Bibliografie tematiche / Downwelling

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Letteratura scientifica selezionata sul tema "Downwelling"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 1 febbraio 2022

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Articoli di riviste sul tema "Downwelling"

Kenyon, Kern E. "Downwelling by Surface Gravity Waves?" Natural Science 09, n. 05 (2017): 143–44. http://dx.doi.org/10.4236/ns.2017.95015.

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Blue, Charles. "Mantle downwelling causes continental depressions". Eos, Transactions American Geophysical Union 74, n. 9 (2 marzo 1993): 98. http://dx.doi.org/10.1029/93eo00359.

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Cenedese, Claudia. "Downwelling in Basins Subject to Buoyancy Loss". Journal of Physical Oceanography 42, n. 11 (1 novembre 2012): 1817–33. http://dx.doi.org/10.1175/jpo-d-11-0114.1.

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Abstract Recent observational, theoretical, and modeling studies all suggest that the upper part of the downwelling limb of the thermohaline circulation is concentrated in strong currents subject to buoyancy loss near lateral boundaries. This is fundamentally different from the traditional view that downwelling takes place in regions of deep convection. Even when resolving the buoyant boundary currents, coarse-resolution global circulation and climate models rely on parameterizations of poorly known turbulent mixing processes. In this study, the first direct measurements of downwelling occurring within a basin subject to buoyancy loss are obtained. Downwelling is observed near the basin’s vertical wall within the buoyant boundary current flowing cyclonically around the basin. Although the entire basin is cooled, large-scale mean downwelling is absent in the basin interior. Laboratory rotating experiments are conducted to explicitly resolve the turbulent mixing due to convective plumes and the baroclinic eddies generated by the boundary current, and to identify where downwelling takes place. Small vertical velocities can be measured more reliably in the laboratory than in many numerical calculations, whereas the measurement of these small vertical velocities is still a challenge for field experiments. Downwelling is observed near the vertical wall within a boundary layer with a thickness that scales with the baroclinic Rossby radius of deformation, consistent with the dynamical balance proposed by a previous numerical study. Hence, downwelling in the Labrador Sea and Lofoten Basin cyclonic boundary currents may be concentrated in a baroclinic Rossby radius of deformation thick boundary layer in regions with large eddy generation.

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Fan, Wei, Dongdong Pan, Canbo Xiao, Tiancheng Lin, Yiwen Pan e Ying Chen. "Experimental Study on the Performance of an Innovative Tide-Induced Device for Artificial Downwelling". Sustainability 11, n. 19 (25 settembre 2019): 5268. http://dx.doi.org/10.3390/su11195268.

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Hypoxia has been increasingly observed in estuaries and coastal marine ecosystems around the world. In this paper, a tide-powered artificial downwelling device is proposed to potentially alleviate hypoxia in bottom waters. The downwelling device mainly consists of a vertical square tube, a 90° bend sitting on the top of the tube, two symmetrical-guide plates which installed alongside the vertical tube, a static mixer, and an artificial reef. Scale model experiments are performed with respect to different density difference heads, horizontal current velocities, and tube geometries. The results show that the downwelling flow rate is dependent on horizontal current velocity, tube geometry parameters, and the density profile of ambient water. In addition, increasing the equivalent diameter and bend radius of the device can decrease the total loss coefficient in the tube, which in turns enhance the downwelling efficiency. The two symmetrical-guide plates also generate obvious downwelling of surface water which further improves the whole performance of the device. Further work will need to determine the influence of the other parts of the device, such as the static mixer and artificial reef, on the downwelling efficiency.

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Brüggemann, Nils, e Caroline A. Katsman. "Dynamics of Downwelling in an Eddying Marginal Sea: Contrasting the Eulerian and the Isopycnal Perspective". Journal of Physical Oceanography 49, n. 11 (novembre 2019): 3017–35. http://dx.doi.org/10.1175/jpo-d-19-0090.1.

