 

How to cite: Ansari, K. and Srikanthan, R.: Aerosol optical and radiative properties over Asia: Ground-based AERONET observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-907, https://doi.org/10.5194/egusphere-egu24-907, 2024.

X5.76
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EGU24-6913
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ECS
Manqiu Cheng, Mikinori Kuwata, and Ying Li

Water content of aerosol particles is important for atmospheric impacts, such as radiative effects and chemical reactivity. Traditionally, crystalline inorganic aerosol particles such as NaCl were known to experience hysteresis in water content, meaning that hygroscopic growth depends on exposure history to water vapor. On the contrary, past laboratory studies for organic aerosol reported absence of hysteresis, especially for ultrafine size range. Here, we show that water contents for ultrafine organic aerosol particles have hysteresis at sub-0 °C. Hygroscopic growth of monodisperse ultrafine particles (diameter = 40, 100, and 200 nm) of sucrose and glucose were investigated for the temperature range of -21 °C to +23 °C. Hygroscopic growth of these particles did not exhibit any hysteresis process at +23 °C, consistent with literature. However, hygroscopic growth of these particles was different for hydration and dehydration experiments at sub-0 °C, demonstrating the occurrence of hysteresis. The lowest relative humidity (RH), at which the two modes of experiments provided the same water content, was defined as merge RH. Merge RH was approximately the same as that for the glass transition point, demonstrating that water diffusion in a highly viscous matrix of organic aerosols is the key for the occurrence of hysteresis. Employment of a kinetic multilayer model provided quantitative prediction of merge RH as a function of temperature, particle size, and residence time. Considering the temperature and RH range of Earth’s atmosphere, we hypothesize that hysteresis in organic aerosol ubiquitously occur in the upper troposphere.

How to cite: Cheng, M., Kuwata, M., and Li, Y.: Hysteresis in water content of ultrafine glassy organic aerosols: Evidence from laboratory and modelling study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6913, https://doi.org/10.5194/egusphere-egu24-6913, 2024.

X5.77
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EGU24-638
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ECS
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Highlight
Arun Nair, Chandan Sarangi, and Yun Qian

Anthropogenic aerosols affect cloud properties and change their
lifetime, a phenomenon dubbed as aerosol-cloud interactions (ACi). Radiation fog is a
surface-level cloud formed due to night-time radiative cooling of the land surface. Each year,
north India experiences several prolonged fog events. These multi-day fog episodes can
affect surface visibility and air quality, affecting human health and the transportation sector.
From long-term observations, we find that the fog duration and foggy days are enhanced
during high aerosol loading periods over north India.
However, the mechanistic role of heavy aerosol pollution on the evolution, lifetime,
and frequency of North Indian fog episodes is still poorly understood. Using chemistry-
coupled regional model simulations, we find ACi leads to fog lifetime enhancement by
producing smaller droplets and reducing the droplet deposition rate. During the daytime, the
enhanced activation of aerosols into droplets prevents evaporation from the surface.
Interestingly, during this period, the aerosol radiative effect also helps produce conducive
surface conditions to delay fog dissipation. The unequivocal role of aerosol effects on the fog
lifetime over North India suggests the urgent need to regulate particulate pollution to reduce
long periods of fog.

How to cite: Nair, A., Sarangi, C., and Qian, Y.: Aerosols enhance winter fog lifetime over North India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-638, https://doi.org/10.5194/egusphere-egu24-638, 2024.

X5.78
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EGU24-9191
Supersaturation and critical size of cloud condensation nuclei in marine stratus clouds
(withdrawn after no-show)
Henrik Svensmark, Martin Bødker Enghoff, Jacob Svensmark, Irina Thaler, and Nir Shaviv
X5.79
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EGU24-2079
Yuan Wang, Jiming Li, Fang Fang, and Ping Zhang

