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

A point-vortex heton model of the lateral dispersion of cold water for med in open-ocean deep convection is developed and studied as an ideal ized representation of the sinking and spreading phase of open-ocean d eep convection. The overturning and geostrophic adjustment of dense fl uid 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 la yer, anticyclonic below, driving a cold baroclinic vortex. The convect ion site is imagined to be made up of many such baroclinic vortices, e ach with a vertically homogeneous core carrying cold, convectively tai nted 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, i s studied using point-vortex Green's function techniques. The current solenoids of the individual elements sum together to drive a large-sca le rim current around the convection site, cyclonic above, anticycloni c 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 ba roclinically 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 he at sufficient to offset loss to the atmosphere.