Tropospheric Response to Stratospheric Sudden Warmings in a Simple Global Circulation Model

Abstract

A composite analysis is made of 132 stratospheric sudden warming (SSW) events obtained in a 10?000-day integration with a simple global circulation model under a perpetual-winter condition. The analysis confirms general features of the SSWs, such as enhanced upward propagation of planetary wave activity from the troposphere to the stratosphere before the SSWs and downward propagation of warming signals to the lower stratosphere after the events. A further dynamical diagnosis shows that the tropospheric circulation is quite different between pre-SSW and post-SSW periods in terms of the zonal mean zonal wind, planetary wave, and synoptic-scale waves. In the pre-SSW period, the planetary wave is more active than normal in relation to the tropospheric westerly jet that shifts poleward. In the post-SSW period, on the other hand, the planetary wave is less active, while the mean zonal wind is close to the climatology. Synoptic-scale waves also exhibit anomalous features in both periods corresponding to the anomalous planetary-scale flow. The less active planetary wave in the post-SSW period is a return signal of the SSWs, or a tropospheric response to the SSWs, since the signal disappears as SSWs are absent by increased thermal damping in the stratosphere.