Extreme Daily Precipitation Events in Spitzbergen: A High Arctic Island

Abstract:

Daily station records and output from the MERRA atmospheric reanalysis are used to examine the characteristics of extreme daily precipitation events in Spitzbergen. Spitzbergen is the largest island of the Svalbard Archipelago, located between about 77-79^oN in the northern North Atlantic. The region is frequently influenced by strong extratropical cyclones associated with the North Atlantic Cyclone track and (in winter) pronounced regional baroclinicity due to proximity to the sea ice margin. Despite the stronger cyclone activity in winter, extreme daily precipitation events, defined as those of at least 25 mm, can occur year round. Based on composite analysis, the average pattern associated with extremes has the island influenced by a strong trough of low sea level pressure extending from the southwest, unusually strong southerly winds in troposphere, positive anomalies in precipitable water and pronounced upward motion (negative omega) at 500 hPa. This is linked aloft to positive anomalies in 500 hPa height over the Barents Sea and negative anomalies over Greenland. The mean pattern for summer-only events is similar. 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. Several of the largest precipitation events can be associated with “atmospheric rivers” seen as narrow corridors of strong positive anomalies in precipitable water extending thousands of kilometers south into the subtropical Atlantic. Reflecting local topography, large precipitation events at one of the Spitsbergen sites are typically not well represented at others, a notable exception being the two-day event of 29-30 January, 2012, which appears to be clearly linked to an atmospheric river and is examined as a case study.