Planetary‐scale wave activity as a source of varying tropospheric response to stratospheric sudden warming events: A case study

Abstract

Stratospheric Sudden Warming (SSW) events are typically, but not always, accompanied by negative Northern Annular Mode anomalies in the troposphere. However, large uncertainties remain as to which dynamical processes are responsible for those anomalies. In order to highlight sources of variability in stratosphere‐troposphere coupling among SSW events, we present a case study of three selected events and show detailed Transformed Eulerian Mean diagnostics for momentum changes in the stratosphere and troposphere in the course of those events. Our results suggest that planetary‐scale waves, especially the zonal wave number 2 component, may play an important role not only for the onset of tropospheric anomalies in response to SSW events but also for introducing variability in the vertical coupling, i.e., whether the tropospheric circulation anomalies lag, lead, or occur simultaneous to the weakening of the vortex. Particularly, the meridional propagation of those waves in the upper troposphere could be an important factor that determines whether SSW events lag or lead tropospheric anomalies.