7. Surface Ocean Circulation

7. Surface Ocean Circulation - Surface Ocean Circulation...

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Surface Ocean Circulation Surface ~ top 100m Controlled by: Wind Coriolis Surface Deep ~100m ~4000m
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Surface Ocean Circulation Surface ocean circulation ultimately driven by solar radiation Insolation drives atmosphere, which in turn drives surface ocean circulation Distinctions Upper ocean absorbs 90% - deep ocean absorbs 10% of incoming radiation Warm surface = stable stratification
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Surface Ocean Circulation
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Surface Ocean Circulation Nansen- Norwegian Explorer (1890’s) Fram Expedition Scientific Experiment- froze ship into Arctic ice for 3 years Fridtjof Nansen
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Nansen’s Expedition
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Surface Ocean Circulation Nansen Expedition Discovered: Ship traveled with ocean circulation below the ice, not with the wind Movement was 20 – 45° (NH vs. SH) Polar Easterlies current
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Surface Ocean Circulation Ekman- Swedish physicist Explained the phenomenon Friction on ocean Coriolis Ekman Spiral
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Ekman Spiral Think of ocean as a series of thin layers Wind ~100 m Assumed- *constant wind *laminar flow *constant seawater density with depth
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Ekman Spiral Wind blows on surface Friction- kinetic energy of air motion is transferred to surface-most layer Sets water into motion (at ~3% of wind speed) Add Coriolis- top layer deflected to right (NH)
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Ekman Spiral Friction sets next layer in motion Starts to move Loss of velocity Coriolis - deflected farther to the right (NH) Continues with each successive layer: - energy transferred to each layer diminishes (friction) - deflected to right
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Ekman Spiral KKC 5-3a Energy rather than water spiraling downward
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Ekman Transport Ekman Transport Sum of Ekman spiral Net water transport Transport of surface-most layer is 45° to right of the wind (NH) Transport of top ~100 m is 90 ° to the wind = wind driven circulation + Coriolis
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Ekman Transport See KKC 5-3a
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Surface Ocean Circulation
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Ekman Transport Theoretically: Wind-driven surface layer (~100 m) deflected 90° from wind Surface-most current deflected 45° from wind Reality: Wind-driven surface layer deflected <90° Surface-most current deflected 20 -45°
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Ekman Transport Theoretical vs. reality Turbulent vs. laminar flow Seawater density not constant with depth Winds variable
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Ocean Gyres Water in each ocean basin circulates in gyres Gyres = closed, circular flow of water around periphery of an ocean basin Gyres are a product of surface winds plus Ekman transport (Coriolis) plus land interference
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Ocean Gyres KKC 5-1
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Ocean Gyres 5 gyres: North Atlantic South Atlantic North Pacific South Pacific South Indian Also West Wind Drift (Antarctic Circumpolar Current) Closed circuit, but not around periphery of basin
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Ocean Gyres See KKC 5-2
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This note was uploaded on 07/08/2011 for the course GLY 3074 taught by Professor Ellenmartin during the Spring '09 term at University of Florida.

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7. Surface Ocean Circulation - Surface Ocean Circulation...

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