Abstract
A regional baroclinic model forced with several tidal constituents at different frequencies is used to investigate the internal tide of the Bay of Biscay. The regional ocean model is free surface, sigma-coordinate and it is implemented in order to accurately take into account the barotropic forcing, the strong bathymetry gradients and the temperature and salinity stratifications. In a previous paper, the barotropic component of the tides was studied in details and the boundary conditions of the three-dimensional model were extracted from the atlases. In the present paper, we focus on the baroclinic component of the tides and the simulations are validated against observations from the MINT94 experiment. The observed currents and stratification are accurately reproduced by the model. The internal tide pattern is consistent with the descriptions found in the literature. Combining wavelet and principal component analysis we extract the patterns of generation and propagation of the internal tide at the semi-diurnal and quarter-diurnal frequencies. Secondary internal wave generation areas are identified over the plain. The vertical displacements of isopycnal surfaces for the M4 internal tide are found to be locally half those induced by the semi-diurnal internal tide. A sensitivity study shows the impact of using a three-dimensional initial stratification over the direction of propagation and wavelengths of the internal tides.
Highlights
Research dealing with the origin of the ocean dyapicnal mixing has been given a renewed interest in the recent years since this mixing appeared to control, at least partially, the ocean stratification, the meridional oceanic circulation, heat transports and the climate response (Saenko, 2006)
This is the first step toward the full understanding of the internal tide dynamics of the area, as an influence of three-dimensional variations in temperature can be expected in the Bay of Biscay
We investigate the generation of the quarter-diurnal internal tide (M4) together with its propagation after a WEof analysis
Summary
Research dealing with the origin of the ocean dyapicnal mixing has been given a renewed interest in the recent years since this mixing appeared to control, at least partially, the ocean stratification, the meridional oceanic circulation, heat transports and the climate response (Saenko, 2006). In the case of internal tides generated at shelf slopes at M2 frequency, the two-dimensional analytical model of Baines (1982), namely the body force approach, gives the energy conversion from barotropic to baroclinic tides. The aim is to qualify and quantify numerically the mechanisms of generation and propagation of internal tides in the abyssal plain, continental slope and shelf of the Bay of Biscay This is achieved by using the three-dimensional regional SYMPHONIE model (Marsaleix et al, 2008). The three-dimensional model is forced by multi-frequency tidal solutions including semi-diurnal, diurnal and quarter-diurnal components that were validated against observations It is, to the best of our knowledge, the first study of internal tide which takes into account an accurate barotropic forcing by the quarter-diurnal tide M4 in the Bay of Biscay.
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