Sara Haines

Operation and application of a regional high-frequency radar network in the Mid-Atlantic Bight

The Mid-Atlantic Regional Coastal Ocean Observing System (MARCOOS) High-Frequency Radar Network, which comprises 13 long-range sites, 2 medium-range sites, and 12 standard-range sites, is operated as part of the Integrated Ocean Observing System. This regional implementation of the network has been operational for 2 years and has matured to the point where the radars provide consistent coverage from Cape Cod to Cape Hatteras. A concerted effort was made in the MARCOOS project to increase the resiliency of the radar stations from the elements, power issues, and other issues that can disable the hardware of the system. The quality control and assurance activities in the Mid-Atlantic Bight have been guided by the needs of the Coast Guard Search and Rescue Office. As of May 2009, these quality-controlled MARCOOS High-Frequency Radar totals are being served through the Coast Guards Environmental Data Server to the Coast Guard Search and Rescue Optimal Planning System. In addition to the service to U.S. Coast Guard Search and Rescue Operations, this data supports water quality, physical oceanographic, and fisheries research throughout the Mid-Atlantic Bight.

IOOS vocabulary and ontology strategy for observed properties

With the rapid growth of coastal ocean observations becoming available for integration by US Integrated Ocean Observing System (IOOS) Regional Associations and federal data assembly centers, there is a need for the establishment of IOOS Parameter Vocabulary strategy. Currently, different data naming conventions are being used by existing regional and subregional coastal ocean observing systems. This makes things complicated for the discovery, access and proper usage of the valuable data. To eliminate the misuse and misinterpretation of the data being made available and to facilitate the discovery and proper use of in data scientific research and other management applications, the authors have presented the development of IOOS Parameter Vocabulary and recommended a strategy to move this forward with ocean observing community engagement.

Marine Hydrokinetic Energy from Western Boundary Currents

The kinetic energy in ocean currents, or marine hydrokinetic (MHK) energy, is a renewable energy resource that can help meet global energy requirements. An ocean circulation model-based census shows that subtropical surface western boundary currents (WBCs) are the only nearshore, large-scale currents swift enough to drive large electricity-generating ocean turbines envisioned for future use. We review several WBCs in the context of kinetic energy extraction. The power density in the Gulf Stream off North Carolina at times reaches several thousand watts per square meter at 75 m below the surface, and the annual average power is approximately 500-1,000 W m-2. Significant fluctuations occur with periods of 3-20 days (Gulf Stream meanders) and weeks to months (Gulf Stream path shifts). Interannual variations in annual average power occur because of year-to-year changes in these WBC motions. No large-scale turbines presently exist, and the road to establishing MHK facilities in WBCs will encounter challenges that are similar in many aspects to those associated with the development of offshore wind power.

A summary of quality control tests for waves and in situ currents and their effectiveness

This paper summarizes the quality control (QC) tests used to verify ocean wave and in situ current data collected and shared by ocean observing systems, federal data centers and oceanographic research institutions. The categories in common for both waves and currents are defined as: (1) sensor health, (2) signal quality, and (3) parameter quality. The main differences being that while wave measurements require an additional category of spectral quality tests, the in situ current measurements from ADCPs require overall profile quality tests. Implementing QC tests and measuring their effectiveness has identified the need for multi-parameter quality control algorithms. While the threshold of a given parameter can vary due to the environment, it can be tuned. The Quality Assurance of Real-Time Ocean Data (QARTOD) workshops and subsequent work has directly led to the results presented in this paper.

Implementing Quality Control of High-Frequency Radar Estimates and Application to Gulf Stream Surface Currents

AbstractQuality control procedures based on nonvelocity parameters for use with a short-range radar system are applied with slight modification to long-range radar data collected offshore of North Carolina. The radar footprint covers shelf and slope environments and includes a segment of the Gulf Stream (GS). Standard processed and quality controlled (QCD) radar data are compared with 4 months of acoustic Doppler current profiler (ADCP) time series collected at three different sites within the radar footprint. Two of the ADCP records are from the shelf and the third is on the upper slope and is frequently within the GS. Linear regression and Bland–Altman diagrams are used to quantify the comparison. QCD data at all sites have reduced scatter and improved correlation with ADCP observations relative to standard processed data. Uncertainty is reduced by approximately 20%, and linear regression slopes and correlation coefficients increase by about 0.1. At the upper slope site, the QCD data also produced a sig...

