Synoptic interactions between Antarctica and lower latitudes

As the southern hemisphere's 'cold source', Antarctica interacts strongly with the atmospheric and oceanic circulations of middle and lower southern latitudes. The relative barotropy of the tropospheric standing waves over most of the southern hemisphere compared with those in the northern hemisphere, ensures that heat and momentum transports are mostly accomplished by the synoptic-scale frontal cyclones, or transient eddies. These synoptic circulations are crucial in the delivery of energy and moisture to the Antarctic. However, as cyclones migrate into higher latitudes they are themselves modified thermally and dynamically by contact with the elevated ice sheets and the extra-continental sea-ice zone. Features involved in this interaction include the circumpolar westerly vortex, the persistent katabatic wind regime, and areas of open water within the pack. Far from being a cyclone 'graveyard', the Antarctic coastline and sea-ice zone is the site of considerable cyclogenesis on the subsynoptic, or meso, scale. This paper reviews the nature of Antarctic-lower latitude interactions in the synoptic context, for both higher frequency (transient) and lower frequency (interannual) variations. The latter includes particularly the teleconnections associated with ENSO (El Niño-Southern Oscillation), which are discussed from the standpoint of observations and also experiments using GCMs (general circulation models). Since our understanding of the variability of Antarctic synoptic processes has been very strongly shaped by the lack of long-term meteorological data sets over large areas of the adjacent southern oceans, a discussion of these data bases is also included.