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Computing FSLE: Some commentsΒΆ

  • FSLE calculations are valid –in the sense that they do reveal hyperbolic structures– as long as the time scale of advection of the hyperbolic structures –typically the mesoscale structure– is large compare to the time scale of tracer advetion within the hyperbolic structure. It would be nice to come up with a ratio that would eliminate FSLE that might be less likely to represent actual hyperbolic structures. One idea would be to use FSLE themselves and perform a test of internal consistency. Calculate FSLE over several time and estimate –not easy– the typical advective velocity of the filaments over that period. If this velocity is as large or larger than the advective velocity of the tracers (delta_f, the final distance used to compute the FSLE, over tau, the FSLE time scale) then the FSLE of this structure should be disregarded.
  • The initial distance is taken as the grid of the dataset and the final distance is the largest distance over which we want to study tracer dispersion. As d’Ovidio et al. (2004) put it: “the FSLE represents the inverse time scale for mixing up fluid parcels between [the two length scales]”.
  • It would be nice to use also independent techniques as advised by Joseph and Legras (2002): see Rom-Kedar et al. (1990), Malhotra et al. (1998), Malhotra and Wiggins (1999), Haller (2000), Haller and Yuan (2000) and Haller (2001).
  • Ask Eric about what he thinks of FSLE.
  • What is the effect of non-divergence on the interpretation of FSLE?
  • Ask Francisco for 1) effect of data resolution, 2) FTLE versus FSLE and 3) effect of wind Ekman layer.