Although rare, atmospheric rivers (ARs) substantially influence the interannual variability of Antarctic surface mass balance. We identify characteristics unique to AR environments by comparing (1) AR, (2) Analog (environments that feature high-low pressure couplets, similar to AR environments, but no AR), and (3) Top AR (high-precipitation AR timesteps) during 1980–2019 around Antarctica. We find significant differences between AR and Analog environments including more intense and poleward-shifted mid-tropospheric geopotential height couplets as well as larger atmospheric moisture anomalies. We find similar significant enhancement in synoptic-scale dynamic drivers of Top ARs compared to AR environments, but no significant difference in local integrated water vapor anomalies. Instead, our results highlight the importance of large-scale dynamic drivers of Top AR timesteps, including connections between high-precipitation ARs and Rossby waves excited by tropical convection. This deeper understanding of Antarctic AR environments provides context for interpreting future changes to the Antarctic surface mass balance.

How to cite: Baiman, R., Winters, A. C., Pohl, B., Favier, V., Wille, J. D., and Clem, K. R.: Discriminators of Antarctic Atmospheric River Environments            , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3624, https://doi.org/10.5194/egusphere-egu24-3624, 2024.

Atmospheric Rivers (AR) are extreme hydrological events that have strong impacts on the different components of the Antarctic ice sheet surface mass balance (SMB), through both snow accumulation and surface melt due to heating and rain. Their evolving characteristics are therefore important to understand for an accurate prediction of future SMB changes.

We use here an ensemble of simulations of the mid-21st century climate using the IPSL-CM6 model. The future Antarctic ARs are identified using a detection algorithm adapted to the region, and taking into account in the detection threshold (based on moisture fluxes) the rising background moisture in a warmer climate. While a constant detection threshold leads to a continuous increase of the number of ARs detected, the use of this adaptative threshold leads instead to a relatively stable frequency of occurence, but with a larger penetration over Antarctica (+5% occurence over the continent). In addition, a wave number 3 component appears in the future change in frequency, as well as in AR-related snowfall.

While the number of ARs does not change much, their intensity, as measured by the associated water vapor transport, increases in line with the Clausius-Clapeyron relation. Their different impacts on the SMB also become larger, with both increasing snowfall, and surface melt and rainfall in the coastal regions. The direct effect on the SMB is however dominated by the increase in snow accumulation.

How to cite: Barthelemy, L., Codron, F., Favier, V., and Wille, J.: Future Atmospheric Rivers in Antarctica using CMIP6-IPSL model : intensity and impacts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3880, https://doi.org/10.5194/egusphere-egu24-3880, 2024.

We calculate a regional surface “melt potential” index (MPI) over Antarctic ice shelves that describes the frequency (MPI-freq, %) and intensity (MPI-int, K) of daily maximum summer temperatures exceeding a melt threshold of 273.15 K. This is used to determine which ice shelves are vulnerable to melt-induced hydrofracture and is calculated using near-surface temperature output for each summer from 1979/80 to 2018/19 from two high-resolution regional atmospheric model hindcasts (using the MetUM and HIRHAM5). MPI is highest for Antarctic Peninsula ice shelves (MPI-freq 23-35%, MPI-int 1.2-2.1 K), lowest (2-3%, < 0 K) for Ronne-Filchner and Ross ice shelves, and around 10-24% and 0.6-1.7 K for the other West and East Antarctic ice shelves. Hotspots of MPI are apparent over many ice shelves, and they also show a decreasing trend in MPI-freq. The regional circulation patterns associated with high MPI values over West and East Antarctic ice shelves are remarkably consistent for their respective region but tied to different large-scale climate forcings. The West Antarctic circulation resembles the central Pacific El Niño pattern with a stationary Rossby wave and a strong anticyclone over the high-latitude South Pacific. By contrast, the East Antarctic circulation comprises a zonally symmetric negative Southern Annular Mode pattern with a strong regional anticyclone on the plateau and enhanced coastal easterlies/weakened Southern Ocean westerlies. Values of MPI are 3-4 times larger for a lower temperature/melt threshold of 271.15 K used in a sensitivity test, as melting can occur at temperatures lower than 273.15 K depending on snowpack properties.

