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

Abstract

[1] 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.

Simultaneous, common‐volume lidar observations and theoretical studies of correlations among Fe/Na layers and temperatures in the mesosphere and lower thermosphere at Boulder Table Mountain (40°N, 105°W), Colorado

“…In fact, previous observations have shown that the associated correlation coefficients among temperature, Fe and Na densities are often quite high (absolute values greater than 0.7) but the sign can vary rapidly near the peaks of the Na and Fe layers [Gardner and Liu, 2010;Gardner et al, 2005;Chen and Yi, 2011]. For chemically active constituents such as Fe and Na, the fluctuations arise from purely dynamical effects associated with wave-induced displacement, as well as chemical effects associated with the perturbed production and loss reactions involving the species.…”

“…However, because the Fe and Na density fluctuations are dominated by dynamics, it is possible to derive useful analytical models for the Fe and Na fluctuations and their covariance functions using the approach developed by Gardner and Liu [2010] for a spectrum of wind perturbations. The key derivations are summarized in Appendix A.…”

“…[36] To evaluate the expectations in (A9), we note that wind and temperature perturbations are Gaussian distributed [Gardner and Yang, 1998;Gardner and Liu, 2010]. Because χ and ξ are linearly related to the wind perturbations through (A6) and (A7), χ, ξ, and T ′ are jointly distributed Gaussian random processes.…”

“…Gardner and Shelton [1985] extended the analysis by deriving an exact solution for the fluctuations of neutral constituent layers caused by a monochromatic gravity wave, which they used to analyze Na layer fluctuations. Most recently, Gardner and Liu [2010] generalized the results by eliminating the gravity wave constraint and extending the calculations to a full spectrum of wind fluctuations. They obtained solutions for the temperature-constituent covariance function and the vertical constituent flux, which include both linear and nonlinear perturbation effects.…”

“…The metal layers are affected by complex dynamical and chemical processes in the MLT region. Wave-induced vertical transport of atmospheric species through mixing, displacement, and advection [Gardner and Liu, 2010], in combination with chemistry and meteor input [Plane, 2012] as well as (horizontal) meridional transport [Marsh, 2011;Gardner et al, 2005], controls the abundance and structure of the metal layers in the MLT. While advective transport (upward in summer and downward in winter) is important in the seasonal variations of metal layers, eddy transport, dynamical transport, and chemical transport play crucial roles in the short-term (within a night) temporal variations of metal layer density [Gardner and Liu, 2010].…”