Climate change is particularly evident in the Arctic, where warming between 1979 and 2021 was almost four times faster than the global average (Rantanen et al., 2022). However, this temperature increase is not uniform across the region. For example, the Svalbard archipelago, situated in the warmest part of the Arctic, has experienced the most significant warming (Dahlke and Maturilli, 2017).

The role of clouds in the rapidly changing Arctic climate system, along with the underlying processes, remains a major area of investigation. While detailed cloud observations are crucial, there are few Arctic locations where continuous, high-resolution vertical cloud measurements are conducted. One such site is the German-French Arctic Research Base AWIPEV, located at the Ny-Ålesund Research Station in Svalbard. Since 2016, a 94 GHz cloud radar has been operational here as part of the Transregional Collaborative Research Centre TR172 on Arctic Amplification (AC)³ (http://www.ac3-tr.de; Wendisch et al., 2023). Combined with existing remote sensing tools such as ceilometers and microwave radiometers, this setup enables continuous monitoring of clouds with high temporal and vertical resolution. This presentation will showcase key findings from these multi-year cloud radar observations.

At Ny-Ålesund, clouds are present 78% of the time, with the highest occurrence observed in low-level clouds between 0.5 and 1.5 km altitude. Pure liquid water clouds display a clear seasonal cycle, whereas mixed-phase clouds, containing both liquid and ice, are present throughout the year, averaging 42% of the time. These liquid-containing clouds significantly influence surface radiative fluxes, with an overall net warming effect of clouds of approximately 11 Wm⁻².

A novel approach to efficiently characterize the long-term observations of diverse cloud systems over Ny-Ålesund is by using a self-supervised deep learning framework. This framework is designed to learn the complex relationships within the sub-hourly, multi-scale measurements from radar collected from 2017 to 2021. During training, it captures the non-linear, orthogonal aspects of the clouds' vertical and temporal structure and distributions over the Ny-Ålesund column and extracts the essential low-dimensional features. Sensitivity tests are conducted by combining different measurements and observing the resulting changes in the extracted features. Analyzing this low-dimensional representation of the entire cloud measurement time series provides valuable insights into cloud evolution and its connection to environmental conditions.

Acknowledgment: We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project Number 268020496 – TRR 172, within the framework of the Transregional Collaborative Research Center “ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)³”. We also acknowledge the support by AWIPEV for the project AWIPEV_0016.

How to cite: Ebell, K., Risse, N., Chatterjee, D., Walbröl, A., Maturilli, M., Bauer, S., Mech, M., and Crewell, S.: Long-term Analysis of Vertically Resolved Cloud Observations at Ny-Ålesund (Svalbard) using Self-Supervised Deep Learning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6488, https://doi.org/10.5194/egusphere-egu25-6488, 2025.

The transport of aerosols to the Arctic plays a key role in shaping local climate processes, particularly in the context of Arctic amplification. Here, we utilize an atmospheric river detection algorithm to identify and analyze extreme aerosol and moisture transport events from mid-latitudes to the Arctic over a 43 year period.By examining the combined effects of aerosol and moisture intrusions, we aim to understand how the presence of aerosols alter the cloud properties compared to scenarios with only moisture. Inorder to evaluate the cloud properties, we use the active remote sensing product DARDAR-Nice dataset.

The findings will provide insights into aerosol-cloud interactions in the Arctic, offering a better understanding of the role of aerosol transport in Arctic climate change and thereby improving the accuracy of climate model projections.

How to cite: Cherichi Purayil, F., Kretzschmar, J., and Quaas, J.: Assessing the aerosol and moisture transport to the Arctic through atmospheric river and their impact on clouds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6347, https://doi.org/10.5194/egusphere-egu25-6347, 2025.

The Arctic has been rapidly moistening over the last forty years, influencing energy fluxes and precipitation. While local changes in
air temperature and sea ice cover partly explain this trend, the role of changing moisture transport to the Arctic is less clear.
Understanding how moisture transport affects Arctic amplification is crucial, as most moisture in the Arctic comes from lower latitudes.
Enhanced warming in the Arctic strengthens meridional transport due to changes in Rossby waves, but current global climate
models struggle to capture these shifts accurately.

The presentation will show results from case studies of moisture transport into the Arctic, analyzing the changing structure of
water vapor isotopes in response to varying moisture transport patterns and phase transition along these transport pathways.
Initial simulations with the isotope-enhanced ICON-ART atmosphere model reveal limitations in its ability to accurately capture
isotopic variations on a global scale. Therefore, the model first needs to be improved and validated for global simulations.
Once these improvements are achieved, case studies are performed to assess phase transition processes in detail and
explore their response to recent warming.

How to cite: Eichholz, H. M., Botsyun, S., Kretzschmar, J., Umlauft, J., Pfahl, S., and Quaas, J.: Diagnosing moisture sources, transport and transformation in the Arctic withwater vapor isotopes in atmospheric modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8990, https://doi.org/10.5194/egusphere-egu25-8990, 2025.

