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1
Lumpkin, Rick, Nikolai Maximenko, and Mayra Pazos. "Evaluating Where and Why Drifters Die*." Journal of Atmospheric and Oceanic Technology 29, no. 2 (February 1, 2012): 300–308. http://dx.doi.org/10.1175/jtech-d-11-00100.1.
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Abstract NOAA ’s Global Drifter Program (GDP) manages a global array of ~1250 active satellite-tracked surface drifting buoys (“drifters”) in collaboration with numerous national and international partners. To better manage the drifter array and to assess the performance of various drifter manufacturers, it is important to discriminate between drifters that cease transmitting because of internal failure and those that cease because of external factors such as running aground or being picked up. An accurate assessment of where drifters run aground would also allow the observations to be used to more accurately simulate the evolution of floating marine debris and to quantify globally which shores are most prone to the deposit of marine debris. While the drifter Data Assembly Center of the GDP provides a metadata file that includes cause of death, the identified cause for most drifters is simply “quit transmitting.” In this study it is shown that a significant fraction of these drifters likely ran aground or were picked up, and a statistical estimate that each drifter ran aground or was picked up is derived.
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Morey, Steven, Nicolas Wienders, Dmitry Dukhovskoy, and Mark Bourassa. "Measurement Characteristics of Near-Surface Currents from Ultra-Thin Drifters, Drogued Drifters, and HF Radar." Remote Sensing 10, no. 10 (October 14, 2018): 1633. http://dx.doi.org/10.3390/rs10101633.
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Concurrent measurements by satellite tracked drifters of different hull and drogue configurations and coastal high-frequency radar reveal substantial differences in estimates of the near-surface velocity. These measurements are important for understanding and predicting material transport on the ocean surface as well as the vertical structure of the near-surface currents. These near-surface current observations were obtained during a field experiment in the northern Gulf of Mexico intended to test a new ultra-thin drifter design. During the experiment, thirty small cylindrical drifters with 5 cm height, twenty-eight similar drifters with 10 cm hull height, and fourteen drifters with 91 cm tall drogues centered at 100 cm depth were deployed within the footprint of coastal High-Frequency (HF) radar. Comparison of collocated velocity measurements reveals systematic differences in surface velocity estimates obtained from the different measurement techniques, as well as provides information on properties of the drifter behavior and near-surface shear. Results show that the HF radar velocity estimates had magnitudes significantly lower than the 5 cm and 10 cm drifter velocity of approximately 45% and 35%, respectively. The HF radar velocity magnitudes were similar to the drogued drifter velocity. Analysis of wave directional spectra measurements reveals that surface Stokes drift accounts for much of the velocity difference between the drogued drifters and the thin surface drifters except during times of wave breaking.
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Haza, A. C., E. D’Asaro, H. Chang, S. Chen, M. Curcic, C. Guigand, H. S. Huntley, et al. "Drogue-Loss Detection for Surface Drifters during the Lagrangian Submesoscale Experiment (LASER)." Journal of Atmospheric and Oceanic Technology 35, no. 4 (April 2018): 705–25. http://dx.doi.org/10.1175/jtech-d-17-0143.1.
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AbstractThe Lagrangian Submesoscale Experiment (LASER) was designed to study surface flows during winter conditions in the northern Gulf of Mexico. More than 1000 mostly biodegradable drifters were launched. The drifters consisted of a surface floater extending 5 cm below the surface, containing the satellite tracking system, and a drogue extending 60 cm below the surface, hanging beneath the floater on a flexible tether. On some floats, the drogue separated from the floater during storms. This paper describes methods to detect drogue loss based on two properties that distinguish drogued from undrogued drifters. First, undrogued drifters often flip over, pointing their satellite antenna downward and thus intermittently reducing the frequency of GPS fixes. Second, undrogued drifters respond to wind forcing more than drogued drifters. A multistage analysis is used: first, two properties are used to create a preliminary drifter classification; then, the motion of each unclassified drifter is compared to that of its classified neighbors in an iterative process for nearly all of the drifters. The algorithm classified drifters with a known drogue status with an accuracy of virtually 100%. Drogue loss times were estimated with a precision of less than 0.5 and 3 h for 60% and 85% of the drifters, respectively. An estimated 40% of the drifters lost their drogues in the first 7 weeks, with drogue loss coinciding with storm events, particularly those with steep waves. Once the drogued and undrogued drifters are classified, they can be used to quantify the differences in material dispersion at different depths.
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Suara, Kabir, Charles Wang, Yanming Feng, Richard J. Brown, Hubert Chanson, and Michael Borgas. "High-Resolution GNSS-Tracked Drifter for Studying Surface Dispersion in Shallow Water." Journal of Atmospheric and Oceanic Technology 32, no. 3 (March 2015): 579–90. http://dx.doi.org/10.1175/jtech-d-14-00127.1.
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AbstractThe use of Global Navigation Satellite System (GNSS)-tracked Lagrangian drifters allows more realistic quantification of fluid motion and dispersion coefficients than Eulerian techniques because such drifters are analogs of particles that are relevant to flow field characterization and pollutant dispersion. Using the fast-growing real-time kinematic (RTK) positioning technique derived from GNSS, drifters are developed for high-frequency (10 Hz) sampling with position estimates with centimeter accuracy. The drifters are designed with small size and less direct wind drag to follow the subsurface flow that characterizes dispersion in shallow waters. An analysis of position error from stationary observation indicates that the drifter can efficiently resolve motion up to 1 Hz. The result of the field deployments of the drifter in conjunction with acoustic Eulerian devices shows a higher estimate of the drifter streamwise velocities. Single particle statistical analysis of field deployments in a shallow estuarine zone yielded estimates of dispersion coefficients comparable to those of dye tracer studies. The drifters capture the tidal elevation during field studies in a tidal estuary.
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Aravind, H. M., Helga S. Huntley, A. D. Kirwan, and Michael R. Allshouse. "Drifter Deployment Strategies to Determine Lagrangian Surface Convergence in Submesoscale Flows." Journal of Atmospheric and Oceanic Technology 41, no. 1 (January 2024): 95–112. http://dx.doi.org/10.1175/jtech-d-22-0129.1.
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Abstract Surface convergence in the ocean is associated with accumulation of buoyant pollutants as well as with vertical transport that is important to biological activity. Such surface convergence regions are marked by a high dilation rate, i.e., the finite time Lagrangian average divergence. Dilation-rate observations are most easily derived from the change of the area encompassed by a drifter swarm over time. The technological advances that have enabled the deployment of large numbers of drifters in a single experiment have raised new questions about optimal deployment strategies for extracting dilation-rate information with acceptable accuracy and as much spatial coverage as possible. Using a submesoscale-resolving operational model of the Mediterranean Sea, we analyze synthetic trajectories of drifter polygons to evaluate the impact of the number of drifters and their initial separation on the accuracy of the resulting dilation-rate estimates. The results confirm that estimates improve as the circumradius of the polygon decreases and as more drifters are added, but with only a marginal improvement for drifter polygons containing more than four drifters. Moreover, GPS positions obtained from drifters in the ocean are subject to uncertainty on the order of 2–50 m, and when this uncertainty is taken into account, an optimal circumradius can be identified that balances uncertainty from position measurements with that from the area approximations. Significance Statement Locating regions of convergence over a finite time interval on the ocean surface can help in pollution mitigation, locating biological hotspots, and even search-and-rescue operations. Finite time convergence can be quantified using the dilation rate, but it is hard to measure in the ocean. Hence, we present a method to estimate the dilation rate using trajectories of drifters, which are instruments widely used by oceanographers during field experiments to understand the local flow features. We show that even though the drifter-based dilation rates are prone to error as a result of a finite number of drifters and limited GPS accuracy, the estimates locate around 90% of the strongest convergent features in our model.
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Pawlowicz, Rich, Cédric Chavanne, and Dany Dumont. "The Water-Following Performance of Various Lagrangian Surface Drifters Measured in a Dye Release Experiment." Journal of Atmospheric and Oceanic Technology 41, no. 1 (January 2024): 45–63. http://dx.doi.org/10.1175/jtech-d-23-0073.1.
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Abstract Many different surface drifter designs have been developed recently to track near-surface ocean currents, but the degree to which these drifters slip through the water because of mechanisms associated with the wind is poorly known. In the 2020 Tracer Release Experiment (TReX), 19 drifters of eight different designs, both commercially available and home-built, were simultaneously released with a patch of rhodamine dye. The dye rapidly spread vertically through the mixed layer but also more slowly dispersed horizontally. Although winds were light, drifters moved downwind from the dye patch at speeds of 3–17 cm s−1 (0.6%–4% of wind speed) depending on the design type. Measurements were made of wind and ocean conditions, and these were incorporated into a boundary layer model at the air–sea interface to estimate complete velocity profiles above and below the surface. Then, a steady-state drag model is used with these profiles to successfully predict drifter slip. Drogued drifters (those with a subsurface drag element) can be affected by Eulerian shear in the upper 0.5 m of the water column, as well as the Stokes drift, but undrogued drifters are in addition greatly affected by direct wind drag, and possibly by resonant interactions with waves. The dye, cycling vertically in the mixed layer, is largely unaffected by all of these factors; therefore, even “perfect” surface drifters do not move with a mixed layer tracer. Significance Statement Surface drifters are used by oceanographers to measure ocean surface currents. However, different designs also slip downwind through the water at rates that are poorly known but are typically around a few percent of the wind speed. In 2020 we simultaneously deployed drifters of eight different designs along with rhodamine dye in a field experiment to see how well the different designs track the water. Here we independently and successfully model drifter slippage for the different designs. Slip factors are then estimated for a range of wind and ocean conditions.
