Warmer and Wetter Winters over the high-latitude North Atlantic : an atmospheric circulation perspective

• Published in: Quarterly Journal of the Royal Meteorological Society
• Main Author: Wickström, Siiri
• Other Authors: orcid:0000-0003-3650-844X
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Bergen 2020
• Subjects: Arctic; Barents Sea; Svalbard; Svalbard Archipelago; North Atlantic; Sea ice
• Online Access: https://hdl.handle.net/1956/22191

The high-latitude North Atlantic -especially the Svalbard archipelago and its surrounding seas - has undergone remarkable changes in the last half-century. These regions are recognized as a hotspot of the Arctic Amplification, referring to the faster warming rates in the Arctic when compared to lower latitudes, manifested in the form of rapid warming and sea ice loss. The most pronounced changes occur in winter, when the sun remains below the horizon, and heat transport from lower latitudes in both atmosphere and ocean is the main energy source. The relationship between atmospheric circulation changes and the AA is not fully understood, and there are knowledge-gaps in particular on the regional scale. This thesis is motivated by the wish to quantify cyclone track changes and increase the knowledge of their role in the documented rapid temperature increases in Svalbard and the sea ice losses in north and east of this archipelago. We utilized an automated cyclone tracking algorithm to create a seasonal cyclone climatology for the high-latitude North Atlantic in the period 1979-2016 based on the mean sea-level pressure from the reanalysis product ERA-Interim from the European Centre of Medium-Range Weather Forecasts (ECMWF). When calculating the trends over this period we find an increase of cyclone densities around Svalbard and a corresponding decrease in the southeastern Barents Sea of a magnitude (+/- 3 cyclones/winter per decade). Based on composite analysis, we find that these changes are in line with a trend towards warmer and wetter winter conditions in the northern Barents Sea and over Svalbard. The opposing trends, i.e. no significant changes in cyclogenesis and an increase in local baroclinicity north of Svalbard, all speak for a shift towards a more meridional winter cyclone track in the seas around Svalbard. To advance the understanding of local 2-m air temperature and precipitation sensitivity to atmospheric circulation in the recent climate, with more winter cyclones around Svalbard, we studied the ...