As warm and moist airmasses are advected into the Arctic, a sequence of turbulent, microphysical and radiative processes is initiated which transfers heat and moisture from the airmass into the Arctic environment, eventually transforming both. Despite the importance of airmass transformation for the evolution of the Arctic climate, it is still relatively poorly understood. In our study, we take on this complex issue from a Lagrangian perspective, using warm-air intrusions captured by different Arctic campaigns (ACSE, MOSAiC, HALO-(AC)³ and ARTofMELT) and the Atmosphere-Ocean Single Column Model (AOSCM). We use trajectory analysis to assess under what conditions and to what extent this Lagrangian AOSCM framework is suitable to study the Arctic airmass transformation. Finally, we use it to simulate the changes in heat-moisture content and vertical structure of the airmass at different stages of the transformation and identify the physical processes that drive them. Comparison with observations, reanalysis and operational forecast data shows that the Lagrangian AOSCM can be used for future model analysis and diagnostics development.

How to cite: Karalis, M., Svensson, G., and Tjernström, M.: Lagrangian single-column modeling of Arctic airmass transformation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13748, https://doi.org/10.5194/egusphere-egu25-13748, 2025.

The central Arctic atmosphere during winter comprises two distinct synoptic states: a radiatively clear state, which is linked to clear sky, strong surface cooling and temperature inversions; and a radiatively opaque state, which is linked to mixed-phase clouds, weak surface radiative cooling, and more neutrally-buoyant boundary layers. Weather and climate models are often reported to lack the representation of processes associated with these states, but most prior work has treated the problem as an aggregate of synoptic conditions. Here, we disaggregate the Arctic states in an evaluation of ERA5 reanalysis and compare to observations from the MOSAiC drift campaign over the central Arctic sea ice from November 2019 – March 2020. Combining near surface winds and liquid water path (LWP), nine different classes describing synoptic conditions spanning the states are derived. Results show that the clear state is primarily formed by weak and moderate winds and the absence of liquid-bearing clouds, while strong wind cases and enhanced LWP forms the occurrence peak in the radiatively opaque state. ERA5 struggles to reproduce these basic statistics, shows too weak sensitivity of thermal radiation to synoptic forcing, and for similar LWP amounts, it overestimates both upward and downward longwave radiation due to a warm bias near the surface. This warm bias has a pronounced vertical structure and is largest in clear and calm conditions, owing to the lack of surface inversions in ERA5. Under strong synoptic forcing, the warm bias is constant with height and discrepancies in mixed-phase cloud altitude appear. Thus, biases in each state are partially opposing in a manner that makes them overlap unrealistically, masking the distinctions that are known to form the first-order variability of the Arctic winter energy budget. Separating between different synoptic conditions in conjunction with the classical two radiative states classification is therefore regarded a useful step for isolating dominant processes for evaluation of the Arctic troposphere in models.  

How to cite: Dahlke, S., Rinke, A., Shupe, M. D., and Cox, C. J.: The two Arctic wintertime boundary layer states: Disentangling the role of cloud and wind regimes in reanalysis and observations during MOSAiC, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15924, https://doi.org/10.5194/egusphere-egu25-15924, 2025.

A TriOS spectroradiometer (RAMSES-ARC) operating in the UV-Vis-NIR spectral range has been operating at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5° N, 68.8° W, 225 m asl, https://www.thuleatmos-it.it/) in Pituffik, Greenland, since 2021. Its measurements are used to study Arctic cloud characteristics and the cloud optical thickness (COT) in particular. This effort will be extended with additional radiance measurements performed by means of a Zeiss PGS ShortWave InfraRed (SWIR) spectrometer which will be installed at the THAAO in March 2025 in order to further characterise cloud properties.

The RAMSES-ARC is used for in situ hyperspectral light field measurements, operating across a wavelength range of 320–950 nm with a field of view (FOV) of approximately 7° in air. The Zeiss spectrometer covers the 1000–2200 nm spectral range, is thermoelectrically cooled, and will be equipped with a custom-designed input optic to reduce the field of view of its standard fiber optic and with an in-house developed software for the data acquisition.

Ensuring long-term, high-quality measurements in extremely cold environments requires rigorous and repeated calibrations to maintain reliability across the entire spectral range. However, practical challenges, such as high costs and limited access to fully equipped calibration laboratories, often hinder the achievement of optimal calibrations. Furthermore, extended operations in low-temperature environments increase the risk of calibration drifts. This study presents a structured and repeatable calibration procedure that can be easily implemented in settings where advanced laboratory equipment is unavailable.

The calibration method employs a Gigahertz Optik GmbH 250 W halogen calibration lamp powered by a highly stabilised current source. The lamp’s optical axis is aligned perpendicularly to the centre of a Labsphere panel with a reflectance factor of about 0,99 for wavelengths shorter than 1800 nm and between 0,98 and 0,94 for wavelengths between 1800 nm and 2200 nm. The panel is positioned at a distance from the lamp optimised using ANSYS SPEOS software to ensure uniform irradiance distribution across the panel.

