Wave Resonance Induced Intensification of Mixed Rossby-Gravity Waves by Extratropical Forcing

Extratropical disturbances are known to exert influence on the Mixed Rossby-gravity waves (MRGW) in the Western Hemisphere (WH). Modeling studies have introduced wave resonance (WR) theory to explain the extratropical forcing of MRGW. We provide observational evidence supporting WR theory to explain the intensification of MRGW by extratropical forcing. Regional wavenumber-frequency cospectral analysis and a bulk measure of growth of the MRGW estimated using reanalysis data reveal that the extratropical forcing manifested in the form of eddy momentum flux convergence can create eddy kinetic energy (EKE) and aid the intensification of MRGW via WR mechanism during boreal winter, while the extratropical forcing acts to dampen MRGW during the boreal summer. The observation of Doppler-shifted eastward MRGW (E-MRGW) in the WH during boreal winter is another highlight of the study. It is noteworthy that the extratropical forcing does not explain the existence of Doppler-shifted eastward MRGW.