The polar climate system is strongly affected by interactions between the atmosphere and the cryosphere. Feedback mechanisms between snow, land ice, sea ice and the atmosphere, such as blowing snow, ice melt, polynya formation, and sea ice production play an important role. Atmosphere-ice interactions are also triggered by synoptic weather phenomena such as cold air outbreaks, katabatic winds, polar cyclones, atmospheric rivers, Foehn winds and heatwaves. However, our understanding of these processes is still incomplete, and to fully capture how atmosphere, land ice and sea ice are coupled on different spatial and temporal scales, remains a major challenge.
This session will provide a setting to foster discussion on the atmosphere-ice coupling in both the Northern and Southern Hemispheres. It will offer the opportunity to review newly acquired knowledge, identify gaps, and which instruments, tools, and studies can be designed to address these open questions.
We invite contributions on all observational and modelling aspects of Arctic and Antarctic meteorology and climatology that address atmospheric interactions with the cryosphere. This may include studies of atmospheric dynamics that influence sea-ice dynamics or ice-sheet mass balance, or investigations into the variability of the atmospheric circulation such as polar jets, the circumpolar trough, storm tracks and their link to changes in the cryosphere.

Co-organized by CR7
Convener: Diana Francis | Co-conveners: Amélie Kirchgaessner, Till Wagner
| Attendance Mon, 04 May, 16:15–18:00 (CEST)

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Chat time: Monday, 4 May 2020, 16:15–18:00

D3453 |
| solicited
| Highlight
Lukas Papritz

Recent decades have revealed dramatic changes in the high Arctic (> 80°N) related to natural variability and anthropogenic climate change. In particular, episodes of extremely warm temperatures in the lower troposphere and their role for sea ice melting have gained considerable attention. While it has been recognized that injections of warm and humid air masses contribute to wintertime warm anomalies, summertime warm anomalies have also been linked to blocking anticyclones within the high Arctic. Yet, the relative importance of the various thermodynamic and atmospheric dynamical processes that can contribute to the formation of extreme warm anomalies in the high Arctic is poorly understood.

In this work, we present a systematic analysis of the processes leading to the formation of winter- and summertime lower tropospheric warm extremes in the high Arctic by means of kinematic backward trajectories based on the ERA-Interim reanalysis. The trajectories enable us to quantify the relative contributions of poleward transport from (potentially) warmer regions, adiabatic warming due to subsidence, and diabatic heating associated with surface sensible heat fluxes and latent heat release. Furthermore, we relate these processes to atmospheric dynamical flow features such as atmospheric blocking and extratropical cyclones.

Our analyses reveal that subsidence in blocking anticyclones over the Barents and Kara Seas and diabatic warming by surface sensible heat fluxes are the dominant mechanisms leading to wintertime warm extremes (contributing about 40% each), whereas the transport from southerly latitudes – predominantly accomplished by the injection of warm and humid air masses associated with an intensified and westward displaced storm track in the Nordic Seas - is of secondary importance (20%). Summertime warm anomalies, in contrast, are essentially the result of subsidence in blocking anticyclones (70%) that are located within the high Arctic. Thus, our findings point towards a rich, seasonally varying spectrum of dynamical and thermodynamic processes contributing to Arctic warm extremes that result from a complex interplay between transport induced by dynamical weather systems and diabatic processes. Furthermore, they emphasize the importance of processes within the Arctic for the formation of warm extremes.

Papritz, L., 2019: Arctic lower tropospheric warm and cold extremes: horizontal and vertical transport, diabatic processes, and linkage to synoptic circulation features, J. Climate, doi: 10.1175/JCLI-D-19-0638.1

How to cite: Papritz, L.: Dynamic and thermodynamic drivers of Arctic lower tropospheric warm extremes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1681, https://doi.org/10.5194/egusphere-egu2020-1681, 2019

