Готові списки джерел за темами / Surface geostrophic currents

Добірка наукової літератури з теми "Surface geostrophic currents"

Автор: Grafiati

Опубліковано: 6 вересня 2023

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Статті в журналах з теми "Surface geostrophic currents"

Armitage, Thomas W. K., Sheldon Bacon, Andy L. Ridout, Alek A. Petty, Steven Wolbach, and Michel Tsamados. "Arctic Ocean surface geostrophic circulation 2003–2014." Cryosphere 11, no. 4 (July 26, 2017): 1767–80. http://dx.doi.org/10.5194/tc-11-1767-2017.

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Abstract. Monitoring the surface circulation of the ice-covered Arctic Ocean is generally limited in space, time or both. We present a new 12-year record of geostrophic currents at monthly resolution in the ice-covered and ice-free Arctic Ocean derived from satellite radar altimetry and characterise their seasonal to decadal variability from 2003 to 2014, a period of rapid environmental change in the Arctic. Geostrophic currents around the Arctic basin increased in the late 2000s, with the largest increases observed in summer. Currents in the southeastern Beaufort Gyre accelerated in late 2007 with higher current speeds sustained until 2011, after which they decreased to speeds representative of the period 2003–2006. The strength of the northwestward current in the southwest Beaufort Gyre more than doubled between 2003 and 2014. This pattern of changing currents is linked to shifting of the gyre circulation to the northwest during the time period. The Beaufort Gyre circulation and Fram Strait current are strongest in winter, modulated by the seasonal strength of the atmospheric circulation. We find high eddy kinetic energy (EKE) congruent with features of the seafloor bathymetry that are greater in winter than summer, and estimates of EKE and eddy diffusivity in the Beaufort Sea are consistent with those predicted from theoretical considerations. The variability of Arctic Ocean geostrophic circulation highlights the interplay between seasonally variable atmospheric forcing and ice conditions, on a backdrop of long-term changes to the Arctic sea ice–ocean system. Studies point to various mechanisms influencing the observed increase in Arctic Ocean surface stress, and hence geostrophic currents, in the 2000s – e.g. decreased ice concentration/thickness, changing atmospheric forcing, changing ice pack morphology; however, more work is needed to refine the representation of atmosphere–ice–ocean coupling in models before we can fully attribute causality to these increases.

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Rio, M. H., R. Santoleri, R. Bourdalle-Badie, A. Griffa, L. Piterbarg, and G. Taburet. "Improving the Altimeter-Derived Surface Currents Using High-Resolution Sea Surface Temperature Data: A Feasability Study Based on Model Outputs." Journal of Atmospheric and Oceanic Technology 33, no. 12 (December 2016): 2769–84. http://dx.doi.org/10.1175/jtech-d-16-0017.1.

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AbstractAccurate knowledge of ocean surface currents at high spatial and temporal resolutions is crucial for a gamut of applications. The altimeter observing system, by providing repeated global measurements of the sea surface height, has been by far the most exploited system to estimate ocean surface currents over the past 20 years. However, it neither permits the observation of currents moving away from the geostrophic balance nor is it capable of resolving the shortest spatial and temporal scales of the currents. Therefore, to overcome these limitations, in this study the ways in which the high-spatial-resolution and high-temporal-resolution information from sea surface temperature (SST) images can improve the altimeter current estimates are investigated. The method involves inverting the SST evolution equation for the velocity by prescribing the source and sink terms and employing the altimeter currents as the large-scale background flow. The method feasibility is tested using modeled data from the Mercator Ocean system. This study shows that the methodology may improve the altimeter velocities at spatial scales not resolved by the altimeter system (i.e., below 150 km) but also at larger scales, where the geostrophic equilibrium might not be the unique or dominant process of the ocean circulation. In particular, the major improvements (more than 30% on the meridional component) are obtained in the equatorial band, where the geostrophic assumption is not valid. Finally, the main issues anticipated when this method is applied using real datasets are investigated and discussed.

