OBSERVATIONS OF HIGHLY NONLINEAR INTERNAL SOLITONS OVER THE CONTINENTAL-SHELF

Surface disturbances caused by strong, near-surface internal waves are widely seen in coastal regions as bands of slick and rough water prop agating shoreward. These surface slicks are typically manifestations o f optical and radar backscatter properties above internal solitons, an d have strong surface current pulses associated with them. During a re cent experiment studying coastal internal waves, extremely strong soli tary internal wave packets were observed over a three week period on a very shallow and strongly stratified pycnocline off Northern Oregon. During periods of strongest tidal forcing, solitons were consistently observed on the leading edge of a semidiurnal internal tide bore, with pycnocline displacements up to 25m downward from a 7m initial depth i n the first few solitons. The extreme nonlinearity of these internal w aves is believed to be unique in ocean observations. This note charact erizes these highly nonlinear Solitary Internal Waves (SIW) and presen ts a second order KdV model which reproduces the form of the displacem ents, and the small change in soliton width with amplitude predicted b y this model.