Influence of Gravity Waves on Transient Heating Response of the Upper Atmosphere.

It is shown that the presence of gravity wave interaction with a transiently heated atmosphere changes the atmospheric response to heating significantly. The energy exchange between wave and ambient atmosphere manifests itself as an apparent increase in effective thermal diffusivity. The present model predicts altitude independent 200 km temperature and density time lags which are in phase and are 6 plus or minus 2 hours for a mean heating duration of 2-6 hours. It is shown that the above response characteristics are essentially independent of the spatial distribution and location of the primary heat source. This tendency is a consequence of the increased heat diffusion due to energy exchange between wave and ambient atmosphere. The energy loss to gravity waves during the falling phase of the response leads to the prediction of a relaxation time of 15 plus or minus 3 hours measured from the beginning of density decrease. The mean relaxation time for discernible major events in the Explorer 9 data is approximately 13 hours. Author