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Spydell, Matthew S., Falk Feddersen, and Jamie Macmahan. "The Effect of Drifter GPS Errors on Estimates of Submesoscale Vorticity." Journal of Atmospheric and Oceanic Technology 36, no. 11 (November 2019): 2101–19. http://dx.doi.org/10.1175/jtech-d-19-0108.1.
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AbstractDifferential kinematic flow properties (DKP), such as vertical vorticity, have been estimated from surface drifters. However, previous DKP error estimates were a posteriori and did not include correlated errors across drifters. To accurately estimate submesoscale (≤1 km) DKPs from drifters, errors must be better understood. Here, the a priori vorticity standard error is derived that depends upon the number of drifters in the cluster, the drifter cluster major and minor axes lengths, the instrument velocity error, and the cross-drifter error correlation. Two stationary GPS experiments, with zero vorticity, were performed at separations of O(101–103) m to understand vorticity error and test the derivation using 1 Hz position differences and Doppler shift velocities. Vorticity errors of ±5f (where f is the local Coriolis parameter)were found for ≈40 m separations. The frequency-dependent velocity variances and GPS-to-GPS correlations are quantified. Vorticity estimated with a “blended” velocity has reduced error. The stationary vorticity error can be well predicted given velocity error, correlation, and minor axis length. Vorticity error analysis is applied to submesoscale-sampling in situ GPS drifters near Point Sal, California. The derivation predicts when large high-frequency vorticity fluctuations (indicating noise) occur. Previously, cluster area or ellipticity were used as criteria to distinguish error. We show that the drifter cluster minor axis (narrowness) is a key time-dependent factor affecting vorticity error, and even for velocity errors <0.004 m s−1, the vorticity error exceeds ±5f when cluster minor axis <50 m. These results will aid submesoscale drifter deployment planning.
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Hormann, Verena, Luca R. Centurioni, and Gilles Reverdin. "Evaluation of Drifter Salinities in the Subtropical North Atlantic." Journal of Atmospheric and Oceanic Technology 32, no. 1 (January 2015): 185–92. http://dx.doi.org/10.1175/jtech-d-14-00179.1.
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AbstractSalinity measurements from drifters constitute an important in situ dataset for the calibration and validation of the sea surface salinity satellite missions. A total of 114 satellite-tracked salinity drifters were deployed within the framework of the first Salinity Processes in the Upper Ocean Regional Study (SPURS) experiment in the subtropical North Atlantic focusing on the period August 2012–April 2014. In this study, a subset of 83 drifters, which provided useful salinity measurements in the central SPURS region from a few weeks to more than one year, is evaluated and an ad hoc quality-control procedure based on previously published work and the new observations is described. It was found that the sampling algorithm of the drifters introduces a predominantly fresh bias in the noise level of the salinity data, probably caused by the presence of air bubbles within the measuring cell. Since such noise is difficult to eliminate using statistical methods, extensive editing was done manually instead. Such quality-control procedures cannot be routinely applied to the real-time data stream from the drifters. Therefore, a revision of the sampling algorithm of the drifter’s salinity sensor is needed. Comparisons of the drifter’s salinity measurements with independent datasets further indicate that the sensor can provide reliable observations for up to one year. Finally, little evidence was found that the quality of the drifter’s salinity measurements depends on the presence of the drogue.
9
Poulain, Pierre-Marie, Riccardo Gerin, Elena Mauri, and Romain Pennel. "Wind Effects on Drogued and Undrogued Drifters in the Eastern Mediterranean." Journal of Atmospheric and Oceanic Technology 26, no. 6 (June 1, 2009): 1144–56. http://dx.doi.org/10.1175/2008jtecho618.1.
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Abstract The wind effects on drogued and undrogued drifters are assessed using Coastal Ocean Dynamics Experiment (CODE) and Surface Velocity Program (SVP) drifter datasets and ECMWF wind products in the eastern Mediterranean. Complex and real linear regression models are used to estimate the relative slip of undrogued SVP drifters and to extract the wind-driven currents from the drifter velocities. The frequency response of the wind-driven currents is studied using cross-spectral analysis. By comparing the velocities of cotemporal and nearly collocated undrogued and drogued SVP drifters, it appears that undrogued SVP drifters have a general downwind slippage of about 1% of the wind speed. Time-lagged complex correlations and cross-spectral results show that the wind response is almost simultaneous. The velocities of SVP drifters drogued to 15 m are poorly correlated with the winds (R2 ≈ 3%): wind-driven currents have a magnitude of 0.7% of the wind speed and are 27°–42° to the right of the wind. For undrogued SVP drifters, the correlation with the winds increases to R2 ≈ 22% and the angle between winds and currents decreases to 17°–20°. The magnitude of the wind-driven currents is about 2% of the wind speed. For CODE designs, wind-driven currents are 1% of the wind speed at an angle of about 28° to the right of the wind (R2 ≈ 8%). Spectral and cospectral analyses reveal that the drifters sampled more anticyclonic than cyclonic motions. The inner coherence spectra show that wind and currents are more correlated at temporal scales spanning 3–10 days. They also confirm that the wind response is quasi-simultaneous and that currents are generally to the right of the wind.
10
Lumpkin, Rick, Luca Centurioni, and Renellys C. Perez. "Fulfilling Observing System Implementation Requirements with the Global Drifter Array." Journal of Atmospheric and Oceanic Technology 33, no. 4 (April 2016): 685–95. http://dx.doi.org/10.1175/jtech-d-15-0255.1.
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AbstractThe Global Ocean Observing System (GOOS) requirements for in situ surface temperature and velocity measurements call for observations at 5° × 5° resolution. A key component of the GOOS that measures these essential climate variables is the global array of surface drifters. In this study, statistical observing system sampling experiments are performed to evaluate how many drifters are required to achieve the GOOS requirements, both with and without the presence of a completed global tropical moored buoy array at 5°S–5°N. The statistics for these simulations are derived from the evolution of the actual global drifter array. It is concluded that drifters should be deployed within the near-equatorial band even though that band is also in principle covered by the tropical moored array, as the benefits of not doing so are marginal. It is also concluded that an optimal design half-life for the drifters is ~450 days, neglecting external sources of death, such as running aground or being picked up. Finally, it is concluded that comparing the drifter array size to the number of static 5° × 5° open-ocean bins is not an ideal performance indicator for system evaluation; a better performance indicator is the fraction of 5° × 5° open-ocean bins sampled, neglecting bins with high drifter death rates.
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Reverdin, G., S. Morisset, H. Bellenger, J. Boutin, N. Martin, P. Blouch, J. Rolland, F. Gaillard, P. Bouruet-Aubertot, and B. Ward. "Near–Sea Surface Temperature Stratification from SVP Drifters." Journal of Atmospheric and Oceanic Technology 30, no. 8 (August 1, 2013): 1867–83. http://dx.doi.org/10.1175/jtech-d-12-00182.1.
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Abstract This study describes how the hull temperature (Ttop) measurements from multisensor surface velocity program (SVP) drifters can be combined with other measurements to provide quantitative information on near-surface vertical temperature stratification during large daily cycles. First, Ttop is compared to the temperature measured at 17 -cm depth from a float tethered to the SVP drifter. These 2007–12 SVP drifters present a larger daily cycle by 1%–3% for 1°–2°C daily cycle amplitudes, with a maximum difference close to the local noon. The difference could result from flow around the SVP drifter in the presence of temperature stratification in the top 20 cm of the water column but also from a small influence of internal drifter temperature on Ttop. The largest differences were found for small drifters (Technocean) for very large daily cycles, as expected from their shallower measurements. The vertical stratification is estimated by comparing these hull data with the deeper T or conductivity C measurements from Sea-Bird sensors 25 (Pacific Gyre) to 45 cm (MetOcean) below the top temperature sensor. The largest stratification is usually found near local noon and early afternoon. For a daily cycle amplitude of 1°C, these differences with the upper level are in the range of 3%–5% of the daily cycle for the Pacific Gyre drifters and 6%–10% for MetOcean drifters with the largest values occurring when the midday sun elevation is lowest. The relative differences increase for larger daily cycles, and the vertical profiles become less linear. These estimated stratifications are well above the uncertainty on Ttop.
