Precipitation and atmospheric rivers from sub-Antarctic Chile to Antarctic Peninsula: transition between rain and snowfall

Abstract

Atmospheric rivers (ARs) impact Antarctic surface mass balance through transport of anomalous heat and moisture from subtropical regions. ARs reaching the Antarctic coast have a prominent impact on moisture and wind profiles, representing an extreme state of the troposphere (Gorodetskaya et al., 2020). Antarctic ARs have been linked to intense snowfall events (Gorodetskaya et al., 2014), a temperature record at the Antarctic Peninsula (Bozkurt et al., 2018) and major surface melt events in West Antarctica (Wille et al 2019). On the Antarctic Peninsula, the surface mass balance can be especially sensitive to AR events during summer, when surface temperatures vary around zero and frequent transitions occur between snow and rainfall. We use radiosonde, cloud and precipitation measurements, along with reanalysis products, to investigate the spatial and vertical structure of the ARs and impact on precipitation at the Antarctic Peninsula. The data from two Year of Polar Prediction endorsed projects are used - the Characterization of the Antarctic Atmosphere and Low Clouds (CAALC) project at King George Island and the Dynamics, Aerosol, Cloud, And Precipitation Observations in the Pristine Environment of the Southern OCEAN (DACAPO-PESO) project in Punta Arenas. We present case studies characterizing the temporal evolution of ARs, focusing on thermodynamic and dynamic conditions, and cloud microphysical properties, accompanying the transition between snowfall and rain. We also show the added value of increased frequency in radiosonde observations in improving the forecast of weather conditions during ARs, particularly precipitation, which have important consequences for air, ship and station operations in Antarctica.