A physics-based parameterization of air-sea momentum flux at high wind speeds and its impact on hurricane intensity predictions

Abstract

A new bulk parameterization of the air-sea momentum flux at high wind speeds is proposed based on coupled wave-wind model simulations for 10 tropical cyclones that occurred in the Atlantic Ocean during 1998-2003. The new parameterization describes how the roughness length increases linearly with wind speed and the neutral drag coefficient tends to level off at high wind speeds. The proposed parameterization is then tested on real hurricanes using the operational Geophysical Fluid Dynamics Laboratory (GFDL) coupled hurricane-ocean prediction model. The impact of the new parameterization on the hurricane prediction is mainly found in increased maximum surface wind speeds, while it does not appreciably affect the hurricane central pressure prediction. This helps to improve the GFDL model-predicted wind-pressure relationship in strong hurricanes. Attempts are made to provide physical explanations as to why the reduced drag coefficient affects surface wind speeds but not the central pressure in hurricanes. © 2007 American Meteorological Society.