Analysis of synoptic-scale low pressure systems within the Antarctic Peninsula sector of the circumpolar trough
Satellite imagery of the Antarctic Peninsula, Bellingshausen Sea, and Weddell Sea region, together with operational meteorological analyses, are used to investigate the development, tracks, and structure of synoptic-scale weather systems within the Antarctic Peninsula sector of the circumpolar trough, which rings the Southern Hemisphere between the latitudes of 60° and 70°S. A number of previous studies have shown that more cyclogenesis events take place within this zone than in any other region of the Southern Hemisphere, although the mechanisms behind these developments have not been investigated previously. This study confirms the large number of cyclogenesis events taking place within the circumpolar trough and, in the year examined, the mean latitude of cyclogenesis within the sector was 64°S. During the year, 504 lows were observed, with 281 developing in the area and 223 moving in. The diameters of the systems observed ranged from 300 to 3500 km, with the smallest vortices being mesocyclones that later grew into synoptic-scale lows. The mean distance travelled by the depressions was only 1377 km (standard deviation 1205 km), reflecting the fact that the systems observed ranged from small quasi-stationary lows to large, very mobile depressions. The mean meridional movement of the lows during their existence was very small. The greatest number of cyclogenesis events were observed over the Bellingshausen Sea, where more than 0.48 events 10 000 km−2 year−1 were found, with a secondary maximum in the lee of the Antarctic Peninsula. The mean lifetime of the systems observed was 22 h, with over half the vortices existing for less than 24 h. A maximum of cyclolysis was found just to the west of the Antarctic Peninsula, with a secondary maximum in the South Atlantic. Of the systems that formed within the area, 36% were developments within pre-existing large areas of low pressure, which were similar to the ‘merry-go-round’ formations of mesocyclones. A further 39% of developments consisted of waves on major frontal bands. The remaining developments comprised lee lows and some cyclogenesis events in synoptically isolated regions.
Authors: Turner, John, Marshall, Gareth J., Lachlan-Cope, Thomas A.