Investigations of the seasonally oscillating sea-ice edge over the Southern Ocean based on Oceansat-1 MSMR and QuikSCAT observations

摘要

Characterising and understanding the variability of polar sea ice cover at different time scales is fundamental to our understanding of role of polar regions in global climate change. The large expanse of seasonally oscillating sea-ice cover around Antarctica is physically bounded by the continent on its poleward boundary and dynamically on its equatorward boundary by the strong Antarctic Circumpolar Current. This paper attempts to investigate the seasonal migration of the sea ice edge over the southern ocean between these two extremities, on a monthly scale using data from MSMR - the passive multi-frequency scanning microwave radiometer system onboard Oceansat-1. The location of sea ice edge is derived from weekly averaged MSMR 18- GH_z H-polarisation channel brightness temperature images. Simultaneously available sea-ice information from SSM/I is used to validate the MSMR derived sea-ice parameters and to arrive at a brightness temperature threshold of 130 K to distinguish between sea ice and open water. It is observed that the amplitude of seasonal summer-to-winter N-S traverse of sea ice ranges from a few degrees of latitude to as much as about 15 degrees of latitude in different sectors of the southern Ocean around Antarctica. These amplitudes are largest over the Weddell Sea and Ross Sea regions. Further, the monthly rates of this migration show a non-uniform and oscillatory behaviour over the year and reach as high as 8-10 degrees of latitude per month just prior to the approach of summer and winter conditions. The observed seasonal variability shows connectivity to the behaviour of sea-ice edge over longer time scales. These observations have important implications for sea-ice interaction with climate.Recently, we have also embarked on use of higher-resolution active microwave scatterometer data from QuikSCAT to delineate the sea-ice edge more precisely. Preliminary results of these investigations are included.