Literatura científica selecionada sobre o tema "Drifting speed of Lagrangian fronts"
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Artigos de revistas sobre o assunto "Drifting speed of Lagrangian fronts"
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Fifani, Gina, Alberto Baudena, Milad Fakhri, Georges Baaklini, Yannice Faugère, Rosemary Morrow, Laurent Mortier e Francesco d’Ovidio. "Drifting Speed of Lagrangian Fronts and Oil Spill Dispersal at the Ocean Surface". Remote Sensing 13, n.º 22 (9 de novembro de 2021): 4499. http://dx.doi.org/10.3390/rs13224499.
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Due to its dire impacts on marine life, public health, and socio-economic services, oil spills require an immediate response. Effective action starts with good knowledge of the ocean dynamics and circulation, from which Lagrangian methods derive key information on the dispersal pathways present in the contaminated region. However, precise assessments of the capacity of Lagrangian methods in real contamination cases remain rare and limited to large slicks spanning several hundreds of km. Here we address this knowledge gap and consider two medium-scale (tens of km wide) events of oil in contrasting conditions: an offshore case (East China Sea, 2018) and a recent near-coastal one (East Mediterranean, 2021). Our comparison between oil slicks and Lagrangian diagnostics derived from near-real-time velocity fields shows that the calculation of Lagrangian fronts is, in general, more robust to errors in the velocity fields and more informative on the dispersion pathways than the direct advection of a numerical tracer. The inclusion of the effect of wind is also found to be essential, being capable of suddenly breaking Lagrangian transport barriers. Finally, we show that a usually neglected Lagrangian quantity, the Lyapunov vector, can be exploited to predict the front drifting speed, and in turn, its future location over a few days, on the basis of near-real-time information alone. These results may be of special relevance in the context of next-generation altimetry missions that are expected to provide highly resolved and precise near-real-time velocity fields for both open ocean and coastal regions.
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Heron, Mal, Roberto Gomez, Bernd Weber, Anna Dzvonkovskaya, Thomas Helzel, Nicolas Thomas e Lucy Wyatt. "Application of HF Radar in Hazard Management". International Journal of Antennas and Propagation 2016 (2016): 1–14. http://dx.doi.org/10.1155/2016/4725407.
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A review is given of the impact that HF radars are having on the management of coastal hazards. Maps of surface currents can be produced every 10–20 minutes which, in real time, improve navigation safety in restricted areas commonly found near ports and harbours. The time sequence of surface current maps enables Lagrangian tracking of small parcels of surface water, which enables hazard mitigation in managing suspended sediments in dredging, in emergency situations where flotsam and other drifting items need to be found, and in pollution control. The surface current measurement capability is used to assist tsunami warnings as shown by the phased-array data from Chile following the Great Tohoku Earthquake in 2011. The newly launched Tsunami Warning Center in Oman includes a network of phased-array HF radars to provide real-time tsunami monitoring. Wind direction maps can be used to locate the position of cold fronts in the open ocean and to monitor the timing and strength of sea-breeze fronts in key locations.
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Nemoto, Masaki, Kouichi Nishimura, Syunichi Kobayashi e Kaoru Izumi. "Numerical study of the time development of drifting snow and its relation to the spatial development". Annals of Glaciology 38 (2004): 343–50. http://dx.doi.org/10.3189/172756404781815202.
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AbstractThe time evolution of drifting snow under a steady wind is estimated using a new numerical model of drifting snow. In the model, Lagrangian stochastic theory is used to incorporate the effect of turbulence on the motion of drifting-snow particles. This method enables us to discuss both the saltation and the suspension process. Aerodynamic entrainment, grain/bed collision (splash process), wind modification and particle size distribution are also taken into account. The calculations show that the time needed by the total mass flux to reach a steady state appears to be 3–5 s. Vertical profiles of horizontal mass flux near the surface show a similar tendency. In contrast, it takes >50 s for the wind speed and the whole mass-flux profile to reach a steady state. This longer time depends on the time-scale of the turbulent diffusion, which is responsible for the mass flux extending to an order of a few meters in height. Applying Taylor’s hypothesis, the estimated length scale at which drifting snow reaches equilibrium is around 400 m. This result is comparable with previously reported field observations.
