Modulations in the planetary wave field induced by upward-propagating Rossby wave packets prior to stratospheric sudden warming events: A case study

A diagnostic framework is introduced in which anomalous zonally-averaged Rossby wave-activity injection into the stratosphere is decomposed into a contribution solely from zonally-confined upward-propagating Rossby wave packets and another from interaction of the wave packets with the climatological stratospheric planetary waves. To pinpoint the tropospheric sources of the wave packets, a particular form of wave-activity flux is evaluated for the associated circulation anomalies. The framework is applied to reanalysis data for the period prior to a major stratospheric sudden warming (SSW) event in January 2006, which was associated with two successive events of above normal injection of wave activity from the troposphere. In the earlier event, a pair of Rossby wave packets that emanated from tropospheric anomalies over the North Pacific and over Europe enhanced the upward wave-activity injection, which was augmented further by their interaction with the climatological planetary wave. Contrastingly in the later period, a wave packet that emanated from an anticyclonic anomaly over the North Atlantic is found to be the primary contributer to the enhanced upward planetary wave-activity injection, while its interaction with the climatological planetary wave contributed negatively. The predominant importance of the sole contribution from a single wave packet is also found in a major SSW event observed in the southern hemisphere in September 2002. These results indicate that the diagnostic framework presented in the present study is a useful tool for understanding the interaction between anomalies associated with zonally-confined Rossby wave packets and climatological-mean planetary waves in the study of stratosphere-troposphere dynamical coupling. Copyright c © 2008 Royal Meteorological Society