High Frequency Radar Wind Turbine Interference Community Working Group Report

Land-based High Frequency (HF) Radars provide critically important observations of the coastal ocean that will be adversely affected by the spinning blades of utility-scale wind turbines. Pathways to mitigate the interference of turbines on HF radar observations exist for small number of turbines; however, a greatly increased pace of research is required to understand how to minimize the complex interference patterns that will be caused by the large arrays of turbines planned for the U.S. outer continental shelf. To support the U.S.’s operational and scientific needs, HF radars must be able to collect high-quality measurements of the ocean’s surface inand around areas with significant numbers of wind turbines. This is a solvable problem, but given the rapid pace of wind energy development, immediate action is needed to ensure that HF radar wind turbine interference mitigation efforts keep pace with the planned build out of turbines

Structure of the coastal current field off Northern California during the coastal ocean dynamics experiment

For 74 days during the spring and summer upwelling seasons of 1981 and 1982, in conjunction with the Coastal Ocean Dynamics Experiment, profiles of upper ocean currents were collected in the waters over the shelf and slope off northern California using a shipboard Doppler acoustic log. These measurements provide detailed information on the spatial structure of the current field. Synoptic maps of near-surface currents often deviate substantially from classical two-dimensional wind-driven upwelling and indicate a close association between the complex temperature structures observed in satellite imagery and the presence of vigorous current structures including squirts (regions of intense seaward flow), eddies, and countercurrents. Well-defined examples of a squirt and of a countercurrent during a cessation of wind forcing (wind relaxation event) are examined in detail. Despite this complexity, the nearshore synoptic current field was found to be anisotropic, varying more rapidly cross shore than alongshore. The structure of the current averages and simple fluctuation statistics were largely as deduced in other upwelling areas from moored measurements. A surface-intensified equatorward jet was found in the average alongshore currents, with vertical shear exceeding -2 x 10^(-3) s^(-1) over much of the shelf. The core of the jet moved offshore south of Point Arena and was better resolved in along-isobath averages. At depths below 80 m the average alongshore flow reversed, giving way to a poleward undercurrent, strongest near the shelf break. The detailed structure of the inferred cross-shore circulation was found to be sensitive to the coordinate system selected. Using nominal (along-coast) coordinates, the average cross-shore current was found to be directed offshore within a surface layer which deepened with distance from the coast out to the shelf break, showed strong vertical shear only near the surface, and was divergent in the upper water column and convergent in the lower water column over the shelf. Current fluctuations about the local mean were strongly polarized along isobaths near the coast and became largely isotropic far from shore except offshore from Point Arena, where squirts were recurrently observed

Enhanced southward flow over the Oregon shelf in 2002: a conduit for subarctic water

Moored current measurements from the Oregon shelf during 1998–2003 are used to estimate time series of anomalous alongshore currents and pseudo-displacements, after accounting for the mean and seasonal cycle. From early January through mid-June, 2002, currents at 10 m were anomalously strong toward the south by an average 12 cm/s, producing an anomalous displacement of more than 1500 km over about 5 months. This may be compared with the finding by Freeland et al. [2003] that waters at the same latitude off Oregon, and off Vancouver Island, were anomalously cool and fresh at depths between 30 and 150 m, suggesting displacement from a more northern source. Anomalous displacements of several hundred kilometers were also found during at least three other periods in the record. Moored temperature measurements at the same location confirm that local waters were persistently cooler during March to October of 2002 than during the previous two years, with the strongest anomaly near 20 m. Coastal sea levels were lower than usual along the northwest coast during spring and early summer 2002, consistent with a southward current anomaly of large scale. Local winds near Newport did not show strong mean anomalies during this period

On the spatial structure of coastal circulation off Newport, Oregon, during spring and summer 2001 in a region of varying shelf width

A time series of hourly surface current maps in the shelf waters off Newport, Oregon, was made during April–September 2001 using five SeaSonde HF current mappers, during Coastal Advances in Shelf Transport (COAST). The surface currents responded rapidly to the changing winds, in repeated patterns that were strongly affected by bottom topography. An equatorward current jet repeatedly formed in response to upwelling winds, its strength, but not its trajectory, covarying with the meridional wind stress. Near Cape Foulweather (44.8°N), where the shelf begins to widen, the jet rotates, weakens, and trends offshore to the south first along, then across, the isobaths. Below Cape Foulweather, inshore of the jet, a lee region of generally weak currents was commonly observed. The equatorward jet core was most commonly observed near the 80-m isobath between 45.0°N and 44.4°N, but transited offshore between spring and summer over Heceta Bank. At Newport (44.6°N), it was rarely observed less than 8 km from the coast. A second, inshore, equatorward jet, previously unknown, was observed repeatedly south of Waldport (44.4°N). Sustained downwelling wind episodes produced poleward currents, though less responsively north of Cape Foulweather. Strongest poleward flow was generally trapped near the coast. Surface currents were correlated with the northward wind, except regionally far from shore over Heceta Bank, responding within half a day. Response to the wind varies spatially, being intensified in the narrow shelf (northern) region. The equatorward jet persists through periods of zero wind forcing. Coastal sea level covaries with the meridional wind and the primary mode of ocean current response

