ZONAL PENETRATION SCALE OF MIDLATITUDE OCEANIC JETS.
(MARSHALL, D and MARSHALL, J), JOURNAL OF PHYSICAL OCEANOGRAPHY, vol. 22, no. 9, pp. pages, 1992.
It is shown that subtle changes in the velocity profile across the seaward extension of midlatitude jets, such as the Gulf Stream, can lead to dramatic changes in the zonal-penetration scale. In particular, if alpha = dq/d-psi > 0, where q is the absolute vorticity and psi is a streamfunction for the geostrophic flow, then the jet tends to penetrate across to the eastern boundary; conversely if alpha < 0, the jet tums back on itself creating a tight recirculation on the scale of order alpha*(-1/2). This behavior is demonstrated in a quasi-geostrophic ocean model in which a jet profile is prescribed as an inflow condition at the western margin of a half-basin, and radiation conditions along the remainder of the western boundary allow the injected fluid to escape. Jet inflows with both vertical and horizontal structure are considered in one and one-half-, two-, and three-layer models. Finally, the implications of our study for numerical simulations of ocean gyres, which frequently show sensitivity of jet penetration to horizontal and vertical resolution and to choice of boundary conditions, are discussed. In particular, it is demonstrated that poor resolution of the horizontal jet structure may lead to a dramatic reduction in penetration.