Generación y propagación de ondas internas en el estrecho de Gibraltarefectos 3-d y de rotación

Resumen

Three-dimensional and Earth's rotation effects on the generation and propagation of internal solitary waves in the Strait of Gibraltar are studied. These tidally generated waves, with horizontal scale of several hundred meters and even one hundred meters amplitude (maximum vertical isopycnal displacement), are the most spectacular phenomenon occurring in the Strait. The analysis of high temporal resolution observations collected during May 2003 at two different locations of the Strait of Gibraltar is the starting point of the thesis. Data set reveals that during neap tides solitary waves are normally generated during alternative tidal cycles due to the influence of the diurnal tide, which induces a remarkable diurnal inequality. It is shown that diurnal tidal currents in fact considerably modulate the propagation velocity of internal waves. About half the detected solitary wave packets present an anomalous structure: in contrast with classical theory predictions, waves are not rank-ordered within the packet, that is, they do not show decreasing amplitude from the front to the tail, due to the nonlinear dispersion. This fact is investigated within the framework of a three-dimensional, fully nonlinear, nonhydrostatic numerical model. It is shown that this unexpected behaviour is the result of the interaction of internal waves with the irregular bottom topography and lateral boundaries of the Strait, that favour the leakage of energy from the leading wave to the waves behind. The effect of rotation on the dynamics of internal solitary waves in a rectangular channel is also numerically investigated. As it happens in the open ocean, rotation plays a fundamental role in the long-term. When a two-dimensional internal solitary wave enters a rotating channel it evolves into a Kelvin solitary wave that losses energy due to the continuous radiation of Poincaré waves. Eventually secondary Kelvin waves may arise at the tail as a result of reflections from the lateral boundaries, and finally reach the leading wave to produce a quasistable wave packet. Finally the numerical model has been used to investigate the generation process of internal waves at Camarinal sill, in the Strait of Gibraltar. Several scenarios of wave generation, which depends on the barotropic tidal forcing, are identified. Rotation and 3D effects related to local variations of the bottom topography are also evaluated.