Woods Hole Oceanographic Institution
Woods Hole, Massachusetts, U. S. A.
Laboratory experiments and theory have revealed \forcenl many different types of gravity currents in rotating fluids. Formulas for width, volume flux, and velocity scales of the currents have been known since the 1970's. Some issues concerning currents upstream of a control section are clarified. Laboratory experiments reveal a current preferably on the left hand side (looking upstream, for counterclockwise fluid rotation). Effects of drag are evident in the laboratory results which make detailed agreement with inviscid theory impossible. Transient experiments reveal that a Kelvin wave initiates a starting current on the right hand wall. Ekman suction removes fluid from this current and builds up the interior fluid depth, making the current on the left hand wall increase until only it remains. A new theory is presented which allows calculation of constant potential vorticity flow through a passage of arbitrary shape. Critically controlled flows are missing from present numerical models, and the need for their inclusion is revealed by a survey of nine important ocean sill flows. Independent calculations by colleagues may show how to include features of real gravity currents in numerical models of the ocean.