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AbstractIn this study, we explore the downward branch of the Atlantic meridional overturning circulation (AMOC) from a perspective in depth space (Eulerian downwelling) as well as from a perspective in density space (diapycnal downwelling). Using an idealized model, we focus on the role of eddying marginal seas, where dense water is formed by deep convection due to an intense surface heat loss. We assess where diapycnal mass fluxes take place, investigate the pathways of dense water masses, and elucidate the role of eddies. We find that there are fundamental differences between the Eulerian and diapycnal downwelling: the strong Eulerian near-boundary downwelling is not associated with substantial diapycnal downwelling; the latter takes place in the interior and elsewhere in the boundary current. We show that the diapycnal downwelling appears to be more appropriate to describe the pathways of water masses. In our model, dense water masses are exported along two routes: those formed in the upper part of the boundary current are exported directly; those formed in the interior move toward the boundary along isopycnals due to eddy stirring and are then exported. This study thus reveals a complex three-dimensional view of the overturning in a marginal sea, with possible implications for our understanding of the AMOC.

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Spall, Michael A. "Buoyancy-Forced Downwelling in Boundary Currents". Journal of Physical Oceanography 38, n. 12 (1 dicembre 2008): 2704–21. http://dx.doi.org/10.1175/2008jpo3993.1.

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Abstract The issue of downwelling resulting from surface buoyancy loss in boundary currents is addressed using a high-resolution, nonhydrostatic numerical model. It is shown that the net downwelling is determined by the change in the mixed layer density along the boundary. For configurations in which the density on the boundary increases in the direction of Kelvin wave propagation, there is a net downwelling within the domain. For cases in which the density decreases in the direction of Kelvin wave propagation, cooling results in a net upwelling within the domain. Symmetric instability within the mixed layer drives an overturning cell in the interior, but it does not contribute to the net vertical motion. The net downwelling is determined by the geostrophic flow toward the boundary and is carried downward in a very narrow boundary layer of width E1/3, where E is the Ekman number. For the calculations here, this boundary layer is O(100 m) wide. A simple model of the mixed layer temperature that balances horizontal advection with surface cooling is used to predict the net downwelling and its dependence on external parameters. This model shows that the net sinking rate within the domain depends not only on the amount of heat loss at the surface but also on the Coriolis parameter, the mixed layer depth (or underlying stratification), and the horizontal velocity. These results indicate that if one is to correctly represent the buoyancy-forced downwelling in general circulation models, then it is crucial to accurately represent the velocity and mixed layer depth very close to the boundary. These results also imply that processes that lead to weak mixing within a few kilometers of the boundary, such as ice formation or freshwater runoff, can severely limit the downwelling forced by surface cooling, even if there is strong heat loss and convection farther offshore.

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Meneghello, Gianluca, John Marshall, Mary-Louise Timmermans e Jeffery Scott. "Observations of Seasonal Upwelling and Downwelling in the Beaufort Sea Mediated by Sea Ice". Journal of Physical Oceanography 48, n. 4 (aprile 2018): 795–805. http://dx.doi.org/10.1175/jpo-d-17-0188.1.

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AbstractWe present observational estimates of Ekman pumping in the Beaufort Gyre region. Averaged over the Canada Basin, the results show a 2003–14 average of 2.3 m yr−1 downward with strong seasonal and interannual variability superimposed: monthly and yearly means range from 30 m yr−1 downward to 10 m yr−1 upward. A clear, seasonal cycle is evident with intense downwelling in autumn and upwelling during the winter months, despite the wind forcing being downwelling favorable year-round. Wintertime upwelling is associated with friction between the large-scale Beaufort Gyre ocean circulation and the surface ice pack and contrasts with previous estimates of yearlong downwelling; as a consequence, the yearly cumulative Ekman pumping over the gyre is significantly reduced. The spatial distribution of Ekman pumping is also modified, with the Beaufort Gyre region showing alternating, moderate upwelling and downwelling, while a more intense, yearlong downwelling averaging 18 m yr−1 is identified in the northern Chukchi Sea region. Implications of the results for understanding Arctic Ocean dynamics and change are discussed.

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Fan, Wei, Weicheng Bao, Yong Cai, Canbo Xiao, Zhujun Zhang, Yiwen Pan, Ying Chen e Shuo Liu. "Experimental Study on the Effects of a Vertical Jet Impinging on Soft Bottom Sediments". Sustainability 12, n. 9 (6 maggio 2020): 3775. http://dx.doi.org/10.3390/su12093775.