How to cite: Orr, A., Deb, P., Clem, K., Gilbert, E., Bromwich, D., Boberg, F., Colwell, S., Hansen, N., Lazzara, M., Mooney, P., Mottram, R., Niwano, M., Phillips, T., Pishniak, D., Reijmer, C., van de Berg, W. J., Webster, S., and Zou, X.: Characteristics of surface melt potential over Antarctic ice shelves based on regional atmospheric model simulations of summer air temperature extremes from 1979/80 to 2018/19, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6344, https://doi.org/10.5194/egusphere-egu24-6344, 2024.

Blowing snow transport is an essential polar boundary layer process and constitutes the major ablation term in the Antarctic ice sheet's surface mass balance (SMB). Here, we present an update to the blowing snow model in the Regional Atmospheric Climate Model (RACMO), version 2.3p3, to include the effect of blowing snow sublimation and transport in the prognostic equations for temperature and water vapour. Updates rectify the numerical artefacts in the modelled blowing snow flux variation with wind speed. Updates include the replacement of uniformly distributed ice particle radius, which limited the maximum ice particle radius to ≤ 50 μm, with an exponentially increasing ice particle radius distribution to include all the relevant range of radii between 2 to 300 μm without any additional computational overhead. We compare the model results against the observations from site D47 in Adèlie Land, East Antarctica. These updates correct the numerical artefacts observed in the previous model results, and RACMO successfully predicts the power-law variation of the blowing snow transport flux with wind speed. Updates also improve the prediction of the magnitude of the blowing snow fluxes. In addition, at site D47, we obtain an average blowing snow layer depth of 230±116 μm, which falls within the range of values obtained from satellite observations. A qualitative comparison of the simulated blowing snow frequency from RACMO with CALIPSO satellite observations shows that the simulated frequency matches well with the satellite product. Compared to the previous model version for the period 2000–2010, the contribution of integrated blowing snow sublimation is increased by 30%, with a yearly average of 176±4 Gt yr^-1. The increase amounts to 1.2% reduction in the integrated SMB of the Antarctic ice sheet. The updates also introduce changes in the climatology of blowing snow in Antarctica. Specifically, we observe significant changes in the sublimation of interior regions of the escarpment zone of Antarctica.

How to cite: Gadde, S. and van de Berg, W. J.: Contribution of blowing snow sublimation to the surface mass balance of Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10663, https://doi.org/10.5194/egusphere-egu24-10663, 2024.

The recent two years have been marked by many regional climate-state extremes particularly over the southern polar region including record-high surface melt over the Antarctic Peninsula in February 2022 (Gorodetskaya et al., 2023; Zou et al., 2023), the strongest heatwave ever recorded over East Antarctica bringing extreme inland snowfall and coastal surface melt in March 2022 (Wille et al., 2024), and an extremely low Antarctic sea ice area observed in winter 2022 outpaced by the lowest record in winter 2023 (Purich and Doddridge, 2023). Increased magnitude and probability of occurrence of extreme events, along with their high impacts on the Antarctic surface mass balance require detailed understanding of the underlying large-scale, regional and local drivers, using comprehensive and high-resolution observations and modeling. Here we will present analysis of extreme surface melt events and their drivers based on targeted observations conducted during 2022-2023 over the northern Antarctic Peninsula, including two austral summer campaigns and the winter Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) enhanced observational period. Cloud and precipitation profiles using radar and lidar measurements are analyzed together with thermodynamic state of the troposphere from radiosonde observations and surface radiative fluxes with a specific focus on the extreme warm events characterized by surface melt and/or rainfall. In particular, the February 2022 extreme warm event showed very high downwelling longwave flux (up to 350 W/m2) due to the low warm-base liquid-containing clouds. Frequent occurrence of supercooled liquid water with low and warm cloud-bases is characteristic of the site during both summer and winter seasons and plays an important role in surface melt events. Another key factor during warm events is the transition from snowfall to rainfall (both with height in the vertical column, indicated by melt layer height derived from the precipitation radar measurements, and with time over the course of the event). Using radiosonde profiling, we identify layers of maximum moisture and heat transport into the Antarctic Peninsula, which showed an outstanding magnitude during the hot spell in February 2022 associated with an intense atmospheric river and which we further compare to other observed warm events. Significant differences are found for cloud and precipitation properties between ground-based measurements and ERA5 reanalysis, prompting the use of state-of-art high-resolution observations to improve representation of relevant processes in the models particularly during surface melt events.

