On the formation of coastal polynyas in the area of Commonwealth Bay, Eastern Antarctica

Antarctica's King George V Land and Adélie Land were first explored by Sir Douglas Mawson and his party during their 1911–1913 expedition. They were astounded by the strength of the katabatic wind, which is so dominant in this area. These strong offshore winds can move the sea ice away from shore, forming coastal polynya, not only in summer but even in midwinter. Poor visibility due to darkness and frequently occurring blowing snow make the study of these polynyas from land-based observations difficult. Recently, coverage of this area by synthetic aperture radar (SAR) satellite imagery, which has a high resolution of 40 m (pixel size 12.5 m), gave additional insight into the characteristics of these polynyas. This high resolution is needed because the width of the polynya is small (10 km or so). Furthermore, of special importance is the fact that SAR data can be obtained during darkness and overcast conditions. Following original Russian work, we modified a simple model for wind-driven coastal polynyas, using actual meteorological data from our coastal automatic weather stations as input. Using mean monthly data for the stations, we show that coastal polynyas are to be expected in the windiest area (Cape Denison-Port Martin); while to the west (Dumont d'Urville) and east (Penguin Point), the average conditions do not produce them. Here, they occur only during strong and long-lasting storms. Our observational data of the polynyas as viewed from SAR and advanced very high resolution radiometer (AVHRR) confirm these findings.