Western Boundary Current Separation Sensitivity Studies Using a Quasigeostrophic Ocean Model

Abstract

The sensitivity of the separation of the western boundary current of an idealized single gyre circulation to the specification of various model parameters is investigated through a series of quasigeostrophic simulations. The model parameters considered are the value of ?, bottom topography, lateral boundary conditions, deformation radius of the first baroclinic mode, horizontal friction, and model resolution. Changes in these model parameters affect western boundary current separation characteristics, but those parameter changes also produced changes in several measures of the global flow field such as level of mean and eddy kinetic energies. A number of flow field statistics are correlated with the average separation point, and it was found that total average baroclinic kinetic energy is the most highly correlated variable to the average separation point, with higher levels of kinetic energy being correlated with more poleward penetration. In the immediate vicinity of the separation point, the advection of relative vorticity is the largest contributor to tendencies conducive to separation. This contribution is especially dominant for the finest horizontal resolution run. An analysis of the convergence of zonal momentum revealed that it is the (u?u?)x term that is the dominant contributor to zonal velocity component tendencies near the separation point. Contributions involving the mean flow tend to be smaller but of larger meridional scale than the terms involving eddy interactions. A wavelet analysis of the time-dependent separation point reveals that the greater the contribution of (u???)y in the convergence of zonal momentum, the greater the low-frequency energy at separation point location. The effect is most pronounced in the finest horizontal resolution experiment.