Non-annular response of sea ice cover in the Indian sector of the Antarctic during extreme SAM events
This study investigates the impact of wind-induced sea ice drift on sea ice cover over the Indian Ocean sector of the Southern Ocean (IOS) in the contrasting Southern Annular Mode (SAM) years during a summer (February) and a winter (July) month. Analysis of reanalysis wind shows that during positive SAM events, westerlies show stronger and more zonal flow over the west IOS (west of 45°E), while a stronger northerly component is seen over the east IOS, to the south of 55°S during both February and July. This is attributed to the zonally asymmetric feature of sea level pressure over the IOS. A coupled ocean–sea ice model was forced with dynamical wind forcing for positive and negative SAM events during above months. The zonal contrast as seen in wind and surface current is transferred to the sea ice drift. A stronger zonal eastward sea ice drift is apparent over the west IOS, suggesting increased transport of sea ice from the Weddell Sea region in July. The eastward advection of sea ice results in piling of sea ice over west IOS and causes an increase in sea ice concentration and thickness. Over east IOS, the sea ice drift shows a strong southeastward anomaly from the sea ice edge towards the coast. This results in a piling of sea ice near the coast and a divergence of sea ice near the edge. This results in a negative anomaly in sea ice concentration and sea ice thickness over east IOS. Thus, the dynamical SAM forcing leads to a non-annular response in sea ice cover over the IOS.