Gravity wave variations during elevated stratopause events using SABER observations

Elevated stratopauses formed at similar to 80-90km altitude during the recovery phase of stratospheric sudden warmings in February 2006 and 2009. These likely occurred in response to changes in the downward circulation due to gravity waves (GWs) and/or planetary waves in the mesosphere and the lower thermosphere (MLT). However, the physical mechanisms are not fully understood, due in part to the lack of global GW observations in the MLT. This study presents global-scale GW observations in the MLT during elevated stratopause events using Thermosphere, Ionosphere, Mesosphere Energetics Dynamics (TIMED)-Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature observation, which provide a better insight into the formation of an elevated stratopause. During the downward movement of elevated stratopause events in 2006 and 2009, GWs were suppressed below similar to 60km and enhanced above similar to 60km at high latitudes compared to non-elevated stratopause years (2005 and 2007). Global SABER GW observations indicate that the regions of GW enhancement propagate from low-mid latitudes to high latitudes in association with the equatorward shift of the polar night jet during elevated stratopause events. Ray-tracing simulations show enhancements of the poleward propagation of GWs during elevated stratopause events as well as continuous propagation of non-orographic GWs within high latitudes. Therefore, our results suggest that meridional propagation of GWs from lower to higher latitudes, which is typically not included in global-scale models, plays an important role in determining GW variations and thus the downward movement of an elevated stratopause, in addition to non-orographic GWs originating at high latitudes.