Cloud condensation nuclei (CCN), ice-nucleating particles (INPs), and secondary ice production (SIP) are central to cloud microphysical processes and radiative feedbacks, with far-reaching influences on weather and climate dynamics. This session focuses on the interactions between aerosols, CCN, INPs, and SIP, and their impacts on cloud properties, based on both laboratory and field studies.
Particular attention will be given to the Southern Ocean (SO), one of the cloudiest regions on Earth. Its pristine aerosol environment offers a natural laboratory for disentangling fundamental aerosol- cloud -radiation interactions in the relative absence of anthropogenic pollution, thereby providing critical insights into cloud microphysical processes.
We invite contributions that address pressing open questions on the coupling between gas-phase chemistry, aerosol nucleation and growth, cloud development, precipitation, and radiative impacts, with an emphasis on the Southern Hemisphere. Special focus will also be placed on advancing our understanding of SIP mechanisms, their influence on cloud evolution, and their representation in weather and climate models.
Topics of interest include:
• Laboratory studies on INPs and secondary ice production
• Aerosol, CCN, and INP sources and characteristics from field measurements (e.g., in-situ flight campaigns)
• Modeling of secondary ice production processes
• Advances in parameterizations of cloud formation and development in models (e.g., deep convective clouds, mixed-phase clouds, mesoscale convective systems)
Solicited Speaker: Prof. Dr. Mira Pöhlker, Leibniz Institute for Tropospheric Research (TROPOS), Germany.
Solicited Presentation: " The interplay of Clouds, Aerosols and Radiation above the Southern Ocean".
The Southern Ocean (SO) is one of the cloudiest regions on Earth. However, cloud radiative effects are not well represented over the SO in atmospheric models, which is mainly due to an underestimation of aerosols. To address this and other fundamental and pressing open questions on the interaction of atmospheric radiation, aerosol nucleation and growth, cloud formation and impacts over the SOI, the HALO-South aircraft mission was conducted in September and October 2025 based in Christchurch, Aotearoa New Zealand. HALO stands for High Altitude and Long Range Research Aircraft. HALO-South covered the full cycle of processes from aerosol formation, cloud evolution, and radiative interaction with a special focus on the characteristics and effects of mixed-phase clouds. The instrumental payload of HALO included a unique and comprehensive in-situ and remote sensing suite of instruments. It was designed to collect data to improve our understanding of fundamental atmospheric processes and to extrapolate and upscale the results using satellite data and global climate models in order to resolve long-standing measurement-modelling discrepancies. In addition, the ground-based stations in Tāwhaki and Invercargill with remote sensing and in-situ long term measurements will extend the data to a larger scale in time. The first analysis of the campaign shows promising insights into cloud and aerosol processes over the SO, which will be presented and discussed.
Acknowledgments: This work was supported by the DFG (Deutsche Forschungsgemeinschaft, German Research Foundation) Priority Program SPP 1294, the Max Planck Society, Priority Program SPP 1294, the German Aerospace Center (DLR)
How to cite: Pöhlker, M. L., McDonald, A., Chang, Y., Coulson, G., Curtius, J., Ehrlich, A., Gordon, H., Henning, S., Kalesse-Los, H., Möhler, O., Mertes, S., Pöhlker, C., Pöschl, U., Sauer, D., Schneider, J., Seifert, P., Stratmann, F., Voigt, C., Wendisch, M., and Ziereis, H.: The interplay of Clouds, Aerosols, and Radiation above the Southern Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16802, https://doi.org/10.5194/egusphere-egu26-16802, 2026.
Ice Nucleating Particles (INPs) are a minor, strongly temperature-dependent subset of atmospheric aerosol particles that initiate primary ice formation (e.g., Forster et al., 2021). In cirrus and mixed-phase clouds (MPCs), they have an influence on the Earth’s radiative budget, and in MPCs, ice crystals often initiate the formation of precipitation. Over the past decades, various measurements were performed at boundary layer field sites to measure the INP concentration at mixed-phase cloud conditions (e.g., data compiled in Kanji et al., 2017). However, there is a lack of INP measurements in the free troposphere, as they can only be conducted by aircraft-based measurements or at high altitude mountain stations. In order to better understand and predict the formation of MPC and cirrus clouds, as well as their role in the climate system, direct INP measurements at different altitudes are required.
The HALO-South campaign, which investigated the interplay of clouds, aerosols and radiation above the Southern Ocean, took place in New Zealand in September/October 2025. For the first time, our newly developed INP instrument, PINEair (Portable Ice Nucleation Experiment airborne; Bogert, 2024), was on board the HALO aircraft. The instrument is a further development of the expansion-type cloud chamber design of PINE (Möhler et al., 2021). PINEair can measure INPs in an automated way at both mixed-phase cloud and cirrus cloud temperatures down to -60 °C with a time resolution of about 2min.
In this contribution, we present first results of the INP concentration measured at different temperatures during various flights, ranging from very clean air masses originating from Antarctica to more polluted ones from Australia. The PINEair measurements were successfully performed over a wide altitude range, covering the boundary layer up to the free troposphere.
References
Bogert, P. Ice-nucleating particles in the free troposphere: long-term observation and first measurements at cirrus formation temperatures using the novel Portable Ice Nucleation Experiment PINEair, Ph.D. thesis, Karlsruhe Institute of Technology, https://doi.org/10.5445/IR/1000174265, 2024.
Kanji, Z., et al. Ice formation and evaluation in clouds and precipitation: Measurement and modeling challenges, Meteorological Monographs, 58, 2017.
Möhler, O., et al. The Portable Ice Nucleation Experiment (PINE): a new online instrument for laboratory studies and automated long-term field observations of ice-nucleating particles, Atmospheric Measurement Techniques, 14, 1143–1166, 2021.
Forster, P., T. Storelvmo, K. Armour, et al. The Earth’s Energy Budget, Climate Feedbacks, and Climate Sensitivity, In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 923–1054, doi:10.1017/9781009157896.009, 2021.
How to cite: Bogert, P., Lacher, L., Klebach, H., Nadolny, J., Richter, S., Russell, D., Curtius, J., and Möhler, O.: Sources and variability of ice-nucleating particles in the Southern Ocean region measured with PINEair on board the HALO aircraft, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11960, https://doi.org/10.5194/egusphere-egu26-11960, 2026.
Mixed-phase clouds associated with cold-air outbreak (CAO) events are natural laboratories to study mixed-phase cloud processes which are important for our estimation of cloud-phase feedback. These CAO clouds have also been shown vital to the radiative bias over the Southern Ocean. Recent studies show that CAO clouds are sensitive to aerosols including cloud condensation nuclei (CCN) and ice-nucleating particles (INPs), as well as secondary ice production (SIP). Therefore, it is vital to understand how these processes affect the radiative properties of CAO clouds and their roles in the cloud-phase feedback mechanism. However, many modelling studies have investigated the effects of these processes by perturbing model parameters individually, limiting the investigation of joint effects from multiple processes on cloud properties.
Here we investigated how six cloud microphysics parameters jointly affect CAO cloud properties by building model emulators trained on output from perturbed parameter ensembles (PPEs) of a high-resolution regional model. The selected CAO case was on 24 October 2022 over the Labrador Sea, which coincided with the M-Phase aircraft campaign. The parameters are cloud droplet number concentration (Nd), ice-nucleating particle concentration (NINP), efficiencies of three SIP processes including the rime-splintering, ice-ice collisional breakup and droplet shattering, as well as the mixed-phase overlap factor (mpof) which controls the spatial overlap between liquid and ice clouds within model grid cells. The perturbed ranges of these parameters either match the observed ranges when available or were chosen based on uncertainty ranges suggested by previous studies.
For the CAO case studied, Nd and NINP most strongly control the cloud radiative properties in the stratocumulus region; whereas in the cumulus region, Nd and mpof are the most important parameters. Variations of SIP efficiencies have stronger effects in the cumulus region compared to their effects in the stratocumulus region, but their effects on radiative properties are generally weaker compared to the other three parameters (Nd, NINP and mpof).
Our results show that these parameters have non-linear joint effects such that the magnitude and even sign of cloud responses to a parameter are highly dependent on the values of other parameters. For example, the sensitivity of cloud albedo to increases in NINP varies between near zero and strongly negative across the sampled parameter space. Therefore, perturbing parameters individually is an inadequate method for determining the cloud responses to model parameters and can potentially lead to misleading conclusions.
This work illustrates the power of using PPEs and model emulation for systematically quantifying the sensitivities of CAO cloud properties to important cloud microphysics parameters and identifying the interactions among model parameters. Exploration of the entire parameter space is compulsory to fully understand the influences on CAO clouds from these parameters, and to constrain the uncertainties from mixed-phase cloud processes on cloud-phase feedback mechanism.
How to cite: Huang, X., Field, P., Herbert, R., Murray, B., Grosvenor, D., Van Den Heuvel, F., and Carslaw, K.: Interacting effects of aerosols and ice formation processes on mixed-phase cold-air outbreak clouds , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17256, https://doi.org/10.5194/egusphere-egu26-17256, 2026.
The region of the Southern Ocean (SO) is a current hot-spot of research related to aerosol-cloud interactions. On the one hand, detailed observations of aerosols and clouds and their interactions are required to explain the shortwave radiation bias in model simulations. On the other hand, the clean environment of the SO atmosphere allows the study of the impact of even slight variabilities in the aerosol load on cloud and precipitation processes and on the radiation budget of the atmosphere.
