3A.1
Breaking waves in hurricanes Isabel & Fabian
J.M. Kleiss, SIO/Univ. of California, La Jolla, CA; and W. K. Melville, J. R. Lasswell, P. Matusov, and E. Terrill
The role of breaking waves in wave dynamics and air-sea fluxes is an area of significant interest in hurricane dynamics. Wave breaking is also a source of aerosols and spray in the air, and bubbles in the water, which may be dynamically and thermodynamically significant, especially in the transition from a well-defined air-sea interface to the more diffuse two-phase flows on either side of the boundary. While aspects of these problems can be studied in the laboratory or with numerical models, observations are necessary to measure the statistics of breaking especially their morphology and kinematics, and their relationship to the dynamics and thermodynamics. As part of the Coupled Boundary Layers/Air-Sea Transfer (CBLAST) experiment, a nadir-looking mega-pixel video camera, along with an inertial motion unit and laser altimeter was mounted on the NOAA P3 (N43RF) aircraft. The imaging system recorded images of the surface below the aircraft at a rate up to 30 Hz . Methods of image sequence analysis were used to identify breaking waves and measure their evolution in space and time. The striking qualitative differences between observations of the sea surface in hurricane force winds and more moderate winds were noted. We calculate L(c)dc, the average length of breaking fronts per unit area of ocean surface with velocities in the range (c, c+dc). The first moment and second moments of the corresponding omni-directional distribution give the fractional area of surface broken per unit time and the active whitecap coverage. Simple scaling arguments and higher moments lead to relationships for the momentum flux from waves to currents and dissipation by breaking. For flight altitudes below 200m the laser altimeter provides wave measurements that can be interpreted in terms of the one-dimensional wavenumber spectra of the sea surface. We discuss the significance of the results for improved coupled boundary layer models in hurricanes. .
Session 3A, CBLAST III
Monday, 3 May 2004, 1:30 PM-2:45 PM, Le Jardin Room
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