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Deepwater Currents

Deepwater Currents. Cortis Cooper Chevron. Internal wave packets off Hainan Island. Preview. Identify types of currents Provide detail physics max. speed time variability spatial coherence sites where found capability to model. Loop Current. Warm Eddy.

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Deepwater Currents

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  1. Deepwater Currents Cortis CooperChevron Internal wave packets off Hainan Island

  2. Preview • Identify types of currents • Provide detail • physics • max. speed • time variability • spatial coherence • sites where found • capability to model Loop Current Warm Eddy Infrared image of the Loop Current in the GOM

  3. Types of Currents 5 Turbidity Currents 4 Boundary Currents & Associated Eddies River Currents Peak Velocity (kt) 3 Solitons Shelf Waves 2 Storm Currents Internal waves 1 Tides Tides 0 0.01 0.10 1.00 10.00 100.00 Period (day)

  4. Storm-Driven Currents • Stratification important • Modeling is “easy” • Reach 200 cm/s • Important in cyclone regions

  5. Inertial Currents • Generated by impulsive force • Propagate down/up • ~50 cm/s • May govern design in rare cases • Modeling possible Inertial current reflected from the bottom, Gulf of Mexico

  6. Boundary Currents • Strong & persistent • Strong vertical coherence • Meanders & eddies • Important at ….. • GOM • Flemish Pass • W. of Shetland • Nigeria Scotian Shelf Warm Ring Cold Ring Gulf Stream Infrared image of the NW Atlantic

  7. Boundary Current Modeling • Presently developing in GOM & W. of Shetland • Very expensive! • Still unproven • Animation • based on model not data • shows current vectors

  8. Eddies • Prolific! • Many different sizes • Cold & Hot Eddies in the Caspian

  9. Cold Core Eddies

  10. Topographic Waves • Moderately strong & last for days • Modeling possible • Important ….. • GOM outer slope • Australia • W. Africa Topographic waves in GOM

  11. Internal Waves & Solitons • Forced by tides, winds • Phase spd ~100 cm/s • 5 km , 30 m high • ~200 cm/s • Modeling ?? • Important…. • Australia • W. Africa ? • S. China Sea Wave Breaking Warmer Water Internal Waves Rankin pipeline! Colder Water

  12. Internal Wave Examples Internal waves in the Red Sea Solitons through Gibraltar

  13. Turbidity Currents • Mud avalanches • 25 m/s currents! • Few measurements • Important… • Cabinda • Scotian Shelf • Manteo Fluid-mud ”avalanche” Accreting Sediment Instability triggers sudden slide Sediment accumulates over months/years

  14. Current Gustiness • Wind gustiness well recognized • Gusts caused by small-scale eddies • For Loop ~5 cm/s at 2 min period

  15. River Currents • Freshwater forms high-speed lens • Lens can persist for 10’s of km • Speeds of 200 cm/s but shallow • Important • Congo • Nile • Orinoco Contours max surface currents off Congo River

  16. Subsurface Jets • Characteristics • last for few days • peaks ~200 cm/s • Important for • riser design (VIV) It’s a mystery! Jet measurements off Cabinda

  17. Summary • Wide range of time scales (mins-yrs) • Wide range of length scales • Can dominate some designs • May be infrequent & “invisible” • Still some “mysteries” Rosby wave & El Nino Eddy in the Gulf

  18. Future Work • Current Gustiness • shorter recording intervals • ADCPs? • Wave Refraction • Vertical Coherency • routine use of EOFs • Local measurements • Improved models

  19. Moral: Take into account the fluid flow !

  20. Total sediment Bed Load Congo Canyon Cable Yearly distribution of breaks

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