Extreme intra-seasonal anomalies in the Amundsen and Bellingshausen sea-ice area, Antarctica, during the austral winter

Abstract

We examine the role of the propagation of atmospheric mid-latitudes wave trains in modulating the Amundsen and Bellingshausen sea-ice area (SIA), Antarctica, on intra-seasonal timescales (20-100 days). Spectral analysis of passive microwave estimates of SIA in the Amundsen and Bellingshausen Seas for 1979-2004 shows significant peaks on intra-seasonal timescales. Previous studies have suggested that variations in SIA are linked to disturbances in atmospheric circulation and sea surface temperature. We show that extreme SIA anomalies on intra-seasonal timescales lag the propagation of subtropical wave trains in the Southern Hemisphere by approximately 10-15 days. The sign of the SIA anomaly depends on the phase of the wave. We present evidence that the number of disturbances that cause extreme anomalies of SIA on intra-seasonal timescales has increased in the last 14 years.