Simulation of the M2 tide in the Gulf of California using the method of characteristics
The oceanographical aspects of the Gulf of California are outlined including bathymetry, thermo-haline patterns and currents. A description of four hydrographic sub-regions is also given, with emphasis on the hydraulic behaviour of the central area containing islands, submarine trenches and natural channels. Values of amplitude and phase for the more important tidal components are presented with co-tidal and co-amplitude maps. A numerical simulation of the Ma tide is made, based on one previously devoped by Chowdhury (1982) from the characteristic forms of the shallow water equations. The first numerical model proves to be very dissipative. Four potential sources of discrepancy between observed and calculated values are identified namely: the discretisation level; large variation of depths; voluntarily-introduced friction losses and inaccurate starting conditions. The first two of these are assessed by means of numerical experiments on basins of constant and linearly-varying depth, whose analytical solutions were known. CFL-dependent values of numerical dissipation are obtained and acceptable levels for these are discussed. A new form of bicharacterislic time-line interpolation is then presented and evaluated. In addition, the idea of a compensation coefficient, based on potential dissipation, is developed. This coefficient modulates the interpolation process at the base of the characteristic cone. Joint use of both concepts finally leads to an acceptable simulation of the M2 tide. The potential applications of such a model are discussed.