D3454 |
John King and Thomas Bracegirdle

The belt of climatological easterly (westward) winds that lies to the south of the circumpolar trough of low pressure surrounding Antarctica has received less attention than the westerlies to the north of the trough, yet it plays a crucial role in atmosphere-ocean-cryosphere interactions in the near-coastal region. The westward-directed wind stress associated with the easterly winds drives a coastal westward ocean current and a westward transport of sea ice around the continent. Easterly winds also inhibit the flow of warm water masses from intermediate depths onto the continental shelves, thus protecting coastal ice shelves from enhanced basal melt. We use the ECMWF ERA-Interim reanalysis to study the mean structure and variability of the coastal easterly winds. The surface component of the easterlies generally extends no more than 200 km to the north of the coast. The easterlies are quite shallow (~ 1-2 km) and are relatively weak (generally < 3 m s-1 at the surface in the annual mean) over the ocean but become both deeper (~ 2-3 km) and stronger (~ 7 m s-1) over the steep coastal slopes of the continent. While persistent katabatic flow down these slopes is a source of easterly momentum (through the action of the Coriolis force), the primary driver of the easterlies appears to be the large-scale baroclinicity of the flow, which is enhanced in the coastal region where isentropes are forced to follow the steep coastal orography. Variability of the easterlies on monthly and longer timescales is related to variations in the strength and latitude of the circumpolar trough. On shorter (synoptic) timescales, large variations in the strength of the easterlies at coastal locations are forced by cyclones that move south from the circumpolar trough and decay in the coastal region.

How to cite: King, J. and Bracegirdle, T.: Structure and variability of the Antarctic coastal easterly winds, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5127, https://doi.org/10.5194/egusphere-egu2020-5127, 2020

D3455 |
Samuel Helsen, Sam Vanden Broucke, Alexandra Gossart, Niels Souverijns, and Nicole van Lipzig

The Totten glacier is a highly dynamic outlet glacier, situated in E-Antarctica, that contains a potential sea level rise of about 3.5 meters. During recent years, this area has been influenced by sub-shelf intrusion of warm ocean currents, contributing to higher basal melt rates. Moreover, most of the ice over this area is grounded below sea level, which makes the ice shelf potentially vulnerable to the marine ice sheet instability mechanism. It is expected that, as a result of climate change, the latter mechanisms may contribute to significant ice losses in this region within the next decades, thereby contributing to future sea level rise. Up to now, most studies have been focusing on sub-shelf melt rates and the influence of the ocean, with much less attention for atmospheric processes (often ignored), which also play a key-role in determining the climatic conditions over this region. For example: surface melt is important because it contributes to hydrofracturing, a process that may lead to ice cliff instabilities. Also precipitation is an important atmospheric process, since it determines the input of mass to the ice sheet and contributes directly to the surface mass balance. In order to perform detailed studies on these processes, we need a well-evaluated climate model that represents all these processes well. Recently, the COSMO-CLM2 (CCLM2) model was adapted to the climatological conditions over Antarctica. The model was evaluated by comparing a 30 year Antarctic-wide hindcast run (1986-2016) at 25 km resolution with meteorological observational products (Souverijns et al., 2019). It was shown that the model performance is comparable to other state-of-the-art regional climate models over the Antarctic region. We now applied the CCLM2 model in a regional configuration over the Totten glacier area (E-Antarctica) at 5 km resolution and evaluated its performance over this region by comparing it to climatological observations from different stations. We show that the performance for temperature in the high resolution run is comparable to the performance of the Antarctic-wide run. Precipitation is, however, overestimated in the high-resolution run, especially over dome structures (Law-Dome). Therefore, we applied an orographic smoothening, which clearly improves the precipitation pattern with respect to observations. Wind speed is overestimated in some places, which is solved by increasing the surface roughness. This research frames in the context of the PARAMOUR project. Within PARAMOUR, CCLM2 is currently being coupled to an ocean model (NEMO) and an ice sheet model (f.ETISh/BISICLES) in order to understand decadal predictability over this region.

