Clouds, moisture, and precipitation in the Polar Regions: Sources, processes and impacts

Clouds play an important role in the polar climate due to their interaction with atmospheric radiation and their role in the hydrological cycle linking poleward water vapour transport with precipitation, thereby affecting the mass balance of the polar ice sheets. Cloud-radiative feedbacks have also an important influence on sea ice. Cloud and precipitation properties depend strongly on the atmospheric dynamics and moisture sources and transport, as well as on aerosol particles, which can act as cloud condensation and ice nuclei.

This session aims at bringing together researchers using observational and/or modeling approaches (at various scales) to improve our understanding of polar tropospheric clouds, precipitation, and related mechanisms and impacts. Contributions are invited on various relevant processes including (but not limited to):

- Drivers of cloud/precipitation microphysics at high latitudes,
- Sources of cloud nuclei both at local and long range,
- Linkages of polar clouds/precipitation to the moisture sources and transport,

- Relationship of the poleward moisture transport to processes in the tropics and extra-tropics, including extreme transport events (e.g., atmospheric rivers, moisture intrusions),

- Relationship of moisture/cloud/precipitation processes to the atmospheric dynamics, ranging from synoptic and meso-scale processes to teleconnections and climate indices,

- Role of the surface-atmosphere interaction in terms of mass, energy, and cloud nuclei particles (evaporation, precipitation, albedo changes, cloud nuclei sources, etc)
- Impacts that the clouds/precipitation in the Polar Regions have on the polar and global climate system, surface mass and energy balance, sea ice and ecosystems.

Papers including new methodologies specific to polar regions are encouraged, such as (i) improving polar cloud/precipitation parameterizations in atmospheric models, moisture transport events detection and attribution methods specifically in the high latitudes, and (ii) advancing observations of polar clouds and precipitation. We would like to emphasize collaborative observational and modeling activities, such as the Year of Polar Prediction (YOPP), Polar-CORDEX, the (AC)3 project on Arctic Amplification, specific measurement campaigns in the Arctic and Southern Ocean/Antarctica and encourage related contributions.

The session is endorsed by the SCAR Antarctic Clouds and Aerosols Action Group.

Co-organized by CR7/HS13
Convener: Irina V. Gorodetskaya | Co-conveners: Susanne Crewell, Tom Lachlan-Cope, Penny Rowe, Manfred Wendisch
vPICO presentations
| Thu, 29 Apr, 14:15–17:00 (CEST)

vPICO presentations: Thu, 29 Apr

Chairpersons: Irina V. Gorodetskaya, Manfred Wendisch, Susanne Crewell
Matthew Shupe and Markus Rex and the MOSAiC Atmosphere team

The atmosphere plays a central role in the Arctic climate system and its recent changes. Enhanced Arctic atmospheric warming over the past decades is linked with many key processes, including variability in large-scale circulation patterns, changes in fluxes of heat, sea-ice decline, impacts on the ecosystem, and many more. It is this collection of interdependent processes, and their recent changes, that has motivated the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC, 2019-2020) expedition. Based on the Polarstern icebreaker, an international and interdisciplinary team of scientists conducted an intensive, year-long scientific exploration of the Central Arctic climate system while drifting with the sea ice. This presentation highlights the atmospheric components of this scientific expedition. These include the most comprehensive set of field observations to ever be made of the Central Arctic atmosphere, spanning from the stratosphere to the surface. Specific research activities examine atmospheric structure, winds, clouds, precipitation, aerosols, and surface fluxes of heat, momentum, gases, and moisture. Complementing these observational aspects are numerous modeling activities, including observation-based model assessment, model development, and regional process studies, among others. Finally, key links between the atmosphere and the sea ice, snow, and ocean through a variety of physical, chemical, and biological processes are discussed.

How to cite: Shupe, M. and Rex, M. and the MOSAiC Atmosphere team: Atmospheric processes in the Central Arctic during MOSAiC, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10447,, 2021.

Felix Pithan and Thomas Jung

As the climate warms, the amount of water vapour in the atmosphere increases by about 7 % per K, following the clausius-clapeyron relation. Globally averaged precipitation only increases by about 1-2 % per K of warming, as it is constrained by the atmospheric energy budget rather than the availability of moisture in the atmosphere. In the Tropics, zonally averaged precipitation mostly increases in the ITCZ near the equator and decreases in the subtropical dry zones (rich get richer, poor get poorer). A fundamental explanation of extratropical precipitation change has yet to be provided.

Here, we show that the structure of zonal mean mid-latitude precipitation changes is largely controlled by circulation changes, whereas amplified Arctic precipitation change is linked to increased atmospheric radiative cooling. The relative change in precipitation per unit of local warming is greater at high latitudes than anywhere else.

How to cite: Pithan, F. and Jung, T.: Amplified Arctic precipitation increases are driven by atmospheric radiative cooling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2439,, 2021.

Maximilian Maahn, Martin Radenz, Christopher Cox, Michael Gallagher, Jennifer Hutchings, Matthew Shupe, and Taneil Uttal

Snow is an essential component of the climate system impacting surface albedo, glaciers, sea ice, freshwater storage, and cloud lifetime. Even though we do not know the exact pathways through which ice, liquid, cloud dynamics, and aerosols are interacting in clouds while forming snowfall, the involved processes can be identified by their fingerprints on snow particles. The general shape of individual crystals (dendritic, columns, plates) depends on the temperature and moisture conditions during growth from water vapor deposition. Aggregation can be identified when multiple individual particles are combined into a snowflake. Riming describes the freezing of cloud droplets onto the snow particle and can eventually form graupel. In order to exploit these unique fingerprints of cloud microphysical processes, optical observations are required.

The Video In Situ Snowfall Sensor (VISSS) was specifically developed for the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) campaign to determine particle shape and particle size distributions. Different to other sensors, the VISSS minimizes uncertainties by combining two-dimensional high-resolution images with a large measurement volume and a design limiting the impact of wind. Here, we show first results from the MOSAiC campaign and present examples for synergy effects that can be obtained by combining radar and VISSS measurements.

How to cite: Maahn, M., Radenz, M., Cox, C., Gallagher, M., Hutchings, J., Shupe, M., and Uttal, T.: Measuring snowfall properties with the Video In Situ Snowfall Sensor during MOSAiC, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3306,, 2021.

Andreas Walbröl, Patrick Konjari, Ronny Engelmann, Hannes Griesche, Martin Radenz, Julian Hofer, Dietrich Althausen, Susanne Crewell, and Kerstin Ebell

The Arctic is currently experiencing a more rapid warming compared to the rest of the
world. This phenomenon, known as Arctic Amplification, is the result of several processes.
Within the Collaborative Research Centre on Arctic Amplification: Climate Relevant Atmospheric
and Surface Processes and Feedback Mechanisms (AC)3, our research focuses
on the influence of water vapour, the strongest greenhouse gas. The collection of data
about water vapour is essential to understand its impact on Arctic Amplification. Over
the past decades, a positive trend in integrated water vapour in the Arctic has been
identified using radiosondes and reanalyses for certain regions and seasons. However, inconsistent
magnitudes of the moistening trend in the reanalyses cause the need of a more
thorough investigation. While radiosondes offer precise measurements of thermodynamic
(temperature and humidity) profiles, they fail to capture the variability of water vapour
because of the low sampling rate (two to four sondes per day) and spatial coverage. To
obtain a more complete picture of water vapour variability, remote sensing instruments
(satellite- and ground-based) are used. Microwave radiometers (MWRs) onboard polar
orbiting satellites allow the coverage of the entire Arctic but suffer from uncertainties
related to surface emission. Observations at the surface gathered during the Multidisciplinary
drifting Observatory for the Study of Arctic Climate (MOSAiC) campaign can
serve as reference measurements in the central Arctic for the assessment of water vapour
products from reanalyses, models and satellite retrievals.

