Wind-forced continental shelf waves in the Florida Current

Abstract

The significance of the wind as a generating mechanism for low (sub-inertial) frequency Florida Current fluctuations is examined. A model of the Florida Straits bottom topography and a baroclinic, steady mean current is considered. An approximate potential vorticity governing equation for the lowest order (barotropic) fluctuation mode is derived. The relative vorticity due to horizontal shear of the mean current is important and is included in the model. Solutions to the governing equation include a class of shear-modified, topographically-trapped, continental shelf waves (CSW's). In the absence of a mean current, CSW's travel with shallow water cum sole, in the direction of simple Kelvin waves. In the presence of the Florida Current, CSW's can travel northward under certain conditions, but in the sheared Current they are subject to critical 'level' absorption where the intrinsic wave speed vanishes. The dispersion characteristics of southward CSW's are profoundly modified by the horizontal shear of the mean current. It is concluded that the fluctuating winds provide a significant energy source for low frequency Florida current fluctuations.