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The equatorial mixed Rossby-gravity wave (MRGW) is an important contributorto tropical variability. Its excitation mechanism capable of explaining theobserved MRGW variance peak at synoptic scales remains elusive. This studyinvestigates wave-mean flow interactions as a generation process for the MRGWsusing the barotropic version of the global Transient Inertia-Gravity And Rossbywave dynamics model (TIGAR), which employs Hough harmonics as the basis ofspectral expansion, thereby representing MRGWs as prognostic variables. Highaccuracy numerical simulations manifest that interactions between wavesemanating from a tropical heat source and zonal mean jets in the subtropicsgenerate MRGWs with the variance spectra resembling the one observed in thetropical troposphere. Quantification of spectral tendencies associated with theMRGW energy growth underscores the significance of wave-mean flow interactionsin comparison to excitation mechanisms driven by external forcing and wave-waveinteractions. The MRGW growth and amplitude depend on the asymmetry in thezonal mean flow that may explain not only seasonal variability but alsodifferences between the troposphere and the middle atmosphere.

Excitation of mixed Rossby-gravity waves by wave-mean flow interactions on the sphere