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Lavrova, O. Yu, D. M. Soloviev, A. Ya Strochkov, K. R. Nazirova, E. V. Krayushkin, and E. V. Zhuk. "The use of mini-drifters in coastal current measurements conducted concurrently with satellite imaging." Исследования Земли из Космоса, no. 5 (November 5, 2019): 36–49. http://dx.doi.org/10.31857/s0205-96142019536-49.
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The results of field measurements of coastal currents using Lagrangian mini-drifters are presented. Drifter experiments were conducted concurrently with satellite imaging using Sentinel-2 MSI, Landsat-8 OLI and Sentinel-3 OLCI sensors. It is shown that the use of an inexpensive and simple to manufacture device, which is a mini-drifter, allows obtaining operational information about the parameters of coastal currents. In the experiments of April-May, 2019, in the northeastern part of the Black Sea, it was possible to estimate the velocity of coastal currents and determine the minimum distance that Black Sea Rim Current approached the coast. The trajectories of mini-drifters revealed the manifestations of inertial oscillations whose spatial characteristics are almost impossible to measure in any other way. The influence of the vortex structures detected in visible satellite images on the distribution of mini-drifters was estimated.
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Schmidt, W. E., B. T. Woodward, K. S. Millikan, R. T. Guza, B. Raubenheimer, and Steve Elgar. "A GPS-Tracked Surf Zone Drifter*." Journal of Atmospheric and Oceanic Technology 20, no. 7 (July 1, 2003): 1069–75. http://dx.doi.org/10.1175/1460.1.
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Abstract A drifter designed to measure surf zone circulation has been developed and field tested. Drifter positions accurate to within a few meters are estimated in real time at 0.1 Hz using the global positioning system (GPS) and a shore-to-drifter radio link. More accurate positions are estimated at 1 Hz from postprocessed, internally logged data. Mean alongshore currents estimated from trajectories of the 0.5-m-draft drifters in 1–2-m water depth agree well with measurements obtained with nearby, bottom-mounted, acoustic current meters. Drifters deployed near the base of a well-developed rip current often followed eddylike paths within the surf zone before being transported seaward.
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GERIN, R., V. KOURAFALOU, P. M. POULAIN, and Ş. BESIKTEPE. "Influence of Dardanelles outflow induced thermal fronts and winds on drifter trajectories in the Aegean Sea." Mediterranean Marine Science 15, no. 2 (January 17, 2014): 239. http://dx.doi.org/10.12681/mms.464.
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The data provided by 12 drifters deployed in the Northern Aegean Sea in the vicinity of the Dardanelles Strait in August 2008 and February 2009 are used to explore the surface circulation of the basin and the connectivity to the Black Sea. The drifters were deployed within the Dardanelles outflow of waters of Black Sea origin in the Northeastern Aegean. Thanks to the particular choice of the drifter deployment positions, the data set provides a unique opportunity to observe the branching behaviour of the surface currents around Lemnos Island. Such pathways were notpossible to study with previous drifter deployments that were far from the Dardanelles Strait. In addition, the drifter tracks covered the Aegean basin quite thoroughly, mapping major circulation features and supporting the overall general circulation patterns described by previous observational and modelling studies. The collected data display cases in which drifters are driven by winds and thermal fronts. Wind products were used to estimate the influence of the atmospheric forcing on the drifter trajectories. Satellite sea surface temperature images were connected to the drifter tracks, demonstrating a high correlation between the remote and in situ observations. The waters of Black Sea origin were traced all the way to the Southern Aegean, establishing a strong connectivity link between the Aegean and Black Sea basins.
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Thompson, Andrew F., Karen J. Heywood, Sally E. Thorpe, Angelika H. H. Renner, and Armando Trasviña. "Surface Circulation at the Tip of the Antarctic Peninsula from Drifters." Journal of Physical Oceanography 39, no. 1 (January 1, 2009): 3–26. http://dx.doi.org/10.1175/2008jpo3995.1.
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Abstract An array of 40 surface drifters, drogued at 15-m depth, was deployed in February 2007 to the east of the tip of the Antarctic Peninsula as part of the Antarctic Drifter Experiment: Links to Isobaths and Ecosystems (ADELIE) project. Data obtained from these drifters and from a select number of local historical drifters provide the most detailed observations to date of the surface circulation in the northwestern Weddell Sea. The Antarctic Slope Front (ASF), characterized by a ∼20 cm s−1 current following the 1000-m isobath, is the dominant feature east of the peninsula. The slope front bifurcates when it encounters the South Scotia Ridge with the drifters following one of three paths. Drifters (i) are carried westward into Bransfield Strait; (ii) follow the 1000-m isobath to the east along the southern edge of the South Scotia Ridge; or (iii) become entrained in a large-standing eddy over the South Scotia Ridge. Drifters are strongly steered by contours of f /h (Coriolis frequency/depth) as shown by calculations of the first two moments of displacement in both geographic coordinates and coordinates locally aligned with contours of f /h. An eddy-mean decomposition of the drifter velocities indicates that shear in the mean flow makes the dominant contribution to dispersion in the along-f /h direction, but eddy processes are more important in dispersing particles across contours of f /h. The results of the ADELIE study suggest that the circulation near the tip of the Antarctic Peninsula may influence ecosystem dynamics in the Southern Ocean through Antarctic krill transport and the export of nutrients.
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Yang, Longqi, Zhida Huang, Zhenyu Sun, and Jianyu Hu. "Surface Currents Along the Coast of the Chinese Mainland Observed by Coastal Drifters in Autumn and Winter." Marine Technology Society Journal 55, no. 5 (September 1, 2021): 161–69. http://dx.doi.org/10.4031/mtsj.55.5.7.
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Abstract This paper analyzes the surface current characteristics along the coast of the Chinese mainland in autumn and winter by the trajectories of coastal drifters and remote sensing data. The results show the following: (1) During autumn and winter 2018, the paths of drifters were consistent with that of the Zhe-Min Coastal Water, while the Zhe-Min Coastal Water had a branch intruding the coast of Taiwan Island. (2) When the northeast monsoon weakened or changed direction in a short period, the Zhe-Min Coastal Water showed a reverse flow. (3) In the northeastern South China Sea, the drifter path meandered due to a dipole's influence. (4) Around the frontal area near the Taiwan Bank, the paths of drifters showed a 12.4-h periodic variation, which was mainly controlled by the tidal current. These findings show that the coastal drifter is a useful tool to observe surface currents.
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Ma, Chunyong, Siqing Li, Yang Yang, Jie Yang, and Ge Chen. "Extraction of Revolving Channels of Drifters around Mesoscale Eddy Centers Based on Spatiotemporal Trajectory Clustering." Journal of Atmospheric and Oceanic Technology 36, no. 9 (September 2019): 1903–16. http://dx.doi.org/10.1175/jtech-d-19-0007.1.
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The global oceanic transports of energy, plankton, and other tracers by mesoscale eddies can be estimated by combining satellite altimetry and in situ data. However, the revolving channels of particles entrained by mesoscale eddies, which could help explain the dynamic process of eddies entraining materials, are still unknown. In this study, satellite altimeter and drifter data from 1993 to 2016 are adopted, and the normalized trajectory clustering algorithm (N-TRACLUS) is proposed to extract the revolving channels of drifters. First, the trajectories of drifters are normalized and clustered by using the density-based spatial clustering of applications with noise (DBSCAN) algorithm. Next, the revolving channels of drifters around the eddy center are extracted. The ring or arc pattern in the middle of a normalized eddy appears when drifters are uninterruptedly entrained by eddies for more than 30 days. Moreover, the revolving channels of drifters in cyclonic eddies are relatively closer to the eddy center than those in anticyclonic eddies. These revolving channels suggest the principal mode of materials’ continuous motion processes that are inside eddies.
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Lodise, John, Tamay Özgökmen, Annalisa Griffa, and Maristella Berta. "Vertical structure of ocean surface currents under high winds from massive arrays of drifters." Ocean Science 15, no. 6 (December 9, 2019): 1627–51. http://dx.doi.org/10.5194/os-15-1627-2019.
