Identifying Antarctic Atmospheric River Families

Despite their rarity, atmospheric rivers (ARs) bring powerful impacts to Antarctica when they make landfall on the ice sheet. Antarctic ARs contribute 10% of the annual precipitation and are major drivers for heatwaves, foehn events, and surface melting on ice shelves. While snowfall is currently the dominant impact of Antarctic ARs, helping to offset sea level rise due to ice discharge from West Antarctica, the relative contribution of ARs to snowfall, rainfall, and surface melt may change in a warming climate, along with the frequency and intensity of AR events themselves, motivating the study of these rare, impactful events. In this study, we examine the occurrence of Antarctic AR families, in which two or more ARs occur in rapid succession in a region. While individual ARs have been shown to have pronounced and widespread impacts in Antarctica, latent heat release from ARs in a family can reinforce associated downstream high-pressure systems to produce extended, high impact AR conditions on the ice sheet, including multiple days of intense snowfall and temperatures above the melting point. Here we present initial results from an Antarctic-wide study of the occurrence and impacts of AR family events. First, we use a density-based clustering algorithm to classify AR events as objects from an Eulerian, Antarctic-specific detection tool based on MERRA-2 reanalysis. From this, we construct a database of AR events around Antarctica from 1980-2022, with information on the location, duration, and landfall (if it occurred) for each AR. Then, we cluster the AR events by location and time once more, to identify the occurrence of AR family events. We explore the sensitivity of the number of AR family events detected, and the number of ARs per family, to the chosen aggregation period (two to six days) and distance parameter (500 – 1000 km). Finally, we utilize a novel atmospheric Rossby wave breaking detection tool to compare the frequency of cyclonic and anticyclonic wave breaking events over the Southern Ocean to the frequency of AR family and non-family events. Ultimately, our study aims to diagnose the occurrence, synoptic drivers, characteristics, and impacts of AR family events on the Antarctic Ice Sheet in the last four decades, to provide a baseline assessment of how these extreme events can compound to produce lasting, high-impact conditions.