Arctic Ocean Eddies and Baroclinic Instability.
Technical rept. Mar-May 81,
LAMONT-DOHERTY GEOLOGICAL OBSERVATORY PALISADES NY
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Baroclinic eddies with diameters of about 10 km and maximum current speeds of about 50 cms have been widely observed in the central Arctic Ocean north of Alaska and Canada. The possible origin of these eddies through an instability of the mean baroclinic flow is investigated using an ocean model with exponential profiles of mean shear and Vaisala frequency. The model includes Ekman pumping at a rigid bottom and at either a free or rigid upper surface. The central Arctic Ocean where the eddies were found is baroclinically stable with no possibility of eddy production. If the eddies are spawned by this mechanism, they must be formed at a site far from where they were observed. On the periphery of the Arctic Ocean north of Alaska the combination of greater current shear, shallower depth and lack of ice cover leads to unstable conditions and the eddies apparently originate in that region. The instability theory predicts maximum velocity at the surface instead of below the surface as observed. Apparently after formation in open water the eddies are advected beneath the ice cover and dissipate the momentum of their upper layers against the ice. This is demonstrated by calculations for the diffusion of vorticity against the ice in the case of an initial exponential profile. A subsurface maximum then develops which resembles the observed profiles. Author
- Physical and Dynamic Oceanography
- Fluid Mechanics