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Submesoscale Currents in the Atlantic

Submesoscale Currents in the Atlantic. Jeroen Molemaker, Jim McWilliams, Jonathan Gula, Florian Lemarie, Alexander Shchepetkin UCLA. Characteristics of submesoscale. Middle sized: L = 10 m-10s km, t = hrs - days. Rotating, stratified dynamics, mostly not waves.

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Submesoscale Currents in the Atlantic

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  1. Submesoscale Currentsin the Atlantic • Jeroen Molemaker, • Jim McWilliams, Jonathan Gula, Florian Lemarie, • Alexander Shchepetkin • UCLA

  2. Characteristics of submesoscale • Middle sized: L = 10 m-10s km, t = hrs - days. • Rotating, stratified dynamics, mostly not waves. • Geostrophic dynamics are relaxed. • Arising out of mesoscale currents. • Disappearing into micro-scale mixing and dissipation

  3. Sources of submesoscale energy • Mixed layer baroclinic instabilities • Horizontal/Vertical shear • Interaction between straining and density gradients • One instability can lead to the next.

  4. Intermezzo:An example of how we use ROMS

  5. Gulf Stream (dx = 5-7 km) Many subsequent nested solutions Improved through reduced diapycnal mixing Marchesiello (2010), Lemarie etal. (2012) Rio

  6. Examples of validation AVISO ROMS – ATLBIG (5-7km)

  7. Surface current Magenta lines are 0.3 m/s contour level of AVISO surface geostrophic velocities Mean path of the Gulf Stream

  8. SSH variability – AVISO SSH variability – ROMS

  9. Mean path of the Malvinas/Brazil currents

  10. Nest level 1 South West Atlantic (dx = 1.5 km, 1500km x 2000km) Submesoscale on top of mesoscale

  11. Nest level 2 (dx = 500 m, 600 km x 400 km ) Rio

  12. Back to submesoscale dynamics • Submesoscale range often start with mixed layer instability • Source is potential energy. • Deep mixed layer or strong horizontal density gradients

  13. Mixed layer depth Summer Winter

  14. Summer Winter

  15. Surface Relative Vorticity (dx = 1.5 km)

  16. Relative Vorticity: PDF Summer Winter Text Blue: Surface, Red: -100 meter

  17. Cold filament

  18. Evolution over 1 day

  19. Cold-core cyclonic eddy with sub-mesoscale features

  20. Relative vorticity (Ro > 4) Velocity amplitude

  21. Radial vorticity structure

  22. Surface relative vorticity [-3f, 3f] Rio, dx = 500 m)

  23. Surface horizontal divergence [-3f, 3f] (Rio, dx = 500 m)

  24. 50km x 40 km dx = 180 m

  25. Thank You

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