How to cite: Helsen, S., Vanden Broucke, S., Gossart, A., Souverijns, N., and van Lipzig, N.: An evaluation of the surface climatology over the Totten region (Antarctica) using COSMO-CLM2, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5211, https://doi.org/10.5194/egusphere-egu2020-5211, 2020

D3456 |
| Highlight
Saiping Jiang and Aizhong Ye

Understanding the change of Greenlandic temperature is important for assessing and predicting Greenland ice sheet mass, which plays an important role in sea level rise. In this study, we analyze the annual and seasonal coastal Greenlandic temperature during period 1952 ~ 2017 based on the dataset obtained from Danish Meteorological Institute (DMI), focusing on the last five years. Overall, the annual coastal Greenlandic temperature increases during period 1952 ~ 2017 with a rate of 0.23 ℃ decade-1, especially in the south-eastern (0.70 ℃ decade-1) and northern (0.42 ℃ decade-1) region of the island. From seasonal coastal Greenlandic composite temperature (CT) change, winter has the largest change rate (0.28 ℃ decade-1), and summer increases 0.25 ℃ decade-1, while spring warms 0.17 ℃ decade-1 with a smaller variation. And temperature increase is accelerating during period 2013 ~ 2017 according to Mann-Kendall test, especially in the north-eastern and northern region of the island; And the order of seasonal temperature change of the whole island is as follows: annual > autumn > summer > winter > spring. And pearson correlation analysis was used to determine the teleconnection relationship between coastal temperature and large-scale atmospheric-ocean climate indexes, and we have found that Greenland Blocking Index (GBI), Atlantic Multi-decadal Oscillation (AMO), Tropical Northern Atlantic Index (TNA), North Tropical Atlantic Index (NTA), Caribbean Index (CAR), Atlantic Meridional Mode (AMM), East Atlantic (EA) and Western Hemisphere warm pool (WHWP) have a significant positive correlation relationship with coastal temperature in most months except February and May. But North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and Eastern Asia/Western Russia (EAWR) show a significant negative correlation relationship with temperature. On the whole, there exists time lag effect between climate indexes and temperature except GBI, AO and NAO. And from Randomforest model result, we find that GBI, NAO, CO2, AMO, N2O, SF6, CH4, and Northern Oscillation Index (NOI) are most important variables that influence CT change during period 1979 ~ 2017. Finally, we calculated the contribution rate of important variables to temperature change during period 1979 ~ 2017, showing that contribution rate of GBI, CO2 and NOI to temperature change is 48.85%, 36.85%, and 17.58%, respectively. 

How to cite: Jiang, S. and Ye, A.: Temperature increase is accelerating in the past five years in Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5515, https://doi.org/10.5194/egusphere-egu2020-5515, 2020

D3457 |
| Highlight
Luca Maffezzoni, Laura Edwards, and Tom Matthews

The Greenland Ice Sheet (GrIS) stores enough freshwater to raise global sea level by more than 7 m, so its response to climate variability and change is of considerable societal significance. In this context, extratropical cyclones are known to impact the surface mass budget (SMB) via their influence on precipitation and the surface energy budget (SEB). However, there has so far been limited research on these pathways. We address this by expanding process-based knowledge of cyclones and their influence on the GrIS. Using a 58-year integration of the Model Atmospherique Regional (MAR) along with a cyclones`dataset covering the Northern Hemisphere for the same period, we show the mean standardized anomalies of SMB and SEB over the GrIS when cyclones are in close proximity. Overall, our results, show a positive contribution of extratropical cyclones to the SMB during warm and cold seasons alike, especially via snowfall. In both winter and summer, cyclones enhance the downwelling longwave radiative flux due to higher temperatures and increased humidity. In summer an increase (decrease) of long-wave downward and relative humidity (sensible heat flux and temperature) is observed. In winter the impact on these surface energy variables is similar, apart for temperature which have an opposite sign. Overall, cyclones suppress melt and run-off, especially in the ablation zone and peripherals areas of the Ice Sheet during the warm season. Results from this study will contribute to better understanding of how the GrIS may respond in terms of SMB and SEB to changes in the North Atlantic storm tracks under global warming scenarios.

