Case Study of a 2015 Atmospheric River Impacting East Antarctica

Atmospheric Rivers (ARs) are defined as narrow filaments of enhanced water vapor transport in the atmosphere. They contribute significantly to the annual snowfall over Antarctica and are important for understanding the Antarctic Ice Sheet (AIS) mass balance. Though the AIS experienced net mass loss between 2002-2023, some areas of the AIS, such as coastal Dronning Maud Land, saw an increase in mass. Investigating ARs is important for understanding these local increases, which can help offset the AIS’s decay.

In this study, we investigate the main synoptic-scale drivers of an AR event that impacted coastal Dronning Maud Land on Jan. 16–17, 2015 using MERRA-2 reanalysis data and the NOAA HYSPLIT Trajectory Model. This event ranks in the top 7% of Antarctic AR event precipitation from 1980-2019 despite only lasting 1 day. We find that the midlatitude cyclone associated with the AR event developed due to the favorable positioning of upper-level divergence induced by two jet streaks above the cyclone center. This cyclone was able to reach the Antarctic coast because a blocking high-pressure system prevented the cyclone from moving west to east. The resulting near-surface circulation pattern funneled moisture within the AR from the midlatitudes towards Antarctica along the cyclone’s warm conveyer belt. A model sounding taken in the AR at 18Z on Jan. 16 revealed that there was potential instability in the AR, which likely enhanced the lift and precipitation associated with the event. Our results reaffirm the importance of large-scale moisture transport and the presence of a blocking high for severe AR events impacting Antarctica. We also highlight the role of jet streaks and potential instability in modulating AR-related precipitation during this event.