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Berta, Maristella, Lucio Bellomo, Annalisa Griffa, Marcello G. Magaldi, Anne Molcard, Carlo Mantovani, Gian Pietro Gasparini, et al. "Wind-induced variability in the Northern Current (northwestern Mediterranean Sea) as depicted by a multi-platform observing system." Ocean Science 14, no. 4 (July 25, 2018): 689–710. http://dx.doi.org/10.5194/os-14-689-2018.

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Abstract. The variability and evolution of the Northern Current (NC) in the area off Toulon is studied for 2 weeks in December 2011 using data from a glider, a high-frequency (HF) radar network, vessel surveys, a weather station, and an atmospheric model. The NC variability is dominated by a synoptic response to wind events, even though the dataset also evidences early stages of transition from late summer to fall–winter conditions. With weak winds, the current is mostly zonal and in geostrophic balance even at the surface, with a zonal transport associated with the NC of ≈1 Sv. Strong westerly wind events (longer than 2–3 days) induce an interplay between the direct-wind-induced ageostrophic response and the geostrophic component: upwelling is observed, with offshore surface transport, surface cooling, flattening of the isopycnals, and reduced zonal geostrophic transport (0.5–0.7 Sv). The sea surface response to wind events, as observed by the HF radar, shows total currents rotated at ≈-55 to -90∘ to the right of the wind. Performing a decomposition between geostrophic and ageostrophic components of the surface currents, the wind-driven ageostrophic component is found to rotate by ≈-25 to -30∘ to the right of the wind. The ageostrophic component magnitude corresponds to ≈2 % of the wind speed.

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Centurioni, L. R., J. C. Ohlmann, and P. P. Niiler. "Permanent Meanders in the California Current System." Journal of Physical Oceanography 38, no. 8 (August 1, 2008): 1690–710. http://dx.doi.org/10.1175/2008jpo3746.1.

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Abstract Surface Velocity Program (SVP) drifter data from 1987 through 2005; Archiving, Validation, and Interpretation of Satellite Oceanographic data (AVISO) sea level anomalies; and NCEP reanalysis winds are used to assemble a time-averaged map of the 15-m-deep geostrophic velocity field in the California Current System seaward of about 50 km from the coast. The wind data are used to compute the Ekman currents, which are then subtracted from the drifter velocity measurements. The resulting proxy for geostrophic velocity anomalies computed from drifters and from satellite sea level measurements are combined to form an unbiased mean geostrophic circulation map. The result shows a California Current System that flows southward with four permanent meanders that can extend seaward for more than 800 km. Bands of alternating eastward and westward zonal currents are connected to the meanders and extend several thousand kilometers into the Pacific Ocean. This observed time-mean circulation and its associated eddy energy are compared to those produced by various high-resolution OGCM solutions: Regional Ocean Modeling System (ROMS; 5 km), Parallel Ocean Program model (POP; 1/10°), Hybrid Coordinate Ocean Model (HYCOM; 1/12°), and Naval Research Laboratory (NRL) Layered Ocean Model (NLOM; 1/32°). Simulations in closest agreement with observations come from ROMS, which also produces four meanders, geostrophic time-mean currents, and geostrophic eddy energy consistent with the observed values. The time-mean ageostrophic velocity in ROMS is strongest within the cyclonic part of the meanders and is similar to the ageostrophic velocity produced by nonlinear interaction of Ekman currents with the near-surface vorticity field.

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Chaudhary, A., N. Agarwal, and R. Sharma. "Estimation of currents using SARAL/AltiKa in the coastal regions of India." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XL-8 (December 23, 2014): 1365–67. http://dx.doi.org/10.5194/isprsarchives-xl-8-1365-2014.

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The present study explores the possibility of deriving the across track currents along the Indian coastal region from SARAL/AltiKa mission. The across track surface geostrophic currents obtained from along track SARAL altimeter data are directly compared (qualitatively) with high frequency (HF) radar observations of surface currents in the Bay of Bengal. The velocity component from HF radar which is perpendicular to the altimeter tracks is considered. Since the ageostrophic velocity contribution is ignored for the moment, the surface geostrophic currents SARAL compare well only under low wind conditions. Due to high along track resolution of SARAL there are large variations in velocity which are not captured by the HF radar observations. In general, the magnitude and variations in surface currents derived from SARAL altimeter are comparable with HF radar observations.

