ALBERT

Description: Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 28 (2011): 1539–1553, doi:10.1175/JTECH-D-11-00001.1.

Description: Turbulent Reynolds stresses are now routinely estimated from acoustic Doppler current profiler (ADCP) measurements in estuaries and tidal channels using the variance method, yet biases due to surface gravity waves limit its use in the coastal ocean. Recent modifications to this method, including spatially filtering velocities to isolate the turbulence from wave velocities and fitting a cospectral model to the below-wave band cospectra, have been used to remove this bias. Individually, each modification performed well for the published test datasets, but a comparative analysis over the range of conditions in the coastal ocean has not yet been performed. This work uses ADCP velocity measurements from five previously published coastal ocean and estuarine datasets, which span a range of wave and current conditions as well as instrument configurations, to directly compare methods for estimating stresses in the presence of waves. The computed stresses from each were compared to bottom stress estimates from a quadratic drag law and, where available, estimates of wind stress. These comparisons, along with an analysis of the cospectra, indicated that spectral fitting performs well when the wave climate is wide-banded and/or multidirectional as well as when instrument noise is high. In contrast, spatial filtering performs better when waves are narrow-banded, low frequency, and when wave orbital velocities are strong relative to currents. However, as spatial filtering uses vertically separated velocity bins to remove the wave bias, spectral fitting is able to resolve stresses over a larger fraction of the water column.

Description: J. Rosman acknowledges funding from the National Science Foundation (OCE-1061108).

Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 29 (2012): 1377–1390, doi:10.1175/JTECH-D-11-00160.1.

Description: Estimates of surface currents over the continental shelf are now regularly made using high-frequency radar (HFR) systems along much of the U.S. coastline. The recently deployed HFR system at the Martha’s Vineyard Coastal Observatory (MVCO) is a unique addition to these systems, focusing on high spatial resolution over a relatively small coastal ocean domain with high accuracy. However, initial results from the system showed sizable errors and biased estimates of M2 tidal currents, prompting an examination of new methods to improve the quality of radar-based velocity data. The analysis described here utilizes the radial metric output of CODAR Ocean Systems’ version 7 release of the SeaSonde Radial Site Software Suite to examine both the characteristics of the received signal and the output of the direction-finding algorithm to provide data quality controls on the estimated radial currents that are independent of the estimated velocity. Additionally, the effect of weighting spatial averages of radials falling within the same range and azimuthal bin is examined to account for differences in signal quality. Applied to two month-long datasets from the MVCO high-resolution system, these new methods are found to improve the rms difference comparisons with in situ current measurements by up to 2 cm s−1, as well as reduce or eliminate observed biases of tidal ellipses estimated using standard methods.

Description: 2013-03-01

Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 2201-2218, doi:10.1175/JPO-D-16-0020.1.

Description: This paper aims to test the validity, utility, and limitations of the lateral eddy diffusivity concept in a coastal environment through analyzing data from coupled drifter and dye releases within the footprint of a high-resolution (800 m) high-frequency radar south of Martha’s Vineyard, Massachusetts. Specifically, this study investigates how well a combination of radar-based velocities and drifter-derived diffusivities can reproduce observed dye spreading over an 8-h time interval. A drifter-based estimate of an anisotropic diffusivity tensor is used to parameterize small-scale motions that are unresolved and underresolved by the radar system. This leads to a significant improvement in the ability of the radar to reproduce the observed dye spreading.

Description: IR, AK, and SL were supported by the NSF OCE Grant 1332646. IR was also supported by NASA Grant NNX14AH29G.