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Abstract. Very-near-surface ocean currents are dominated by wind and wave forcing and have large impacts on the transport of buoyant materials in the ocean. Surface currents, however, are under-resolved in most operational ocean models due to the difficultly of measuring ocean currents close to, or directly at, the air–sea interface with many modern instrumentations. Here, observations of ocean currents at two depths within the first meter of the surface are made utilizing trajectory data from both drogued and undrogued Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) drifters, which have draft depths of 60 and 5 cm, respectively. Trajectory data of dense, colocated drogued and undrogued drifters were collected during the Lagrangian Submesoscale Experiment (LASER) that took place from January to March of 2016 in the northern Gulf of Mexico. Examination of the drifter data reveals that the drifter velocities become strongly wind- and wave-driven during periods of high wind, with the pre-existing regional circulation having a smaller, but non-negligible, influence on the total drifter velocities. During these high wind events, we deconstruct the total drifter velocities of each drifter type into their wind- and wave-driven components after subtracting an estimate for the regional circulation, which pre-exists each wind event. In order to capture the regional circulation in the absence of strong wind and wave forcing, a Lagrangian variational method is used to create hourly velocity field estimates for both drifter types separately, during the hours preceding each high wind event. Synoptic wind and wave output data from the Unified Wave INterface-Coupled Model (UWIN-CM), a fully coupled atmosphere, wave and ocean circulation model, are used for analysis. The wind-driven component of the drifter velocities exhibits a rotation to the right with depth between the velocities measured by undrogued and drogued drifters. We find that the average wind-driven velocity of undrogued drifters (drogued drifters) is ∼3.4 %–6.0 % (∼2.3 %–4.1 %) of the wind speed and is deflected ∼5–55∘ (∼30–85∘) to the right of the wind, reaching higher deflection angles at higher wind speeds. Results provide new insight on the vertical shear present in wind-driven surface currents under high winds, which have vital implications for any surface transport problem.
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Novelli, Guillaume, Cédric M. Guigand, and Tamay M. Özgökmen. "Technological Advances in Drifters for Oil Transport Studies." Marine Technology Society Journal 52, no. 6 (November 1, 2018): 53–61. http://dx.doi.org/10.4031/mtsj.52.6.9.
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AbstractAdvances in drifter technology applied to oil spill studies from 1970 to the present are summarized here. Initially, drifters designed for oil spill response were intended to remotely track trajectories of accidental spills and help guide responders. Most recently, inexpensive biodegradable drifters were developed for massive deployments, making it possible to significantly improve numerical transport models and to investigate, via observations, the processes leading to dispersion and accumulation of surface pollutants across multiple scales. Over the past 50 years, drifters have benefited from constant improvements in electronics for accurate and frequent location and data transmission, as well as progress in material sciences to reduce fabrication costs and minimize the environmental impact of sacrificial instruments. The large amount of in-situ data provided by drifters, covering a broad area, is crucial to validate the numerical models and remote sensing products that are becoming more important in guiding response and policy decisions.
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Mardani, Neda, Mohammadreza Khanarmuei, Kabir Suara, Richard Brown, Adrian McCallum, and Roy C. Sidle. "Lagrangian Data Assimilation for Improving Model Estimates of Velocity Fields and Residual Currents in a Tidal Estuary." Applied Sciences 11, no. 22 (November 20, 2021): 11006. http://dx.doi.org/10.3390/app112211006.
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Numerical models are associated with uncertainties that can be reduced through data assimilation (DA). Lower costs have driven a recent tendency to use Lagrangian instruments such as drifters and floats to obtain information about water bodies. However, difficulties emerge in their assimilation, since Lagrangian data are set out in a moving frame of reference and are not compatible with the fixed grid locations used in models to predict flow variables. We applied a pseudo-Lagrangian approach using OpenDA, an open-source DA tool to assimilate Lagrangian drifter data into an estuarine hydrodynamic model. Despite inherent challenges with using drifter datasets, the work showed that low-cost, low-resolution drifters can provide a relatively higher improvement over the Eulerian dataset due to the larger area coverage of the drifter. We showed that the assimilation of Lagrangian data obtained from GPS-tracked drifters in a tidal channel for a few hours can significantly improve modelled velocity fields (up to 30% herein). A 40% improvement in residual current direction was obtained when assimilating both Lagrangian and Eulerian data. We conclude that the best results are achieved when both Lagrangian and Eulerian datasets are assimilated into the hydrodynamic model.
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Lumpkin, Rick, Semyon A. Grodsky, Luca Centurioni, Marie-Helene Rio, James A. Carton, and Dongkyu Lee. "Removing Spurious Low-Frequency Variability in Drifter Velocities." Journal of Atmospheric and Oceanic Technology 30, no. 2 (February 1, 2013): 353–60. http://dx.doi.org/10.1175/jtech-d-12-00139.1.
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Abstract Satellite-tracked drifting buoys of the Global Drifter Program have drogues, centered at 15-m depth, to minimize direct wind forcing and Stokes drift. Drogue presence has historically been determined from submergence or tether strain records. However, recent studies have revealed that a significant fraction of drifters believed to be drogued have actually lost their drogues, a problem that peaked in the mid-2000s before the majority of drifters in the global array switched from submergence to tether strain sensors. In this study, a methodology is applied to the data to automatically reanalyze drogue presence based on anomalous downwind ageostrophic motion. Results indicate that the downwind slip of undrogued drifters is approximately 50% higher than previously believed. The reanalyzed results no longer exhibit the dramatic and spurious interannual variations seen in the original data. These results, along with information from submergence/tether strain and transmission frequency variations, are now being used to conduct a systematic manual reevaluation of drogue presence for each drifter in the post-1992 dataset.
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Wu, Guoheng, Zhongyue Lu, Zirong Luo, Jianzhong Shang, Chongfei Sun, and Yiming Zhu. "Experimental Analysis of a Novel Adaptively Counter-Rotating Wave Energy Converter for Powering Drifters." Journal of Marine Science and Engineering 7, no. 6 (June 1, 2019): 171. http://dx.doi.org/10.3390/jmse7060171.
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Nowadays, drifters are used for a wide range of applications for researching and exploring the sea. However, the power constraint makes it difficult for their sampling intervals to be smaller, meaning that drifters cannot transmit more accurate measurement data to satellites. Furthermore, due to the power constraint, a modern Surface Velocity Program (SVP) drifter lives an average of 400 days before ceasing transmission. To overcome the power constraint of SVP drifters, this article proposes an adaptively counter-rotating wave energy converter (ACWEC) to supply power for drifters. The ACWEC has the advantages of convenient modular integration, simple conversion process, and minimal affection by the crucial sea environment. This article details the design concept and working principle, and the interaction between the wave energy converter (WEC) and wave is presented based on plane wave theory. To verify the feasibility of the WEC, the research team carried out a series of experiments in a wave tank with regular and irregular waves. Through experiments, it was found that the power and efficiency of the ACWEC are greatly influenced by parameters such as wave height and wave frequency. The maximum output power of the small scale WEC in a wave tank is 6.36 W, which allows drifters to detect ocean data more frequently and continuously.
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Reverdin, G., S. Morisset, J. Boutin, N. Martin, M. Sena-Martins, F. Gaillard, P. Blouch, et al. "Validation of Salinity Data from Surface Drifters." Journal of Atmospheric and Oceanic Technology 31, no. 4 (April 1, 2014): 967–83. http://dx.doi.org/10.1175/jtech-d-13-00158.1.
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Abstract Salinity measurements from 119 surface drifters in 2007–12 were assessed; 80% [Surface Velocity Program with a barometer with a salinity sensor (SVP-BS)] and 75% [SVP with salinity (SVP-S)] of the salinity data were found to be usable, after editing out some spikes. Sudden salinity jumps are found in drifter salinity records that are not always associated with temperature jumps, in particular in the wet tropics. A method is proposed to decide whether and how to correct those jumps, and the uncertainty in the correction applied. Northeast of South America, in a region influenced by the Amazon plume and fresh coastal water, drifter salinity is very variable, but a comparison with data from the Soil Moisture and Ocean Salinity satellite suggests that this variability is usually reasonable. The drifter salinity accuracy is then explored based on comparisons with data from Argo floats and from thermosalinographs (TSGs) of ships of opportunity. SVP-S/SVP-BS drifter records do not usually present significant biases within the first 6 months, but afterward biases sometimes need to be corrected (altogether, 16% of the SVP-BS records). Biases start earlier after 3 months for drifters not protected by antifouling paint. For the few drifters for which large corrections were applied to portions of the record, the accuracy cannot be proven to be better than 0.1 psu, and it cannot be proven to be better than 0.5 psu for data in the largest variability area off northeast South America. Elsewhere, after excluding portions of the records with suspicious salinity jumps or when large corrections were applied, the comparisons rule out average biases in individual drifter salinity record larger than 0.02 psu (midlatitudes) and 0.05 psu (tropics).
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Licari, Rosanna E. "Drifters." Antipodes 35, no. 1-2 (2021): 10–11. http://dx.doi.org/10.1353/apo.2021.0006.
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Ohlmann, Carter, Peter White, Libe Washburn, Brian Emery, Eric Terrill, and Mark Otero. "Interpretation of Coastal HF Radar–Derived Surface Currents with High-Resolution Drifter Data." Journal of Atmospheric and Oceanic Technology 24, no. 4 (April 1, 2007): 666–80. http://dx.doi.org/10.1175/jtech1998.1.
