Observations and Modelling of Fronts and Frontogenesis

(1) The upwelled horizontal profiles of surface layer
density scale with the initial internal deformation radii.
The upwelling process (in this simple model) rotates the
vertical density profile to the horizontal and stretches it
by a factor of the order of an initial deformation radius.
(2) There is surface transport divergence around the
upwelling fronts of the same magnitude as the divergence in
the upwelling zone adjacent to the coastal boundary. (The
magnitude is roughly the offshore Ekman transport divided by
the local internal deformation radius associated with the
mixed layer base.) However, this divergence is associated
only with the deformation of the mixed layer base near the
moving fronts. Interior stratification inhibits the depth
penetration of the local divergence around the offshore
front, and upwelling of the deep interior occurs only at the
coastal boundary.
The model retains the essential physics of wind-driven
thermocline upwelling. However, it has limitations. Any
attempt to directly model specific oceanic conditions must
take alongshore variability into account. The neglect of
inertio-gravity waves forces the instantaneous establishment
of the modified Ekman balance far offshore and shortens the
upwelling time scales. The inclusion of shear mixing in the
entrainment parameterization would lead to reduced velocities
in the geostrophic jets.
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