TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 55 (No. 1), pp. 65-78, 1999

Fission of Heton-like Vortices under Sea Ice

Shenn-Yu Chao1 and Ping-Tung Shaw2

1Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, Maryland 21613-0775, U.S.A.
2Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695-8208, U.S.A.

(Received 30 April 1998; in revised form 21 August 1998; accepted 10 November 1998)

Abstract: Close interactions among vertically stacked pairs of counter-rotating eddies under sea ice were investigated in numerical experiments. The numerical 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 anticyclone, while a shallow freshening source generates a top anticyclone and a submerged cyclone. Ice-exerted friction would dissipate the top eddy, leaving the submerged one in lone existence. In this work the winning vorticity is sought from group settings. Arrays of equally spaced salinity sources and sinks, alternate in sign but equal in strength, are employed to produce rows of vertically stacked eddy pairs. Fission occurs when adjacent vortex centers are separated by less than one Rossby radius. This process ejects parcels of density anomalies to the ambient ocean in upper depths. Low salinity anomalies are quickly dispersed into a thin surface layer and are unable to regenerate submerged eddies. High salinity parcels, being difficult to disperse, often maintain or regenerate submerged anticyclones below. Fission is particularly effective if a single row of salinity forcing is used. With multiple rows, fission is active only in the outer rows. The strong interaction among closely packed eddies operates in time scales of tens of days, helping explain the predominance of submerged anticyclones under Arctic sea ice.

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