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Lee, Daniel, Amandine Schaeffer e Sjoerd Groeskamp. "Drifting dynamics of the bluebottle (<i>Physalia physalis</i>)". Ocean Science 17, n.º 5 (1 de outubro de 2021): 1341–51. http://dx.doi.org/10.5194/os-17-1341-2021.
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Abstract. Physalia physalis, also called the bluebottle in Australia, is a colonial animal resembling a jellyfish that is well known to beachgoers for the painful stings delivered by its tentacles. Despite being a common occurrence, the origin of the bluebottle before reaching the coastline is not well understood, and neither is the way it drifts at the surface of the ocean. Previous studies used numerical models in combination with simple assumptions to calculate the drift of this species, excluding complex drifting dynamics. In this study, we provide a new parameterization for Lagrangian modelling of the bluebottle by considering the similarities between the bluebottle and a sailboat. This allows us to compute the hydrodynamic and aerodynamic forces acting on the bluebottle and use an equilibrium condition to create a generalized model for calculating the drifting speed and course of the bluebottle under any wind and ocean current conditions. The generalized model shows that the velocity of the bluebottle is a linear combination of the ocean current velocity and the wind velocity scaled by a coefficient (“shape parameter”) and multiplied by a rotation matrix. Adding assumptions to this generalized model allows us to retrieve models used in previous literature. We discuss the sensitivity of the model to different parameters (shape, angle of attack and sail camber) and explore different cases of wind and current conditions to provide new insights into the drifting dynamics of the bluebottle.
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Poulain, Pierre-Marie, Luca Centurioni e Tamay Özgökmen. "Comparing the Currents Measured by CARTHE, CODE and SVP Drifters as a Function of Wind and Wave Conditions in the Southwestern Mediterranean Sea". Sensors 22, n.º 1 (4 de janeiro de 2022): 353. http://dx.doi.org/10.3390/s22010353.
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Instruments drifting at the ocean surface are quasi-Lagrangian, that is, they do not follow exactly the near-surface ocean currents. The currents measured by three commonly-used drifters (CARTHE, CODE and SVP) are compared in a wide range of sea state conditions (winds up to 17 m/s and significant wave height up to 3 m). Nearly collocated and simultaneous drifter measurements in the southwestern Mediterranean reveal that the CARTHE and CODE drifters measure the currents in the first meter below the surface in approximately the same way. When compared to SVP drogued at 15 m nominal depth, the CODE and CARTHE currents are essentially downwind (and down-wave), with a typical speed of 0.5–1% of the wind speed. However, there is a large scatter in velocity differences between CODE/CARTHE and SVP for all wind and sea state conditions encountered, principally due to vertical and horizontal shears not related to the wind. For the CODE drifter with wind speed larger than 10 m/s and significant wave height larger than 1 m, about 30–40% of this difference can be explained by Stokes drift.
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Ochoa, José, e Peter P. Niiler. "Vertical Vorticity Balance in Meanders Downstream the Agulhas Retroflection". Journal of Physical Oceanography 37, n.º 6 (1 de junho de 2007): 1740–44. http://dx.doi.org/10.1175/jpo3064.1.
