Residual Mean Meridional Circulation in the Stratosphere and Upper Troposphere

Climatological Aspects

Abstract

The climatological variation of the residual mean meridional circulation in the stratosphere, and the upper troposphere is investigated for 10 years from December 1985 to November 1995. The residual circulation is calculated from the transformed Eulerian-mean (TEM) zonal momentum and continuity equations. The method takes account of the Rayleigh friction and the mean zonal flow change.
The tropical upward mass flux across the 100hPa surface is maximum in November and minimum in June, and the annual mean is 101.8×10⁸kg/s, with a turnover time of 1.6 years for the atmosphere above 100hPa. The cause of differences in magnitude and seasonal variation of the Mass flux between previous studies, and the present study, is discussed. It is shown that the present results is more reasonable than previous studies. In the stratospheric mass budget, it is found that the spring and summer circulations are stronger in the southern hemisphere as compared with the same seasons in the north, and the reverse is true during fall and winter. The annual mean circulation is stronger in the northern hemisphere than in the southern hemisphere. The poleward flow is weak in the winter middle stratosphere. In addition, it is suggested that the mass exchange at 100hPa surface is mainly controlled by wave forcings in the lower stratosphere.