Experiments on Tropical Stratospheric Mean-Wind Variations in a Spectral General Circulation Model

Abstract

Abstract A 30-level version of the rhomboidal-15 GFDL spectral climate model was constructed with roughly 2-km vertical resolution. In common with other comprehensive general circulation models, this model fails to produce a realistic quasi-biennial oscillation (QBO) in the tropical stratosphere. A number of simulations were conducted in which the zonal-mean winds and temperatures in the equatorial lower and middle stratosphere were instantaneously perturbed and the model was integrated while the mean state relaxed toward its equilibrium. The time scale for the mean wind relaxation varied from somewhat over one month at 40 km to a few months in the lower stratosphere. This is similar to the time scales of observed QBO wind reversals. The wind relaxations in the model also displayed the downward phase propagation characteristic of QBO wind reversals, and mean wind anomalies of opposite sign to the imposed perturbation appear at higher levels. In the GCM, however, the downward propagation is clear only abov...