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04.26.11: Comparison of FSLE calculated with different SSH productsΒΆ

The sensitivity of the calculation of finite-size Lyapunov exponent (FSLE) to the type of sea surface height (SSH) products is explored. The first product is the sum of the SSH anomaly of type REF added to the 1992-2002 mean dynamic ocean topohraphy (MDOT) of Maximenko and Niiler (colors in Fig. 1). The second product is the absolute SSH of type REF, where the absolute SSH is obtained by adding to the SSH anomaly the mean of the 1993-1999 period sea surface above geoid, corrected from geophysical effects. The two mean mean SSH product are thus comparable which explains why the two FSLE fields obtained in each case resemble well each other (Fig. 1a).

The third product is similar to the first one with SSH type UPD used instead of SSH type REF. The difference is in the numbers of satellite used. Less satellites is used for REF but the quality of the data is homogeneous with time; all available satellites are used for UPD but the quality of the data varies with time. Fig. 1b shows the difference in FSLE fields when using either the first or third product. Overall, the patterns are similar but in some occasions, filaments can be shifted by more than several times the width of a filament.

In conclusion, in publication, I should always show two different FSLE products when focusing on one specific location: the one computed with REF, the other with UPD. No need to add the difference in FSLE computed with different mean SSH.


Figure 1: FSLE on Oct. 3, 2004 calculated (a) with MDOT and REF SSHA (colors) and without MDOT and REF SSH (contours for values larger than 0.06 1/day), (b) with MDOT and REF SSHA (colors) and with MDOT and UPD SSHA (contours, same as in a). This is the same day as the FSLE computed by Calil and Richards (2010) in their Fig. 9.

I used manifold_SSH_AVISO.m in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/FSLE/analysis/SSH_AVISO on the central disk to compute the FSLE from AVISO SSH.