Numerical investigation of baroclinic tides in the Red Sea

Abstract

Baroclinic tides play a significant role in driving deep-ocean mixing, which not only influences the transport of nutrients and other biological tracers, but also affects the large scale circulations. This thesis combines advanced numerical modeling techniques and available observations to investigate the characteristics of baroclinic tides in the Red Sea, and understand their formation and fate, and their influence on the circulation and ecosystem. Based on a validated 3D, non-hydrostatic and high-resolution MIT General Circulation Model (MITgcm), we first established four potential areas for the generation of baroclinic tide in the Red Sea: the Strait of Bab-el-Mandeb (BAM), the southern Red Sea, the Gulf of Suez, and the Strait of Tiran. These areas are consistently suggested by the spatial distribution of baroclinic tidal kinetic energy and energy fluxes. The majority of the baroclinic energy disappears within the basin; either dissipates due to friction and bottom drag or converts back into barotropic energy due to pressure. We next conducted 2D numerical simulations to investigate the generation mechanism behind the formation of the observed internal solitary waves(ISWs) in the southern Red Sea, revealing the dominant role of tide-topography interactions. Instead of evolving from the disturbed thermocline due to a locally impinging tidal beam ISWs are generated from the depression formed near the shelf. As this depression propagates out of the shelf, it gradually steepens and ultimately breaks into a group of ISWs. To further study the breaking and dissipation processes of the ISWs, we implemented a regional high-resolution MITgcm for the southern Red Sea with a realistic topography revealing that the breaking process is triggered by the fission mechanism. The associated particles transport is further quantitatively analyzed, revealing a significant transport, both vertically and horizontally. The thesis, finally examined the tidal influences on the basin-scale circulation of the Red Sea. Comparison experiments with and without tides show that, the intrusion of the Gulf of Aden Intermediate Water (GAIW) in summer is strongly influenced by the tides. It is suggested that tides enforce more turbulence and mixing at the strait, which significantly increase the diffusivity of heat and salinity.