THE ARCTIC CIRCULATION IN SUMMER

Abstract

On the basis of a number of synoptic and synoptical-climatological studies, the following picture of the arctic circulation in summer is presented. A secondary baroclinic zone, distinct from the polar front, develops along the northern shores of Siberia, Alaska and Canada. Cyclones which originate in this zone, and to a lesser extent in the polar frontal zones to the south, frequently invade the central Arctic. The stagnation of these lows near the pole leads to a high frequency of occurrence of low pressure centers and a weak area of low pressure in the mean. There is no evidence for the often assumed semi-permanent anticyclone near the pole. Anticyclones are most frequent in the belt between 70N and 75N, favored locations being central Greenland and the area about the Beaufort Sea. The disturbances of the polar region in summer are shown to be similar to typical middle-latitude storm systems. An example of a typical baroclinic wave development is discussed, a cross section through a high-latitude frontal zone and associated jet stream is presented, composite cloud distributions in arctic weather systems are shown, and the results of a series of dynamical predictions for the area north of 60 deg are compared with similar results for middle latitudes. The question of the representativeness of the present results, which were based entirely on data for the five summers, 1952 to 1956, is considered, and it is concluded that the characteristics of the circulation during these summers were not significantly different than during a number of years, dating back to 1894, for which expedition data were available.