Cloud activation over the Tibetan Plateau (TP) plays a pivotal role in regional cloud-precipitation processes and, by extension, global climate. However, its characteristics remain elusive due to the absence of observations in the TP. Leveraging the Second Tibetan Plateau Scientific Expedition and Research Program, we conducted a ground in-situ aerosol-cloud-precipitation experiment in the southern TP (GACPE-STP) from August to October 2023, thereby unveiling, for the first time, the aerosol activation characteristics in this crucial region. Our findings reveal a discernibly weak aerosol activation capacity, with mean cloud condensation nuclei number concentration (NCCN) ranging from 24 to 483 cm-3 and activation fraction from 2% to 48% at the supersaturation (SS) range from 0.07% to 0.7%. Through multi-method measurements of aerosol hygroscopicity (k), including derivation from both dry and humidified particle number size distribution (PNSD) and scattering coefficients, along with calculations based on NCCN(SS) and dry PNSD, we consistently observe low hygroscopicity with mean values below 0.1. This contrasts starkly with the recommended continental k value of 0.3, a departure that may be linked to unique surface characteristics and local fuel-usage practices in the TP region. As the dry aerosol diameter (D) increases, k exhibits an initial rise followed by a decline, adhering to a Gaussian distribution. The resulting k(D) fitting serves as a parameterization for predicting cloud activation in this region. Notably, utilizing the recommended continental κ value of 0.3 leads to a significant overestimation of cloud droplet number concentration (77% to 426%), subsequently contributing to an overestimation of cloud optical thickness and an underestimation of cloud-rain autoconversion. This cascade effect results in a substantial overestimation of the aerosol indirect effects. Employing the k(D) parameterization can significantly enhance the precision of cloud activation predictions in this region. These findings peel back a layer of mystery surrounding cloud activation in the TP region. To construct a comprehensive understanding, we advocate for additional in-situ experiments, including ice nuclei measurements, crucial for a nuanced depiction of cloud activation in the TP region.

How to cite: Wang, Y., Li, J., Fang, F., and Zhang, P.: Weak Aerosol Hygroscopicity Measured over the Southern Tibetan Plateau: Implication for Cloud Activation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2079, https://doi.org/10.5194/egusphere-egu24-2079, 2024.

X5.80
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EGU24-4059
Yannian Zhu, Jihu Liu, Minghuai Wang, and Daniel Rosenfeld

Clouds can be classified into regimes by the cloud appearance or by the cloud meteorological controlling factors. The cloud appearance regimes inherently include adjustments to aerosol effects, such as transitions between closed and open cells. Therefore, aggregation of cloud susceptibilities to aerosols over the cloud-appearance regimes excludes much of the cloud adjustment component of the susceptibilities. In contrast, aggregating susceptibilities over regimes defined by cloud-controlling factors includes the full effects of cloud adjustments. Here we compared the susceptibilities of the two kinds of cloud regimes and demonstrated this effect. Overall, increasing cloud droplet number concentration (Nd) consistently leads to precipitation suppression, higher cloud fraction (CF), and reduced liquid water path (LWP), regardless of how the regime is defined. However, their susceptibilities to Ndaggregated over cloud-appearance regimes are significantly lower than those aggregated over cloud-controlling factors regimes, with lower-tropospheric stability (LTS) serving as an example to define cloud-controlling factors regimes. This underestimation is more pronounced for CF susceptibility, where the susceptibility for cloud appearance regimes is only 1/4 of the susceptibility for cloud controlling regimes. These findings imply that relying solely on cloud-appearance regimes may underestimate the effective radiative forcing produced by cloud adjustment (ERFaci). Nevertheless, the substantial variability in the magnitude of cloud adjustment across appearance regimes at similar LTS also suggests that a single cloud-controlling factor is not sufficient to fully separate cloud regimes to quantify cloud adjustment. Therefore, identifying a comprehensive set of cloud-controlling factors is essential for accurately quantifying cloud adjustments in future studies.

How to cite: Zhu, Y., Liu, J., Wang, M., and Rosenfeld, D.: Cloud Susceptibility to Aerosols: Comparing Cloud-Appearance vs. Cloud-Controlling Factors Regimes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4059, https://doi.org/10.5194/egusphere-egu24-4059, 2024.