The goSouth-2 project led by Leibniz Institute for Tropospheric Research (TROPOS) contributes with a unique long-term dataset of remote-sensing and in-situ measurements of cloud-relevant aerosol properties and associated cloud properties for the northern edge of the SO. The core facility of goSouth-2 is the ACTRIS station LACROS (Leipzig Aerosol and Cloud Remote Observations System) which has been deployed on the premises of the New Zealand MetService in Invercargill (46.4173 °S, 168.3307 °E, 3 m a.s.l., https://cloudnet.fmi.fi/site/invercargill) at the southern tip of the New Zealand’s South Island. The characterization of aerosol optical properties is observed by a newly-built PollyXT lidar. This system yields backscatter coefficient and depolarization ratios at 355, 532, and 1064 nm. Extinction coefficients are derived from Raman scattering at 387 and 607 nm. Raman scattering by water vapour at 407 nm yields observations of the water vapour mixing ratio. In addition, it is the first PollyXT lidar which includes a 460-nm fluorescence channel enabling a more refined discrimination between smoke, biological aerosols, and other types of pollution. Cloud properties are covered by 94- and 35-GHz cloud radar observations, of which the latter provides RHI and PPI scans for characterization of hydrometeor shapes and the horizontal wind field. Surface in-situ observations of the aerosol size distribution, cloud condensation nuclei concentrations, and off-line characterization of ice nucleating particle (INP) concentrations are performed. goSouth-2 is involved in the project ACADIA jointly run by Leipzig University and TROPOS, the HALO-South aircraft campaign, ongoing EarthCARE Cal/Val activities, and is conducted in close collaboration with partners from University of Canterbury, Earth Sciences New Zealand, and MetService, NZ. The latter contributes 2 radiosonde launches per day and weather radar observations.
First conclusions drawn from the dataset to date are that aerosol in the cloud-free troposphere is rare. If present, it can mostly be assigned to wildfires or dust from Africa or Australia. In SO air masses ice formation in clouds warmer than -4°C is frequently absent, confirming the lack of efficient INPs. The majority of stratiform precipitation systems is found to be embedded in Australian air masses. A remarkable feature is that enhanced loads of Australian aerosols (dust, smoke) are frequently associated with enhanced turbulence in the affected cloud systems, similar to the dusty-cirrus phenomenon. Observations of the lowest 3 km of marine atmosphere, show a complex aerosol structure containing multiple embedded sub-layers of differing aerosol properties, whose effects on cloud formation remain to be identified. We use co-located observations from goSouth-2, the HALO-South aircraft campaign, and EarthCARE to characterize the observed scenarios.
How to cite: Seifert, P., Radenz, M., Gaudek, T., Lukas, P., McCosh, G., Ohneiser, K., Engelmann, R., Baars, H., Skupin, A., Henning, S., Wehner, B., Pöhlker, M., Wandinger, U., Ansmann, A., Alder, K., Kalesse-Los, H., McDonald, A., and Coulson, G.: The goSouth-2 campaign in Invercargill, New Zealand:First insights into heterogeneous ice formation and the effects of Australian aerosols on clouds at the edge of the Southern Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19921, https://doi.org/10.5194/egusphere-egu26-19921, 2026.
Secondary ice production (SIP) is increasingly recognized as a key regulator of ice crystal number concentrations and cloud phase in mixed-phase clouds (MPCs). In the EC-Earth3-AerChem model, we recently showed that SIP, implemented via a machine-learning-based parameterization, may strongly amplify ice crystal numbers in MPCs, particularly in regions with weak primary ice nucleation such as the Southern Ocean, and can substantially modify cloud phase partitioning and radiative effects. However, those findings were obtained within a model configuration with known limitations in cloud microphysics and supersaturation treatment, motivating their re-examination in the next generation of EC-Earth.
Here we present the implementation of SIP in EC-Earth4, using its new atmospheric core OIFS48r1, which features major updates to mixed-phase cloud microphysics. Building on the EC-Earth3 framework, we implemented in OIFS48r1 aerosol-aware immersion freezing with a machine-learning-based SIP parameterization (RaFSIP), allowing ice multiplication to respond dynamically to cloud thermodynamic and microphysical conditions. This configuration provides, for the first time in EC-Earth4, a physically consistent link between aerosol-controlled primary ice formation and secondary ice amplification.
The model is evaluated against satellite-derived cloud properties from MODIS and CALIPSO, and radiative fluxes from CERES-EBAF. The experimental design enables us to quantify how SIP modifies ice crystal number concentrations and liquid–ice phase partitioning relative to both temperature-based and aerosol-aware primary ice nucleation. Before introducing aerosol-driven ice nucleation and SIP, OIFS48r1 already shows substantial baseline improvements relative to EC-Earth3, including reduced biases in liquid and ice water paths across latitudes. These improvements provide a more robust framework for isolating the climatic role of SIP in a next-generation model.
By extending the SIP analysis from EC-Earth3 to EC-Earth4, this work establishes a consistent modelling framework to assess how secondary ice production interacts with aerosol-controlled primary ice formation, paving the way for more reliable projections of mixed-phase cloud feedbacks in future climate simulations.
How to cite: Costa-Surós, M., Chatziparaschos, M., Gonçalves Ageitos, M., Vacondio, S., Bergman, T., Georgakaki, P., Holopainen, E., Huijnen, V., Kokkola, H., Laakso, A., Le Sager, P., Nenes, A., van Noije, T., Wu, L., and Pérez García-Pando, C.: The Role of Secondary Ice Production in Shaping Mixed-Phase Clouds in EC-Earth4, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17587, https://doi.org/10.5194/egusphere-egu26-17587, 2026.
Aerosol particles play a critical role as cloud condensation nuclei (CCN) in the atmosphere. The capacity of aerosol particles to activate into cloud droplets is measured experimentally using CCN counters (CCNCs). Recent findings suggest that the co-condensation effect of semi-volatiles can enhance aerosol particle growth and cloud droplet activation. Conventional CCNCs, such as the streamwise CCNC, heat particles (>30°C) as they transit the CCNC column and may inadvertently not capture the co-condensation effect, leading to an underestimate in CCN concentrations. Additionally, streamwise CCNCs struggle to achieve supersaturations (SS) below 0.13%. In pristine marine environments like the Southern Ocean, where particles are highly hygroscopic (κ≈0.9), getting reliable activation (i.e., critical supersaturation) of particles above 120 nm (i.e., the accumulation mode) could be challenging. This could result in 'activation blindness,' preventing precise CCN characterization of these climatically relevant particles.
To address these limitations, we developed the Horizontal CCNC (HCCNC), which can generate SS at temperatures down to 4 °C and SS level to 0.05%. This capability provides researchers with a unique platform to investigate the co-condensation effect, enabling studies that test the hypothesis that preserving semi-volatile fractions at atmospherically relevant temperatures may significantly enhance droplet activation. Furthermore, the ability to achieve stable SS down to 0.05% extends the observational window to include larger CCN (200 nm for pure ammonium sulfate) and highly hygroscopic particles characteristic of pristine marine environments like the Southern Ocean, as well as those used in weather modification and cloud seeding. The HCCNC also addresses operational inefficiencies inherent in current technology: streamwise CCNCs suffer from thermal inertia, requiring minutes to stabilize new SS setpoints, resulting in measurement dead time and data loss. In contrast, the HCCNC demonstrates rapid thermal response, enabling a “Flash Scan” capability that spans 0.05% to 0.8% SS in under one minute, combined with a modular, user-friendly design.
This study presents the development of the HCCNC, providing a detailed technical description of its 3D geometry, computational fluid dynamics simulations, and the key components that demonstrate its performance. Sampling and humidity generation followed the principle of the previously used continuous-flow thermal-gradient diffusion chambers. The instrument’s performance is validated by conducting laboratory tests using ammonium sulfate ((NH₄)₂SO₄) particles in the size range between 50 and 200 nm and for temperatures between 30 and 8 °C. To ensure these advancements are accessible to the wider scientific community, the HCCNC technology has been patent-filed, and commercialization efforts are currently underway to allow researchers to fully leverage its potential.
How to cite: Sapkal, M. G., Rösch, M., and Kanji, Z. A.: Development of the Horizontal Cloud Condensation Nuclei Counter (HCCNC) to Detect Particle Activation Down to 4 °C Temperature and 0.05% Supersaturation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3295, https://doi.org/10.5194/egusphere-egu26-3295, 2026.
Methanesulfonic acid (MSA) has recently been identified as an efficient driver of new particle formation and growth under cold atmospheric conditions, exhibiting ultra low volatility the same way sulfuric acid (SA) does. Both MSA and SA originate from the oxidation of volatile methylated sulfur compounds (VMS), particularly dimethyl sulfide (DMS) and methyl mercaptan (MeSH), with MeSH acting as a significant but previously overlooked source of these compounds, which constitute a major natural source of atmospheric sulfur. In cold regions, oxidation pathways favour MSA over SA production, leading to elevated MSA-to-SA ratios over the polar regions and the Southern Ocean.
In this study, the representation of marine sulfur was revised in the global chemistry–climate model EMAC by updating DMS emissions, explicitly including MeSH, and extending the associated gas-phase, multiphase, and aerosol chemistry of SA and MSA. The model is evaluated against observations from four ship campaigns and nine ground-based stations in oceanic regions, spanning four years and covering diverse latitudes and longitudes. MSA condensation onto particles, its aqueous-phase processing in aerosols and clouds, and its contribution to particle growth are treated explicitly. A volatility-dependent MSA nucleation parameterization is implemented to capture efficient particle formation in cold, MSA-rich environments.
Including MSA-driven particle formation and growth in EMAC leads to an increase of at least 50% in cloud condensation nuclei (CCN) concentrations over the Antarctic and Southern Ocean. This demonstrates that MSA is a major driver of particle formation and growth in these climate-critical regions, which have traditionally been associated with large uncertainties in CCN abundance and associated aerosol–cloud–climate interactions in global climate models.
How to cite: Ruhl, S., Kohl, M., Xenofontos, C., Baalbaki, R., Vella, R., Tost, H., Christoudias, T., Sander, R., and Pozzer, A.: Methanesulfonic acid revealed as major driver of particle formation over polar regions and the Southern Ocean: a global EMAC study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18230, https://doi.org/10.5194/egusphere-egu26-18230, 2026.