How to cite: Maffezzoni, L., Edwards, L., and Matthews, T.: The Impact of Extratropical Cyclones on the Greenland Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8064, https://doi.org/10.5194/egusphere-egu2020-8064, 2020

D3458 |
Jonathan Wille, Vincent Favier, Irina V. Gorodetskaya, Cécile Agosta, Jai Chowdhry Beeman, Ambroise Dufour, Francis Codron, and John Turner

Atmospheric rivers, broadly defined as narrow yet long bands of strong horizontal vapor transport typically imbedded in a low level jet ahead of a cold front of an extratropical cyclone, provide a sub-tropical connection to the Antarctic continent and are observed to significantly impact the affected region’s surface mass balance over short, extreme events. When an atmospheric river makes landfall on the Antarctic continent, their signature is clearly observed in increased downward longwave radiation, cloud liquid water content, surface temperature, snowfall, surface melt, and moisture transport.

Using an atmospheric river detection algorithm designed for Antarctica and regional climate simulations from MAR, we created a climatology of atmospheric river occurrence and their associated impacts on surface melt and snowfall. Despite their rarity of occurrence over Antarctica (maximum frequency of ~1.5% over a given point), they have produced significant impacts on melting and snowfall processes. From 1979-2017, atmospheric rivers landfalls and their associated radiative flux anomalies and foehn winds accounted for around 40% of the total summer surface melt on the Ross Ice Shelf (approaching 100% at higher elevations in Marie Byrd Land) and 40-80% of total winter surface melt on the ice shelves along the Antarctic Peninsula. On the other side of the continent in East Antarctica, atmospheric rivers have a greater influence on annual snowfall variability. There atmospheric rivers are responsible for 20-40% of annual snowfall with localized higher percentages across Dronning Maud Land, Amery Ice Shelf, and Wilkes Land.

Atmospheric river landfalls occur within a highly amplified polar jet pattern and often are found in the entrance region of a blocking ridge. Therefore, atmospheric river variability is connected with atmospheric blocking variability over the Southern Ocean. There has been a significant increase in atmospheric river activity over the Amundsen-Bellingshausen sea and coastline and into Dronning Maud Land region from 1980-2018. Meanwhile, there is a significant decreasing trend in the region surrounding Law Dome. Our results suggest that atmospheric rivers play a significant role in the Antarctic surface mass balance, and that any future changes in atmospheric blocking or tropical-polar teleconnections may have significant impacts on future surface mass balance projections.

How to cite: Wille, J., Favier, V., Gorodetskaya, I. V., Agosta, C., Beeman, J. C., Dufour, A., Codron, F., and Turner, J.: Antarctic Atmospheric River Climatology and Impacts , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8476, https://doi.org/10.5194/egusphere-egu2020-8476, 2020

D3459 |
| Highlight
Deniz Bozkurt, David H. Bromwich, and Roberto Rondanelli

This study assesses the recent (1990-2015) and near future (2020-2045) climate change in the Antarctic Peninsula. For the recent period, we make the use of available observations, ECMWF’s ERA5 and its predecessor ERA-Interim, as well as regional climate model simulations. Given the different climate characteristics at each side of the mountain barrier, we principally assess the results considering the windward and leeward sides. We use hindcast simulations performed with Polar-WRF over the Antarctic Peninsula on a nested domain configuration at 45 km (PWRF-45) and 15 km (PWRF-15) spatial resolutions for the period 1990-2015. In addition, we include hindcast simulations of KNMI-RACMO21P obtained from the CORDEX-Antarctica domain (~ 50 km) for further comparisons. For the near future climate change evaluation, we principally use historical simulations and climate change projections (until 2050s, RCP85) performed with PWRF (forced with NCAR-CESM1) on the same domain configuration of the hindcast simulations. Recent observed trends show contrasts between summer and autumn. Annual warming (cooling) trend is notable on the windward (leeward) coasts of the peninsula. Unlike the reanalysis, numerical simulations indicate a clear pattern of windward warming and leeward cooling at annual time-scale. These temperature changes are accompanied by a decreasing and increasing trend in sea ice on the windward and leeward coasts, respectively. An increasing trend of precipitation is notable on the central and northern peninsula. High resolution climate change projections (PWRF-15, RCP85) indicate that the recent warming trend on the windward coasts tends to continue in the near future (2020-2045) and the projections exhibit an increase in temperature by ~ 1.5°C and 0.5°C on the windward and leeward coasts, respectively. In the same period, the projections show an increase in precipitation over the peninsula (5% to 10%). The more notable warming projected on the windward side causes more increases in surface melting (~ +20% to +80%) and more sea ice loss (-4% to -20%) on this side. Results show that the windward coasts of central and northern Antarctic Peninsula can be considered as "hotspots" with notable increases in temperature, surface melting and sea ice loss.

