Dissipation Mechanisms for Ducted Gravity Waves in the Mesosphere and Lower Thermosphere

Details Dissipation Mechanisms for Ducted Gravity Waves in the Mesosphere and Lower Thermosphere Dissipation Mechanisms for Ducted Gravity Waves in the Mesosphere and Lower Thermosphere

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsa54a..04s&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SA54A-04

Other

0310 Airglow And Aurora, 3332 Mesospheric Dynamics, 3334 Middle Atmosphere Dynamics (0341, 0342), 3384 Acoustic-Gravity Waves, 3389 Tides And Planetary Waves

Scientific paper

Gravity waves of short period (4-12 minute) and small scale (15-40 km horizontal wavelength) are frequently observed in mesopause airglow imaging experiments. The propagation of small-scale gravity waves, however, is strongly affected by local background structure and dynamics associated with large-scale waves and tides, and existing background conditions [Fritts et al., JASTP, 68, 247, 2006]. Vertical variations of temperature or wind can also produce ducts, in which trapped waves are frequently observed to propagate [e.g., Isler et al., JGR, 102(D22), 26301, 1997; Walterscheid et al., JASTP, 61, 461, 1999]; spatially- periodic structure of large-scale waves and tides may lead to formation of alternating layers of evanescence and ducted propagation [e.g., Snively et al., JGR, 112, A03304, 2007; Fritts and Janches, JGR, 113, D05112, 2008]. At higher altitudes, and for larger wave magnitudes, interactions between the small and large scales become increasingly nonlinear. Small-scale perturbations to large-scale wave fields may contribute to the formation of dynamic or convective instabilities [e.g., Fritts and Alexander, RG, 41(1), 1003, 2003, and references cited therein]; strong wind flows may also provide critical layers to some portion of the wave spectrum that would otherwise be propagating or ducted. Ducted or evanescent waves can produce strong airglow signatures, due to long vertical wavelengths and strong induced vertical fluid perturbations [Hines and Tarasick, GRL, 21(24), 2729, 1994], and form a significant fraction of observed waves in airglow data. Although commonly assumed to be horizontally- propagating, waves that appear locally trapped may still be subject to vertical tunneling [e.g., Sutherland and Yewchuk, JFM, 511, 125, 2004, and references cited therein]. Stable ducted waves may therefore tunnel into adjacent ducts, or into regions that may include critical layers, or alternatively facilitate instability or breaking, leading to turbulence and mixing. These processes may contribute to slow dissipation of the stored wave energy. Using numerical and analytical models, we investigate case studies of ducted wave dissipation under MLT conditions.

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