On the origins of mesospheric gravity waves

Abstract

Using hourly data from a three‐year simulation based on a gravity‐wave resolving general circulation model, we have first inferred a global view of gravity wave sources and propagation affecting significantly the momentum balance in the mesosphere. The meridional cross section of momentum fluxes suggests that there are a few dominant propagation paths originating from the subtropics in summer and the middle to high latitudes in winter. These gravity waves are focused into the mesospheric jets in their respective seasons, acting effectively to decelerate the jets. The difference in the source latitudes likely contributes to the hemispheric asymmetries of the jets. The horizontal distribution of the momentum fluxes indicates that the dominant sources are steep mountains and tropospheric westerly jets in winter and vigorous monsoon convection in summer. The monsoon regions are the most important window to the middle atmosphere in summer because of the easterlies associated with the monsoon circulation.