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Abstract Dense arrays of surface drifters are used to quantify the flow field on time and space scales over which high-frequency (HF) radar observations are measured. Up to 13 drifters were repetitively deployed off the Santa Barbara and San Diego coasts on 7 days during 18 months. Each day a regularly spaced grid overlaid on a 1-km2 (San Diego) or 4-km2 (Santa Barbara) square, located where HF radar radial data are nearly orthogonal, was seeded with drifters. As drifters moved from the square, they were retrieved and replaced to maintain a spatially uniform distribution of observations within the sampling area during the day. This sampling scheme resulted in up to 56 velocity observations distributed over the time (1 h) and space (1 and 4 km2) scales implicit in typical surface current maps from HF radar. Root-mean-square (RMS) differences between HF radar radial velocities obtained using measured antenna patterns, and average drifter velocities, are mostly 3–5 cm s−1. Smaller RMS differences compared with past validation studies that employ current meters are due to drifter resolution of subgrid-scale velocity variance included in time and space average HF radar fields. Roughly 5 cm s−1 can be attributed to sampling on disparate time and space scales. Despite generally good agreement, differences can change dramatically with time. In one instance, the difference increases from near zero to more than 20 cm s−1 within 2 h. The RMS difference and bias (mean absolute difference) for that day exceed 7 and 12 cm s−1, respectively.
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Gorbunov, Igor G., Vladimir I. Veremyev, Vadim D. Shestak, Gleb V. Komarov, Stanislav A. Myslenkov, and Ksenia P. Silvestrova. "Verifying Measurements of Surface Current Velocities by X-Band Coherent Radar Using Drifter Data." Journal of the Russian Universities. Radioelectronics 26, no. 3 (July 6, 2023): 99–110. http://dx.doi.org/10.32603/1993-8985-2023-26-3-99-110.
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Introduction. Conventional contact measurements of hydrographic parameters frequently fail to provide the necessary accuracy of data in the field of water area monitoring. This problem can be solved using coherent radars enabling direct measurements of surface current velocities.Aim. To establish the accuracy of surface current velocities measured by a Doppler radar using drifter data.Materials and methods. In June 2022, coastal operational oceanography studies were conducted at the hydrophysical test site of the Institute of Oceanology of the Russian Academy of Sciences in the Black Sea near Gelendzhik. Measurements were carried out using a coherent X-band radar installed on the Ashamba research vessel simultaneously with drifter experiments using Lagrangian drifters of the near-surface layer with an underwater 0.5 m sail. Coordinates were transmitted via mobile communication. The drifter data on the current velocity and direction were used to verify radar measurements. Measurements were taken onboard of the research vessel at a low speed and different distances from the shore, near the drifters. The tracks of the vessel and drifters were recorded simultaneously. Processing of the radar data involved obtaining Doppler spectra of signals to estimate the dynamic processes on the sea surface, including the current velocity.Results. Radial components of the near-surface current velocity were calculated. Then, the current velocity values obtained based on the drifter and radar data were compared.Conclusion. The present work makes a contribution to the advancement of methods for measuring surface currents from the board of a moving ship by Doppler radars. The obtained results confirm the suitability of the radar hardware and software and signal processing algorithms for measuring currents. The radar measurement data were found agree well with drifter data in the velocity range from 15 cm/s.
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Chiswell, Stephen M. "Mean Velocity Decomposition and Vertical Eddy Diffusivity of the Pacific Ocean from Surface GDP Drifters and 1000-m Argo Floats." Journal of Physical Oceanography 46, no. 6 (June 2016): 1751–68. http://dx.doi.org/10.1175/jpo-d-15-0189.1.
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AbstractWith the relatively recent development of Global Drifter Program (GDP) drifters that measure the near-surface ocean velocity and Argo floats that can be used to derive both the intermediate-ocean (1000 m) velocity and the mean dynamic height of the surface relative to 1000 dbar, there now exists the opportunity to directly observe the mean velocity decomposition of the ocean. This study computes the mean Ekman velocity by subtracting the mean referenced velocity derived from Argo data from the mean surface velocity derived from GDP data. This Ekman velocity is slightly stronger than previous observations and shows a spatial structure consistent with a vertical eddy diffusivity that is linearly dependent on wind stress. To do this analysis, the author has to deal with the fact that GDP drifters often lose their drogues, and a product of this research is validation of the wind-slip correction applied to GDP drifters that have lost their drogues.
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Rypina, I. I., A. R. Kirincich, R. Limeburner, and I. A. Udovydchenkov. "Eulerian and Lagrangian Correspondence of High-Frequency Radar and Surface Drifter Data: Effects of Radar Resolution and Flow Components." Journal of Atmospheric and Oceanic Technology 31, no. 4 (April 1, 2014): 945–66. http://dx.doi.org/10.1175/jtech-d-13-00146.1.
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Abstract 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.
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Novelli, Guillaume, Cédric M. Guigand, Charles Cousin, Edward H. Ryan, Nathan J. M. Laxague, Hanjing Dai, Brian K. Haus, and Tamay M. Özgökmen. "A Biodegradable Surface Drifter for Ocean Sampling on a Massive Scale." Journal of Atmospheric and Oceanic Technology 34, no. 11 (November 2017): 2509–32. http://dx.doi.org/10.1175/jtech-d-17-0055.1.
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AbstractTargeted observations of submesoscale currents are necessary to improve science’s understanding of oceanic mixing, but these dynamics occur at spatiotemporal scales that are currently challenging to detect. Prior studies have recently shown that the submesoscale surface velocity field can be measured by tracking hundreds of surface drifters released in tight arrays. This strategy requires drifter positioning to be accurate, frequent, and to last for several weeks. However, because of the large numbers involved, drifters must be low-cost, compact, easy to handle, and also made of materials harmless to the environment. Therefore, the novel Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) drifter was designed following these criteria to facilitate massive sampling of near-surface currents during the Lagrangian Submesoscale Experiment (LASER). The drifting characteristics were determined under a wide range of currents, waves, and wind conditions in laboratory settings. Results showed that the drifter accurately follows the currents in the upper 0.60 m, that it presents minimal wave rectification issues, and that its wind-induced slip velocity is less than 0.5% of the neutral wind speed at 10 m. In experiments conducted in both coastal and deep ocean conditions under wind speeds up to 10 m s−1, the trajectories of the traditional Coastal Ocean Dynamics Experiment (CODE) and the CARTHE drifters were nearly identical. Following these tests, 1100 units were produced and deployed during the LASER campaign, successfully tracking submesoscale and mesoscale features in the Gulf of Mexico. It is hoped that this drifter will enable high-density sampling near metropolitan areas subject to stress by the overpopulation, such as lakes, rivers, estuaries, and environmentally sensitive areas, such as the Arctic.
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Edwards, K. P., F. E. Werner, and B. O. Blanton. "Comparison of Observed and Modeled Drifter Trajectories in Coastal Regions: An Improvement through Adjustments for Observed Drifter Slip and Errors in Wind Fields." Journal of Atmospheric and Oceanic Technology 23, no. 11 (November 1, 2006): 1614–20. http://dx.doi.org/10.1175/jtech1933.1.
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Abstract Lagrangian particle tracking using three-dimensional (3D) numerical modeling approaches has become an important tool in coastal oceanography. In this note, an approach is described that can reduce the difference between observed and numerical drifter trajectories in the coastal ocean by including corrections to the water velocity due to differences between observed winds and the wind field used to drive the 3D circulation model and some specific characteristics of the observed drifters in the algorithm that estimate the numerical trajectory. Quantitative improvements are obtained whereby the separation distance between the numerical and observed drifters is almost halved (in this particular field case from 2.6 to 1.4 km day−1).
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Blockley, E. W., M. J. Martin, and P. Hyder. "Validation of FOAM near-surface ocean current forecasts using Lagrangian drifting buoys." Ocean Science 8, no. 4 (July 30, 2012): 551–65. http://dx.doi.org/10.5194/os-8-551-2012.
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Abstract. In this study, the quality of near-surface current forecasts from the FOAM ocean forecasting system is assessed using the trajectories of Lagrangian drifting buoys. A method is presented for deriving pseudo-Eulerian estimates of ocean currents from the positions of Surface Velocity Program drifters and the resulting data are compared to velocities observed by the global tropical moored buoy array. A quantitative analysis of the global FOAM velocities is performed for the period 2007 and 2008 using currents derived from over 3000 unique drifters (providing an average of 650 velocity observations per day). A potential bias is identified in the Southern Ocean which appears to be caused by wind-slip in the drifter dataset as a result of drogue loss. The drifter-derived currents are also used to show how the data assimilation scheme and a recent system upgrade impact upon the quality of FOAM current forecasts.
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Blockley, E. W., M. J. Martin, and P. Hyder. "Validation of FOAM near-surface ocean current forecasts using Lagrangian drifting buoys." Ocean Science Discussions 9, no. 2 (April 17, 2012): 1705–40. http://dx.doi.org/10.5194/osd-9-1705-2012.
