Between March 15-19th 2022, East Antarctica experienced an unprecedented heatwave with widespread 30-45° C temperature anomalies across the ice sheet. This record-shattering event saw numerous monthly temperature records being broken including a new all-time temperature record of -9.4 °C on March 18th at Concordia station despite March typically being a transition month to the Antarctic coreless winter. The driver for these temperature extremes was an unprecedently intense atmospheric river (AR) advecting heat and moisture deep into the Antarctic interior. The scope of the temperature records spurred a large, diverse collaborative effort to study the heatwave’s meteorological drivers, impacts, and historical climate context using an array of observations, models, and analysis techniques. 

 From these efforts, we present the following

• Temperature observations and records
• Meteorological drivers including tropically forced Rossby wave activity along with AR and warm conveyor belt dynamics
• Radiative forcing impacts on surface temperatures and inversions
• Surface mass balance impacts
• Discussion of the AR impacts on isotope and cosmic ray measurements from Concordia station
• AR influence on the Conger Ice Shelf disintegration
• Event return time analysis
• Implications on past climate reconstructions
• Future event likelihood from IPSL-CM6 simulations

How to cite: Wille, J. and the East Antarctica heatwave project: The extraordinary March 2022 East Antarctica heatwave, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8107, https://doi.org/10.5194/egusphere-egu23-8107, 2023.

Northern sections of the Larsen Ice Shelf, eastern Antarctic Peninsula (AP) have experienced dramatic break-up and collapse since the early 1990s due to strong summertime surface melt, linked to strengthened circumpolar westerly winds. Here we show that extreme summertime surface melt and record-high temperature events over the eastern AP and Larsen C Ice Shelf are triggered by deep convection in the central tropical Pacific (CPAC), which produces an elongated cyclonic anomaly across the South Pacific coupled with a strong high pressure anomaly over Drake Passage. Together these atmospheric circulation anomalies transport very warm and moist air to the southwest AP, often in the form of “atmospheric rivers”, producing strong foehn warming and surface melt on the eastern AP and Larsen C Ice Shelf. Therefore, variability in CPAC convection, in addition to the circumpolar westerlies, is a key driver of AP surface mass balance and the occurrence of extreme high temperatures.

How to cite: Clem, K., Bozkurt, D., Kennett, D., King, J., and Turner, J.: Central tropical Pacific convection drives extreme high temperatures and surface melt on the Larsen C Ice Shelf, Antarctic Peninsula, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10530, https://doi.org/10.5194/egusphere-egu23-10530, 2023.

On the East Antarctic Plateau, in winter, rapid warming events originated by the advection of warm, moist air from lower latitudes, cause the disruption of the stable thermal structure of the atmosphere, and can be linked to the warming of the Plateau region itself. Continuous monitoring of these events can shed light on temperature trends in East Antarctica, trends which are still not clearly defined in terms of origin and amount.

Since the main mechanism acting in the warming events is the strong increase in cloud cover linked to the higher water content of the advected air, for a systematic monitoring of warming phenomena a simultaneous detection of water vapor vertical profile and cloud properties is needed. These two tasks can be both performed through the analysis of spectrally resolved atmospheric downwelling emitted radiances.

The REFIR (Radiation Explorer in the Far Infrared) Fourier transform spectroradiometer was installed at Concordia station, in the Dome C region of the Antarctic Plateau, in December 2011, and it has been performing continuous measurement since then. REFIR measures the downwelling atmospheric radiance in the 100-1500 cm^-1 (6.7-100 µm) spectral interval, with a resolution of 0.4 cm^-1, and with a repetition rate of about 10 minutes. The measured spectral interval extends from the far infrared, which includes the water vapor rotational band, to the atmospheric window region (8-14 µm), which provides information about the radiative effects of clouds.

A dedicated inversion code was developed to retrieve vertical profiles of water vapor and temperature from the measured emission spectra. The retrieved profiles allow for the monitoring of the evolution of the vertical structure of the troposphere on a 10 minutes timescale, whereas the spectral radiance itself provides, in a more direct way, information on the cloud cover. Therefore, the dataset produced by the REFIR instrument allow us to detect and obtain statistics about warming events in the Dome C region.

