Elongation and Contraction of the Western Boundary Current Extension in a Shallow-Water Model: a Bifurcation Analysis

A numerical bifurcation analysis of a shallow water equation model of the doublegyre ocean circulation. The analysis is performed in a two parameter space where one parameter controls the viscosity of the model and a second parameter controls the symmetry of the wind forcing. The two parameter analysis is used to find “isolated” steady-state solution branches that were not and could not have been found in previous one-parameter continuation studies. The new branches come into existence at lower viscosity, have a jet extension that penetrates further eastward and are more stable than steady-state solution branches from previous studies. The intrinsic lowfrequency variability at lower viscosity is shown to be associated with a sequence of bifurcations originating from the new steady-state solution branch. Preprint submitted to Journal of Physical Oceanography 27 June 2006