Middle atmosphere effects of the quasi-two-day wave determined from a General Circulation Model

A set of numerical experiments have been conducted using the National Cente r for Atmospheric Research Thermosphere-Ionosphere-Mesosphere-Electrodynami cs General Circulation Model (NCAR TIME-GCM) to understand the effects of t he quasi-two-day wave (QTDW) on the middle atmosphere horizontal wind and t emperature fields. A zonal wavenumber three perturbation with a period of 4 8 hours and a latitudinal structure identical to the (3, 0) Rossby-gravity mode has been included at the lower-boundary of the model. A response in th e middle atmosphere horizontal wind fields is observed with a structure qua litatively similar to observations and other model results. There is also s ome evidence to suggest an increase in the lower-thermosphere QTDW response due to the interaction with gravity waves. Changes are observed in the zon al mean wind and temperature fields that are clearly related to the QTDW, h owever it is unclear if these changes are the direct result of wave driving due to the QTDW or are from another source. Evidence for nonlinear interac tions between the QTDW and the migrating tides is presented. This includes significant (40-50%) decreases in the amplitude of the migrating tides when the QTDW is present and the generation of wave components which can be tra cked back to an interaction between the QTDW and the migrating tides. Clear evidence for the existence of a westward propagating zonal wavenumber six nonmigrating diurnal tidal component which results from the nonlinear inter action between the QTDW and the migrating tides is also presented.