Assessment of Surface Currents Measured With High-Frequency Phased-Array Radars in Two Regions of Complex Circulation

Wyatt, L.R.; Mantovanelli, Alessandra; Heron, M.L.; Roughan, Moninya; Steinberg, Craig

doi:10.1109/joe.2017.2704165

Cited by 17 publications

(18 citation statements)

References 39 publications

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“…Multitaper rotary spectra [ Lilly , ] detected two main peaks at the semidiurnal and diurnal signals but more pronounced in the u component of the wind velocity (Figure a). Analysis of the HF radar current spectra at Coffs Harbour mooring locations also showed diurnal and semidiurnal peaks both for surface (HF radar) and subsurface (ADCP) measurements [ Wyatt et al ., ]. Wind varied in direction almost daily over the analyzed year, with a maximum persistence in each direction of less than 6 days (not shown).…”

Section: Resultsmentioning

confidence: 98%

“…The variance of the constant term, and hence that of the smoothed current, is determined from the original variances through the least squares fitting procedure [Wyatt et al, 2017]. Figure 1a shows the HF radar standard deviations after the 6 h smoothing for the v component of the flow, calculated as the square root of the averaged variances over September 2012; the errors for the u component were smaller and were not shown (more details on the HF radar error estimation are found in Wyatt et al [2017]). The data smoothing further reduced data noise while retaining the short-time response of the flow to high-frequency winds on time scales of 7-27 h (Figure 2a).…”

Section: Hf Radar Measurementsmentioning

confidence: 99%

“…(a) HF radar domain offshore Coffs Harbour (Eastern Australia) with data coverage above 50% (September 2012 to September 2013) and locations of the radar stations (RRK, NNB; black circles), ADCP moorings (CH70 and CH100; black squares), and Coffs Harbour weather station (black star). Color legend shows the standard deviation (STD, m s 21 ) of the v-component of the HF radar currents (6 h smoothed) calculated from the mean variance for September 2012 following methodology described in Wyatt et al [2017]; (b) validation of surface HF radar currents against 10 m deep ADCP currents (6 h smoothed data; speed 5 ffiffiffiffiffiffiffiffiffiffiffiffiffi u 2 1v 2 p ) at CH100 mooring shown by the linear regression (red line; equation in the figure; p < 0.01) and the joint probability density function normalized by its maximum value (PDF; color legend); (c) 6 h smoothed meridional (V-component, solid black line) and zonal (U-component, dotted black line) wind velocity components (m s 21 ) measured at Coffs Harbour weather station (black star in Figure 1a) every 30 min; durations of the frontal jet (blue line), cold-core eddy (CCE; orange line), and warm-core eddy (WCE; green line) events are highlighted (see legend on the top).…”

Section: Introductionmentioning

confidence: 99%

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Lagrangian and Eulerian characterization of two counter‐rotating submesoscale eddies in a western boundary current

et al. 2017

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In recent decades, high‐spatial resolution ocean radar and satellite imagery measurements have revealed a complex tangle of submesoscale filaments and eddies, in the surface velocity, temperature, and chlorophyll a fields. We use a suite of high‐resolution data to characterize two counter‐rotating, short‐lived eddies formed at the front between the warm East Australian Current (EAC) and temperate coastal waters (30°S, Eastern Australia). In this region, submesoscale filaments and short‐lived eddies are dynamically generated and decay at time scales of hours to days. Dominant cyclonic filaments of O(1) Rossby number formed along frontal jets and eddy boundaries, generating localized ageostrophic circulations at the submesoscale. Measurements of over‐ocean wind direction and surface currents from high‐frequency radars reveal the influence of the short‐term, small‐scale wind forcing on the surface circulation, enhancement of the horizontal shear, frontal jet destabilization, and the generation and decay of the cyclonic eddy. By contrast, the anticyclonic eddy formation was most likely associated with EAC mesoscale instability and anticyclonic vorticity. Lagrangian tracks show that surface particles can be temporarily trapped in the eddies and frontal convergent zones, limiting their transport. Mixing between EAC‐derived and coastal waters was increased along the frontal regions, and particles starting at the divergent regions around the eddies experienced significant dispersion at submesoscales. The cyclonic cold‐core eddy entrained high chlorophyll a shelf waters on its convergent side, suggesting spiral eddy cyclogenesis.