Funding acknowledgements: Portuguese Polar Program projects APMAR/TULIP/APMAR2; FCT projects MAPS and ATLACE; ANR project ARCA; KOPRI; NSF awards 2127632 and 2229392.

References:

Gorodetskaya et al. (2023): Record-high Antarctic Peninsula temperatures and surface melt in February 2022: a compound event with an intense atmospheric river. npj Clim Atmos Sci, https://doi.org/10.1038/s41612-023-00529-6

Purich and Doddridge (2023): Record low Antarctic sea ice coverage indicates a new sea ice state. Commun Earth Environ, https://doi.org/10.1038/s43247-023-00961-9

Wille et al (2024): The Extraordinary March 2022 East Antarctica “Heat” Wave. Part I: Observations and Meteorological Drivers. J. Climate, https://doi.org/10.1175/JCLI-D-23-0175.1.

Zou et al (2023): Strong warming over the Antarctic Peninsula during combined atmospheric River and foehn events: Contribution of shortwave radiation and turbulence. J. Geophys. Res. Atmos., https://doi. org/10.1029/2022JD038138 

How to cite: Gorodetskaya, I. V., Durán-Alarcón, C., Rowe, P., Zou, X., Park, S., and Favier, V.: Surface melt over the Antarctic Peninsula: targeted observations capturing recent extreme events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20816, https://doi.org/10.5194/egusphere-egu24-20816, 2024.

Recent research has extensively analyzed summertime atmospheric river (AR) events in the Antarctic Peninsula (AP) using ground-based and atmospheric observations, yet a significant gap remains in understanding the occurrence and impacts of ARs during the Antarctic winter. This study focuses on an extraordinary warming event in the AP between 1 and 3 July 2023, utilizing data from recent wintertime field campaigns and ERA5 reanalysis. On 2 July, the Frei station in northern AP recorded a remarkable daily maximum near-surface air temperature of 2.7°C, significantly higher than the mean winter value of -3.8°C and surpassing the winter 99th percentile of 1.8°C. On 2-3 July, at least 6 hours of liquid precipitation were recorded, as corroborated by ERA5 data, leading to notable rain-on-snow and melt events. This occurrence challenges conventional expectations, as liquid precipitation during the depths of the southern winter is exceedingly rare in Antarctica. Radiosonde observations indicated a substantial elevation of the freezing level to about 650 meters, a stark contrast to the 20 meters observed before the event. These observations also revealed a moist and nearly saturated atmospheric profile. The event was synoptically characterized by a distinct trough over the Bellingshausen Sea and a pronounced northwest-southeast oriented blocking ridge from the southwestern Atlantic to the Weddell Sea, resulting in a dipole-like pressure pattern around the AP. These conditions were instrumental in the development of an AR with a north-to-south flow. This flow was marked by maximum integrated vapor transport values exceeding 500 kg m^-1 s^-1, channeling warm, moisture-laden air from continental South America towards the AP. A long-term winter trend analysis reveals a significant strengthening of the dipole pattern, which correlates with increased frequencies of ARs and consequently leads to notable warm temperature anomalies over the northern AP. The study underscores the importance of understanding the complex relationship between local, synoptic conditions, and the dynamics of ARs in influencing winter climate patterns in the AP. This study's ongoing high-resolution simulations and isotope analysis aim to uncover the detailed characteristics and isotopic signatures of this extraordinary warming event, enhancing our understanding of its origins and impacts.

How to cite: Bozkurt, D., Carrasco, J. F., Cordero, R. R., Fernandoy, F., Gómez, A., Carillo, B., and Guan, B.: Atmospheric river brings warmth and rainfall to the northern Antarctic Peninsula during the mid-austral winter of 2023, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13437, https://doi.org/10.5194/egusphere-egu24-13437, 2024.

