Waves beneath the Sea

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"Waves beneath the Sea"

• Phenomenon
• Physics
• Field Experiment
• Teaching Aspects

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Dan KelleyOceanography Dept.Dalhousie
Universityhttp//www.phys.ocean.dal.ca/kelley/
papers/presentations/2001/AST
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"Dead" water

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

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External and Internal Waves restoring forces

• External waves gravity g
• Internal waves reduced gravity ggDr/r0

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Physics of Waves

• Restoring force ...
• ... key to all oscillators!

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Class Experiment 1
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Class Experiment 2
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Internal Waves in Atmosphere 1

• Wave crests ...
• rising air ...
• condensation...
• ... clouds.

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Internal Waves in Atmosphere 2
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Banded Surface Slicks

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

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Ocean from Airplane
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Ocean from Space
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Ship Radar

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

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SurfaceTidal Bore
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Physics of (Tidal) Bore
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Other Surface Bores 1
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Other Surface Bores 2
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Peter Galbraith

• PhD at Dalhousie
• Mixing, internal waves, estuarine physics
• Works at DFO in Quebec

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Internal Tidal Waves
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Chopper - a new type of ship!
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(No Transcript)
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Daniel Bourgault

• PhD at McGill
• Estuarine physics, ocean modelling, internal
  waves
• Works with me at Dalhousie

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St. Lawrence Est. Internal Wave
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Modelled Internal Wave
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View from Shore
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St. Lawrence Estuary
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Geometrically Corrected View
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Enhanced View
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Internal Waves on Rotating Planet

• Wave "phase" goes one way...
• ... wave "energy" goes another!
• Important to climate...

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Scientific Summary

• Ocean/atmosphere has internal as well as external
  waves
• These waves may break ...
• ... causing ocean mixing ...
• ... affecting biology,
• ... affecting chemistry,
• ... affecting climate...

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Teaching Summary

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