65th IHC Booklet/Program (pdf - 4.9MB) - Office of the Federal ...

The influence of cyclones on the BP oil spill
Pat Fitzpatrick, Yee Lau, Chris Hill, and Haldun Karan
(fitz@gri.msstate.edu)
Geosystems Research Institute, Mississippi State University
The Deepwater Horizon oil spill impacted the Mississippi River Delta, Barataria Bay, the barrier
islands east of Louisiana, and the Alabama and Florida coast for an extended period of time from
May through July. However, the Rigolets and western Mississippi coast were impacted for a
briefer period from late June to early July. An important component to understanding the oil
transport is to distinguish the influences behind this apex moment. A simulation was conducted
for the period 20 June to 10 July 2010 to understand this inland transport.
The simulation was based on a Lagrangian particle tracker with random walk diffusion. Input
consisted of latitude and longitude positions of oil-contaminated parcels, wind, current, and a
large array of random numbers. In addition, new parcels were released at the damaged Macondo
rig location at each time step. Twenty-five parcels are released at each position, and when
combined with the diffusion coefficient (set to 10m 2 s -1 ), resulted in a realistic spread of the
parcels with time. The initial parcel locations were subjectively determined based on a
combination of NASA MODIS satellite imagery, SAR imagery, NOAA oil trajectory maps, and
the NOAA/NESDIS Satellite Analysis Branch (SAB) experimental surface oil analysis. The
parcels were advected at 80% of the ocean current speed and at 3% of the wind speed. Bilinear
interpolation was applied every timestep to determine the currents and winds at each parcel. The
pseudo-random numbers were uniformly distributed between 0 and 1 and generated by the
Mersenne Twister algorithm. The initial seed was randomly obtained from machine noise.
The 10-m wind and near-surface ocean currents were provided from NAVOCEANO’s 3-km
Navy Coastal Ocean Model (NCOM) in the Intra-Americas Sea (AMSEAS) domain, with
atmospheric forcing from COAMPS. The wind forcing was validated against buoys using
statistical and vector correlation techniques, concluding that the winds were reasonably accurate.
An examination of NCOM data, the oil spill simulation, buoy data, weather reanalysis maps, tide
gauge data, scatterometer data, and HF radar currents show that two weather systems altered the
currents and water levels such that oil was pushed into the western Mississippi Sound and the
Rigolets. An easterly wind fetch from intensifying Hurricane Alex provided the first inland push,
followed by a westward-drifting non-tropical low which had formed off the western edge of a
Gulf cold front. In both cases, a weak pressure gradient was replaced by strong easterly winds
which not only switched alongshore westerly coastal currents to an easterly direction, but also
increased inland water levels by 0.6-0.8 m as mini-surge events. These results showed that
cyclones can dramatically alter oil transport, even by fringe effects. The study also showed that
this modeling formulation was capable of reproducing the oil spill transport and is being used in
follow-up BP research.
Poster Session – Page 32