Processes that account for the ozone maximum at the mesopause

The presence of a maximum in ozone density and mixing ratio in the mesopause region has been known for several decades although the measurement database is still quite limited. This ozone layer is formed in the vicinity of the maximum in atomic oxygen number density. In this paper, we present simulations of the ozone maximum from a three-dimensional dynamical chemical model. Ozone variability is dominated by the diurnal cycle in ozone, which fluctuates between low concentrations in sunlight and high concentrations in darkness. However, the diurnal variability also has strong contributions from atmospheric tides and from slow changes in chemical concentrations following sunrise and sunset. In this study, we find that the magnitude of the ozone secondary maximum is closely tied to the temperature. The very low temperatures at the mesopause accelerate the formation of ozone and inhibit the loss. This factor and the location of the atomic oxygen density maximum both contribute in approximately equal measure to determining the altitude of the ozone layer. The magnitude of the nighttime ozone maximum is sensitive to the eddy and molecular diffusion rates primarily through the influence of these processes on the concentration of hydrogen.