Stationary Rossby waves in western boundary current extensions

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Meteorology and Physical Oceanography

First Committee Member

Donald B. Olson - Committee Chair

Second Committee Member

Douglas B. Boudra - Committee Member


The existence of temporally growing, spatially damped long waves on a zonal flow is considered with a local analysis of a simple analytical model. This model consists of an investigation of the possible solutions of the quasi-geostrophic equation for a spatially uniform, zonal mean flow with Laplacian lateral dissipation. The realizability of these analytical solutions is investigated in a number of numerical simulations consisting of barotropic (one-layer) and baroclinic (two-layer) experiments.In the barotropic simulations, in addition to a study of the dynamics in the region of confluence of wind-driven western boundary currents, an evaluation of the effects of boundary conditions, geometry and form of representation of the western boundary is considered. Among the results of these one-layer cases are indications that stationary wave-like meandering of the mid-latitude jet can result from north-south asymmetries introduced either in the wind-stress distribution or in the western boundary geometry. Other conclusions from the barotropic experiments are that the solution in the vicinity of the western boundary can be greatly distorted if the ratio of the resolution to the viscous boundary layer width is greater than unity. This distortion is enhanced when step-like forms are used for representing a tilted western boundary, especially in the no-slip case.In the baroclinic experiments, a two-layer simulation with a realistic South American coastline and free-slip condition results in an energetic stationary pattern in the model's confluence region. This feature, although stationary in phase, has a time varying amplitude, that is reminiscent of observations in the Brazil-Malvinas confluence.Comparison with no-slip experiments show that the existence of the stationary feature is not dependent on the boundary condition, even though in the no-slip case there is much less activity in the confluence region. An experiment consisting of a continuation of the free-slip run, with eddy-viscosity coefficient reduced to one-third of its original value, is performed to investigate the effect of increased turbulence on the existence of stationary waves. Despite the different equilibrium state reached, a well defined stationary feature is obtained in the confluence region. (Abstract shortened with permission of author.)


Physical Oceanography

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