In this study, we give a first insight into the variability of integrated water vapour (IWV),
liquid water path (LWP) and thermodynamic profiles retrieved from two ground-based
MWRs onboard the research vessel Polarstern throughout the MOSAiC campaign. The
first radiometer is a standard low frequency HATPRO system and the other one is the
high-frequency MiRAC-P, which is particularly suited for low water vapour contents. The
retrieved quantities are compared with radiosonde measurements. A first analysis reveals
that the IWV is very well captured by the MWR measurements. Over the observation
period (October 2019 - October 2020), a large variety of meteorological conditions occurred.
Besides the considerable seasonal cycle, which is especially interesting because of
the contrast between polar night and polar day, several synoptic events contribute to the
variety of conditions, which will be highlighted as well.

We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research
Foundation) — Project 268020496 — TRR 172, within the Transregional Collaborative Research Center
"Arctic Amplification: Climate Relevant Atmospheric and Surface Processes, and Feedback Mechanisms
(AC)3". Data used in this manuscript was produced as part of the international Multidisciplinary drifting
Observatory for the Study of the Arctic Climate (MOSAiC) with the tag MOSAiC20192020 and the
Polarstern expedition AWI_PS122_00.

How to cite: Walbröl, A., Konjari, P., Engelmann, R., Griesche, H., Radenz, M., Hofer, J., Althausen, D., Crewell, S., and Ebell, K.: First insight into thermodynamic profiles, IWV and LWP from ground-based microwave radiometers during MOSAiC, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9053,, 2021.

Michael Lonardi, Christian Pilz, Ulrike Egerer, André Ehrlich, Matthew D. Shupe, Holger Siebert, and Manfred Wendisch

Arctic boundary layer clouds play an important role in the Arctic amplification due to their impact on the radiative energy budget, e. g., local cooling at cloud top which strongly affects boundary-layer dynamics. High resolution in-situ data characterizing the irradiance profile in clouds over the Arctic sea ice are rare due to the accessibility of this region, the challenges posed by icing and the limited resolution of airborne measurements.

The tethered balloon system BELUGA (Balloon-bornE moduLar Utility for profilinG the lower Atmosphere) was deployed from the ice camp of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) in July 2020. BELUGA consists of a 90 m³ helium-filled tethered balloon with maximum flight altitude of 1500 m and an adaptable scientific payload to characterize radiation, cloud, aerosol and turbulence properties which was specifically developed for Arctic tethered balloon operations.

Here a first analysis of vertical profiles of upwards and downwards solar and terrestrial irradiances in cloudy and cloud-free conditions is presented. Profiles of radiative heating were calculated and compared for different cloud covers. The case studies were evaluated by radiative transfer simulations  to quantify the impact of different cloud and atmospheric properties on the heating rate profiles. In combination with surface-based measurements, the cloud radiative forcing in the summer Arctic was assessed.

How to cite: Lonardi, M., Pilz, C., Egerer, U., Ehrlich, A., Shupe, M. D., Siebert, H., and Wendisch, M.: Impact of Clouds on Broadband Radiation Profiles in the Summer Arctic Measured by a Tethered Balloon During MOSAiC: First Results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4923,, 2021.

Benjamin Kirbus, Michael Schäfer, André Ehrlich, and Manfred Wendisch

Large-scale air mass exchanges between lower latitudes and the inner Arctic are one key aspect in understanding Arctic climate change. Of particular interest are Warm and Moist Air Intrusions (WMAI). These events, albeit covering only 10 % of the time, drive >60 % of the overall moisture flux into the Arctic. Conveyed by surging downward longwave radiation, WMAI can trigger pronounced sea-ice melt and alter local atmospheric conditions for weeks.

However, many models struggle with a correct representation of air mass transformations during these events. Thus, a Lagrangian approach is suggested to perform airborne measurement campaigns and to analyze numerical weather forecast and reanalysis data. Here, we present a combination of the Lagrangian analysis tool Lagranto with ECMWF forecast datasets and the atmospheric flight planning tool MSS. This approach was applied during the September 2020 MOSAiC airborne campaign. Additionally, five-day forward and backward trajectories were calculated to identify air masses linking the airborne observations with ground-based observations at the MOSAiC camp. A first analysis of the air mass characteristics and their change along the trajectories is presented.

Due to vertical wind shear, such an air mass analysis is not trivial. It requires a detailed flight planning in order to sample the temporal and spatial (horizontal and vertical) development of the air masses. As an outlook for the upcoming spring 2022 HALO-(AC)3 campaign, the potential of combining Lagranto with MSS in predicting the most effective flight track is therefore demonstrated.

How to cite: Kirbus, B., Schäfer, M., Ehrlich, A., and Wendisch, M.: Combining model-based quasi-Lagrange tracking of air mass intrusions into the Arctic with airborne observations , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5239,, 2021.

Luca Lelli, Narges Khosravi, Marco Vountas, and John Burrows

It is now well known that the sea ice extent in the Artic has been shrinking in the past three decades in the period known as the Arctic Amplification. A simple assumption would be that if the sea ice extent has been reduced, then the spectral reflectance at the top of the atmosphere - RTOA - would have also decreased across the Arctic. On the other hand, Arctic reflectivity also largely depends on the presence of clouds, shielding the underlying surface, and on changes of their optical and physical properties. Thus, the assessment of trends of spectral reflectivity and cloud properties are essential to understand those forcings and feedbacks considered drivers of Arctic Amplification as well as the interactions between the components of the Arctic cryosphere. In the reported study we observationally tackle the stated problem investigating changes of RTOA at selected wavelengths making use of spaceborne measurements of the Global Ozone Monitoring Experiment (GOME onboard ERS-2 and MetOp A/B/C) and of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY onboard Envisat) for the period 1995-2018. We complement this record with cloud properties and fluxes at top of the atmosphere and at the surface, inferred from measurements of the post-meridiem orbits of the Advanced Very High Resolution Radiometer (AVHRR onboard POES). Although the Pan-Arctic reflectivity has decreased, the analysis of regional trends shows distinct areas where the reflectivity trends diverge. While darkening areas can be attributed to seasonal sea ice decline, an increase of Arctic brightness over sea ice free regions can be largely attributed to changes in the optical properties of clouds. While the multiyear mean of the radiative forcing by clouds points to a TOA cooling and a surface warming, its trends exhibit opposite tendencies. In the last two decades, the cloud radiative effect at TOA is expected to warm the lower latitudes (below 75 N) and to cool the circumpolar belt, while an opposite trend at BOA, amounting to 5 W m-2 per decade, cools the lower Arctic latitudes and warms the permanent sea ice region, this effect being more pronounced in spring months (April to June) than in summer months (July to September).

How to cite: Lelli, L., Khosravi, N., Vountas, M., and Burrows, J.: Pan-Arctic and regional trends of reflectance, clouds and fluxes: implications for Arctic Amplification, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15276,, 2021.

