Nonlinear airglow signatures of ducted gravity waves in the mesosphere and lower thermosphere

Details Nonlinear airglow signatures of ducted gravity waves in the mesosphere and lower thermosphere Nonlinear airglow signatures of ducted gravity waves in the mesosphere and lower thermosphere

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsa23a1781s&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SA23A-1781

Physics

[0310] Atmospheric Composition And Structure / Airglow And Aurora, [3384] Atmospheric Processes / Acoustic-Gravity Waves

Scientific paper

Signatures of short-period gravity waves are detected frequently in airglow data, revealing typical horizontal wavelengths of ˜15-35 km and periods of ˜4-8 minutes [e.g., Simkhada et al., Ann. Geophys., 27, 3213, 2009]. Many of such waves are ducted within the mesosphere and lower thermosphere (MLT) region [e.g., Walterscheid and Hickey, 114, D19109, 2009], and typical airglow intensity perturbations suggest amplitudes on the order of a few to tens of Kelvin within the airglow layers. At these amplitudes, trapped small-scale waves may be intermittently subject to nonlinear dissipation, potentially contributing to the local small-scale dynamics and variability of the lower thermosphere. For exceptionally strong small-scale waves, nonlinear behavior may become detectable in airglow data, including examples of wave breakdown [e.g., Yamada et al., GRL, 28(11), 2153, 2001], or apparent bore formation [e.g., Smith et al., JGR, 108(A2), 1083, 2003]. For moderately strong gravity waves with principally-linear propagation characteristics, however, airglow signatures may also exhibit nonlinearity in the form of harmonics, due to strong perturbations of reacting minor species at steep gradients of density [Huang et al., JGR, 108(A5), 1173, 2003; Snively et al., JGR, In Press, 2010]. Two scenarios are investigated numerically, using a nonlinear photochemical-dynamical model to simulate ducted gravity wave perturbations to the hydroxyl airglow layer. First, signatures of ducted waves are considered that exhibit nonlinearity associated with the wave perturbations to minor species participating in the emission processes. In this case, the nonlinear signatures are not indicative of changes in the wave packet spectrum. Second, we consider signatures of ducted waves at sufficient amplitudes to exhibit nonlinear propagation as they approach dissipation. In this second case, observable nonlinearity in the airglow signatures arise simultaneously from the overall wave perturbation and the minor species density perturbations. Assessment of wave characteristics, amplitudes, and evolutions in the MLT region therefore may require additional consideration of nonlinearities associated with the observed airglow system, particularly for cases of ducted waves at realistic amplitudes.

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