Secondary planetary waves in the middle and upper atmosphere following the stratospheric sudden warming event of January 2012

The role of planetary waves in causing stratospheric sudden warmings (SSWs) is well understood and quantified. However, recent studies have indicated that secondary planetary waves are excited in the mesosphere and lower thermosphere following SSWs. We use a version of the Whole Atmosphere Community Climate Model constrained by reanalysis data below 50 km to simulate the SSW of January 2012, a minor warming followed by the formation of an elevated stratopause. We document the occurrence of enhanced Eliassen-Palm flux divergence in the mesosphere and lower thermosphere associated with faster, secondary westward-propagating planetary waves of wave number 1 and period <10 days. We confirm the presence of these secondary planetary waves using observations made by the Sounding of the Atmosphere using the Broadband Emission Radiometry instrument onboard NASA's Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics satellite. Key Points2012 SSW is a minor SSW with an elevated stratopauseSSWs lead to wind reversals and reversal of potential vorticity gradientPV gradient reversal leads to instability driven secondary PWs in MLT