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Abstract. In this study, the quality of near-surface current forecasts from the FOAM ocean forecasting system is assessed using the trajectories of Lagrangian drifting buoys. A method is presented for deriving pseudo-Eulerian estimates of ocean currents from the positions of Surface Velocity Program drifters and the resulting data are compared to velocities observed by the global tropical moored buoy array. A quantitative analysis of the global FOAM velocities is performed for the period 2007 and 2008 using currents derived from over 3000 unique drifters (providing an average of 650 velocity observations per day). A potential bias is identified in the Southern Ocean which appears to be caused by wind-slip in the drifter dataset as a result of drogue loss. The drifter-derived currents are also used to show how the data assimilation scheme and a recent system upgrade impact upon the quality of FOAM current forecasts.
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Sotillo, Marcos García, Emilio Garcia-Ladona, Alejandro Orfila, Pablo Rodríguez-Rubio, José Cristobal Maraver, Daniel Conti, Elena Padorno, et al. "The MEDESS-GIB database: tracking the Atlantic water inflow." Earth System Science Data 8, no. 1 (March 29, 2016): 141–49. http://dx.doi.org/10.5194/essd-8-141-2016.
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Abstract. On 9 September 2014, an intensive drifter deployment was carried out in the Strait of Gibraltar. In the frame of the MEDESS-4MS Project (EU MED Program), the MEDESS-GIB experiment consisted of the deployment of 35 satellite tracked drifters, mostly of CODE-type, equipped with temperature sensor sampling at a rate of 30 min. Drifters were distributed along and on both sides of the Strait of Gibraltar. The MEDESS-GIB deployment plan was designed as to ensure quasi-synoptic spatial coverage. To this end, four boats covering an area of about 680 NM2 in 6 h were coordinated. As far as these authors know, this experiment is the most important exercise in the area in terms of number of drifters released. Collected satellite-tracked data along drifter trajectories have been quality controlled and processed to build the presented MEDESS-GIB database. This paper reports the MEDESS-GIB data set that comprises drifter trajectories, derived surface currents and in situ SST measurements collected along the buoys tracks. This series of data is available through the PANGAEA (Data Publisher for Earth and Environmental Science) repository, with the following doi:10.1594/PANGAEA.853701. Likewise, the MEDESS-GIB data will be incorporated as part of the Copernicus Marine historical products. The MEDESS-GIB data set provides a complete Lagrangian view of the surface inflow of Atlantic waters through the Strait of Gibraltar and thus, very useful data for further studies on the surface circulation patterns in the Alboran Sea, and their links with one of the most energetic Mediterranean Sea flows: the Algerian Current.
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Sotillo, M. G., E. Garcia-Ladona, A. Orfila, P. Rodríguez-Rubio, J. C. Maraver, D. Conti, E. Padorno, et al. "The MEDESS-GIB database: tracking the Atlantic water inflow." Earth System Science Data Discussions 8, no. 2 (November 4, 2015): 863–87. http://dx.doi.org/10.5194/essdd-8-863-2015.
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Abstract. On 9 September 2014, an intensive drifter deployment was carried out in the Strait of Gibraltar. In the frame of the EU MED Program MEDESS-4MS, the MEDESS-GIB experiment consisted of the deployment of 35 satellite tracked drifters, mostly of CODE-type, equipped with temperature sensor sampling at a rate of 30 min. Drifters were distributed along and on both sides of the Strait of Gibraltar. The MEDESS-GIB deployment plan was designed as to ensure quasi-synoptic spatial coverage. To this end, 4 boats covering an area of about 680 NM2 in 6 h were coordinated. As far as authors know, this experiment is the most important exercise in the area in terms of number of drifters released. Collected satellite-tracked data along drifter trajectories have been quality controlled and processed to build the here presented MEDESS-GIB database. This paper reports the MEDESS-GIB dataset that comprises drifter trajectories, derived surface currents and in situ SST measurements collected along the buoys tracks. This series of data is available through the PANGAEA (Data Publisher for Earth and Environmental Science) repository, with the following doi:10.1594/PANGAEA.853701. Likewise, the MEDESS-GIB data will be incorporated as part of the Copernicus Marine historical products. The MEDESS-GIB dataset provides a complete Lagrangian view of the surface inflow of Atlantic waters through the Strait of Gibraltar and thus, very useful data for further studies on the surface circulation patterns in the Alboran Sea, and their links with one of the most energetic Mediterranean Sea flows: the Algerian Current.
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Mullarney, Julia C., and Stephen M. Henderson. "LAGRANGIAN MEASUREMENTS OF TURBULENT DISSIPATION OVER A SHALLOW TIDAL FLAT FROM PULSE COHERENT ACOUSTIC DOPPLER PROFILERS." Coastal Engineering Proceedings 1, no. 33 (December 15, 2012): 49. http://dx.doi.org/10.9753/icce.v33.currents.49.
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We present high resolution (25 mm spatial, 8 Hz temporal) profiles of velocity measured over a shallow tidal flat using pulse-coherent Acoustic Doppler Profilers mounted on surface drifters. The use of Lagrangian measurements mitigated the problem of resolving velocity ambiguities, a problem which often limits the application of high-resolution pulse-coherent profilers. Turbulent dissipation rates were estimated from second-order structure functions of measured velocity. Drifters were advected towards, and subsequently trapped on, a convergent surface front which marked the edge of a freshwater plume. Measured dissipation rates increased as a drifter deployed within the plume approached the front. A drifter then propagated with and along the front as the fresh plume spread across the tidal flats. Near-surface turbulent dissipation measured at the front roughly matched a theoretical mean-shear-cubed relationship, whereas dissipation measured in the stratified plume behind the front was suppressed. After removal of estimates affected by surface waves, near-bed dissipation matched the velocity cubed relationship, although scatter was substantial. Dissipation rates appeared to be enhanced when the drifter propagated across small subtidal channels.
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Merlino, Silvia, Vincenzo Calabrò, Carlotta Giannelli, Lorenzo Marini, Marco Pagliai, Lorenzo Sacco, and Marco Bianucci. "The Smart Drifter Cluster: Monitoring Sea Currents and Marine Litter Transport Using Consumer IoT Technologies." Sensors 23, no. 12 (June 9, 2023): 5467. http://dx.doi.org/10.3390/s23125467.
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The study of marine Lagrangian transport holds significant importance from a scientific perspective as well as for practical applications such as environmental-pollution responses and prevention (e.g., oil spills, dispersion/accumulation of plastic debris, etc.). In this regard, this concept paper introduces the Smart Drifter Cluster: an innovative approach that leverages modern “consumer” IoT technologies and notions. This approach enables the remote acquisition of information on Lagrangian transport and important ocean variables, similar to standard drifters. However, it offers potential benefits such as reduced hardware costs, minimal maintenance expenses, and significantly lower power consumption compared to systems relying on independent drifters with satellite communication. By combining low power consumption with an optimized, compact integrated marine photovoltaic system, the drifters achieve unlimited operational autonomy. With the introduction of these new characteristics, the Smart Drifter Cluster goes beyond its primary function of mesoscale monitoring of marine currents. It becomes readily applicable to numerous civil applications, including recovering individuals and materials at sea, addressing pollutant spills, and tracking the dispersion of marine litter. An additional advantage of this remote monitoring and sensing system is its open-source hardware and software architecture. This fosters a citizen-science approach, enabling citizens to replicate, utilize, and contribute to the improvement of the system. Thus, within certain constraints of procedures and protocols, citizens can actively contribute to the generation of valuable data in this critical field.
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Driessen, Miriam. "Africa Drifters." Made in China Journal 5, no. 3 (February 11, 2021): 48–51. http://dx.doi.org/10.22459/mic.05.03.2020.05.
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Pearson, Jenna, Baylor Fox-Kemper, Roy Barkan, Jun Choi, Annalisa Bracco, and James C. McWilliams. "Impacts of Convergence on Structure Functions from Surface Drifters in the Gulf of Mexico." Journal of Physical Oceanography 49, no. 3 (March 2019): 675–90. http://dx.doi.org/10.1175/jpo-d-18-0029.1.
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AbstractThere are limitations in approximating Eulerian statistics from surface drifters, due to biases from surface convergences. By contrasting second- and third-order Eulerian and surface drifter structure functions obtained from a model of the Gulf of Mexico, the consequences of the semi-Lagrangian nature of observations during the summer Grand Lagrangian Deployment (GLAD) and winter Lagrangian Submesoscale Experiment (LASER) are estimated. By varying launch pattern and location, the robustness and sensitivity of these statistics are evaluated. Over scales less than 10 km, second-order structure functions of surface drifters consistently have shallower slopes (~r2/3) than Eulerian statistics (~r), suggesting that surface drifter structure functions differ systematically and do not reproduce the scalings of the Eulerian fields. Medians of Eulerian and cluster release second-order statistics are also significantly different across all scales. Synthetic cluster release statistics depend on launch location and weakly on launch pattern. The observations suggest little seasonal difference in the second-order statistics, but the LASER third-order structure function shows a sign change around 1 km, while GLAD and the synthetic cluster releases show a third-order structure function sign change around 10 km. Further, synthetic surface drifter cluster releases (and therefore likely the GLAD observations) show robust biases in the negative third-order structure functions, which may lead to significant overestimation of the spectral energy flux and underestimation of the transition scale to a forward energy cascade. The Helmholtz decomposition, and curl and divergence statistics, of Eulerian and cluster releases differ, particularly on scales less than 10 km, in agreement with observations of drifters preferentially sampling convergences in coherent structures.
