What we can Learn from General Circulation Models about the Spectrum of Middle Atmospheric Motions

Abstract

This article presents an informal survey of some recent results from the GFDL “SKYHI” general circulation model that relate to the spectrum of stratospheric and mesospheric gravity waves. Attention is focussed on the extratropical summer hemisphere where upward propagating gravity waves should dominate the eddy component of the circulation. After a brief description of the SKYHI model, an examination is made of the large scale simulation and its dependence on model resolution. Then a comparison is made of statistics relating to the gravity wave field derived from rocketsonde observations at a number of extratropical stations with comparable model results. The spatial spectra of both kinetic energy and vertical eddy momentum transport in the simulated summer middle atmosphere are then discussed. The results of these investigations show that the SKYHI model gravity wave field has some impressively realistic features. On the other hand the present results also strongly suggest that much of the gravity wave vertical momentum flux resides at scales that are not practically resolvable in current global models.