Large-Scale Variations in Observed Antarctic Sea Ice Extent and Associated Atmospheric Circulation

Abstract

The 1974 3-day averaged sea ice extent data for the Southern Ocean determined from the Electrically Scanning Microwave Radiometer aboard Nimbus 5 have been compared with 1000 mb temperature and sea level pressure fields from the Southern Hemisphere meteorological data set of the Australian Bureau of Meteorology. A Fourier decomposition of each of these variables defines the dominant spatial scales during the course of the year. The first three harmonics are sufficient to explain most of the variance of the ice extent and temperature for any 3-day period during the year, with the pressure field generally requiring at least the first four. Three case studies are presented to illustrate ice/atmosphere associations for different times of the year. For the period mid-March through mid-May a correspondence is found between the phase of harmonic 2 in sea level pressure and regions of rapid ice growth. During a 2-week period in September, the month of maximum ice extent, the location of the circumpolar trough was further poleward than in the earlier period, consistent with its semiannual migration. This resulted in a generally strong circumpolar flow in the vicinity of the ice margin with the largest observed changes in the location of the ice edge associated with the circulation pattern in the region of the Ross Sea. Weaker correspondences occur during the time of ice decay, January and December, and are attributed to the more equatorward position of the circumpolar trough and to oceanic influences. The results demonstrate an ice/atmosphere coupling of varying strength throughout the year on time scales ranging from weeks to months and on space scales ranging from synoptic to planetary.