Lagrangian Coherent Structures in Coastal Waters: Sensitivities to Interpolation Schemes, and Mesh Resolution

Lagrangian coherent structures (LCSs) are the locally strongest repelling or attracting material lines and represent the cores of Lagrangian patterns that cannot be crossed by an ideal tracer. LCSs are a useful way to investigate material transport and have only recently been applied to coastal waters. Because coastal waters have complex boundaries and bathymetry, modelling is done more accurately by using unstructured grid systems. Structured grids are needed for easy derivation of flow diagnostics for LCSs. However associated sensitivity of the interpolation scheme for the conversion from unstructured to structured grid requires some investigation. Therefore, the present study investigates, using an analytical kinematic model (double gyre), the sensitivities of the LCSs to interpolation scheme and mesh resolutions as it applies to coastal water. We also present the result using a case study of Moreton Bay Australia. Overall, the results showed that LCSs are robust to the errors due to interpolation schemes used in the unstructured to structured grid conversion. The Finite time Lyapunov (FTLE) diagnostic method is applied in this study for extracting the LCSs.