Antarctic Atmospheric River Climatology and Impacts

The mass balance of Antarctica is sensitive to intrusions of extremely warm, moist airmasses from the mid-latitudes in the form of atmospheric rivers (ARs). These storms provide a sub-tropical link to the Antarctic continent and are very consequential to the mass balance of the ice sheet. Using an AR detection algorithm designed for Antarctica and regional climate simulations from MAR, we created a climatology of AR occurrence and their associated impacts on surface melt, ice shelf stability, and snowfall.

Despite their rarity of occurrence over Antarctica (maximum frequency of ~1.5% over a given point), ARs have a relatively large impact on the surface melt processes in West Antarctica and snowfall patterns of East Antarctica. In West Antarctica, AR landfalls and their associated radiative flux anomalies and foehn winds accounted for around 40% of the total summer surface melt on the Ross Ice Shelf (approaching 100% at higher elevations in Marie Byrd Land) and 40-80% of total winter surface melt on the ice shelves along the Antarctic Peninsula from 1979-2017. During the summer season along the Larsen ice shelves, ARs contribute less to the total surface melt, but cause 60-80% of the most intense melt, runoff, and high temperature extremes. Through a combination of melt pond formation and subsequent hydrofracturing initiated by leeward Foehn winds and radiative fluxes, and sea ice disintegration that allows swells to stress the ice shelf margins, ARs can destabilize the leeward ice shelves. Intense AR landfalls coincided with the collapse of the Larsen A in January 1995 and the Larsen B in the summer of 2002.

In East Antarctica, ARs are responsible for 20-30% of snowfall and a majority of the heaviest precipitation events with ramifications for past climate reconstruction using ice cores. Despite ARs having a modest impact on total precipitation, annual snowfall trends across East Antarctic were primarily driven by trends in AR frequency while ARs controlled the inter-annual variability of precipitation across most of the Antarctic ice sheet from 1980-2018.

Our results suggest that atmospheric rivers play a significant role in the Antarctic surface mass balance. Thus any future changes in atmospheric blocking or tropical-polar teleconnections, which control AR behavior around Antarctica, may have significant impacts on future surface mass balance projections and subsequent sea level changes.