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Aksamit, Nikolas O., Themistoklis Sapsis, and George Haller. "Machine-Learning Mesoscale and Submesoscale Surface Dynamics from Lagrangian Ocean Drifter Trajectories." Journal of Physical Oceanography 50, no. 5 (May 2020): 1179–96. http://dx.doi.org/10.1175/jpo-d-19-0238.1.
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AbstractLagrangian ocean drifters provide highly accurate approximations of ocean surface currents but are sparsely located across the globe. As drifters passively follow ocean currents, there is minimal control on where they will be making measurements, providing limited temporal coverage for a given region. Complementary Eulerian velocity data are available with global coverage but are themselveslimited by the spatial and temporal resolution possible with satellite altimetry measurements. In addition, altimetry measurements approximate geostrophic components of ocean currents but neglect smaller submesoscale motions and require smoothing and interpolation from raw satellite track measurements. In an effort to harness the rich dynamics available in ocean drifter datasets, we have trained a recurrent neural network on the time history of drifter motion to minimize the error in a reduced-order Maxey–Riley drifter model. This approach relies on a slow-manifold approximation to determine the most mathematically relevant variables with which to train, subsequently improving the temporal and spatial resolution of the underlying velocity field. By adding this neural-network component, we also correct drifter trajectories near submesoscale features missed by deterministic models using only satellite and wind reanalysis data. The effect of varying similarity between training and testing trajectory datasets for the blended model was evaluated, as was the effect of seasonality in the Gulf of Mexico.
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Davulienė, Lina, Loreta Kelpšaitė, and Inga Dailidienė. "Surface drifters experiment in the south-eastern part of the Baltic Sea." Baltica 27, no. 2 (February 20, 2014): 151–60. http://dx.doi.org/10.5200/baltica.2014.27.24.
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In November 2013, the first short-term surface drifter experiment has been carried out along the Lithuanian coast. Three drifters were deployed from R/V Vėjūnas at a location ~6 km offshore and 2.5 km north of Klaipėda. During the period of observation from 22-30 November, the drifting direction has shifted up to five times by more than 90 degrees mainly due to changes in the mean wind direction. After seven days, the drifters have reached the coast approximately 30 km south of Klaipėda. The analysis of the relationships between the mean wind speed and the mean drift speed for the three periods differentiated based on meteorological conditions yielded a regression coefficient of 0.031, with the entire experiment period characterized by a lower value of 0.014.
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Sansón, Luis Zavala, Paula Pérez-Brunius, and Julio Sheinbaum. "Surface Relative Dispersion in the Southwestern Gulf of Mexico." Journal of Physical Oceanography 47, no. 2 (February 2017): 387–403. http://dx.doi.org/10.1175/jpo-d-16-0105.1.
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AbstractSurface dispersion properties in the southwestern Gulf of Mexico are studied by using a set of 441 drifters released during a 7-yr period and tracked for 2 months on average. The drifters have a drogue below the surface Ekman layer, so they approximately follow oceanic currents. This study follows two different approaches: First, two-particle (or pair) statistics are calculated [relative dispersion and finite-scale Lyapunov exponents (FSLEs)]. Relative dispersion estimates are consistent with theoretical dispersion regimes of two-dimensional turbulence: an exponential growth during the first 3 days, a Richardson-like regime between 3 and 20 days (in which relative dispersion grows as a power law in time), and standard dispersion (linear growth) for longer times. The FSLEs yield a power-law regime for scales between 10 and 150 km but do not detect an exponential regime for short separations (less than 10 km). Robust estimates of diffusivities based on both relative dispersion and FSLEs are provided. Second, two different dispersion scenarios are revealed by drifter trajectories and altimetric data and supported by two-particle statistics: (i) a south-to-north advection of drifters, predominantly along the western shelf of the region, and (ii) a retention of drifters during several weeks at the Bay of Campeche, the southernmost part of the Gulf of Mexico. Dominant processes that control the dispersion are the arrival of anticyclonic Loop Current eddies to the western shelf and their interaction with the semipermanent cyclonic structure in the Bay of Campeche.
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George Giazitzoglu, Andreas. "Learning not to labour: a micro analysis of consensual male unemployment." International Journal of Sociology and Social Policy 34, no. 5/6 (June 3, 2014): 334–48. http://dx.doi.org/10.1108/ijssp-07-2013-0083.
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Purpose – The Drifters are ten long-term unemployed British men. The Drifters’ unemployment is consensual: the men believe they have chosen to “not work” and rely upon welfare benefits for their socio-economic survival. The purpose of this paper is to present micro sociological analysis of the Drifters’ existences which focuses upon first, exploring why the Drifters’ consensual unemployment has resulted in them experiencing high levels of stigma in their everyday lives; second, analysing the Drifters’ (micro) relationships with (macro) unemployment policies. Design/methodology/approach – Primary, qualitative data were elicited from the Drifters during two phases of fieldwork. In both phases of fieldwork, the author conducted semi-structured qualitative interviews and participant observation-based research with the Drifters to generate data on how the men subjectively experience and account for the intersection of consensual non-work, welfare reliance and stigma in their lives. Findings – In the pseudonymous locale where the Drifters reside (Dramen) displaying a willingness to work is – despite high rates of local unemployment – a social expectation and marker of “respectable” masculinity. By living lives of consensual non-work and welfare reliance, the Drifters violate a localised cultural code and are accordingly stigmatised. Rather than attempting to manage their stigma, the Drifters ritually indulge in secondary deviant behaviours. This amplifies the Drifters’ statuses as reviled agents. The Drifters lack employment options. The Drifters have been able to successfully exploit unemployment benefits. Accordingly, the Drifters’ non-work is somewhat inevitable, rather than lamentable, as many citizens in Dramen believe; and as wider current right-leaning political and media rhetoric relating to unemployment implies. Originality/value – Examinations into the lives of non-consensually unemployed males exist. However, the lives of males who are unemployed apparently consensually – i.e. out of choice – remain under-researched. This paper functions as a micro empirical corrective, which diversifies the way male unemployment in capitalist societies can be viewed; and which offers a fresh look at how proposed unemployment welfare reform may impact the Drifters and the group in British society which the Drifters represent more broadly.
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Oscroft, Sarah, Adam M. Sykulski, and Jeffrey J. Early. "Separating Mesoscale and Submesoscale Flows from Clustered Drifter Trajectories." Fluids 6, no. 1 (December 31, 2020): 14. http://dx.doi.org/10.3390/fluids6010014.
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Drifters deployed in close proximity collectively provide a unique observational data set with which to separate mesoscale and submesoscale flows. In this paper we provide a principled approach for doing so by fitting observed velocities to a local Taylor expansion of the velocity flow field. We demonstrate how to estimate mesoscale and submesoscale quantities that evolve slowly over time, as well as their associated statistical uncertainty. We show that in practice the mesoscale component of our model can explain much first and second-moment variability in drifter velocities, especially at low frequencies. This results in much lower and more meaningful measures of submesoscale diffusivity, which would otherwise be contaminated by unresolved mesoscale flow. We quantify these effects theoretically via computing Lagrangian frequency spectra, and demonstrate the usefulness of our methodology through simulations as well as with real observations from the LatMix deployment of drifters. The outcome of this method is a full Lagrangian decomposition of each drifter trajectory into three components that represent the background, mesoscale, and submesoscale flow.
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Muscarella, Philip, Matthew J. Carrier, Hans Ngodock, Scott Smith, B. L. Lipphardt, A. D. Kirwan, and Helga S. Huntley. "Do Assimilated Drifter Velocities Improve Lagrangian Predictability in an Operational Ocean Model?" Monthly Weather Review 143, no. 5 (May 1, 2015): 1822–32. http://dx.doi.org/10.1175/mwr-d-14-00164.1.
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Abstract The Lagrangian predictability of general circulation models is limited by the need for high-resolution data streams to constrain small-scale dynamical features. Here velocity observations from Lagrangian drifters deployed in the Gulf of Mexico during the summer 2012 Grand Lagrangian Deployment (GLAD) experiment are assimilated into the Naval Coastal Ocean Model (NCOM) 4D variational (4DVAR) analysis system to examine their impact on Lagrangian predictability. NCOM-4DVAR is a weak-constraint assimilation system using the indirect representer method. Velocities derived from drifter trajectories, as well as satellite and in situ observations, are assimilated. Lagrangian forecast skill is assessed using separation distance and angular differences between simulated and observed trajectory positions. Results show that assimilating drifter velocities substantially improves the model forecast shape and position of a Loop Current ring. These gains in mesoscale Eulerian forecast skill also improve Lagrangian forecasts, reducing the growth rate of separation distances between observed and simulated drifters by approximately 7.3 km day−1 on average, when compared with forecasts that assimilate only temperature and salinity observations. Trajectory angular differences are also reduced.
