Stratospheric Antarctic Intraseasonal Oscillation during the Austral Winter

Abstract

This study discovered an eastward-propagating circulation pattern in the stratosphere of the Southern Hemisphere based on the Met Office stratospheric assimilated data and the TOMS total ozone. This pattern is named the Stratospheric Antarctic Intraseasonal Oscillation (SAIO) because of its intraseasonal time scale and its repeated appearance in the high latitudes of the Southern Hemisphere. The SAIO exhibits a wave-number-one structure and propagates eastward around the globe in about 30 days, indicating a periodicity of 30 days. It is characterized by a deep vertical structure extending from the upper troposphere to the upper stratosphere with the amplitude increasing rapidly with height below 5 hPa and decreasing slowly with height above. The pattern exhibits a westward-tilting vertical structure with increasing height below 5 hPa and a more barotropic structure above. This westward-tilting feature is most evident in the eastern hemisphere. The close correspondence between the total ozone and circulation implies the impacts of the SAIO on the ozone hole.
The SAIO exhibits active wave activity in the longitudinal band outside the jet stream, i.e., from 60°E eastward to 90°W, and tends to grow in the longitudinal band from 60°E to 120°E where energy is converted both barotropically an baroclinically from the mean flow to the SAIO. Outside this region, the SAIO tends to decay and feed energy back to the mean flow mostly through barotropic processes. The SAIO wave activity propagates upward from the upper troposphere to the upper stratosphere downstream of the high-rising topography in Antarctica. The feature is likely to be the manifestation of a topographically forced planetary wave. However, the periodicity cannot explained by the Rossby wave dispersion. Possible mechanisms are discussed.