Arctic sea ice and warm season North American extreme surface air temperatures

A growing amount of evidence points to a notable linkage between the changing Arctic cryosphere and weather in the middle latitudes of the Northern Hemisphere. Recent studies propose a series of mechanisms that make plausible the connection between Arctic amplification/ sea ice decline and extreme weather. Using composite analyses, this study examines associations between the frequency of occurrence of boreal summer daily extreme surface air temperatures across North America and simultaneous mean Arctic sea ice concentration (SIC) conditions during the period 1979-2013. Four distinct regions show coherent relationships including large sections of the eastern USA, Canada and the Canadian Arctic, central North America, southeast USA, and the west coast from southern Canada to Alaska. Across the eastern USA and Canada, as well as in western North America, the connections are principally shaped by low ice conditions with an expected decline in the incidence of cool nights/ days and an increase in the incidence of warm nights/ days. The ice-temperature relationships observed in the other regions aremostly shaped by high ice conditions. Synoptic analyses indicate the associations to be reflected in mean summer surface air temperature (SAT) and surface anomaly flows, as well as in the 500 and 200 hPa geo potential height flow and mean zonal wind anomaly patterns. Areas with the greatest atmospheric flow modifications have been generally associated with regions that display most notable extreme temperature frequencymodifications.