How to cite: Bianchini, G., Belotti, C., Di Natale, G., and Palchetti, L.: Exploiting a decadal time-series of spectrally resolved downwelling infrared radiances at Dome C, Antarctica to assess the occurrence of advective warming events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1528, https://doi.org/10.5194/egusphere-egu23-1528, 2023.

Observations at the surface in Antarctica have always been challenging, but cloud observations are particularly scarce due to different factors, among which the polar night and lack of instruments and observers. One way to obtain information on cloud cover, and fill the gap, is through broadband radiation measurements thanks to methods based on the effect that clouds have on solar and terrestrial radiation. In this work three different algorithms have been studied and implemented: i) Long et al.[1] method, which exploits global and diffuse shortwave radiation components; ii) Kasten and Czeplak[2], based on global shortwave component alone; iii) APCADA[3] algorithm, which requires longwave downward radiation measurements and meteorological variables data, and is specially chosen as it yields results also at (polar) night. Different methods were selected to adapt to the data available at each site and to cross-check the results. The algorithms are tested on common-time data sets from three different stations: Marambio (64°14’50’’S - 56°37’39’’W), where upward and downward components for shortwave and longwave radiation are measured along with diffuse shortwave radiation; Professor Julio Escudero (62°12’57’’S - 58°57’35’’W) where downward shortwave and longwave radiation data are available; and Concordia (75°05’59’’S - 123°19’57’’E) where data on all components of both solar and terrestrial radiation are collected. Before any computation, data quality control is executed following tests[4] recommended by the Baseline Surface Radiation Network[5], showing good quality for all three data sets. Sky conditions depend on the location of the stations: Marambio and Escudero are coastal sites located on islands on opposite sides of the Antarctic Peninsula where cloudy skies are expected to occur, while Concordia is situated on the East Antarctic Plateau where the sky should be clearer. Such expectations are confirmed by the preliminary results obtained from the tested algorithms, indicating that clouds occur very often with almost scarce clear sky periods at the coastal stations. 

Bibliography
[1] Long C. N., Ackerman T. P., Gaustad K. L., and Cole J. N. S. (2006): “Estimation of fractional sky cover from broadband shortwave radiometer measurements”, J. Geophys. Res. 111, doi: 10.1029/2005JD006475
[2] Dürr B. and Philipona R. (2004): “Automatic cloud amount detection by surface longwave downward radiation measurements”, J. Geophys. Res. 109, doi: 10.1029/2003JD004182
[3] Kasten F., Czeplak G. (1980): “Solar and terrestrial radiation dependent on the amount and type of cloud”, Solar Energy 24, doi: 10.1016/0038-092X(80)90391-6
[4] Long and Shi (2008): “An automated quality assessment and control algorithm for surface radiation measurements”, Open Atm. Science J. 2, doi: 10.2174/1874282300802010023
[5] https://bsrn.awi.de/

How to cite: Frangipani, C., Cordero, R., Gulisano, A. M., Lupi, A., Ochoa, H. A., Rowe, P., and Vitale, V.: Cloud cover estimation using different methods exploiting solar radiation measurements at various sites in Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-643, https://doi.org/10.5194/egusphere-egu23-643, 2023.

Intense moist intrusions originating from the lower latitudes of the Pacific Ocean have been found to have a significant impact on the Antarctic Peninsula (AP), including enhancement of surface melt events, increased runoff, reduction in sea-ice cover and ice shelves destabilization. Clouds play an important role in the surface energy budget during these events and in precipitation formation. Precipitation phase and amounts determine local and regional surface mass and energy budget. Our  research focuses on cloud and precipitation microphysical and dynamic characteristics over the AP region, using  ground based remote sensing at the Ukrainian Antarctic Station Akademic Vernadsky Moreover, an enhanced radiosonde program was launched during the austral winter at the Vernadsky station as part of the Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) international initiative (May-August 2022). Here we present detailed analysis of one of the Targeted Observing Periods (TOPs) during an intense moisture and heat intrusion affecting the AP.

Although there is a lot of research on the atmospheric processes over the AP region, the local dynamic and microphysical characteristics of clouds and precipitation are still poorly understood and misrepresented in the models due to the lack of direct measurements, particularly in winter.

