Extreme daily precipitation events at Spitsbergen, an Arctic Island

Abstract

ABSTRACTDaily station records and output from the MERRA atmospheric reanalysis for the period 1979 onwards are used to examine extreme daily precipitation events at Ny Ålesund and three other sites located on Spitsbergen. Spitsbergen, lying between 77°N and 80°N, is the largest island of the Svalbard Archipelago. The region is frequently influenced by extratropical cyclones associated with the North Atlantic cyclone track and (in winter) regional baroclinicity due to proximity to the sea ice margin. Despite the stronger cyclone activity in winter, extreme precipitation events at Ny Ålesund, defined as those in the top 1% of the statistical distribution, can occur year round. On the basis of a composite analysis, extreme events tend to occur when the region is influenced by a trough of low sea level pressure extending from the southwest, southerly winds in the troposphere, positive anomalies in precipitable water, and pronounced upward motion (negative omega) at 500 hPa. This is linked to positive anomalies in 500 hPa heights over the Barents Sea and negative anomalies over Greenland. While individual extreme events do not share all of these characteristics, strong southerly flow and positive anomalies in precipitable water provide a near common thread. Reflecting local topography, extremes at Ny Ålesund are typically not well represented at other stations on the island, but there are notable exceptions. Some of the largest precipitation events can be associated with features resembling ‘atmospheric rivers’, seen as narrow corridors of pronounced positive anomalies in precipitable water extending thousands of kilometres south into the subtropical Atlantic. There is no systematic pattern of temporal trends in the frequency or magnitude of extremes.