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Artificial downwelling, which is an ecological engineering method, potentially alleviates bottom hypoxia by bringing oxygen-rich surface water down below the pycnocline. However, the downward flow is likely to disturb sediments (or induce sediment resuspension) when reaching the bottom and then have unwanted side effects on the local ecosystem. To evaluate this, our paper presents a theoretical model and experimental data for the sediment resuspension caused by artificial downwelling. The theoretical model considers the critical conditions for sediment resuspension and the scour volume with the downwelling flow disturbing sediment. Experiments with altered downwelling flow speeds, discharge positions relative to the bottom, and particle sizes of sediment were conducted in a water tank, and the results were consistent with our theoretical model. The results show that the critical Froude number (hereinafter Fr) for sediment resuspension is 0.5. The prevention of sediment resuspension requires the downwelling flow speed and the discharge position to be adjusted so that Fr < 0.5; otherwise a portion of sediment is released into the water and its volume can be predicted by the derived formulation based on the Shields theory. Furthermore, sediment resuspension has side effects, such as a water turbidity increase and phosphorus release, the magnitudes of which are discussed with respect to engineering parameters. Further study will focus on field experiments of artificial downwelling and its environmental impacts.

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Liu, Shuo, Lige Zhao, Canbo Xiao, Wei Fan, Yong Cai, Yiwen Pan e Ying Chen. "Review of Artificial Downwelling for Mitigating Hypoxia in Coastal Waters". Water 12, n. 10 (13 ottobre 2020): 2846. http://dx.doi.org/10.3390/w12102846.

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Hypoxia is becoming a serious problem in coastal waters in many parts of the world. Artificial downwelling, which is one of the geoengineering-based adaptation options, was suggested as an effective means of mitigating hypoxia in coastal waters. Artificial downwelling powered by green energy, such as solar, wind, wave, or tidal energy, can develop a compensatory downward flow on a kilometer scale, which favors below-pycnocline ventilation and thus mitigates hypoxia in bottom water. In this paper, we review and assess the technical, numerical, and experimental aspects of artificial downwelling all over the world, as well as its potential environmental effects. Some basic principles are presented, and assessment and advice are provided for each category. Some suggestions for further field-based research on artificial downwelling, especially for long-term field research, are also given.

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Spurgin, J. M., e S. E. Allen. "Flow dynamics around downwelling submarine canyons". Ocean Science 10, n. 5 (14 ottobre 2014): 799–819. http://dx.doi.org/10.5194/os-10-799-2014.

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Abstract. Flow dynamics around a downwelling submarine canyon were analysed with the Massachusetts Institute of Technology general circulation model. Blanes Canyon (northwestern Mediterranean) was used for topographic and initial forcing conditions. Fourteen scenarios were modelled with varying forcing conditions. Rossby and Burger numbers were used to determine the significance of Coriolis acceleration and stratification (respectively) and their impacts on flow dynamics. A new non-dimensional parameter (χ) was introduced to determine the significance of vertical variations in stratification. Some simulations do see brief periods of upwards displacement of water during the 10-day model period; however, the presence of the submarine canyon is found to enhance downwards advection of density in all model scenarios. High Burger numbers lead to negative vorticity and a trapped anticyclonic eddy within the canyon, as well as an increased density anomaly. Low Burger numbers lead to positive vorticity, cyclonic circulation, and weaker density anomalies. Vertical variations in stratification affect zonal jet placement. Under the same forcing conditions, the zonal jet is pushed offshore in more uniformly stratified domains. The offshore jet location generates upwards density advection away from the canyon, while onshore jets generate downwards density advection everywhere within the model domain. Increasing Rossby values across the canyon axis, as well as decreasing Burger values, increase negative vertical flux at shelf break depth (150 m). Increasing Rossby numbers lead to stronger downwards advection of a passive tracer (nitrate), as well as stronger vorticity within the canyon. Results from previous studies are explained within this new dynamic framework.

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Più fonti

Tesi sul tema "Downwelling"

Spurgin, Jessica Michelle. "Flow dynamics around downwelling submarine canyons". Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46533.