Further we performed  Polar-WRF model simulations, forced by ERA5 reanalysis and configured with Morrison double moment cloud microphysical scheme. The simulations were run at 1-km spatial resolution with 10-minute temporal output centered over the Vernadsky region. Simulation results were verified with precipitation properties derived from Micro Rain Radar-Pro measurements and radiosonde profiles. We found that there is  more snow in PolarWRF outputs in comparison to MRR-Pro measurements. Thus it does not represent mixed phased precipitation properly. At the same time Polar WRF shows warm temperature bias compared to radiosounding. 

Measurements and model output are used to analyze cloud ice and water particle distribution, thickness and precipitation particle spectra over the Vernadsky station and the AP mountains during the extreme precipitation events in the Antarctic Winter. In overall there were five TOPs over the AP region. However, not all of them were associated with extreme precipitation on Vernadsky station.

Our preliminary results show the importance of the transition between dry and wet snowfall during intense moisture transport events at the AP (particularly remarkable during winter at the location of Vernadsky station). Polar-WRF shows differences in simulating the timing and intensity of such transitions probably related to the biases in temperature profiles influencing the melting layer height.

How to cite: Chyhareva, A., Krakovska, S., Gorodetskaya, I., and Palamarchuk, L.: Cloud and precipitation profiles from observations  and Polar-WRF simulations over Vernadsky station (western Antarctic Peninsula) during austral winter 2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-667, https://doi.org/10.5194/egusphere-egu23-667, 2023.

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 is 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.

In February 2022 we installed a suite of instruments at the Rothera research station on the Antarctic peninsula to measure the physical and chemical properties of aerosol, the number concentrations of Cloud Condensation Nuclei and Ice Nucleating Particles, and cloud height and thickness all year round. Here we will report the first observations and statistics of one full year of aerosol and cloud measurements from the Rothera research station.

How to cite: van den Heuvel, F., Lachlan-Cope, T., Witherstone, J., Dyson, J., Squires, F., Smith, D., and Flynn, M.: One year of Aerosol and Cloud measurements in Rothera on the Antarctic Peninsula, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16007, https://doi.org/10.5194/egusphere-egu23-16007, 2023.

Antarctica, the coldest and driest continent, is home to the largest ice sheet. A common feature of polar regions is the warming associated with snowfall, as moist oceanic air and cloud cover contribute to increase the surface temperature. Consequently, the ice accumulated onto the ice sheet is deposited under unusually warm conditions. Here we use the polar-oriented atmospheric model MAR to study the statistical difference between average and snowfall-weighted temperatures. Most of Antarctica experiences a warming scaling with snowfall, although with strongest warming at sites with usually low accumulation. Heavier snowfalls in winter contribute to cool the snowfall-weighted temperature, but this effect is overwritten by the warming associated with atmospheric perturbations responsible for snowfall, which particularly contrast with the extremely cold conditions in winter. Disturbance in apparent annual temperature cycle and interannual variability may have major implications for water isotopes, which are deposited with snowfall and commonly used for paleo-temperature reconstructions.

How to cite: Servettaz, A., Agosta, C., Kittel, C., and Orsi, A.: Warm Temperature Anomalies Associated with Snowfall in Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-901, https://doi.org/10.5194/egusphere-egu23-901, 2023.

The projected increase in poleward moisture transport (PMT) towards warmer climate has mainly been linked to the larger moisture holding capacity of warmer air masses. However, the future of interannual fluctuations of PMT and associated driving mechanisms are fairly uncertain. This study demonstrates the extent to which atmospheric rivers (ARs) explain the interannual variability of PMT, as well as related variables such as temperature, precipitation and sea ice. Such linkages help to clarify if extreme precipitation or melt events over Arctic regions are dominantly caused by the occurrence of ARs. A main focus is set on the impact of ARs on Arctic sea ice on interannual timescales, which so far has been poorly studied, and varies from colder to warmer climates.

