Interannual Variability and Trends in the Southern Hemisphere Annular Mode

The leading mode of month-to-month and interannual variability of the Southern Hemisphere circulation in the troposphere and stratosphere is an annular mode, associated with opposite variations of pressure between the polar cap and middle latitudes. A brief review will be presented of this SH annular mode in the troposphere and lower stratosphere, including its links to variations of zonal wind, temperature and total ozone. Recent observed trends in the SH annular mode will be described, including variations of the zonal flow in the troposphere and strengthening of the polar vortex in the lower stratosphere. Possible mechanisms for the trends in the lower stratosphere and troposphere will be described, including stratospheric ozone depletion and greenhouse climate change. The possibility of feedbacks between these two mechanisms and dynamical links between the troposphere and the lower stratosphere in the SH will be discussed.