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Flow dynamics around a downwelling submarine canyon were analyzed with the Massachusetts Institute of Technology general circulation model. Blanes Canyon (Northwest Mediterranean) was used for topographic and initial forcing conditions. Fourteen scenarios were modelled with varying forcing conditions. Rossby number and Burger number were used to determine the significance of Coriolis acceleration and stratification (respectively) and their impacts on flow dynamics. A new non-dimensional parameter (χ) was introduced to determine the significance of vertical variations in stratification. Downwelling (downwards advection of density) occurs under all forcing conditions and is enhanced within the canyon. High Burger numbers lead to negative vorticity and a trapped anticyclonic eddy within the canyon, as well as an increased density anomaly. Low Burger numbers lead to positive vorticity, cyclonic circulation and weaker density anomalies. Vertical variations in stratification affect zonal jet placement. Under the same forcing conditions, the zonal jet is pushed offshore in more uniformly stratified domains. Offshore jet location generates upwards density advection away from the canyon, while onshore jets generate downwards density advection everywhere within the model domain. Increasing Rossby values across the canyon axis, as well as decreasing Burger values, increase negative vertical flux at shelf break depth (150 m). Increasing Rossby numbers lead to stronger downwards advection of a passive tracer (nitrate). Comparisons were made to previous studies to explain how variations in initial forcing conditions impact regional flow dynamics.

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Bhandari, Purushottam. "The Design of a Polarimeter and its Use for the Study of the Variation of Downwelling Polarized Radiance Distribution with Depth in the Ocean". Scholarly Repository, 2011. http://scholarlyrepository.miami.edu/oa_dissertations/605.

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The spectral polarized radiance distribution provides the most complete description of the light field that can be measured. However, this is a very difficult parameter to measure near the surface because of its large dynamic range, dependence on incoming sky conditions, and waves at the air-sea interface. The measurement of the Stokes vector of the downwelling polarized light field requires the combination of at least four images, all of which must be obtained simultaneously. To achieve this, a new polarimeter (which we call DPOL) has been designed, characterized, calibrated and deployed. The description of the DPOL, its calibrations and characterizations are discussed. The uncertainties in the retrieval of Stokes vector and other derived parameters are also discussed. This instrument is equipped with four fish-eye lenses (180° field of view) with polarizers behind each lens in a different orientation, a coherent optical fiber bundle with 4 arms, a spectral filter changer assembly and a charged coupled-device (CCD) imaging camera. With this system, a single image contains 4 separate fisheye images, each a whole hemisphere of the same scene, each with different polarization information. Using these 4 images and applying appropriate calibration parameters allows us to calculate the four-element Stokes vector and then the total degree of polarization and the angle of plane of polarization of the incoming light field in a hemisphere of desired directions. Under the Office of Naval Research RaDyO (Radiance under a Dynamic Ocean) program, DPOL has been used in the Santa Barbara Channel and Hawaii field experiments. In most cases, data on sky polarization were collected with a separate camera (Sky-Cam) simultaneously with the DPOL. The data and results with these two camera systems in these experiments are presented and are compared. Data on the inherent optical properties of water from the same field experiments collected by collaborators will be shown. Our measurements show that very near the surface, for clear sky conditions, the dominant source of polarization is the refracted sky light. As one progresses in the water column, the polarization due to light scattering by the water increases and polarization due to the water becomes dominant. The dependence of the in-water light field polarization on the sky and surface wave conditions, solar zenith and azimuth angles, the depth of the instrument, the viewing angle, the wavelength of light, the inherent optical properties (IOP’s) of water are discussed.

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Mehta, Payal. "The microphysical properties of Saharan dust obtainable from downwelling infrared radiances". Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526395.

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Wang, Haixing. "Impact Of Canyon Upwelling And Downwelling In The Mid-Atlantic Bight". W&M ScholarWorks, 2021. https://scholarworks.wm.edu/etd/1627407406.

