Atmospheric Variations: Vacillations and Index Cycles

Zonal indices, momentum flux, and mean and perturbation kinetic energies of the Southern Hemisphere upper troposphere, derived from the EOLE constant density balloon data set, are found to possess strong 18–23 day variations which are statistically significant to a posteriori levels. Cross-spectra and phase relationships suggest that the variation appears as a barotropic interaction between the middle latitude mean westerlies and ultra large-scale perturbations. Long-period and high-amplitude variations in energy conversion between eddy and mean kinetic energies are found which average out in the long term mean to be very small and positive, consistent with previously measured average hemispheric energetics. Furthermore, the variation is shown to possess an ultra-long wave preference. Examination of two independent data sources, time series of total ozone and stratospheric thickness data from the Selective Chopper Radiometer, suggests that the periodicity is a property of general hemispheric motion rather than just a property of the EOLE data set. Finally, the periodicity is discussed with reference to hemispheric energetics along with its relevance to numerical weather prediction.