X5.81
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EGU24-4997
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ECS
Bishuo He and Chunsheng Zhao

The accurate assessment of influencing factors in multi-factor systems is crucial, but current methodologies face challenges in evaluating uncertainty comprehensively. In aerosol radiative forcing, existing methods may lack completeness, potentially leading to erroneous conclusions. This study introduces a universally applicable method for precise sensitivity analysis of influencing factors in multi-factor systems. Two measurement dimensions for sensitivity analysis methods are established: accurately expressing sensitivity and quantifying sensitivity. Combined utilization of different methods allows for a comprehensive analysis. The proposed method can simultaneously express and quantify sensitivity, including the analysis of nonlinear components unaffected by the absence of factors. In a sensitivity analysis on aerosol optical parameters, the aerosol shell complex refractive index (CRI_shell) emerges as the most sensitive factor. Calculations reveal substantial variability (5% to 91%) in the proportion of nonlinear components resulting from factor interactions. This emphasizes the importance of employing methods resistant to nonlinear influences, as susceptible methods may introduce significant biases. The proposed sensitivity analysis facilitates factor importance assessment at three levels: primary and secondary factors, sensitivity ranking, and quantified sensitivity. This method exhibits universality and holds promising prospects for practical applications in the field. Results provide a valuable reference for future model parameter settings and routine observations.

How to cite: He, B. and Zhao, C.: A Comprehensive Method to Unveiling Uncertainty in Multi-Factor Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4997, https://doi.org/10.5194/egusphere-egu24-4997, 2024.

X5.82
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EGU24-12776
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ECS
Svetlana Melnik, Silvio Schmalfuß, Frank Stratmann, Mira Pöhlker, and Dennis Niedermeier

The study of cloud formation is a crucial aspect of understanding the Earth's weather and climate system. Cloud droplet formation, growth, and the resulting size distributions are influenced by various atmospheric conditions. Despite extensive research, the impact of turbulence on droplet formation and growth remains incompletely understood.

To address this knowledge gap, we investigated the effect of turbulent saturation fluctuations on these mentioned processes. The respective study was conducted using the turbulent Leipzig Aerosol Cloud Interaction Simulator (LACIS-T, Niedermeier et al., 2020) which is a closed-loop, moist-air wind tunnel. LACIS-T is an ideal facility for pursuing mechanistic understanding of these processes and interactions under well-defined and reproducible laboratory conditions.

In LACIS-T, by mixing of three conditioned air streams (i.e. two particle-free air streams, and one aerosol stream), it is possible to precisely adjust temperature and water vapor fields so as to achieve various (super)saturation levels. A passive or active grid are used to introduce turbulence.

In our study, we examined the growth of size-selected monodisperse NaCl particles under various conditions of saturation and temperature at different turbulence patterns. Results of the study provide new experimental insights into the effect of turbulence on cloud droplet formation, growth, and consequently, the shape of cloud droplet size distributions.

Niedermeier et al. (2020), Atmos. Meas. Tech., 13, 2015-2033, https://doi.org/10.5194/amt-13-2015-2020.

Keywords: Cloud droplet growth, Droplet size distribution, Turbulence, Saturation fluctuations

How to cite: Melnik, S., Schmalfuß, S., Stratmann, F., Pöhlker, M., and Niedermeier, D.: Study of cloud droplet formation and growth under turbulent conditions in LACIS-T, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12776, https://doi.org/10.5194/egusphere-egu24-12776, 2024.

X5.83
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EGU24-5454
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ECS
Palwasha Khattak, Jan Cermak, Syeda Hira Fatima, and Julia Fuchs

This study investigates the relationship between aerosols and cloud properties in the South Asian monsoon over two decades, using satellite data. We conducted a 20-year analysis of aerosols and diverse cloud properties during the monsoon months. Precipitation patterns were categorized into high and low years based on anomalies. Significant correlations emerged between aerosol optical depth (AOD) and cloud properties, including cloud fraction, cloud droplet size, cloud top features, column-integrated water vapor, ice water path, and liquid water path. AOD and cloud fraction showed positive correlations, though not always translating to increased precipitation, underlining the role of cloud microphysics. AOD influenced cloud droplet size differently across regions, with some showing smaller droplets with higher AOD. Cloud height, temperature, and reflectivity were affected by AOD, indicating its influence on cloud properties through droplet concentration. Column-integrated water vapor positively correlated with AOD, implying aerosol involvement in water vapor condensation into cloud droplets. These findings uncover the intricate regional dynamics of aerosol-cloud interactions during the South Asian monsoon, offering valuable insights into the delicate relationships between aerosols, cloud properties, and precipitation variations across the diverse landscape of South Asia. This underscores the significance of considering regional variations in aerosol-cloud interactions when evaluating their impact on South Asian monsoon systems.

