Anomalous peak in Antarctic sea-ice area, winter 1998, coincident with ENSO

Abstract

The results of an updated satellite analysis of hemispheric and regional Antarctic sea-ice cover are presented based on October 1987-September I999 Special Sensor Microwave/Imager (SSM/I) data. These show an ongoing slight but significant hemispheric increase of 3.7(±0.3)% in extent and 6.6(±1.5)% in area. In the two principal sectors, Weddell Sea ice extent (area) decreased by 3.4(±1.0) (3.9(±4.6)) % and Ross Sea ice extent (area) increased by 10.9(±1.0) (18.3(±4.6))%. Hemispheric, Ross Sea and Western Pacific Ocean ice peaks in September 1998 were anomalously high, and may have been related to atmospheric and oceanic anomalies in the Pacific Ocean and beyond associated with that year's exceptionally strong ENSO. Preliminary comparison of Antarctic sea-ice-concentration data with European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses fields suggests that the unusually extensive sea ice in winter 1998 was concomitant with an equatorward shift of the circumpolar westerly surface winds over the southern Pacific Ocean.