Lagrangian Coherent Structures 


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 Lagrangian coherent structures (LCS) partition a flow field into regions that undergo similar experiences. The LCS can be obtained by computing Lagrangian parameters such as finitesize Lyapunov exponents and finitetime Lyapunov exponents (Shadden et al. 2005; Cotté et al. 2011; HernandezCarrasco et al. 2014; StOngeDrouin et al. 2014). These parameters translate particle trajectories into scalar fields that represent the structure of the advective regime, showing, for example, “ridges” that illustrate barriers to transport.
The 24 hour forward finite time Lyapunov element (FFTLE, red, represent repelling LCS) and reverse time Lyapunov element (RFTLE, blue, representing attracting LCS) are depicted for 1 Jan 2011 until 28 Feb 2011 (see animation on the right side). Although the exact location of large FFTLE values varies in time, they are consistently in the general vicinity of Father’s Island and along a path extending from Cape Heusner to Wulai. The overall magnitude of both FFTLE and RFTLE is lower in February than January.
Particles were released hourly from 1 Jan 2011 until 28 Feb 2011. The particles were released every 500m from 5.6S to 4.8S and 149.9E to 151.5E. Trajectories were integrated in time at a fixed 1m depth using a 10minute time step for 24 hours, and the final location of each particle was saved. The FFTLEs and RFTLEs were calculated from the particle locations using the methods given by Harrison et al. (2013). Only FFTLEs and RFTLEs whose magnitude is greater than 0.75 were plotted.

