Variations in Antarctic sea ice conditions and relationships with Southern Hemisphere cyclonic activity, winters 1973-77

Interannual variations in the extent of Antarctic sea ice are investigated for the winter growth season (June through September) for the five years 1973-77. Statistical correlations between the synoptic-scale atmospheric circulation, given by the frequencies of satellite-observed extratropical depressions, and the latitudinal extent of the ice are evaluated on hemispheric and regional scales for each winter. Marked differences in winter cyclone activity accompany the year-to-year variations in ice growth and extent on a zonally-averaged basis, and are particularly evident for the extreme ice winters of 1973 and 1977. A link between the expansion of the sea ice zone during winter and the frequencies of new cyclonic developments (cyclogenesis) is evident for latitudes immediately north of the ice-ocean boundary. Three key regions of high interannual variability in ice conditions are identified and examined statistically for ice-cyclone interactions. Correlations between ice-edge latitude and cyclone frequencies show least variation between years in the East Antarctic sector, emphasizing the role of the semi-permanent low pressure center in the winter ice regime of this region. Conversely, ice-cyclone correlations vary markedly from year-to-year in the Weddell Sea, where ocean-related ice advection patterns are of additional significance. Case studies from the five-winter period are used to support the statistical results obtained for each sector.