A numerical study of internal tide generation due to interaction of barotropic tide with bottom topography in the Oman Gulf


Malek Ashtar University of Technology, Shiraz, Iran


A major part of tidal energy is usually dissipated by the interaction of tidal currents with bottom topography. Gulf of Oman is a marginal sea which has variable topography and its dominant tidal constituent is M2 semi-diurnal tide. In this paper, the interaction of barotropic tidal current with bottom topography is evaluated. This phenomenon causes the formation of internal tide. Internal tide is a large scale and baroclinic phenomena which causes long wave oscillations of water column. Whereas the M2 semi-diurnal constituent is dominant, therefore this constituent is the main force for formation of internal tide in the Gulf of Oman. In this paper, numerical modeling of internal tide due to M2 semi-diurnal constituent is  presented. This modeling is done using iTides model. This model is a software package which produces the internal wave field from the barotropic tide. The iTides package provides a graphical user interface (GUI) that combines all the theoretical elements necessary for producing a desired internal tide field given a set of system parameters. The model setup begins by specifying the pathway of the file to the topography, where the topography shape is specified by the horizontal coordinate assigned x, topography height h and the topographic change dh (both h and dh are functions of x). We use this dataset to define the maximum depth of the problem Ho as the maximum depth reached by the topography. Then, the density stratification must be given. The final step requires the user to specify the tide (forcing) frequency and the Coriolis frequency of the problem. After all parameters have been declared, the topography shape and stratification profile can be reviewed. This work has been done by implementation of iTides numerical model, which is a borotropic model, and forcing of an oscillating tidal current with semi-diurnal period. The model results show the formation of internal tide with a wavelength of order of O (10km) which reduces to O (1km) when reaches the shallow water. According to studied profiles of stability frequency, density stratification is quite stable in the Gulf of Oman and this Gulf is capable for formation of internal tide. Internal tide wavelength is of order of tens kilometers which reduces to a few kilometers when reaching the shallow zones. In the results, also the energy dissipation over the topography is visible. Most of internal tide energy is related to first modes. This phenomenon is mostly extended to deep zones, but for shallow zones internal tide energy is considerable between 1 to 3th internal tide modes. This fact may be due to iterated reflection of internal tidal beams from continental shelf and coastal shallow waters. The maximum energy Flux of primary modes in deep water (with depth of about 3000 meters) reaches to 20 kiloWatt per meter, whereas by decreasing the water depth, this amount of energy Flux reduces. The amount of internal tidal energy Flux in the Strait of Hormuz shallow water reaches bellow five kiloWatt per meter.  


Main Subjects

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