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1.Introduction

The seasonal march and the year-to-year variation of the stratospheric circulation are significantly different between the northern and southern hemispheres. In the northern hemisphere(NH), monthly mean (steady state) planetary waves show the maximum amplitudes in mid-winter associated with the occurrence of sudden warmings, but in general the phase of east-west wavenumber 1 is almost fixed due to the topographic effect of the surface.

On the other hand, planetary waves in the southern hemisphere(SH) stratosphere show large amplitudes in late winter or early spring (Sept.and Oct.), and the off-pole pattern of the polar vortex which means the phase and amplitude of wavenumber 1 varies from year to year, as can be seen in the "Antarctic ozone hole"

In view of the fact that the topographic conditions are quite different between the two hemispheres, it is interesting to examine the generation mechanism of planetary waves in the SH stratosphere, as well as their interannual variability, in terms of the dynamical coupling between the troposphere and stratosphere.

In this study a statistical analysis is made of interannual variations of planetary waves in the wintertime SH stratosphere with the aid of NCEP/NCAR reanalysis data-set for 20 years(1979-1998), in conjunction with the upper tropospheric circulations such as the mean zonal flow and short-period disturbances.