Gulf stream marine hydrokinetic energy resource characterization off Cape Hatteras, North Carolina USA

The Gulf Stream off North Carolina (NC), USA has current velocities that approach 2 ms-1 and average volume transports of 90 Sv (1 Sv= 106 m3s-1) off of Cape Hatteras, making it the most abundant MHK (Marine Hydrokinetic Energy) resource for the state. Resource availability at a specified location depends primarily on the variability in Gulf Stream position, which is least offshore of Cape Hatteras after the stream exits the Florida Straits. Proximity to land and high current velocities in relatively shallow waters on the shelf slope make this an optimal location to quantify the MHK energy resource for NC. Multi-years of consistent current measurements beginning in August of 2013 from a moored 150 kHz ADCP at an optimal location for energy extraction quantify the available energy resource and its variability, and establish the skill of a regional ocean circulation model in predicting the MHK energy resource. The model agrees well with long term observed current averages and weekly to monthly fluctuations in the currents. Comparisons between the model and ADCP observed currents, and power density demonstrate the significant inter-annual variability in the Gulf Stream power density.

An Observational, Spatially Explicit, Stability-Based Estimate of the Wind Resource off the Shore of North Carolina

AbstractAs part of ongoing studies of the feasibility of utility-scale wind energy off the shore of North Carolina, winds at 80-m elevation are estimated with a stability-based height-adjustment scheme. Data sources are level-3 daily Advanced Scatterometer (ASCAT) 10-m wind fields as measured by the MetOp-A satellite, North American Regional Reanalysis (NARR) estimates of near-surface atmospheric temperature and humidity, and the National Climatic Data Center’s optimally interpolated Advanced Very High Resolution Radiometer (AVHRR-OI) sea surface temperature (SST). A height-adjustment assuming neutral atmospheric stability provides reference conditions. The SST from AVHRR-OI was more accurate than SST from NARR and was used with NARR atmospheric data to represent atmospheric stability in the study region. The 5-yr average of the ASCAT 10-m winds is 6.5–9.0 m s−1 off the shore of North Carolina, with the strongest winds found over the Gulf Stream. Neutral-scheme 80-m wind speeds are 7.5–10.5 m s−1 and foll...

Impact of atmospheric stability on wind resource estimates off North Carolina

Large spatial changes in average sea surface temperature offshore of North Carolina due to the poleward flow of the Gulf Stream and equatorward flow on the mid-Atlantic shelf produce strong variations in static stability of the overlying lower atmosphere. The dependence of turbine-height winds (80-100 m above sea level) off North Carolina on atmospheric stability was examined using historical buoy observations as input to a variety of one-dimensional (vertical) extrapolation schemes. Stable stability conditions were common at buoy locations on the shelf north of Cape Hatteras and within roughly 10 km of the shoreline south of Cape Hatteras. Unstable conditions were more common on the mid- and outer shelf south of Cape Hatteras and in the Sargasso Sea. Monin-Obukhov similarity scaling was used to estimate winds during non-neutral conditions based on a modified version of the TOGA COARE 2.0 algorithms. Unstable conditions reduced extrapolated turbine height wind speeds relative to neutral stability conditions by as much as 5%. A power-law representation of wind speed using an exponent of 0.07, empirically determined in previous work, was consistent with the winds estimated for neutral conditions under a number of assumptions; variations between schemes were less than 2%. Stable conditions led to larger extrapolated winds relative to neutral conditions, sometimes by more than 10%. The vertical extent of stable conditions is unclear and could impact the validity of the estimated winds. Of particular concern are locations near the coastline where an internal boundary layer (IBL) would form in response to cool underlying sea surface temperatures. A correction for distortion of the wind field measured from buoys by surface waves led to a 2-3% increase in turbine height winds regardless of extrapolation scheme. Satellite winds at 10m elevation have been used to develop a more highly resolved spatial depiction of the wind field, both on the shelf, over the Gulf Stream and in the western Sargasso Sea. Winds from the QuikSCAT and ASCAT missions were used, each with 25 km resolution. Comparison of the two satellite wind products during an 18-month overlap time period found the QuikSCAT winds to be stronger by 0.2 to 0.9 m/s where unstable conditions dominate over the Gulf Stream and on the shelf immediately south of Cape Hatteras. Buoy-based winds were found to be most consistent with ASCAT winds. Both wind products suggest strongest winds at 10m elevation on the shelf lie between Cape Hatteras and Cape Fear. Strongest winds were observed in deep water over the Gulf Stream north of Cape Hatteras. Wind speeds increase moving offshore, making the shelfbreak the region of greatest wind resource where water depths are less than 50 m.