To robustly study these interannual linkages of ARs and Arctic Climate, we examine Arctic ARs in long climate runs of one present and two future climates (+2°C and +3°C), simulated by the global climate model EC-Earth 2.3. To enhance the significance of the results, three different moisture thresholds were used to detect ARs. Further, the use of additional thresholds relative to the 2°C and 3° warmer climates allowed a distinction between thermodynamic and dynamic processes that lead to changes of ARs from colder to warmer climates. It is found that most PMT variability is driven by ARs, and that the share of ARs which explain moisture transport increases towards warmer climates. We also discuss the role of the position and strength of the jet stream in driving AR variability and highlight the importance of ARs in generating interannual fluctuations of Arctic climate variables such as temperature and precipitation.

How to cite: Kolbe, M., Sonnemans, J., Bintanja, R., van der Linden, E., van der Wiel, K., Whan, K., and Benedict, I.: Impact of Atmospheric Rivers on Poleward Moisture Transport and Arctic Climate on Interannual Timescales, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6007, https://doi.org/10.5194/egusphere-egu23-6007, 2023.

Clear indications of the phenomenon of Arctic Amplification include the above-average increase of the near-surface air temperature and the related dramatic retreat of sea ice observed in the last decades. The mechanisms behind these features are widely discussed. Especially the role of clouds and of air mass transports into and out of the Arctic associated with related transformation processes are still poorly understood. Therefore, the HALO-(AC)³ campaign was performed to provide observations of meridional air mass transports and corresponding transformations in a quasi-Lagrangian approach. Three research aircraft equipped with state-of-the-art instrumentation performed measurements over the Arctic ocean and sea ice in March/April 2022. The German High Altitude and Long Range Research Aircraft (HALO), equipped with a comprehensive suite of active and passive remote sensing instruments and dropsondes, was operated from Kiruna, Sweden. The flight pattern covered long distances at high altitudes up to the North Pole probing air masses multiple times on their way into and out of the Arctic. The Polar 5 (remote sensing) and Polar 6 (in-situ) aircraft from the Alfred Wegener Institute operated in the lower troposphere out of Longyearbyen in the lower troposphere over Fram Strait West of Svalbard. Several coordinated flights between the three aircraft were conducted with Polar 6 sampling in-situ aerosol, cloud, and precipitation particles within the boundary layer, Polar 5 observing clouds and precipitation from above roughly at 3 km altitude, and HALO providing the large scale view on the scene following air masses.
The observations cover a major warm air intrusion event with atmospheric river embedded bringing warm and moist air far into the Arctic. Multiple cold air outbreaks were characterized in their initial stage close to the sea ice edge with Polar 5 and 6 and in a quasi-Lagrangian perspective with HALO, which allowed to quantify the air mass transformation by changes of thermodynamic profiles, large scale subsidence, and cloud properties over a period of 24 hours. Single events of high latitude Arctic cirrus and the formation of a polar low are included in the data set. The presentation reports on first results of the campaign by illustrating the capabilities of the multi-aircraft operation.

How to cite: Ehrlich, A., Wendisch, M., Klingebiel, M., Mech, M., Crewell, S., Herber, A., and Lüpkes, C. and the HALO-(AC)3 team: HALO-(AC)3: Airborne Observations of Arctic Clouds in Airmass Transformations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7246, https://doi.org/10.5194/egusphere-egu23-7246, 2023.

How to cite: Wallentin, G., Hoose, C., Achtert, P., and Tesche, M.: Mixed-phase Multilayer Clouds in the Arctic: A Simulation Study using ICON, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5650, https://doi.org/10.5194/egusphere-egu23-5650, 2023.

Variability in the components of the Arctic surface energy budget and the atmospheric boundary layer (ABL) structure are to a large extent controlled by synoptic-scale changes and associated air mass properties. The transition of air masses between the radiatively clear and cloudy states, along with their characteristic surface impacts in radiation and ABL structure, can occur in either direction and on short time scales. In both states as well as during the transition, insufficient model representation of radiative processes and cloud microphysical properties cause biases in numerical weather prediction- and climate models. We employ observations from radiosondes, MET tower, and the ShupeTurner cloud microphysics product, which itself synthesizes a wealth of instruments, for the classification of an event of transition between low-level mixed phase cloud and clear conditions. The observed air mass properties and transition process are compared to ERA5 reanalysis data and output from a simulation of the coupled regional climate model HIRHAM-NAOSIM which applied non-spectral nudging to ERA5 in order to reproduce the observed synoptic-scale changes. The approach highlights the potential of event-based analysis of transformations of cloudy Arctic air masses by confronting models with observations.