Hélène Bresson, Annette Rinke, Vera Schemann, Mario Mech, Susanne Crewell, Carolina Viceto, Irina Gorodetskaya, and Kerstin Ebell

The Arctic climate changes faster than the ones of other regions, but the relative role of the individual feedback mechanisms contributing to Arctic amplification is still unclear. Atmospheric Rivers (ARs) are narrow and transient river-style moisture flows from the sub-polar regions. The integrated water vapour transport associated with ARs can explain up to 70% of the precipitation variance north of 70°N. However, there are still uncertainties regarding the specific role and the impact of ARs on the Arctic climate variability. For the first time, the high-resolution ICON modelling framework is used over the Arctic region. Pan Arctic simulations (from 13 km down to ca. 6 and 3 km) are performed to investigate processes related with anomalous moisture transport into the Arctic. Based on a case study over the Nordic Seas, the representation of the atmospheric circulation and the spatio-temporal structure of water vapor, temperature and precipitation within the limited-area mode (LAM) of the ICON model is assessed, and compared with reanalysis and in-situ datasets. Preliminary results show that the moisture intrusion is relatively well represented in the ICON-LAM simulations. The study also shows added value in increasing the model horizontal resolution on the AR representation.

How to cite: Bresson, H., Rinke, A., Schemann, V., Mech, M., Crewell, S., Viceto, C., Gorodetskaya, I., and Ebell, K.: Case study of an Arctic atmospheric river with the ICON model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1344,, 2021.

Carolina Viceto, Irina Gorodetskaya, Annette Rinke, Alfredo Rocha, and Susanne Crewell

A significant increase in the atmospheric moisture content over the Arctic region has been recently documented, that might be caused by the enhanced poleward moisture flux which is expected to continuously increase in the future. This change can be attributed to different causes, in which increasing moisture transport intensity is included. In this study we focus on events with anomalous moisture transport confined to long, narrow and transient corridors, known as atmospheric rivers (ARs), which are expected to have a strong influence on Arctic mass and energy budget.

This study is based on MERRA-2 reanalysis (Modern-Era Retrospective analysis for Research and Applications, Version 2) extending from an historical period until present (1980-2020). ARs are identified using the tracking algorithms by Gorodetskaya et al. (2020) and Guan et al. (2018). We explored the frequency of ARs focusing on annual, seasonal and monthly values. Spatial patterns were analysed for the Arctic latitudes, covering both Atlantic and Pacific moisture transport pathways, and showing the importance of the Siberian moisture pathway during summer. Furthermore, we include a more detailed analysis performed at different sites north of the Arctic circle. Specific attention is given to the ARs characteristics during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from September 2019 to October 2020, as compared to the forty-year climatology and variability of the ARs in the Arctic.

Preliminary results show a higher frequency of ARs over the Norwegian and Barents Sea (Atlantic pathway), mainly during autumn and winter, although during May and June there is a high frequency of ARs over Western Siberia and Barents Sea. In contrast, the Canadian Artic has a lower frequency of ARs regardless the season, which is explained by a steep decrease of ARs frequency in the Gulf of Alaska and Bering Sea that block their progression to further north latitudes.



Gorodetskaya, I. V., Silva, T., Schmithüsen, H., and Hirasawa, N., 2020: Atmospheric River Signatures in Radiosonde Profiles and Reanalyses at the Dronning Maud Land Coast, East Antarctica. Adv. Atmos. Sci.,

Guan, B., Waliser, D. E. and Ralph, F. M., 2018: An Intercomparison between Reanalysis and Dropsonde Observations of the Total Water Vapor Transport in Individual Atmospheric Rivers. J. Hydrometeorol., 19, 321–337,



This work is supported by FCT PhD Grant SFRH/BD/129154/2017 and developed in collaboration with Transregional Collaborative Research Centre (AC)3, AWI and U. Cologne.

How to cite: Viceto, C., Gorodetskaya, I., Rinke, A., Rocha, A., and Crewell, S.: Forty-year climatology and variability of atmospheric rivers in the Arctic using MERRA-2 reanalysis from 1980 to 2020, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14554,, 2021.

Leif-Leonard Kliesch, Elena Ruiz Donoso, Birte Kulla, Melanie Lauer, Mario Mech, Nils Risse, Vera Schemann, Manfred Wendisch, and Susanne Crewell

Despite the strong influence of cloud liquid water on the radiative budget, the knowledge of its amount and variability in the Arctic is rather limited. The Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign took place from May 22 to June 28, 2017 and offers the possibility to investigate the Liquid Water Path (LWP) during various environmental conditions. In this period synoptic conditions were characterized as a cold air outbreak, warm air advection resulting in a period of warm conditions, and a normal period with conditions in between the cold and warm period. Deployed on the research aircraft Polar 5, the Microwave Radar/radiometer for Arctic Clouds (MiRAC) collected downward observations of radar reflectivity and Brightness Temperatures (Tb) over sea-ice-free ocean from aircraft altitudes above 2.8 km. From Tb a unique high-resolution data set of cloud LWP over remote sea-ice-free Arctic ocean is retrieved. The airborne microwave retrieved LWP is compared with LWP retrieved from visible/near-infrared techniques taken on board the aircraft as well as with two different satellite products. The respective uncertainties and the agreement among the different techniques are discussed.  

The different cloud situations observed during the three ACLOUD periods are investigated to identify differences in LWP distribution from the airborne measurements. To analyze the representativity of the limitation to specific flight tracks, continuous ground-based observations at Ny-Ålesund, ERA5 reanalysis, and simulations with the ICON model are used. While in general the airborne sampling seems to be representative for the larger region systematic difference in LWP amount between the different products occurs which will be discussed in this presentation.

How to cite: Kliesch, L.-L., Ruiz Donoso, E., Kulla, B., Lauer, M., Mech, M., Risse, N., Schemann, V., Wendisch, M., and Crewell, S.: How do synoptic conditions affect Liquid Water Path over the sea-ice-free Arctic Ocean during ACLOUD?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2334,, 2021.

Melanie Lauer, Annette Rinke, Irina Gorodetskaya, and Susanne Crewell

The Arctic as a whole has been experiencing significant warming and moistening with several potential factors at play. In general, the warming amplifies the Arctic hydrological cycle. There are two processes which could affect the water vapour content in the Arctic. These are the enhanced local evaporation due to reduced sea-ice concentration and extent and the modified poleward moisture transport from lower latitudes due to changing circulation patterns. An important contribution to the total poleward moisture transport comes from Atmospheric rivers (ARs). ARs have rare occurrence but are associated with anomalously high moisture transport compared to tropical cyclones. ARs are typically associated with not only moisture but also with significant heat advection. They can bring precipitation as rain and/or snow. Moreover, additional feedbacks can occur: the warming effect of the ARs on the surface, coupled with rain lowering surface albedo, can cause thinning and melting of Arctic sea ice and snow. This, in turn, could increase the relative role of the local evaporation compared to the moisture transported from lower latitudes.

In this study, we investigate the relationship between the poleward moisture transport by ARs and the precipitation in the Arctic. The focus is on AR events during the ACLOUD (May/June 2017) and AFLUX (March/April 2018) campaign within the Collaborative Research Center “Arctic Amplification: Climate Relevant Atmospheric and Surface Processes, and Feedback Mechanisms (AC)3”. For these campaigns, existing AR catalogues with the input of ERA5 reanalyses are used to detect AR events. Six ARs are detected: two coming from Siberia and four from the Atlantic.

