The transport of thermospheric nitric oxide into the mesosphere

A ratio phi/K of vertical nitric oxide flux to the eddy diffusion coefficient is derived to estimate the magnitude of nitric oxide transport from the thermosphere into the mesosphere. Rocket measurements of NO vertical profiles are used to show the existence of a latitudinal-seasonal dependence on the efficiency of thermosphere-mesosphere coupling. One peak is observed in each auroral zone at 100 km, but there is evidence of only one peak in the mesospause. This trend is considered to be in good agreement with the results of a recent two-dimensional odd nitrogen model and is explained by the combined effects of particle precipitation at high winter latitudes and photodissociation of the NO downward flow in the sunlit regions.