How to cite: Dahlke, S., Solbès, A., Shupe, M. D., Cox, C. J., Maturilli, M., Rinke, A., Dorn, W., and Rex, M. D.: Transforming cloudy air masses and surface impacts: a case study confronting MOSAiC observations, reanalyses and coupled model simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5802, https://doi.org/10.5194/egusphere-egu23-5802, 2023.

Clouds play an important role in the climate system of the Arctic. The interaction of clouds with atmospheric radiation has a significant influence on the radiative energy budget (REB) of the Arctic surface, which is quantified by the surface cloud radiative effect (CRE). Due to the counteraction of the cooling effect of clouds in the solar and their warming effect in the thermal-infrared spectral range, the total CRE depends on a complex interplay of the illumination, surface, thermodynamic, and cloud conditions.

To characterize the CRE for a variety of environmental conditions, broadband radiation measurements were performed during three seasonally distinct airborne campaigns. The flights were conducted over sea ice and open ocean surfaces in the eastern Fram Strait. The analysis focusses on the differences of the CRE with respect to the different campaigns and surface types. It was found that clouds cool the open ocean surface during all campaigns. In contrast, clouds mostly have a warming effect on sea ice–covered surfaces, which neutralizes during mid-summer. Given the seasonal cycle of the sea ice distribution, these results imply a cooling effect of clouds on the surface during the sea ice minimum in late summer and a warming effect during the sea ice maximum in spring in the Fram Strait region. The variability of, e. g., cloud and synoptic conditions causes deviations of the CRE from these statistics. In particular, the study presents the evolution of the CRE during selected cases of warm air intrusions and marine cold air outbreaks.

How to cite: Becker, S., Ehrlich, A., Schäfer, M., and Wendisch, M.: Airborne measurements of the cloud impact on the surface radiative energy budget in the Fram Strait, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5876, https://doi.org/10.5194/egusphere-egu23-5876, 2023.

The presence of clouds significantly affects Arctic boundary layer dynamics. However, the accessibility of clouds over the Arctic sea ice for in-situ observations is challenging. Measurements from tethered balloon platforms are one option to provide high-resolution data needed for model evaluation.

The tethered balloon system BELUGA (Balloon-bornE moduLar Utility for profilinG the lower Atmosphere) was deployed to profile the boundary layer at the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC), and in Ny-Alesund. A set of scientific payloads for the observation of broadband radiation, turbulence, aerosol particles, and cloud microphysics properties were operated to study the interactions in the cloudy and cloud-free boundary layer.

Measurements obtained under various cloud conditions, including single-layer and multi-layer clouds, are analyzed. Heating rates profiles are calculated to validate radiative transfer simulations and to study the temporal development of the cloud layers. 

The in-situ observations display the importance of radiation-induced cloud top cooling in maintaining stratocumulus clouds over the Arctic sea ice. Case studies also indicate how the subsequent turbulent mixing can lead to the entrainment of aerosol particles into the cloud layer.

How to cite: Lonardi, M., Pilz, C., Akansu, E. F., Ehrlich, A., Shupe, M. D., Siebert, H., Wehner, B., and Wendisch, M.: The effect of cloud top cooling on the evolution of the Arctic boundary layer observed by balloon-borne measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7692, https://doi.org/10.5194/egusphere-egu23-7692, 2023.

In the last decades scientist have noticed that the average global temperature of the Earth has been increasing. Moreover, the arctic is warming significantly faster than the global average, a phenomenon labeled Arctic Amplification. Two atmospheric components contributing to the warming of the atmosphere in the arctic are water vapor and cirrus clouds. Both have an effect on the radiation budget of the atmosphere and more specifically the longwave radiation. A Warm Air Intrusion (WAI) event is defined as the meridional transport of warm, water-vapor-rich airmasses into the arctic. During such events large amounts of water vapor can be transported into the arctic, which also leads to high supersaturations aiding the formation and longevity of cirrus clouds. There is a strong hypothesis that WAI events in the high arctic are becoming more frequent, so it is important to study the effects these events have on the macrophysical and optical properties of cirrus clouds in the arctic.

