Interannual and Intraseasonal Variability in the Southern Hemisphere

Abstract

The aim of this chapter is to examine the temporal and spatial variability of the troposphere over the Southern Hemisphere and, in the case of El Nino/Southern Oscillation, link it to fluctuations in the tropical oceans as well. In the time since the first volume on Southern Hemisphere meteorology appeared in 1972, it has been possible to examine in much more detail the variability of the Southern Hemisphere (SH) atmosphere, due to the vast improvements in the amount and quality of data that have since become available. Despite this progress, vast regions of the southern oceans remain very poorly observed. Fortunately, advances in remote sensing by satellite have done much to fill in some of the existing gaps in the ship-and ground-based observing network. We deal specifically here with interannual (IA) and intraseasonal (IS) variability, with respect to the mean state of the atmosphere as outlined in sections 1 and 2. As discussed in those sections, over most regions the SH atmosphere displays a lower amplitude mean seasonal cycle than does the Northern Hemisphere, where continental effects result in a much larger first annual harmonic in the meridional temperature gradient and circulation strength. This is also reflected in less of a seasonal dependence in the variability of the SH troposphere. Despite the dominance of ocean over the SH, however, continental effects, orography, and forcing from the Tropics still produce substantial zonal asymmetries in both the time-mean flow and statistics of IA and IS variability.