Phase IIIa-CCS: Latitudinal variation of upwelling, retention, nutrient supply and freshwater effects in the California Current System

US-GLOBEC NEP AbstractThis proposal requests funding to: a) synthesize the moored current meter, shore-based HF radar, ship-based hydrographic, and remotely sensed data from the GLOBEC Northeast Pacific (NEP) Long-Term Observation Program (LTOP) and related programs into a coherent, best description of the mesoscale variability along the Pacific Northwest coast from 42 to 48N; and b) relate this physical variability to primary production, zooplankton distributions, and salmon year-class strength in the region. The long-term moorings will allow quantification of the relevant time scales from internal waves to the inter-annual; the satellite images of sea surface temperature and chlorophyll will show the spatial scales; and the HF surface fields will allow timeand space-varying statistics of the mesoscale currents and quasi-Lagrangian pathways to be assessed. The primary scientific objective will be to characterize the alongshelf variability in the upwelling, the nutrients it supplies to the photic zone for utilization by marine organisms, and the retention times of plankton. This variability is affected by the alongshore distribution of the wind stress and fresh water input, by the changes in the bottom topography and coastline orientation, and by pre-conditioning established by inter-annual variability and climate change

A Shallow Zonal Jet South of Fiji

No abstract available

Observations of near-inertial surface currents off Oregon: Decorrelation time and length scales

High-resolution (km in space and hourly in time) surface currents observed by an array of high-frequency radars off Oregon are analyzed to quantify the decorrelation time and length scales of their near-inertial motions. The near-inertial surface currents are dominantly clockwise with amplitudes of 9-12 cm s⁻¹. However, they appear asymmetric and elliptical as a result of counterclockwise inertial motions with magnitudes in a range of 2-5 cm s⁻¹. The decorrelation time and length scales are computed from the decay slope of the near-inertial peak and the spatial coherence in the near-inertial frequency band, respectively. Decorrelation time scales of clockwise near-inertial motions increase from 2 days nearshore (within 30 km from the coast) to 6 days offshore, and their length scales increase from 30 to 90 km seaward possibly due to coastal inhibition. The local spatial coherence has an exponentially decaying structure for both clockwise and counterclockwise rotations, and their phases propagate northwestward (offshore) for clockwise and northeastward (onshore) for counterclockwise rotations.Keywords: coastal inhibition, near-inertial oscillations, spectral analysis, Mixed layer, decorrelation time scales, surface currents, Internal wave spectrum, Upper ocean, Wind, decorrelation length scales, Gravity wave

Two coastal upwelling domains in the northern California Current system

A pair of hydrographic sections, one north and one south of Cape Blanco at 42.9N, was sampled in five summers (1998–2000 and 2002–2003). The NH line at 44.6N lies about 130 km south of the Columbia River, and spans a relatively wide shelf off Newport, Oregon. The CR line at 41.9N off Crescent City, California, lies 300 km farther south and spans a narrower shelf. Summer winds are predominantly southward in both locations but the southward winds are stronger on the CR line. Sampling included CTD/rosette casts (to measure temperature, salinity, dissolved oxygen, nutrients, chlorophyll), zooplankton net tows and continuous operation of an Acoustic Doppler Current Profiler. We summarize and compare July-August observations from the two locations. We find significant summer-season differences in the coastal upwelling domains north and south of Cape Blanco. Compared to the domain off Newport, the domain off Crescent City has a more saline, cooler, denser and thicker surface mixed layer, a wider coastal zone inshore of the upwelling front and jet, higher nutrient concentrations in the photic zone and higher phytoplankton biomass. The southward coastal jet lies near the coast (about 20–30 km offshore, over the shelf) on the NH line, but far from shore (about 120 km) on the CR line; a weak secondary jet lies near the shelf-break (35 km from shore) off Crescent City. Phytoplankton tend to be light-limited on the CR line and nutrient-limited on the NH line. Copepod biomass is high (15 mg C m−3) inshore of the mid-shelf on both NH and CR lines, and is also high in the core of the coastal jet off Crescent City. The CR line shows evidence of deep chlorophyll pockets that have been subducted from the surface layer. We attribute these significant differences to stronger mean southward wind stress over the southern domain, to strong small-scale wind stress curl in the lee of Cape Blanco, and to the reduced influence of the Columbia River discharge in this region