Marine hydrokinetic energy in the gulf stream off North Carolina: An assessment using observations and ocean circulation models

There has been global interest in renewable energy for meeting energy demands, and as these demands increase, it will become of greater importance to utilize low-carbon energy sources to mitigate anthropogenic impact on the environment. Onshore hydropower is responsible for half of the electricity generated by a renewable source in the USA. In the ocean, marine hydrokinetic (MHK) energy in western boundary currents (WBCs) can be considered for electricity generation by submarine turbines. WBCs are a continuous and sustainable source of energy that could be transmitted to shore to support coastal communities in future years. The Gulf Stream is the WBC of the North Atlantic subtropical gyre, and it flows for part of its course along the upper continental slope off the southeastern USA. This large-scale current has maximum flow speeds exceeding 2 m s−1, and this together with its proximity to the coastline distinguishes it as a potential source of MHK energy. Using current data from a moored acoustic Doppler current profiler (ADCP) and a regional ocean circulation model, MHK power densities offshore of North Carolina were found to average 798 W m−2 for the ADCP and 641 W m−2 for the model during a nine-month period at a potential turbine site, a difference of about 20%. The model was shown to have similar current speeds to the ADCP for slowly varying currents (fluctuations of weeks to months due to Gulf Stream path shifts), and lower speeds for higher frequency current variations (fluctuations of several days to a couple of weeks due to wavelike Gulf Stream meanders). This article considers the Gulf Stream as a prospective renewable energy source and assesses the power density of this WBC at multiple locations offshore of North Carolina. Understanding the Stream’s power density character, including its spatial and temporal variations along the North Carolina coast, is essential in considering the Gulf Stream as a future alternative energy resource.

An observational, stability-based estimate of 80 m wind speed offshore of North Carolina - seasonal patterns

Winds at 80 m elevation have been estimated with a stability-based height adjustment scheme to study the feasibility of utility-scale wind energy offshore of North Carolina. Data sources are the daily ASCAT 10 m wind field as measured by the METOP-A satellite, the North American Regional Reanalysis (NARR) estimates of near-surface atmospheric temperature, pressure and humidity and the National Climate Data Centers optimally-interpolated Advanced Very High Resolution Radiometer (AVHRR-OI) sea surface temperature (SST). The study focuses on the 2008-2012 time period. The COARE V3.0 algorithm is used to provide the stability-based height adjustment scheme. Data from six buoys have been used to establish validity of the remotely-sensed and modeled fields. A variety of results were produced, including long-term average wind speeds, wind power density and capacity factor at hub height, and a monthly climatology of these quantities. In this note the focus is on seasonal variations utilizing the monthly climatologies. Using the climatologies the largest differences between the neutral and stability-based schemes occur in winter and spring when and where stable atmospheric conditions are most common. There is a significant difference in the annual variation of atmospheric stability north and south of Cape Hatteras. Only the inner shelf region is prone to stable conditions during winter and spring south of Cape Hatteras, whereas the full width of the shelf is prone to stable conditions from fall into early summer north of Cape Hatteras. Where stable conditions occur the stability-based 80 m wind speeds are 2-3 m/s greater than 80 m neutral wind speeds, and where unstable conditions occur the stability-based 80 m wind speeds are 0.5-1 m/s less than the 80 m neutral wind speeds. The result is a pattern in the 80 m stability-based winds with notably greater speeds near the coastline than expected from a neutral height adjustment.