These AR events are analysed in terms of the macro- and microphysical precipitation properties, including frequency, intensity, and type of precipitation (rain or snow).  For this purpose, we use ERA5 reanalyses data for the water vapour transport, precipitation amount and type, rain and snow profiles (convective, large-scale, total), as well as vertical profile of hydrometeors. Reanalysis products are evaluated using a set of observational data (satellite data and ground-based remote sensing measurements). This new multi-parameter, multi-dataset set will allow to investigate the occurrence of ARs and its influence on precipitation in the Arctic for the last decades.


“We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) –Projektnummer 268020496 –TRR 172, within the Transregional Collaborative Research Center “ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3.“

How to cite: Lauer, M., Rinke, A., Gorodetskaya, I., and Crewell, S.: Evaluating atmospheric rivers and their influence on precipitation in the Arctic - comparing observational with reanalysis data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2506,, 2021.

Carola Barrientos Velasco, Hartwig Deneke, Hannes Griesche, Anja Hünerbein, Patric Seifert, and Andreas Macke

Clouds influence the shortwave (SW) and longwave (LW) radiative fluxes, thereby affecting the radiative budget by enhancing or diminishing the heat budget at the surface (SFC), at the top of the atmosphere (TOA), and through the atmosphere. In the Arctic, their complexity enhances due to their intrinsic interactions with several physical processes and feedback mechanisms.

With the aim to further investigate the Arctic system, the project (AC)³ (Arctic Amplification: Climate Relevant Atmospheric and SurfaCe Processes and Feedback Mechanisms) established two major field campaigns in summer of 2017. Both performed in situ and remote sensing observations over the ocean with PS106 and in the air with ACLOUD (Macke and Flores, 2018, Wendisch et al., 2019). The observations collected during PS106 are considered to investigate the effects and influence of clouds in the radiation budget for the summer central Arctic.

The PS106 expedition took place aboard the German research vessel Polarstern which was equipped with active and passive remote sensing instrumentation (Griesche et al., 2020). The synergistic operation of this instrumentation was used to derive macro and microphysical properties of clouds by applying the Cloudnet algorithm. These retrievals together with vertical profiles of temperature and relative humidity are used as input to the Rapid Radiative Transfer Model for GCM applications (RRTMG). The results of the broadband SW and LW radiative simulations along with hourly satellite products from Clouds and the Earth’s Radiant Energy System (CERES) Synoptic 1-degree Ed.4. are compared to ship-borne observations indicating a better agreement for single-level liquid clouds than for more challenging sky conditions. The results of the comparison bring sufficient information to discuss a radiative closure assessment for selected case studies and for the entire PS106 expedition. Based on these results the cloud radiative effect (CRE) is calculated indicating a net effect of -8.1 W/m².

The study is extended by applying this methodology to the recent Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC). Preliminary results will be presented for the first leg which will allow a direct comparison of the contrasting properties of cloud radiative effects during summer and winter season.


Griesche, H. J., and coauthors. (2020): Application of the shipborne remote sensing supersite OCEANET
for profiling of Arctic aerosols and clouds during Polarstern cruise PS106, Atmos. Meas. Tech., 13,

Macke, A. and Flores, H. (2018): The Expeditions PS106/1 and 2 of the Research Vessel POLARSTERN
to the Arctic Ocean in 2017 , Berichte zur Polar- und Meeresforschung = Reports on polar and marine
research, Bremerhaven, Alfred Wegener Institute for Polar and Marine Research, 719 , 171 p.

Wendisch, M., and coauthors. (2019): The Arctic Cloud Puzzle: Using ACLOUD/PASCAL Multiplatform
Observations to Unravel the Role of Clouds and Aerosol Particles in Arctic Amplification. Bull. Amer.
Meteor. Soc., 100, 841–871,

How to cite: Barrientos Velasco, C., Deneke, H., Griesche, H., Hünerbein, A., Seifert, P., and Macke, A.: Analysis of cloud radiative effects and radiative budget in the Central Arctic based on satellite and ship-borne observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7721,, 2021.

Roya Ghahreman, Wanmin Gong, Stephen R. Beagley, Ayodeji Akingunola, and Paul A. Makar

Investigation of the cloud microphysics is carried out by using a fully coupled version of GEM-MACH, the Environment and Climate Change Canada’s (ECCC) online air quality forecast model, (Global Environmental Multiscale–Modelling Air quality and Chemistry) for the Arctic domain during summer 2014. Simulation results indicate that model is capable of simulating the low clouds prevailing in summertime Arctic, particularly thin water clouds (or clouds with liquid water path < 50 g m-2), which have a significant effect on cloud radiative forcing in the Arctic.

Model simulations are also compared with the July 2014 NETCARE field campaign aircraft observations based from Resolute NU. The field campaign consisted of two periods with distinct metrological conditions: relatively pristine and relatively polluted Arctic atmosphere with the influence of transport from lower latitudes. For the relatively polluted period, simulations of cloud’s microphysics suggested more and smaller droplets with higher liquid water content (LWC), and hence lower precipitation and longer cloud lifetime. The model agrees well with the observation results showing that aerosols in the size range of 50-100 nm are commonly activated in the summer Arctic, with even smaller aerosols (< 50 nm) being activated during the pristine period.

How to cite: Ghahreman, R., Gong, W., Beagley, S. R., Akingunola, A., and Makar, P. A.: Modelling Study of the Summer Time Arctic Liquid Clouds, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12409,, 2021.

Marcus Klingebiel, André Ehrlich, Elena Ruiz-Donoso, and Manfred Wendisch

Over the last decades, the Arctic has experienced an enhanced warming, which is known as Arctic amplification. This process leads to a decrease in the amount of Arctic sea ice, which is linked by different feedback mechanisms to clouds and the related radiative properties. To analyze how the properties of these Arctic clouds could change in a future sea ice free Arctic, we completed three airborne campaigns in the marginal sea ice zone between 2017 and 2020 covering summer and winter conditions. During these campaigns we performed in-situ and remote sensing measurements to study cloud micro- and macrophysical properties and analyzed how these clouds affect the radiation budget. In this study we use the passive remote sensing measurements from these airborne observations to retrieve cloud top effective radius, liquid water path and cloud optical thickness. We found that these cloud properties differ between a sea ice surface and over open water. The airborne observations are supported by an analysis of the cloud product from the MODIS satellite. The systematic differences of clouds over sea ice and the open ocean suggests that clouds may change in a future warming Arctic environment.

How to cite: Klingebiel, M., Ehrlich, A., Ruiz-Donoso, E., and Wendisch, M.: Comparison of Arctic cloud properties over sea ice and open ocean based on airborne spectral solar remote sensing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2012,, 2021.

Chairpersons: Penny Rowe, Tom Lachlan-Cope, Irina V. Gorodetskaya
Jennifer Kay

Understanding the influence of clouds and precipitation on global warming remains an important unsolved research problem. This talk presents an overview of this topic, with a focus on recent observations, theory, and modeling results for polar clouds. After a general introduction, experiments that disable cloud radiative feedbacks or “lock the clouds” within a state‐of‐the‐art,  well‐documented, and observationally vetted climate model will be presented. Through comparison of idealized greenhouse warming experiments with and without cloud locking, the sign and magnitude cloud feedbacks can be quantified. Global cloud feedbacks increase both global and Arctic warming by around 25%. In contrast, disabling Arctic cloud feedbacks has a negligible influence on both Arctic and global surface warming. Do observations and theory support a positive global cloud feedback and a weak Arctic cloud feedback?  How does precipitation affect polar cloud feedbacks? What are the implications especially for climate change in polar regions?  

How to cite: Kay, J.: How do polar clouds and precipitation affect global warming?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6444,, 2021.

