Observations and Modelling of Fronts and Frontogenesis

that around the offshore front, except that it extends
deeper.
The geostrophic (alongshore) velocities in each layer at
t 25.4 are shown in Figure 111.3. There are jets at the
upwelled fronts at y 5 [0.5 kin], y 45 [4.5 kin], with
maximum velocities of 15, 50 [15, 50 cm s1] respectively.
The asymmetry in mixed layer depth and density gradients
across the front results in asymmetry in the jets: the
trailing edge is sharper.
The leading edge of the inshore front moves offshore
faster than the point Y2 As a result, it overtakes Y2 soon
after t = 25.4 [23.3 hr], and convective instability occurs.
Fluid originating in layer 3 that has been entrained into
layer 1 is advected in the mixed layer over layer 2, causing
an unstable density profile. The numerical integration was
halted at this point.
The positions of the two fronts versus time are shown in
Figure III.4a. The fronts move offshore with velocities that
decrease slightly with time. Figures III.4b and III.4c show
the positions of the two fronts for Cases 2 and 3,
respectively. The three cases are similar, quantitatively as
well as qualitatively. The time of upwelling of each
interface and the position of each front scale with the
initial internal deformation radii: the times and positions
for Cases 2 and 3 may be obtained from Case 1 by multiplying
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