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

Abstract

A set of numerical experiments have been conducted using the National Center for Atmospheric Research Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (NCAR TIME-GCM) to understand the effects of the quasi-two-day wave (QTDW) on the middle atmosphere horizontal wind and temperature fields. A zonal wavenumber three perturbation with a period of 48 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 the middle atmosphere horizontal wind fields is observed with a structure qualitatively similar to observations and other model results. There is also some evidence to suggest an increase in the lower-thermosphere QTDW response due to the interaction with gravity waves. Changes are observed in the zonal mean wind and temperature fields that are clearly related to the QTDW, however 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 interactions 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 tracked 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 interaction between the QTDW and the migrating tides is also presented.