Changes in polar stratospheric temperature climatology in relation to stratospheric sudden warming occurrence

Abstract

Stratospheric Sudden Warmings (SSWs) strongly affect the polar stratosphere during winter months mainly in the Northern Hemisphere. The intraseasonal distribution and type of SSWs for the 1958-1979 and 1979-2002 periods in ERA-40 and NCEP-NCAR reanalyses reveal differences. In the pre-satellite era, most events occur in January and are vortex splits. In the post-satellite era, the distribution is bimodal (peaking in December and February), and shows more displacement events. The difference in the seasonal distribution of SSWs leads to changes in the climatological state of stratospheric temperatures, with differences up to 5.9 K at 10 hPa and 3.6 K at 20 hPa in February between pre- and post-1979 periods. We find that the temperature evolution at 20 hPa is in better qualitative agreement with theoretical expectations than at 10 hPa. Hence, 10 hPa may be affected more strongly by artifacts related with satellite data assimilation, which have, however, limited impact on identification of SSWs.