Validation of HF radar probing of the vertical shear of surface currents by acoustic Doppler current profiler measurements

Abstract A dual-station high-frequency (HF) Wellen Radar (WERA) transmitting at 16 MHz has observed near-real-time surface currents over an approximate range of 100 km across the Florida Straits since July 2004. During a 10-day period in April 2005 (15–25 April), a pair of 12.6-MHz SeaSondes (SS) were deployed south of the WERAs sites by NOAA's Center for Operational Oceanographic Products and Services (CO-OPS). The resulting SS grid overlapped the southern portion of the WERA domain. During the same period of time, a bottom-mounted acoustic Doppler current profiler (ADCP) acquired subsurface current measurements within these HF radar grids starting at 14 m below the surface in water of 86-m depth. The interoperability of beam-forming (WERA) and direction-finding (SS) HF radar technologies was examined. Comparisons of radial and vector currents for an 8-day concurrent time series suggested good agreement in current direction over both domains, where the surface currents' magnitudes were a maximum of 1.2 m s−1. In the core of the radar domains consisting of 108 cells, hourly vector currents were obtained by combining WERA and SS radials. Generally, this can be done in a relatively straightforward manner, considering the geometric dilution of precision (GDOP). A second key issue is downscaling the SS measurements from a 3-km grid to a 1.1-km grid to match the WERA output. This enhanced grid spacing is important along the western flank of the Florida Current, where energetic, small-scale surface features have been observed.

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Variability of the Horizontal Velocity Structure in the Upper 1600 m of the Water Column on the Equator at 10°W

Journal of Physical Oceanography ◽

10.1175/jpo2908.1 ◽

2006 ◽

Vol 36 (7) ◽

pp. 1287-1304 ◽

Cited By ~ 16

Author(s):

Lucia Bunge ◽

Christine Provost ◽

Jonathan M. Lilly ◽

Marc D’Orgeville ◽

Annie Kartavtseff ◽

...

Keyword(s):

Water Column ◽

Velocity Component ◽

Velocity Structure ◽

Strong Dependence ◽

Acoustic Doppler Current Profiler ◽

Horizontal Velocity ◽

Vertical Shear ◽

Equatorial Atlantic ◽

Entire Water Column ◽

Current Profiler

Abstract This paper presents initial results from new velocity observations in the eastern part of the equatorial Atlantic Ocean from a moored current-meter array. During the “EQUALANT” program (1999–2000), a mooring array was deployed around the equator near 10°W that recorded one year of measurements at various depths. Horizontal velocities were obtained in the upper 60 m from an upward-looking acoustic Doppler current profiler (ADCP) and at 13 deeper levels from current meters between 745 and 1525 m. To analyze the quasiperiodic variability observed in these records, a wavelet-based technique was used. Quasiperiodic oscillations having periods between 5 and 100 days were separated into four bands: 5–10, 10–20, 20–40, and 40–100 days. The variability shows (i) a strong seasonality (the first half of the series is dominated by larger periods than the second one) and (ii) a strong dependence with depth (some oscillations are present in the entire water column while others are only present at certain depths). For the oscillations that are present in the entire water column the origin of the forcing can be traced to the surface, while for the others the question of their origin remains open. Phase shifts at different depths generate vertical shears in the horizontal velocity component with relatively short vertical scales. This is especially visible in long-duration events (>100 days) of the zonal velocity component. Comparison with a simultaneous lowered acoustic Doppler current profiler (LADCP) section suggests that some of these flows may be identified with equatorial deep jets. A striking feature is a strong vertical shear lasting about 7 months between 745 and 1000 m. These deep current-meter observations would then imply a few months of duration for the jets in this region.

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Dynamics of tidal mixing fronts in the North Sea

Philosophical Transactions of the Royal Society of London Series A Physical and Engineering Sciences ◽

10.1098/rsta.1993.0057 ◽

1993 ◽

Vol 343 (1669) ◽

pp. 431-446 ◽

Cited By ~ 27

Keyword(s):

North Sea ◽

Baroclinic Instability ◽

Acoustic Doppler Current Profiler ◽

Hf Radar ◽

Tidal Mixing ◽

The North ◽

Current Profiler ◽

Shelf Sea ◽

The North Sea ◽

New Generation

Twenty years since the discovery of tidal mixing fronts there are still few convincing observations of the velocity field associated with these structures. Simple models of shelf sea fronts predict strong along-front jets, weaker convergent circulations and instabilities. During the North Sea Project a series of studies of the Flamborough frontal system has used a new approach based upon novel combinations of modern instrumentation (HF radar, acoustic Doppler current profiler, Decca-Argos drifting buoys and towed undulating CTD) and have provided one of the first directly observed pictures of shelf sea frontal circulation. Observational confirmation of jetlike along-front flow has been found together with evidence of cross-frontal convergence. A new generation of eddy-resolving models will help to focus the next phase of frontal circulation studies in relation to questions concerning baroclinic instability and eddy generation.

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The Finescale Response of Lowered ADCP Velocity Measurements Processed with Different Methods

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-11-00158.1 ◽

2012 ◽

Vol 29 (4) ◽

pp. 597-600 ◽

Cited By ~ 9

Author(s):

A. M. Thurnherr

Keyword(s):

Acoustic Doppler Current Profiler ◽

Processing Method ◽

Vertical Shear ◽

Inversion Method ◽

Velocity Data ◽

Velocity Measurements ◽

Processing Methods ◽

Velocity Inversion ◽

Current Profiler ◽

Specific Implementation

Abstract In a paper published in 2002 in this journal, K. Polzin et al. derive corrections for spectra of vertical shear calculated from lowered acoustic Doppler current profiler (LADCP) velocity data. To illustrate and validate the corrections, they use velocities derived with a specific implementation of the shear method for LADCP processing that is no longer supported or widely used. In several recent publications, spectral corrections specific to this old processing method have been applied without modification to LADCP data processed with the more modern and much more widely used velocity-inversion method, which is associated with significantly less damping at high vertical wavenumbers than the older method. The purpose of this work is to derive and validate spectral corrections appropriate for different LADCP processing methods.

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