How to cite: Khattak, P., Cermak, J., Fatima, S. H., and Fuchs, J.: Spatiotemporal Impacts of Aerosols on Cloud Properties and Precipitation Patterns in South Asian Monsoon Region: Contrasting High and Low Precipitation Years., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5454, https://doi.org/10.5194/egusphere-egu24-5454, 2024.

X5.84
|
EGU24-2679
Meihua Wang

Different cloud types have distinct radiative effects on the energy budget of the earth–atmosphere system. To better understand
the cloud radiative impacts, it is necessary to distinguish the effects of different cloud types, which can be achieved through
the cloud radar data that can provide cloud profiles for both day-to-day and diurnal variations. In this study, we use 6-year
high-temporal resolution data from the Ka-Band Zenith Radar (KAZR) at the Semi-Arid Climate and Environment Observa-
tory of Lanzhou University (SACOL) site to analyze the physical properties and radiative effects of main cloud types. The
three types of clouds that occur most frequently at the SACOL site are single-layer ice clouds, single-layer water clouds, and
double-layer clouds with the annual occurrence frequencies being 29.1%, 3.4%, and 8.3%, respectively. By using the Fu–Liou
radiative transfer model simulation, it is found that the distinct diurnal variations of both the occurrence frequency and their
macro- and micro-physical properties significantly affect the cloud-radiation. On annual mean, the single-layer ice clouds
have a positive radiative forcing of 7.4 W/m 2 to heat the system, which is a result of reflecting 12.9 W/m 2 shortwave (SW)
radiation and retaining 20.3 W/m 2 longwave (LW) radiation; while the single-layer water clouds and double-layer clouds
have much stronger SW cooling effect than LW warming effect, causing a net negative forcing of 8.5 W/m 2 . Although all
these clouds have an overall small cooling effect of 1.1 W/m 2 on the annual radiative energy budget, the significant differ-
ences of the diurnal and seasonal distributions for different type clouds can lead to distinct radiative forcing. Especially the
LW warming effect induced by the exclusive ice clouds in the cold season may have an important contribution to the rapid
winter warming over the semi-arid regions.

How to cite: Wang, M.: Radiative contributions of different cloud types to regional energy budget over the SACOL site, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2679, https://doi.org/10.5194/egusphere-egu24-2679, 2024.

X5.85
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EGU24-4574
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ECS
Smoke-weather Interaction Affects Clouds, Precipitation and Extreme Wildfires in Southeast Asia
(withdrawn)
Ke Ding, Aijun Ding, Yafang Cheng, and Huang Xin
X5.86
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EGU24-7148
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ECS
Chengyi Fan and Chunsheng Zhao

Acidity stands as a pivotal physicochemical parameter influencing aerosol particles, impacting their morphology and environmental interactions, such as phase separation and the formation of secondary organic aerosols. However, directly measuring particles pH remains a challenge, necessitating urgent exploration. This study utilizes optical tweezers to investigate and compare methods for measuring pH of particle. Initial steps involved preparing a solution with sodium carbonate and sodium bicarbonate system, followed by measurement of ion concentration calibration curves for HCO3- and CO32-. Droplets were then generated using an atomizer and prepared solution. A single-beam Gaussian optical tweezers captured individual particles and obtained their Raman spectra in conjunction with a Raman spectrometer. Four methods—Henderson-Hasselbalch equation, Debye-Hückel theory, specific ion interaction theory, and thermodynamic model—were then applied to calculate pH values based on HCO3-/CO32- conjugate acid/base pairs and ion concentration calibration curves. The experimental results demonstrated small error in each calculated pH value. Additionally, the study revealed a rapid decomposition process of HCO3- in droplets, possibly attributed to the high specific surface area of small droplets or the absence of CO2 in the optical tweezers chamber. The study also monitored the evolution of pH values in sodium bicarbonate particles over time. Furthermore, the study investigated difference in pH values calculated by the four calculation methods under different ion strengths and pH values. The study also measured the pH value of sodium carbonate particles in relation to relative humidity. Overall, the experimental outcomes were reasonable and validated the capability of optical tweezers in probing the pH of atmospheric particles, offering insights into the applicable conditions of different methods and directions for refining thermodynamic models.