Additionally, this presentation will discuss the impact of the new calibration on COT estimates obtained by using the method described in Calì Quaglia et al. (2024).

The primary objective is to prove that the new calibration method maintains measurement integrity while guaranteeing repeatability and accuracy, particularly in scenarios requiring frequent recalibration.

Calì Quaglia, Filippo, et al. (2024), On the Retrieval of Cloud Optical Thickness from Spectral Radiances - A Sensitivity Study with High Albedo Surfaces, Journal of Quantitative Spectroscopy and Radiative Transfer, https://doi.org/10.1016/j.jqsrt.2024.109108.

How to cite: Focardi, A., Muscari, G., Calì Quaglia, F., Tosco, M., Meloni, D., Di Bernardino, A., Ciardini, V., Di Iorio, T., Pace, G., and di Sarra, A.: A calibration method for the UV-Vis-NIR and SWIR spectrometers installed at THAAO and its impact on the retrieval of cloud properties, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17572, https://doi.org/10.5194/egusphere-egu25-17572, 2025.

Virga known as precipitation that fails to reach to the ground due to evaporation/sublimation beneath the cloud base. Virga is commonly observed in hot and arid regions where dry air helps in the process [1]. In a warming climate, virga is increasingly observed in cold environments such as Antarctica and Switzerland as sublimation of snow [2,3]. Virga precipitation constitutes occurrences over 30% in TRMM, GPM and 50% in Cloudsat in arid regions and accounts for 50% (30%) of false precipitation detections by TRMM (GPM) satellites. Virga plays a crucial role in quantifying total precipitation, particularly in remote regions like the Arctic where virga is poorly studied. Accurate identification of virga is essential to improve precipitation estimates derived from satellite radar observations, which are limited in Arctic regions. This study introduces the Arctic Virga Detection Algorithm (ArViDAM), which uses ground-based vertical precipitation observations from Micro Rain Radar (MRR) deployed at Ny-Ålesund (78° 55' N, 11° 56' E) in the Arctic to identify virga events based on reflectivity and fall velocity profiles up to 6 km.

Figure: (top) Time-height series profile of (a) Ze, (b) W, and (c) SW for 13th–14th June, 2020 includes virga and surface precipitation with detected virga height with black line. (bottom) Seasonal variation of occurrence of virga and surface precipitation during 2020-2023.

A summer event presented in Figure shows the sensibility of the ArViDAM with detected virga height on the time-height profile of reflectivity (Ze), fall velocity (W), and spectral width (SW) during 13th–14th June, 2020. ArViDAM outcomes from 2020–23 indicate that summer has the highest virga occurrence with∼40%, followed by spring and autumn with∼30% and winter with the lowest∼22%. The outcomes are expected to enhance understanding of Arctic precipitation processes and contribute to quantitative precipitation estimation. 

Keywords—Virga, Arctic Precipitation, Sublimation, Micro Rain Radar, Climate Change

References

[1] Wang, Y. You, and M. Kulie, “Global virga precipitation distribution derived from three spaceborne radars and its contribution to the false radiometer precipitation detection,” Geophysical Research Letters, vol. 45, no. 9, pp. 4446–4455, 2018. [Online]. Available: https://agupubs.onlinelibrary.wiley. com/doi/abs/10.1029/2018GL077891.

[2] N. Jullien, E. Vignon, M. Sprenger, F. Aemisegger, and A. Berne, “Synoptic conditions and atmospheric moisture pathways associated with virga and precipitation over coastal ad´elie land in Antarctica,” The Cryosphere, vol. 14, no. 5, pp. 1685–1702, 2020. [Online]. Available: https://tc.copernicus.org/articles/14/1685/2020/. 

[3] R. Beynon and K. Hocke, “Snow virga above the swiss plateau observed by a micro rain radar,” Remote Sensing, vol. 14, no. 4, 2022. [Online]. Available: https://www.mdpi.com/2072-4292/14/4/890.

How to cite: Saini, L., Das, S., and Murukesh, N.: Virga Detection Tool based on Micro Rain Radar in Arctic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20517, https://doi.org/10.5194/egusphere-egu25-20517, 2025.

Arctic clouds, which cover the region for around 70-80% of the year, are a key component of the Arctic climate system, influencing, among others, surface temperature, ice melt and atmospheric dynamics. Mixed-phase clouds, containing both supercooled liquid water and ice crystals, are of particular concern due to their prevalence in the Arctic and their role in the local energy budget. Because their variability and their lifecycle are inaccurately represented in models, they are an important source of uncertainty, as the cloud phase impacts both radiative effects, cloud lifetime and precipitation amounts. Assessing the vertical distribution of clouds, their optical properties and their phase distribution is therefore critical to accurately determine the surface energy balance (SEB). 

