A Hemispheric and Seasonal Comparison of Tropospheric to Mesospheric Gravity‐Wave Propagation

Abstract

AbstractDeep convection from monsoons has been shown to be a major tropospheric source of gravity waves (GWs) in the summer hemisphere. These GWs can propagate up to the upper mesosphere, either vertically (over the same latitude) or obliquely (latitudinal propagation away from their source), where they dissipate and release their momentum. These waves play an important role in the global dynamical structure of the middle atmosphere. Understanding their hemispheric and seasonal variations could improve the GW parameterization schemes in present global models. To this end, this paper reports on a GW ray‐tracing analysis using the GROGRAT model to simulate the propagation of GWs from the monsoon regions in the northern and the southern hemispheres during both the summer and the winter seasons. The 20 simulations show the southern hemisphere to be more conducive to both the vertical and the oblique propagation of mesospheric GWs compared to the northern hemisphere, regardless of season. This is partially due to a stronger GW filtering in the northern hemisphere near the tropopause where a third of the waves have been vertically reflected. We also show that an increase in the horizontal wavelength increases not only the latitudinal component but also the longitudinal component of the oblique propagation of GWs. The broad spectrum of waves with different horizontal wavelengths and horizontal phase speeds used in this study highlights the existence of an upper limit in the horizontal wavelength of GWs that can reach the upper mesosphere.