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"Waves beneath the Sea"

"Waves beneath the Sea". Phenomenon Physics Field Experiment Teaching Aspects. Dan Kelley Oceanography Dept. Dalhousie University http://www.phys.ocean.dal.ca/ ~kelley/ papers/ presentations/ 2001/ AST. "Dead" water. Boat slows to a crawl... ... surfing internal wake

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"Waves beneath the Sea"

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  1. "Waves beneath the Sea" • Phenomenon • Physics • Field Experiment • Teaching Aspects

  2. Dan KelleyOceanography Dept.Dalhousie Universityhttp://www.phys.ocean.dal.ca/~kelley/papers/presentations/2001/AST

  3. "Dead" water • Boat slows to a crawl... • ... surfing internal wake • Nansen observation 189x • Ekman explanation 1904

  4. External and Internal Waves: restoring forces • External waves: gravity g • Internal waves: reduced gravity g=gDr/r0

  5. Physics of Waves • Restoring force ... • ... key to all oscillators!

  6. Class Experiment [1]

  7. Class Experiment [2]

  8. Internal Waves in Atmosphere [1] • Wave crests ... • rising air ... • condensation... • ... clouds.

  9. Internal Waves in Atmosphere [2]

  10. Banded Surface Slicks • Convergent zones over troughs • Sweeps oil into lines • Visible by eye, radar, satellite, etc.

  11. Ocean from Airplane

  12. Ocean from Space

  13. Ship Radar • Internal waves yield banded slicks... • ... banded roughness... • ...surface signature of internal waves

  14. SurfaceTidal Bore

  15. Physics of (Tidal) Bore

  16. Other Surface Bores [1]

  17. Other Surface Bores [2]

  18. Peter Galbraith • PhD at Dalhousie • Mixing, internal waves, estuarine physics • Works at DFO in Quebec

  19. Internal Tidal Waves

  20. Chopper - a new type of ship!

  21. Daniel Bourgault • PhD at McGill • Estuarine physics, ocean modelling, internal waves • Works with me at Dalhousie

  22. St. Lawrence Est. Internal Wave

  23. Modelled Internal Wave

  24. View from Shore

  25. St. Lawrence Estuary

  26. Geometrically Corrected View

  27. Enhanced View

  28. Internal Waves on Rotating Planet • Wave "phase" goes one way... • ... wave "energy" goes another! • Important to climate...

  29. Scientific Summary • Ocean/atmosphere has internal as well as external waves • These waves may break ... • ... causing oceanmixing ... • ... affecting biology, • ... affecting chemistry, • ... affecting climate...

  30. Teaching Summary • Explains cloud patterns • Explains "dead water" • Illustrates universality of Physics (here, across Ocean & Atmosphere) • Illustrates idea of restoring force • Illustrates resonance

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