The stratopause evolution during different types of sudden stratospheric warming event

Abstract

Recent work has shown that the vertical structure of the Arctic polar vortex during different types of sudden stratospheric warming (SSW) events can be very distinctive. Specifically, SSWs can be classified into polar vortex displacement events or polar vortex splitting events. This paper aims to study the Arctic stratosphere during such events, with a focus on the stratopause using the Modern Era-Restrospective analysis for Research and Applications reanalysis data set. The reanalysis dataset is compared against two independent satellite reconstructions for validation purposes. During vortex displacement events, the stratopause temperature and pressure exhibit a wave-1 structure and are in quadrature whereas during vortex splitting events they exhibit a wave-2 structure. For both types of SSW the temperature anomalies at the stratopause are shown to be generated by ageostrophic vertical motions. Transformed Eulerian mean diagnostics are used to show differences in the planetary wave activity between displacement and splitting events. The convergence of Eliassen-Palm flux, which leads to SSWs is longer for displacement events and a persistent mesospheric Eliassen-Palm flux divergence can be observed about 20 days after displacement events. Finally, although this work focuses on the stratopause at high latitudes, associated observations of the equatorial middle atmosphere are also examined to explore links between the equator and polar evolution during SSWs.