Mechanisms for the variation of sea ice extent in the northern hemisphere

Abstract

Using daily sea ice data derived from satellite‐borne sensors and atmospheric data, we examined processes controlling the variation of sea ice extent in the Northern Hemisphere. The daily ice motion field was computed from imagery of the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSM/I) for seven winters (December to April) from 1991/1992 to 1997/1998, by employing the maximum cross‐correlation method. In order to examine mechanisms of the temporal variation of the ice extent, we analyzed 50 specified lines across the daily ice edge. Although a high correlation between the ice motion and the geostrophic wind speed was observed in all the ice edge areas, the degree for correlation between the speed of the ice edge displacement and the wind speed varied with region. The degree for response of the ice edge speed to the wind speed largely depended upon that of the ice edge speed to the ice motion. The following mechanisms controlling the variation of ice extent for regions in the Northern Hemisphere were anticipated. In the Barents Sea, Bering Sea, and the Sea of Okhotsk the ice extent advances by wind‐driven ice advection and the daily scale variation of the ice extent were also controlled by the variation in wind speed. In contrast, the ice extent in the Labrador Sea and the Greenland Sea seemed to be considerably affected by oceanographic factors such as the location of the thermal front and was not related to the variation in wind speed. The regional difference of the variation mechanism was also reflected in the interannual variation in maximum ice extent.