Here, the mesoscale WRF (Weather Research and Forecasting) updated for application in polar regions is run over the European Arctic from January to June 2015. The simulations are evaluated using observations from the N-ICE campaign, conducted from January through June 2015 in the drifting sea ice north of Svalbard (surface radiation and meteorology, atmospheric profiles), as well as satellite data derived from CALIPSO and CloudSat observations. The simulated SEB as well as low-level cloud distributions and phase partitioning are evaluated to get insight on the limitations of the model to represent Arctic clouds and the factors underlying these biases. 

This study reveals strong biases in radiative fluxes at the surface, even when cloudy conditions are successfully represented in the model, with effects varying across seasons. Results show that these discrepancies are likely to be strongly linked to the accurate phase characterization of clouds. Sensitivity tests based on variations in CCN and INP number concentrations reveal moderate effects on the radiative budget through changes in liquid water content, insufficient to account for the observed biases.

How to cite: Le Gars, Y., Raut, J.-C., and Marelle, L.: Modelling cloud phase and radiative effects in the European Arctic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18439, https://doi.org/10.5194/egusphere-egu25-18439, 2025.

To investigate the role of synoptic systems for Arctic precipitation, Lauer et al. (2023) established a new methodology to attribute precipitation to Atmospheric Rivers (AR), cyclones, and also atmospheric fronts and tested it for two field campaigns in the Arctic North Atlantic (ANA) sector (ACLOUD, AFLUX). The results led us to hypothesize that during early summer, precipitation is mainly associated with cyclones, while during early spring, ARs and fronts are more effective. About one-third of the precipitation was classified as residual, which reduced significantly when a precipitation threshold was applied as often used to eliminate “artificial” precipitation. To investigate whether these results can be generalized we now apply the methodology of Lauer et al. (2023) to the long-term (1979-2022) ERA-5 reanalysis record over the full Arctic north of 70 deg.

When: Most precipitation falls in August as a consequence of rain peaking in July and the highest amount of snowfall in September at the time of the sea ice minimum and thus the highest evaporation from the ocean. Where: The ANA region is by far the one with the most precipitation, and the only region with significant rain outside the summer months. How: Cyclone-associated precipitation dominates in all regions, while ARs are more important for summer rainfall and, in some regions, can even bring rain in winter. We can pinpoint the high occurrence of residual precipitation over the ANA region to Marine Cold Air Outbreaks, while in the central Arctic the residual stems from very light precipitation.

How to cite: Lauer, M., Rinke, A., Crewell, S., and Pant, A.: What are the most important contributors to Arctic precipitation: When, where and how?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17930, https://doi.org/10.5194/egusphere-egu25-17930, 2025.

For the first time, measurements of high-resolution water vapor profiles are available for the central Arctic winter North of 85°N. The measurements were conducted with the Raman lidar PollyXT during the MOSAiC-campaign. Using those observations, the impact of the vertical distribution of tropospheric water vapor on the cloud-free downward, broadband thermal-infrared irradiance (F_TIR) was quantified.

Values of the integrated water vapor (IWV) were determined from the lidar-derived vertical water vapor profiles up to the tropopause region and correlated to the F_TIR at the surface. Colocated radiosonde measurements were used to consider the influence of the temperature of the vertically distributed water vapor on this correlation with means of a water-vapor-weighted mean temperature (representative temperature of the water vapor distribution).

In the study, seven measurement cases of several hours duration were examined representing slowly changing air masses. Furthermore, 53 rather short-term (10 minutes) measurement cases were investigated. The temporal evolution of the slowly changing air masses revealed a linear relationship between F_TIR and IWV with slopes between 7.17 and 12.95 W kg⁻¹ and a coefficient of determination larger than 0.95 for most of the selected cases. A dependence of the slopes and ordinate-intercepts on the water-vapor-weighted mean temperature was found with smaller ordinate-intercepts at lower temperatures. A linear relationship was found between the water-vapor-weighted mean temperature and the temperature determined with the Stefan-Boltzmann law from F_TIR. The analysis of 53 independent short-term observations of different air masses confirmed the linear relationship between F_TIR and IWV at wintertime cloud-free conditions in the Arctic with a coefficient of determination of 0.75 and a slope of 19.95 W kg⁻¹.

The evaluations of the profile measurements showed a clear influence of the temperatures of the water vapor along its profile on the F_TIR at the surface and the importance of the vertical water vapor and temperature distribution for radiation investigations at the surface.

How to cite: Seidel, C., Althausen, D., Ansmann, A., Wendisch, M., Griesche, H., Radenz, M., Hofer, J., Dahlke, S., Maturilli, M., Walbröl, A., Baars, H., and Engelmann, R.: Observations of the vertical water vapor distribution and the downward, broadband thermal-infrared irradiance at the ground in the Central Arctic during MOSAiC, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11015, https://doi.org/10.5194/egusphere-egu25-11015, 2025.

