Compound atmospheric phenomena driving Antarctic mean and extreme precipitation

Abstract

Antarctic precipitation is the dominant positive term in the ice sheet surface mass balance, directly influencing its contribution to global sea level rise. In some coastal and ice-shelf regions, episodic extreme precipitation events can account for more than half of the annual snowfall total; yet while individual atmospheric phenomena such as atmospheric rivers (ARs) and cyclones are known to play important roles, their combined effects remain largely unquantified, as most existing studies focus on the impact of individual drivers. Here, we assess how atmospheric phenomena interact and shape Antarctica’s hydroclimate by applying the Multi-Object Analysis of Atmospheric Phenomena to ERA5 reanalysis over the 2001–2020 period. The algorithm simultaneously detects ARs, mid-level cyclones, anticyclones, atmospheric fronts, and upper-level jets, enabling quantification of their individual and joint contributions to mean and extreme precipitation in Antarctica within a unified framework. Our results reveal that mean and extreme precipitation are linked to broadly the same synoptic-scale systems, with cyclones showing the strongest association throughout the entire analysis domain. However, ARs play a disproportionately large role at the highest precipitation intensities, consistent with their ability to deliver concentrated moisture streams to the Antarctic coastline. Most importantly, an analysis of the 100 events with the highest peak hourly precipitation across coastal and near-coastal Antarctic regions confirms that extreme events are rarely driven by a single phenomenon acting in isolation, with the large majority involving two or more co-occurring systems. ARs, cyclones, and jet streams are consistently the most frequently co-involved phenomena, though the precise magnitude of their co-occurrence is sensitive to the spatial association method used. These findings suggest that evaluating potential changes in co-occurrence patterns among these synoptic-scale systems will be an important consideration for future projections of Antarctic precipitation extremes.