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

Extratropical disturbances are known to impact the genesis and intensification of Mixed Rossby-Gravity waves (MRGW) in the Western Hemisphere (WH). The study provides observational evidence supporting the wave resonance (WR) theory which attempts to explain the intensification of MRGW by extratropical forcing. Wavenumber-frequency cospectral analysis and a bulk measure of growth of 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 season. However, the WR mechanism does not hold during boreal summer season as the extratropical forcing tends to dampen the MRGW. The analysis also reveals that the Doppler-shifted eastward propagating MRGW in the WH during boreal winter season are not maintained by extratropical forcing, marking another highlight of this study.