Page 5 - Ciappa_Costabile_2014

48 A. Ciappa, S. Costabile / Marine Pollution Bulletin 84 (2014) 44–55
Table 1
October wind histogram extracted from NCEP wind dataset from 2006–2011 near the Egadi PMA.
Speed (m/s) dir (°) 1.0–3.5 3.5–6.5 6.5–10.5 10.5–15.5 15.5–20.5 20.5–26.5 26.5–33.5 33.5–40.5
0–30 1.8 2.1 0.3
30–60 0.8 3.1
60–90 1.8 1.0 0.3
90–120 3.6 4.9 0.5 0.3
120–150 2.9 6.5 3.9 0.5
150–180 3.1 6.3 3.1 0.3
180–210 2.6 0.5 1.6 0.3
210–240 0.8 1.8 0.3
240–270 2.1 1.6 1.3
270–300 2.9 3.9 2.3 1.3 0.5
300–330 1.0 6.8 3.6 2.3 0.3
330–360 1.8 5.7 2.1 1.6
Calm = 3.6

Table 2
October wind histogram from multi-decadal wind measurements in Trapani.
Speed (m/s) dir (degrees) 1.0–3.5 3.5–6.5 6.5–10.5 10.5–15.5 15.5–20.5 20.5–26.5 26.5–33.5 33.5–40.5
0–30 0.4 1.2 2.6 2.0 0.8 0.2
30–60 0.6 1.8 2.2 1.1 0.4 0.2
60–90 0.4 1.8 1.3 0.4 0.2 0.1
90–120 0.6 2.1 1.0 0.4 0.1
120–150 0.5 2.2 2.4 1.3 0.8 0.6 0.3 0.1
150–180 0.7 3.0 3.4 3.6 2.1 1.4 0.2 0.1
180–210 0.3 2.1 2.2 1.8 0.9 0.6 0.1
210–240 0.3 1.1 2.2 0.8 0.3 0.1
240–270 0.2 1.2 1.7 0.8 0.3 0.2
270–300 0.1 1.4 1.8 1.4 0.7 0.3 0.2
300–330 0.3 1.7 2.6 2.0 1.1 0.3 0.1
330–360 0.6 2.5 2.6 1.5 0.9 0.3
Calm = 16

particles are tracked for a few days, the real wind and current fields sufficiently short to reduce the truncation error in the Euler for-
could differ substantially from the fields depicted by wind statis- mula, and diffusion was simulated by random walk with coeffi-
2
tics and mean current. cient K h =5m /s added to each trajectory at each timestep
The use of the long-term sequence of wind and current data (Viikmäe et al., 2013). Oil trajectories were reported on the refer-
implies that the Lagrangian particles are continuously released ence grid by storing the number and time of the particles in transit
and back-tracked for a few days during the full period of the ocean in each cell of the grid. Two particles per timestep were released at
model run, i.e. 6 years. The study area around the MPA was each receptor point, corresponding to an average of 18000 trajecto-
6
subdivided into a regular grid sufficiently large to include all the ries per month per point and to a total of 125 * 10 particles used in
oil trajectories (about 500 km wide, with a spatial resolution of 97 receptor points from 2006 to 2011.
250 m; not shown). Particles seeded at the 97 receptor points were Monthly probability and arrival time maps for each receptor
tracked backwards in time for 5 days with a timestep of 5 min, point were obtained from about 6*18000 trajectories in 6 years.

Fig. 4. Mean surface current in October (panel a) and maximum transport cases (to north, east, south and west in clockwise order) in the October months from 2006 to 2011.
The adopted scale of the wind vectors allows visual comparison of the transports due to the wind (oil moving at 3% of wind speed) and the current.