Observations of gravity wave breakdown into ripples associated with dynamical instabilities





Citation of Original Publication

Li, F., A. Z. Liu, G. R. Swenson, J. H. Hecht, and W. A. Robinson (2005), Observations of gravity wave breakdown intoripples associated with dynamical instabilities,J. Geophys. Res.,110, D09S11, doi:10.1029/2004JD004849.


This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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The breakdown of a high-frequency quasi-monochromatic gravity wave into small-scale ripples in OH airglow was observed on the night of 28 October 2003 at Maui, Hawaii (20.7°N, 156.3°W). The ripples lasted ∼20 min. The phase fronts of the ripples were parallel to the phase fronts of the breaking wave. The mechanism for the ripple generation is investigated using simultaneous wind and temperature measurements made by a sodium (Na) lidar. The observations suggest that the wave breaking and the subsequent appearance of ripples were related to dynamical (or Kelvin-Helmholtz) instabilities. The characteristics of the ripples, including the alignment of the phase fronts with respect to the wind shear, the motion of the ripples, and the horizontal separation of the ripple fronts were consistent with their attribution to Kelvin-Helmholtz billows. It is likely that the dynamical instability was initiated by the superposition of the background wind shear and the shear induced by the wave. The wind shear, the mean wind acceleration, and the propagation of the breaking wave were found to be in the same direction, suggesting that wave-mean flow interactions contributed significantly to the generation of the strong (>40 m/s/km) wind shear and instability.