Floortje van den Heuvel, Thomas Lachlan-Cope, Jonathan Witherstone, Dean Hurren, and Anna Jones

Our limited understanding of clouds is a major source of uncertainty in climate sensitivity and climate model projections. The Southern Ocean is the largest region on Earth where climate models present large biases in short and long wave radiation fluxes which in turn affect the representation of sea surface temperatures, sea ice and ultimately large scale circulation in the Southern Hemisphere. Evidence suggests that the poor representation of mixed phase clouds at the micro- and macro scales is responsible for the model biases in this region. The Southern Ocean Clouds (SOC) project will be a multi-scale, multi-platform approach with the aim of improving understanding of aerosol and cloud microphysics in this region, and their representation in numerical models.

Although this years’ first SOC measurement season has suffered greatly from travel restrictions, we have installed an Optical Particle Counter (OPC) on a ship (The James Clark Ross – JCR) and recorded aerosol measurements as it was travelling through the Atlantic sector of the Southern Ocean towards the Antarctic Peninsula, and while the ship was moored at South Georgia and Port Stanley. Over the course of one month, the OPC recorded particle sizes between 0.35 and 40 micrometers every six seconds. This study will present the data from this first, rather short Antarctic SOC season. It will present the analyses of the obtained OPC data alongside satellite observations and model reanalyses in the same region.

How to cite: van den Heuvel, F., Lachlan-Cope, T., Witherstone, J., Hurren, D., and Jones, A.: Ship-based aerosol measurements in the Southern Ocean , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12327,, 2021.

Anastasiia Chyhareva, Svitlana Krakovska, Irina Gorodetskaya, Denis Pishniak, Jonathan Wille, and Penny Rowe

Synoptic-scale atmospheric circulation that transports moisture from lower latitudes highly influences the Antarctic coastal climate, warming and moistening the lower troposphere and causing both precipitation and temperature increases. During recent decades, it has been shown that the highest warming rate over Antarctica is observed over the Antarctic Peninsula region. Heat and moisture transport from lower latitudes, particularly associated with atmospheric rivers (ARs), could play a crucial role in this warming. Among the most complex and understudied processes relate to microphysical properties of clouds and precipitation and understanding phase transitions during intense precipitation events associated with ARs and their representation in polar weather and climate models.

The goal of this research is  to investigate the temporal and spatial evolution of precipitation, including its intensity and phase transition and associated cloud properties during AR events over the Antarctic Peninsula in austral summer. We focus on two sites representing different regional and micro-climates around the Antarctic Peninsula - Escudero station, situated on King George Island at the northern tip of the peninsula, and Vernadsky station – located on Galindez Island at the western (upwind) side closer to the central part of the peninsula. Although both stations have typical maritime climate, the Vernadsky site is more affected by orographic enhancement of precipitation and cold air advection from the continent.

We use ground-based observations of meteorology, conducted during The Year of Polar Prediction Special Observing Period (YOPP-SOP) in summer 2018/2019 over the Antarctic Peninsula region and compare against ERA-5 and AMPS Polar WRF. After evaluating ERA-5 reanalysis , it is used for large-scale analysis of clouds and precipitation type. The timings of precipitation phase transitions in ERA-5 and Polar WRF are determined for the grid cells where the two stations are located. Sensitivity to microphysics parameterization in Polar WRF is tested with several double moment cloud microphysics parameterization schemes.

We analyze two cases with observed precipitation phase transitions, during the first week of December 2018. Higher precipitation amounts were observed over Vernadsky station during the first event and over Escudero during the second event. Total precipitation during the whole week is higher for Vernadsky station compared to Escudero station, related to the AR landfall position and strength, as well as the orographic enhancement at the upwind side of the Antarctic Peninsula ridge. This is confirmed by assessment of ERA-5 data. Comparison with the YOPP-SOP observations at Escudero shows that ERA-5 represents major precipitation type accurately and thus can be used for further study of precipitation microphysics. For Vernadsky station, ERA-5 showed a few cases of phase transition from snow to wet snow, associated with ARs events according to ERA-5 data; unfortunatly observations for comparison were lacking. Compared to ERA-5, Polar WRF shows a finer structure of precipitation fields disturbed by the mountains. We intend to test different parameterizations of cloud microphysics in Polar WRF with fine resolution against the complex of measurements at Vernadsky station in order to find the optimal configuration in the region to use during the upcoming winter YOPP in the Southern Hemisphere.

How to cite: Chyhareva, A., Krakovska, S., Gorodetskaya, I., Pishniak, D., Wille, J., and Rowe, P.: Cloud and precipitation microphysics evaluated with ERA-5 and Polar WRF over the northern Antarctic Peninsula, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13058,, 2021.

Sergi Gonzalez and Francisco Vasallo

Extreme weather records are important in determining the boundaries of the atmospheric system and in determining whether the Earth’s climate is changing or becoming more extreme (Cerveny, 2007). For this reason, the WMO Commission for Climatology decided to create a database to archive and verify the world weather extreme records. Due to the lack of an extensive database of reliable precipitation measurements in Antarctica, the only continental value in this table that has yet to be determined is the greatest precipitation in the Antarctic Region (average annual), which is estimated at more 800 mm. In order to evaluate the extreme precipitation records in Antarctica, in this communication the most extreme records are determined on different timescales, from 1 day to 2 years, using the RACMO2.3p2 model reanalysis (van Wessem et al. 2014), whose evaluation indicates that it performs well concerning the precipitation estimates. Records of extreme precipitation in Antarctica are found on the west side of the Antarctic Peninsula and are likely produced by utmost atmospheric river events (Gorodetskaya 2014). Extreme precipitation records closely follow a potential scaling such as the global precipitation records (Galmarini, 2004). Extreme precipitation in Antarctica has a higher exponent, indicating that small timescales (days) have less impact with respect to the large timescales (years) in relation to the global extreme precipitation. In addition, we show the regional variability of the extreme values and scaling in Antarctica. Although the values shown in this research emanate from model simulations and are not effectively measured, they help to constrain the upper limit of the maximum annual precipitation on the continent to well above one thousand millimeters.



Cerveny, R. S., Lawrimore, J., Edwards, R., & Landsea, C. (2007). Extreme weather records: Compilation, adjudication, and publication. Bulletin of the American Meteorological Society, 88(6), 853-860.

Galmarini, S., Steyn, D. G., & Ainslie, B. (2004). The scaling law relating world point‐precipitation records to duration. International Journal of Climatology: A Journal of the Royal Meteorological Society, 24(5), 533-546.

Gorodetskaya, I. V., Tsukernik, M., Claes, K., Ralph, M. F., Neff, W. D., & Van Lipzig, N. P. (2014). The role of atmospheric rivers in anomalous snow accumulation in East Antarctica. Geophysical Research Letters, 41(17), 6199-6206.

Van Wessem et al., 2014. Improved representation of East Antarctica surface mass balance in a regional climate model. J. Glac., 60(222), 761-770


How to cite: Gonzalez, S. and Vasallo, F.: Scaling of extreme precipitation records in Antarctica from 1 day to 2 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-281,, 2020.

