The role of eddies in maintaining the westerlies in the Southern Hemisphere winter

Abstract

The distribution of the mean westerly wind over the globe is described for June, July and August, the southern winter. The tropospheric momentum budget is analyzed from both the traditional Eulerian and the transformed Eulerian perspectives. Thus, an assessment is made of the Eliassen-Palm flux divergence and the diabatically driven residual mean circulation. The vertical mean budget is also analyzed to allow deductions about the mean surface torque by the atmosphere on the earth and the gross surface stress. The traditional Eulerian view reveals that the midlatitude westerlies are maintained mainly by convergence of westerly momentum by the transient eddies, while the induced Ferrel cell decelerates the westerlies aloft and transports momentum down to the surface to balance losses by surface friction. The vertical mean budget clearly shows that is the meridional transport of west erly molmentum by the eddies that is primarily acting to maintain the midlatitude westerlies against losses by surface friction. -from Author