A stochastic parameterization of nonorographic gravity waves: Formalism and impact on the equatorial stratosphere
Abstract
A formalism is proposed to represent a broadband spectrum of Gravity Waves (GWs) via the superposition of a large ensemble of statistically independent monochromatic ones. To produce this large ensemble at a reasonable numerical cost, we use the fact that the life cycles of the waves needed to be parameterized in General Circulation Models (GCMs) have time scales that largely exceed the time step of the model. We can therefore launch few waves with characteristics chosen randomly at each time step, and make them having an effect on a longer time scale by applying an AR1 relation between the gravity waves drag at a given time and that at the next time step. The stochastic GW parameterization is applied to a GCM in the tropics, and its additional drag causes a realistic QuasiBiennial Oscillation (QBO). The more realistic wind structure also results in a better representation of the large scale equatorial waves, like the Rossby Gravity Waves (RGWs) with periods around 45 day.
 Publication:

Geophysical Research Letters
 Pub Date:
 March 2012
 DOI:
 10.1029/2012GL051001
 Bibcode:
 2012GeoRL..39.6807L
 Keywords:

 Global Change: Climate variability (1635;
 3305;
 3309;
 4215;
 4513);
 Global Change: Coupled models of the climate system;
 Mathematical Geophysics: Stochastic processes (3235;
 4468;
 4475;
 7857);
 Atmospheric Processes: Stratospheric dynamics;
 Atmospheric Processes: Subgridscale (SGS) parameterization