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Airglow Layer Perturbations by Ducted Gravity Waves: Effects of Duct Altitude and Vertical Wave Structure

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Atmospheric gravity waves with short periods and small spatial scales are frequently observed in airflow imaging experiments. Many of these waves propagate in ducts formed by the local temperature and wind fields [e.g., Walterscheid et al., JASTP, 61, 461, 1999; Isler et al., JGR, 102(D22), 26301, 1997]. Ducted waves contribute to strong airglow signatures, as a result of large vertical velocities, long vertical wavelengths, and standing wave structure [e.g., Hines and Tarasick, GRL, 21(24), 2729, 1994]. However, the vertical structure of ducted waves, and the altitude of trapping, is significantly determined by local temperature and wind conditions, and associated dynamics [e.g., Snively et al., JGR, 112, A03304, 2007; Fritts and Janches, JGR, 113, D05112, 2008].

For large-scale propagating waves, vertical wave structure may be assessed via comparisons of multiple airglow layer emissions [e.g., Vargas et al., JGR, 112, D14102, 2007, and references cited therein]. However, complications arise for airglow signatures due to small-scale ducted waves. As a consequence of the limited vertical extent of ducted wave packets, and strong vertical velocities, the integrated airglow response is dependent both on the structure of the wave packet, and on the density profiles of minor species participating in photochemistry [ e.g., Snively and Pasko, JGR, In Preparation, 2008].

Using numerical and analytical models, and comparing with observations, we investigate ducted gravity wave signatures within the OI (557.7 nm) and OH (Meinel band NIR) airglow layer emissions. First we investigate cases where ideal ducted wave packets perturb the airglow layers from ducts at different altitudes near mesopause. Results suggest the altitude of the wave packet relative to the minor species profiles significantly affects the phase and magnitude of the integrated intensity response. Second, we investigate cases where Doppler-ducted wave parameters vary with altitude throughout the airglow region. Results suggest that these waves perturb the airglow layers strongest as they approach reflection, such that the altitudes of duct boundaries may determine the integrated signature. Observational implications are discussed.


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