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The double-diffusive modon. (English) Zbl 1147.76058

Summary: Fully developed two-dimensional salt-finger convection is characterized by the appearance of coherent dipolar eddies which carry relatively fresh and cold fluid upward and salty and warm fluid downward. Such structures - the double-diffusive modons - are prevalent in the regime in which density stratification is close to neutral and the salt-finger instability is extremely vigorous. The structure and translation velocities of modons are discussed in terms of the asymptotic expansion in which the background density ratio approaches unity. It is argued that the vertical salt flux is driven primarily by double-diffusive modons, which makes it possible to derive explicit expressions for mixing rates of temperature and salinity as a function of their background gradients. Predictions of the proposed mixing model are successfully tested by direct numerical simulations.

MSC:

76R50 Diffusion
76M45 Asymptotic methods, singular perturbations applied to problems in fluid mechanics
86A05 Hydrology, hydrography, oceanography
80A20 Heat and mass transfer, heat flow (MSC2010)
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