Gravity wave fluxes of O3 and OH at the nightside mesopause

Abstract

A dynamical‐chemical model is used to determine concentration fluctuations, fluxes, mixing ratio fluxes, and flux divergences of the minor constituents OH, O3, HO2, H and O driven by gravity waves propagating through the nightside mesopause region. The model includes a five reaction chemical scheme for the production and loss of the minor species and the complete dynamics of linearized gravity waves in a motionless atmosphere. Wave fluxes of O3 and OH are small except for a 5 km thick region at about the level of the mesopause wherein the fluxes are large and downward. Wave‐induced transport of O3 and OH opposes diffusive down‐gradient transport of these species which would result in upward fluxes above ∼ 75 km for OH and above ∼ 81 km for O3, except for localized regions. Gravity wave fluxes of O3 can cause large changes in O3 number densities in times comparable to the O3 chemical time constant and they are therefore major contributors to the balance that determines O3 concentrations at the mesopause. Because of the short chemical time constant of OH, gravity wave fluxes of OH do not directly change OH concentrations. However, wave fluxes can alter OH concentrations indirectly through the modifications to O3 number densities and the rapid adjustment of OH to O3. By modulating the intensity and intrinsic frequency of gravity wave activity, tides can force diurnal and semidiurnal variations in the divergence of O3 and OH wave fluxes and in the concentrations or O3 and OH. Gravity wave fluxes are able to alter the mixing ratios of O3 and OH as a consequence of the chemistry. The coupling of wave dynamics and chemistry acts to reduce the mixing ratios of O3 and OH around 80 km.