Internal tide in the northwestern part of Banderas Bay, Mexico

Abstract

The results of a special experiment measuring the spatiotemporal parameters of internal waves on the wide continental shelf of northwestern Banderas Bay (Mexico) are discussed. The oceanographical measurements consisted of: (a) a fast survey with an undulating CTD along a transect perpendicular to the coast, (b) the towing of an array of temperature and depth sensors several times over the continental shelf along transects perpendicular to the coast, and (c) time series of velocity components registered by an acoustic Doppler current profiler placed on the seabed of the bay at 28 m depth. The presence of internal waves generated by semidiurnal tides and corresponding to the second normal oscillation mode (according to the linear theory of internal waves) was determined. Analysis of the data showed that, in the study area, the internal waves generated over the continental slope by the barotropic tide have the shape of an oscillatory bore, which quickly disintegrates during their propagation shoreward, producing short nonlinear waves that dissipate close to the coast and intense vertical mixing of the whole water column. The interpretation of the results was based on the linear and nonlinear (Korteweg-de Vries equation) theories of internal waves.