A comparison of Arctic and Antarctic mesoscale vortices

The mesoscale (less than 100km) vortices occurring in the two polar regions are considered in terms of their geographical and seasonal distribution, satellite cloud signatures and forcing mechanisms. Environmental conditions important in the development of the vortices are considered, including sensible heat flux, stability throughout the troposphere and synoptic factors, such as baroclinicity and upper air cold pools. A scheme to classify the observed vortices in the two polar regions in terms of the physical mechanisms behind their formation and development is proposed. The processes considered important are baroclinic instability, convection and vorticity generation through cyclonic vorticity advection and topographic forcing. The major difference between the systems observed in the two polar regions is the lack of deep convection in the southern hemisphere, which precludes the development of many of the vigorous types of system found in the north and the major role that topography plays in the Antarctic coastal region. The most common type of vortex found in the Antarctic occurs over the ice-free ocean to the west of synoptic scale disturbances and is similar to the type of northern system know as a comma cloud.