 

How to cite: Fan, C. and Zhao, C.: Probing pH of Particle in HCO3-/CO32- System through Optical Tweezers Coupled with Raman Spectroscopy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7148, https://doi.org/10.5194/egusphere-egu24-7148, 2024.

X5.87
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EGU24-8451
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ECS
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Yichen Jia, Hendrik Andersen, and Jan Cermak

This ongoing study uses machine learning to quantify and compare observation- and global climate model-based sensitivities of cloud fraction (CF) for marine boundary layer clouds (MBLCs) to atmospheric aerosols. In addition, differences in the meteorological influence on these sensitivities between the model and observation are examined.

Aerosol-cloud interactions in MBLCs remain one of the most substantial sources of uncertainties in climate simulations. Recent studies have reported that climate forcing from an increase in low-level liquid cloud fraction due to aerosol perturbations may be dominant. However, the impact of ambient meteorological conditions on the aerosol influence on CF continues to pose challenges as their covariability and interactions obscure the quantification of the aerosol–CF relationship.

We established a data-driven framework based on cloud droplet number concentration (Nd, as a proxy for aerosol) and CF retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) and meteorological parameters from the European Centre for Medium-Range Weather Forecasts Reanalysis v.5 (ERA5). The eXtreme Gradient Boosting (XGBoost) machine learning is applied to the daily collocated MODIS-ERA5 data (2011-2019) from 60°N to 60°S to predict CF with Nd and meteorological predictors. The Nd–CF sensitivity and its dependence on meteorological factors are quantified by SHapley Additive exPlanation (SHAP) values and SHAP interaction values. We found that both CF sensitivities and their interactions with meteorology derived from the SHAP approach exhibit distinct and coherent regional characteristics.

The ongoing work is intended to implement an identical XGBoost-SHAP setup on outputs from the ICOsahedral Non-hydrostatic-Hamburg Aerosol Module (ICON–HAM) global atmospheric-aerosol model, and to compare the magnitudes and geographical patterns of the sensitivities and interactive effects derived from observations with those from ICON-HAM. Discrepancies may point to the physics parameterization schemes in ICON-HAM which may need further evaluation of their representativity with respect to relevant processes. This novel explainable machine learning framework can potentially provide insights into parameterization tuning and enhance our knowledge of the complex aerosol-cloud-climate system.

How to cite: Jia, Y., Andersen, H., and Cermak, J.: Comparison between model and observational cloud fraction adjustment using explainable machine learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8451, https://doi.org/10.5194/egusphere-egu24-8451, 2024.

X5.88
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EGU24-16133
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ECS
Frederik Vieira Fischer and Anna Possner

Marine stratocumulus clouds contribute a significant cooling effect to the Earth's climate, but their role in global climate change hasn't been well quantified. Aerosols from anthropogenic and natural sources alter the characteristics of stratocumulus clouds, although the extend of all cloud adjustments is not yet fully quantified. In particular the cloud fraction adjustment is associated with potentially large radiative forcings, but also high uncertainties.

We used cloud retrievals from the GOES-East satellite to explore cloud fraction adjustments in raining stratocumuli structures, and MERRA-2 aerosol reanalysis data as a proxy for the aerosol-dependent cloud droplet size.

We found that increases in aerosol loading coincide with both increases and decreases in cloud fraction relative to the climatological mean. Decreases in aerosol loading coincide with increases in the fraction of optically thin cloud features which were calculated for various maximum thresholds of optical depth.

For cloud covers with cloud fractions and optically thin cloud areas close to the climatological mean, increased aerosol loading tends to coincide with increases in both of these properties. This is not the case for cloud covers that differ significantly from the climatological mean.

A better understanding of the link between how cloud fraction and optical density respond to aerosol loading could help to improve our knowledge of the effects of aerosols on the radiative properties of stratocumuli.

How to cite: Vieira Fischer, F. and Possner, A.: Exploring cloud fraction adjustments in the South Pacific marine stratocumulus cloud deck using 3 years of GOES 16 retrievals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16133, https://doi.org/10.5194/egusphere-egu24-16133, 2024.

