Mixed Layer Restratification Due to a Horizontal Density Gradient

The restratification in the surface mixed layer driven by a horizontal density gradient following a storm is examined. For a constant layer depth H and constant buoyancy gradient |bx| = M2, geostrophic adjustment leads to new stratification with N2 = M4/ f2 and Richardson number Ri = 1. With the inclusion of time dependence, inertial oscillations result and give Ri = ½. If the horizontal buoyancy gradient is confined, the minimum Ri for an initial distribution of buoyancy b(x) is given by 1 − ½ H|bxx|max/f2. The resulting maximum restratification is N2 = M4/ (f2− ½ H|bxx). This restratification can be significant in coastal oceans and possibly in some frontal areas of the open ocean.