Assessing Lagrangian coherent structures and uncertainties using RELO ensemble system in the Gulf of Mexico

The US Navy's RELO ensemble system with 32 members consists of an ocean model (NCOM) and NCODA 3D-Var DA system. The RELO ensemble with 3km resolution is used to compute Lagrangian coherent structures (LCSs) during the period of June - August 2012 for the Gulf of Mexico (GOM).

Repelling and attracting LCSs, which represent the stable and unstable manifolds and have large impacts on the ocean tracer dispersion such as oil spills in the GOM, are identified by using the finite-time Lyapunov exponents. The uncertainties of LCSs are assessed using the RELO ensemble. The advantages of using an ensemble over a single forecast in predicting the Lagrangian trajectories in GOM are demonstrated. The impacts of the ensemble spread and model resolutions on Lagrangian predictions are studied.