Biases in surface radiation and sea surface temperature in climate models are larger over the Southern Ocean than anywhere else in the world, severely impacting on our ability to predict global climate. These biases are thought to be caused by the poor representation of mixed-phase clouds in the region, including aerosol-cloud interactions such as the role of atmospheric ice-nucleating particles (INPs). INPs can trigger the freezing of supercooled liquid cloud droplets, greatly influencing the lifetime and radiative properties of mixed-phase clouds. To better understand the role of INPs in the Southern Ocean, it is crucial to know their sources and concentrations, but there are relatively few INP measurements from the region, particularly around the Antarctic Peninsula. Further, discrepancies have been noted between INP measurements from traditional polycarbonate filter analysis techniques and other methodologies during recent field campaigns
We have collected the first ever set of combined real-time and offline measurements of INPs around the Antarctic Peninsula, South Sandwich Islands, and South Georgia during the Southern Ocean Clouds (SOC) research cruise during the austral summer of 2024. The cruise took place aboard the RRS Sir David Attenborough over a period of 5 weeks in November/December, and covered an area from 50° S to 67° S and 70° W to 25° W. Online INP measurements were collected every 6 min using a Portable Ice Nucleation Experiment (PINE) chamber, which uses adiabatic expansion to generate a cloud and then detects the INP concentrations within the cloud. Even with such a short time resolution, INP concentrations >0.5 INP L−1 were measured throughout the cruise at temperatures of −25 to −28 °C.
These measurements were supported by offline filter measurements, with INP concentrations measured using a traditional droplet freezing assay. Importantly, two types of filter were used to collect and analyse the samples: polycarbonate filters prepared using a traditional “wash off” procedure, and Teflon filters using a “drop on” droplet freezing technique. The traditional polycarbonate method yielded very low INP concentrations, consistent with recent literature data for the Southern Ocean region, while the Teflon filters showed much higher concentrations, including when the two filter types were run side-by-side. This suggests, in line with our recent lab-based studies, that the traditional polycarbonate washing technique employed in INP analysis may be missing a fraction of INPs during measurements, and that INP concentrations may be undercounted in some scenarios including in the Southern Ocean
Here, we present initial findings of the INP concentrations collected throughout the SOC cruise, including discussion of the inconsistencies between filter techniques.
How to cite: Tarn, M., Wadlow, I., Robinson, J., Herbert, R., Kirchgaessner, A., Lachlan-Cope, T., and Murray, B.: Higher than expected ice-nucleating particle concentrations in the Southern Ocean: Preliminary findings from the SOC 2024 cruise, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20619, https://doi.org/10.5194/egusphere-egu26-20619, 2026.
How to cite: Portman, B., Connolly, P., Blyth, A., and Wu, H.: Secondary ice production in summer deep convective clouds over New Mexico during the DCMEX campaign, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12512, https://doi.org/10.5194/egusphere-egu26-12512, 2026.
The radiative budget, atmospheric charging and the ability of mixed-phase clouds to form precipitation strongly depends on the presence of ice crystals. Observations indicate that secondary ice formation processes play an important role in increasing ice crystal number concentration in mixed-phase clouds. We focus on secondary ice formation during riming, which is also knows as rime-splintering (RS) or Hallett-Mossop process. Most knowledge about RS is based on old laboratory experiments with quantitatively inconsistent results and lacks a fundamental mechanistic understanding.
To overcome this knowledge gap, we developed an experimental set-up IDEFIX (Ice Droplets splintering on FreezIng eXperiment) to study RS using high-speed video microscopy, thermography system and custom-built ice counter to detect secondary ice particles. In contrast to earlier studies - no efficient secondary ice formation was observed under near-atmospheric conditions. This fundamentally questions the RS process and motivates further laboratory investigations in a broader parameter range to elucidate under which conditions RS is existing. Recent insights on the dependence of RS efficiency on ice surface roughness and the role of small riming droplets will be presented.
Our study will contribute to the development of new parameterizations of secondary ice formation for cloud microphysics-resolving models.
How to cite: Hartmann, S., Reiser, M., Lloyd, P., Seidel, J., Kiselev, A., Niedermeier, D., Leisner, T., and Pöhlker, M.: New insights on Secondary Ice Production during Riming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12977, https://doi.org/10.5194/egusphere-egu26-12977, 2026.
Ice formation in clouds has long been studied through field measurements and also in laboratories under controlled conditions in cloud chambers. It has been frequently observed that ice particle concentration exceeds those of ice-nucleating particles by several orders of magnitude. This discrepancy suggests the involvement of Secondary Ice Production (SIP) via different mechanisms which remain only partially understood. Consequently, ice multiplication is only very crudely included in cloud models. Another fundamental characteristic of clouds is their turbulent nature. It is already known that turbulence plays a major role in the droplets growth but it could also be important for SIP-mechanisms as it affects the hydrometeors dynamics. In this work, we focus on SIP-mechanisms that involve collisions between particles. Using Direct Numerical Simulations (DNS) of homogeneous-isotropic turbulence at low Reynolds numbers with Lagrangian point-particle tracking allows us to study the influence of turbulence on the collision rate between particles and to compare it with the gravitational collision rate traditionally used in cloud modelling simulations. Furthermore, a model simulating the emission of secondary ice fragments when a collision is detected has been implemented in the code. This enables the analysis of how ice particle population evolves across different scenarios, helping to identify which parameters play a significant role and under which conditions a significant increase in ice concentration occurs. Preliminary results show that it is indeed possible to reproduce an ice explosion phenomenon and its magnitude and triggering moment depend on the initial concentration of ice particles and the turbulent Reynolds number.
How to cite: Le Roy De Bonneville, F., Uhlmann, M., and Hoose, C.: Turbulence effects on Secondary Ice Production: Insights from Point-Particle Direct Numerical Simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10720, https://doi.org/10.5194/egusphere-egu26-10720, 2026.
Several observational studies show that ice crystal number concentrations in relatively warm (temperatures above -10 °C) Arctic mixed-phase clouds can exceed 1 L-1 while concentrations of ice-nucleating particles (INPs), which produce primary ice by initiating cloud droplet freezing, are several orders of magnitude lower. The difference is often explained by secondary ice production (SIP). The three most common SIP mechanics are Hallet-Mossop process also called as rime splintering (RS), ice-ice collisional breakup (IIBR), and droplet shattering during freezing (DS). Our large-eddy simulation (LES) model called UCLALES-SALSA accounts for these processes in addition to aerosol-cloud interactions and different primary freezing processes. In our recent study (Raatikainen et al., EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-4470, 2025) we used observations from the ACLOUD (Arctic CLoud Observations Using airborne measurements during polar Day) campaign to derive setups for LES simulations which aim at reproducing the observed ice crystal number concentrations exceeding 1 L-1 at about -5 °C cloud top temperatures. At this temperature, INP concentrations are about three orders of magnitude lower than the observed ice concentration, so secondary ice production is likely occurring. The first simulations showed that rime splintering is the most effective SIP process while IIBR and DS have negligible impact. However, RS cannot produce enough secondary ice to match the observations. The observed ice concentrations can be reached by artificially increasing the efficiency of RS SIP. When ice concentration becomes high enough, SIP starts to maintain itself so that primary cloud droplet freezing is not needed at all. Additional sensitivity tests showed that the same result can be obtained by using different model parameterizations (e.g., mass-dimension-fall velocity or the temperature-dependent efficiency of the RS parameterization) or slightly cooler cloud temperatures. Overall, these results show that rime splintering can explain the observed high ice concentrations in such relatively warm and shallow mixed-phase clouds, but the process is also sensitive to model parameterizations and cloud temperatures.
How to cite: Raatikainen, T., Calderón, S., Järvinen, E., and Romakkaniemi, S.: Modelling the impacts of secondary ice production in Arctic mixed-phase clouds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16134, https://doi.org/10.5194/egusphere-egu26-16134, 2026.
The contribution of newly formed aerosol particles to cloud condensation nuclei (CCN) via gas-to-particle (GTP) conversion is highly uncertain. Here, we present results from a one-month simultaneous measurement of aerosol number concentration (N10-299.6) and CCN concentrations (NCCN) over a seemingly unpolluted location, Dibrugarh, in the Eastern Himalayan Foothills, during the winter of 2023. The average diurnal variation of NCCN at different supersaturations is in line with the scanning mobility particle sizer (SMPS)-measured N10-299.6 with a systematic diurnal variation of highest (lowest) concentrations during nighttime (daytime) under the influence of planetary boundary layer (PBL) dynamics. We have identified four new particle formation (NPF) events during the study period, with a frequency of ~13% of the study days. The distinct mode of average PNSD at the lower size regime (<25 nm) determines the NPF burst. Later, they continue to grow through coagulation and condensation processes with a growth rate ranging from 4.5 to 7.2 nm h−1. The growth process begins with coagulation, followed by condensation, which becomes the dominant mechanism in the formation of CCN. Moreover, the enhancement factor of CCN due to NPF (E_NCCN) was estimated to examine the aerosol-CCN interaction and was found to vary between 2.32 to 7.74 for all four NPF events at the supersaturation range of 0.2-1%. These values are in line with many urban places across the globe. However, state-of-the-art instruments and longer temporal analyses of CCN concentrations, as well as NPF precursor dynamics, are required to evaluate the seasonality and in-depth understanding of the processes.
How to cite: Das, B., Pathak, B., Bhattacharjee, U., Kundu, A., Kundu, S. S., Gogoi, M. M., Borgohain, A., and Bhuyan, P. K.: Enhancement of Cloud Condensation Nuclei during NPF events over a location in Eastern Himalayan Foothills , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-589, https://doi.org/10.5194/egusphere-egu26-589, 2026.
