Eddy viscosity and diffusivity in the modon-sea model
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Authors
Radko, Timour
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2012
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Abstract
A deterministic model is developed to evaluate and explain the rate of dissipation of momentum
in eddying oceanic flows. Theory is based on a classical conceptualization of mesoscale variability
– Stern’s modon-sea solution – which represents a closely packed array of steady compact dipolar
vortices on the barotropic beta-plane. In our model, the periodic modon-sea pattern is subjected to a
large-scale perturbation, weakly modulating the amplitude of the individual modons. The asymptotic
multiscale analysis makes it possible to explicitly describe the interaction between the modon-sea
eddies and the perturbing flow. This interaction results in a systematic weakening of the large-scale
perturbation. The eddy viscosity in the model is found to be only weakly dependent on the explicit
dissipation but rapidly decreases with increased separation of the modons. The estimates based on
the modon-sea model are comparable to, but less than, the values of viscosity typically used in coarse
resolution numerical ocean models. The eddy diffusivity of passive tracers is also evaluated and
discussed in terms of a combination of analytical and numerical methods. The asymptotic theories
are successfully tested by direct numerical simulations.
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Article
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Oceanography
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Journal of Marine Research, 69, 723–752, 2012
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.