Chemical transport of neutral atmospheric constituents by waves and turbulence: Theory and observations

摘要

Vertical chemical transport occurs when the density fluctuations of a species, caused by perturbations of its chemistry, are strongly correlated with the vertical wind fluctuations. Chemical transport can exceed dynamical and eddy transport of chemically active species. Theoretical expressions are derived for the chemical fluxes and transport velocities and used to characterize the vertical transport of mesospheric O_3 and meteoric Na and Fe between 85 and 100 km. Chemical transport is dependent on the intrinsic frequency spectrum of the temperature fluctuations and on the chemical cutoff periods of the species. For O_3 only high-frequency fluctuations contribute to chemical transport because slower, larger-amplitude density perturbations are damped by chemistry. The cutoff periods for O_3 range from ~15 min during the day when photolysis is important to ~200min at night. The chemical transport velocities of Na and Fe are proportional to the O_3, O_2~+, and NO~+ densities above 85km. For O_3, Na, and Fe themagnitudes of the vertical transport velocity can be as large as 10cm/s, and they exhibit strong diurnal variations. O_3 chemical transport is downward at night and upward during the day. Na and Fe chemical transport are largely upward with the strongest upward velocities at night near 85 and 100 km.