Gravity-Wave Modulation of Vertical Mixing Near the Mesopause

Gravity waves generated near the tropopause are able to propagate to the mesosphere, where their breaking action can create turbulent diffusion and vertical mixing. As the transmission of gravity waves to the mesopause is modulated by seasonal variations in the wind field of the lower atmosphere, so too will this vertical mixing in the mesosphere vary. This, in turn, will modulate the intensity of airglow emissions, such as hydroxyl (OH) and oxygen, whose production chemistry depends upon minor species that have altitude gradients in mixing ratio. We present the seasonal variation of hydroxyl nightglow emission at high (60N) and mid (42N) latitudes derived from long-term (10 and 7 year), ground-based observational data sets. The gravity-wave transmission through modeled wind fields has been calculated, and the resulting seasonal variations in vertical mixing and airglow emission will be compared with the measurements. It will be shown that the fluctuations in airglow intensity may be attributed to seasonal increases in gravity-wave flux and turbulent dissipation in the mesosphere.