Double-Diffusive Convection in a Stochastic Shear

Timour Radko Department of Oceanography, Naval Postgraduate School, Monterey, California

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James Ball Department of Oceanography, Naval Postgraduate School, Monterey, California

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John Colosi Department of Oceanography, Naval Postgraduate School, Monterey, California

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Jason Flanagan Department of Oceanography, Naval Postgraduate School, Monterey, California

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Abstract

An attempt is made to quantify the impact of stochastic wave–induced shears on salt fingers associated with internal waves in the ocean. The wave environment is represented by the superposition of Fourier components conforming to the Garrett–Munk (GM) spectrum with random initial phase distribution. The resulting time series of vertical shear are incorporated into a finger-resolving numerical model, and the latter is used to evaluate the equilibrium diapycnal fluxes of heat and salt. The proposed procedure makes it possible to simulate salt fingers in shears that are representative of typical oceanic conditions. This study finds that the shear-induced modification of salt fingers is largely caused by near-inertial motions. These relatively slow waves act to align salt fingers in the direction of shear, thereby rendering the double-diffusive dynamics effectively two-dimensional. Internal waves reduce the equilibrium vertical fluxes of heat and salt by a factor of 2 relative to those in the unsheared three-dimensional environment, bringing them close to the values suggested by corresponding two-dimensional simulations.

Corresponding author address: Timour Radko, Department of Oceanography, Naval Postgraduate School, 833 Dyer Rd., Room SP-344, Monterey, CA 93943. E-mail: tradko@nps.edu

Abstract

An attempt is made to quantify the impact of stochastic wave–induced shears on salt fingers associated with internal waves in the ocean. The wave environment is represented by the superposition of Fourier components conforming to the Garrett–Munk (GM) spectrum with random initial phase distribution. The resulting time series of vertical shear are incorporated into a finger-resolving numerical model, and the latter is used to evaluate the equilibrium diapycnal fluxes of heat and salt. The proposed procedure makes it possible to simulate salt fingers in shears that are representative of typical oceanic conditions. This study finds that the shear-induced modification of salt fingers is largely caused by near-inertial motions. These relatively slow waves act to align salt fingers in the direction of shear, thereby rendering the double-diffusive dynamics effectively two-dimensional. Internal waves reduce the equilibrium vertical fluxes of heat and salt by a factor of 2 relative to those in the unsheared three-dimensional environment, bringing them close to the values suggested by corresponding two-dimensional simulations.

Corresponding author address: Timour Radko, Department of Oceanography, Naval Postgraduate School, 833 Dyer Rd., Room SP-344, Monterey, CA 93943. E-mail: tradko@nps.edu
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