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Ollitrault, Michel, and Alain Colin de Verdière. "The Ocean General Circulation near 1000-m Depth." Journal of Physical Oceanography 44, no. 1 (January 1, 2014): 384–409. http://dx.doi.org/10.1175/jpo-d-13-030.1.

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Abstract The mean ocean circulation near 1000-m depth is estimated with 100-km resolution from the Argo float displacements collected before 1 January 2010. After a thorough validation, the 400 000 or so displacements found in the 950–1150 dbar layer and with parking times between 4 and 17 days allow the currents to be mapped at intermediate depths with unprecedented details. The Antarctic Circumpolar Current (ACC) is the most prominent feature, but western boundary currents (and their recirculations) and alternating zonal jets in the tropical Atlantic and Pacific are also well defined. Eddy kinetic energy (EKE) gives the mesoscale variability (on the order of 10 cm2 s−2 in the interior), which is compared to the surface geostrophic altimetric EKE showing e-folding depths greater than 700 m in the ACC and northern subpolar regions. Assuming planetary geostrophy, the geopotential height of the 1000-dbar isobar is estimated to obtain an absolute and deep reference level worldwide. This is done by solving numerically the Poisson equation that results from taking the divergence of the geostrophic equations on the sphere, assuming Neumann boundary conditions.

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Cadden, Dara D. H., Richard Styles, and Bulusu Subrahmanyam. "Estimates of Geostrophic Surface Currents in the South Atlantic Bight." Marine Geodesy 32, no. 3 (August 11, 2009): 334–41. http://dx.doi.org/10.1080/01490410903094908.

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Sudre, Joël, Christophe Maes, and Véronique Garçon. "On the global estimates of geostrophic and Ekman surface currents." Limnology and Oceanography: Fluids and Environments 3, no. 1 (February 2013): 1–20. http://dx.doi.org/10.1215/21573689-2071927.

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Zhang, ZiZhan, Yang Lu, and HouTse Hsu. "Detecting surface geostrophic currents using wavelet filter from satellite geodesy." Science in China Series D: Earth Sciences 50, no. 6 (June 2007): 918–26. http://dx.doi.org/10.1007/s11430-007-0038-4.

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Poulain, Pierre-Marie, Milena Menna, and Elena Mauri. "Surface Geostrophic Circulation of the Mediterranean Sea Derived from Drifter and Satellite Altimeter Data." Journal of Physical Oceanography 42, no. 6 (June 1, 2012): 973–90. http://dx.doi.org/10.1175/jpo-d-11-0159.1.

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Abstract Drifter observations and satellite-derived sea surface height data are used to quantitatively study the surface geostrophic circulation of the entire Mediterranean Sea for the period spanning 1992–2010. After removal of the wind-driven components from the drifter velocities and low-pass filtering in bins of 1° × 1° × 1 week, maps of surface geostrophic circulation (mean flow and kinetic energy levels) are produced using the drifter and/or satellite data. The mean currents and kinetic energy levels derived from the drifter data appear stronger/higher with respect to those obtained from satellite altimeter data. The maps of mean circulation estimated from the drifter data and from a combination of drifter and altimeter data are, however, qualitatively similar. In the western basin they show the main pathways of the surface waters flowing eastward from the Strait of Gibraltar to the Sicily Channel and the current transporting waters back westward along the Italian, French, and Spanish coasts. Intermittent and long-lived subbasin-scale eddies and gyres abound in the Tyrrhenian and Algerian Seas. In the eastern basin, the surface waters are transported eastward by several currents but recirculate in numerous eddies and gyres before reaching the northward coastal current off Israel, Lebanon, and Syria and veering westward off Turkey. In the Ionian Sea, the mean geostrophic velocity maps were also produced separately for the two extended seasons and for multiyear periods. Significant variations are confirmed, with seasonal reversals of the currents in the south and changes of the circulation from anticyclonic (prior to 1 July 2007) to cyclonic and back to anticyclonic after 31 December 2005.

