Topographic Dispersal of Bottom Water

Abstract

The time-dependent response of a 1½-layer, f-plane ocean with topography to a source of buoyancy is studied analytically and numerically. The topography consists of an infinitely long escarpment. Linear theory interprets the growth of a tube of fluid along the escarpment due to a point buoyancy source in terms of topographic waves The large-time, far-field asymptotic behavior of the topographic wave tube is discussed. In addition, there is a nonpropagating disturbance for which the interface elevation grows linearly with time. For an arbitrary source distribution only part of the source flux is carried away from the source in the topographic wave tube and nonlinear effects must eventually become important. Numerical results show that if the source area is located predominantly on the shallow side of the escarpment, eddies form at the source and self-propagate along the escarpment. The mass transport by these eddies compensates for the shortfall in the flux in the topographic wave tube. There is little eddying if the source is located predominantly on the deep side of the escarpment. Eddy speeds decrease as their centers are located farther from the escarpment. Consequently, as the source is located farther from the escarpment, the eddying rate decreases, but the eddy size increases. Such eddying could explain the periodic surging reported in bottom water flux measurements.