An Energetics Perspective on the Intensification of Mixed Rossby-Gravity Waves by Tropical Convection

Tropical convection is widely recognized as an essential factor for the growth and maintenance of Mixed Rossby–gravity waves (MRGWs), although the mechanisms through which it exerts this influence remain unclear. This study investigates the energy cycle associated with the MRGWs and identifies the sources and sinks of energy and the associated energy flow in the troposphere during boreal summer. Analysis of Eddy Available Potential Energy (EAPE) and Eddy Kinetic Energy (EKE) equations in the wavenumber-frequency domain reveals that diabatic heating aids the generation of EAPE in the mid-to-upper troposphere at spatial and temporal scales corresponding to MRGWs. This energy is subsequently converted to EKE via direct in-scale energy transfer. The diabatic heating does not directly play a role in energizing MRGWs in the lower troposphere and near the tropopause; rather, MRGWs at these levels are maintained by vertical transport of EKE from the mid-to-upper tropospheric source region. The physical consistency of these results is corroborated by analysing the EAPE and EKE tendency terms in physical space. These analyses reveal that physical processes contributing to the growth and maintenance of MRGWs are largely confined to the equatorial Pacific. Additionally, this study demonstrates that convectivelycoupled MRGWs extend over the central-eastern Pacific, as opposed to earlier studies suggesting MRGW signals confined near the dateline. Overall, this study underscores the importance of tropical convective processes, particularly linear in-scale energy transfer, in maintaining MRGWs throughout the troposphere over the equatorial Pacific during boreal summer. Plain Language Summary A strong overlap between periods of enhanced convective activity and MRGWs over the equatorial Pacific suggests a possible association between these two phenomena. However, it remains unclear whether tropical convection is a key factor in sustaining and strengthening MRGWs or if the observed relationship is largely coincidental. In this study, we investigate this issue by examining the energy cycle associated with MRGWs. The diagnostic analyses show that diabatic heating associated with tropical convection helps in generating MRGWs in the mid-to-upper troposphere. In contrast, MRGWs in the lower troposphere are not directly impacted by diabatic heating but are instead strengthened through the downward dispersion of energy from these upper-level source regions. Overall, this study highlights the central role of tropical convective processes and their coupling with circulation, especially the processes involving linear in-scale flow of energy, in the existence of MRGWs in the troposphere over the equatorial Pacific during boreal summer.