Gravity Wave Effects on Polar Vortex Evolution During Sudden Stratospheric Warmings

Reanalysis (JRA25) data, including parameterized gravity wave drag, that extends upwards into the lower mesosphere (~55 km) is used to explore gravity wave variability before, during, and after major sudden stratospheric warming events. We find that different vortex breakdown types (displacement events versus vortex splitting events) are associated with very different gravity wave drag evolutions and zonal-mean flow feedback responses. In particular, gravity wave drag is suppressed throughout the extratropical stratosphere prior to vortex displacement events. In contrast, gravity wave drag is enhanced poleward of ~50° N and suppressed equatorward of ~50° N prior to vortex splitting events. The nature of the gravity wave drag response during vortex splitting events is considered as a possible factor that helps to modulate key vortex and wave features during the onset period of a major sudden stratospheric warming. In particular, we discuss the impact of gravity wave drag on the location and width of the planetary wave surf-zone and the amplitude of planetary wave forcing.