X5.89
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EGU24-9408
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ECS
Ayodeji Oluleye, Julius Akinyoola, Ezekiel Imole Gbode, and Mariano Mertens

Outgoing Longwave Radiation (OLR) across West Africa is characterized by significant variability as a consequence of the region's diverse landscape or landuse/landcover and the influence of various climatic drivers. This study revealed spatiotemporal patterns of OLR over West Africa, aiming to enhance our understanding through the assessment of the WRF-Chem model's ability to accurately capture these dynamic processes. CAMS reanalysis dataset was used to scrutinizing the model's performance on a regional scale. Two experiments were also conducted to investigate non-aerosol and aerosol perturbation on OLR variability in the region. 

Our findings revealed a distinctive spatial heterogeneity in OLR across West Africa, particularly during different seasons. Notably, during the June-July-August (JJA) period, the Guinea coast exhibited lower OLR values (160 – 195 W/m²) attributable to dense cloud cover, increased precipitation, and elevated water vapor content. In contrast, the Sahel and Sahara Desert regions displayed an average OLR value of 225 W/m², associated with lower humidity and precipitation levels. The December-January-February (DJF) and March-April-May (MAM) seasons revealed higher OLR values (255 W/m²) in the Sahel and Sahara Desert, attributed to clear skies and reduced humidity. The evaluation of the WRF-Chem model demonstrated its competency in reproducing observed data, evidenced by a positive correlation and relatively low Root Mean Square Error (RMSE). Variations in model performance across different data points and seasonal periods were indicated by the Standard Deviation. Trend analyses also indicated an increasing trend and variability in OLR values from February to August in the Guinea Coast and Sahara Desert, contrasting with a decreasing trend in the Sahel region. In a pristine atmosphere devoid of aerosol perturbation, OLR exhibited less variability and greater consistency from the Guinea coast to the Sahara Desert, with occasional extreme values noted in the latter. Conversely, periods of aerosol perturbation revealed a wider range of OLR values, signifying increased variability influenced by aerosol-induced alterations to the atmosphere's radiative balance and energy exchange.

The study concludes that the influence of aerosol perturbations emerges as a key factor, introducing heightened variability in OLR values, which holds implications for our understanding of radiative processes in this region.

How to cite: Oluleye, A., Akinyoola, J., Imole Gbode, E., and Mertens, M.: WRFChem Simulation of Aerosol perturbation on Outgoing Longwave Radiation over West Africa's Heterogeneous Landscapes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9408, https://doi.org/10.5194/egusphere-egu24-9408, 2024.

X5.90
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EGU24-20480
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ECS
Maor Sela, Philipp Weiss, and Philip Stier

The climate impact and radiative effect of clouds and aerosols are significant. Both are among the most considerable sources of uncertainties in the climate system and in modelling the climate system. This arises not only from the fundamental uncertainty in cloud microphysics processes but also from their representation in models, and in particular in Cloud-Resolving Models (CRMs). CRMs are powerful tools for weather prediction, climate study, and investigating aerosol-cloud interactions at regional and global scales. However, they introduce a substantial degree of uncertainty due to model construction and parameterisation. To further investigate the sources of uncertainty in CRMs, we isolate two key aspects: the model's configuration (global and regional) and the employed cloud microphysics scheme (single- and double-moment schemes). Then, for each key aspect, we compare the simulated data to identify any discrepancies.
We present results from regional simulation with ICON-Sapphire in limited area mode. The region we focused on in this study is the Amazon basin, using a horizontal resolution of about 1.2 km and a time period of 8 days. First, we compare results obtained using both single- and double-moment bulk microphysics schemes, maintaining consistency in other simulation parameters. Then, we compare results obtained from both regional and global simulations utilising the single-moment bulk microphysics scheme, again maintaining consistency in other simulation parameters. 
We find that the double-moment cloud microphysics scheme yields increased ice levels and reduced precipitation rates compared to the single-moment cloud microphysics scheme. We also find that the Amazonian diurnal cycle of precipitation rate, ice, and liquid water paths is more pronounced in the global runs compared to the regional runs.
These results and other results that we will present may have implications on global radiation balance in global km-scale climate models.

