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Jennifer Miletta Adams
,
Nicholas A. Bond
, and
James E. Overland

Abstract

In the Arctic atmosphere, the fall cooling cycle involves the evolution of the zonally symmetric circulation in late summer into the asymmetric flow of winter. This paper uses historical reanalysis data to document how the dominant components of the Arctic heat budget influence the summer–winter transition. The spatial variability of 20-yr climatologies of 700-mb temperature and geopotential height, the net surface flux, and the horizontal convergence of eddy sensible heat fluxes are examined for September through February.

The development of the zonal asymmetries in the temperature and geopotential height fields in the Arctic is linked to the land–water–ice distribution that regulates the surface fluxes and the baroclinic zones in the hemispheric circulation, which lead to regional heating/cooling by the transient and standing eddies. These eddies serve to transport the heat energy gained via the surface fluxes over the North Atlantic and North Pacific to the continental and ice-covered regions of the central Arctic, where the net surface flux is small. The transient eddies are especially important in the Atlantic and Eurasian sectors of the Arctic, while the standing eddies play the larger role in the heat budget on the Pacific side of the Arctic in early to mid-winter.

The Arctic oscillation (AO) has a small effect on the basinwide pattern of heating and cooling by the eddy circulations, but on smaller spatial scales there are isolated regions where the AO influences the Arctic heat budget.

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James E. Overland
,
Jennifer Miletta Adams
, and
Nicholas A. Bond

Abstract

The surface temperature field in the Arctic winter is primarily controlled by downward longwave radiation, which is determined by local atmospheric temperature and humidity profiles and the presence of clouds. The authors show that regional differences in the atmospheric thermal energy budget are related to the tropospheric circulation in the Arctic. Data sources include several gridded meteorological datasets and surface and rawinsonde observational data. Four independent climatologies of mean January surface temperature show consistent spatial patterns: coldest temperatures in the western Arctic north of Canada and warmer regions in the Chukchi, Greenland, and Barents Seas. Data from the five winters of 1986–90 illustrate the coupling between the surface temperature, the downward longwave radiative fields, and the tropospheric temperature and humidity fields, with monthly surface–upper-air correlations on the order of 0.6. Upper-level circulation patterns reveal features similar to the surface temperature fields, notably a persistent low center located over northern Canada; the cyclonic flow around the low is a tropospheric extension of the polar vortex. Colder and drier conditions are maintained within the vortex and communicated to the surface through radiative processes. The polar vortex also steers transient weather systems, the most important mechanism for horizontal heat transport, into the eastern Arctic, which results in as much as 25 W m−2 more heat flux into the eastern Arctic than the western Arctic. A reason for the colder temperatures in the western Arctic is that the polar vortex tends to be situated downstream of the northern Rocky Mountains; this preferred location is related to orographic forcing of planetary waves. Monthly and interannual variability of winter temperatures is conditioned by the interaction of the Arctic and midlatitude circulations through the strength and position of the polar vortex.

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