The HALO-(AC)³ flight campaign was conducted in March/April 2022 with the central goal of studying WAI events in the arctic regions of the Northern Hemisphere. For this campaign the German research aircraft HALO was equipped with remote sensing instrumentation, including the airborne LIDAR system WALES which we use in this study. WALES is a combined water vapor differential absorption and high spectral resolution lidar. It provides water vapor measurements in a 2D field along the flight track. We combine these measurements with ECMWF temperature data and calculate the Relative Humidity with respect to ice (RHi) inside and in the vicinity of cirrus clouds. For each flight we studied the synoptic situation and created two groups: One containing flights were cirrus that formed in arctic airmasses were measured and another were cirrus were measured during WAI events, henceforth arctic cirrus and WAI cirrus respectively. Our main goal is to compare the humidity characteristics inside and in the vicinity of arctic cirrus clouds and WAI cirrus clouds.

For the arctic cirrus we find that 49 % of the in-cloud data points are supersaturated with RHi mostly below the lower threshold for heterogeneous nucleation (low HET). The cloud-free air around these clouds has a supersaturation percentage of 8.5 %. The WAI cirrus are measured in a wider temperature range and also have a significantly higher supersaturation percentage inside as well as in the cloud-free air, 61.7 % and 9.3 % respectively. The majority is again in the low HET regime. Additionally, WAI cirrus are on average geometrically thicker than arctic cirrus. Finally, regarding the vertical distribution of RHi within these clouds we find that WAI cirrus have their highest supersaturations near the cloud top and become gradually subsaturated towards cloud-bottom. On the other hand, arctic cirrus have their highest supersaturations near cloud-middle, with lower supersaturations at cloud-top and subsaturated cloud-bottom.

How to cite: Dekoutsidis, G., Groß, S., and Wirth, M.: The effects of warm air intrusions in the high arctic on cirrus clouds, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8500, https://doi.org/10.5194/egusphere-egu23-8500, 2023.

Atmospheric water vapor plays an enormously important role in the water cycle and energy budget of the Arctic. Water vapor in the Arctic also participates in many important feedback mechanisms influencing the climate response to forcing agents and the Arctic amplification. In this study, we conduct analysis of atmospheric moisture transport into the Arctic based on reanalysis products and CMIP6 model simulations. We are particularly interested in the episodic atmospheric-river-like features (AR or moisture intrusion) that play an important role in delivering water to the Arctic. Based on the method of using column-integrated meridional vapor transport for characterizing AR events, we find that the mean AR frequency peaks in the Atlantic sector in all seasons except that it’s more zonally widespread in summer. An increasing trend in the Arctic AR frequency in the recent decades identified from ERA5 can be captured by few CMIP6 models. The historical Arctic AR frequency, sea ice concentration and Arctic warming are highly correlated. Atmospheric circulation patterns that drive the interannual and decadal Arctic AR variation contribute substantially to the historical Arctic warming. We also use the Community Earth System Model (CESM), equipped with a water tagging capability, to quantify contributions of surface evaporation within the Arctic versus from lower-latitude regions as a source of water to the Arctic and characterize moisture transport pathways that control the Arctic water vapor distribution.

How to cite: Wang, H., Zhang, R., Zou, Y., Ma, W., Rasch, P., and O'Brien, T.: Atmospheric moisture intrusion into the Arctic: sources, impact, and trends, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10197, https://doi.org/10.5194/egusphere-egu23-10197, 2023.

The Arctic is warming at a faster rate than the rest of the globe. There are both remote and local mechanism identified driving this process. While albedo changes and atmospheric stability happens within in the Arctic, transfer transport processes, both in the ocean and atmosphere, heat and moisture into the Arctic. These processes can be analysed in a Eulerien way, by observing the fluxes through a curtain defining the Arctic or/and by Lagrangian analysis which follows this transport processes all the way from uptake in the mid/high latitudes until the inflow into the Arctic. 

We use a Lagrangian Particle Transport model FLEXPART running with ECMWF reanalysis data as well as with data from the norwegian earth system model NorESM, which represents the future climate scenarios until 2100. In this way we investigate the inflow of moisture and energy for the last 50 years, but can also project it in the future by considering the climate model output.

