Previous work by the authors documented the regional variations in the wintertime climate of the Arctic and their relationships to upper air structure and processes controlling the surface energy budget. The present study extends this analysis to the period of autumnal cooling, with an emphasis on the role played by standing and transient eddies.
The analysis uses the NCAR/NCEP and NASA/GEOS-1 reanalyses to specify tropospheric structures and sensible heat fluxes, and the Arctic Ocean Radiative Flux (AORF) data set to specify surface temperatures and radiative fluxes, for the period 1985 through 1996. Composites are formed to illustrate the typical character of the cooling in the fall.
The western Arctic tends to be cooler than the eastern Arctic in early winter. This can be attributed largely due to an earlier onset to the period of the rapid cooling in the western Arctic, rather than systematic differences in the typical rate of cooling. The net radiative heat flux lost to space is comparable over the entire Arctic, so it is the standing and transient eddies that account for longitudinal asymmetries in the cooling. Both types of eddies act to warm the Arctic in the mean and hence mitigate the radiative cooling. The transient eddies appear to be especially important for delaying the cooling in the eastern Arctic. Over the North Atlantic/Barents Sea, these transients are associated with storms featuring substantial sensible and latent heat fluxes at the sea surface and enhanced downward longwave radiative fluxes from clouds. The relatively warm conditions in the east Arctic north of Asia are maintained by the convergence of the horizontal heat transports with these eddies/storms as they propagate eastward and decay.