How to cite: Bozkurt, D., Bromwich, D. H., and Rondanelli, R.: Recent and near future climate change in the Antarctic Peninsula, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11296, https://doi.org/10.5194/egusphere-egu2020-11296, 2020

D3460 |
Adrian McDonald

This study investigates the impacts of strong wind events on the sea ice concentration within polynya regions, with a focus on the Ross Sea Polynya (RSP). In particular, this work quantifies the sensitivity of sea ice concentrations to surface winds and whether there are threshold wind speeds required for regions of the polynya  to open up with subsequent impacts on air-sea heat fluxes. To analyse these processes, we examine version 3.1 of the Bootstrap sea ice concentration (SIC) satellite data set derived from SSM/I brightness temperatures and how they are connected to the surface winds from the ERA5 reanalysis over the period 1979 to 2018. While we examine these relationships around the entire Antarctic continent, we focus on the RSP and low-level jets in the Ross Sea. In particular, we examine how strong wind events which impact SIC in the RSP are linked to Ross Ice Shelf Air Stream events (strong low-level jets in the region). The hypothesis that the increase in Ross Ice Shelf Air Stream events, associated with a strengthening of the Amundsen Sea Low, has contributed to trends in sea ice production in this region is examined.

How to cite: McDonald, A.: Impacts of strong surface winds on Antarctic Polynya, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11468, https://doi.org/10.5194/egusphere-egu2020-11468, 2020

D3461 |
Xiaoming Hu, Sergio Sejas, Ming Cai, Zhenning Li, and Song Yang

In January of 2016, the Ross Sea sector of the West Antarctic Ice Sheet experienced a three-week long melting episode. Here we quantify the association of the large-extent and long-lasting melting event with the enhancement of the downward longwave (LW) radiative fluxes at the surface due to water vapor, cloud, and atmospheric dynamic feedbacks using the ERA-Interim dataset. The abnormally long-lasting temporal surges of atmospheric moisture, warm air, and low clouds increase the downward LW radiative energy flux at the surface during the massive ice-melting period. The concurrent timing and spatial overlap between poleward wind anomalies and positive downward LW radiative surface energy flux anomalies due to warmer air temperature provides direct evidence that warm air advection from lower latitudes to West Antarctica causes the rapid long-lasting warming and vast ice mass loss in January of 2016.

How to cite: Hu, X., Sejas, S., Cai, M., Li, Z., and Yang, S.: Atmospheric Dynamics Footprint on the January 2016 Ice Sheet Melting in West Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12285, https://doi.org/10.5194/egusphere-egu2020-12285, 2020

