Evaluation and Improvement of Spray-Modified Air-Sea Enthalpy and Momentum Flux Parameterizations for Operational Hurricane Prediction

The bulk parameterization scheme of sea-spray mediated air-sea heat and momentum fluxes developed at NOAA/ESRL has been implemented and calibrated in the operational HWRF model. The scheme was developed as an extension of the TOGA-COARE bulk flux model (Fairall et al. 1994), and has been refined with observations from new field campaigns (such as the CBLAST experiment) and updated theoretical understanding. It was designed to address the lack of proper treatment of sea spray under high wind conditions in the traditional air-sea flux parameterizations commonly used in operational weather predictions models. Results from the tests of the scheme with the current operational setup of the HWRF model indicate that the thermal flux component of the scheme may be used as a way to reduce the intensity bias since its impact on hurricane track prediction is small enough to be neglected. Our experiment with the HWRF model is also the first to investigate the sea-spray effect on the air-sea momentum flux in an operational model. It is found that because the very turbulence that transports momentum and heat across the air-sea interface is also responsible for the generation of sea spray, the resultant effect of sea spray on both the momentum and heat fluxes is complicated by the interaction between the sea spray, turbulence and mean flow.