Climatological Aspects of Mesoscale Cyclogenesis over the Ross Sea and Ross Ice Shelf Regions of Antarctica

Abstract

A one-year (1988) statistical study of mesoscale cyclogenesis near Terra Nova Bay and Byrd Glacier. Antarctica, was conducted using high-resolution digital satellite imagery and automatic weather station data. Results indicate that on average two (one) mesoscale cyclones form near Terra Nova Bay (Byrd Glacier) each week, confirming these two locations as mesoscale cyclogenesis areas. The maximum (minimum) weekly frequency of mesoscale cyclones occurred during the summer (winter). The satellite survey of mesoscale vortices was extended over the Ross Sea and Ross Ice Shelf. Results suggest southern Maric Byrd Land as another area of mesoscale cyclone formation. Also, frequent mesoscale cyclonic activity was noted over the Ross Sea and Ross Ice Shelf, where, on average, six and three mesoscale vortices were observed each week, respectively, with maximum (minimum) frequency during summer (winter) in both regions. The majority (70%?80%) of the vortices were of comma-cloud type and were shallow. Only around 10% of the vortices near Terra Nova Bay and Byrd Glacier were classified as deep vortices, while over the Ross Sea and Ross Ice Shelf around 20% were found to be deep. The average large-scale pattern associated with cyclogenesis days near Terra Nova Bay suggests a slight decrease in the sea level pressure and 5OO-hPa geopotential height to the northwest of this area with respect to the annual average. This may be an indication of the average position of synoptic-scale cyclones entering the Ross Sea region. Comparison with a similar study but for 1984-85 shows that the overall mesoscale cyclogenesis activity was similar during the three years, but 1985 was found to be the year with greater occurrence of ?Significant? mesoscale cyclones. The large-scale pattern indicates that this greater activity is related to a deeper circumpolar trough and 5OO-hPa polar vortex for 1985 in comparison to 1984 and 1988. This means that 1985 had more frequent and/or stronger warm air advection toward the Ross Sea area caused by synoptic-scale cyclones decaying near Maric Byrd Land and had more frequent and/or stronger cold katabatic air outbreaks from East Antarctica onto the southwestern corner of the Ross Sea. The convergence of these two air masses creates boundary layer baroclinic zones that can undergo mesoscale cyclogenesis.