D3462 |
Shuoyi Ding, Bingyi Wu, and Wen Chen

The present study investigated dominant characteristics of autumn Arctic sea ice concentration (SIC) interannual variations, and examined impacts of SIC anomalies in the East Siberian-Chukchi-Beaufort (EsCB) Seas on winter Eurasian climate variability and the associated possible physical mechanism. Results showed that the Arctic SIC variations in both September and October display a certain continuity to some extent, thus, we chose the September-October (SO) mean SIC as a factor to explore its delayed impacts on winter atmosphere. Dominant features of Arctic SIC variability in SO is characterized by sea ice loss in the EsCB Seas, with more evident interannual variability since the late 1990s. Such a change can be attributed to the central Arctic pattern of atmospheric variability. Along with the global warming, the interannual variation of sea ice in the EsCB Seas seemingly exerts an increasingly role in the Northern Hemispheric climate variability. When the EsCB sea ice decreases in the early autumn (SO), a barotropic response of wave number 2 structure with significant warming and positive geopotential height anomaly dominates the Arctic region a month later. Then, in the early winter (ND(0)J(1)), the Arctic anticyclonic anomaly extends southward into the central-western Eurasia and leads to evident surface cooling there. Two month later, it further develops toward downstream accompanied by a deepened trough, making the East Asia experience a colder late winter (JFM(1)), especially in the northeastern China. Meanwhile, enhanced North Pacific anticyclonic perturbation excites an eastward wave train and contributes to positive geopotential height anomaly around the Greenland. Combined with a cyclonic anomaly to its southeast, a dipole structure forms and favors negative surface temperature anomaly covering the western Europe. In addition, a weakened polar vortex in the lower stratosphere can be observed during the boreal winter. Similar atmospheric responses to EsCB sea ice loss are well reproduced in the simulation experiments, not only supporting the conclusions from observational analyses, but also illustrating the possible physical mechanism to some extent.

How to cite: Ding, S., Wu, B., and Chen, W.: Dominant Characteristics of early autumn Arctic sea ice variability and its impact on Winter Eurasian climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12370, https://doi.org/10.5194/egusphere-egu2020-12370, 2020

D3463 |
Mauro Hermann, Lukas Papritz, and Heini Wernli

Specific atmospheric circulation patterns can lead to strongly positive near-surface temperature anomalies over Greenland, fostering the occurrence of extensive surface melt events. In this study, we objectively identify 77 Greenland melt events in June-August 1979-2017, which also affect high-elevated regions of the Greenland ice sheet (GrIS), from ERA-Interim reanalysis data. Eight-day backward trajectories from the lowermost 500 m above the GrIS are used to investigate the air mass history and the synoptic, dynamical, and thermodynamic drivers of Greenland melt events. The key synoptic feature is a high-pressure system, in 65% of the events classified as atmospheric blocking, southeast of the GrIS. It is favorably located to induce rapid and long-range poleward transport of anomalously warm air masses (compared to climatology) from the lower troposphere to the GrIS. Due to orographic and dynamical lifting, latent heating from condensation of water vapor contributes additionally to the air mass’ warm anomaly - most important for melt events on top of the GrIS. Adiabatic warming by subsidence, however, is insignificant, in contrast to warm events in the central Arctic. Exemplarily, the warm anomaly of air masses arriving in the Summit area during the most extensive melt event in early July 2012 arose due to strong meridional transport, mainly from the western North Atlantic, and latent heat release during ascent to Greenland. The simultaneous occurrence of a North American record heat wave did not play any direct role for the Greenland melt event. Further, regionally varying short- and longwave radiative effects induced by the warm-moist air masses enhance melt all over the GrIS. The identified mechanisms that cause Greenland melt events imply that the understanding of the formation of high-pressure systems and their representation in climate models is crucial in determining future GrIS melt. More generally, we highlight the importance of atmospheric dynamics and air flow patterns for Greenland melt events as they eventually determine the temperature pattern and surface energy budget over the GrIS with consequences for global sea-level rise.

How to cite: Hermann, M., Papritz, L., and Wernli, H.: Lagrangian Analysis of the Dynamical and Thermodynamic Drivers of Greenland Melt Events during 1979-2017, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13492, https://doi.org/10.5194/egusphere-egu2020-13492, 2020

D3464 |
Iris Hansche, Jakob Abermann, Sonika Shahi, and Wolfgang Schöner

Air temperature inversion, a situation in which atmospheric temperature increases with height, is a common feature in the Arctic planetary boundary layer. This stable layer has multiple consequences for the Arctic environment. While vertical gradients of flora and fauna are impacted by them, they also have a direct consequence on physical characteristics such as permafrost thaw depths and snow cover. Therefore, a comprehensive knowledge about the spatial and temporal variability of temperature inversion parameters such as thickness, intensity, magnitude and frequency is crucial for the surface impact of Arctic climate change.