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Section: Resultsmentioning

confidence: 98%

Section: Hf Radar Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Lagrangian and Eulerian characterization of two counter‐rotating submesoscale eddies in a western boundary current

et al. 2017

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“…Radial (10 min) and vector (1 h) maps are available from the AODN portal (www.aodn.org.au) in both raw (''FV00'') and quality controlled (''FV01'') formats (Middleditch & Cosoli, 2016). Wyatt et al (2017) conducted a data validation and error analysis with in situ measurements on this same data set, obtaining median root-mean-square differences of 0.12 m s 21 , similar to WERA comparisons in the Florida Current (Parks et al, 2009;Shay et al, 2007). They concluded that the data set can be used with confidence for scientific and operational oceanography, as has been proven elsewhere (Paduan & Washburn, 2013;Rubio et al, 2017).…”

Section: Hf Radar Surface Current Mapsmentioning

confidence: 92%

On the Variability of the East Australian Current: Jet Structure, Meandering, and Influence on Shelf Circulation

et al. 2017

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Given the importance of western boundary currents over a wide range of scales in the ocean, it is crucial that we understand their dynamics to accurately predict future changes. For this, we need detailed knowledge of their structure and variability. Here we investigate the jet structure of the East Australian Current (EAC), using observations from HF radars and moorings deployed at 30°S–31°S. Meandering, core velocity, width, and eddy kinetic energy (EKE) are quantified from 4 years of hourly 1.5 km resolution surface current maps (2012–2016), to obtain the most detailed representation of the surface EAC jet to date. The EAC flows predominantly over the ∼1,500 m isobath 50 km offshore but makes large amplitude displacements eastward every 65–100 days—the time scale associated with mesoscale eddy shedding at the EAC separation. Smaller‐amplitude, higher‐frequency meanders occur every 20–45 days. Using a coordinate frame that follows the jet, we show core velocity and EKE exhibit seasonality in both magnitude and variance, being maximum in summer (1.55 m s−1 mean core velocity), minimum in winter (0.8 m s−1). However, it is the eddy‐shedding time scale that dominates jet variability. As the EAC moves shoreward, shelf temperature and along‐stream velocity vary linearly with jet movement, within ∼35 km of the core. The EAC is within this range 75% of the time, demonstrating its importance to the shelf circulation. Temperature and velocity fluctuations at the 70 m (100 m) isobath are more influenced by wind (EAC encroachment), with the strongest response occurring when wind and EAC act constructively.

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“…In the EAC (Figures 1b and 1d), 4 years of HF radar data (March 2012 to July 2016) are analyzed from two sites operating at 13.92 MHz near Coffs Harbour (30-31°S), deployed as part of Australia's Integrated Marine Observing System (IMOS; Roughan et al, 2015;Wyatt et al, 2017). Each radial velocity data set is combined using the unweighted least squares method of Gurgel (1994) to a Cartesian grid with 1.5-km resolution at 10-min intervals smoothed with a 17-point (3 hr) Hann window.…”

Section: Methodsmentioning

confidence: 99%

The Kinematic Similarity of Two Western Boundary Currents Revealed by Sustained High‐Resolution Observations

Archer

Keating

Roughan

et al. 2018

Geophysical Research Letters

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Western boundary currents (WBCs) modulate the global climate and dominate regional ocean dynamics. Despite their importance, few direct comparisons of the kinematic structure of WBCs exist, due to a lack of equivalent sustained observational data sets. Here we compare multiyear, high‐resolution observations (1 km, hourly) of surface currents in two WBCs (Florida Current and East Australian Current) upstream of their separation point. Current variability is dominated by meandering, and the WBCs exhibit contrasting time‐mean velocities in a Eulerian coordinate frame. By transforming to a jet‐following coordinate frame, we show that the time‐mean surface velocity structure of the WBC jets is remarkably similar, considering their distinct local wind, bathymetry, and meandering signals. Both WBCs show steep submesoscale kinetic energy wavenumber spectra with weak seasonal variability, in contrast to recent findings in other ocean regions. Our results suggest that it is the mesoscale flow field that controls mixing and ocean dynamics in these regions.

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Assessment of Surface Currents Measured With High-Frequency Phased-Array Radars in Two Regions of Complex Circulation

Cited by 17 publications

References 39 publications

Lagrangian and Eulerian characterization of two counter‐rotating submesoscale eddies in a western boundary current

Lagrangian and Eulerian characterization of two counter‐rotating submesoscale eddies in a western boundary current

On the Variability of the East Australian Current: Jet Structure, Meandering, and Influence on Shelf Circulation

The Kinematic Similarity of Two Western Boundary Currents Revealed by Sustained High‐Resolution Observations

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