Vertical coupling in the polar middle atmosphere during Stratospheric Sudden Warming events

A stratospheric sudden warming (SSW) is a dynamical phenomenon that occurs in the wintertime stratosphere, caused by the interaction between upward propagating planetary Rossby waves from the troposphere and the stratospheric zonal mean flow. SSW events have profound effects on temperature and composition of the stratosphere as well as on atmospheric layers above and below it due to the changes in the zonal mean wind, gravity wave filtering and changes in residual circulation. An SSW is also accompanied by a mesospheric cooling and a warming in the lower thermosphere immediately above. The formation of the normal wintertime polar stratopause is a gravity wave driven phenomena. However during an SSW event, the stratospheric warming and polar stratopause becomes a planetary wave driven phenomena while gravity waves drive the mesospheric cooling and the formation of the polar mesopause. Over the last decade, the wintertime Arctic stratosphere has shown significant inter-annual variability with multiple instances of extreme SSW events followed by the formation of an elevated stratopause in the lower mesosphere. We document the stratosphere-mesosphere coupling during normal wintertime circulation, during an SSW event and after an SSW event during the formation of an elevated stratopause using simulations of past Arctic winters from a Specified Dynamics version of the Whole Atmosphere Community Climate Model (SD-WACCM) which is run by using reanalysis data in the lower atmosphere. We also present characteristics of secondary planetary waves which are excited in the middle atmosphere following SSW events, from baroclinic/barotropic instabilities which occur due to reversals in the zonal mean wind. We compare the characteristics of secondary planetary waves during the major SSW events in the past decade to determine the effect of duration and type (vortex splitting or vortex displacement) of the SSW on the generation of such planetary waves.