Interactions between Gravity Waves and Planetary-Scale Flow Simulated by the GFDL “SKYHI” General Circulation Model

Abstract

In order to study interactions between gravity waves and planetary flow in the middle atmosphere, a 3° latitude by 3.6° longitude version of the 40-level GFDL “SKYHI” general circulation model is analyzed using bihourly sampled output data. It is shown by a space-time spectral analysis that gravity waves in the mean zonal westerlies (easterlies) mainly consist of westward- (eastward-) moving components, and carry easterly (westerly) momentum upward, and decelerate the mean zonal westerlies (easterlies) in the mesosphere. Zonal momentum flux convergence due to gravity waves accounts for nearly all of the Eliassen–Palm (E–P) flux divergence in the summer mesosphere. This convergence accounts for 30%–50% of that in the winter upper mesosphere. However, this percentage is probably an underestimate since the convergence is significantly enhanced in a high resolution (1° × 1.2°) model currently being integrated. Vertical propagation of gravity waves is affected not only by the, mean zonal wind but also by velocity perturbations associated with planetary waves. The drag force due to gravity waves acts to suppress stationary planetary waves in the winter mesosphere.