Major West Antarctic Surface Melt Event in January 2016 in Wake of Strong El Niño

In December 2015, two important ingredients seemed to be present to produce above-average summer snowmelt in West Antarctica. First, one of the strongest El Niño events on record was reaching its peak intensity in the Tropical Pacific, and its typical teleconnection pattern (high pressure anomalies) was forming in the South Pacific. If this pattern were to move far enough south, it could lead to warm air advection toward the Ross Ice Shelf area. This in turn could raise surface temperatures over many low-lying areas enough for them to reach the melting point. The second ingredient was at higher latitudes: the daily Southern Annular Mode (SAM) Index was oscillating between weakly positive and negative values. In other words, the El Niño Southern Oscillation (ENSO) and the SAM were close to being “in phase” (i.e., El Niño-like conditions coinciding with a low-polarity SAM). It is generally under these conditions that the ENSO teleconnection has the greatest impact on the climate of West Antarctica. Yet December remained largely uneventful: passive microwave satellite observations revealed no unusual surface melt in the area. As 2015 was coming to an end, the SAM Index had switched to large positive values indicative of unusually strong circumpolar westerly winds, unfavorable to melting conditions in West Antarctica. Things abruptly changed on January 10, 2016 when a strong stationary pressure ridge over the Amundsen-Bellingshausen Seas began steering warm offshore air toward Marie Byrd Land and the Ross Ice Shelf. This warm episode persisted for about three weeks, during which most areas below 1000 m in the Ross Ice Shelf sector of West Antarctica experienced surface melting at one point, according to satellite data. In the end, both in terms of duration and areal extent, this melt event was one of the most prominent observed since the beginning of the satellite record in 1978. In this presentation, I will describe how the melt event unfolded, discuss the synoptic weather conditions surrounding the event and the role played by El Niño and the SAM, and will place it in the context of previous major melt events.