Lagrangian Mapping and Modeling of Thermohaline Intrusions in the Subtropical Front

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Thermohaline intrusions are observed throughout the ocean, but they are most prominent near fronts. Lateral diffusivities of heat, salt and perhaps buoyancy are estimated to be as large as those produced by baroclinic instabilities and mesoscale eddies, but . . . present knowledge is insufficient to predict the structure, length-scales and lateral fluxes of thermohalines with confidence (Ruddick and Richards, 2003). Until their basic structure and phenomenology are better understood by observations at sea, intrusions and their fluxes cannot be represented realistically in large-scale or regional models. In this study, researchers at the University of Washington will take intensive measurements and perform high-resolution modeling of the intrusions in the N. Pacific subtropical front. The goals of this research are to determine the length scales and slopes of the intrusions in 2D sections and in 3D patterns, relate intrusion length scales, slopes and structures to the front, and follow the evolution of several intrusions in a Lagrangian frame around a commandable neutrally-buoyant float and infer their lateral fluxes. If possible, the team of researchers will identify the processes producing and modifying the intrusions, and develop high-resolution models that reproduce essential aspects of intrusion formation and growth. The need for measurements and modeling like these has long been apparent, but only during the last few years have all of the necessary tools become available. This includes a depth-cycling towed body with upward and downward ADCPs, microstructure profilers, and a commandable neutrally buoyant Lagrangian float, and flexible high-resolution numerical code. Though not all issues regarding thermoahaline intrusions can be solved from this work, the results gathered from this research will advance our understanding of the structure of the intrusions in the subtropical front, and provide further insight into how some of the intrusions evolve. In addition to the intellectual merit of the work, this research will provide the support and training of a graduate students and a postdoc.