Environmental Engineering Reference
In-Depth Information
fields can be found at
www.aoml.noaa.gov/phod/dhos
and
http://www.roffs.com/
1.4 Analysis and Discussion
1.4.1 Surface Oil Spill Extent
The extent of the surface oil was primarily estimated and analysed from blended
satellite observations as explained in Sect.
1.3.1
. The dailyMPSRswere used to assess
the daily extent of the surface oil and to link their temporal and spatial variability to
the surface current fields (Fig.
1.4
). The time series of the areal extent of the surface
oil (Fig.
1.5
b), as obtained from the MPSRs, had a mean value of approximately
20
10
3
km
2
and exhibited large temporal variability. An evaluation of these reports
indicates that the total cumulative area of oil detected over the open water during the
87 days of the oil spill between April and August 2010, was at least 130
×
10
3
km
2
(Fig.
1.5
c). The area covered by surface oil for more than 40 days was slightly smaller
than 10
×
10
3
km
2
) between
approximately May 14 and June 29, 2010, with one noticeable minimum value of
less than 15
10
3
km
2
. The surface oil extent was at a maximum (40
×
×
10
3
km
2
around June 6, 2010.
Between April 22 and May 22, 2010, when the first maximum in surface area
extent occurred, the surface oil extent increased at an average rate of 1.3
×
10
3
km
2
×
10
3
km
2
were observed during May 20-25, June
16-22, and June 24-27, 2010 (Fig.
1.5
a). On the other hand, the areal extent of the
surface oil decreased between June 27 and July 5 at a rate of
per day. Areas larger than 40
×
10
3
km
2
per day,
a rate approximately three times faster than the increase rate during April 22-May
22, 2010. Significant progress had already been made by responders in dispersing,
burning, or recovering the oil during this time period. The magnitude of the June
2-6, 2010 apparent decrease of approximately
−
4
.
4
×
10
3
km
2
, was partly due to
particularly limited satellite coverage during this time, although a true decrease in
oil extent cannot be ruled out.
Wind fields used in the analysis of this work correspond to the 0.25
ⓦ
surface wind
grid from NCEP Reanalysis-2 data [
36
]. The prevailing winds over the GOM during
the oil spill were from the southeast and with an average speed of approximately
5m/s, while winds from other directions were, in general, weaker, with average
speeds around 2m/s (Fig.
1.5
a).
By the end of June, high winds, rough seas, and distant thunderstorm activity
occurred as Hurricane Alex moved through the southwestern GOM, affecting con-
ditions in the spill area, and causing satellite analysis to underreport the surface oil
coverage during this relatively short time period. During the passage of the strong
southeasterly winds associated with Hurricane Alex, the daily average wind speed at
the oil spill site was approximately 7.4
−
20
×
2.5m/s, while outside this time period
the daily average wind speed was approximately 4.1
±
±
2.3m/s (Fig.
1.5
a). The
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