A numerical study of wind forcing of eddies and jets in the California Current System

Abstract

A high-resolution, multi-level, primitive equation ocean model is used to examine the response to wind forcing of an idealized flat-bottomed oceanic regime along an eastern ocean boundary. A band of steady alongshore, upwelling favorable winds, either with or without alongshore variability, is used as forcing on both anf-plane and a ,a-plane. In each experiment a wind-driven equatorward coastal jet and a poleward undercurrent are generated. In time the coastal jet and undercurrent become unstable and lead to the development of eddies and jets with relatively strong onshore and offshore directed flows. The alongshore variation in alongshore wind stress plays a role in determining the location of eddy generation regions. A comparison of model results with available observations shows that the time-averaged model coastal jet and undercurrent are consistent in scale and magnitude with the observed data. Although the instantaneous eddies and jets are weaker than the corresponding observed features, they have horizontal scales typical of the observed scales. The results of this study support the hypothesis that steady wind forcing is one of several possible important generation mechanisms for eddies in the California Current System.

Process-oriented modeling studies of the 5500-km-long boundary flow off western and southern Australia

“…The generation of a poleward undercurrent along the west coast is consistent with previous process-oriented modeling studies which have shown that a poleward undercurrent can be generated due to meridional variability in the predominantly equatorward wind stress (Batteen et al, 1989) and/or to the planetary beta effect (e.g., McCreary et al, 1986;Batteen, 1997). The beta effect allows the existence of freely propagating planetary waves, i.e., Rossby waves (Gill, 1982).…”

Modeling studies of the effects of wind forcing and thermohaline gradients on the California Current System

“…2.0;10 cm s\) as in Batteen et al (1989). Holland (1978) showed that the highly scale-selective biharmonic diffusion acts predominantly on submesoscales, while Holland and Batteen (1986) found that baroclinic mesoscale processes can be damped by Laplacian lateral heat diffusion.…”

“…The numerical model in this study was originally used for a coarse resolution, closed basin by Haney (1974), and later adapted for eddy-resolving, limited EBC regions with open borders on the northern, western, and southern boundaries by Batteen et al (1989), Batteen (1997), and Batteen and Butler (1998). The limited area EBC model is multi-level, uses non-adiabatic primitive equations on a beta-plane, and has both baroclinic and barotropic velocity components.…”

“…As a result, the use of biharmonic lateral diffusion should allow mesoscale eddy generation via barotropic (horizontal shear) and/or baroclinic (vertical shear) instability mechanisms. As in Batteen et al (1989), weak (0.5 cm s\) vertical eddy viscosities and conductivity are used. Bottom stress is parameterized by a simplified quadratic drag law (Weatherly, 1972), as in Batteen et al (1989).…”

“…This generative mechanism in the CCS has been explored by Batteen et al (1989), McCreary et al (1991, Auad et al (1991), andPares-Sierra et al (1993). In these model studies, externally imposed currents are not necessary; rather, the wind-forced models develop their own currents, which can subsequently become unstable.…”