Generation of internal tides: An interaction of tides with variable topography and coastal geometry

Abstract

The paper describes tide-topography interaction with changeable width and angle of continental shelf. Experiments are designed with MITgcm over a study area representative of the western Bay of Bengal with an idealized bathymetry. As the actual coastline consists of an irregular configuration, the experiments are set with different coastline geometry. The tidal forcing is incorporated in the model to generate internal tides by adding tidal components in the momentum equations. The density stratification represents the region during May and is kept invariant for all the experiments. Spectral analysis suggests that semi-diurnal internal tides possess the maximum spectral estimate. The peak semi-diurnal estimate is computed to understand its variation over the shelfslope region. The analysis demonstrates that the estimate is smaller for wider shelves against narrow continental shelves. The peak estimate is observed close to 100m local depth over the shelf regardless of the angle and width. Experiments are further continued to distinguish the effect of rotation and geometry of the coast as the shelf width and shelf angle are kept constant. Comparison of spectral estimate is performed without and with rotation for three different coastline configurations: concave, convex and straight. The estimate is noticed maximum in the concave and minimum in the convex shape of the coast. Significant contribution of the rotational effect is seen as an increase in the semi-diurnal peak estimate towards the north of the domain. In order to confirm the effect of the rotation, a similar experiment is performed for the southern hemisphere revealing an enhancement of the estimate towards the south of the domain.