Title

Mesoscale Eddy Dynamics By The Method Of Point Vortices

Date of Award

1987

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Meteorology and Physical Oceanography

Abstract

The subject of mesoscale eddies is considered from the vantage of vorticity dynamics in a numerical model based on the point vortex model developed by Christiansen (1973). Barotropic and equivalent barotropic inviscid eddies on an f -plane are considered; full baroclinic and planetary effects are not included. The study considers a wide parameter range to describe and demonstrate under which circumstances the separate and combined effects of adjacent vortices, mean flow (in this case a jet), and nearby topography (in the form of sidewalls) can alter the translation and evolution of an isolated eddy.The interaction of equivalent barotropic eddies is seen to be similar to their two-dimensional counterparts, but with an important difference: the scale at which the vortices interact is reduced. This is a consequence of the weakening strain field associated with introducing the vertical stretching contribution to the potential vorticity.The interaction of an eddy with a jet usually results in an upstream motion of the eddy. The controlling factor for this motion is the formation of a vortex that forms from the adjacent shear vorticity of the jet. Eddies that are initialized near the side of the jet opposite their own vorticity generally lose some portion of their mass field to the jet, but total absorption during one encounter does not occur. Paradoxically weaker eddies are absorbed less because the oppositely signed edge vortex that forms is more able to affect the motion of the eddy and carry it away from the original interaction site. Eddy intensification is also possible and requires an intense eddy initialized near the side of the jet with vorticity identical to the eddy's.Near complete absorption does occur if the eddy is trapped between a solid boundary and the jet or in situations where the eddy interacts more than once with the jet over the course of the simulation. Subsequent interactions result in a larger amount of the original mass field being absorbed than was lost in the initial interaction. Furthermore, interactions with jets confined near boundaries result in larger eddy absorption than interactions with freely meandering jets.

Keywords

Physical Oceanography

Link to Full Text

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