A Model for the Generation of Coastal Seiches by Deep-Sea Internal Waves

Abstract

A dynamical mechanism for the generation of coastal sciches by deep-sea internal waves is investigated using a linear, two-layer coastal model in which internal waves from the deep ocean impinge upon a step-shelf bottom topography. For periodic incident waves, a pronounced peak in the shelf response occurs at each coastal seiche frequency. The maximum amplitude over the shelf is almost directly proportional to the degree of stratification, suggesting that sciche activity should vary with seasonal changes in the stratification. Based on the periodic solutions, Fourier transforms are used to determine the response to one or more internal-wave pulses, and the results are qualitatively consistent with observations. For geometry and gratification which are representative of the Caribbean coast of Puerto Rico, reasonably realistic incident pulses preferentially excite the basic seiche frequency, and a rather small amplitude pulse (10 m) can easily generate currents at the shelf break of 8–10 cm s−1. Further, as is typical of the observed sciches, the time history of the modeled motions over the shelf can be rather irregular, depending on the pulse shape and the time delay between pulses.