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Abstract The Agulhas Current flows poleward along the western boundary of the southeastern Indian Ocean where, at the southernmost latitude of the African continent, it executes a dramatic anticyclonic turn, or retroflection, to the east. Since 1978, a large number of drifting buoys have passed through this eastward-flowing Agulhas Return Current (ARC), or the zonal frontal boundary between subtropical and subpolar waters of the south Indian Ocean. The spatial distribution of the ensemble-averaged near-surface velocity along the ARC axis reveals a series of steady-state meanders of 700-km wavelength and amplitudes that decrease from 170 km in the first meander to 50 km in the following four meanders. Here an analysis of vorticity balance of the meandering ARC speed axis is presented that demonstrates a balance between the β term and advection of curvature vorticity. This balance implies that the ARC axis, or frontal region, is horizontally nondivergent in agreement with the other observations of flow in the surface layers of near-zonal oceanic fronts.
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Wang, Tianyu, Yan Du e Minyang Wang. "Overlooked Current Estimation Biases Arising from the Lagrangian Argo Trajectory Derivation Method". Journal of Physical Oceanography 52, n.º 1 (janeiro de 2022): 3–19. http://dx.doi.org/10.1175/jpo-d-20-0287.1.
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Abstract An Argo simulation system is used to provide synthetic Lagrangian trajectories based on the Estimating the Circulation and Climate of the Ocean Model, phase II (ECCO2). In combination with ambient Eulerian velocity at the reference layer (1000 m) from the model, quantitative metrics of the Lagrangian trajectory–derived velocities are computed. The result indicates that the biases induced by the derivation algorithm are strongly linked with ocean dynamics. In low latitudes, Ekman currents and vertically sheared geostrophic currents influence both the magnitude and the direction of the derivation velocity vectors. The maximal shear-induced biases exist near the equator with the amplitudes reaching up to about 1.2 cm s−1. The angles of the shear biases are pronounced in the low-latitude oceans, ranging from −8° to 8°. Specifically, the study shows an overlooked bias from the float drifting motions that mainly occurs in the western boundary current and Antarctic Circumpolar Current (ACC) regions. In these regions, a recently reported horizontal acceleration measured via Lagrangian floats is significantly associated with the strong eddy–jet interactions. The acceleration could induce an overestimation of Eulerian current velocity magnitudes. For the common Argo floats with a 9-day float parking period, the derivation speed biases induced by velocity acceleration would be as large as 3 cm s−1, approximately 12% of the ambient velocity. It might have implications to map the mean middepth ocean currents from Argo trajectories, as well as to understand the dynamics of eddy–jet interactions in the ocean.
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Romero, Leonel, J. Carter Ohlmann, Enric Pallàs-Sanz, Nicholas M. Statom, Paula Pérez-Brunius e Stéphane Maritorena. "Coincident Observations of Dye and Drifter Relative Dispersion over the Inner Shelf". Journal of Physical Oceanography 49, n.º 9 (setembro de 2019): 2447–68. http://dx.doi.org/10.1175/jpo-d-19-0056.1.
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AbstractCoincident Lagrangian observations of coastal circulation with surface drifters and dye tracer were collected to better understand small-scale physical processes controlling transport and dispersion over the inner shelf in the Gulf of Mexico. Patches of rhodamine dye and clusters of surface drifters at scales of O(100) m were deployed in a cross-shelf array within 12 km from the coast and tracked for up to 5 h with airborne and in situ observations. The airborne remote sensing system includes a hyperspectral sensor to track the evolution of dye patches and a lidar to measure directional wavenumber spectra of surface waves. Supporting in situ measurements include a CTD with a fluorometer to inform on the stratification and vertical extent of the dye and a real-time towed fluorometer for calibration of the dye concentration from hyperspectral imagery. Experiments were conducted over a wide range of conditions with surface wind speed between 3 and 10 m s−1 and varying sea states. Cross-shelf density gradients due to freshwater runoff resulted in active submesoscale flows. The airborne data allow characterization of the dominant physical processes controlling the dispersion of passive tracers such as freshwater fronts and Langmuir circulation. Langmuir circulation was identified in dye concentration maps on most sampling days except when the near surface stratification was strong. The observed relative dispersion is anisotropic with eddy diffusivities O(1) m2 s−1. Near-surface horizontal dispersion is largest along fronts and in conditions dominated by Langmuir circulation is larger in the crosswind direction. Surface convergence at fronts resulted in strong vertical velocities of up to −66 m day−1.