The pronounced warming observed in the Arctic region has significantly altered the atmospheric energy budget, leading to a transition in the prevailing equilibrium state from radiative-advective to radiative-convective-advective. This study uses data from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to analyze the emergence and characteristics of convective events in the Arctic. Using historical simulations and future projections, we examine the spatiotemporal evolution of convection and its interactions with key climatological parameters such as temperature and humidity. By providing a detailed assessment of these processes, this research contributes to improving our understanding of Arctic climate dynamics and the implications for global climate systems in a warming world.

How to cite: Vliegen, S. and Quaas, J.: Model analysis of the changing role of convection in the Arctic climate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9487, https://doi.org/10.5194/egusphere-egu25-9487, 2025.

In the Arctic, cloud optical thickness (COT) estimations are scarce due to limited site accessibility, short sunlit seasons, and high surface albedo, which enhances the multiple scattering. This work presents a comparison of estimates of COT obtained by means of different types of measurements collected on the north-western coast of Greenland, an area presenting alternatively high and low surface albedo, depending on the season. Our approach exploits ground-based zenith spectral radiance (ZSR) measurements in the 320-950 nm wavelength range as well as downward shortwave irradiance (DSI, 310-2800 nm) and Liquid Water Path (LWP) measurements. All measurements are carried out at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5° N, 68.8° W, 225 m asl, https://www.thuleatmos-it.it/), where  LWP measurements have been performed from 2016 to 2024, while DSI and ZSR measurements started in 2009 and 2021, respectively, and are still ongoing. The analysis also includes COT values from MODIS aboard Terra/Aqua. 

COT values are calculated for two case studies of low and high surface albedo values, focusing on total cloud cover conditions and liquid clouds. The COT values retrieved from the ZSRs are obtained by using various combinations of transmissivities at different wavelengths. Numerical simulations allowed us to provide uncertainties for the ZSR COT estimates. We found that the use of broadband albedo values in the retrievals instead of spectrally-resolved ones is the largest source of uncertainties. The COT values obtained with the different methods during the two case studies range between 1 and 45.

Results show that the ZSR-based retrievals lack sensitivity for clouds with COT between 6 and 14. Numerical simulations can explain this shortcoming and they will also be presented. For COT larger than 14, the ZSR-based estimates agree very well with the other methods employed. We will discuss in detail how the different estimates compare to one another and show that, given the observatory measurements capabilities, estimates of COT could be performed continuously and with good accuracy in high surface albedo conditions by means of ZSR and DSI measurements.

How to cite: Muscari, G., Calì Quaglia, F., Tosco, M., Meloni, D., Di Bernardino, A., Di Iorio, T., Focardi, A., Pace, G., Schmidt, S. K., and di Sarra, A.: Cloud optical thickness measurements in high albedo conditions at the Thule High Arctic Atmospheric Observatory (THAAO), Greenland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18587, https://doi.org/10.5194/egusphere-egu25-18587, 2025.

The Thule High Arctic Atmospheric Observatory (THAAO, www.thuleatmos-it.it) is a strategically important site for collecting atmospheric measurements in the Arctic. Located in Pituffik (76.5° N, 68.8° W, 225 m asl) on the Greenland west coast, it experiences harsh environmental conditions and offers invaluable atmospheric measurements otherwise scarce in the region. Over the past decade, increased visits to the observatory have facilitated the expansion, maintenance, and upgrading of its instruments. More than 15 instruments are currently operating at the THAAO, measuring atmospheric and surface climate parameters. Among those are upward- and downward-looking pyranometers and pyrgeometers, radiosondes, microwave spectrometers for atmospheric composition, lidar and ceilometer systems, and a weather station also providing precipitation measurements.

This study compares two prominent reanalysis datasets - ERA5 and the C3S Arctic Regional Reanalysis (CARRA) - produced by the Copernicus Climate Change Service (C3S). Ground-based measurements of various atmospheric parameters, including local and column-integrated variables, are used for this comparison. CARRA delivers higher spatial resolution (2.5 km) but lower temporal resolution (3-hourly) data, concentrating on Greenland and utilising ERA5's global reanalysis (0.25° x 0.25° and hourly) as lateral boundary conditions.

The analysis extends over a period ranging from 3 to 15 years, depending on the parameter, and includes key variables such as temperature, relative humidity, integrated water vapour, radiation components (shortwave and longwave), precipitation, cloud base height, wind speed and direction. In addition, over 50 radiosonde measurements, unevenly distributed between 2016 and 2024, are exploited in the comparison. The data used in this study have not been assimilated into the reanalysis under consideration, allowing an independent evaluation.

The impact of different temporal and spatial resolutions of the reanalyses will be assessed. The climatological length of the reanalyses (> 30 years) allows the assessment of seasonal and annual trends, as well as the regional impact of extreme events over a long time span.

How to cite: Calì Quaglia, F., Muscari, G., Focardi, A., Ciardini, V., Di Bernardino, A., Di Iorio, T., Meloni, D., Pace, G., Tosco, M., and di Sarra, A.: Comparison of ERA5 and CARRA reanalyses with long-term atmospheric measurements at the THAAO, Greenland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19437, https://doi.org/10.5194/egusphere-egu25-19437, 2025.

