The impact of subtropical atmospheric rivers on Patagonian glaciers

Identifying mechanisms causing glacier mass loss is becoming more critical as global temperatures warm. This study investigated the highest rainfall events recorded at weather stations near the major icefields in Patagonia, South America and correlated them to Atmospheric River events and their corresponding synoptic characteristics. The events were then determined to be either producing rain or snow depending on whether the temperature reached a snowfall threshold of ≤ 2°C and included rainfall. Each event was clustered based on overall direction of the Atmospheric River and their association with weather station location. The study found that more northerly clusters that were more zonally orientated were generally warmer and contained rainfall thereby potentially causing ablation, while more southward clusters had potential for snowfall at lower elevations thereby potentially adding to the accumulation of glacier mass. The synoptic characteristics that generally governed the warmer Atmospheric River events were low pressure systems located in the Amundsen Sea, with the South Pacific anticyclone extending a ridge over northern parts of Patagonia. This was reflected in the upper levels, with a long wave ridge over the southern part of the continent being the main feature. Conversely, cooler events maintained low pressure centres closer to the continent in the Bellingshausen Sea and weak ridging, with upper levels exhibiting a long wave trough to the west of the continent. The study provides a detailed synoptic overview of Atmospheric River events impacting Patagonia, and their potential for delivering glacial melt in the form of rain and warmer temperatures or snowfall.