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Pingree, R. D., e Linda Maddock. "Stokes, Euler and Lagrange Aspects of Residual Tidal Transports in the English Channel and the Southern Bight of the North Sea". Journal of the Marine Biological Association of the United Kingdom 65, n.º 4 (novembro de 1985): 969–82. http://dx.doi.org/10.1017/s0025315400019445.
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INTRODUCTIONThe dust cart on the Isles of Scilly did not end its service at the local tip, over the cliffs at Deep Point on the eastern side of St Mary's on 14 October 1983. Instead it floated off and continued in service as a Lagrangian drifter, indicating the residual transport of water around the islands. As a hazard to shipping its position was given out as a navigation warning and it was allegedly sighted on the western side of Scilly. The interesting oceanographic question is whether the dust cart was (or would have had it not sunk) circumnavigating the islands in a clockwise or anticlockwise sense. Accordingly this experiment has been repeated using satellite tracked Argos drifting buoys, drogued with parachutes (~ 10 m diameter), and set at depths of about 15 m. The releases showed that the residual transport was clockwise around the islands. In one instance a drogue circumnavigated the islands in about 12 h (i.e. ~ one tidal period) at an average speed of about 100 cm s−1 (Fig. 1).
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Dhareshwar, L. J., P. A. Naik, T. C. Kaushik e H. C. Pant. "Study of laser-driven shock wave propagation in Plexiglas targets". Laser and Particle Beams 10, n.º 1 (março de 1992): 201–11. http://dx.doi.org/10.1017/s0263034600004328.
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An experimental study of laser-driven shock wave propagation in a transparent material such as Plexiglas using a high-speed optical shadowgraphy technique is presented in this paper. A Nd:glass laser was used to produce laser intensity in the range 1012-1014 W/cm2 on the target. Optical shadowgrams of the propagating shock front were recorded with a second-harmonic (0.53-μm) optical probe beam. Shock pressures were measured at various laser intensities, and the scaling was found to agree with the theoretically predicted value. Shock pressure values have also been obtained from a one-dimensional Lagrangian hydrodynamic simulation, and they match well with experimental results. Shadowgrams of shock fronts produced by nonuniform spatial laser beam irradiation profiles have shown complete smoothing when targets with a thin coating of a material of high atomic number such as gold were used. Shock pressures in such coated targets are also found to be considerably higher compared with those in uncoated targets.
Teses / dissertações sobre o assunto "Drifting speed of Lagrangian fronts"
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Fifani, Gina. "Lagrangian dispersion and oil spills : with a case study in the Eastern Mediterranean". Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS243.