Here, we investigate the spatial and temporal variations of temperature inversions over different surface types on Ammassalik Island in East Greenland. During a field campaign in summer 2019, high temporal resolution profiles of atmospheric variables such as air temperature, humidity and pressure were collected using UAVs. We acquired 147 profiles in a period of 13 days (06/07/2019-18/07-2019) over different surface types (rock, gravel, snow, ice) and with varying distance to the ocean (between 0 and 6 km). We found a distinct air temperature inversion present in most of the profiles whereby height and thickness differ considerably. Both ocean and ice surface act as near-surface cooling agents, which favours the development of surface inversions. The ice-free area between ocean and glacier tends to warm up strongly during Arctic summer and those different drivers manifest in an intricate pattern of air temperature stratification along a valley axis.

Our high-frequency and high-resolution profiles are compared with longer time series from the nearby Tassiilaq radiosonde and with ERA-5 reanalysis data in order to bring our campaign data into a larger spatio-temporal context. We conclude that the radiosonde is able to resolve the general pattern well but it fails in adequately representing the stratification relevant for glacio-meteorological processes.

How to cite: Hansche, I., Abermann, J., Shahi, S., and Schöner, W.: Spatial and temporal variations of air temperature inversions over different surface types on Ammassalik Island (East Greenland), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15597, https://doi.org/10.5194/egusphere-egu2020-15597, 2020

D3465 |
Hyeong-Gyu Kim, Joowan Kim, Sang-Yoon Jun, and Seong-Joong Kim

Paleoclimate data shows a good correlation between the concentration of CO2 and atmospheric temperature in the geological timescale. Many studies compare the Last Glacial Maximum (LGM) and the Pre-Industrial era (PI), to understand the coupling processes. A popular mechanism explaining this coupling process is a modulation of the ocean circulation and related CO2 emission over the Southern Ocean due to atmospheric westerly. The atmospheric westerly plays an important role in driving ocean circulation; however, the related processes are not fully understood for the LGM period.

In this study, we examine physical processes determining the characteristics of the atmospheric westerly focusing on the Southern Ocean. Atmospheric states for LGM and PI are reproduced using a coupled earth system model with different sea ice conditions. A poleward intensification of the Southern Hemispheric Westerlies is observed for the LGM experiment. A comparison to PI shows that the meridional temperature gradient largely determines this intensification, and the enhanced meridional gradient is observed due to decreased heat flux from the subantarctic ocean in the LGM experiment. This result suggests that the Antarctic sea ice is a crucial component for understanding the Southern Hemispheric Westerly.

How to cite: Kim, H.-G., Kim, J., Jun, S.-Y., and Kim, S.-J.: Dynamical mechanism of the poleward intensification of the Southern Hemispheric Westerlies due to sea ice extent change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15627, https://doi.org/10.5194/egusphere-egu2020-15627, 2020

D3466 |
Franziska Gerber, Varun Sharma, and Michael Lehning

On the windiest, coldest and driest continent of the world, blowing snow is frequently active, especially during the winter months. Coastal regions with strong katabatic winds are especially prone to blowing snow and its sublimation. However, the contribution of blowing snow to the surface mass balance from snow blown off the continent and blowing snow sublimation is not well constraint by direct measurements. Furthermore, model and satellite assessments disagree on the magnitude of the effect.

Current studies of the Antarctic surface mass balance are mainly based on regional climate models. However, most models rely on rather simple representations of the snow cover as well as blowing snow. With the aim of improving the surface mass balance representation and specifically snow transport and sublimation due to blowing snow, we coupled the well-established snow model SNOWPACK to the Weather Research and Forecasting Model (WRF). The new coupled model, called ‘CRYOWRF’, is aimed at an improved representation of snow and snow-atmosphere interaction in all cryospheric environments.