Description: 2016-12-29

Description: DESCRIPTION_HFR; The WHOI HF radar system, as operated during the field periods, consisted of 6 land-based sites spaced between the islands of Nantucket, MA and Block Island, RI. A series of four multi-antenna HFRs built by the University of Hawaii [described by Kirincich et al. 2019] were deployed in the region and augmented by two existing high resolution SeaSonde HFRs previous deployed with funding from NOAA-IOOS. Using a grid of 8 separate receive antennas and recently developed analysis methods, the UH systems maximize both the temporal and azimuthal resolution of surface currents over a wide area, producing fully independent, 30-min averages of high-resolution--2 km everywhere-- low error surface currents over a 150 km x 80 km stretch of the NES. Rms differences of the system against in situ observations were 5-7 cm/s. DESCRIPTION_INSITU_MOORING; The HFR observations were paired with detailed, in situ observations of hydrography, currents, and winds during three separate study periods, spanning July to December of 2018 and 2019, and October to December of 2020. For the two 6-month periods in both 2018 and 2019, trio of surface moorings and one subsurface mooring were deployed in the center of the eastern HFR coverage area. The central surface mooring, stationed along the 40-m isobath, hosted a Vaisala WXT520 weather station and water column hydrography using 8 temperature-conductivity (CT) sensors (SBE37 Microcats). A nearby subsurface mooring supported upward- and downward-looking ADCPs to collect high resolution velocity profiles of the top 8 m of the water column and coarser resolution velocity profiles of the lower 30 m of the water column. The two additional flanking surface moorings, each with 7 CT sensors, were located 10 km away in both the across- and along-shelf (2018 only) directions, allowing estimates of the depth-dependent lateral hydrographic gradients. While all mooring data was returned during 2018, the western flanking mooring was irretrievably lost during the 2019 season, limiting the fixed hydrographic observations that year. During an additional three-month period in fall 2020, a single mooring pair, similar to the central surface and sub-surface moorings described above, was deployed further west along the 40-m isobath. DESCRIPTION_INSITU_MOBILE; Two WHOI-owned, Liquid Robotics SV2 Wave Glider autonomous surface vehicles (ASVs) were deployed for 3-month periods during both 2018 and 2019 to collect along-track observations of winds and surface hydrography. Outfitted with AirMar 2-axis sonic anemometers at 1 m above sea level and SeaBird CTDs at water depths of 0.3 and 6.5 m, the ASVs followed a butterfly-shaped regular survey pattern centered on the central mooring site, which allowed repeated, detailed sampling of horizontal gradients of temperature and salinity within the surface layer at multiple scales around the mooring locations. With transit speeds of 0.5-1 m/s, the ASV is 3-5 times faster than a Slocum-type glider, allowing O(10 km) features to be sampled on synoptic timescales (2-4 hours). Combined, the ASV surveys sampled each transect line approximately once per day. Acquisition Description: SENSOR_INFORMATION_HFR; The two eastern systems were deployed on the islands of Nantucket (NWTP, 41.2deg N 70.1degW) in June 2017 and Martha's Vineyard (LPWR, 41.3degN 70.7degW) in April 2018, while the two western systems, at Westport, MA (HBSR, 41.5degN 71.1degW) and Narragansett, RI (CPVN, 41.5degN 71.4degW), were deployed and operational in June and July 2019 respectively. Thus, the eastern systems were in operation for all years, 2018-2020, but the western systems were only available during 2019 and 2020. All systems were operated using range-resolutions of 2 km and run in a novel `hybrid' configuration that combines qualities of phased-array and direction-finding radars to increase the azimuthal resolution of the HFRs to be less than or equal to the 2-km range resolution. Augmenting these hybrid radar systems, data from two existing high resolution, 25-MHz SeaSonde radars deployed within the study area with funding from NOAA-IOOS and owned by WHOI and the University of Rhode Island, respectively, were also used. With ranges of 40 km and range resolutions of 1 km, these systems each approximate the azimuthal resolution of the UH systems over a smaller area. Using recently developed methods Kirincich et al (2019) and Kirincich et al (2012), the full HF radar array maximizes azimuthal--and therefore spatial--resolution, producing 30-min independent averages of surface currents at 2-km resolution within a 10,000 km$^2$ region of the NES. The effective measurement depth of the WHOI HF radars is 0.5 m below the ocean surface. Received Doppler spectra from each were processed using the advanced methods of Kirincich et al. (2012, JOAT) or Kirincich et al (2019) into radial velocity estimates every 30 min based on a 30 min averaging window. Radial velocity estimates were quality controlled before inclusion into the vector velocity estimates using standard time-series QC techniques. SENSOR_INFORMATION_INSITU_MOORING; The detailed deployment information for each station and year are::: In July-November 2018 and July-November 2019: The center surface mooring was deployed at 41.0669degN 70.4828degW in 40 m of water and sampled surface vector winds, air temperature, air pressure, and relative humidity using a Vaisala WXT520 located at 2 m above mean sea level at 10 min ensemble averages, of 1 Hz data. The Center surface mooring also had 8 temperature-conductivity sensors (SBE37s) that sampled the oceanic water column at fixed depths below the surface of 0.6,4,6.5,10,15,20,30, and 35-m at 2 min increments. The center subsurface mooring was deployed at 41.0669degN 70.4828degW and contained a sub-surface float at 8-m below sea level in 40 m of water. The float held an upward looking Nortek Signature 1000 AD2CP that collected 2048 pings @4Hz every 20 min at 0.25 m bin depths. The west surface mooring was deployed at 41.1185degN 70.5812degW in 40 m of water and had 7 temperature-conductivity sensors (SBE37s) that sampled the oceanic water column at fixed depths below the surface of 0.6,4,6.5,10,15,20, and 30-m at 2 min increments. The south surface mooring was deployed at 40.9881degN 70.5455degW in 50 m of water and had 7 temperature-conductivity sensors (SBE37s) that sampled the oceanic water column at fixed depths below the surface of 0.6,4,6.5,10,15,20, and 30-m at 2 min increments. In October-December 2020: A similar surface and subsurface mooring pair were deployed to the west of the 2018-2019 mooring locations. The surface mooring was located at 41.0706degN 70.8177degW in 40 m of water and sampled surface vector winds, air temperature, air pressure, and relative humidity using a Vaisala WXT520 located at 2 m above mean sea level at 10 min ensemble averages, of 1 Hz data. The 2020 surface mooring also had 5 temperature-conductivity sensors (SBE37s) that sampled the oceanic water column at fixed depths below the surface of 0.6,4,6.5,10, and 20-m at 2 min increments. Finally the 2020 subsurface mooring was deployed at 41.0706degN 70.8177degW and contained a sub-surface float at 8-m below sea level in 40 m of water. The float held an upward looking Nortek Signature 1000 AD2CP that collected 2048 pings @4Hz every 20 min at 0.25 m bin depths. SENSOR_INFORMATION_INSITU_MOBILE; The Mobile Liquid Robotics SV2 Wave Glider autonomous surface vehicles (ASVs) deployed in July to September of both 2018 and 2019 to collected along-track observations of winds and surface hydrography. Only the surface hydrography was used here, collected via SeaBird temperature-conductivity sensors (SBE37s) at water depths of 0.3 and 6.5 m as 10 min averages.

