John F. Middleton and Guennadi Platov

Dept. Applied Mathematics Rep.00/21 UNSW, Sydney 2052

A numerical study is made of the dynamics of the slope circulation set-up by steady downwelling favourable winds backward of a rectangular strait. First mode Coastal-Trapped Waves (CTWs), generated within the region of wind-forcing propagate towards the strait where they are in part, scattered into out of phase mode 2 waves. By day 7, the resultant circulation just forward of the strait is bimodal, with an equatorward current at the coast, and a poleward current that is bottom intensified over the slope. The equatorward current upwells dense water into the strait. The poleward slope current is found to be very similar to that obtained without a strait where the initial set-up is largely determined by the first mode waves. The likely explanation for the initial similarity over the slope, is that the first mode waves, while reduced in magnitude due to the scattering by the strait, are reinforced by the out of phase, second mode waves. At later times, the thermal-wind shear within the bottom boundary layer becomes important to the slope current. However, the slope currents are again similar in each case, since the effects due to friction result from similar overlying alongshore currents.