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Les déversements d'hydrocarbures nécessitent une intervention immédiate qui commence par une bonne connaissance de la dynamique océanique de la région contaminée. L'approche Lagrangienne a été proposée comme un outil soutenant la gestion de la pollution marine. L'objectif de cette thèse est d'utiliser et développer des outils lagrangiens pour analyser deux événements de marée noire s'étendant sur une échelle plus petite que celle de la marée noire de DeepWater Horizon: une marée noire offshore en mer de Chine orientale (2018) et un accident côtier dans la Méditerranée orientale (2021). Le calcul des fronts lagrangiens s'est avéré robuste et plus informatif que l'advection directe d'un traceur numérique. L'inclusion de l'effet du vent s'avère également essentielle, étant capable de briser les fronts lagrangiens. Une nouvelle technique a été aussi proposée, ancrée dans la théorie de Lyapunov, par laquelle la vitesse de dérive d'un front lagrangien peut être estimée sur la base de la seule information en temps quasi réel. Cette information permet de prédire la position future du front lagrangien sur quelques jours et d'étudier les vitesses de dérive des fronts à l'échelle globale et méditerranéenne. Une contribution à une expérience lagrangienne en Méditerranée met en évidence le défaut lagrangien de l'altimétrie au nadir et le besoin de futures missions altimétriques tel SWOTDue to their dire impacts on marine life, public health, and services, accidental oil spills require an immediate response. Effective action starts with a good knowledge of the ocean dynamics prevailing in the contaminated region. The Lagrangian approach has been proposed as a supportive tool in marine pollution management. The goal of this thesis is to use and develop Lagrangian tools to analyze two oil spill events extending on a scale smaller than that of the DeepWater Horizon oil spill. These are an offshore East China sea oil spill (2018) and a near-coast East Mediterranean accident (2021). The calculation of Lagrangian fronts have been more robust and more informative on the dispersion pathways than the direct advection of a numerical tracer. The inclusion of the wind effect is also found to be essential, being capable of suddenly breaking Lagrangian fronts. A new technique is also proposed, rooted in the Lyapunov theory, by which the drifting speed of a Lagrangian front can be estimated based on near real-time information alone. This information allows to predict the Lagrangian front future location over a few days and to study frontal drifting speeds at global and Mediterranean scales. A further contribution to a Lagrangian experiment in the Mediterranean highlights the Lagrangian shortcoming of nadir altimetry and the need for future altimetry missions like SWOT
Trabalhos de conferências sobre o assunto "Drifting speed of Lagrangian fronts"
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Storie, Jill, Rafael Ramos, Michael Leber, Heather Nowak, Michelle Young e Bruce Magnell. "Evaluation of Loop Current/Loop Current Eddy Fronts to Guide Offshore Oil & Gas Operations". In Offshore Technology Conference. OTC, 2023. http://dx.doi.org/10.4043/32643-ms.
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Abstract The unique circulation characteristics of the Gulf of Mexico (GOM) pose a significant threat to the safety of offshore oil and gas operations pertaining to installation of new production systems, drilling, and maintenance of existing offshore infrastructure. Operators in the area rely on realistic estimates of the location of the sharp fronts (regions of high horizontal shear) characteristic of the warm-core Loop Current (LC) and Loop Current Eddies (LCEs) and smaller cold core cyclonic eddies (CEs) to estimate working windows. However, locating these features is not a trivial undertaking because it requires review and analysis of multiple observational and model data sources. In this paper, we describe the frontal analysis (FA) methodology used to define such features. This technique has been accepted by industry as the best representation of the continuous front that delineates the most distinct current gradients defining the sharp outside edge of the LC/LCEs. Definition of LC/LCE features is accomplished by defining the position and extent of the associated front, defined as the 1.5 knot current threshold. This involves performing an analysis of satellite imagery (snapshots and composites) and satellite-derived products (altimetry and geostrophic velocities), in-situ measurements (i.e., public and proprietary drifting buoys, rig-mounted ADCPs, vessel-mounted ADCP transects, etc.), and previous feature location/progression analyses, all weighted appropriately. The resulting front is then used to map these features and provide actionable information regarding their surface current velocities, migration speed and direction, angular rotation, and axis orientation. Systematic analysis of the behavior of the LC system since 1984 has resulted in a unique oceanographic dataset comprising the location and evolution of LCEs. By incorporating frequent deployment of aircraft-deployed, satellite-tracked, drogued drifting buoys and the analysis of their track data, the FA provides the most accurate and extensive near-real-time information available regarding the location and intensity of currents affecting offshore operations. WHG’s FA product is commonly accepted throughout the industry and within the scientific community as the closest to ground truth for the placement of the major oceanographic features in the region. Understanding the details of this methodology will provide the basis for comparison of observations with new numerical modeling efforts (under development as part of the NASEM UGOS program) to effectively assess the accuracy of nowcast results and will eventually lead to better model forecasts for the benefit of various stakeholders.