83rd Annual

Tuesday, 11 February 2003: 11:30 AM
Air-sea flux estimation in high wind boundary layers: a Coupled Boundary Layer Air-Sea Transfer (CBLAST) experiment for 2003-04
Peter G. Black, NOAA/AOML/HRD, Miami, FL
An upcoming ONR/NOAA hurricane air-sea interaction experiment is described and results from the initial test year in summer 2002 are described. The primary goal of the experiment is to improve the accuracy of hurricane intensity prediction through an improved understanding of the air-sea flux processes at high winds, followed in out-years by a suitable technology transfer strategy for operational implementation. Instrument testing and calibration as well as flight plan experimentation will be conducted in 2002 followed by intensive experimental work in 2003-04.

The specific objective of this experiment is to develop a new surface wave-dependent flux parameterization for the high wind hurricane boundary layer containing secondary (roll-vortex) circulations over fetch limited seas in the presence of sea spray and one or more swell components from an airborne platform. We propose to test the following hypotheses:

1) that surface momentum exchange coefficients increase with wind speed for moderate winds (>30 m/s), are enhanced by fetch-limited waves or opposing swell, but level off or decrease above a high wind threshold (>45 m/s), especially in quadrants where swell has a significant downwind component, 2) that compensating mechanisms for enhanced surface air-sea enthalpy fluxes over and above current parameterizations must exist for storm maintenance and growth above some high-wind speed threshold, and 3) that candidate mechanisms are separable and can be estimated, such as a) enhanced turbulent fluxes due to wave interactions, b) spray evaporation and c) secondary flow circulations (roll-vortex type).

Various instrument systems will be discussed that will obtain the requisite observations.

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