Geoscience Reference
In-Depth Information
z
(b)
(a)
Sea surface
D
η
r
-
r
d
ecrea
ses
v
p
3
p
2
p
1
-
∇
p
fv
r
in
creas
es
r
+
x
z
y
(c)
(d)
Isopycnals
v
max
Stratified
v
3
Mixed
v
2
v
v
1
x
x
v
=0
Figure B8.1
(a) Density (solid lines) and pressure surfaces (dotted lines) across a tidal mixing
front; (b) the balance of forces within the box marked inside the front in (a); (c) plan view
of the frontal jet; (d) vertical structure of the expected along-front jet.
as the surface is approached
(
Fig. B8.1d
). Detailed calculations of the velocity from
the density field assuming the geostrophic balance can be made with
Equation (8.7)
.
8.3.2
Observed frontal jets
Patterns of flow similar to geostrophic predictions have been observed in tidal mixing
fronts, and generally the predominant flow has been found to be parallel to the front.
In some cases, the velocities inferred from the density field have been corroborated by
direct measurements of the residual, non-tidal, flow by an acoustic Doppler current
profiler (ADCP). In the example from the north eastern Celtic Sea shown in
Fig. 8.6
,
the density and velocity fields have been observed on a section through a large
meander in the front, crossing from mixed to stratified water and then back again,
thus intersecting the front twice. The isopycnals in
Fig. 8.6a
have a pattern which is
almost symmetrical about the centre of the strongly stratified region. This near
symmetry is reflected in the inferred geostrophic flow in
Fig. 8.6b
with comparable
jets flowing in opposite directions parallel to the front. These flows are confirmed by
direct measurements with a shipborne ADCP (
Fig. 8.6c
) after removal of the baro-
tropic tidal flow (Carrillo et al.,
2005
). In this case, the mean flow was also measured
Search WWH ::
Custom Search