Secular variations of OI 5577 angstrom airglow in the mesopause region induced by transient gravity wave packets

We employ a 2-dimensional, time-dependent, fully nonlinear model of minor s pecies in the mesopause region and our Spectral Full-Wave Model to simulate the response of minor species and the OI 5577 Angstrom airglow to a gravit y wave packet in the mesopause region. Gravity waves affect the time-averag ed distribution of minor species in the mesosphere and lower thermosphere ( MLT) region through constituent fluxes induced by violation of the non-acce leration conditions due to wave transience and dissipation. In addition, wa ve perturbed chemistry can induce a flux of chemically active species. Simu lations are performed with nominal values of eddy diffusion coefficients in the MLT region, and also using very small values in order to assess the co mparative effects of diffusion and wave fluxes. The wave-driven secular var iation leads to a strong increase in airglow brightness over a time period of similar to2 hrs. In contrast to this, diffusion of minor species leads t o a decrease in airglow brightness. The combined effects of the two can lea d to secular variations of airglow brightness that resemble those for a lon g period (> 6 hr) wave. These results have important implications for the i nterpretation of airglow variations observed in the MLT region.