Intermediate-depth Eddies East of Mindanao: Causes and Consequences

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Recent observations have shown surprisingly strong eddies below the thermocline in the Pacific low-latitude western boundary region east of the Philippines. Maximum velocities have exceeded 0.5 m s-1, and the eddies extend to at least 2000 m in depth. However, observations of eddies to date are imprecise, and obtaining detailed measurements, with good temporal and spatial coverage, is expensive. Fortunately, recent numerical ocean general circulation models with a 0.1-degree horizontal grid agree well enough with existing observations to indicate that a detailed analysis of the output from these models, in conjunction with existing measurements and new numerical process studies, will be a cost-effective method for achieving the project objectives.In this study, researchers at the University of Hawaii will update and refine their description of the variability and vertical structure of the currents off Mindanao using available observations and high-resolution model output. By using energy budgets, shear mode analysis, and a series of numerical process studies the team of researchers will determine the processes generating energetic flows at intermediate depths. They will also conduct Lagrangian tracer experiments with the numerical output models to examine the consequences of the eddies for water property distributions. Finally, the scientists will describe the eddies' role in the dynamics of the larger-scale circulation via analysis of vorticity and energy balances. The results gathered from this work will address major physical oceanographic questions, such as: what determines the characteristics of the mesoscale energy field, how does it vary in space and time, and what are the larger-scale consequences? Though the questions do not have global answers, a general understanding must be accumulated in part by detailed studies of specific processes in specific regions, followed by predictions of other regions in which similar processes are likely to be active. In addition to the intellectual merit of the work, this research will strengthen international collaborations with the Japanese at the Marine Science and Technology Center (JAMSTEC) and the Earth Simulator Center in Japan. It will also support and train a PhD candidate.