Antarctic Warm Extremes Across Seasons and Their Response to Advection.

Antarctic warm extremes impact the cryosphere, with very warm extremes driving surface melt on ice shelves. Here, we analyze temperatures exceeding the 90th percentile and the associated circulation patterns and radiation anomalies. ERA5 reanalysis data show positive geopotential height anomalies related to the occurrence of warm extremes. The highest temperature during warm extremes appears on the western periphery of high‐pressure systems, consistent with anticyclonic advection. Temperature anomalies during warm extremes are strongest in winter due to the transport of warm and moist air and a strong meridional temperature gradient. In summer, the weak meridional gradients of top‐of‐atmosphere downward solar radiation flux and surface air temperature contribute to weak temperature anomalies. Warm extremes are associated with positive longwave radiation anomalies in all seasons, but with negative shortwave radiation anomalies at the surface except during polar night. These relationships are verified by station observations. Our results confirm that Antarctic warm extremes are mostly driven by meridional advection of warm air, and suggest that these warm air masses are predominantly moist and cloudy. Plain Language Summary: Changes in Antarctic climate will alter the amount of water stored in the kilometer‐thick Antarctic ice cover, and thereby global sea level. So far, only some regions of the continent have experienced substantial warming under climate change, while others remain largely unaffected. In this study, we analyze the relatively warmest Antarctic temperatures in each place and season. We find that these warm extremes depart more strongly from seasonal mean temperatures in winter than in summer. Warm extremes are often a consequence of warmer air being transported from further North and coincide with moist, probably cloudy air that emits more infrared radiation to the surface than dry, cold air. Key Points: Warm extremes accompanied by high‐pressure systems are driven by advectionWinter experiences strongest temperature anomalies during warm extremesLongwave radiation anomalies during warm extremes are positive and contribute to warm extremes, shortwave radiation anomalies are negative [ABSTRACT FROM AUTHOR]