A mesosphere and lower thermosphere dynamics study using the extended Canadian Middle Atmosphere Model (CMAM)

The extended Canadian Middle Atmosphere Model (CMAM) is used to study the large-scale waves present in the Mesosphere and Lower Thermosphere (MLT) region. The extended CMAM is one of the first General Circulation Models (GCMs) in the world to extend from the Earth's surface to about 210 km. This high upper boundary allows dynamical processes in the MLT to be studied without the artificial influence of sponge layers. Outputs (e.g. temperature, horizontal winds, etc.) from the model are analyzed to delineate diurnal, semidiurnal and terdiurnal tides with zonal wavenumber from -5 to 5 and Stationary Planetary Waves (SPWs) with zonal wavenumber of 1 to 5.;Comprehensive comparisons of the modeled diurnal and semidiurnal tidal winds with observations are conducted to validate the model. Seven nonmigrating diurnal components and four nonmigrating semidiurnal components from the model are compared to the corresponding TIMED Doppler Interferometer (TIDI) satellite wind observations. The 11 diurnal and semidiurnal components from the model are then superimposed to generate the total diurnal and semidiurnal winds at Jakarta (6°S, 106°E) and Kototabang (0°, 100° E) and are then compared to the measurements from these two meteor radar stations. Overall, the extended CMAM captures the salient features of the latitudinal, altitudinal and seasonal variability of the diurnal and semidiurnal tides although wind amplitudes of the eastward propagating components and the total winds tend to be bigger than those observed.;Possible generation mechanisms in the model of the migrating terdiurnal tide in the MLT region and of SPWs in the upper mesosphere are also examined. It appears that the migrating terdiurnal tide is mainly generated by direct solar heating rather than the nonlinear interaction between diurnal and semidiurnal migrating components as has been previously hypothesized. The SPWs in the upper mesosphere are most likely generated in-situ by systematic spatial variations of gravity wave breaking in this region rather than propagation of the SPWs from below.;;Altitudinal-latitudinal distributions and seasonal variations of migrating and 10 nonmigrating components of the diurnal, semidiumal and terdiurnal tides and 5 SPWs are presented in detail. Each component has its own particular structure and seasonal variation. Nonmigrating components have amplitudes as large as or even larger than the migrating components at some latitudes and time periods.