CRYOWRF simulations show good agreement with measurements at meteorological stations on the Antarctic continent. Moreover, the timing of modeled blowing snow events agrees well with few local blowing snow measurements. Monthly frequencies of simulated and satellite-derived spatial blowing snow distributions result in similar patterns. We will present estimates of the amount and importance of blowing snow on the surface mass balance in Antarctica based on 8 years of simulations (2010-2018), with a special focus on blowing snow sublimation. The introduced model will be useful for future predictions of surface mass balance estimates, which are important to assess the contribution of the Antarctic ice sheet to sea level rise in a warming world.

How to cite: Gerber, F., Sharma, V., and Lehning, M.: Blowing snow in Antarctica and its contribution to the surface mass balance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18765, https://doi.org/10.5194/egusphere-egu2020-18765, 2020

D3467 |
Len Shaffrey, Helene Bresson, Kevin Hodges, and Giuseppe Zappa

Polar lows are small, intense cyclones that form at high latitudes during winter. Their high wind speeds and heavy precipitation can have substantial impacts on shipping, coastal communities and infrastructure. However, climate models typically have low resolutions and therefore poorly simulate Polar Lows. This reduces the confidence that can be placed in future projections of extreme high latitude weather and associated risks.

In this study, Polar Lows are assessed for the first time in a high-resolution (25 km) global climate atmosphere-only model, N512 HadGEM3-GA3, for both present-day and future RCP 8.5 climate scenarios. Using an objective tracking algorithm, the representation of Polar Lows in the N512 HadGEM3-GA3 present-day simulation is found to agree reasonably well the NCEP-CFS reanalysis. RCP8.5 scenario conditions are generated by adding SST changes between 1990-2010 and 2090-2110 from the RCP8.5 experiments with the HadGEM2-ES model to observed SSTs from the present-day climate. In the RCP8.5 N512 HadGEM-GA3 simulations, the number of Northern Hemisphere Polar Lows are projected to substantially decrease (by over 60%) by the end of the 21st century, which is largely due to an increase in atmospheric static stability. However, new regions of Polar Low activity along the northern Russian coastlines are found where the Arctic sea ice is projected to retreat.

How to cite: Shaffrey, L., Bresson, H., Hodges, K., and Zappa, G.: The response of Northern Hemisphere polar lows to2climate change in a 25 km high-resolution global climate model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19488, https://doi.org/10.5194/egusphere-egu2020-19488, 2020

D3468 |
| solicited
| Highlight
Thomas Mote, Jonathon Preece, Lori Wachowicz, Kyle Mattingly, and Thomas Ballinger

The Greenland ice sheet has experienced increased surface melt and mass loss since the mid-1990s. Surface melt and surface mass balance are partially driven by large-scale changes in atmospheric circulation, which can direct anomalously warm and humid air masses over the ice sheet and lead to pulses of extensive melt and high runoff rates. However, the connection between the air mass source regions and ice sheet surface melt is poorly understood. Here we examine extreme melt pulses (>95th percentile melt extent for 3 or more days) for topographically defined regions of the ice sheet during the months of June, July, and August. Daily melt extent is determined from a satellite passive microwave product. The NOAA Air Resources Laboratory HYSPLIT model is used to calculate 10-day back-trajectories leading up to melt pulses. We apply a clustering algorithm separately for each region and initialization altitude to visualize the predominant tracks of air masses that impact the ice sheet during extensive melt events. Potential temperature at 2 PVU is used to trace atmospheric motion prior to melt onset. Particular attention is given to extreme events that led to melt at the highest elevations of the ice sheet, Summit Station. Results show the difference in source region east and west of the ice divide, and the important role of air mass source regions from North America and Europe.

How to cite: Mote, T., Preece, J., Wachowicz, L., Mattingly, K., and Ballinger, T.: Air mass source regions associated with enhanced surface melting of the Greenland Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19718, https://doi.org/10.5194/egusphere-egu2020-19718, 2020