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Sensitivity of FSLE events to SSH products

The finite-size Lyapunov exponents (FLSE) have been calculated onward in time for Aug. 25, 2004 using different products of geostrophic flows. A snapshot of the zonal geostrophic flow on Aug. 25, 2004 is shown in Fig. 1. Except the geostrophic flow from Paulo, all resemble to each other although they are not exactly equal. NOTA: It was found that Paulo has been rightly using the absolute sea surface height while I was so far using the sea surface height anomaly.

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Figure 1: Zonal geostrophic flow on Aug. 25, 2004 from different products. First panel is the geostrophic flow given by Paulo. In the other panels, the geostrophic flow has been deduced from different sea surface height (SSH): SSH from Sachiko, SSH from AVISO DT-ref, SSH from AVISO DT-upd, SSH from AVISO NRT (see AVISO website for details).

The FSLE for the different products are shown in Fig. 2 and 3. Overall, the structures are similar and they differ only in details. However, if we want to compare the time series of FSLE for a particular location, it is likely the time series will vary with the sea surface height (SSH) product chosen, given that FSLE are made mostly of sporadic short events. This is illustrated for instance by a section along 25°N (Fig. 4) that could be considered as a time series. It would be nice to come up with an index of closeness to a filament, that is not less sensitive to the product. An average within 0.1° did not do the job in Fig. 4 (not shown).

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Figure 2: FSLE onward-in-time on Aug. 25 2004 from different products of geostrophic flows.

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Figure 3: Same as Fig. 2.

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Figure 3: Same as Fig. 2 but along 25°N only.