Ice-nucleating particles (INPs) play a critical role in cloud microphysics by initiating ice formation in mixed-phase clouds. Ice nucleation (IN) on mineral dust, which is the most abundant atmospheric INP type, is controlled by rare surface sites that may not represent the average mineral surface. Soil dusts containing biogenic material have shown to contribute to IN at even higher temperatures than pure mineral dusts. The question therefore arises how interactions between minerals and organic macromolecules, such as proteins, modify the IN ability of either. To date, the potential of proteins to directly adsorb onto mineral surfaces and contribute to IN remain largely unknown.
Using an experimental bottom-up approach, we investigate protein adsorption on a clay mineral and its implications for immersion freezing with the Super DRoplet Ice Nuclei Counter Zurich (S-DRINCZ) offering the option of parallel cooling several well plates. The clay mineral kaolinite (0.1–0.01 wt%), which exhibits a median freezing temperature T(50) of −7.5 °C at a concentration of 0.1 wt% was mixed with the protein ferritin (0.1–0.0025 wt%), which shows a slightly higher T(50) of −6.9 °C at the same concentration in its pure form, and the mixtures were analyzed with respect to their IN ability. Complementary UV/VIS spectroscopy is employed to determine the adsorption capacity onto kaolinite, while transmission electron microscopy (TEM) combined with EDX spectroscopy is used to localize ferritin on mineral surfaces to identify preferential adsorption sites via the iron- rich core of the protein. These results provide new insights into how mineral–protein interactions modify IN in atmospheric dust particles.
How to cite: Krautwig, T. and Marcolli, C.: Protein Adsorption on Clay Minerals: Implications for Ice Nucleation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9745, https://doi.org/10.5194/egusphere-egu26-9745, 2026.
Cloud ice forms primarily through immersion freezing in the mixed-phase regime between 0°C and -38°C. Immersion freezing is the nucleation of a liquid cloud droplet with an immersed ice nucleating particle (INP), which reduces the energy barrier for cloud ice formation. INPs are rare aerosols, and due to measurement challenges and limitations in instrument capabilities, the availability of atmospheric observations of INPs remains scarce. Thus, obtaining a global distribution of INPs using observations has so far been challenging.
Here, we will show that, through the use of the gradient boosting machine learning algorithm XGBoost, we can predict a realistic global distribution of INPs based on temperature and Copernicus Atmosphere Monitoring Service (CAMS) reanalysis aerosols. The aerosols included are three modes of dust and sea salt, sulfate, and anthropogenic black and organic carbon, both hydrophilic and hydrophobic components. We further add a land mask, a binary identifier to contrast the oceans from land. Aerosols are collocated with about 40 observed INP datasets, sparsely distributed across the globe. Approximately 85% of the data are land-based locations.
The XGBoost model performs well. Predicted regional INP spectra with temperature using CAMS four-year climatology show a good agreement with the observations, with values within one order of magnitude for most regions. Antarctica is an outlier, and a large model bias is obtained. Spatially, the XGBoost predicts a realistic pattern with peaks over deserts and lower values across the oceans. Model sensitivity to hyperparameters reveals large variations in predicted INPs over the Arabian Peninsula and North Africa, followed by Antarctica. The presented approach can act as a cost-effective immersion freezing parameterisation in global and regional weather and climate models. To this end, some preliminary results using the ICOsahedral Non-hydrostatic (ICON) model with this new parameterisation will be shown.
How to cite: Wallentin, G. and the Modelling INPs Team: Modelling a Global Distribution of Ice Nucleating Particles using Machine Learning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12119, https://doi.org/10.5194/egusphere-egu26-12119, 2026.
Alkali feldspars have been identified as the most efficient ice-nucleating particles in airborne mineral dust [1, 2]. However, alkali feldspars exhibit large mineralogical variations which is also reflected in substantial differences in their ice-nucleating efficiency [2,3,4]. Identifying the mineralogical or surface characteristics responsible for the high ice-nucleation activity of certain alkali feldspars could advance our understanding of ice nucleation in mixed-phase clouds.
For this study, seven natural alkali feldspars, ranging from homogeneous gem-quality sanidines to hydrothermally altered, micropore-rich perthitic microclines were characterized with petrographic microscopy, electron probe micro analysis (EPMA) and powder X-ray diffraction (pXRD). The ice nucleation efficiency was investigated by means of cooling ramp experiments conducted at a cooling rate of 2 K min-1 on a cold stage, using (001) and (010) cleavage plates as well as 1 wt% suspensions of 2–8 µm powder from each sample. For two gem-quality samples and one perthitic microcline, additional experiments were performed using 0.05 wt% suspensions of 2–8 µm powder as well as 0.5–2 µm powder to assess the influence of particle surface area and grain size. In these experiments, 7 nl droplets of the suspension were dispensed on Si-wafers, while for cleavage plate experiments, 7 nl droplets of nanopure water were dispensed onto the samples. Droplet freezing events were detected using an infrared camera.
Hydrothermally altered perthitic microclines exhibit the highest ice nucleation activity in both cleavage plate and suspension experiments. The lowest ice-nucleation activity was observed for gem-quality sanidine in suspension experiments and for (001) cleavage plates of gem-quality orthoclase. For microcline, and more prominently for orthoclase (both perthitic and gem-quality), (010) cleavage plates showed higher freezing temperatures than (001) plates. The freezing sequence of droplets on cleavage plates was more strongly influenced by surface topography in gem-quality samples than in perthites, indicating that freezing in perthites is predominantly controlled by mineralogical features.
The ice-nucleation activity of gem-quality samples was more sensitive to particle surface area than that of perthitic samples, showing a stronger decrease in freezing temperatures at lower suspension concentrations and a more pronounced increase with decreasing particle size.
We conclude that features related to perthitic exsolution, a high degree of Al-Si-ordering and - for orthoclase and microcline - the crystallography of (010) surfaces are key factors for the high ice-nucleating activity of alkali feldspars.
[1] Atkinson et al., Nature (2013) 498(7454), 355-358, doi:10.1038/nature12278
[2] Whale et al. Phys. Chem. Chem. Phys. (2017) 19, 31186—31193, doi:10.1039/c7cp04898j
[3] Harrison et al., Atmos. Chem. Phys. (2016), 16, 10927–10940, doi:10.5194/acp-16-10927-2016
[4] Welti et al., Atmos. Chem. Phys. (2019), 19, 10901–10918, doi:10.5194/acp-19-10901-2019
How to cite: Heuser, D. A., Hagn, M., Seidel, J., Kiselev, A., Petrishcheva, E., and Abart, R.: The role of microfeatures, Al-Si-ordering and surface topography on the ice nucleation activity of alkali feldspars, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19575, https://doi.org/10.5194/egusphere-egu26-19575, 2026.
Predicting when water freezes, in the lab or in clouds, hinges on heterogeneous nucleation events that remain difficult to describe across scales. A synthesis of recent “purified” water experiments shows that droplets larger than ~10 nL almost always freeze at temperatures warmer than homogeneous nucleation allows, with the median freezing temperature increasing linearly with log(volume)—as found by Bigg (1953). Our compilation of recent results produces a trend line that closely matches that reported by Langham and Mason (1958). This empirical trend lacks a satisfactory theoretical basis. We advance a “chance nucleator” hypothesis: any somewhat disordered material in contact with supercooled water can, by combinatorial chance, present nanoscale patches that achieve a low effective contact angle with ice and trigger freezing. A simple classical nucleation theory (CNT) treatment captures much of the observed trend and predicts pronounced flattening at larger volumes, implying that carefully isolated millilitre- to litre-scale water volumes might supercool to lower temperatures than is reported in most of the literature.
We then apply the chance nucleator framework to interpret recent results on the nature of ice‑nucleating macromolecules (INMs) produced by pollen (Kinney et al., 2024). In this view, a statistical, non‑adaptive origin naturally explains why ice‑nucleation activity (INA) shows high interspecific variability and no consistent correlation with phylogeny, growth biome, seasonality, or pollination mode, yet still permits exceptional nucleators in which macromolecular composition or aggregation fortuitously produces rare, low‑contact‑angle patches. Thus, pollen INMs can be widespread and diverse despite the lack of an evolutionary driver for ice‑nucleation ability.
References
Bigg, E. K.: The supercooling of water, Proceedings of the Physical Society. Section B, 66, 688, 10.1088/0370-1301/66/8/309, 1953.
Kinney, N. L. H., Hepburn, C. A., Gibson, M. I., Ballesteros, D., and Whale, T. F.: High interspecific variability in ice nucleation activity suggests pollen ice nucleators are incidental, Biogeosciences, 21, 3201–3214, 10.5194/bg-21-3201-2024, 2024.
Langham, E. J. and Mason, B. J.: The Heterogeneous and Homogeneous Nucleation of Supercooled Water, Proceedings of the Royal Society of London Series A-Mathematical and Physical Sciences, 247, 493-&, 10.1098/rspa.1958.0207, 1958.
How to cite: Whale, T. F., Fakhoury, Z., Daily, M. I., Kinney, N. L. H., and Sosso, G.: Incidental Ice: Why purified water freezes and pollen macromolecules nucleate ice, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5683, https://doi.org/10.5194/egusphere-egu26-5683, 2026.
Aerosol-cloud interactions (ACI) remain among the largest sources of uncertainty in assessing anthropogenic impacts on climate (IPCC, 2023), largely due to limited understanding of aerosol sources and their evolution into cloud condensation nuclei (CCN). Reducing this uncertainty requires improved characterization of CCN concentrations and their spatiotemporal variability.
Although CCN measurements are increasingly available at ground-based station, long-term and spatially extensive datasets remain scarce. Harmonized CCN datasets such as those by Schmale et al. (2017) and Andrews et al. (2025) provide quality-assured observations across multiple stations and environments.
