The importance of spatial variability in the generation of secondary gravity waves from local body forces

Abstract

We hypothesized earlier that the zonal mean body force required to close the mesospheric jets is sporadic in time, and is composed of a large number of spatially and temporally localized body forces. To explore the effects of such localization, we randomly generate a series of localized, 3D body forces in the mesosphere which create a mean acceleration of ∼100 m s-1 day-1 over this forcing volume. Secondary waves are also generated, and because they have large vertical scales, phase speeds, and vertical group velocities, they may induce important variabilities in the lower thermosphere where they dissipate. We find that the secondary waves from spatially smoothed body forces have much smaller momentum fluxes, frequencies, and vertical group velocities. Thus, global models having coarse resolution may be missing a significant source of sporadic wave drag and its effect throughout the middle atmosphere and lower thermosphere.