The Arctic is experiencing rapid climate change, with warming rates four times higher than the global average. This warming has a profound impact on the Arctic hydrological cycle, including cloud formation and precipitation processes. Bioaerosols are critical components driving these processes as they can act as high-temperature ice nucleating particles (INPs). Despite their importance, the representation of bioaerosol-cloud interactions in climate models remains highly uncertain, primarily due to limited understanding of biogenic INPs, their sources and specific properties. Recent studies have highlighted the need for long-term studies and detailed source characterization of INPs and their characteristics in the Arctic to bridge these knowledge gaps.

Here, we present preliminary data from the first long-term dataset of bioaerosol concentration and composition in the High Arctic, complementing detailed high-temperature INP measurements. The samples were collected at the Villum Research Station in North Greenland over three years (2021–2023) at a time resolution of 3.5 days. INP concentrations were measured using the Micro-PINGUIN cold-stage setup, focusing on activity between 0°C and -20°C. Simultaneously, bacterial communities in the air were characterized through qPCR and 16S rRNA gene amplicon sequencing. Source-tracking analyses were performed using potential environmental sources, including soils, glacial runoff, plant material, and seawater, supplemented with publicly available Arctic sequence datasets. Meteorological data and aerosol microphysical and chemical data, such as black carbon and particle number size distributions, were incorporated to support the analysis of bioaerosol drivers.

Preliminary results reveal that INP_-12 concentrations ranged from 2.2 • 10^-5 to 7.2 • 10^-2 • L^-1, consistent with previous observations in the High Arctic. Airborne bacterial concentrations were exceedingly low, ranging from 2.7 • 10⁰ to 4.2 • 10³ • m^-3 of air, and the taxonomic diversity varied seasonally. During the Arctic haze season, the microbial community was dominated by spore-forming taxa, such as Bacillus, likely transported via long-range atmospheric transport from mid latitudes. In contrast, post-haze conditions were marked by increased microbial diversity, dominated by phototrophic taxa such as Tychonema and other members of the core cryospheric microbiome, including Sphingomonas and Hymenobacter. These taxa likely originated from regional terrestrial and marine sources, exposed to the atmosphere as snow and ice melted during summer. Both bacterial concentrations and the taxonomic diversity were positively correlated with the warm-temperature INP concentrations (ρ = 0.66, p = 3.6 • 10^-12 and ρ = 0.59, p = 1.2•10^-9,  respectively), suggesting a direct link between bioaerosol abundance and INP concentration in the Arctic atmosphere. Finally, Spearman rank correlations also revealed significant relationships between warm-temperature INP concentrations and the relative abundances of 177 microbial genera, giving insights into the potential sources of these INPs.

These findings provide new insights into the seasonal dynamics of bioaerosols and their role as INPs in the High Arctic. Our long-term dataset highlights the importance of integrating microbial ecology, aerosol microphysics and chemistry, and meteorological observations to improve our understanding of aerosol-cloud interactions. Future work will focus on disentangling the contributions of source environments and microbial taxa to Arctic INP populations, with the goal of refining aerosol-cloud interaction parameterizations in climate models.

How to cite: Jensen, L. Z., Massling, A., Sørensen, L. L., Skov, H., Stratmann, F., Wex, H., Finster, K., and Šantl-Temkiv, T.: Seasonal Dynamics of Bioaerosols and Ice Nucleating Particles in the High Arctic Atmosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16625, https://doi.org/10.5194/egusphere-egu25-16625, 2025.

We deployed an Aerosol Mass Spectrometer (AMS) on the British Antarctic Survey Research Vessel Sir David Attenborough (SDA) during November and December 2024 as part of the Southern Ocean Clouds (SOC) campaign. The AMS measures sub 1 micron aerosol particle chemical composition and size distributions, using thermal vaporization and electron impact ionization, followed by time-of-flight mass spectrometry.

The cruise track covered a broad area (50 S to 67 S and 70 W to 25 W) and encountered a wide variety of atmospheric environments, including seasonal sea ice zones, open ocean, and areas near islands with penguin colonies and volcanoes. Different ratios of organics, sulphate and methane sulphonic acid (MSA) were observed for different sympagic and pelagic air masses and associated with distinct aerosol size distributions. We also observed distinct plumes of NH4Cl particles from a volcano and we saw aqueous processing of aerosol particles during a multi-day fog event. As is typical of ship campaigns, the AMS organics showed that we were sampling ship emissions, both from the engines and from the kitchen, at least half of the time.

How to cite: Williams, L., Allan, J., Flynn, M., Beddows, D., Brean, J., Tarn, M., Dall'Osto, M., Kirchgaessner, A., and Lachlan-Cope, T.: Aerosol particle measurements on the Southern Ocean during the Southern Ocean Clouds (SOC) campaign in November and December 2024, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13186, https://doi.org/10.5194/egusphere-egu25-13186, 2025.