To extend CCN information beyond direct measurements, several approaches have been proposed to predict CCN concentrations from more routinely measured aerosol properties, such as aerosol optical properties (AOPs). Using the harmonized Andrews et al. (2025) dataset, Zabala et al. (2025) developed two AOP-based approaches: (i) an empirical parameterization and (ii) a Random Forest (RF) method, based on observations from nine stations (blue in Figure 1). Both methods demonstrate significant potential to extend CCN estimates across space and time.
Harmonized CCN observations have also enabled model evaluation studies. Fanourgakis et al. (2019) evaluated 14 general circulation models against CCN observations from nine stations (orange in Figure 1) over 2011–2015, showing systematic underestimation and substantial variability across environments.
Figure 1. Map of the sites considered in this work.
Motivated by the skill of AOP-based CCN prediction methods, this study applies the two approaches proposed by Zabala et al. (2025) to additional stations with available measurements. The predicted CCN values are evaluated against independent harmonized CCN observations from Schmale et al. (2017) and compared with multimodel CCN estimates reported by Fanourgakis et al. (2019), enabling a consistent assessment across diverse environments.
As an example, Figure 2 shows monthly median CCN concentrations (NCCN) at 0.5% supersaturation (SS) for the SMEAR (SMR, 61°51'N, 24°17'E, 181 m) station in Finland, including observations, AOP-based predictions and CAM5-MAM3 model simulations. The empirical parameterization and the model generally underestimate NCCN (median relative biases of -30% and -14%), whereas the RF approach overestimates observations (MRB=75%). Both prediction approaches capture the seasonal cycle, with larger amplitude in the RF estimates. This behavior is consistent across all tested SS.
Figure 2. Monthly median NCCN (SS=0.5%) at the SMR station from observations, AOP-based predictions, and the CAM5–MAM3 model; shaded area shows the interquartile model range.
Overall, this work demonstrates that AOP-based CCN prediction approaches can reliably extend CCN information beyond observational gaps when evaluated across multiple environments and benchmarked against observations and models. These approaches provide a pathway to improve global CCN datasets, support model evaluation, and reduce uncertainties in ACI in climate models.
This work was supported by the US Department of Energy (DE-SC0022886), the University of Granada (UCE-PP2017-02), and the NUCLEUS (PID2021-128757OB-I00) and MIXDUST (PID2024-160280NB-I00) projects funded by MICIU/AEI, EU NextGenerationEU/PRTR, and FEDER. We acknowledge EBAS (NILU) for the observational data.
References
- Andrews et al. (2025). Sci. Data. 12, 937. Dataset.
- Fanourgakis et al. (2019). Atmos. Chem. Phys., 19, 8591–8617.
- IPCC (2023). Cambridge Uni. Press., Cambridge.
- Schmale et al. (2017). Sci. Data. 4, 937. 170003.
- Zabala et al. (2025). EGUsphere [preprint].
How to cite: Zabala, I., Casquero-Vera, J. A., Andrews, E., and Titos, G.: Estimating cloud condensation nuclei from aerosol optical properties across diverse environments: observations, models, and prediction approaches, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10431, https://doi.org/10.5194/egusphere-egu26-10431, 2026.
Aerosol-cloud-radiation interactions remain one of the largest sources of uncertainty in climate projections. The Southern Ocean is one of the cloudiest regions on Earth and among the most pristine atmospheric environments. It is characterized by persistent low-level stratocumulus clouds that frequently occur in mixed-phase state, owing to exceptionally low concentrations of cloud condensation nuclei and, in particular, ice-nucleating particles. This combination makes the Southern Ocean a unique natural laboratory for investigating the coupling between aerosols, cloud microphysics, and radiation.
Understanding the formation and persistence of mixed-phase clouds in this region critically depends on the availability and chemical nature of aerosol particles acting as cloud condensation nuclei and ice-nucleating particles. Here, we present measurements of aerosol chemical composition in the Southern Ocean obtained during the HALO-South aircraft campaign (https://halo-research.de/sience/previous-missions/halo-south). The HALO-South campaign took place in September and October 2025 with the HALO aircraft operating from Christchurch, New Zealand, and comprised 19 research flights over the Southern Ocean and 8 transfer flights from and to Germany (spanning the globe).
Combined with observations of cloud and radiation properties, we aim to identify particle sources and investigate how aerosol chemistry influences cloud microphysics.
During the campaign we operated a compact time-of-flight aerosol mass spectrometer (C-ToF-AMS, Schulz et al., 2018) to measure the composition of the non-refractory aerosol particles (organics, nitrate and sulphate) in a size range of 40-800 nm. The C-ToF-AMS was operated behind the HALO aerosol sampling inlet HASI and the cloud residual inlet HALO-CVI (Counterflow Virtual Impactor). The measurement altitudes ranged between 150 m to 12.4 km, thus including liquid, mixed-phase and ice cloud conditions.
First results indicate that residues from ice clouds contain more organic compounds, while liquid cloud residuals contain mainly sulphate and nitrate. The aerosol mass concentrations in the troposphere over the Southern Ocean were generally low, however we observed occasionally aerosol layers from biomass burning over Australia, from volcanic plumes, and from long-range transport.
Schulz, C., et al.: Aircraft-based observations of isoprene-epoxydiol-derived secondary organic aerosol (IEPOX-SOA) in the tropical upper troposphere over the Amazon region, Atmos. Chem. Phys., 18, 14979-15001, 2018.
How to cite: Hartmann, A. V., Kaiser, K., Joppe, P., Clemen, H.-C., Schaefer, J., Wetzel, B., Mertes, S., Schneider, J., and Cheng, Y.: Aerosol and Cloud Residual Particle Measurements during HALO-South 2025: Overview and first Results, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11661, https://doi.org/10.5194/egusphere-egu26-11661, 2026.
The interactions and effects of aerosols and clouds are significant uncertainties in assessing and modeling climate change. Remote regions on earth with frequent pristine aerosol conditions, where the effect of aerosols on clouds are largest, are becoming increasingly rare due to human influence. Understanding climate and global environmental changes makes these locations of particular scientific interest. The Southern Ocean (SO), is one of the cloudiest regions on earth with a high cloud radiative effect and a high bias in atmospheric models due to an underestimation of aerosols. To address this, the HALO-South aircraft campaign, conducted in September and October 2025, aimed to investigate the interplay between aerosols, clouds, and radiation in this region. Within this framework, cloud particle habit – encompassing particle shape, complexity, phase, size and number concentration – is a key microphysical property linking atmospheric thermodynamics to cloud optical properties and precipitation processes.
The optical sensor PHIPS-HALO was employed to produce images of individual cloud particles allowing to analyse microphysical characteristics in great detail. We present an overview of cloud particle habits observed in the SO during the HALO-South campaign, providing insight into the evolution of cloud types and relating observed particle characteristics to established temperature and saturation regimes.
Acknowledgments: This work was supported by the DFG (Deutsche Forschungsgemeinschaft, German Research Foundation), Priority Program SPP 1294, the Max Planck Society, the German Aerospace Center (DLR) and the Leibniz Institute for Tropospheric Research (TROPOS).
How to cite: Lloyd, P., Abdelmonem, A., Menekay, D., Nehlert, F., Hartmann, S., Klimach, T., Pöhlker, C., Niedermeier, D., Leisner, T., and Pöhlker, M.: Cloud Particle Habits over the Southern Ocean during the HALO-South Aircraft Campaign, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20050, https://doi.org/10.5194/egusphere-egu26-20050, 2026.
Atmospheric and climate models exhibit large radiative flux biases over the Southern Ocean, largely due to deficiencies in representing supercooled liquid and mixed-phase low-level clouds. These biases propagate into errors in sea surface temperature, sea ice, and large-scale circulation. We evaluate a convection-permitting configuration of the Met Office Unified Model using aircraft and satellite observations in February 2023 and aircraft, ship-borne and satellite observations in November 2024 collected during the two Southern Ocean Clouds field campaigns.
From the first campaign the analysis focuses on three mixed-phase cloud properties: ice nucleating particle (INP) concentrations, droplet number concentration, and the spatial mixing of liquid and ice. Using lower temperature-dependent INP concentrations, that are consistent with observations, reduces ice mass and number, increases cloud liquid water, and decreases the net surface cloud radiative effect by up to 14 W m⁻². Reducing droplet number concentrations to observed campaign averages produces a comparable but oppositely signed radiative impact (up to 22 W m⁻²), indicating compensating errors. Changes in phase partitioning also strongly affect radiation, with impacts of up to 31 W m⁻². These results demonstrate that all three of these mixed-phase processes are critical for accurately simulating Southern Ocean clouds and their radiative effects.
We also present analysis from the second field campaign, providing an independent evaluation of the Met Office Unified Model and assessing its sensitivity to aerosol-aware parameterisations and secondary ice processes.
How to cite: Smith, D., Renfrew, I., van den Heuvel, F., Lachlan-Cope, T., Crawford, I., Bower, K., Flynn, M., Evans, M., Abel, S., and Field, P.: Convection permitting simulations of mixed-phase clouds over the Southern Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19894, https://doi.org/10.5194/egusphere-egu26-19894, 2026.
Clouds play a key role in the hydrological cycle and the Earth’s radiation budget. Their macroscopic properties are strongly influenced by the size, number, and phase of suspended particles. Understanding the evolution of these microphysical properties is therefore essential for weather prediction and for quantifying the impact of clouds on the Earth’s climate. In mixed-phase clouds, one process that can strongly modify the ice particle population is secondary ice production (SIP), which encompasses all mechanisms that increase the number of ice particles from pre-existing ice. While numerous SIP pathways have been proposed, no consensus has been reached about their relative importance and quantitative contributions, since observational studies often yield contradictory results.
In this work, a two-dimensional model of SIP is introduced which utilizes a combination of a cellular automaton approach pioneered by Clifford A. Reiter (Reiter, 2004) and a finite elements stress solver as well as concepts from graphs theory. The model represents the temporal evolution of the growth and
sublimation of an ensemble of ice crystals, their shape, and the formation of new crystals through SIP. Secondary ice production in the model is governed by two simplified mechanisms: shear-force induced breakup and fragmentation during sublimation.
