A study of internal wave propagation in the Strait of Gibraltar using shore-based marine radar images

Abstract

An X-band marine radar on Windmill Hill, Gibraltar, was used to monitor the propagation of internal waves in the Strait of Gibraltar during March, April, and June 1986. Surface roughness features of the waves were observed out to a range of approximately 15 km. From photographic images of the radar screen, the positions of image features were measured manually using a digitizing table, and these data were then computer processed to give wave arrival times and phase speeds. During most tidal cycles, an internal undular bore generated at Camarinal Sill was observed to pass eastward (A-waves). Wave phase speed was observed to be dependent on the propagation direction and on water depth, in qualitative agreement with theory. Other results included the observation of many wave packets propagating northward across the eastern Strait. These were named 'O-waves', and it is suggested that they were generated at prominent features on the Moroccan coast, gaining large amplitudes as shock waves in the supercritical flow. (from authors' abstract)