Effects of Bubbles and Sea Spray on Drag Coefficient in Hurricane Conditions
Alexander V. Soloviev, Nova Southeastern Univ., Dania Beach, FL; and R. Lukas
The lower limit on the drag coefficient under hurricane force winds depends on the breakup of the air-sea interface (e.g., due to Kelvin-Helmholtz instability) and formation of the two-phase transitional layer consisting of sea spray and air bubbles. As a consequence, a regime of marginal stability is expected to develop at the air-sea interface. In this extreme regime, the energy supply to surface waves from the atmosphere is cut off; the air-sea drag coefficient is then solely determined by the turbulence characteristics of the two-phase transitional layer. At the same time, the upper limit on the drag coefficient is determined by the Charnok-type wave resistance. Most of the observational estimates of the drag coefficient obtained in hurricane conditions and in laboratory experiments appear to compact between the two extreme regimes: wave resistance and marginal stability. The state of the sea surface in hurricane conditions varies in azimuth and distance from the hurricane center because of the variation in swell characteristics relative to the wind. The relative contribution of the wave and two-phase layer mechanisms into the drag coefficient is also expected to vary. Development of a parameterization taking into account the impact of both mechanisms is important for the realistic representation of the air-sea interface in hurricane models.
Session 8, Sea-Surface Physics, Including Waves, Whitecaps, and Aerosol Generation: Part 1
Wednesday, 14 January 2009, 8:30 AM-9:45 AM, Room 128A
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