The Dynamical Climatology of the Stratosphere in the Southern Hemisphere during Late Winter 1973

Abstract

The heat, momentum and energy budgets of the region between 100 and 0.2 mb are investigated for the period 1 July to 6 September, 1973, using data derived from the Nimbus 5 meteorological satellite. The heat balance indicates that the high temperatures observed in the upper stratosphere in the south polar region are maintained against radiative cooling by intense zonal-mean subsidence. The eddy momentum flux is large in the upper stratosphere and indicates substantial driving of the mean flow by the eddies. The mean meridional circulations which were estimated independently from the heat balance and the dissipationless momentum balance for the upper stratosphere are inconsistent. The estimated heat balance requires subsidence in the polar upper stratosphere while the momentum balance suggests rising motion there. The generation of eddy kinetic energy was found to be dominated by the conversion from eddy available potential energy in the lower stratosphere and by the convergence of the vertical eddy geopotential flux in the upper stratosphere. Most of the eddy geopotential flux through the 100 mb level is absorbed in the region above 10 mb with relatively free propagation through the 100–10 mb layer during the period studied. The climatological importance of transient and stationary waves are observed to be approximately equal. Comparison of the present results with energy calculations for the 100–10 mb layer in the Northern Hemisphere during a period without a major warming indicates that the estimated zonal mean energies in the Southern Hemisphere are larger, while eddy energies are smaller than in the Northern Hemisphere. Nonetheless, the energy conversion terms are nearly the same in the two cases.