Diogo Luis, Irina Gorodetskaya, Katherine Leonard, Elisabeth Schlosser, Etienne Vignon, F. Martin Ralph, and Michael Lehning

Precipitation is still a poorly known variable in the Southern Ocean/Antarctica due to the lack of measurements. Unique precipitation measurements were carried out during the Swiss Polar Institute’s Antarctic Circumnavigation Expedition (ACE) (December 2016 - March 2017). High temporal resolution measurements of precipitation were performed by a Snow Particle Counter (SPC) and by a micro rain radar (MRR) aboard the RV Akademik Tryoshnikov. Radiosondes were launched periodically to observe the vertical structure of the atmosphere. Additionally, MRR and radiosonde measurements from Dumont D’Urville station (DDU) were available when the expedition was in the Mertz Glacier region. These data offer a rare opportunity to evaluate model and reanalysis products performance in a region without regular precipitation measurements. In this study, ECMWF’s ERA5 reanalysis product and Antarctic Mesoscale Prediction System (AMPS) model data are evaluated using ACE and DDU in-situ observations. Two snowfall events that occurred around Mertz Glacier during the ACE campaign were chosen to compare ERA5 and AMPS data with in-situ measurements. The first event on 2 February 2017 was associated with an extratropical cyclone east of Adelie Land and a moderate along-shore moisture transport. The second event on 8-10 February 2017 was associated with a cyclone west of Mertz blocked by a high-pressure ridge, directing an intense moisture transport (identified as an atmospheric river) and precipitation to DDU. To assess if ERA5 reanalysis and AMPS (Antarctic Mesoscale Prediction System using Polar-WRF model) are able to represent these different types of precipitation events, we analyse the differences in precipitation amount between in-situ, model and reanalysis data and compare modelled vertical profiles with radiosonde measurements.

How to cite: Luis, D., Gorodetskaya, I., Leonard, K., Schlosser, E., Vignon, E., Ralph, F. M., and Lehning, M.: Precipitation over the Southern Ocean: synoptic analysis and model evaluation using ground-based remote sensing and in-situ measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13544,, 2021.

Denys Pishniak, Svitlana Krakovska, Anastasia Chyhareva, and Sergii Razumnyi

Measurements of precipitation has always had well known difficulties that caused inaccuracies. This is especially acute in Polar regions where prevailing solid precipitation is accomplished with strong winds. Alternatively some indirect methods of precipitation measurements still in development and numerous meteorological instruments have been created on their basis.

The Akademik Vernadsky station is located in the Antarctic Peninsula region with a large amount of precipitation and  the problem of its measuring has always been relevant here. Although the data of monthly precipitation have been found for Vernadsky (Faraday) station since 1964, the first standard Tretyakov precipitation gauge was set up there only in 1997. But in recent years, several new instruments for indirect precipitation measurement have been installed at the meteorological site. The consistency of their data are the subject for this study. 

Direct comparison of all measurement devices as well as investigation of their estimations dependencies from other meteorological parameters are analysed and will be presented for the period 2019-2020. Originally various instruments showed huge differences in precipitation estimates. Deep analysis and correction of the measurement results according to weather conditions is obviously needed for bias reduction. But the local features of the extremely heterogeneous underlying surface of the region affect the vertical component of the wind, and can cause the natural small scale precipitation variability. 

The advantages of indirect methods for precipitation measuring is a high sensitivity to registering even individual falling precipitation particles and, hence, the really high temporal resolution of the data. Therefore, it can be used for investigation of physical atmospheric processes. As an example, the case study of a cyclone with precipitation phase transition over Vernadsky station on December 5-6, 2020 is investigated and will be presented. A comparison of the measurement data of various devices (Tretyakov Precipitation Gauge, Snow Stick, Vaisala PWD22, Lufft WS100, METEK MRR-PRO) and the ERA-5 reanalysis was carried out. A vertical radar MRR-PRO is of special interest as a measuring instrument for polar regions because it can ignore surface snow transport and has proved reliability in the Antarctic environment recently. In Marine Antarctica this device can identify the height of precipitation melting and also show a number of other useful parameters. This complex of precipitation measurement instruments is planned to be used in the frames of the forthcoming YOPP-SH field campayne.

How to cite: Pishniak, D., Krakovska, S., Chyhareva, A., and Razumnyi, S.: Preliminary analysis and main problems of instrumental measurement complex at the Vernadsky Antarctic Station, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13591,, 2021.

Suginori Iwasaki, Hajime Okamoto, and Kaori Sato

We show that thin cirrus clouds, whose particle radius is greater than 50 μm and number concentration is less than 10 /L, extinct supercooled water clouds (SC) by use of the data of the space-borne lidar, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), and the space-borne 94-GHz cloud profiling radar (CPR). We call the cirrus Large-and-Sparse-particle Clouds (LSC).

The space-borne imagers, such as Moderate Resolution Imaging Spectroradiometer (MODIS), cannot measure LSC; hence, LSC had been difficult to be found by satellites. CALIOP is less sensitive to LSC than CPR though CALIOP is usually more sensitive to clouds than CPR because of the cloud particle size distribution of LSC.

The most significant feature of LSC is that LSC extinct SC and cloud particles of SC are changed into pristine ice particles. This is because (1) SC and LSC do not tend to coexist while horizontally oriented ice particle clouds (2D) and LSC tend to coexist, (2) the cloud top height of LSC is higher than that of SC, and (3) the terminal velocity of LSC particles is about 1 km/h.

Because 10-20% of clouds in the Arctic are LSC, LSC would indirectly impact on radiative forcing in the Arctics.

How to cite: Iwasaki, S., Okamoto, H., and Sato, K.: Thin cirrus clouds that extinct supercooled water clouds in the Arctics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5010,, 2021.

Giandomenico Pace, Tatiana Di Iorio, Alcide di Sarra, Antonio Iaccarino, Daniela Meloni, and Giovanni Muscari

The radiative effects of clouds and their microphysical structure in Polar regions are still object of large uncertainty, that contribute to determine the large inaccuracies of climate model in the representation of clouds and their effects.

In the frame of the CLouds And Radiation in the Arctic and Antarctica (CLARA2) project, a celiometer has been installed in November 2019 at the Thule High Arctic Atmospheric Observatory, THAAO, an international infrastructure located in proximity of Thule Air Base (76.5°N, 68.8°W), Greenland ( with the aim of strengthening the cloud observational capability at the Observatory already including, among the other instruments, a microwave profiler and upward- and downward-looking pyranometers and pyrgeometers operating since July 2016.

CLARA2 should have contributed to the YOPP 2020 Arctic Special Observing Period (SOP) in February-March with intensive measurements of the atmospheric vertical structure by means of a microwave profiler, a celiometer and daily radiosoundings, but the arrival of the COVID19 prevented the involved researchers to carry out the field campaign at THAAO. Nonetheless the automatic measurements were collected regularly also during the 2020 SOP.

The temporal evolution of the cloud’s presence and characteristics during the two months SOP will be presented and discussed in terms of meteorological conditions, broadband surface radiation fluxes, cloud’s geometrical characteristics, phase and liquid water path.

How to cite: Pace, G., Di Iorio, T., di Sarra, A., Iaccarino, A., Meloni, D., and Muscari, G.: Cloud observations at THAAO Observatory during the Arctic YOPP 2020, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9114,, 2021.

Arno Hammann and Kirsty Langley

Surface air temperatures have been rising roughly twice as fast in the Arctic as in the global average (“Arctic amplification”). Not all responsible physical mechanisms are understood or known, and current climate models frequently underestimate the pace of Arctic warming. Knowledge is lacking specifically about processes involving moisture and the formation of clouds in the the atmospheric boundary layer (ABL). This reduces the reliability of Arctic and global climate change projections and short-term weather predictions.

