Collaborative Research: Air-Sea Fluxes at High Wind Speeds with Application to Tropical Cyclone Intensity Prediction

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Theory and numerical experiments demonstrate that the intensity achieved by tropical cyclones is sensitive to the relative importance of surface fluxes of momentum and enthalpy in the storm core, yet very little is known about such fluxes in extremely high wind speeds. Extrapolation to high winds of the functional form of surface exchange coefficients deduced from observations at moderate wind speeds leads to the prediction that storms of greater than nominal tropical storm strength should never be observed. It is hypothesized that this paradox can be resolved by a proper account of the physical processes affecting surface fluxes at high wind speeds. Attacking this problem requires a multi-disciplinary program of theoretical, numerical and laboratory work in order to address several crucial physical processes that are neglected or poorly handled in present tropical cyclone models. Accordingly, Principal Investigators from four institutions (Woods Hole Oceanographic Institution, University of Rhode Island, Massachusetts Institute of Technology and the Cold Regions Research and Engineering Laboratory) have formed a research team to perform this research. Specifically, the Principal Investigators will: 1. Investigate the effect of re-entrant sea spray on air-sea enthalpy exchange through theoretical analysis and laboratory experiments:2. Conduct a program of theoretical and experimental research designed to yield quantitative estimates of air-sea heat exchange by bubbles; and3. Produce better estimates of the effect of waves on air-sea momentum exchange.This research should lead to better formulations of surface fluxes in very high wind speeds. These formulations will be implemented in numerical weather prediction models to improve the accuracy of tropical cyclone intensity prediction.