Global characteristics of gravity waves in the whole stratosphere and mesosphere revealed by one-year hindcasts using a GW-permitting GCM

A one-year hindcast simulation for 2022 was performed using a high-resolution gravity-wave-permitting general circulation model to quantify the seasonal variation and global distributions of momentum fluxes associated with gravity waves (GWs) in the stratosphere and mesosphere. The global-mean absolute momentum flux (GM-AMF) associated with GWs exhibits clear semiannual variations, with maxima in the solstitial seasons and minima in the equinoctial seasons. GM-AMF is larger in June–August than in December–February in the solstitial seasons throughout the stratosphere and mesosphere. Meanwhile, in the equinoctial seasons, it is larger in September–November than in March–May below z = ∼65 km. The larger GW activity in September–November than in March–May in both hemispheres is consistent with the stronger stratospheric residual circulation in September–November as indicated by a previous study. The zonal and meridional momentum fluxes in meridional cross-sections suggest the presence of GW sources in the summer high-latitudes, in addition to the well-known source of subtropical monsoon convection. The characteristics of the meridional momentum fluxes indicate that, in the stratosphere and mesosphere, upward-propagating GWs generally have poleward intrinsic phase velocities, except in the winter hemisphere above z = ∼75 km where GWs with equatorward intrinsic phase velocities are dominant. The analysis of energy and momentum fluxes as functions of ground-based zonal phase velocity and height suggests that the equatorward-propagating GWs are generated in situ near the winter westerly jet core.