How to cite: Sela, M., Weiss, P., and Stier, P.: The sensitivity of cloud micro- and macrophysical properties to cloud microphysics parameterisations and simulation setup, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20480, https://doi.org/10.5194/egusphere-egu24-20480, 2024.

X5.91
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EGU24-16381
Ana A. Piedehierro, André Welti, Yrjö Viisanen, and Ari Laaksonen

The critical supersaturation of cloud droplet activation by water-soluble aerosols increases at lower temperatures. This is due to the Kelvin effect, with the logarithm of the saturation ratio being inversely proportional to the absolute temperature and linearly proportional to the surface tensions and molecular volume of water. Less is known about the temperature dependence of critical supersaturation when the cloud condensation nuclei (CCN) are water-insoluble. 

The FHH activation theory describes the CCN activation of insoluble particles by combining the FHH (Frenkel-Halsey-Hill) adsorption isotherm and the Kelvin equation. The temperature dependence induced by the Kelvin term is inherently similar to that observed in water-soluble particles. However, the influence of the adsorption term on critical supersaturation as a function of temperature remains unclear. 

The typical temperature dependence of water vapour adsorption is such that an increase in the adsorption layer thickness is expected with decreasing temperature at a constant saturation ratio. Nevertheless, it is known that some adsorbent materials behave differently, adsorbing water vapour more efficiently at higher temperatures, while a third class of adsorbents shows no temperature dependence at all. In this study, we investigate the temperature dependencies of critical supersaturations for water-insoluble particle types that exhibit diverse temperature responses in adsorption measurements. We interpret the results in terms of the FHH adsorption activation model.

How to cite: Piedehierro, A. A., Welti, A., Viisanen, Y., and Laaksonen, A.: Temperature dependence of cloud drop activation of insoluble particles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16381, https://doi.org/10.5194/egusphere-egu24-16381, 2024.

X5.92
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EGU24-6013
Paul Zieger, Gabriel Pereira Freitas, Ben Kopec, Kouji Adachi, Radovan Krejci, Dominic Heslin-Rees, Karl Espen Yttri, Alun Hubbard, and Jeffrey M. Welker

Mixed-phase clouds are integral to the Arctic climate system as they regulate the energy transport to and from the surface. Their ice content, which influences the cloud's optical and physical properties, is regulated by the presence of ice nucleating particles (INP).  Despite this, knowledge of the sources and concentrations of INP in the Arctic is notably lacking.  Here, we investigate the abundance and variability of fluorescent primary biological aerosol particles (fPBAP) within cloud residuals at a key site at 79° North over an entire year. fPBAP have been found to be active INP at warmer temperatures. Samples were continuously collected using a multiparameter bioaerosol spectrometer coupled to a ground-based counterflow virtual impactor inlet at the Zeppelin Observatory in Ny-Ålesund, Svalbard. We found that fPBAP concentrations within cloud residuals closely aligned with the expected concentration of high-temperature INP. Transmission electron microscopy confirmed the presence of fPBAP, likely bacteria, in the cloud residual samples. Seasonal analysis demonstrated a higher presence of fPBAP within cloud residuals over the summer, with water vapor isotope measurements revealing a connection between summer cloud formation and regionally sourced air masses. Low-level MPC were predominantly observed at the beginning and end of summer, possibly due to the presence of high-temperature INP. Our study - currently under interactive discussion* - provides observational evidence supporting the role of fPBAP in determining the phase of low-level Arctic clouds, with implications for the composition of respective cloud condensation nuclei sources in the future under rapid Arctic climate and environmental change.

*Pereira Freitas, G., Kopec, B., Adachi, K., Krejci, R., Heslin-Rees, D., Yttri, K. E., Hubbard, A., Welker, J. M., and Zieger, P. 2023: Contribution of fluorescent primary biological aerosol particles to low-level Arctic cloud residuals, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-2600.

How to cite: Zieger, P., Pereira Freitas, G., Kopec, B., Adachi, K., Krejci, R., Heslin-Rees, D., Yttri, K. E., Hubbard, A., and Welker, J. M.: Determining the influence of fluorescent primary biological aerosol particles on low-level Arctic clouds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6013, https://doi.org/10.5194/egusphere-egu24-6013, 2024.

