Quasi-Stationary Waves in the Southern Hemisphere. Part I: Observational Data

Abstract

This Part I presents selected major features of the quasi-stationary (monthly mean) wave field in the troposphere and stratosphere of the Southern Hemisphere. It is confirmed that the quasi-stationary wave with zonal wavenumber 1 (QS-wave 1) is by far the dominant component of the geopotential height field at tropospheric and stratospheric levels. The amplitude of this wave is largest at about 60°S all year round and reaches a maximum during September and October in the upper troposphere and stratosphere. Analysis of the Elliasen-Palm flux vector suggests that at high latitudes the quasi-stationary wave field is primarily forced from lower latitudes, most prominently from the Indian Ocean region during June and October. Orographic and thermal forcing from Antarctic regions seem to also be important sources of wave activity in polar and high latitudes, particularly over southern South America and the Atlantic Ocean. The contribution to the quasi-stationary flow by the transient component of the flow is also analyzed. This analysis suggests that at high latitudes, the low-frequency transients act to strengthen QS-wave 1, while high-frequency transients weaken it. The values found for these contributions suggest that the low-frequency component is dominant.