Evolution of the Southern Hemisphere Subpolar Middle Atmosphere during Summer and Autumn

Abstract

The evolution of zonal wind and zonal wavenumber one (wave 1) in the Southern Hemisphere subpolar middle atmosphere is described for the period December 1978?May 1979 using temperature and ozone measurements from the Limb Infrared Monitor of the Stratosphere (LIMS) experiment. In late December maximum zonal easterlies of ? ?70 m s?1 are observed at 0.1 mb, 60°S. A zonal flow reversal occurs during late February and westerlies subsequently increase to 60?70 m s?1 in the upper stratosphere by April?May. LIMS zonal winds are compared with rocketsonde measurements and nadir sounder (derived) winds for summer and autumn. Although quantitative agreement is found at stratospheric levels, substantial discrepancies are evident in the mesosphere, most likely a reflection of sampling and resolution differences in the respective datasets. Stationary and traveling wave 1 temperature disturbances (amplitudes ?1?2 K at 60°S) are observed by LIMS during summer. The stationary wave is confined to the lower stratosphere near the level of zero zonal mean wind flow, whereas the traveling wave is prominent in the middle stratosphere, moves west at a rate similar to the zonal-mean wind, and exhibits a vertical-meridional structure similar to a P14 normal mode Rossby wave. A substantial intensification of wave 1 activity occurs during autumn (amplitudes ?5?10 K), which is found to be associated with an upward-directed Eliassen?Palm flux near the subpolar tropopause level. Evidence relating wave 1 activity in the lower-middle stratosphere to the occurrence of zonal ozone perturbations of 10%?20% amplitude is presented for summer and autumn.