Observations and Modelling of Fronts and Frontogenesis

h/W = )12/v10 9.5 [8.7 hr]. (45)
A similar estimate for the time t2 of surfacing of the lower
interface is,
t2 t1 + h20/(x12W/.X23) t1 + h20).23/v10h10
- 19.5 [17.9 hr}.
The main sequence of events during the numerical
integration of Case 1 is depicted in Figure 111.2, which
shows the evolution of 13l (normalized by 32; Fig.
III.2a,d,g,j), the layer depths h1 and h2 (Fig.
III.2b,e,h,k), and the normal-to-shore transport
i=l,2,3 (Fig. III.2c,f,i,l). The dashed lines in Figs.
(46)
III.2a and III.2e indicate the initial conditions 31 1100,
h1 0.5, h 1.0. By time t 8.1 [7.3 hr], somewhat
earlier than the estimate (45), the base of the mixed layer
has nearly surfaced at the coastal boundary (Fig. III.2b).
Enhanced entrainment driven by the shallowing has decreased
3l near the boundary. For y > 60 [6 km], the transport
(Fig. III.2c) is nearly independent of y and accurately given
by the modified Ekman balance (35). For y < 5 [0.5 km],
layer 2 supplies more onshore transport than layer 3, despite
being roughly one-eighth as thick. The small density
difference between layers 2 and 3 inhibits the near-shore
intensification of the surface divergence from penetrating
into the deep interior flow.