M₂ tidal currents on the shelf off Goa, West coast of India

Abstract

Current meter records collected during three different months from a site off Goa (15 ° 08'N, 73 ° 16'E) over the western continental shelf of India have been used to describe the M₂ tidal structure in a water column of depth about 100 m. Tidal ellipse parameters and Greenwich phases were estimated using the least squares fit technique. M₂ tidal currents have shown significant variations from one season to another (15 cm/s during May 1984 to 3.7 cm/s during November 1986). The baroclinic M₂ tide have been interpreted in terms of linear internal wave dynamics. The results show that the M₂ baroclinic tide is dominatEd. by the first mode. The horizontal wavelength over the shelf predictEd. by this method is about 22 km. This is smaller than the shelf width of about 110 km. The group velocity for the first baroclinic mode is about 0.45 m/s, which means that energy takes. approximately two and a half days to cross the shelf. Evidence presented here suggests that stratification over the continental shelf and the adjacent slope has influenced the amplitude of internal tidal currents. The bottom slope switches from being supercritical to subcritical in the shelf break region during May and remains subcritical all over the shelf and the slope during November.