In previous studies of tidal generation of mean flow over varying topography, the rectification mechanism has generally invoked bottom friction as a source of tidal flux of momentum and vorticity (hence referred as "friction" mechanism). The author proposes a different mechanism based on horizontal mixing of potential vorticity. Drawing analogy from tidal dispersion of passive tracers, this mixing is parameterized through a diffusivity (hence called "diffusivity" mechanism) that is quadratic in the tidal amplitude. In this, Part 1, the mean along-isobath flow near a shelf break is determined for a homogeneous ocean and contrasted with that induced by friction mechanism. In Part 2, the effect of a front will be considered.It is found that although the mean flow is pointing in the same direction as that induced by friction mechanism (i.e., to the right when facing deep water in the Northern Hemisphere), it varies more slowly with the tidal amplitude. In the typical situation when the mean shear is small compared with the Coriolis parameter, this dependence is linear rather than quadratic, as is the case for the friction mechanism. This linear dependence compares more favorably with observations over Georges Bank.
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