The generation and propagation of internal wave forms in the Strait of Gibraltar studied by ERS-1 SAR imagery and a numerical model

Abstract

The generation and propagation of internal waves in the Strait of Gibraltar has been studied by analyzing 131 ERS-1 SAR scenes from 78 satellite overflights over this area in the period from December 1991 to February 1994. From the analysis of the ERS-1 SAR images the authors obtain the following results: (1) roughness patterns over the Camarinal Sill are visible from 1h after low tide at Gibraltar until 6h after low tide, (2) sea surface manifestations of eastward propagating internal waves are observed at distances from 23 km to 160 km from the Camarinal Sill, (3) the mean propagation speed of these internal waves is 2.0 ms/sup -1/, and (4) the spatial separation between the first two internal waves in a wave train ranges from 1.1 km inside the strait to 10 km in the Alboran Sea. The roughness pattern inside the strait are explained by a one-dimensional numerical model based on the Boussinesq equations for two water layers of different densities. The non-hydrostatic primitive shallow water equations include horizontal diffusion, bottom and interfacial friction. The model allows mean flows in both layers and is driven by a tidal flow at the open boundary. The proposed model explains the observed temporal and spatial evolution of roughness patterns inside the Strait of Gibraltar as well as the east-west asymmetry of the internal wave field. >