Horizontal Stirring over the Northeast U.S. Continental Shelf: the Spatial and Temporal Evolution of Surface Eddy Kinetic Energy
Kirincich, Anthony R.
Flament, Pierre J.
Hodges, Benjamin A.
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KeywordHF radar; Surface currents; Mooring hydrography; In situ velocity; Remote sensing; Coastal ocean; New England Shelf
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_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.
Suggested CitationDataset: Kirincich, Anthony R., Flament, Pierre J., Futch, Victoria, Hodges, Benjamin A., "Horizontal Stirring over the Northeast U.S. Continental Shelf: the Spatial and Temporal Evolution of Surface Eddy Kinetic Energy", 2021-09-30, DOI:10.26025/1912/27599, https://hdl.handle.net/1912/27599
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