BIFURCATION OF EASTWARD JETS INDUCED BY MIDOCEAN RIDGES AND DIVERGINGISOBATHS

A three-dimensional primitive-equation model is employed to investigat e how a mid-ocean ridge affects an eastward incoming jet overlying iso baths that diverge eastward. The diverging isobaths contain a major no rtheastward continental slope and a minor deeper southeastward bottom slope, both with shallow waters to the north. The southwest-northeast trending mid-ocean ridge is placed at about 1700 km east of the northe astward continental slope. In the barotropic regime, the diverging iso baths force an initially eastward jet to widen and follow f/h contours after a hydraulic jump. The mid-ocean ridge radiates barotropic Rossb y waves, further enhancing the lateral widening of the jet. The northe rn portion of the jet expands northward and forms a western boundary c urrent along the northeastward continental slope. The bifurcated curre nt system consists of the northeastward flow and the remnant of the or iginal eastward current. When the ridge is removed, the jet diverges b ut does not bifurcate. In the baroclinic regime, continuous meander an d eddy activities reinforce the meridional spreading of the jet and ca use greater portion of the jet to diverge northward. Consequently, a s tronger western boundary current is formed along the northeastward con tinental slope. As in the barotropic regime, the mid-ocean ridge exert s its influence upstream by radiating barotropic Rossby waves westward , further enhancing the jet splitting. Among possible applications, th e model is particularly relevant to the bifurcation of the Gulf Stream as it passes by the southern tail of the Grand Banks.