Lagrangian Coherent Structures in the Norwegian Sea

Buoyant particles in the ocean, such as oil spills, microplastics and pelagic plankton tend to accumulate in elongated streaks at the ocean surface, known as Lagrangian Coherent Structures (LCS). While the exact location of each individual particle is sensitive to its initial condition, the location of LCS, in which particles tend to be organized after some time, does not depend on initial conditions. LCS do therefore present a promising tool for ocean forecasting.

LCS can be calculated from output fields of ocean circulation models or from HF-radar derived ocean currents. Particles are traced using a Lagrangian trajectory model, and subsequently the fastest growing modes in initial particle displacements are described by the Lyapunov exponents that represent the Lagrangian Coherent Structure. An open question is how steady the LCS in the Norwegian Sea are, and if there are re-appearing patterns that can be mapped for ocean forecasting and process studies.

The Master student will get familiar with ocean circulation model output and run the trajectory model OpenDrift to calculate the Lyapunov exponents that display Lagrangian Coherent Structures in the Norwegian Sea. To build some theoretical understanding of chaos theory, Lyapunov exponents and LCS will be a central part of the master project, and finally the mapped patterns of LCS will be interpreted and compared with observational data of ocean currents.
 

Fig: Lagrangian Coherent Structures (LCS) calculated from MET's operational ocean model Norkyst. Red areas indicate attracting LCS, blue areas repelling LCS. Black dots are particles that were uniformly seeded and traced for 24 hours.

 

Published Mar. 1, 2018 3:53 PM - Last modified Mar. 1, 2018 3:53 PM

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