On the stability of fronts near shelfbreak

Using a two-dimensional semi-geostrophic model.the stability of fronts near shelf break (shelfbreak font,western boundary current front) and its mechanism are studied.We find that the stability of the front is related to the frontal structure.In general,the increase of the lower layer depth lowers the unstable growth rate (α₁).(1) The shelfbreak front is baroclinically unstable and α₁ increases with the increase of the bottom slope,different from the conclusion of Flagg and Beardsley (1978).(2) A western boundary current front with uniform vorticity in the upper layer is barotropically unstable,due to the strong horizontal shear of the mean current.The unstable growth rate of this front for a realistic topography is only one seventh of that of the flat bottom case.(3) For a western boundary current front with hyperbolic tangent structure,we find its wave propagation speed to be about 0.5 m/s,in agreement with the observed values.The front is baroclinically unstable.(4)The unstable growth rate of a domed structure front and its wave speed do not to be related to its wavelength.The front is batoclinically unstable.