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

Abstract

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 are mostly 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 geopotential 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 frequency modifications.

Spatio-Temporal Linkages between Declining Arctic Sea-Ice Extent and Increasing Wildfire Activity in the Western United States

“…In turn, ASIE and the strength of the polar vortex have been linked [5,6], with some of the most noticeable impacts experienced as anomalously cold winter conditions in the eastern North American mid-latitudes [2] and western North American anticyclogenesis [7,8]. However, warm-season impacts associated with increased meridionality and persistence also occur [9][10][11], including more frequent ridging (i.e., higher atmospheric pressure) over the Pacific Northwest and Northern Rockies regions of the coterminous U.S.…”

“…Our understanding of the processes is constantly evolving (e.g., [13,14]) with recent research suggesting that, among others, ASIE is potentially a controlling factor or interacts with (1) the Atlantic multidecadal oscillation (AMO; [14]); (2) the NAO [13,15]; (3) the western Pacific pattern (WP) and El Nino Southern Oscillation (ENSO; [15]); (4) declining summertime total kinetic energy and zonal flow [16]; (5) the Pacific Decadal Oscillation (PDO; [17]); (6) surface temperature extremes [10]; and (7) surface precipitation extremes [18,19]. An example of the evolution of our understanding of the linkages includes studies [13,20], which found that contrary to earlier work based on empirical data [2,5], model simulations show that lower levels of ASIE are associated with reductions in wintertime cold events in Northern Europe, not increases in these events.…”

Connections between north‐central United States summer hydroclimatology and Arctic sea ice variability

“…From a hemispheric perspective (Figure (a) and (b)), low ice summers are also characterised by the presence of anticyclonic flow over the Arctic and cyclonic flow over large sections of the extratropical Atlantic, resembling the negative phase of the NAO (Hurrell, ). The spatial correlation between the canonical summer NAO and Figure (a) is −0.71, a value statistically significant at the 95% confidence level (Budikova and Chechi, ). One important source of discrepancy between the NAO and Figure (a) are the positive height anomalies over the Arctic and western Greenland that extend toward the eastern United States, which likely stem from anomalous ocean‐atmosphere heat fluxes (Liu et al ., ).…”

“…Parallel analyses at the 200 hPa level (not shown) reveal similar geographic patterns of atmospheric flow over the NA continent, but with larger anomalies of similar sign. These atmospheric conditions reflect a potential barotropic response in agreement with Tang et al ., () and Budikova and Chechi (). Examination of the jet‐level (300 hPa) vector wind fields over North America (Figure (a) and (b)) suggest increased meridional jet flow around a low pressure system and increased wind speeds to the west of the study area, while a slower‐than‐expected wind pattern is found around an upper‐level ridge positioned over the eastern sections of the continent.…”

“…Overall, summer atmospheric warming and the potential for increased incidences of extreme heat waves across large portions of the central and eastern North American continent also have been reported by others including Tang et al . (), Francis and Vavrus (), and Budikova and Chechi ().…”