Wave–Mean Flow Interactions in a General Circulation Model of the Troposphere and Stratosphere

Abstract

Results are studied from a numerical experiment using a version of the NCAR Community Climate Model with high vertical resolution and extending from the surface to the lower mesosphere. The model was integrated for 370 days using external forcing fixed at values appropriate to 15 January (perpetual January), in order to isolate the effects of variability due purely to wave-mean flow interactions from variations due to other sources. The model gives a reasonably accurate simulation of the mean atmospheric state from the surface to the stratopause, including the winter stratosphere. Two qualitatively different mean states are found in the winter stratosphere for periods separated in time by a sudden warming. The changes in the atomspheric state between the two periods extend from the surface to the stratopause. By use of the refractive index and the EP flux, the zonal mean state in the two periods is shown to affect the vertical propagation of waves quite differently. The momentum balance of the two mean states is examined using transformed Eulerian diagnostics. Substantial changes in the Eliassen?Palm (EP) flux divergence are found between the two periods, indicating that the eddies affect the zonal mean state differently. A positive feedback mechanism appears to exist through which a strong lower stratospheric jet tends to favor weak wave forcing of the jet, while a weak jet favors stronger wave forcing.