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Alternative Parameterizations of Downward Irradiance and Their Dynamical Significance

J. J. SimpsonScripps Institution of Oceanography, La Jolla, CA 92093

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T. D. DickeyInstitute for Marine and Coastal Studies and Department of Geological Sciences, University of southern California, Los Angeles 90007

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Abstract

The effect of solar flux divergence on upper ocean dynamics and energetics under both low and high wind speeds was determined using four different parameterizations of downward irradiance. The first (case I) involved only one attenuation length, the second (case II) involved two attenuation lengths, the third (case III) used a spectral decomposition of the incident solar flux over nine wavelength bands, and the fourth (case IV) used an arctangent model of downward irradiance. The Mellor-Yamada turbulence closure scheme (level 2½) was used for the simulations. Cases II–IV predict the existence of an intensified shallow shear zone which is consonant with recent observations. At low wind speeds, the turbulent energy budget is dominated by shear production, dissipation and the diffusion of turbulent kinetic energy, regardless of parameterization. At high wind speeds, shear production is balanced by dissipation. Specific recommendations are made for parameterizing the downward irradiance in the context of numerical studies of upper ocean dynamics, general circulation and climate studies.

Abstract

The effect of solar flux divergence on upper ocean dynamics and energetics under both low and high wind speeds was determined using four different parameterizations of downward irradiance. The first (case I) involved only one attenuation length, the second (case II) involved two attenuation lengths, the third (case III) used a spectral decomposition of the incident solar flux over nine wavelength bands, and the fourth (case IV) used an arctangent model of downward irradiance. The Mellor-Yamada turbulence closure scheme (level 2½) was used for the simulations. Cases II–IV predict the existence of an intensified shallow shear zone which is consonant with recent observations. At low wind speeds, the turbulent energy budget is dominated by shear production, dissipation and the diffusion of turbulent kinetic energy, regardless of parameterization. At high wind speeds, shear production is balanced by dissipation. Specific recommendations are made for parameterizing the downward irradiance in the context of numerical studies of upper ocean dynamics, general circulation and climate studies.

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