Circulation and surface controls on the lower tropospheric air temperature field of the Arctic

摘要

Characteristics of the 925 hPa Arctic air temperature field are evaluated with respect to controls by horizontal temperature advection, vertical motion, and characteristics of the underlying land and ocean surface. The highest winter mean temperatures in the Arctic, found in the Norwegian and Barents seas, are maintained primarily by cold horizontal advection countered by diabatic heating, the latter linked to open ocean waters. By comparison, temperatures over the central Arctic Ocean are primarily maintained by warm advection and diabatic cooling. Depending on the region, vertical motion opposes (notably off the east coast of Greenland) or reinforces forcing by advection. For summer, cold advection over snow-free land is countered by diabatic warming. This contrasts sharply with the Arctic Ocean, where warm advection and (locally) downward vertical motion combine to oppose pronounced diabatic cooling, the latter linked to surface melt and heat uptake in the ocean mixed layer. Prominent temperature anomalies in all seasons accompany onshore and offshore flow. For example, summer northerlies, blowing off the Arctic Ocean, yield cold anomalies over northern Eurasia extending far inland from the coast. While onshore winter westerlies yield above-average temperatures over northwestern Eurasia and the Barents and Kara seas, easterlies yield cold anomalies in the same regions. The most recent decade (2000-2009) has seen positive temperature anomalies over most of the Arctic for northerlies, easterlies, southerlies, and westerlies and for all seasons. Influences of recent shifts in atmospheric circulation, reduced sea ice extent, and rising sea surface temperature are prominent, especially for winter and autumn.