3-DIMENSIONAL SIMULATIONS OF OVERFLOWS ON CONTINENTAL SLOPES

Three-dimensional features and instabilities of dense overflows from m arginal seas onto continental slopes are investigated using a three-di mensional, primitive equation numerical ocean model. The numerical sim ulations reveal important instability and three-dimensional features o f the overflow plumes that have not been included in previous simulati ons with a one-dimensional streamtube model and a two-dimensional plum e model. It is shown that the large primary plume breaks into a number of smaller subplumes on the offshore side of the plume due to instabi lities manifested as growing topographic Rossby waves over the slope. The observed high temporal and spatial variabilities in the Denmark St rait overflow could be caused by the inherent dynamic instabilities as revealed by the numerical simulations. The simulations indicate that the initial overflow velocity and width, the properties of the source water, the planetary rotation, and the slope steepness play major role s in determining the scales of the breaking-away subplumes and the acr oss-slope penetration of the large plume. The model simulations also s how that a chain of surface cyclonic eddies form and travel almost par allel to the isobaths toward the right and downstream of the plume sou rce. These eddies provide a surface signature of the sinking, breaking -away subplumes, as a result of vortex stretching in the upper part of the water column above the subplumes. Such surface features may have been observed in satellite IR imagery along the East Greenland contine ntal shelfbreak, and it may be possible to use satellite imagery and f urther modeling studies to monitor the Denmark Strait overflow, which produces most of the North Atlantic Deep Water.