Abstract

Digital satellite imagery and automatic weather station data are used to study mesoscale cyclones and their characteristics over the Ross Sea and Ross Ice Shelf for the calender year of 1991. Results confirm the high frequency of mesoscale cyclone formation near Terra Nova Bay and Byrd Glacier (annual average of 2-3 and 1-2 mesoscale cyclones each week, respectively), and identify southern Marie Byrd Land as another source of mesoscale cyclones. The findings are compared with similar studies for 1985 and 1988. The annual frequency of mesoscale cyclone formation is similar for the three years, indicating that the katabatic wind is the primary forcing for mesoscale cyclogenesis; however, the fraction of 'significant' mesoscale cyclones varied and was significantly higher in 1985. Annual averages of synoptic-scale analyses showed a deeper circumpolar trough and polar vortex for 1985 than for 1988 and 1991. That is, more synoptic-scale support implies more vigorous mesoscale cyclones. This indicates that interannual variations in the development of mesoscale cyclones are associated with interannual variations of the synoptic-scale flow.