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One year of stable and unstable manifolds in the northeastern equatorial Pacific in OFES QUICKSCAT run

The finite-size Lyapunov exponents (FSLE) were computed for every 6 days for the northeastern equatorial Pacific using the OFES QUICKSCAT run. A snapshot of these FSLE is given in Fig. 1 and the time-averaged over year 2001 in Fig. 2. Both figures locate areas where horizontal stirring is important: along the North America Pacific coast, along the North Equatorial Countercurrent, east and west of the Hawaiian archipelago, along the Central America Pacific coast,as well as in the Gulf of Mexico.

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Figure 1: (a) Stable and (b) unstable manifolds for Feb. 3, 2001 with initial distance of 0.1° and final distance of 1° using trajectory separations.

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Figure 2: Averaged (a) stable and (b) unstable manifolds for the year 2001 with initial distance of 0.1° and final distance of 1° using trajectory separations.

Because the average still contains some structure resembling to a single event, more than one year should be included in the average. This calculation would also enable to have an idea on the interannual variability of the stirring which should be significant given the time series during year 2001 alone (Fig. 3). The stirring is highly variable but without any trend during the first half of the year. Less high-frequency variability is observed during the second half and the stirring decreases by almost 50% with possibly a hint of increase for the beginning of the following year. Notice during the first half how the peaks and lows for the stable manifolds lag by about 10-15 days those for the unstable manifolds. Any reason for this?

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Figure 3: Locally-averaged stable and unstable manifolds during 2001 with initial distance of 0.1° and final distance of 1° using trajectory separations. The two areas over which the averages are performed are: around (170°W-150°W) and east of (170°W-150°W) the Hawaiian archipelago.