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Observational Studies of Lateral Mixing – Overview

This presentation provides an overview of observational studies on lateral mixing, aiming to understand and test hypotheses for the processes controlling mixing at scales below the grid scale of most numerical models. It includes case studies on NATRE streaks, CMO dye experiment, and field plans for sub-tropical gyre and strong frontal region experiments.

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Observational Studies of Lateral Mixing – Overview

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  1. Title Slide Observational Studies of Lateral Mixing – Overview Jim Ledwell, WHOI With contributions from: Eugene Terray, WHOI Miles Sundermeyer, UMass. Dartmouth Craig Lee, APL/U. Washington

  2. Motivation • To Understand lateral mixing at scales from 100 m to 10 km, i.e., below the grid scale of most numerical models. • To test hypotheses advanced for the processes controlling lateral mixing at these scales.

  3. NATRE Streaks At 5 to 6 months rms width ~ 3 km strain ~ 10-7 s-1 Kh ~ 2 m2/s What mechanism?

  4. CMO Dye Experiment Kh ~ 0.5 m2/s Shear dispersion accounts for ~0.1 m2/s What mechanism enhances this?

  5. Field Plans Need to look closer and more synoptically 2010: Pilot Experiment to test technology 2011: Experiments in a moderate energy, open ocean site e.g., out of Bermuda. 2012: Experiments in a high energy frontal region e.g. Kuroshio/Oyashio Confluence

  6. Medium Energy Experiment • Test of up scale generation of lateral mixing energy, due, for example to collapse of vertically mixed packets. • Also possible test of down scale generation from instability of weak fronts. • In a subtropical eddy field in late spring, e.g., off Bermuda. • Clear water needed for airborne LIDAR, as well as wind forcing for mixing.

  7. Design – Subtropical Gyre Experiments • Three to four 1 to 3 Day Experiments over 21 days • Supported by remote sensing and modeling to find features • Dye releases (Sundermeyer, Ledwell, Terray, Levine) • Airborne LIDAR (Concannon, plus the dye people) • AUV with microstructure (Goodman) • Towed CTD/Fluorometry (Lee) • Lagrangian floats (D’Asaro) • Profiling EM APEX floats (Sanford) • IR remote sensing (Baschek) • Gliders (Shearman) • Towed Hammerhead with fine and microstructure sensors (Kunze)

  8. Medium Energy Exp Cartoon Lateral Mixing DRI Medium Energy Experiment (2011) Satellite Remote Sensing Airborne LIDAR Airborne IR Imagery EM APEX Floats TowYo CTD/F GPS-tracked Drifters Lagrangian Floats Miles A. Sundermeyer T-Remus Gliders

  9. Strong Front Experiments • Test of role of submesoscale instabilities at strong fronts to cross-frontal exchange, i.e. down scale generation of mixing. • Strong frontal region, deep mixed layer, consistent strong wind forcing, away from side and bottom boundaries • For example at the Kuroshio/Oyashio confluence in late winter or early spring.

  10. Design – Frontal Experiments • Three to four 1 to 3 Day Experiments over 21 days • Supported by remote sensing and modeling to find fronts • Lagrangian Float(D’Asaro) • Dye releases (Ledwell, Sundermeyer) • CTD/Fluorometer to sample the parcel (Lee) • Profiling EM APEX floats (Sanford) • Satellite remote sensing (Baschek) • Gliders (Shearman) • Towed thermistor chain survey (Baschek, pending) • Large scale surveys with MVP (Klymak, pending)

  11. Strong Front Experiment (2012)

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