Vertical dynamical transport of mesospheric constituents by dissipating gravity waves

Abstract

Over 400 h of Na wind/temperature lidar observations, obtained at the Starfire Optical Range, NM, are used to study the vertical dynamical transport of Na in the mesopause region between 85 and 100 km . Dynamical transport occurs when dissipating, non-breaking gravity waves impart a net vertical displacement in atmospheric constituents as they propagate through a region. We show that the vertical constituent flux can be related in a simple way to the vertical heat flux. Breaking gravity waves also contribute to eddy transport by generating turbulence. Because eddy transport is a mixing process, it only occurs in the presence of a gradient in the concentration profile of the constituent, while dynamical transport can be sustained even in the absence of such a gradient. The dynamical Na flux is compared with the predicted eddy flux. The maximum downward dynamical flux of Na is −280 m/ s cm 3 at 88 km . The maximum downward eddy flux is −160 m/ s cm 3 at the same altitude assuming the diffusion coefficient is 200 m 2/ s . The observational results are consistent with theoretical predictions below 93 km and show that dynamical transport often exceeds the vertical transport associated with eddy diffusion. The theoretical models are used to predict the dynamical and eddy fluxes of atomic oxygen and show that for this constituent, dynamical transport is also a significant transport mechanism.