We use a comprehensive multi-sensor observational dataset from the Greenland Ecosystem Monitoring (GEM, research site in Qeqertarsuaq, Greenland, in order to identify dominant structural and dynamic patterns of the ABL. Central to this dataset are the atmospheric column profiles of air temperature and water content acquired by a passive microwave radiometer, one of only three such instruments operating in Greenland. The in situ data is related to the large-scale circulation via an analysis of the global ERA5 reanalysis dataset, with a focus on moisture transport from humid latitudes.

The statistical analysis comprises both process-level relationships between observed variables (regressions) for individual events and pattern recognition techniques (clustering) for the identification of dominant patterns on the small and large scale, an approach particularly suited for the study of an unsteady, changing climate. Moisture enters the Arctic in narrow and infrequent atmospheric bands termed atmospheric rivers, and climate change may alter the frequency of such events, but also the thermodynamic reaction of the ABL to the moisture influx. The current knowledge of the cloudy polar ABL is insufficient to predict important aspects of its behavior, e.g. the lifetime of clouds and the strength of their radiative effect, as well as how large-scale atmospheric dynamics and the presence of elevated inversion layers interact with the structure of the ABL.

How to cite: Hammann, A. and Langley, K.: Characterizing the atmospheric boundary layer over Disko Bay: local structure and links to global dynamics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8957,, 2021.

Henning Dorff, Heike Konow, Vera Schemann, and Felix Ament

Regarding arctic amplification, meridional transports of moisture and heat from subpolar regions represent a crucial phenomenon. Among such intrusions, Atmospheric Rivers (ARs) are characterized by narrow and transient moisture flows, which are responsible for up to 90% of vertical integrated water vapour transport (IVT) into the Arctic. Moreover, they are relevant for meridional air mass transformations and precipitation events. To identify local sources and sinks of moisture associated with such AR pathways, the accurate determination of total IVT along the AR cross-sections is indispensable. However, since ARs primarily occur over ocean basins, e.g. the North Atlantic, there is a lack of measurements inside ARs. Spaceborne sensors struggle to profile the interior of AR cores, leading to a blind zone where the majority of water vapour is located.

Conversely, airborne released dropsondes currently provide the most detailed insights on ARs. The frequency of dropsonde releases is, however, technically limited, so that uncertainties in the calculated total IVT of the AR transect may be significant. In particular, when the IVT within the AR core has high lateral variability, unresolved AR-IVT characteristics can constrain the moisture budget analysis. During the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX), conducted in autumn 2016, the High Altitude and LOng- Range research aircraft (HALO) performed several flight segments along high-latitude AR cross-sections. From these North Atlantic ARs associated with strong meridional water vapour transport, we exemplarily present high-resolution measurements and sounding profiles in the interior of AR cross-sections. We focus on a polar case (research flight RF10, 13th October 2016) and include simulations from the cloud-resolving model ICON-2km, to investigate the lateral AR-IVT variability.  

Comparing dropsonde IVT values with the simulations from ICON-2km, the model shows a valid representation of the AR. Therefore, we use the high-resolution simulations to generate additional synthetic observations. They allow us to identify major sources of error for observational representation of IVT variability in AR cross-sections. Analysing the vertical profile of water vapour transport, we find that specific humidity and wind speed contribute to lateral IVT variability at different heights. With regard to the total cross-section IVT, we derive across-track sounding resolutions required for typical arctic AR-IVT characteristics. The considered AR shows the presence of a low-level jet, a pre-cold-frontal strong wind corridor below 1000 m, resulting from the temperature gradient across the cold front. Since maximum values and increasing lateral variability of IVT appear close to this low-level jet, our results emphasize the need of high-resolution, i.e frequent sonde releases, around the low-level jet to calculate the cross-section total IVT. Our findings aim at optimizing observational airborne strategies for future campaigns, e.g. HALO-AC³ in 2022, in order to lower the uncertainties of IVT in high-latitude and arctic ARs.

How to cite: Dorff, H., Konow, H., Schemann, V., and Ament, F.: High-Latitude Atmospheric River Cross-Sections over the North Atlantic: Assessing Optimized Airborne Sounding Strategies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2031,, 2021.

Weng Yongbiao, Aina Johannessen, and Harald Sodemann

Heavy precipitation at the west coast of Norway is often connected to high integrated water vapour transport within Atmospheric Rivers (AR). Here we present high-resolution measurements of stable isotopes in near-surface water vapour and precipitation during a land-falling AR event in southwestern Norway on 07 December 2016. We analyze the influences of moisture sources, weather system characteristics, and post-condensation processes on the isotopic signal in near-surface water vapour and precipitation.

During the 24-h sampling period, a total of 71 precipitation samples were collected, sampled at intervals of 10-20 min. The isotope composition of near-surface vapour was continuously monitored with a cavity ring-down spectrometer. In addition, local meteorological conditions were monitored from a vertical pointing rain radar, a laser disdrometer, and automatic weather stations.

During the event, we observe a "W"-shaped evolution of the stable isotope composition. Combining isotopic and meteorological observations, we define four different stages of the event. The two most depletion periods in the isotope δ values are associated with frontal transitions, namely a combination of two warm fronts that follow each other within a few hours, and an upper-level cold front. The d-excess shows a single maximum, and a step-wise decline in precipitation and a gradual decrease in near-surface vapour. Thereby, isotopic evolution of the near-surface vapour closely follows the precipitation with a time delay of about 30 min, except for the first stage of the event. Analysis using an isotopic below-cloud exchange model shows that the initial period of low and even negative d-excess in precipitation was most likely caused by evaporation below cloud base. At the ground, a near-constant signal representative of the airmass above is only reached after transition periods of several hours. For these steady periods, the moisture source conditions are partly reflected in the surface precipitation.

Based on our observations, we revisit the interpretation of precipitation isotope measurements during AR events in previous studies. Given that the isotopic signal in surface precipitation reflects a combination of atmospheric dynamics through moisture sources and atmospheric distillation, as well as cloud microphysics and below-cloud processes, we recommend caution regarding how Rayleigh distillation models are used during data interpretation. While the isotope compositions during convective precipitation events may be more adequately represented by idealized Rayleigh models, additional factors should be taken into account when interpreting a surface precipitation isotope signal from stratiform clouds.

How to cite: Yongbiao, W., Johannessen, A., and Sodemann, H.: High-resolution stable isotope signature of a land-falling Atmospheric River in southern Norway, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9124,, 2021.

Manuel Moser, Christiane Voigt, Valerian Hahn, Olivier Jourdan, Christophe Gourbeyre, Regis Dupuy, Guillaume Mioche, Alfons Schwarzenboeck, Johannes Lucke, Tina Jurkat-Witschas, Yvonne Boose, Susanne Crewell, Andreas Herber, Christof Lüpkes, and Manfred Wendisch

Two airborne campaigns (AFLUX and MOSAiC-ACA) were conducted in spring 2019 and late summer 2020 to investigate low- and midlevel clouds and related atmospheric parameters in the central Arctic. The measurements aim at better understanding the role of Arctic clouds and their interactions with the surface - open ocean or sea ice - in light of amplified climate change in the Arctic.
During the campaigns the Basler BT-67 research aircraft Polar 5 based in Svalbard (78.24 N, 15.49 E) equipped with a comprehensive in-situ cloud payload performed in total 24 flights over the Arctic ocean and in the Fram Strait. A combination of size spectrometers (CDP and CAS) and 2-dimensional imaging probes (CIP and PIP) covering the size range of Arctic cloud hydrometeors from 0.5µm to 6.2mm measured the total particle number concentration, the particle size distribution and the median volume diameter. Liquid water content and ice water content were measured with the Nevzorov bulk probe. The cloud water content (liquid and ice water content) from the Nevzorov probe is compared to the cloud water content derived from particle size measurements using consistent mass-dimension relationships.
Here we give an overview of the microphysical cloud properties measured in spring and late summer in high northern latitudes at altitudes up to 4 km. We derive the temperature and altitude dependence of liquid, mixed phase and ice cloud properties and investigate their seasonal variability. Differences in cloud properties above the sea ice and the open ocean are examined, supporting the hypothesis of an enhanced median volume diameter over open ocean compared to clouds formed over the sea ice. The comprehensive data set on microphysical cloud properties enhances our understanding of cloud formation and mixed phase cloud processes over the Arctic ocean, it can be used to validate remote sensing retrievals and models and helps to assess the role of clouds for stronger impact of climate change in the Arctic. 

