The Unusual Southern Hemisphere Stratosphere Winter of 2002

Abstract

he Southern Hemisphere (SH) stratospheric winter of 2002 was the most unusual winter yet observed in the SH climate record. Temperatures near the edge of the Antarctic polar vortex were considerably warmer than normal over the entire course of the winter. The polar night jet was considerably weaker than normal and was displaced more poleward than has been observed in previous winters. These record high temperatures and weak jet resulted from a series of wave events that took place over the course of the winter. The propagation of these wave events from the troposphere is diagnosed from time series of Eliassen?Palm flux vectors and autoregression time series. Strong levels of planetary waves were observed in the midlatitude lower troposphere. The combinations of strong tropospheric waves with a low index of refraction at the tropopause resulted in the large stratospheric wave forcing. The wave events tended to occur irregularly over the course of the winter, and the cumulative effect of these waves was to precondition the polar night jet for the extremely large wave event of 22 September. This large wave event resulted in the first ever observed major stratospheric warming in the SH and split the Antarctic ozone hole. The combined effect of all of the 2002 winter wave events resulted in the smallest ozone hole observed since 1988. The sequence of stratospheric wave events was also found to be strongly associated with unusually strong levels of wave 1 in the SH tropospheric subtropics.