Quasi Real Time Cruise Deployment Guidance to Coherent Regions Using Lagrangian Methods

We describe Lagrangian strategies that were used to help plan a field experiment in the North Pacific Subtropical Gyre in July 2015 close to Station ALOHA. The field study, part of the Simons Collaboration on Ocean Processes and Ecology (SCOPE), aimed to characterize diel changes in the composition and activity of the surface ocean microbial community. The study required forecasting a coherent water mass would remain relatively isolated from neighboring waters over 10 days. To this end, we used near-real-time remote-sensed altimetric data with 0.25 degree resolution (provided by Colorado Center for Astrodynamics Research) to compute particle trajectories and Finite-Time Lyapunov Exponent (FTLE) techniques to pinpoint the candidate coherent regions and exclude undesirable, highly dispersive regimes. We will demonstrate the utility of the approach, which was successful at the identification of the coherent region as evidenced by the trajectories of Surface Velocity Program drifters. It accurately identified a poorly suited field of strong transport close to Station ALOHA and identified a well suited region, associated with an anti-cylonic eddy that provided an ideal context for the field campaign. This talk will describe the methodology and the results from the Summer 2015 expedition as well as the potential to apply the approach more broadly.