The prediction of both hurricane track and intensity relies heavily on weather prediction models. However, great uncertainties still remain in the formulation of a few key model physics components that are critical to the development of hurricanes. One of these components is identifying the variables (or parameterizing) of momentum and heat fluxes across the air-sea interface. All the flux parameters currently used in the operational models were developed using observations taken under winds weaker than those associated with a typical hurricane. Furthermore, under hurricane conditions, the air and sea is separated by a spray-filled transition layer. Parameterizations of momentum and heat fluxes across such a layer need to take into account the effect of sea spray, but they currently do not.
Over the past decade, research has been carried out to combine atmospheric observations, laboratory experiments and numerical modeling studies to develop, test and improve the parameterizations of air-sea momentum and heat fluxes under hurricane conditions.
Research Activities and Outcomes
We developed a method for parameterizing air-sea heat fluxes as an extension of the TOGA-COARE bulk flux model, which has been refined with observations from new field campaigns and updated theoretical understanding. The unique aspect of this scheme is that it includes the sea-spray contribution to the air-sea heat fluxes for winds greater than 25 m/s. We are currently testing and evaluating the ESRL air-sea heat flux parameterization scheme in the operational hurricane model (HWRF) and the community weather research and forecast model (WRF-ARW). The goals of the ongoing research with both the operational and research models are (1) to determine the sensitivity of the sea-spray mediated air-sea heat flux calculation to the uncertainties in the wave dynamics and the kinematic and thermodynamic feedbacks of sea spray, and (2) to make the scheme more general by including both the spray evaporation feedback and stress reduction effects. We are also closely collaborating with researchers from NOAA and universities to evaluate the impact of the improved air-sea flux scheme on the marine boundary layer dynamics under hurricane conditions.