Chemistry Reference
In-Depth Information
The pressure gradients at sea level were quite small and the wind speed
was 5 ms
-1
at two stations close to the area under study. The absence of
pronounced sharp changes or organized structures in the surface wind field
also follows from the brightness distribution of the SAR image. A wind
shadow (darker area west of Lutao in Figure 1a) indicates that the wind di-
rection, from east to west, was in agreement with the weather map (Figure
2).
Fig. 2.
Surface analysis map for 20 May 1994, at 12:00 UTC from the Japan Me-
teorological Agency
A large vessel (likely, a tanker) is clearly visible as a bright short line at
the origin of the band. It can be assumed that the band was formed by a
spill due to the cleaning of the oil-tanks and that the source of the polluted
water was a point. Usually, such a spill (or turbulent ship wake) is ob-
served as a straight line along the ship's heading. Variable winds and sur-
face currents cause the drift of the film and disturbances of its shape
(MacDonald et al. 1993, Espedal and Wahl 1999, Hamre and Espedal
1997, Monin and Krasitskii 1985, Ochadlick et al. 1992, Read et al. 1999).
The magnitude of the perturbations increases as the time, wind speed and
current velocity increase. Thus the shape of a spill represents an integral
imprint of the joint action of wind and currents between the oil discharge
and the time of SAR observation. Under low wind conditions, or with