We find that the the transport through the 65N Latitude, defining the Arctic area is highly inhomogenious in space, but has also a distinct seasonal variability. The end of the storm tracks, especially the Northern Atlantic stormtrack show the most important region of inflow. While moisture origins over ocean areas in winter, continental areas in summer act as a source. The patterns in the reanalysis data from ECMWF and in the climate simulations are very similar. Those patterns are stable over time, but intensify in a warming climate.

How to cite: Eckhardt, S., Svendby, T., Steensen, B., Myhre, G., Germundsen, A., and Olivie, D.: Moisture transport into the Arctic in a past and future climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11436, https://doi.org/10.5194/egusphere-egu23-11436, 2023.

The regulation of energy transfer by clouds and fog is a key process affecting the climate of the Arctic, a region that exhibits frequent cloud cover and suffers an extreme vulnerability to climate change. Measurements were performed over a whole year at the Zeppelin station, Ny-Ålesund, Svalbard, Norway from October 2019 to October 2020 in the framework of the NASCENT campaign (Ny-Ålesund AeroSol Cloud ExperimeNT). Aiming at a better understanding of the susceptibility of cloud droplet formation, we analyzed particle number size distributions obtained from differential mobility particle sizers and chemical composition derived from filter samples and an aerosol chemical speciation monitor. Combined with updraft velocity information from a wind lidar and an ultrasonic anemometer, the data were used as input parameters for a state-of-the-art cloud droplet formation parameterization to investigate the particle sizes that can activate to cloud droplets, the levels of supersaturation as well as potential cloud droplet formation and its susceptibility to aerosol. We showed that low aerosol levels in fall and early winter led to clouds that are formed under an aerosol-limited regime, while higher particle concentrations centered around the Arctic Haze together with a drop in cloud supersaturation could be linked to periods of updraft velocity-limited cloud formation regime. In the latter case, we observed that the maximum number of cloud droplets forming - also called the limiting droplet number - and the updraft velocity follow a relationship that is universal, as proved by similar studies previously performed in different environments and cloud types. Finally, we successfully performed a droplet closure, proving, for the first time, the ability of our cloud droplet parameterization to predict cloud droplet number not only in liquid clouds but also in mixed-phase clouds with a very high degree of glaciation. This closure suggests that rime splintering may not be significant enough to affect droplet concentrations, which is consistent with previous observations and model simulations.

How to cite: Motos, G., Freitas, G., Georgakaki, P., Wieder, J., Aas, W., Lunder, C., Krejci, R., T. Pasquier, J., Henneberger, J., O. David, R., Mohr, C., Zieger, P., and Nenes, A.: Linking aerosol size distribution and hygroscopicity to cloud droplet formation at an Arctic mountain site, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13074, https://doi.org/10.5194/egusphere-egu23-13074, 2023.

Marine cold air outbreaks (MCAOs) are important parts of the high-latitude climate system and are characterised by strong surface fluxes generated by the air-sea temperature gradient. These fluxes promote cloud formation, which can be identified in satellite imagery by the distinct transformation of stratiform cloud 'streets' into a broken field of cumuliform clouds downwind of the outbreak. This evolution of cloud morphology changes the radiative properties of the cloud and therefore is of importance to the surface energy budget.  

While the drivers of stratocumulus-to-cumulus transitions have been extensively studied for subtropical clouds, such as aerosols or the sea surface temperature gradient, the factors influencing transitions at higher latitudes are relatively poorly understood. This work uses reanalysis data to create a set of composite trajectories of cold air outbreaks moving off the Arctic ice edge and co-locates these trajectories with data from multiple satellites to generate a unique view of cloud development within cold air outbreaks. 

Clouds embedded in MCAOs have distinctive properties relative to clouds following other, more stable trajectories in the region. The initial instability and aerosol environments have distinct impacts on cloud development within outbreaks. The strength of the outbreak has a lasting effect on the magnitude of cloud properties along the trajectory. However, it does not strongly affect the timing of the transition to cumuliform clouds. In contrast, the initial aerosol concentration changes the timing of cloud break-up rather than the size of the cloud response.

How to cite: Murray-Watson, R. and Gryspeerdt, E.: The evolution of clouds in Arctic marine cold air outbreaks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13191, https://doi.org/10.5194/egusphere-egu23-13191, 2023.