X5.93
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EGU24-18214
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ECS
Julien Lenhardt, Johannes Quaas, Dino Sejdinovic, and Daniel Klocke

Clouds are key regulators of the Earth’s energy budget. Their microphysical and optical properties lead to vastly disparate radiative properties. Retrieving information about clouds is thus crucial to reduce uncerntainties in our estimation of climate change. In this study, we present a common approach to the retrieval of cloud type and cloud base height (CBH), two useful aspects to characterise clouds and their radiative effects.

We leverage surface observations of these two cloud characterictics from the network made available by the UK Met Office, linked to satellite retrievals of relevant cloud properties from the MODIS instrument, namely cloud top height, cloud optical thickness and cloud water path. Our approach relies on a convolutional auto-encoder (AE) to project a data cube (dimension of 3 channels, 128 km, 128 km), comprised of the aforementioned cloud properties, to a latent space of lower dimensionality. The latter is then used as predictor for the cloud characteristics of interest.

We demonstrate the skill of the developed method by applying it to CBH retrievals. We create a global dataset of retrieved CBH which exhibits accuracy and precision, in particular for low-level cloud bases, achieving a mean absolute error of 379 m and a standard deviation of the absolute error of 328 m. This is also compared to active satellite retrievals and other CBH retrieval methods. The second application focuses on cloud types, defined following the standards of the WMO. With our approach, we retrieve cloud type occurences at a global scale and are able to study their spatial and temporal patterns. We further use the developed method on km-scale global climate model outputs from the ICON model to help diagnostic cloud representation in this new generation of climate models. Lastly, the presented applications illustrate how fusing surface observations and satellite retrievals still constitutes a resourceful approach to study clouds and their properties.

How to cite: Lenhardt, J., Quaas, J., Sejdinovic, D., and Klocke, D.: Leveraging surface observations and passive satellite retrievals of cloud properties: Applications to cloud type classification and cloud base height retrieval, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18214, https://doi.org/10.5194/egusphere-egu24-18214, 2024.

Posters virtual: Fri, 19 Apr, 14:00–15:45 | vHall X5

Display time: Fri, 19 Apr, 08:30–Fri, 19 Apr, 18:00
Chairperson: Edward Gryspeerdt
vX5.5
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EGU24-4329
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ECS
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Highlight
Peter Manshausen, Duncan Watson-Parris, and Philip Stier

Aerosol-cloud interactions continue to resist reliable quantification, partly owing to their strong dependence on cloud and weather regimes. For a long time, opportunistic experiments such as ship tracks have been used to overcome issues of confounding. Recent advances leverage (i) Machine Learning (ML) to drastically enlarge ship track data bases, and (ii) ‘invisible ship tracks’, found by advecting ship emissions, to overcome selection biases in ship track studies. Here, we combine both approaches, to advance our understanding of how meteorology controls cloud responses to aerosol emissions. Firstly, we show that even though the ML dataset is much larger than previous hand-logged data sets, it still contains only a fraction of less than 1% of the cloud regions polluted by shipping. This means less than 1% of ship tracks are visible. Secondly, we find that this fraction varies strongly with location and season, with the Southern Hemisphere winter leading to most visible tracks in the Stratocumulus regions of the SE Pacific and SE Atlantic. Thirdly, we identify meteorological regimes favourable to the visibility of tracks, using ML methods such as Random Forests and Explainable AI, alongside traditional methodsThe regime favourable to visible tracks is defined by a stable lower troposphere and little vertical movement, low sea surface temperatures, high cloud cover, and low boundary layer heights. Lastly, we quantify the link between ship track visibility and albedo change in polluted clouds, establishing to what extent days with visible tracks are those when cloud albedo is most susceptible to aerosol. Building on this relationship, a predictive model like our Random Forest has applications in deliberate Marine Cloud Brightening by predicting the days that are most susceptible to aerosol perturbations.

How to cite: Manshausen, P., Watson-Parris, D., and Stier, P.: Comparing ML retrieved and invisible ship tracks to probe the meteorological dependence of cloud susceptibility to aerosol, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4329, https://doi.org/10.5194/egusphere-egu24-4329, 2024.