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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D09S11, doi:10.1029/2004JD004849, 2005

Observations of gravity wave breakdown into ripples associated with dynamical instabilities

Feng Li

Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA


Alan Z. Liu

Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA


Gary R. Swenson

Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA


James H. Hecht

Space Science Application Laboratory, The Aerospace Corporation, Los Angeles, California, USA


Walter A. Robinson

Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA


Abstract

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.

Received 1 April 2004; accepted 4 February 2005; published 30 March 2005.

Keywords: gravity wave breaking; ripple; dynamical instability.

Index Terms: 0310 Atmospheric Composition and Structure: Airglow and aurora; 3332 Atmospheric Processes: Mesospheric dynamics; 3334 Atmospheric Processes: Middle atmosphere dynamics (0341, 0342); 3384 Atmospheric Processes: Acoustic-gravity waves.

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