Interannual Variability of Tidal Dynamics in the Tropical MLT

The impact of the stratospheric Quasi-Biennial Oscillations (QBO) and Semi-Annual Oscillations (SAO) and physics of gravity waves (GW) on the dynamics and transport in the Mesosphere and Lower Thermosphere (MLT) has been examined in simulations of two Whole Atmosphere Models (WAM and WACCM-X) during the last decade. In the low-latitude MLT the year-to-year variations of the diurnal tide amplitudes and mean flow of whole atmosphere simulations constrained below 40 km by reanalysis data are in the good agreement with the observed interannual variability. The Mar-Apr diurnal tide amplitudes simulated by models display the observed enhancements (~50-100%) of amplitudes during the westerly QBO years. The observed influence of QBO and SAO on the tidal dynamics in the MLT is well captured by simulations that are capable to reproduce the global and regional tidal variability deduced from the space-borne and ground-based measurements of temperature and winds. Comparisons between simulations and observations, along with the model sensitivity studies highlight needs to quantify and constrain impact of mesoscale GW dynamics and physics in whole atmosphere predictions.