David Marshall

Abstract:

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 α-dq/dψ >0, where q is the absolute vorticity and ψ is a streamfunction for the geostrophic flow, then the jet tends to penetrate across to the eastern boundary; conversely if α <0, the jet turns back on itself creating a tight recirculation on the scale of order [α]-1/2. This behavior is demonstrated in a quasigeostrophic ocean model. The implications of this study for numerical simulations of ocean gyres are discussed. In particular, it is demonstrated that poor resolution of the horizontal jet structure may lead to a dramatic reduction in penetration. -from Authors