Close interactions between two pairs of heton-like vortices under sea ice

Close interactions between two pairs of vertically stacked counterrotating eddies under sea ice were investigated in numerical experiments. The numeri cal model contains a stratified ocean capped by an ice layer. Under the ice layer a shallow brine source produces a top cyclone and a submerged anticy clone, while a shallow freshening source generates a top anticyclone and a submerged cyclone. Ice-exerted friction dissipates the top eddies in time, leaving submerged ones in lone existence. In this work, winning vortices ar e sought from a brine-brine pair, a freshening-brine pair, and a freshening -freshening pair. Brine and freshening sources are made equal in strength t o level the playing field. When closely paired, fission, an increase in the number of subsurface vortices, occurs from a brine-brine pair and a freshe ning-brine pair but not from a freshening-freshening pair. Consequences of fission invariably increase the number of submerged anticyclones. A heurist ic argument is given to explain this polarity. The strong interaction among closely packed eddies operates in timescales of tens of days, helping to e xplain the predominance of submerged anticyclones under the Arctic sea ice.