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FSLE, EKE and Chl around Hawaii from observationsΒΆ

Fig. 1 shows the 2000-2008 averaged finite-size Lyapunov exponents (FSLE) corresponding to the unstable manifolds, Fig. 2, the 2000-2008 averaged eddy kinetic energy (EKE), both deduced from AVISO sea surface heigth (SSH). Fig. 3 shows the averaged chlorophyll (Chl) for years 2003, 2004, 2005, 2006 and 2008 (there was a missing data during 2007, and years 2000, 2001, 2002 and 2009 are either absent or incomplete).

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Figure 1: 2000-2008 averaged FSLE corresponding to unstable manifolds. Computed with RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/FSLE/analysis/fsle_hr_back_around_Hawaii/fsle_hr_back_around_Hawaii.m from AVISO SSH.

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Figure 2: 2000-2008 averaged EKE deduced from AVISO SSH.

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Figure 3: Averaged Chl for years 2003, 2004, 2005, 2006 and 2008.

FSLE and EKE are somewhat correlated with strong values behind the Hawaiian islands, especially Big Island, and a decrease of both quantities in the northeastern direction. The comparison with Chl, however, do not show a correlation on average between FSLE/EKE and Chl: the band of locally high Chl extends in the northeastern direction across the contours of FSLE and EKE. This comparison does not necessarily rule out a connection between FSLE/EKE and Chl, but it shows that this connection is not apparent on average, over a long time.

Fig. 4 shows the time series of each quantity averaged spatially over a small region to the northeast of the archipelago (155W-150W and 22.5N-27.5N). The correlation is 0.82 between FSLE and EKE, and is negative between FSLE/EKE and Chl. FSLE and EKE regularly peak at the beginning of each year while Chl tends to have two peaks a year, one in winter, one in summer. It is not clear from this figure, however, that any of the Chl peak could be attributed to the peak in FSLE/EKE.

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Figure 4: (a) Chl, (b) EKE (red) and FSLE (blue) averaged spatially within 155W-150W and 22.5N-27.5N.