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Більше джерел

Дисертації з теми "Surface geostrophic currents"

Müller, Felix Lucian [Verfasser], Florian [Akademischer Betreuer] Seitz, Per [Gutachter] Knudsen, Martin [Gutachter] Horwath, and Florian [Gutachter] Seitz. "Improved polar geostrophic surface currents from satellite altimetry / Felix Lucian Müller ; Gutachter: Per Knudsen, Martin Horwath, Florian Seitz ; Betreuer: Florian Seitz." München : Universitätsbibliothek der TU München, 2021. http://d-nb.info/122758055X/34.

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Chi-HungChang and 張繼鴻. "Analysis of Surface and Subsurface Geostrophic Currents Derived from Satellite Altimetry and In-situ Hydrographical Data." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/42066379829858480894.

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碩士
國立成功大學
測量及空間資訊學系
103
Studies have shown that ocean circulations are highly important for the climate stability and human life. Their variations are also highly connected to potential natural hazards; therefore, continuous monitoring of ocean circulations has been a highly respected issue over the past centuries. The research uses multiple satellite altimetry data, satellite-only geoid model (GOCE or GRACE), in-situ hydrographical data to determine mesoscale geostrophic current velocities globally. To reduce the errors remain in ADT, the research adopts conventional pointwise approach, spectral approach, and profile approach to process Sea Surface Height (SSH) and geoid models. In-situ current meter observations at 23 stations fixed at 10m depth from TAO/TRITON and PIRATA were taken as ground truth. Results show that when adopting the spectral approach, around 70%~90% of stations gives Root Mean Square (RMS) smaller than or at same accuracy level (within 1 cm/s) compared with the pointwise approach and the averaged RMS is about 10~15 cm/s, while there are over 90% of stations giving RMS smaller than or at same accuracy level with pointwise approach and averaged RMS is around 8~10 cm/s when adopting profile approach, which better improves the conventional pointwise approach. GOCE geoid model was also proved to perform better than GRACE geoid in determining geostrophic currents from time-variant perspective with 60%~80% of stations giving smaller RMS. On the other hand, the average correlation coefficients are all around 0.6~0.7 and 0.3~0.4 in zonal and meridional direction, respectively, with no significant discrepancy when adopting different approach or geoid model (average difference within 0.1). The correlation coefficients between geostrophic current velocities, volume transports through the Gulf Stream (GS), Labrador Current (LC) and wintertime North Atlantic Oscillation (NAO) were estimated, while the correlations of Kuroshio Current (KC) and El Niño/Southern Oscillation (ENSO) were evaluated by using Multivariate ENSO Index (MEI). Results show the correlation coefficient of 0.7 with 1-year lag between GS and wintertime NAO in zonal direction which may relate to the north-southward shift of GS pathway, while LC velocities show the correlation coefficient of 0.5 in meridional direction with zero-lag. The meridional volume transport through the transect also shows the same maximum correlation coefficient and lag time. Such fast response may due to the barotropic nature of LC variability. In the North Pacific Ocean, transects through the Bashi Channel, the northeast of Taiwan, and Kuroshio Extension were chosen. Comparatively higher correlations with MEI are in the meridional currents through the Kuroshio Extension and near-surface zonal currents through the Bashi Channel with maximum negative correlation coefficient of -0.4 and -0.3~ -0.4 for volume transports; Zonal currents through Kuroshio Extension shows maximum positive correlation coefficient of 0.4 and 0.3 for volume transports. Results indicate that correlations in the transect through Bashi Channel and Kuroshio Extension are all higher than those in the transect of the northeast of Taiwan where only gives correlation coefficient of 0.1~0.2.

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Zheng, Zhe-Wen, and 鄭志文. "Seasonal and interannual variability of multi-satellite derived Sea Surface Heights and Geostrophic Currents in the South China Sea." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/08316759647731497673.

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Yu, Yunyue. "Sea surface temperature, geostrophic current and surface heat advection in the western tropical Pacific." 1996. http://catalog.hathitrust.org/api/volumes/oclc/37356621.html.

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Тези доповідей конференцій з теми "Surface geostrophic currents"

Storie, Jill, Rafael Ramos, Michael Leber, Heather Nowak, Michelle Young, and 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.

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