Effects of surface waves on air -sea momentum and energy fluxes and ocean response to hurricanes

Yalin Fan, University of Rhode Island

Abstract

In existing ocean models, momentum and turbulent kinetic energy (TKE) fluxes through the air-sea interface are parameterized by the bulk formulae, neglecting their dependence on the sea state. In this study, numerical experiments are performed to investigate the momentum and TKE flux budget across the air-sea interface under steady homogenous wind forcing and idealized hurricanes. The wave fields are simulated using the WAVEWATCH III model for all experiments. The air-sea momentum and TKE fluxes from the wind are estimated using a coupled wave-wind model and the fluxes into currents are estimated using an air-sea momentum and energy budget model. The results show that the effect of time variation of the wave field is small but the effect of spatial variation is important for momentum flux calculations across the air-sea interface. Both effects, however, are important for energy flux calculations. The spatial variation of the hurricane-induced surface waves plays an important role in reducing TKE and momentum fluxes into currents in the rear-right quadrant of the hurricane. Our results also suggest that the TKE flux varies with wave age and friction velocity, and it is roughly proportional to the 3.5th power of the friction velocity rather than the 3rd power as suggested in the literature. The wave age dependence become more complex under hurricanes suggesting it is necessary to explicitly resolve the wave field in order to accurately predict the momentum and TKE fluxes into currents. The wind/wave/current coupling mechanisms and their effect on the ocean and surface wave field response is also investigated through a set of numerical experiments. The Princeton Ocean Model is used to simulate the ocean response. The results show that during wave/current interaction, the momentum flux is mainly affected by the reduction of wind speed relative to currents while the wave field is mostly affected by refraction due to the current shear. Results of a case study in Hurricane Ivan (2004) suggest that an improved drag parameterization and the wave-current interaction improve the wave forecasts. ^

Subject Area

Physical Oceanography

Recommended Citation

Yalin Fan, "Effects of surface waves on air -sea momentum and energy fluxes and ocean response to hurricanes" (2007). Dissertations and Master's Theses (Campus Access). Paper AAI3276981.
http://digitalcommons.uri.edu/dissertations/AAI3276981

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