A qualitative analysis of the model results shows that this reduced approach, which does not explicitly represent all known SIP pathways, is nevertheless able to reproduce key features of secondary ice production.
References
Reiter, Clifford A. "A local cellular model for snow crystal growth." Chaos, Solitons & Fractals 23.4 (2005): 1111-1119.
How to cite: Hey, M. and Spichtinger, P.: Secondary ice production - A cellular automaton approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18212, https://doi.org/10.5194/egusphere-egu26-18212, 2026.
Ice nucleating particles (INPs) are a minor subset of atmospheric aerosols that can influence clouds, precipitation and climate by promoting the formation of ice at warm temperatures. Mineral dust is a dominant source of INPs in the atmosphere because of its relatively high ice nucleating efficiency and abundance. Despite its importance, there are considerable uncertainties about the impacts of atmospheric processing (chemical "aging") on the INP activity of dust - especially on the role of species that acidify (like sulfuric acid and nitric acid) upon condensation onto INPs.
Motivated by the above uncertainties, we carry out the CleanCloud PIANO campaigns - which involve laboratory studies of the INP activity of dust generated from soils originating from Iceland, Morocco, and Chile. We study the properties of freshly generated dust, as well as dust that has been exposed to acidic species (HNO3 and H2SO4) using the FORTH/ICEHT environmental chamber facility in Patras, Greece. Dust was generated two ways - using a cyclone generator in the case of fresh dust, or mixed with sea salt using the AEGOR sea spray simulation chamber.
INP activity was measured online with a Portable Ice Nucleation Experiment (PINE) and offline using a cold-plate droplet freezing assay on dust samples collected from the chamber using an impinger. Size-resolved INP was also characterized using an Aerodynamic Aerosol Classifier (AAC) to select dust particles below a defined size cut prior to entering the PINE instrument.
Our results show that aging by acidification can strongly suppress the ice nucleation efficiency of mineral dust. In particular, aging reduced mass-normalized INP concentrations by a median of 86.3% for Icelandic dust, 77.2% for Moroccan dust, and 84.7% for Chilean dust across the investigated temperature range, demonstrating that chemical processing during atmospheric transport can substantially weaken the ability of desert dust particles to act as INPs.
How to cite: Mitsios, C., Molina, C., Theodoropoulos, G., Foskinis, R., Zhang, J., Gkretsi, S., Gini, M. I., Eleftheriadis, K., Horchler, E. J., Bilde, M., Krautwig, T., Gao, K., Kanji, Z. A., Querol, X., Pérez, C., Pandis, S. N., and Nenes, A.: Ice nucleation ability of different desert dusts during PIANO chamber campaigns, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17610, https://doi.org/10.5194/egusphere-egu26-17610, 2026.
Aerosol particles capable of acting as ice-nucleating particles (INPs) play a key role in Earth’s radiative forcing by controlling ice crystal formation and, consequently, the microphysical and optical properties of clouds. At high-mountain sites characterized by near-pristine conditions, natural aerosols become particularly important and may dominate key atmospheric processes. Among these, pollen particles have been shown to exert a non-negligible regional impact on ice nucleation (Prenni et al., 2009), together with re-suspended local soil dust, which often exhibits higher activity than transported mineral dust (O’Sullivan et al., 2014). Wind-blown snow particles represent an additional natural aerosol in high-mountain environments during the snow season, increasingly affected by the production of artificial snow (Baloh et al., 2019). The present study focuses on the characterization of regional natural INPs in the Sierra Nevada environment.
Dominant pollen types in the region are Olea, Pinus, Cupressaceae and Quercus (Cariñanos et al., 2025). Pollen samples collected directly from the vegetation, together with soil samples collected at different elevations in the Sierra Nevada slope - to account for the influence of wind-driven aerosol transport - and snow samples were analysed for their INP ability. Ice-nucleating activity was analysed using GRAINS (Bazo et al., 2025), an immersion droplet freezing array with 100 µL droplets. To assess the contribution of heat-labile components to ice nucleation, all samples were subjected to heat treatment at 95 °C for 30 minutes and subsequently reanalyzed.
Figure 1 shows the INP spectra of Pinus pollen suspension prepared at a concentration of 1 mg mL⁻¹. The suspension was obtained by dispersing 20 mg of sieved (2 mm) pollen in 20 mL of ultrapure water, followed by agitation, filtration with a 0.45 µm syringe filter, and a resting period of 1 h at 4 °C. The sample was then divided into two laboratory tubes, one analysed directly and the other analysed after heat treatment. The Pinus suspension activates at approximately −12 °C, a temperature influenced by the intrinsic ice-nucleating activity of the sample and experimental factors (droplet volume and suspension concentration). A reduction in activity is observed from −17.5 °C onward after heat treatment, likely associated with the removal of heat-labile compounds. This behavior is consistent with previous studies (Duan et al., 2023), although comparison across the literature remains challenging due to differences in methodology.
Figure 1: INP spectra (normalized by droplet volume) of Pinus.
In this study we will jointly present the overall impact of natural-origin particles in high-mountain sites, that highlight the ice-nucleating relevance of local natural aerosols and provide insight into the role of heat-sensitive components in their activity. This is particularly relevant for disentangling the respective influences of natural and anthropogenic aerosols on aerosol–cloud interaction (ACI) processes.
This work was supported by MIXDUST project (PID2024.160280NB.I00) and NUCLEUS project (PID2021-128757OB-I00) funded by MCIU/ AEI/10.13039/501100011033 and "ERDF/EU".
Prenni et al. (2009), Nat. Geosci., 2
O’Sullivan et al. (2014), Atmos. Chem. Phys., 14
Cariñanos et al. (2025), Atmos. Environ., 340
Bazo et al. (2025), EGUsphere
Duan et al. (2023), Atmos. Res., 285
How to cite: Ruiz-Galera, O., Bazo, E., Casquero-Vera, J. A., Zabala, I., Cariñanos, P., Olmo, F. J., Alados-Arboledas, L., Titos, G., and Cazorla, A.: Ice-Nucleating Activation Capacity of Natural-Origin Aerosols in Sierra Nevada National Park (Spain), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10330, https://doi.org/10.5194/egusphere-egu26-10330, 2026.
Hailstorms regularly damage assets, destroy crops, and harm people. A single hailstorm can cause more than USD $1b in damage, and hail is a significant contributor to insured losses in many areas. For decades, glaciogenic cloud seeding (GCS) has been applied in an attempt to reduce hail damage, and yet there are important gaps in our understanding of how hailstorms are affected by release of highly efficient ice-nucleating particles into developing convective cells. While careful cloud-resolving modeling based on in-situ and remote observations before and after the hailstone event is critical for estimating the potential effect of GCS, some microphysics parameters and mechanisms are insufficiently understood or completely missing.
To partly fill these gaps, we have conducted measurements of the ice-nucleating efficiency of GCS particles emitted by the generator built by the hail prevention cooperative "Steirische Hagelabwehr Genossenschaft eGen" based in Graz, Austria [1]. The generator, normally mounted on an aircraft, is designed to deploy steady flux of sub-micrometer AgI-containing particles into the area of the strongest updraft beneath a developing thunderstorm cell. The IN efficiency of fresh and aged GCS particles has been measured with the Portable Ice Nucleation Experiment (PINE) setup [2] and by sampling the GCS particles on Nuclepore® membrane filters for further analysis. The IN material has been washed from the filters and studied with the Ice Nucleation Spectrometer of the KIT (INSEKT) at IMKAAF. Additionally, the morphology and chemical composition of GCS particles have been analyzed with nanometer-scale resolution using scanning electron microscopy (SEM), providing detailed insights into the mechanism of ice nucleation by AgI-containing particles. The preliminary results of this study, as well as their implications for the GCS approach, will be presented in this contribution.
References:
[1] Steirische Hagelabwehrgenossenschaft eGen (https://hagelabwehr.at/)
[2] Möhler, O., et al.: The Portable Ice Nucleation Experiment (PINE): a new online instrument for laboratory studies and automated long-term field observations of ice-nucleating particles, AMT, https://doi.org/10.5194/amt-14-1143-2021, 2021.
How to cite: Kiselev, A. A., Arnold, L., Böhmländer, A., Bartoli, A., Lacher, L., Möhler, O., Mündler, J., Mossbacher, F., Zinser, E., and Tani, S.: Ice nucleating properties of glaciogenic cloud seeding (GCS) material, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18672, https://doi.org/10.5194/egusphere-egu26-18672, 2026.
Alkali feldspar is the most effective ice nucleating particle in airborne mineral dust and can initiate heterogeneous cloud ice formation at high temperatures [1]. It may thus influence precipitation formation and the Earth's radiation budget. The particularly high ice nucleation ability of microcline within the group of alkali feldspars was attributed to its complex perthitic microstructure in the form of Na-rich and K-rich exsolution lamellae [2], which naturally result from phase transformations during the cooling process after the magmatic and metamorphic crystallization, and defects like step edges, cracks, pores or cavities [2,3]. The lamellae and surface features are usually aligned with the non-rational Murchison plane with Miller indices between (-601) and (-801), subparallel to the direction where the elastic energy associated with exsolution is minimized [4]. Those features were hypothesized to expose small facets of particularly highly ice-nucleation active, but non-cleavable surfaces with the crystallographic (100) orientation [3]. This would explain the epitaxial relationship between feldspar (100) and the primary prismatic crystal planes of macroscopic ice crystals, observed in microscopic freezing experiments [3,5,6,7], but an understanding of this epitaxial relationship on the molecular level is still missing.
