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Eddy Formation in 2½-Layer, Quasigeostrophic Jets

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  • 1 Departamento de Oceanografia Física, Instituto Oceanográfico, Universidade de São Paulo, São Paulo, Brazil
  • | 2 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts
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Abstract

The formation of nonlinear eddies in unstable 2½-layer, quasigeostrophic jets is investigated using a piecewise constant potential vorticity, “contour dynamical” model. Both infinite and semi-infinite jet dynamics are explored, considering a potential vorticity configuration with one front in each dynamically active layer. Unlike previous studies, the infinite basic jets have a double baroclinic mode structure, which allows the lower-layer transport to range from westward to eastward (with the upper-layer transport considered eastward in all cases). A variety of eddy-shedding events are obtained, and dipole vortices can form even with eastward lower-layer flows. For semi-infinite jets connecting to coastal currents along the boundary, coastal and retroflection eddies can be shed when baroclinic instability mechanisms are included. However, it seems that the unstable waves must either propagate westward or slowly in the eastward direction to allow this process to occur.

Corresponding author address: Dr. Ilson C. da Silveira, Departmento de Oceanografia Física, Instituto Oceanográfico da USP, Praça do Oceanográfico 191, São Paulo SP 05508-900, Brazil. Email: ilson@ipanema.io.usp.br

Abstract

The formation of nonlinear eddies in unstable 2½-layer, quasigeostrophic jets is investigated using a piecewise constant potential vorticity, “contour dynamical” model. Both infinite and semi-infinite jet dynamics are explored, considering a potential vorticity configuration with one front in each dynamically active layer. Unlike previous studies, the infinite basic jets have a double baroclinic mode structure, which allows the lower-layer transport to range from westward to eastward (with the upper-layer transport considered eastward in all cases). A variety of eddy-shedding events are obtained, and dipole vortices can form even with eastward lower-layer flows. For semi-infinite jets connecting to coastal currents along the boundary, coastal and retroflection eddies can be shed when baroclinic instability mechanisms are included. However, it seems that the unstable waves must either propagate westward or slowly in the eastward direction to allow this process to occur.

Corresponding author address: Dr. Ilson C. da Silveira, Departmento de Oceanografia Física, Instituto Oceanográfico da USP, Praça do Oceanográfico 191, São Paulo SP 05508-900, Brazil. Email: ilson@ipanema.io.usp.br

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