The Zonal Men Westerlies over the Southern Hemisphere

A brief review and evaluation of various analyses of the Southern Hemisphere westerlies is given along with the presentation of some relent results. Several features characterize the westerlies of the Southern Hemisphere as quite different from those in the Northern Hemisphere and, in the past, thew have typically been difficult to reproduce well in general circulation modes. They are the double jet structure in winter, the stronger midlatitude tropospheric winds in summer than in winter, and the ensuing much smaller amplitude of the annual cycle which is associated with a maximum of global atmospheric angular momentum in January. New values for the hemispheric angular momentum integrals are than previously reported. Two estimates of the distribution and strength of the southern westerlies that have been widely used are considered to be seriously biased. Factors contributing to discrepancies among different results am large natural variability, missing data and biases in observing systems, and methods of analysis. Over the sparsely observed Southern Hemisphere, the latter is the main reason why biases exist in analyses based only on mean station data, and the absence of imposed dynamical constraints has led to internally inconsistent fields. Even recent estimates of the southern westerlies from global operational analyses should be used judiciously with proper consideration given to reliability and biases.