We study ice formation from the vapor phase on (001) and (010) cleavage plates of gem quality (featureless reference), gem quality with chemically induced fractures along the Murchison plane, and natural perthitic alkali feldspar under atmospheric pressure using a newly developed in situ X-ray diffraction setup and synchrotron radiation. The high-resolution information allows us to quantify the average ice crystal orientation with respect to the crystallographic domains of feldspar and complement previous electron microscope experiments. For the first time, we confirm the epitaxial relationship between ice and feldspar on defect-rich samples under atmospheric-relevant conditions, as observed in our experiments through a narrow orientation distribution in reciprocal space. The highest fraction of oriented ice crystals is found on natural perthite surfaces of (010) orientation, while ice grows rather randomly on the gem quality reference. In addition, we always detect the XRD-signal of oriented ice well before the XRD-signal of the ice fraction growing with random orientation.
[1] Atkinson et al., Nature (2013) 498(7454), 355-358, doi:10.1038/nature12278
[2] Whale et al. Phys. Chem. Chem. Phys. (2017) 19, 31186—31193, doi:10.1039/c7cp04898j
[3] Kiselev et al., Science (2017) 355, 367-371, doi:10.1126/science.aai8034
[4] Petrishcheva et al., Contrib. Mineral. Petrol. (2023) 178, 77, doi:10.1007/s00410-023-02059-z
[5] Pach and Verdaguer, J. Phys. Chem. C (2019) 123, 34, 20998–21004, doi:10.1021/acs.jpcc.9b05845
[6] Kiselev et al., Atmos. Chem. Phys. (2021) 21, 11801-11814, doi:10.5194/acp-21-11801-2021
[7] Keinert et al., Faraday Discussions (2022) 235, 148-161, doi:10.1039/d1fd00115a
How to cite: Seidel, J. S., Kiselev, A. A., Krause, B., Kaminski, M., Heuser, D., Petrishcheva, E., and Abart, R.: In situ X-ray diffraction during ice formation on alkali feldspar, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19492, https://doi.org/10.5194/egusphere-egu26-19492, 2026.
Atmospheric aerosol particles have been known for the large variability in their ice nucleating propensities as well as their physico-chemical properties. This complexity creates challenges in linking observed particle properties with their ice nucleating activity. In this study, we present results for simple synthetic particle analogues and contrast them with more complex ambient samples that consistently show higher ice nucleation activities. In particular, we focus on analogues for carbonaceous particles and dust. Soot particles have been known to show only limited ice nucleation activity in immersion freezing mode. In this study, we use carbonaceous particles as an experimental platform to explore which surface modifications can lead to a substantial change in ice nucleation propensities. Additionally, we contrast these results with binary systems that mimic the properties of ambient dust particles.
How to cite: Steinke, I., Hut, R., and Kelesidis, G.: Investigating properties of synthetic analogues for ice nucleating particles, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22655, https://doi.org/10.5194/egusphere-egu26-22655, 2026.
Mixed-phase clouds represent a major source of uncertainty in the representation of cloud microphysical processes in climate models. These clouds, consisting of supercooled liquid droplets and ice crystals, strongly influence precipitation formation and cloud radiative properties. Ice formation in mixed-phase clouds occurs predominantly via heterogeneous ice nucleation, enabling freezing at temperatures well above the homogeneous freezing limit of pure water [1].
Aerosol particles suspended in clouds can act as ice-nucleating particles (INPs), promoting heterogeneous ice formation through interactions between water molecules and particle surfaces. Numerous studies have shown that ice-nucleating (IN) activity [2] is governed by surface properties that influence the structure of interfacial water. Among atmospheric INPs, feldspars have received particular attention due to their high IN efficiency relative to other mineral dust components, especially alkali feldspars [3]. This efficiency has been linked to feldspar surface properties such as surface chemistry, crystallographic structure, and morphology [4].
Feldspar IN activity is not static but evolves in response to environmental and physicochemical processing. Here, we investigate the effect of mechanical comminution on the immersion freezing behavior of feldspars. Powdered feldspar samples were ground using different mortars and grinding durations, producing particle populations with distinct size distributions and specific surface areas. Our results demonstrate that changes in granulometry significantly affect ice-nucleating activity, indicating that particle size and surface state play an important role in controlling ice nucleation.
[1] Burrows, S. M., McCluskey, C. S., Cornwell, G., Steinke, I., Zhang, K., Zhao, B., Zawadowicz, M., Raman, A., Kulkarni, G., China, S., Zelenyuk, A., and DeMott, P. J.: Ice-Nucleating Particles That Impact Clouds and Climate: Observational and Modeling Research Needs, Rev. Geophys., 60, e2021RG000745, https://doi.org/10.1029/2021RG000745, 2022.
[2] Shimizu, T. K., Maier, S., Verdaguer, A., Velasco-Velez, J. J., and Salmeron, M.: Water at surfaces and interfaces: From molecules to ice and bulk liquid, Prog. Surf. Sci., 93, 87-107, https://doi.org/10.1016/j.progsurf.2018.09.004, 2018.
[3] Canet, J., Rodríguez, L., Renzer, G., Alfonso, P., Bonn, M., Meister, K., Garcia-Valles, M., Verdaguer, A.: Measurement report: Ice nucleation ability of perthite feldspar powder, EGU [preprint], https://doi.org/10.5194/egusphere-2025-5014, December 2025.
[4] Pach, E. and Verdaguer, A.: Pores Dominate Ice Nucleation on Feldspars, J. Phys. Chem. C, 123, 20998-21004, https://doi.org/10.1021/acs.jpcc.9b05845, 2019.
How to cite: Canet, J., Rodriguez, L., Renzer, G., Alfonso, P., Bonn, M., Meister, K., Garcia-Valles, M., and Verdaguer, A.: Influence of granulometry on the ice-nucleating efficiency of alkali feldspars, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5955, https://doi.org/10.5194/egusphere-egu26-5955, 2026.
Ice nucleating particles (INPs) are aerosols that lower the energy barrier for ice formation in mixed phase clouds, and therefore impact the liquid water fraction in these clouds. Hence, the prevalence of INPs affects the radiative properties of the cloud, as well as the precipitation formation. In addition, the liquid water fraction of clouds is one factor thought to be contributing to the consistent Southern Ocean radiation bias found across CMIP6 models. Cloud-aerosol interactions remain a major area of uncertainty in climate modelling, and non-aerosol-aware models use INP parameterisations that are purely temperature dependent and do not take into account the regional variation in aerosol concentration and type.
Here, we will present modelled global distributions of mineral dust and marine organic INPs – and their relative contributions to the total INP – calculated from simulations with the Aerosol and Reactive Trace (ART) gases module of the ICOsahedral Nonhydrostatic NWP model (ICON). The INPs are calculated offline using the Ice-nucleating active site (INAS) densities for immersion freezing provided by Ullrich et al 2014 for dust INP and McCluskey et al 2018 for marine INP. The simulations run for one year at 80km horizontal grid spacing. A comparison to the temperature-only parameterisations and observations of INPs is made, with a particular focus on Antarctica (data from Wex et al 2025) and the Southern Ocean (Antarctic Circumnavigation Expedition ship campaign).
Furthermore, we calculate INPs using a preliminary version of the seamless ICON-ART (ICON-SmART) model and evaluate this. Ultimately, the aim is to improve online INP modelling in ICON-SmART, in part to address the Southern Ocean radiation bias found in seasonal to decadal simulations.
How to cite: Winstone, J., Chawang, N., Klose, M., Hoshyaripour, G., and Hoose, C.: Global distributions of Ice-nucleating particles using ICON-ART, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1744, https://doi.org/10.5194/egusphere-egu26-1744, 2026.
A cloud-resolving model with a two-moment bulk microphysical scheme was used to investigate the indirect impact of three cloud condensation nuclei (CCN) parameters – the mean radius (rm), the standard deviation of the CCN spectrum (lnσ), and their solubility in water (εm)—on surface hail accumulation under various aerosol conditions. A sensitivity study was conducted using numerical simulations. Different combinations of these three CCN parameters were tested in continental and maritime environments for both unseeded (control) and seeded cases. The spatial distributions of surface rain and hail were analysed. Continental conditions characterised by extremely low CCN solubility in water were not suitable for hail suppression. Hail suppression was favourable (–26.2% and –8.7%) over continents with typical CCN concentrations (100–1000 cm–3). A highly polluted continental environment showed the greatest reduction in surface hail due to cloud seeding (–84.7%). Over maritime areas, a surplus of rain was observed in all seeded simulations. The effectiveness of hail prevention was discouraging (136.3%) under certain maritime conditions (εm = 1; lnσ = 1; rm = 0.1 μm). An extreme maritime condition resulted in very little hail suppression (–0.3%). It can be concluded that different CCN characteristics strongly affect surface amounts of rain and hail, as well as operational decisions on whether to conduct cloud seeding to prevent damaging hail on the ground.
Acknowledgement: This research was supported by the Science Fund of the Republic of Serbia, No. 7389, Project: "Extreme weather events in Serbia - analysis, modelling and impacts” - EXTREMES and by the Ministry of Science, Technological Development and Innovations of Serbia under Grant No. 451-03-136/2025-03/200162.
How to cite: Kovačević, N. and Filipović, L.: Hail suppression effectiveness for different populations of cloud condensation nuclei, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2579, https://doi.org/10.5194/egusphere-egu26-2579, 2026.
The contribution to effective radiative forcing (ERF) of climate due to interactions between clouds and atmospheric aerosols remains highly uncertain after decades of research. One key piece of information needed to reduce this uncertainty and better understand such aerosol-cloud interactions (ACI) is knowledge about the vertical distribution of cloud condensation nuclei (CCN), or the subset of aerosols that activate into cloud droplets and directly impact cloud microphysical properties. Recently, many studies have taken advantage of lidar observations to glean information about the vertical distribution of aerosols and CCN. Specifically, Redemann & Gao (2024) developed a machine learning (ML) technique that uses lidar observables to predict CCN concentration (NCCN) with mean relative errors of about 15% for the most complete sets of lidar observables.
