TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 56 (No. 4), pp. 473-483, 2000

Numerical Modeling of Wave-Enhanced Turbulence in the Oceanic Upper Layer

Le Ngoc Ly* and Roland W. Garwood, Jr.

Department of Oceanography, Naval Postgraduate School, Monterey, CA 93943-5100, U.S.A.

(Received 28 June 1999; in revised form 31 January 2000; accepted 31 January 2000)

Abstract: A coupled model of air-wave-sea interaction is modified based on a new roughness formulation and the latest data. The model parameters for aerodynamic roughness from below (ARB) and wave-dependent roughness from above (ARA, z0a) are assumed equal. The combined roughness is assumed to be a function of friction velocity, gravity, air and seawater densities, and wave age (cw). The model is used in a study of wave-enhanced turbulence under breaking waves to predict turbulent dissipation (e), ARA, and drag coefficient (Cd). Both waves and shear production are considered as sources of ocean turbulent energy. The atmospheric part of the model is used only to specify a correct condition at the interface. Numerical experiments are performed to study the e-distribution, z0a and Cd, and to compare with data. The major achievement is model verification using all available data. The first full application of this model is in conjunction with an ocean circulation model in a coupled circulation-wave system. Simulations show that the e-distribution is strongly dependent on local wind-forced wave heights. For each wind and wave state there is a particular wave-dependent depth that is verified by data. The comparison shows that the model predicted eagrees well with the observed eof the z-4 law distribution of Gargett (1989). Simulations also show that waves have an important role in causing eto differ from the classical wall-layer theory and z0a, with a value of 0.30 for the empirical constant aa. The model-predicted e, z0a, Cd and Cgdagree well with data.

*Corresponding author E-mail: lely@nps.navy.mil

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