Distribution and Characteristics of Mesoscale Cyclones in the Antarctic: Ross Sea Eastward to the Weddell Sea*

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Abstract
The mesoscale cyclone activity observed in the portion of Antarctica that faces the South Pacific Ocean and Weddell Sea area is summarized from a study of 1991. In general, area-normalized results reveal much greater mesoscale cyclonic activity over the Ross Sea/Ross Ice Shelf and southern Marie Byrd Land than on both sides of the Antarctic Peninsula. More than 50% of the observed mesoscale vortices are of the comma cloud type. The average diameter of mesoscale vortices is approximately 200 km near Terra Nova Bay, 270 km near Byrd Glacier, and 280 km near Siple Coast. Near the Antarctic Peninsula, the average diameter is about 370 km over the Bellingshausen Sea and 380 km on the Weddell Sea side. The largest percentage of deep vortices occurs over the Bellingshausen Sea sector (38% of all cases), where convective instability frequently occurs. Over the Ross Sea/Ross Ice Shelf and Weddell Sea sectors the majority of the mesoscale vortices are low cloud features that probably do not exceed the 700-... Abstract The mesoscale cyclone activity observed in the portion of Antarctica that faces the South Pacific Ocean and Weddell Sea area is summarized from a study of 1991. In general, area-normalized results reveal much greater mesoscale cyclonic activity over the Ross Sea/Ross Ice Shelf and southern Marie Byrd Land than on both sides of the Antarctic Peninsula. More than 50% of the observed mesoscale vortices are of the comma cloud type. The average diameter of mesoscale vortices is approximately 200 km near Terra Nova Bay, 270 km near Byrd Glacier, and 280 km near Siple Coast. Near the Antarctic Peninsula, the average diameter is about 370 km over the Bellingshausen Sea and 380 km on the Weddell Sea side. The largest percentage of deep vortices occurs over the Bellingshausen Sea sector (38% of all cases), where convective instability frequently occurs. Over the Ross Sea/Ross Ice Shelf and Weddell Sea sectors the majority of the mesoscale vortices are low cloud features that probably do not exceed the 700-...