Experiments on tropical stratospheric mean-wind variations in a spectral general circulation model

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. The mean flow relaxations above 20 mb were mostly driven by the vertical Eliassen-Palm flux convergence. The anomalies in the horizontal Eliassen-Palm fluxes from extratropical planetary waves, however, were found to be the dominant effect forcing the mean flow back to its equilibrium at altitudes below 20 mb. The vertical eddy momentum fluxes near the equator in the model were decomposed using spacetime Fourier analysis. While total fluxes asociated with easterly and westerly waves are comparable to those used in simple mechanistic models of the QBO, the GCM has its flux spread over a very broad range of wavenumbers and phase speeds. -from Authors