The Arctic is warming four times faster than the rest of the globe, with a concurrent rapid loss of sea ice extent and thickness. Cyclones are synoptic weather events that transport heat and moisture into the Arctic, and have complex impacts on sea ice, marine ecosystems, and socio-economic activities. However, the effect of a changing climate on Arctic cyclone behavior remains poorly understood. This study uses a combination of reanalysis data, cyclone tracking techniques, and high-resolution numerical modeling to explore the effect of recent and future climate change on Arctic cyclone behavior across seasons.

This work first examines the relative importance of changes in local surface conditions and turbulent fluxes and broader changes in pressure patterns, steering flow, and baroclinicity with recent climate change in governing cyclone frequency, intensity, and trajectories. Our analysis suggests that cyclone activity is shifting throughout the autumn with competing effects of turbulent fluxes and large-scale conditions. With recent climate change, sea ice is declining, and surface temperatures and turbulent fluxes are increasing, resulting in slight increases in Autumn cyclone intensity. In early autumn, cyclone frequency and trajectories are strongly governed by the large-scale flow despite increases in surface turbulent fluxes and baroclinicity. By late autumn, land-sea temperature contrast is increasing with sea ice loss, and changes in baroclinicity and large-scale flow work in concert to increase cyclone activity in the Arctic.

This work then uses regional, high resolution, convection-permitting Weather Research and Forecasting (WRF) model simulations to demonstrate the sensitivity of cyclone characteristics to recent and future climate change. Simulations with downscaled CMIP6 global climate projections reveal that future sea ice loss and increasing surface temperatures by the year 2100 drive large increases in the near-surface vertical temperature gradient, sensible and latent heat fluxes into the atmosphere, and deep convection during spring cyclone events. The changes in the future (warmer) climate alter cyclone trajectories and increase and prolong intensity, with significantly increased wind speeds, temperatures, and precipitation. Such changes in cyclone lifecycles and characteristics may exacerbate sea ice loss and Arctic warming through positive feedback mechanisms. The increasing extreme nature of weather events such as Arctic cyclones has important implications for atmosphere-ice-ocean interactions in the new Arctic.

How to cite: Parker, C., Webster, M., Mooney, P., Valkonen, E., and Boisvert, L.: Understanding local and large-scale changes in the Arctic and the effect on Cyclone activity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12356, https://doi.org/10.5194/egusphere-egu24-12356, 2024.

Recent Greenland ice-sheet melt constitutes an alarming contribution to global sea-level rise. Observations indicate an approximate balance of the ice sheet until the late 1990s, after which a strong increase in melting occurred. This cannot be attributed linearly to gradually-increasing global warming. Instead the abrupt shift is suggested to be linked to atmospheric circulation changes, although causality is not fully understood. Here we show that changes of atmospheric waves over Greenland have significantly contributed to the shift into a strong melting state. This is evident from applying a newly-developed methodology effectively decomposing atmospheric flow patterns into parts associated with Rossby waves and smaller perturbations. A westerly-flow reduction, consistent with anthropogenic Arctic warming, affected transports by atmospheric waves and led to a decrease in precipitation and an increase in surface warming, contributing to ice-sheet mass loss, in particular over the southwestern regions. Hence the Greenland ice-sheet melt is an example of a climate response non-linearly coupled to global warming.

How to cite: Graversen, R. G., Heiskanen, T., Bintanja, R., and Goelzer, H.: Abrupt increase in Greenland melt governed by atmospheric wave change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12942, https://doi.org/10.5194/egusphere-egu24-12942, 2024.

How to cite: Haacker, J., Wouters, B., Fettweis, X., Box, J., and Glissenaar, I.: Atmospheric drivers of the rapid decline of Novaya Zemlya's glaciers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16268, https://doi.org/10.5194/egusphere-egu24-16268, 2024.

How to cite: Barrell, C., Renfrew, I., Methven, J., and Elvidge, A.: Melt ponds and atmosphere-ice-ocean exchange in the UK Met Office Unified Model during the Arctic Summertime Cyclones field campaign, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18137, https://doi.org/10.5194/egusphere-egu24-18137, 2024.