Ice-nucleating particle (INP) concentration in the atmosphere over the Southern Ocean represents a significant source of uncertainty in the representation of clouds in global climate models. A better understanding of the sources, properties and abundance of INPs in this region is essential to reduce this uncertainty (Murray, 2021). There is increasing evidence to suggest that ice nucleators are produced ubiquitously by land plants. Yet, the molecular basis and evolutionary origins of these ice nucleators remain obscure. Adapted for cold- and drought-tolerance, mosses dominate the Antarctic flora, with over one hundred species colonising the ice-free coastal regions of Antarctica and their land cover increasing (Roland 2024). Ice nucleation by moss spores and leaves was recorded separately by Weber (2016) and by Moffett (2015), who suggested that this activity may afford benefit as a means of gathering essential water in dry climates. In the years since, the atmospheric and biological significance of these ice nucleators has remained unexplored. Here we present evidence that mosses produce water-soluble ice-nucleating macromolecules that are present in the gametophyte and sporophyte generations. We hypothesise that the same class of ice-nucleating macromolecules are produced by the spore-producing mosses and ferns and the pollen-producing seed plants, tracing back to an ancient common ancestor. The widespread and variable nature of ice-nucleating activity in plants suggests that this activity is secondary or ‘incidental’ in function (Kinney, 2024). Nevertheless, it is conceivable that such activity may constitute an exaptation, having been selected for in the evolution of taxa adapted to specific environmental conditions. Notably, we find Antarctic moss species exhibit high ice-nucleating activity, reaching temperatures of -7.4 °C, within the range where secondary ice-production may further enhance ice crystal numbers in clouds. As such, we suggest that mosses may represent a previously unknown source of ice nucleators in the atmosphere over the Southern Ocean.

References:

N. L. H. Kinney, C. A. Hepburn, M. I. Gibson, D. Ballesteros, and T. F. Whale. High interspecific variability in ice nucleation activity suggests pollen ice nucleators are incidental. Biogeosciences, 21(13):3201–3214, 2024.

B. F. Moffett. Ice nucleation in mosses and liverworts. Lindbergia, 38(1):14–16, 2015.

B. J. Murray, K. S. Carslaw, and P. R. Field. Opinion: Cloud-phase climate feedback and the importance of ice-nucleating particles. Atmospheric Chemistry and Physics, 21(2):665–679, 2021.

T. P. Roland, O. T. Bartlett, D. J. Charman, et al. Sustained greening of the Antarctic peninsula observed from satellites. Nature Geoscience, 17:1121–1126, 2024.

C. F. Weber. Polytrichum commune spores nucleate ice and associated microorganisms increase the temperature of ice nucleation activity onset. Aerobiologia, 32(2):353–361, 2016.

How to cite: Kinney, N. L. H., van den Heuvel, F., Kirchgaessner, A., Lachlan-Cope, T., Tarn, M. D., Ballesteros, D., and Whale, T. F.: Investigating the Atmospheric and Biological Significance of Ice-Nucleating Macromolecules Produced by Antarctic Mosses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18964, https://doi.org/10.5194/egusphere-egu25-18964, 2025.

How to cite: van den Heuvel, F., Smith, D., Squires, F., Witherstone, J., Flynn, M., Girdwood, J., Xu, J., and Lachlan-Cope, T.: Airborne in-situ cloud observations around the Antarctic peninsula from the Southern Ocean Clouds project , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19981, https://doi.org/10.5194/egusphere-egu25-19981, 2025.

Atmospheric rivers (ARs), increasingly recognized for their substantial influence on polar regions, are characterized as long, narrow corridors of intense moisture transport that play a crucial role in the redistribution of heat and water vapor toward higher latitudes. These systems profoundly affect precipitation regimes, surface melt dynamics, and, consequently, the surface mass balance of Antarctica (Wille et al., 2021). Additionally, ARs interact with oceanic processes, influencing wave activity, sea spray aerosol production, and feedback mechanisms that can impact cloud microphysics and precipitation. In the Antarctic Peninsula (AP), ARs have been associated with anomalous snowfall, extreme melting events, and transitions between snowfall and rainfall. A notable example occurred in February 2022, when an intense AR event resulted in unprecedentedly high temperatures, extensive surface melting across the AP and anomalously high rainfall amounts in the northern AP, underscoring their significant role in regional climate variability (Gorodetskaya et al., 2023).

Building on prior findings, this study examines a February 2023 AR event using observations at King Sejong Station, King George Island (radiosondes and precipitation radar MRR-PRO), ERA5 reanalysis and WAVEWATCH III model. The AR was driven by a deep low-pressure system west of the AP and a high-pressure ridge to the northeast, creating strong moisture advection and cyclonic uplift. Integrated Vapor Transport (IVT) values exceeded 400–600 kg/m−1 s−1 during peak days, with a distinct influence of baroclinic zones and fronts identified using wet-bulb potential temperature gradients at 850-hPa level. These conditions facilitated enhanced vertical motion, cloud development, and significant precipitation, primarily as snowfall in inland and higher- altitude regions of the AP. Concurrently, the strong winds associated with the AR enhanced wave activity and whitecapping in the surrounding Southern Ocean, increasing sea spray aerosol production, which could potentially influence cloud microphysical properties.

