Dynamics of the 4-Day Wave in the Southern Hemisphere Polar Stratosphere

Abstract

Dynamics of the 4-day wave in the Southern Hemisphere polar stratosphere is investigated using horizontal wind and temperature data. These were derived from synoptic maps of satellite-measured brightness temperatures, which were generated using the fast Fourier synoptic mapping technique of Salby. Circulation statistics from these data are compared to those from the National Meteorological Center (NMC) operational stratospheric analyses, demonstrating improvements afforded by detailed treatment of asynoptic sampling effects. The 4-day wave is isolated using temporally filtered data. 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 1 mb. 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.