John Marshall

Cecil and Ida Green Professor of Oceanography, MIT

A HETON MODEL OF THE SPREADING PHASE OF OPEN-OCEAN DEEP CONVECTION

A HETON MODEL OF THE SPREADING PHASE OF OPEN-OCEAN DEEP CONVECTION.

(LEGG, S and MARSHALL, J), JOURNAL OF PHYSICAL OCEANOGRAPHY, vol. 23, no. 6, pp. pages, 1993.

Abstract

A point-vortex heton model of the lateral dispersion of cold water formed in open-ocean deep convection is developed and studied as an idealized representation of the sinking and spreading phase of open-ocean deep convection. The overturning and geostrophic adjustment of dense fluid on and below the radius of deformation scale, formed by cooling on the large-scale, are parameterized in the model by introducing paired, discrete point vortices (hetons) of cyclonic sense in the surface layer, anticyclonic below, driving a cold baroclinic vortex. The convection site is imagined to be made up of many such baroclinic vortices, each with a vertically homogeneous core carrying cold, convectively tainted waters. The point vortices are introduced at a rate that depends on the large-scale cooling and the intensity assumed for each vortex. The interaction of many cold baroclinic vortices, making up a cloud, is studied using point-vortex Green’s function techniques. The current solenoids of the individual elements sum together to drive a large-scale rim current around the convection site, cyclonic above, anticyclonic below, which is associated with a baroclinic zone on a scale of the order of the ambient radius of deformation. For parameters typical of open-ocean deep convection, the cloud of point vortices breaks down baroclinically on a time scale of a few days, into Rossby radius-scale “clumps”. These extended hetons efficiently flux the cold water away laterally from the convection site and affect an inward transfer of heat sufficient to offset loss to the atmosphere.

doi = 10.1175/1520-0485(1993)0232.0.CO;2