STUDY OF THE GENERATION AND PROPAGATION OF INTERNAL WAVES IN THE STRAIT OF GIBRALTAR USING A NUMERICAL-MODEL AND SYNTHETIC-APERTURE RADAR IMAGES OF THE EUROPEAN ERS-1 SATELLITE

A weakly nonhydrostatic, two-layer numerical model based on the Boussi nesq equations is presented which is capable of describing, among othe rs, the generation and propagation of nonlinear weakly dispersive inte rnal waves in the Strait of Gibraltar. The model depends on one space coordinate only, but it retains several features of a fully three-dime nsional model by including a realistic bottom profile, a variable chan nel width, and a trapezoidal channel cross section. The nonlinear prim itive Boussinesq equations include horizontal diffusion, bottom fricti on, and friction between the two water layers. The model is driven by a height difference of the mean interface depth between the Atlantic a nd the Mediterranean boundaries and by semidiurnal tidal oscillations of the barotropic transport. The model presented in this paper describ es (1) the mean and tidal flow in the Strait of Gibraltar, (2) the var iation of the depth of the interface during a tidal cycle, (3) the gen eration of strong depressions of the interface at the western sides of the Spartel Sill and the Camarinal Sill, (4) the generation of strong eastward propagating internal bores, and (5) their disintegration int o trains of internal solitary waves. The surface convergence patterns associated with depressions of the interface at the Camarinal Sill, in ternal bores, and internal solitary waves are calculated and compared with roughness patterns visible on synthetic aperture radar (SAR) imag es of the first European Remote Sensing Satellite ERS 1. In total, 155 ERS 1 SAR scenes from 94 satellite overflights over the Strait of Gib raltar, which were acquired in the period from January 1992 to March 1 995, have been analyzed. It is shown that the proposed model is capabl e of explaining the observed temporal and spatial evolution of surface roughness patterns associated with eastward propagating internal wave s inside the Strait of Gibraltar as well as the observed east-west asy mmetry of the internal wave held.