Surface Currents off the Outer Banks of North Carolina

Luke Stearns, UNC Chapel Hill

Site Installation

• Duck and Buxton sites installed Summer 2003

• Transponder calibrations occurred that summer also

• Both sites “operational-ish” since then

Theoretical Coverage

• Overlap region leaves large areas of radial coverage unused

• NOAA plans to make long range Codar at Cape Henry operational soon

Cape Henry

Duck

Buxton

Percent Coverage: Measured PatternsDecember 2003

What Happens to the signal in these radial directions?

Why is there less coverage?

Site Configuration

Aerial photographs provided by North Carolina Department of Environment and Natural Resources. images.enr.state.nc.us

Duck Buxton

Could the pier be causing some of this interference?

Could the distance behind the dunes cause losses?

Obstacles at Duck

Large metal tower Steel and

concrete pier

Obstacles at Buxton

Metal fence

Extensive sewage pipes and the treatment shed

The dune

Objectives

• Optimize beam patterns

• Compare with other observations

• Evaluate system performance

• Provide information to local community and partner institutions or organizations

Ideal Beam Patterns

Coverage for locations reporting data at least 40% of the time is shown

Places where we don’t expect coverage (like land) don’t show up much at all

Totals look fairly reasonable in most areas

Extent is fairly good, but buxton is bad to the north (where the overlap is with duck)

Ideal Beam Patterns

Measured Beam Patterns

Measured Beam Patterns

Duck Radials have slightly increased coverage

Buxton radials have increased coverage in some areas worse in others

The first and last direction bins look to be contaminated

Overall extent of totals is reduced

The divergence pattern at the Southern limit of coverage is more reasonable

Objectives

• Optimize beam patterns

• Compare with other observations

• Evaluate system performance

• Provide information to local community and partner institutions or organizations

Codar M2 Tides

60% Coverage criteria used

Tides computed with t_tide package for matlab

M2 Tidal Comparison

• Orientation and ellipticity agree reasonably well with ADCIRC and Lentz et. al. observations

• Codar Magnitude smallest (surface), largest for ADCIRC (depth average), in between for Lentz (near surface)Lentz et. al. 2001 (Barotropic Tides on the North Carolina Shelf)

• The amplitudes of the M2 tidal component are different for Adcirc, Codar, and Lentz et. al. WHY?

• How different are they?

• What does this tell us about data quality?

M2 Tidal Amplitude Ratio (ADCIRC/Codar)

Major Minor

Only in a few locations do they agree on Major amplitude. Almost everywhere else ADCIRC amplitudes are larger

The structure seems much noisier in Minor amplitudes.

SST and Codar(Snapshot 1)

• Captures the Gulf Stream front well

• Seems to show currents turning spatially where the cool filament turns

• Passes the “Looks Good” test

AVHRR Satellite SST data from www.imars.usf.edu

SST and Codar(Snapshot 2)

• Shows reasonable along isobath flow

• Shows Southward jet slamming into the Gulf Stream

• Convergence looks huge, and SST Gulf Stream front no longer consistent with Codar observations

Objectives

• Optimize beam patterns

• Compare with other observations

• Evaluate system performance

• Provide information to local community and partner institutions or organizations

Monthly Mean Currents(Measured, 40% coverage)

Southward, along isobath flow 5 month mean

Offshore transport

Increasing offshore veering of MAB Southward jet

Consistent with Gawarkiewicz and Lozier

Gulf Stream

Gulf Stream shows up in all images

Gulf Stream fairly consistent

Gulf Stream decrease

Gulf Stream shows up in all images

Gulf Stream apparent but weak

Objectives

• Optimize beam patterns

• Compare with other observations

• Evaluate system performance

• Provide information to local community and partner institutions or organizations

Providing Information Products: Data Plots

• Provide Data plots for laymen, technicians, and scientists

Providing Information Products:Radial Currents

• Radials provide a good diagnostic tool for technicians and scientists

Providing Information Products:Data Access

• DODS access provides real-time data to scientific users

• Real Time access provides skill assessment for modeling community

What Next?• Get direct data comparison to provide more confidence in the data

• ADCP comparison is soon to come

• Drifter track comparison likely for summer to fall

• Work towards actively distributing information products

• Expand the network of HF Radars!

Thanks!!!

• Codar Ocean Sensors (outstanding support!)

• Josh Kohut, Scott Glenn and the Rutgers Crew

• Mike Muglia for keeping everything alive, processing and many good ideas

• Harvey Seim for guidance, direction, hard work, and the master plan!

• SEACOOS (Observing and Data Management)

• Nick Shay and Tom Cook (the SEACOOS HF Radar experts)

• John Bane, Sara Haines, Brian Blanton, Catherine Edwards, Karen Edwards for ideas and support

• Glen Gawarkiewicz for MAB expertise

• Friends and Family for support and patience!