Dynamics of the 4-day wave in the Southern Hemisphere polar stratosphere

Several events of wave growth and decay are observed in the upper stratosphere during August 1980. Derived zonal-mean and eddy statistics suggest that the 4-day wave results from an instability of the zonal-mean flow near 55°-60°S, at and above 1mb. Inspection of climatological data suggests the source of the instability to be the "double-jet' structure in the upper stratosphere and mesosphere (the subtropical mesospheric jet near 30°S and the high-latitude extension of the polar night jet near 70°S). Contribution of the 4-day wave to the general circulation of the stratosphere is discussed: one feature attributable to the 4-day wave is a region of positive EP flux divergence in the upper stratosphere near 50°-60°S. -from Authors