The generation mechanism of mixed Rossby-gravity waves in the equatorial troposphere

Abstract

Numerical experiments are performed to clarify the excitation mechanism of mixed Rossby-gravity waves (Yanai waves) in the tropical troposphere, as well as the selection of zonal wavenumbers 4-5 and of the five-day period. The model used is governed by the primitive equations on the equatorial β-plane. Moisture budgets are calculated explicitly. A nonlinear wave-CISK mechanism produces Yanai waves with the same spectral peaks in wavenumber and frequency as observed. Finally, our results indicate that the vertical wavenumber, and hence the period of Yanai waves are selected by the height of cumulus convection, while the lateral forcing selects the horizontal wavenumber within a certain band provided by the nonlinear wave-CISK mechanism. -from Authors