Description: This data was collected by Kirincich as part of the Submesoscale Dynamics Over The Shelf Study, with field observations in 2018 and 2019, as well as the HFR_winds project with field work in 2020. The analysis products presented were used to examine the space and time scales of eddy kinetic energy over the wide, shallow, NES continental shelf using a novel implementation of HFR to achieve spatial and temporal resolutions sufficient to capture the horizontal scales of velocity variability. The data consists of estimates of the near-surface horizontal (East and North) ocean currents made via High Frequency (HF) radar-based remote sensing of the Ocean backscatter spectrum as well as in situ moored hydrographic, velocity, and surface winds, and mobile surface hydrographic observations collected via autonomous vehicles. Data were collected within three separate measurement periods: July to December 2018, July to December 2019, and October to December 2020.

Description: U.S. National Science Foundation to the Woods Hole Oceanographic Institution. OCE-#1736930, OCE-#1923927

Description: Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 43 (2013): 1940–1958, doi:10.1175/JPO-D-13-020.1.

Description: The spatial structure of the tidal and background circulation over the inner shelf south of Martha's Vineyard, Massachusetts, was investigated using observations from a high-resolution, high-frequency coastal radar system, paired with satellite SSTs and in situ ADCP velocities. Maximum tidal velocities for the dominant semidiurnal constituent increased from 5 to 35 cm s−1 over the 20-km-wide domain with phase variations up to 60°. A northeastward jet along the eastern edge and a recirculation region inshore dominated the annually averaged surface currents, along with a separate along-shelf jet offshore. Owing in part to this variable circulation, the spatial structure of seasonal SST anomalies had implications for the local heat balance. Cooling owing to the advective heat flux divergence was large enough to offset more than half of the seasonal heat gain owing to surface heat flux. Tidal stresses were the largest terms in the mean along- and across-shelf momentum equations in the area of the recirculation, with residual wind stress and the Coriolis term dominating to the west and south, respectively. The recirculation was strongest in summer, with mean winds and tidal stresses accounting for much of the differences between summer and winter mean circulation. Despite the complex bathymetry and short along-shelf spatial scales, a simple model of tidal rectification was able to recreate the features of the northeastward jet and match an estimate of the across-shelf structure of sea surface height inferred from the residual of the momentum analysis.

Description: 2014-03-01

Description: Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 31 (2014): 945–966, doi:10.1175/JTECH-D-13-00146.1.