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Submarine canyons can impact regional oceanography and provide a conduit for shelf-slope exchanges via topographically induced processes such as canyon upwelling and downwelling. Between Virginia and New York in the Mid-Atlantic Bight (MAB), there are five major shelf-incising canyons (Norfolk, Washington, Baltimore, Wilmington, and Hudson canyons) and four sizable slope-confined canyons (Accomac, Spencer, Lindenkhol, and Toms canyons). Canyon upwelling and downwelling at these canyons have not been well studied. Consequently, the associated hydrographic variability and dynamics inside the canyons and on the adjacent shelf are largely unknown, and the integrated impact of submarine canyons on MAB shelf hydrography and shelf-slope exchanges is poorly understood. This dissertation was inspired by a glider-based survey at Wilmington Canyon, and mainly used numerical modeling simulations for the MAB with an unstructured-grid three-dimensional ocean model to answer these questions. Using glider observations and realistic numerical modeling for February 25–March 7, 2016, Chapter 2 investigated the hydrographic variability associated with the Wilmington Canyon and adjacent outer shelf and shelf-break amid two consecutive events of upwelling and downwelling. Then focusing on the same Wilmington Canyon upwelling and downwelling events and using a realistically forced numerical modeling simulation as well as one without tidal forcing, Chapter 3 tested the dynamical drivers of winds and tides in canyon upwelling and downwelling events, also compared the differences in dynamics between the canyon and adjacent shelf-break. Chapter 4 presented the occurrences and integrated impact of 12 cycles of spatially coherent upwelling and downwelling through nine canyons between Virginia and New York, based on a realistic numerical modeling experiment and a No-Canyon experiment for January 1–April 14, 2016. Chapter 4 also analyzed the frequency of canyon upwelling and downwelling based on a 22-year record (1994–2015) of sea surface elevation. This dissertation found that the submarine canyons in the MAB induced significant spatial and temporal hydrographic variabilities on the shelf and enhanced shelf-slope water exchange. Due to favorable winds, sea surface tilts, and shelf-scale background ocean currents, as well as canyon topography, cycles of spatially coherent multi-canyon upwelling and downwelling frequently occurred in the MAB. Plumes of upwelled slope water from the canyons intruded the outer and mid shelf during the upwelling episodes, and dense water from the shelf retreated into the canyons during the downwelling episodes. For each cycle of upwelling and downwelling, upwelled water from the canyons caused shelf-scale anomalies of low temperature, high density, and northeastward velocity on the MAB outer shelf that were significant when averaged over the course of the season. This thesis suggests that submarine canyons are an integral part of MAB oceanography and deserve further investigations.

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Rodríguez, Cruz Elisabet. "Circulation patterns of Ría de Pontevedra under upwelling and downwelling conditions". Master's thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/23481.

