Breaking of Rossby Waves in the Stratosphere: Part II—Factors Leading to Sudden Stratospheric Warmings

Studying the occurrence of sudden stratospheric warmings (SSWs) and their complex interrelation with tropospheric and stratospheric processes is of fundamental value for improving of our understanding of the dynamics of atmospheric circulation. This is especially important under phenomena but of global climate changes, which not only increase the frequency of anomalous atmospheric phenomena, but also intensify them. Based on a developed and adapted method for identifying Rossby wave breaking (RWB), which accounts for the specifics of stratospheric circulation, an analysis of the conditions for the occurrence of major SSWs in the Northern Hemisphere was conducted. The method relies on examining the geometry of potential vorticity contours in the stratosphere at the 850 K level using ERA5 reanalysis data. It is shown that anomalous RWB processes in November and December play a key role in preconditioning the onset of SSWs. Most of the analyzed SSW events are associated with an increase in the number of RWB events in the Asia-Pacific (AP) region in November and December, and occasionally in January. In cases where SSW initiation is linked to RWB over the Atlantic and Europe, it is also preceded by RWB anomalies in the AP region. For the identified types of wave breaking in the stratosphere, atmospheric blocking is characteristic in the troposphere, accompanied by negative near-surface temperature anomalies over Eurasia and/or North America. The increased frequency of early- and midwinter major SSW events aligns with the previously identified trend of enhanced negative temperature responses to atmospheric blocking in the Northern Hemisphere. The results of the work can be used to improve the prediction of SSWs and the associated extreme weather events, as well as for climate modeling to account for the RWB effects on stratospheric processes.