Description: This study investigated the correspondence between the near-surface drifters from a mass drifter deployment near Martha’s Vineyard, Massachusetts, and the surface current observations from a network of three high-resolution, high-frequency radars to understand the effects of the radar temporal and spatial resolution on the resulting Eulerian current velocities and Lagrangian trajectories and their predictability. The radar-based surface currents were found to be unbiased in direction but biased in magnitude with respect to drifter velocities. The radar systematically underestimated velocities by approximately 2 cm s−1 due to the smoothing effects of spatial and temporal averaging. The radar accuracy, quantified by the domain-averaged rms difference between instantaneous radar and drifter velocities, was found to be about 3.8 cm s−1. A Lagrangian comparison between the real and simulated drifters resulted in the separation distances of roughly 1 km over the course of 10 h, or an equivalent separation speed of approximately 2.8 cm s−1. The effects of the temporal and spatial radar resolution were examined by degrading the radar fields to coarser resolutions, revealing the existence of critical scales (1.5–2 km and 3 h) beyond which the ability of the radar to reproduce drifter trajectories decreased more rapidly. Finally, the importance of the different flow components present during the experiment—mean, tidal, locally wind-driven currents, and the residual velocities—was analyzed, finding that, during the study period, a combination of tidal, locally wind-driven, and mean currents were insufficient to reliably reproduce, with minimal degradation, the trajectories of real drifters. Instead, a minimum combination of the tidal and residual currents was required.

Description: I.R. was supported by the WHOI Coastal Ocean Institute Project 27040148 and by the WHOI Access to the Sea Program 27500036. I.R. and A.K. acknowledge support fromthe NSF project 83264600. A.K. acknowledges support from the Massachusetts Clean Energy Center (MassCEC) via the New England Marine Renewable Energy Center (MREC).

Description: 2014-10-01

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(6), (2022): e2021JC017307, https://doi.org/10.1029/2021jc017307.

Description: This study examines the spatial and temporal variability of eddy kinetic energy over the Northeast Shelf using observations of surface currents from a unique array of six high frequency radar systems. Collected during summer and winter conditions over three consecutive years, the horizontal scales present were examined in the context of local wind and hydrographic variability, which were sampled concurrently from moorings and autonomous surface vehicles. While area-averaged mean kinetic energy at the surface was tightly coupled to wind forcing, eddy kinetic energy was not, and was lower in magnitude in winter than summer in all areas. Kinetic energy wavenumber spectral slopes were generally near k−5/3, but varied seasonally, spatially, and between years. In contrast, wavenumber spectra of surface temperature and salinity along repeat transect lines had sharp k−3 spectral slopes with little seasonal or inter-annual variability. Radar-based estimates of spectral kinetic energy fluxes revealed a mean transition scale of energy near 18 km during stratified months, but suggested much longer scales during winter. Overall, eddy kinetic energy was unrelated to local winds, but the up- or down-scale flux of kinetic energy was tied to wind events and, more weakly, to local density gradients.

Description: This analysis was supported by NSF grants OCE-1657896 and OCE-1736930 to Kirincich, OCE-1736709 to Flament, and OCE-1736587 to Futch. Flament is also supported by NOAAs Integrated Ocean Observing System through award NA11NOS0120039.

Description: 2023-11-21

Description: Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 36(10), (2019): 1997-2014, doi: 10.1175/JTECH-D-19-0029.1.

Description: While land-based high-frequency (HF) radars are the only instruments capable of resolving both the temporal and spatial variability of surface currents in the coastal ocean, recent high-resolution views suggest that the coastal ocean is more complex than presently deployed radar systems are able to reveal. This work uses a hybrid system, having elements of both phased arrays and direction finding radars, to improve the azimuthal resolution of HF radars. Data from two radars deployed along the U.S. East Coast and configured as 8-antenna grid arrays were used to evaluate potential direction finding and signal, or emitter, detection methods. Direction finding methods such as maximum likelihood estimation generally performed better than the well-known multiple signal classification (MUSIC) method given identical emitter detection methods. However, accurately estimating the number of emitters present in HF radar observations is a challenge. As MUSIC’s direction-of-arrival (DOA) function permits simple empirical tests that dramatically aid the detection process, MUSIC was found to be the superior method in this study. The 8-antenna arrays were able to provide more accurate estimates of MUSIC’s noise subspace than typical 3-antenna systems, eliminating the need for a series of empirical parameters to control MUSIC’s performance. Code developed for this research has been made available in an online repository.

Description: This analysis was supported by NSF Grants OCE-1657896 and OCE-1736930 to Kirincich, OCE-1658475 to Emery and Washburn and OCE-1736709 to Flament. Flament is also supported by NOAA’s Integrated Ocean Observing System through Award NA11NOS0120039. The authors thank Lindsey Benjamin, Alma Castillo, Ken Constantine, Benedicte Dousset, Ian Fernandez, Mael Flament, Dave Harris, Garrett Hebert, Ben Hodges, Victoria Futch, Matt Guanci, and Philip Moravcik for assistance in building, deploying, and operating the radars.

