Localization of Deep Ocean Convection by a Mesoscale Eddy

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Abstract
Observations of open-ocean deep convection indicate that it is a highly localized phenomenon, occurring over areas of tens of kilometers in diameter. The cause of this localization has been ascribed to “preconditioning”—the local weakening of the stable density stratification associated with upwardly domed isopycnal surfaces in a surface-intensified cyclonic circulation. However, most numerical and laboratory studies of localized convection have prescribed the localization artificially, by confining the surface buoyancy loss to a circular disk. In contrast, in the numerical simulations described here, deep convection forced by horizontally uniform buoyancy loss is localized within a region of initially weaker stratification than its surroundings. The preconditioned region is associated with a cold-core cyclonic eddy in geostrophic and cyclostrophic balance. As in previous studies of disk-shaped cooling, the localized convection region undergoes baroclinic instability at late times, causing the br... Abstract Observations of open-ocean deep convection indicate that it is a highly localized phenomenon, occurring over areas of tens of kilometers in diameter. The cause of this localization has been ascribed to “preconditioning”—the local weakening of the stable density stratification associated with upwardly domed isopycnal surfaces in a surface-intensified cyclonic circulation. However, most numerical and laboratory studies of localized convection have prescribed the localization artificially, by confining the surface buoyancy loss to a circular disk. In contrast, in the numerical simulations described here, deep convection forced by horizontally uniform buoyancy loss is localized within a region of initially weaker stratification than its surroundings. The preconditioned region is associated with a cold-core cyclonic eddy in geostrophic and cyclostrophic balance. As in previous studies of disk-shaped cooling, the localized convection region undergoes baroclinic instability at late times, causing the br...

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