Furthermore, thermodynamic conditions during the AR were characterized by pronounced baroclinicity and the interaction of warm, moist subtropical air with cold polar air, which sustained cloud formation and moisture convergence. Later in February, as cyclonic activity weakened and IVT values decreased below 200 kg/m−1 s−1, precipitation became less intense and spatially confined. However, residual moisture flux and localized thermodynamic forcing supported light snowfall, even as synoptic features transitioned toward zonal flow. The dynamic interplay between AR-driven moisture transport, cyclonic uplift, oceanic feedback, and synoptic transitions underscores the significant role of ARs in modulating cloud and precipitation properties over the AP.

Acknowledgements: We are grateful for financial and logistical support via FCT projects MAPS and MICROANT, PROPOLAR and KOPRI

References:

Gorodetskaya, I.V. et al. “Record-high Antarctic Peninsula temperatures and surface melt in February 2022: a compound event with an intense atmospheric river” (2023) https://www.nature.com/articles/s41612-023-00529-6

Wille, J. D. et al. (2021) “Antarctic atmospheric river climatology and precipitation impacts” J. Geophys. Res. Atmos. 126, e2020JD033788

How to cite: Rafacho, M., De Groodt, A., Avilez-Valente, P., Durán-Alarcón, C., Park, S., and Gorodetskaya, I.: Landfalling Atmospheric Rivers in the Antarctic Peninsula: Synoptic Evolution and Oceanic Feedback , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21627, https://doi.org/10.5194/egusphere-egu25-21627, 2025.

Atmospheric rivers (AR) are long, narrow, transient corridors of intense atmospheric moisture transport affecting many regions around the world including Antarctica, where they play an important role in surface mass and energy balance. Over the Antarctic Peninsula (AP), one of the most rapidly warming regions, ARs have been increasing in frequency and intensity causing major heatwaves, anomalous precipitation and surface melt [1,2]. The impact of ARs would not be as intense without global warming [3] and thus it is urgent to understand processes driving ARs and their impacts using observations and improve their representation in the models used for weather forecasts and for future climate projections. One of the most worrying impacts is the increasing frequency of rain both during summer and winter seasons over the AP, which can drastically change surface energy and mass balance as well as impact fragile ecosystems. Understanding processes driving the transitions from snowfall to rainfall in time, location and in vertical profile - during all-weather events and particularly during ARs - is one of our key goals for collecting precipitation and radiosonde measurements at King Sejong station on King George Island, north of the AP. Since February 2023, we have been operating MRR-PRO, a 24-GHz vertically profiling precipitation radar from which we can derive effective reflectivity, Doppler velocity, melting layer height and precipitation rates. King Sejong is also equipped with automatic weather stations providing near-surface meteorological parameters, broadband surface radiation, precipitation-gauge measurements and snow height. Cloud lidar measurements using miniMPL at Escudero station are available via NASA’s MPLnet [4]. Here we present the evolution of ARs and associated snowfall and rainfall properties during two years of observations (2023-2024). The spatial distribution of precipitation from ERA5 and high-resolution Polar-WRF simulations for specific events demonstrates a transition from rainfall in the northern AP to snowfall in its southern part with significant orographic enhancement over the western upwind side of the AP. Vertical profiling with MRR at King Sejong shows significant variability in the melting layer attaining higher altitudes (up to 3km) during AR events. Combining MRR and radiosonde observations during a selected AR in February 2024 showed strong temperature inversions in the first 3 km with a melting layer varying in height between 3 km and near surface, accompanied by a sharp transition from snowfall to rain. Observations are used to evaluate representation of precipitation in ERA5 and in Polar WRF.

Acknowledgements: We thank FCT (projects MAPS/MICROANT); PROPOLAR; KOPRI; ANR (project ARCA).

References:

[1] Wille, J.D., et al. (2019): West Antarctic surface melt triggered by atmospheric rivers. Nat. Geosci.

[2] Gorodetskaya et al. (2023): Record-high Antarctic Peninsula temperatures and surface melt in February 2022: a compound event with an intense atmospheric river. npj Clim Atmos Sci.

[3] González-Herrero et al. (2022): Climate warming amplified the 2020 record-breaking heatwave in the Antarctic Peninsula. Commun. Earth Env..

[4] Rowe et al. (2025) Observations of Clouds and Radiation Over King George Island and Implications for the Southern Ocean and Antarctica, JGR, in review.

How to cite: Gorodetskaya, I. V., Durán-Alarcón, C., Zou, X., Rowe, P., Favier, V., and Park, S.: Atmospheric Rivers and Antarctic Peninsula Precipitation Phase Transitions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21662, https://doi.org/10.5194/egusphere-egu25-21662, 2025.