Description: 2020-04-11

Description: High-frequency radar-based observations of surface currents along the east coast of Taiwan, obtained over a 50-day period in early 2017, are used to examine the occurrence, generation, and downstream advection of submesoscale eddies in the Kuroshio. Measured at an effective depth of 2 m and radial resolution of 3 km from four land-based HF radar systems spanning an 250-km along-stream distance, the surface current observations reveal the instantaneous position of the Kuroshio on hourly time scales as well as the occurrence of numerous high relative vorticity features. Vortex features with spatial scales of 5-20 km were concentrated in the first 30 km offshore, with many created at the southern tip of Taiwan on tidal timescales. Most features, with relative vorticities approaching zeta/f=1, translated northward along the coast at the speed of the Kuroshio itself and were coherent over the 250-km length of the Taiwanese coastline. Both tides and regional winds appear to influence when long-lived features form, and the offshore advection of surface waters by the vortices are observable in intermittent Satellite images of surface chlorophyll. While most features are advected northward with the current, a submarine ridge acts to impede the flow, scattering northward moving features and causing occasional southward-migrating vortices. Data Description: DESCRIPTION; The surface current observations used here were obtained from four long-range (4 MHz transmit frequency) land-based coastal radar systems, operated by the Taiwan Ocean Research Institute (TORI) and the National Taiwan University (NTU). All systems were Codar Ocean Sensors SeaSondes, with the three southern stations operated by TORI, and the northern-most station by NTU. Collected over the time period spanning February 1st to March 26th, 2017, the hourly observations of Doppler cross-spectra had a radial resolution of 3 km. Horizontal resolution was dependent on both the resolution of the measured antenna patterns (1 degree in azimuth) as well as the inherent azimuthal resolution of the radar returns themselves. DATA_PREPARATION_DESCRIPTION; Observed Doppler cross-spectra were reprocessed following Kirincich et al. (2012) using adjusted measured antenna patterns and advanced quality control metrics to estimate the radial surface currents observed at each site. Measured antenna response patterns were adjusted iteratively to reduce radar-to-radar inconsistencies defined using synthetic radials estimated from adjacent radars as well as systematic biases in mean vorticity and divergence patterns. Vector combinations of the radial surface currents, representative of the average currents over the top 2 m of the water column (StewartJoy, 1974) were estimated using power-weighed least-squares methods (Kirincich et al. 2012, Kaplan et al 2005) with a fixed horizontal averaging length-scale of 3 km, and masked for errors due to the geometric dilution of precision (GDOP) greater than 2 (Barrack, 2002). Acquisition Description: SENSOR_INFORMATION; Radio frequency interference from the ionosphere is a particular problem for the TORI and NTU radars, due to a combination of latitude and transmit frequency, causing elevated background noise during local nighttime. Returns at ranges of 90 km, the distance to the primary scattering layer within the ionosphere, are especially affected. SNR was used as an effective screening tool to isolate and eliminate data contaminated by ionospheric radio noise common in the region, adding further improvements to the radial velocity results. However, data from a 50x50 km region directly offshore of the radar site near 23deg 30' N 121deg 30' E was excised during the hours of 11 to 17 UTC each day during the observational period due to poor data returns during times of high ionospheric reflections and radio noise that resulted in poorly resolved and inaccurate vector current estimates. Using synthetic radials from adjacent HFR sites (Emery et al 2019), surface current uncertainties are estimated to be 5-10 cm/s. the west of the 2018-2019 mooring locations. The surface mooring was located at 41.0706degN 70.8177degW in 40 m of water and sampled surface vector winds, air temperature, air pressure, and relative humidity using a Vaisala WXT520 located at 2 m above mean sea level at 10 min ensemble averages, of 1 Hz data. The 2020 surface mooring also had 5 temperature-conductivity sensors (SBE37s) that sampled the oceanic water column at fixed depths below the surface of 0.6,4,6.5,10, and 20-m at 2 min increments. Finally the 2020 subsurface mooring was deployed at 41.0706degN 70.8177degW and contained a sub-surface float at 8-m below sea level in 40 m of water. The float held an upward looking Nortek Signature 1000 AD2CP that collected 2048 pings @4Hz every 20 min at 0.25 m bin depths.

Description: HF Radar observations used here were funded by Taiwan's National Applied Research Laboratories as well as the National Taiwan University. A. Kirincich was funded by the U.S. Office of Naval Research under contract #N000141712761.