Date of Award

Fall 1989

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

Chester E. Grosch

Committee Member

Gabriel T. Csanady

Committee Member

Ronald E. Johnson

Committee Member

John A. Adam

Abstract

The Gulf Stream shows a large meander off Cape Hatteras. This is driven by an energy conversion process known as baroclinic instability and observations suggest that nonlinearity is an important part in this process. In order to understand the fundamental role of nonlinearity in baroclinic instability, an inviscid 2-layer quasi-geostrophic model is studied.

The linear solution is obtained by methods of normal mode and Fourier-Laplace transforms. It is found that the set corresponding to the continuous spectrum is null and the set corresponding to the discrete spectrum is complete.

The nonlinear solution is expanded in terms of the complete set of the eigenfunctions in the north-south direction and a Fourier series in the east-west direction. Using a certain form of orthogonality of the eigenfunctions, a 6-dimensional dynamical system which solves for the amplitudes of the components is derived. A solution to this system is obtained for certain initial conditions using the Runge-Kutta method. In particular, it is found that stability of any solution of this system, such as a fixed point x = 0, can be determined by transforming the system into a set of Hamiltonian equations.

A computed meander represents either an eastward or a westward propagating wave with an amplitude vacillation. Effects of severe truncation appear to be significant in some cases. Judging from the solution of the dynamical system, the computed meander is found to be quasi-periodic and sensitive to initial conditions.

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DOI

10.25777/r3sz-5g62

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