How to cite: Moser, M., Voigt, C., Hahn, V., Jourdan, O., Gourbeyre, C., Dupuy, R., Mioche, G., Schwarzenboeck, A., Lucke, J., Jurkat-Witschas, T., Boose, Y., Crewell, S., Herber, A., Lüpkes, C., and Wendisch, M.: Airborne in-situ observations of Arctic clouds in spring and summer above sea ice and the open ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7749,, 2021.

Sebastian Becker, Johannes Stapf, André Ehrlich, Michael Schäfer, and Manfred Wendisch

Clouds can cause a significant change to the radiative energy budget of the Earth's surface compared to clear-sky conditions, which is referred to as surface cloud radiative forcing (CRF). The CRF in the Arctic strongly depends on the surface properties (absorbing open ocean vs. strongly reflecting sea ice) and is affected by the low or even absent sun and the special thermodynamic conditions. Therefore, in contrast to the mid and low latitudes, in the Arctic, clouds mostly warm the surface on annual average. However, the CRF will change as the sea ice retreats in a warming climate, which might be accelerated due to the enhanced warming of the Arctic, known as Arctic Amplification. Thus, to quantify the contrast of the CRF over sea ice-covered and sea ice-free ocean surfaces, several airborne campaigns have been conducted in the vicinity of Svalbard in the recent years. The measurements of cloud macrophysical and microphysical properties as well as radiative and turbulent fluxes cover different seasons (spring to early autumn).

Airborne broadband radiation measurements under all-sky conditions were used to calculate the surface CRF during low-level flight sections. In this study, observations from the concurrent campaigns Multidisciplinary drifting Observatory for the Study of Arctic Climate – Airborne observations in the Central Arctic (MOSAiC-ACA) and MOSAiC-Icebird, conducted in August/September 2020, are presented. First results of the CRF over open ocean and the marginal sea ice zone (MIZ) of late summer/early autumn conditions are assessed and compared to the previous airborne spring and early summer campaigns to analyse the seasonal variability of the CRF.

How to cite: Becker, S., Stapf, J., Ehrlich, A., Schäfer, M., and Wendisch, M.: Airborne observations of surface cloud radiative forcing over different surface types of the Arctic Ocean during late summer/early autumn, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5292,, 2021.

Tom Lachlan-Cope, Amelie Kirchgaessner, Anna Jones, Jo Browse, David Topping, Ferracci Valeria, Neil Harris, Floortje Van Den Heuval, Ian Renfrew, Jonathan Witherstone, Keith Bower, Daniel Partridge, and Thomas Bracegirdle

The Southern Ocean Cloud (SOC) project is funded by the UK Natural Environment Research Council to investigate clouds, particularly mixed-phase, in the Atlantic sector of the Southern Ocean and how aerosol sources and production control clouds properties. Here we aim to introduce the community to the project and any associated opportunities that might be available. At high Southern latitudes models are relatively poor at representing clouds and this has an impact on the energy balance and hence atmospheric and oceanic circulation both locally and globally. This project will investigate those processes that control cloud development and will concentrate on the aerosol that act as cloud nuclei, the source of these nuclei and how aerosol and microphysical processes are modelled.


It is planned to deploy instruments to the British Antarctic Survey (BAS) research stations Rothera and Bird Island research stations as well as on the BAS research vessel. These instruments will measure the aerosol size spectrum at all stations and in addition CCN and INP numbers, cloud properties (with a polarized lidar) and aerosol composition at Rothera. The instruments will be deployed for at least 3 years, although some instruments may be moved from Rothera to the ship for special observing periods.


In addition to the long-term measurements there will be two special observing periods (SOPs), the first in the 2022/23 Antarctic season will consist of a dedicated ship cruise and an airborne campaign using the BAS instrumented twin otter aircraft along with enhanced observations at the surface stations. The second SOP will also have enhanced observations at the surface stations along with an airborne campaign.


The observations will be backed up with a programme of aerosol, weather and climate modelling. The combination of modelling and observations should enable us to identify the major sources of cloud nuclei over the Southern Ocean, examine their role in cloud development, and improve the representation of these processes in models.


How to cite: Lachlan-Cope, T., Kirchgaessner, A., Jones, A., Browse, J., Topping, D., Valeria, F., Harris, N., Van Den Heuval, F., Renfrew, I., Witherstone, J., Bower, K., Partridge, D., and Bracegirdle, T.: The Southern Ocean Cloud project, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9998,, 2021.

Susanne Crewell, Kerstin Ebell, Patrick Konjari, Mario Mech, Tatiana Nomokonova, Ana Radovan, David Strack, Aranxta Triana-Gomez, Stefan Noel, Raul Scarlat, Gunnar Spreen, Marion Maturilli, Rinke Annette, Gorodetskaya Irina, Carolina Viceto, Thomas August, and Marc Schröder

Water vapor is an important component in the water and energy cycle of the Arctic. Especially in the light of Arctic amplification, changes of water vapor are of high interest but are difficult to observe due to the data sparsity of the region. The ACLOUD/PASCAL campaign performed in May/June 2017 in the Arctic North Atlantic sector offers the opportunity to investigate the quality of various satellite and numerical model reanalysis products. For this purpose reference Integrated Water Vapor (IWV) measurements at R/V Polarstern frozen into the ice (around 82° N, 10° E) and at t Ny-Ålesund are used to investigate the quality of instantaneous satellite retrievals from AIRS, AMSR2, GOME2, IASI and MIRS. These products use different parts of the electromagnetic spectrum and have different uncertainty characteristics related to the presence of clouds and/or surface characteristics. Therefore, the analysis is expanded to all radiosonde stations within the region. Due to the strong spatio-temporal variability of IWV - in particular during atmospheric river events - sampling issues are important that arise due to the different satellite orbits as well the synoptic radiosonde launch times. Following up on this analysis the question arises whether the satellite data are suitable for a long-term monitoring and trend assessment of water vapor in the Arctic. For this purpose we will also present an analysis of monthly mean values for May and June 2017 - two months with strongly changing surface characteristics in the Arctic - and investigate their performance relative to various reanalyses.

How to cite: Crewell, S., Ebell, K., Konjari, P., Mech, M., Nomokonova, T., Radovan, A., Strack, D., Triana-Gomez, A., Noel, S., Scarlat, R., Spreen, G., Maturilli, M., Annette, R., Irina, G., Viceto, C., August, T., and Schröder, M.: A systematic assessment of water vapor products in the Arctic: from instantaneous measurements to monthly means, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7152,, 2021.