An Inter-hemisphere comparison of the persistent stratospheric polar vortex

Abstract

Based on 19 years (1979-1998) of NCEP/NCAR reanalyses data and potential vorticity (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 the 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 almost complete ozone loss, but did not persist at higher altitudes where ozone was not depleted. However, the NH vortex persisted in a broader vertical range not limited to the ozone-depletion layer. We show that wave activity has weakened in recent years in the NH, but not in the SH. The springtime Antarctic ozone hole seems to be the main cause for the SH polar vortex persistence, while the cause for the NH vortex persistence involves changes in polar ozone as well as changes in dynamics.