Wave‐induced transport of atmospheric constituents and its effect on the mesospheric Na layer

Abstract

Extensive observations of winds, temperatures, and Na densities between 80 and 105 km at the Starfire Optical Range, New Mexico, are used to characterize the seasonal variations of the vertical flux of atomic Na and its impact on the Na layer. The largely downward Na flux and its convergence enhance the transport of Na from meteoric sources above 90 km to chemical sinks below 85 km, altering the height, width, and abundance of the Na layer. From theoretical considerations, it is shown that the effective vertical velocity associated with dynamical transport by dissipating waves is the same for all species and is about 3 times faster than the effective heat transport velocity. Dynamical transport is generally downward with velocities as high as −5 cm s−1 below 90 km in midwinter when and where gravity wave activity and dissipation are strongest. Chemically induced transport of atomic Na by both dissipating and nondissipating waves is also significant so that the total effective transport velocity for Na below 90 km approaches −8 cm s−1 in midwinter. The observations show that at the solstices, dynamical and chemical transport play far more important roles than turbulent mixing in transporting Na downward, while at the equinoxes the impacts of all three wave‐induced transport mechanisms are comparable. These results have important implications for chemical modeling of the mesopause region.