8-OcSPRING08-SurfCirc_notes

8-OcSPRING08-SurfCirc_notes - Surface Ocean Circulation...

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Surface Ocean Circulation Gulf Stream Current: Satellite image of sea surface temperature
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Introduction Surface Ocean Circulation Mixed layer ~ top 200m (10%) Controlled by wind plus Coriolis Deep Ocean Circulation Below ~ 200m (90%) Controlled by density (T and S) variation Ultimate Driver (Energy Source) = Sun (Differential Heating) + via Force of Gravity Surface Deep ~200m: pycnocline ~4000m
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Introduction Direct methods Float meters drifters moored Propeller meters drifter
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Introduction Direct methods - Float meters - Inadvertent
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Introduction Direct methods Float meters Inadvertent
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Indirect method – via Satellite - since 1996. - based on altimeter derived sea level data
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Introduction Predominant Winds
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Introduction Wind pushes on ocean surface Transfer Energy by friction Sets water into motions Flows at ~1-2% of the wind speed Wind ~ 5-20 m/s, Currents ~ 0.1 – 1 m/s (0.2-3 mph) Add Coriolis
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Fridtjof Nansen (1861-1930) observed; V. Walfrid Ekman calculated/explained Introduction 45 o
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Ekman Transport Because of Coriolis Surface water flows at ~45° to the wind direction Northern Hemisphere: 45 o to right Southern Hemisphere: 45 o to left NE Trades current SE Trades current
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Ekman Transport Predominant Winds Surface Water
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Ekman Transport Think of surface layer as an infinite number of layers Wind friction puts uppermost layer into motion (Speed ~ 1/100) deflected by Coriolis Each successive layer is deflected by Coriolis and has a lower velocity = Ekman Spiral Wind ~200 m
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Ekman Transport
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Ekman Transport Net effect (Sum of the layers) Transport of the upper ocean at 90° to the wind 90° to right of the wind (North Hem.) 90° to left of the wind (South Hem.) = Ekman Transport
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Ekman Transport Polar Easterlies Polar Easterlies Predominant Winds Net Surface Water Movement = Ekman Transport *naming of winds and currents
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In the northern hemisphere, a southeasterly wind will cause a net Ekman current that is…. 1. northeasterly 2. northwesterly 3. southeasterly 4. southwesterly QUESTION N S E W WIND Ekman
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Surface Ocean Currents Creates a Gyre: Closed, circular flow around the periphery of an ocean basin
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Surface Ocean Currents 5 gyres
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Surface Ocean Currents 5 gyres N. Atlantic (clockwise) S. Atlantic (counterclockwise) N. Pacific (clockwise) S. Pacific (counterclockwise) S. Indian (counterclockwise) Also Antarctic Circumpolar Current (circular flow but not around periphery of
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Surface Ocean Currents Each gyre has 4 currents North Atlantic Basin : Gulf Stream, N. Atl. Current, Canary Current, N. Equatorial C.
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South Atlantic Basin : S. Equatorial C. Brazil C.
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This note was uploaded on 04/08/2008 for the course OCE 1001 taught by Professor Smith during the Spring '08 term at University of Florida.

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8-OcSPRING08-SurfCirc_notes - Surface Ocean Circulation...

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