CLIMATOLOGICAL ASPECTS OF CYCLONE DEVELOPMENT AND DECAY IN THE ARCTIC

Climatological aspects of Arctic cyclones are examined for winter and summer over a 20-year (1973-1992) period. The primary objective is to characterize patterns of cyclone distribution examined in previous studies in terms of cyclone sea level pressure tendency (SLPT), maximum deepening rates and the frequency of cyclogenesis and cyclolysis. Results rely on output from a system detection and tracking algorithm applied to twice-daily National Meteorological Center sea level pressure fields. Winter peaks in cyclonic activity off the east coast of southern Greenland, over the Norwegian and Kara seas, Baffin Bay/Davis Strait, and south of Baffin Island are in general associated with frequent cyclogenesis and cyclolysis. The Atlantic side of the Arctic is the most synoptically active, characterized by a more frequent occurrence of deepening and larger mean latitude-adjusted maximum deepening rates, peaking at -6.8 mb (12 h(-1) for the Greenland Sea/N. Atlantic sector. Average adjusted maximum deepening rates over continental areas and the ice-covered Arctic Ocean are less than -2 mb (12 h(-1)). The synoptically-active Atlantic Arctic is reflected in positive departures from zonal symmetry of mean 500-mb cyclonic vorticity advection, illustrating the stronger dynamical support along the North Atlantic cyclone track. Although mean maximum deepening rates for summer over continental regions and the Arctic Ocean are slightly greater than for winter they decline elsewhere, with this change most pronounced for the Greenland Sea/N. Atlantic. This is reflected aloft in a decrease in the magnitude of 500-mb cyclonic vorticity advection. Cyclolysis now dominates the Atlantic side of the Arctic. By contrast, events of cyclogenesis and cyclolysis increase sharply over land especially over Eurasia, contributing to local cyclone frequency maxima. A distinct summer cyclone maximum over the Arctic Ocean is confirmed as a region of essentially cyclolysis only, associated with the decay of systems migrating from the Eurasian coast as well as along the weaker North Atlantic track.