Investigation of in scale and mean flow interactions of MRG waves using scale energetics framework.

Abstract

Mixed Rossby Gravity (MRG) waves are westward propagating equatorial waves that explain a significant amount of tropical variability. There exists a strong coupling between mean background state and MRG activity and the thesis focuses on exploring the qualitative and quantitative aspects of this MRG-mean flow interaction. Scale energetics in the frequency as well as the wavenumber domain is used to study the out-of-scale (in our study, energetic interactions with mean flow) and in-scale (energy exchange within a scale) interactions of MRG over the Pacific domain and a zonal belt around the globe extending 15॰ south and north of the equator. Horizontal eddy KE over the tropical Pacific domain is found to be higher for strong MRG seasons at high and low altitudes. The in-scale energetics (baroclinic conversion) in the frequency domain indicate that the APE and KE exchange on the MRG scale is not only pivotal for its maintenance but also affects its strength. Mean flow interactions of MRG scale in frequency domain shows that MRG scale KE generation is limited to eastern Pacific during weak seasons while during strong seasons, KE flows from mean flow to MRG scale in the eastern and central Pacific as well. Scale energetic in the wavenumber domain showed no relationship with that in the frequency domain. For strong seasons, higher KE was observed in the mid-altitudes about the equator and mean flow interactions showed higher MRG scale KE generation in similar pressure levels.