Spatial Current Structure Observed with a

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Spatial Current Structure Observed with a
Validated HF Radar System The Influence of
Local Forcing, Stratification, and Topography on
the Inner Shelf
Josh Kohut Scott Glenn Hugh Roarty Bob Chant Dale
Haidvogel Rutgers University Jeff Paduan Naval
Postgraduate School
(and MANY more!!!)
Coastal Ocean Observation Lab Institute of Marine
and Coastal Sciences Rutgers University
2
ROW 2 Meeting

• Role of antenna pattern distortion on system
  accuracy
• Kohut, J.T. and S.M. Glenn. 2003.
  Improving HF radar surface current
• measurements with measured antenna beam
  patterns. - accepted Journal of
• Atmospheric and Oceanic Technology.
• The Long-Range 5 MHz network setup
• Roarty, H. J., J. T. Kohut, and S. M.
  Glenn. 2003. Intercomparison of an
• ADCP, ADP, standard and long-range HF
  radar Influence of horizontal and
• vertical shear. IEEE Current
  Measurement Proceedings.
• Introduced seasonal and event scale variability
  over the
• inner shelf (25 MHz System)
• mean fields and transient fields

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Test
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Seasonal Variability Data
Annual Mean
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Seasonal Variability Data
30 25 20 15 10 5 0
Temperature (ºC)
Winds HF radar ADCP
Stratified Mixed
150 200 250 300 350
35 85
Time (year-day)
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Seasonal Variability
Stratified Regime Response
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Seasonal Variability Stratified Regime
Wind Forcing
Number of Hourly Occurrences
Wind Speed (m/s)
Wind Direction (degrees CW from true north)
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Seasonal Variability Stratified Regime
Stratified Water Column
Complex Correlation
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0
0 3 4 5 6 7 8 9 10
Depth (m)
1.0
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Seasonal Variability Stratified Regime
Upwelling Response
Mean (U)
Spatial Structure

• Strong mean flow

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Bathymetric Variability on Upwelling
Seasonal Variability Stratified Regime
1 m/s current velocity
Along shore subsurface deltas cause upwelling to
be 3d, not 2d.
wind

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Seasonal Variability Stratified Regime
Downwelling Response
Mean (U)
Spatial Structure

• Strong mean flow

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Seasonal Variability Stratified Regime
Downwelling Regime
Sea-Surface Temperature
Correlation
0.0 0.1 0.2 0.3 0.4
0.5 0.6 0.7 0.8 0.9 1.0
Correlation
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Seasonal Variability Stratified Regime
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Seasonal Variability
Mixed Regime Forcing
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Seasonal Variability Mixed Regime
Wind Forcing
Wind Speed (m/s)
Number of Hourly Occurrences
Wind Direction (degrees CW from true north)
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Seasonal Variability Mixed Regime
Mixed Water Column
Complex Correlation
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0
0 3 4 5 6 7 8 9 10
Depth (m)
1.0
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Seasonal Variability Mixed Regime
Frictional Layer
300 250 200 150 100 50 0
Linear eddy viscosity
Frictional Velocity
Depth Scale (m)
Frictional Length Scale
240 260 280 300
320 340 360
Time (year-day)
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Seasonal Variability
Mixed Regime Bottom topography
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Seasonal Variability Mixed Regime
Topography
20 km
5 km
minimize
Depth (m)
h depth L horizontal scale
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Seasonal Variability Mixed Regime
Influence of Gradient Maximum
30 20 10 0 -10 -20 -30 -40 -50 -60
Angular Offset (degrees)
Negative angle Principle axis right of
topography
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Storm Response

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Storm Event Forcing
Floyds Track
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Storm Event Forcing
Wind (m/s)
Wind speed (m/s)
Inertail amp (m/s)
Pressure (mbars)
Rainfall (cm/hour)
Time (year-day)
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Storm Event Response
Wind Surface 3m 10m
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Storm Event Response
Surface 3m 4m 5m 6m 7m 8m 9m 10m Depth-Averaged
CW CCW
Time (year-day)
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Storm Event Response
Near-Inertial Response
Angle
4 3 2 1 0 -1 -2 -3 -4
Depth (m)
Phase (degrees)
25 cm/s
Amplitude (cm/s)
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Storm Event Models
Single Layer Model Equations
t
t
h


v
by
wy
-

-
-

fu
g
r
r

H
H
dy
t
Pressure Gradient
Depth-averaged Acceleration
Bottom Stress
Wind Stress
Coriolis
?w
TOGA-COARE2.6 algorithm (Fairall et al.,
1996) Local Wind (10m) Air temperature Sea
temperature relative humidity
r
t

2
u

b
ADCP/HF Radar ADCP Winds Inferred
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Along-shore Velocity (cm/s)
Acceleration Pressure Gradient
Coriolis Bottom stress Wind Stress
Along-shore Momentum Balance
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Storm Response
Larger Spatial Scales
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M2 Tidal Ellipses
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NJSOS
NEOS Northeaster Oct 16, 2002
GoMOOS
MVCO
LEO 15
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Spatial Maps 10/16/2002 0700 GMT
1002 mb
Contour resolution 1 mb
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10/16/2002 1500 GMT
991 mb
Contour resolution 1 mb
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10/16/2002 1800 GMT
989 mb
Contour resolution 1 mb
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10/17/2002 0000 GMT
992 mb
Contour resolution 1 mb
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NEOS
Existing Sub-Regional Observatories
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• NVODS OPeNDAP CODAR Pilot Project (Peter
  Cornillon and Dave Ullman)
• Develop Capability to Provide CODAR Data from
  Multiple Systems in a Seamless Manner.
• Client requests data from a user selected region
  that may contain more than one CODAR system.
• Aggregation server Combines data from a number
  of different CODAR systems and provides to
  client.
• http//www.nvods.org http//www.opendap.org

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Current operational prediction
CODE drifter
CODAR based prediction
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Building1
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Equipment Box
Transmitter Receiver
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Receive Antenna
Transmit Antenna
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Transmit Antenna
Receive Antenna
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Seasonal Variability
Conclusions

• Annual mean flow is primarily along-isobath.
• Stratification
• strong mean currents and weak variability
  primarily oriented
• along-shore.
• surface currents are highly correlated with the
  wind.
• currents tend to be to the right of the wind at
  the surface and
• rotate the the left with depth.
• current fields uncorrelated with the wind are
  generally weak
• and not aligned with topography.
• Mixed
• strong variability with a cross-shore component.
• surface currents are less correlated with the
  wind.
• currents tend to be to the left of the wind at
  the surface and
• rotate slightly to the left with depth.
• surface current fields uncorrelated with the
  wind resemble the
• observed fields and tend to
  follow topography in regions
• were the gradient is maximum.

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Storm Response
Conclusions

• Before the Storm
• Cross-shore geostrophic balance.
• Small-scale along-shore pressure gradient
  balanced by bottom stress.

• During the Storm
• Cross-shore winds build up a pressure gradient
  that accelerates the current
• offshore in the eye.
• Along-shore rectilinear response is driven by a
  propagating storm surge
• and balanced by bottom friction.

• After the storm
• Single layer flow becomes stratified with
  freshwater inflow.
• Surface layer moves toward the north driven by
  an along-shore pressure
• gradient.

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Future Work
Support the US contribution to the International
Ocean Observing System (IOOS) HF radar has
potential high impact for coastal component of
IOOS Expand existing HF radar working
groups Benefit scientific and operational users
http//marine.rutgers.edu/cool
http//www.thecoolroom.org