Chemistry Reference
In-Depth Information
scale deviations superimposed on the topography-induced shift reflected
the influence of instabilities in the currents near the Kuroshio boundary.
3 Estimates of average current velocity and wind drift
Case 1
Estimates of average surface currents were obtained under the assumption
that the ship in Figure 1b moved in a straight line
AB
(axis
x
), connecting
point
A
at the beginning of the wastewater discharge and point
B
, its loca-
tion during the SAR observations. This indicates that no wind- or current-
induced drift were prevailing, only oil spreading was observed at point
A
during the ship's movement to point
B
. In such a case deviations of the
spill from line
AB
were caused by the action of a single factor, the surface
current, or more accurately, by a component of surface current normal to
line
AB
. The average velocity of this normal component in point
x
can be
found from the relation
>
@
1
V
c
(
x
)
y
(
x
)
'
t
(
x
)
(1)
where
y
(
x
) is the distance of the centre of the spill band from line
AB
,
x
is
the distance of point
x
from point
A
and '
t
(
x
) is the time elapsed after the
discharge of wastewater at point
x
.
Since '
t
(
x
)
=
(
L - x
)(
V
s
)
-1
, where
L
is the distance between points
A
and
B
, and
V
s
is the ship's velocity, the average current velocity can be rewrit-
ten as
1
V
(
x
)
y
(
x
)
L
x
V
(2)
c
g
It is known that SAR observations of a moving target (ship) allow us to
calculate the target's velocity. In a case under study, the radial component
of the ship's velocity accounted for 0.4
V
s
and the eastward shift of the ship
relative to its wake (spill) caused by this component was estimated with a
large error, that hindered the accurate determination of ship velocity. Thus,
assume that
V
s
= 25 km h
-1
.
The maximum displacement from line
AB
was observed in area
C
, east
of Lutao (Figure 1b). This displacement was most likely caused by an east-
ward component of the Kuroshio Current. The shape of the spill in area
C
is similar to the shape of feature
4
. The interaction of the Kuroshio flow
with Lutao and underwater rising around it were responsible for the ap-
pearance of both feature
4
and the eastward component of the current. The
change in velocity of this component with distance manifested itself as the
shape of departure
y
(
x
). The maximum displacement was found at a dis-
