Increasing Greenland Melt and Blocking in Recent Decades Modulated by Large-Scale and Regional Circulation Changes

A shift towards increased melt over the Greenland Ice Sheet (GrIS) has been linked with a higher frequency of high pressure blocking events over the ice sheet since the mid-1990s. During the same period, the North Atlantic subpolar gyre underwent a shift towards increased heat content and warmer sea surface temperatures.  Various observational and reanalysis products, as well as output from the Modèle Atmosphérique Régional (MAR) coupled land-atmosphere regional climate model, are used to assess these changes in the extratropical North Atlantic region.  Using composite analysis during years with extreme GrIS melt, we investigate the contribution of atmospheric and oceanographic conditions to ice sheet variability in recent decades.  Extreme melt and blocking conditions over Greenland are associated with a weakened jet stream, enhanced northward winds over the southwest GrIS, and anomalously warm sea surface temperatures in the North Atlantic subpolar gyre on the regional scale.  On a hemispheric scale, heightened blocking over Greenland during high melt years is part of an enhancement of the three climatological blocking centers in the Northern Hemisphere.  Changes in the lead-lag relationship between different atmospheric and oceanic variables over the region suggest changes in the ocean-atmosphere system over recent decades, with implications for enhanced GrIS melt.  This research links increasing GrIS meltwater production to large-scale and regional circulation changes and distinguishes the importance of each component before and after the mid-1990s.