Antarctic Peninsula warming and precipitation phase transition during atmospheric river events

Polar amplification has been pronounced in the Arctic with near-surface air temperatures increasing at more than twice the global warming rate during the last several decades. At the same time, over Antarctica temperature trends have exhibited a large regional variability. In particular, the Antarctic Peninsula (AP) stands out as having a warming rate much higher than the rest of the Antarctic ice sheet and other land areas in the Southern Hemisphere (SH). Future projections indicate that warming and ice loss will intensify in both polar regions with important impacts globally. In addition to the warming amplification, there has been also an enhancement of the polar water cycle with increases in poleward moisture transport and precipitation in both polar regions. An important process linking warming and precipitation enhancement is a shift towards more frequent rainfall compared to snowfall. Future projections show that the rain fraction will significantly increase in coastal Antarctica, especially in the AP. Atmospheric rivers (ARs), long corridors of intense moisture transport from subtropical and mid-latitude regions poleward, are known for their prominent role in both heat and moisture transport with impacts ranging from intense precipitation to temperature records and major melt events in Antarctica. Limited observations have hampered process understanding and correct representation of these extreme events in models. This presentation will give an overview of the enhanced observations targeting ARs in the AP (including surface meteorology, radiosonde, cloud and precipitation remote sensing, and radiative fluxes) as part of the Year of Polar Prediction (YOPP)-SH international collaborative effort. In-depth analysis of transport of heat and moisture, atmospheric vertical structure, cloud properties and precipitation phase transition from snowfall to rainfall during selected AR cases will be presented and compared with ERA5 reanalysis and high-resolution Polar-WRF model simulations. We will highlight three different local regimes around the AP: large-scale precipitation over the Southern Ocean north of the AP, orographic enhancement of precipitation in the western AP and the role of foehn, cloud/precipitation clearing and temperature increase in the northeastern AP.