In this study, we take advantage of the high vertical resolution of this ML-derived NCCN dataset to investigate ACI over the Southeast Atlantic (SEA), where a seasonal biomass burning aerosol plume resides atop a semi-permanent deck of marine stratocumulus clouds. We assess the simultaneous impact of above- and below-cloud NCCN on cloud top microphysical properties via clear-sky, cloud-adjacent lidar profiles and collocated polarimetric retrievals of cloud properties. Through this method we observe a decrease in cloud droplet effective radius (Reff) and an increase in cloud droplet number concentration (Nd) associated with an increase in above-cloud NCCN concentration within 100 m of the cloud top, which aligns well with previous in situ-based results. We find that the relationship between below-cloud NCCN and cloud top microphysical properties is weaker than those with above-cloud NCCN. Additionally, we find that the magnitude of these ACI are strongly dependent on lower tropospheric stability (LTS), with ACIREFF = -∂ln(Reff)/∂ln(NCCN) and ACICDNC = dln(Nd)/dln(NCCN) both decreasing by approximately 74% as LTS increases from 10 to 22 K. These findings demonstrate the importance of vertically resolved NCCN in ACI studies and establish a remote sensing-based analysis method which future satellite-based studies can employ to investigate ACI.
How to cite: Lenhardt, E., Redemann, J., Gao, L., Gupta, S., McFarquhar, G., Xu, F., Cairns, B., Ferrare, R., and Hostetler, C.: Peeking Beneath Clouds: An Investigation of Aerosol-Cloud Interactions over the Southeast Atlantic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15523, https://doi.org/10.5194/egusphere-egu26-15523, 2026.
Aircraft campaigns have shown high concentrations of ultrafine particles related to tropical convective outflow (Andreae et al. 2018; Williamson et al., 2019; Curtius et al., 2024). In the marine environment, dimethylsulfide (DMS) is a likely precursor for aerosols. It is a major sulfur source to the atmosphere and can be oxidised to sulfuric acid (SA) and methanesulfonic acid (MSA), which play important roles in the formation and growth of aerosol particles in the boundary layer (Kirkby et al., 2011; Hodshire et al., 2019; Shen et al., 2022). However, direct observations of the particle compositions at high altitudes and their connection to convection are sparse.
The CAFE-Pacific (Chemistry of the Atmosphere Field Experiment - Pacific) campaign provided valuable insights into the chemical composition of the tropical troposphere over Australia and the Indo-Pacific region around North-Eastern Australia. Seventeen research flights from Cairns were conducted with the HALO (High Altitude and LOng range) aircraft, ranging from the boundary layer up to 14 km altitude. With our nitrate CI-APi-TOF specially adapted for aircraft operation, we measured MSA and SA, among other species. Due to adiabatic heating in our inlet and subsequent evaporation of particles our instrument responds also to the particle phase composition in addition to the gas phase concentration. This evaporation effect is largest at high altitudes, where a large fraction of the total signal can be attributed to particle phase mass. It enables us to derive the composition of particles smaller than the aerosol size cut-off diameter of the AMS, which was also part of the HALO payload.
We find high concentrations of MSA throughout the entire measurement region. While SA is more variable, MSA is usually the dominant acid and mainly responsible for the particle mass, often exceeding SA by more than a factor of 10. Using our measurements in combination with HYSPLIT back trajectories and satellite data, we were able to trace back most of our data points to deep convective events in the past five days and thereby identify transport and oxidation of DMS as a source for ultrafine particles in the upper troposphere. The highest values of both acids are detected 15–20 hours after contact with a convective system, aligning well with the DMS lifetime.
Due to the large spatial extent and high frequency of convection around the marine ITCZ, this process represents most likely a substantial production mechanism of high-altitude aerosols which is not yet properly represented in most current models.
Andreae, M. O. et al. (2018), Atmospheric Chemistry and Physics 18, 921–961.
Curtius, J. et al. (2024), Nature, 636, 124–130.
Hodshire, A.L. et al. (2019), Atmospheric Chemistry and Physics 19, 3137-3160.
Kirkby, J. et al. (2011), Nature 218, 429-433.
Shen et al. (2022), Environ. Sci. Technol. 56, 13931–13944.
Williamson, C. J. et al. (2019), Nature 574, 399-403.
How to cite: Klebach, H., Heinritzi, M., Beck, L., Kaiser, K., Joppe, P., Schneider, J., Lloyd, P., Pöhlker, M., Richter, S., Granzin, M., Keber, T., Zauner-Wieczorek, M., Russell, D., Bhattacharyya, N., Caudillo-Plath, L., and Curtius, J.: MSA and sulfuric acid as important components of particle composition in the tropical upper troposphere of the Indo-Pacific, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6441, https://doi.org/10.5194/egusphere-egu26-6441, 2026.
Dust particles impose significant effects on the microphysics of mixed-phase and ice clouds. Previous studies mainly focused on dust-cloud interaction at the scale of convection, lacking the investigation of dust’s indirect effect in extratropical cyclone (EC) systems. In this study, we investigate dust effect on cloud properties by examining a decade (2016–2025) of Mongolian cyclones, which are primary drivers of East Asian dust-infused baroclinic storms (DIBS). Using automated tracking, satellite observations, and reanalysis data, we compare cloud properties under various dust conditions during DIBS events. Increasing dust loading enhances ice cloud fraction but reduces ice effective radius in both mixed-phase and ice regime in DIBS. This indicates that ice formation in East Asian DIBS ice clouds is dominated by heterogeneous rather than homogeneous nucleation. These results establish the significant role of dust in modulating the cloud phase partitioning and microphysical properties within ECs.
How to cite: Zeng, Y., Wang, M., Zhu, Y., and Huang, K.-E.: Dust effects on cloud properties in dust-infused baroclinic storm (DIBS) over East Asia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3153, https://doi.org/10.5194/egusphere-egu26-3153, 2026.
The radiative response of deep convective anvil clouds to anthropogenic aerosols is a major source of uncertainty. While aerosol-cloud interactions (ACI) in the convective core have been extensively studied, the microphysical mechanisms governing the full anvil lifecycle, from detrainment to dissipation, remain poorly constrained.
This study examines the Cloud Radiative Effect (CRE) of deep convection through a microphysical process-rate lens. We perform three regional simulations with interactive aerosol using ICON-HAM-lite, comprising baseline, clean, and polluted runs. The simulations follow the TRACER-MIP protocol for a sea-breeze event over Houston, Texas. Using Lagrangian tracking with the tobac cloud tracking algorithm, we isolate individual convective cells and track their evolution from convective onset to the detrainment and dissipation of the resulting anvils. We then assess aerosol-cloud interactions over the lifecycle of the tracked cells by aligning their evolution with the onset of freezing, to ensure a consistent lifecycle comparison.
Our results show that a 9-fold increase in aerosol concentration leads to a 2.5-fold increase in cloud droplet number concentration (CDNC). This suppresses warm-rain processes and enhances upward mass flux above the melting layer. As a result, it also lofts higher droplet concentrations, which can shape anvil characteristics by modulating the total ice surface area available for deposition and the net cross-section for riming. This creates a competition between enhanced riming, which promotes mass fallout, and increased vapour deposition, which sustains smaller ice crystals aloft. We conclude by investigating how these competing factors change the lifetime of the anvil and its net CRE.
How to cite: Sela, M., Ritman, M., De, S., and Stier, P.: Aerosol effects on deep convective cloud microphysics and anvil lifecycle during TRACER using ICON HAM-lite, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21597, https://doi.org/10.5194/egusphere-egu26-21597, 2026.
New particle formation (NPF) and subsequent growth are key processes controlling cloud condensation nuclei (CCN) number concentrations, as newly formed particles can grow into the CCN size range and thereby influence cloud properties and climate. In this study, we investigate particle number size distributions, CCN activity, and hygroscopicity during the Cloud–Aerosol Interactions in a Nitrogen Dominated Atmosphere (CAINA) campaign conducted in spring 2025 at a coastal site in the northern Netherlands, using a combination of a Scanning Mobility Particle Sizer (SMPS), a Particle Size Magnifier (PSM), and size-resolved CCN measurements. SMPS measurements covering the size range 6.7–969 nm were conducted between 29 March and 13 May 2025, while PSM measurements (1.19–12.0 nm) were available from 4 April to 9 May 2025. Based on visual classification of particle size distribution evolution, 19 NPF events were identified during the 46-day period (41%), 5 days were classified as undefined (11%), and the remaining 22 days as non-event days (48%). In addition, size-resolved CCN measurements were performed between 12 and 23 April 2025 to investigate in more detail the processes governing new particle formation and their growth towards CCN-relevant sizes. The measurements were carried out using a CCN counter operating at supersaturations (SS) of 0.3% and 1% downstream of a Differential Mobility Analyzer (DMA), covering particle diameters between 40 and 140 nm. The data were used to derive CCN activation fractions, characteristic activation diameters (D50), and the apparent hygroscopicity parameter kappa for the two different supersaturations. Our results show a clear size dependence of particle hygroscopicity, with particles activated at 0.3% SS generally exhibiting higher kappa values than particles activated at 1% SS. Average kappa values are around 0.1–0.2 for larger particles and 0.3–0.4 for smaller particles. A detailed case study of a NPF event shows a higher particle hygroscopocity before and during the start of the event, while the hygroscopicity decreases when the particles grow. These findings provide new insights into the link between NPF, particle chemical properties, and their ability to act as CCN.
How to cite: van den Born, M., Mulder, J., Bezantakos, S., Kellermann, M., Liu, X., Wehner, B., Biskos, G., and Dusek, U.: New particle formation and growth to CCN sizes at a coastal site in the Netherlands: insights from the CAINA campaign, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20422, https://doi.org/10.5194/egusphere-egu26-20422, 2026.
