An inter-hemisphere comparison of the persistent stratospheric polar vortex

Based on 19 years(1979-1998) of NCEP/NCAR reanalyses data and potential vor ticity (PV) area diagnostics, we Found that in the southern hemisphere (SH) the polar vortex has lasted about two weeks longer in the 1990s than in th e early 1980s and the northern hemisphere (NH) polar vortex has lasted four weeks longer. The SH vortex persisted within the layer(12-22 km) with almo st complete ozone loss, but did not persist at higher altitudes where ozone was not depleted. However, the NH vortex persisted in a broader vertical r ange not limited to the ozone-depletion layer. We show that wave activity h as weakened in recent years in the NH, but not in the SH. The springtime An tarctic ozone hole seems to be the main cause for the SH polar vortex persi stence, while the cause for the NH vortex persistence involves changes in p olar ozone as well as changes in dynamics.