Observations and Modelling of Fronts and Frontogenesis

The present model includes an entraining, diabatic
surface mixed layer with variable density. The flow is
driven by an alongshore wind stress and surface heating. A
modified Ekman balance forces surface layer fluid offshore
and interior fluid onshore, causing a surface divergence and
upwelling of isopycnals near the coastal boundary. The
horizontal scale of this divergence is allowed to adjust
dynamically by careful consideration of the normal-to-shore
momentum balance. The model is inviscid (except for the
viscosity implicit in the vertical mixing in the surface
layer).
We solve the reduced equations numerically. Initially,
the layer depths and surface layer density are constant, and
the horizontal scale of the surface divergence is determined
by a single internal deformation radius. After the mixed
layer base "surfaces" near the coast and the upwelled front
propagates offshore, there are two zones of surface layer
transport divergence. One of these is associated with the
coastal boundary, the other with the upwelled front.
The surface divergence has comparable magnitude in these
two zones. At the front, the divergence is associated only
with deformations of the mixed layer base, and does not
penetrate beyond the uppermost interior layer. At the
boundary, the divergence is associated with upwelling of both
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