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Mestrado em Ciências do Mar e da Atmosfera
Circulation patterns inside some of the Rías Baixas have been widely studied, but this is not the case of the Ría de Pontevedra. Through this thesis, we try to enhance the knowledge about the circulation pattern of this Ría. A ROMS-AGRIF system con guration was used in this study. This con guration was validated through the comparison with weekly temperature and salinity data measured by INTECMAR. The analysis done in this work is based on the study of three representative events of the circulation patterns: one upwelling event and two downwelling events, one of them with Lérez river ow increase. Also, was analyzed temporal series of uxes and ushing times through the external mouths and the correlations between these series and the forcing parameters (winds and average of the rivers ow). An EOF's study was applied to the subinertial normal velocities at the sections. Upwelling events are characterized by a reinforcement of the positive estuarine circulation, consistent with surface layer out ows and deep layer in ows at the main channel of the Ría, and in ows/out ows at the north/south mouths. Downwelling events have an opposite behaviour to the event described before. There are evidences of the vertical mixing through clockwise circulations at the outer part of the Ría, associated with the ocean waters subduction that enter into the Ría through the surface layer. As a consequence, a blocking can be generated at the middle part of the Ría, which has been associated by other authors with the "red tides". Fluxes for downwelling events are higher than for upwelling events. Flushing times are around 2 days for downwelling and around 4 days for upwelling events. The EOF's study con rms the circulation described for upwelling and downwelling events, in this work. The forecast of the physical conditions at Ría de Pontevedra are important for the understanding of the processes behind the production of HABs.
Diversos estudos tem sido realizados sobre os padrões de circulação em algumas das Rías Baixas, mas este não é o caso da Ría de Pontevedra. Ao longo desta tese tentaremos completar os conhecimentos sobre esta Ría. Uma con guração do sistema ROMS-AGRIF foi utilizada neste estudo, sendo esta validada com base na comparação com dados de temperatura e salinidade medidos semanalmente pelo INTECMAR. A analise realizada baseia-se no estudo de três episódios representativos da circulação: um de a oramento e dois de afundamento, um destes com caudal do río Lérez signi cativo. Foram ainda analisadas séries temporais de uxos e de tempos de renovação através de diversas secções. Foi analisada a correlação entre estas séries e os parâmetros forçadores (ventos e caudais dos rios). Foi realizado um estudo utilizando técnicas de funções empíricas ortogonais aplicado ao campo de velocidades normal às secções. Os eventos de a oramento são caracterizados por um reforço da circulação positiva na Ría, consistente com os uxos de saída pela camada superior e uxos de entrada pela camada inferior do canal principal da Ría, e com uxos de entrada pela boca norte e os uxos de saída pela boca sul. Nos eventos de afundamento o comportamento é oposto ao anterior. São discutidas evidências de recirculação vertical em forma de células no sentido dos ponteiros do relógio na zona externa da Ría, associado à subdução de águas oceânicas que entram na Ría pela camada superior. Este fenómeno parece criar uma zona de bloqueio no meio do eixo da Ría, que pode ser um mecanismo responsável pelo desenvolvimento das denominadas marés vermelhas. Os uxos para o evento de afundamento são superiores aos dos eventos de a oramento. O tempo de renovação é próximo dos 2 dias para o afundamento e dos 4 dias para o a oramento. O estudo por funções empíricas ortogonais con rma a circulação descrita durante os episódios de a oramento e afundamento discutidos neste trabalho. A previsão das condições físicas na Ría de Pontevedra é importante para a compreensão dos processos associados ao desenvolvimento de marés vermelhas.

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Zhang, Zhenxi. "Modeling downwelling circulation over continental shelf in the northern South China Sea /". View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?AMCE%202009%20ZHANG.

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Neal, David A. "Maximum Likelihood Temperature/Emissivity Separation of Hyperspectral Images with Gaussian Distributed Downwelling Radiance". DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/5873.

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Hyperspectral images are made up of energy measurements at different wavelengths of light. The case is considered where these measurements are dependent on temperature, the self-emitted energy (emissivity), and reflected energy (downwelling radiance) from the surroundings. The process where the downwelling radiance is fixed and the temperature and emissivity are estimated is referred to as temperature/emissivity separation. Due to the way these terms mix, for a given set of measurements, there exist many pairs of temperatures and emissivities that satisfy the model. This creates ambiguity in the solution that must be resolved for the result to have any significance. A new model is developed which reduces this ambiguity. This model is used to form an objective function. The temperature and emissivity which maximize the value of the objective function are solved for given a set of measurements. As part of the solution, a new algorithm is developed which exploits the shape of the objective function to estimate the temperature and emissivity quickly and accurately. Extensive testing of this algorithm is performed to gain an understanding of its average speed and accuracy.

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Viúdez, i. Mora Antoni. "Atmospheric downwelling longwave radiation at the surface during cloudless and overcast conditions. Measurements and modeling". Doctoral thesis, Universitat de Girona, 2011. http://hdl.handle.net/10803/31841.