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Downes, Barbara J., Alecia Bellgrove, and Jodie L. Street. "Drifting or walking? Colonisation routes used by different instars and species of lotic, macroinvertebrate filter feeders." Marine and Freshwater Research 56, no. 6 (2005): 815. http://dx.doi.org/10.1071/mf04281.
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Many views of stream invertebrate populations centre on drift as the major route of larval dispersal, but few studies have presented unambiguous information about the role of drift. We present the results from an experiment designed to determine whether the major route of colonisation of substrata by hydropsychid larvae (commonly found in the drift) is by drifting directly onto substrata or by walking along the stream bottom. The experimental design contained four treatments: substrata open to drifters and walkers; fenced substrata open to drifters only; and two treatments open to drifters and walkers that provided forms of fence controls. Fifteen replicates of each treatment were set out at random locations within a riffle at each of three sites, with each site on a different river (the Little River, the Steavenson River and the Acheron River) in the Acheron River catchment. The experiment was run twice, once during autumn (April 1999) and once during early summer (January 2000). Both experiments were colonised by three species of hydropsychids, Asmicridea sp. AV1, and Smicrophylax sp. AV1 and AV2. We found that 2nd/3rd instars of Asmicridea sp. AV1 walked as well as drifted, whereas all others primarily drifted. No relation between numbers of recruits and water speed was found when substrata were open only to drifters, whereas substrata open also to walkers gained more recruits in faster flows. Additionally, larvae more frequently abandoned nets in slow than fast flows, indicating that drifting into unfavourable flow environments may result in mortality or redispersal of larvae. These findings demonstrate that, although drift is important, it is not necessarily the only method used by hydropsychids to colonise substrata. Larvae may have more capacity to choose substrata in fast flows when they colonise substrata by walking. Spot measures of hydropsychid distribution cannot distinguish between these explanations. The finding that walkers can sometimes comprise significant numbers of recruits raises the prospect that hydropsychids can be sourced locally and have not inevitably drifted in from upstream locations.
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Fuentes-Pérez, Juan Francisco, Francisco Javier Sanz-Ronda, and Jeffrey A. Tuhtan. "An Open Surface Drifter for River Flow Field Characterization." Sensors 22, no. 24 (December 16, 2022): 9918. http://dx.doi.org/10.3390/s22249918.
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The continuous observation of flows is required to assess a river’s ecological status, to allocate irrigation withdrawals, to provide sustainable hydropower production and to plan actions as well as develop adaptive management plans. Drifters have the potential of facilitating the monitoring and modeling of river behavior at a fraction of traditional monitoring costs. They are floating objects equipped with sensors able to passively follow the movements of water. During their travel, they collect and transmit information about their movement and their surrounding environment. In this paper, we present and assess a low-cost (<150 EUR) customizable drifter developed with off-the-shelf components. The open drifter is capable of handling the majority of use cases defined in the specialized literature and in addition it offers a general river flow characterization toolkit. One of the main goals of this work is to establish an open hardware and software basis to increase the use of drifters in river studies. Results show that the proposed drifter provides reliable surface velocity estimates when compared to a commercial flow meter, offering a lower cost per data point and in contrast to traditional point measurements it can be used to identify and classify large-scale surface flow patterns. The diverse sensor payload of the open drifter presented in this work makes it a new and unique tool for autonomous river characterization.
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Leppäranta, Matti, Zhang Zhanhai, Jari Haapala, and Tapani Stipa. "Sea-ice kinematics measured with GPS drifters." Annals of Glaciology 33 (2001): 151–56. http://dx.doi.org/10.3189/172756401781818789.
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AbstractA sea-ice dynamics experiment was performed in the Baltic Sea in March 1997. A new type of drifter was constructed based on the global positioning system and mobile-phone data transmission. The drifters worked well and the accuracy was reasonable (std dev. 40 m). Five drifters were used to map ice kinematics in a 20 km size array in the coastal drift-ice zone. The study included periods of onshore motion with ridge formation, and alongshore motion with narrow shear lines. The motion of ice largely occurred in short pulses between which the field stood nearly still. The level of ice speed was much less than that of free drift, while the deformation field was more uniaxial due to the presence of the solid boundary. Drift-ice strength was estimated as 4 × 104 N m−2. Large deformation rates of up to 2% h−1 were observed.
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Youngs, Madeleine K., Andrew F. Thompson, M. Mar Flexas, and Karen J. Heywood. "Weddell Sea Export Pathways from Surface Drifters." Journal of Physical Oceanography 45, no. 4 (April 2015): 1068–85. http://dx.doi.org/10.1175/jpo-d-14-0103.1.
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AbstractThe complex export pathways that connect the surface waters of the Weddell Sea with the Antarctic Circumpolar Current influence water mass modification, nutrient fluxes, and ecosystem dynamics. To study this exchange, 40 surface drifters, equipped with temperature sensors, were released into the northwestern Weddell Sea’s continental shelf and slope frontal system in late January 2012. Comparison of the drifter trajectories with a similar deployment in early February 2007 provides insight into the interannual variability of the surface circulation in this region. Observed differences in the 2007 and 2012 drifter trajectories are related to a variable surface circulation responding to changes in wind stress curl over the Weddell Gyre. Differences between northwestern Weddell Sea properties in 2007 and 2012 include 1) an enhanced cyclonic wind stress forcing over the Weddell Gyre in 2012; 2) an acceleration of the Antarctic Slope Current (ASC) and an offshore shift of the primary drifter export pathway in 2012; and 3) a strengthening of the Coastal Current (CC) over the continental shelf in 2007. The relationship between wind stress forcing and surface circulation is reproduced over a longer time period in virtual drifter deployments advected by a remotely sensed surface velocity product. The mean offshore position and speed of the drifter trajectories are correlated with the wind stress curl over the Weddell Gyre, although with different temporal lags. The drifter observations are consistent with recent modeling studies suggesting that Weddell Sea boundary current variability can significantly impact the rate and source of exported surface waters to the Scotia Sea, a process that determines regional chlorophyll distributions.
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Ohlmann, J. Carter, Peter F. White, Andrew L. Sybrandy, and P. Peter Niiler. "GPS–Cellular Drifter Technology for Coastal Ocean Observing Systems." Journal of Atmospheric and Oceanic Technology 22, no. 9 (September 1, 2005): 1381–88. http://dx.doi.org/10.1175/jtech1786.1.
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Abstract A drifter for observing small spatial and temporal scales of motion in the coastal zone is presented. The drifter uses GPS to determine its position, and the Mobitex terrestrial cellular communications system to transmit the position data in near–real time. This configuration allows position data with order meter accuracy to be sampled every few minutes and transmitted inexpensively. Near-real-time transmission of highly accurate position data enables the drifters to be retrieved and redeployed, further increasing economy. Drifter slip measurements indicate that the drifter follows water to within ∼1–2 cm s−1 during light wind periods. Slip values >1 cm s−1 are aligned with the direction of surface wave propagation and are 180° out of phase, so that the drifter “walks” down waves. Nearly 200 drifter tracks collected off the Santa Barbara, California, coast show comparisons with high-frequency (HF) radar observations of near-surface currents that improve by roughly 50% when the average drifter values are computed from more than 25 observations within a 2-km square HF radar bin. The improvement is the result of drifter resolution of subgrid-scale eddies that are included in time–space-averaged HF radar fields. The average eddy kinetic energy on 2-km space and hour time scales is 25 cm2 s−2, when computed for bins with more than 25 drifter observations. Comparisons with trajectories that are computed from HF radar data show mean separation velocities of 5 and 9 cm s−1 in the along- and across-shore directions, respectively. The drifters resolve scales of motion that are not present in HF radar fields, and are thus complementary to HF radar in coastal ocean observing systems.
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Toner, M., and A. C. Poje. "Lagrangian velocity statistics of directed launch strategies in a Gulf of Mexico model." Nonlinear Processes in Geophysics 11, no. 1 (February 25, 2004): 35–46. http://dx.doi.org/10.5194/npg-11-35-2004.
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Abstract. The spatial dependence of Lagrangian displacement and velocity statistics is studied in the context of a data assimilating numerical model of the Gulf Mexico. In the active eddy region of the Western Gulf, a combination of Eulerian and Lagrangian measures are used to locate strongly hyperbolic regions of the flow. The statistics of the velocity field sampled by sets of drifters launched specifically in these hyperbolic regions are compared to those produced by randomly chosen launch sites. The results show that particle trajectories initialized in hyperbolic regions preferentially sample a broader range of Eulerian velocities than do members of ensembles of randomly launched drifters. The velocity density functions produced by the directed launches compare well with Eulerian velocity pdfs. Implications for the development of launch strategies to improve Eulerian velocity field reconstruction from drifter data are discussed.