Circulation, structure and dynamics of a buoyant coastal current'

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Circulation, structure and dynamics of a buoyant
coastal current. Bob Chant, Scott Glenn,
Phillip Bogden American Meteorological
Society Albuquerque New Mexico January 13-19,
2001
Cold
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• Motivation
• Characterize Circulation and Dynamics of Coastal
  Current
• Provides target for numerical modeling
• Results can be used to assess accuracy of other
  techniques.
• -Airborne altimetery
• -Turbulence Sensors
• -Modeling

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Buoyant Coastal Current
Warm
Fresh
Warm
Cold and Salty
Cold
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Towed ADCP/CTD data-July 28, 2000
Along-Shelf (color) and Cross-Shelf
(vectors) Currents.
Salinity (color) and Temperature (contour)
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. ADCPs at 2,3,4,5 p-sensor T-chain at 2
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REMUS 2
REMUS 3
REMUS 4
REMUS 5
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Depth Average Flow
Sectionally Averaged Flow
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Along-shore flow fluctuations are in geostrophic
balance
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Sectionally averaged Along-shore
Analyze Flow during Southward Flows V lt -10 cm/s
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Mean Flow (red) and Stratification (blue) (v lt
-10)
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Along Shore Flow
-10
10
10
-10
-10
10
4
4
4
4
-4
-4
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Warm
Fresh
Cold
Cold
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Cross-Shore Momentum Equations
Depth Averaged
Depth Dependent
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Conclusions

• Surface and bottom Ekman layers are evident in
  event-averaged moored ADCP data. However,
  transport in the bottom layer is approximately
  one third of tb/rf.

• Sectionally averaged fluctuating along-shore
  currents are geostrophically balanced.

• In the near shore, weak stratification prevents
  bottom-stress from penetrating the entire water
  column. Mixing coefficients are strongest in the
  bottom mixed layer (10-2 m2/s), weakest in the
  interior (510-4 m2/s) and of intermediate values
  towards the surface (10-3 m2/s)

• Fluctuating depth averaged and near bottom
  currents are highly
• constrained by bathymetry. Surface currents are
  constrained by the coastline only within an
  internal Rossby radius from the coast.

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20 cm/s 0.5 dyne/cm2
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Principle Components of fluctuating
currents Surface-red Bottom-Blue Depth
Average-Black
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Record Mean Flow
fu
tb/rH
Residual
ts/rH
10 cm/s
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Surface Stress is Red Bottom Stress is Blue
Along-Shelf Stress
tbgtts (despite tb underestimate)
Cross-Shelf Stress