Observations of Wave-Mean Flow Interaction in the Southern Hemisphere

Abstract

Variations of zonal mean and eddy properties in the Southern Hemisphere during the winter of 1979 are studied. Several periods of enhanced wave activity and rapid zonal-mean changes are observed. During these periods of rapid change both the actual zonal wind tendency and the Eliassen-Palm flux divergence have a dipole pattern in the upper stratosphere, with positive values in high latitudes and negative values in middle and low latitudes. The positive values of E-P flux divergence near the pole are particularly interesting, since they suggest a possible source of wave activity in this region. The stationary component of wavenumber 1 and the eastward traveling component of wavenumber 2 contribute most to the dipole pattern of wave driving in the stratosphere. A nearly uniform deceleration of the mean flow in the troposphere is contributed to by all zonal wavenumbers from 1 to 10. The lower wavenumbers contribute most to the driving in high latitudes, while the driving in lower latitudes is contributed mostly by high wavenumbers. Wave forcing of the mean flow as measured by the E-P flux divergence and actual changes in the mean flow are correlated with each other, but the actual mean flow tendencies are often significantly smaller than the eddy driving. The largest correlations between E-P flux divergence and the observed zonal mean wind changes exceed 0.5 and occur both in the upper stratosphere near the jet core and near the tropopause across a broad range of latitudes.