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Atmospheric downwelling longwave radiation is an important component of the terrestrial energy budget; since it is strongly related with the greenhouse effect, it remarkably affects the climate. In this study, I evaluate the estimation of the downwelling longwave irradiance at the terrestrial surface for cloudless and overcast conditions using a one-dimensional radiative transfer model (RTM), specifically the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART). The calculations performed by using this model were compared with pyrgeometer measurements at three different European places: Girona (NE of the Iberian Peninsula), Payerne (in the East of Switzerland), and Heselbach (in the Black Forest, Germany). Several studies of sensitivity based on the radiative transfer model have shown that special attention on the input of temperature and water content profiles must be held for cloudless sky conditions; for overcast conditions, similar sensitivity studies have shown that, besides the atmospheric profiles, the cloud base height is very relevant, at least for optically thick clouds. Also, the estimation of DLR in places where radiosoundings are not available is explored, either by using the atmospheric profiles spatially interpolated from the gridded analysis data provided by European Centre of Medium-Range Weather Forecast (ECMWF), or by applying a real radiosounding of a nearby site. Calculations have been compared with measurements at all sites. During cloudless sky conditions, when radiosoundings were available, calculations show differences with measurements of -2.7 ± 3.4 Wm-2 (Payerne). While no in situ radiosoundings are available, differences between modeling and measurements were about 0.3 ± 9.4 Wm-2 (Girona). During overcast sky conditions, when in situ radiosoundings and cloud properties (derived from an algorithm that uses spectral infrared and microwave ground based measurements) were available (Black Forest), calculations show differences with measurements of -0.28 ± 2.52 Wm2. When using atmospheric profiles from the ECMWF and fixed values of liquid water path and droplet effective radius (Girona) calculations show differences with measurements of 4.0 ± 2.5 Wm2. For all analyzed sky conditions, it has been confirmed that estimations from radiative transfer modeling are remarkably better than those obtained by simple parameterizations of atmospheric emissivity.
La radiació infrarroja a l’atmosfera és una component important del balanç energètic del planeta; en estar fortament relacionada amb l’efecte hivernacle influeix de manera remarcable en el clima. En aquest estudi s’avalua la bondat de les estimacions de la irradiància infrarroja incident en superfície (DLR) fetes amb un model unidimensional de transferència radiativa, el Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART), per a condicions de cel serè o bé completament ennuvolat. Els càlculs realitzats amb aquest model han estat comparats amb mesures de pirgeòmetre realitzades en tres emplaçaments a Europa: Girona (NE de la Península Ibèrica), Payerne (a l’est de Suïssa), i Heselbach (a la Selva Negra, Alemanya). Els estudis de sensibilitat fets amb el model de transferència radiativa han mostrat l’especial importància que tenen els perfils atmosfèrics de temperatura i contingut d’aigua en absència de núvols; per cels completament ennuvolats l’estudi de sensibilitat mostra que, a banda dels perfils atmosfèrics esmentats, l’altura de la base dels núvols és molt rellevant. S’ha estimat la DLR per indrets on no es disposava de radiosondatges, substituint-los bé per un radiosondatge proper, o bé per perfils interpolats espacialment en l’anàlisi del model de predicció meteorològica de l’European Centre of Medium-Range Weather Forecast (ECMWF). Els càlculs han estat comparats amb mesures per tots els llocs. Per condicions de cel serè, i quan es disposa de radiosondatge, els càlculs mostren una diferència amb les mesures de -2.7 ± 3.4 Wm-2 (Payerne). Quan no es disposa d’aquests perfils, la diferència entre les modelitzacions i les mesures és de 0.3 ± 9.4 Wm-2 (Girona). Per condicions de cel cobert, quan es disposa del radiosondatge i les propietats dels núvols (derivades a partir d’un algoritme que empra mesures espectrals en infraroig i en la banda de microones en superfície, Selva Negra), els càlculs mostren una diferència amb les mesures de -0.28 ± 2.52 Wm-2. Quan es fan servir els perfils del ECMWF i es fixa el valor de la columna d’aigua líquida i el radi efectiu de les gotes d’aigua (Girona) els càlculs mostren una diferència amb les mesures de 4.0 ± 2.5 Wm-2. També s’ha confirmat per totes les condicions estudiades que les estimacions amb el model de transferència radiativa són notablement millors que les obtingudes amb parametritzacions senzilles de l’emissivitat atmosfèrica.

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Batifoulier, François. "Hydrodynamique du plateau continental aquitain et influence sur les épisodes à Dinophysis dans le Bassin d’Arcachon". Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14441/document.

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Des épisodes à Dinophysis affectent périodiquement l'exploitation des fruits de mer dans le Bassin d'Arcachon. Le réseau de surveillance interne au Bassin d'Arcachon montre que Dinophysis est advecté de l'océan ouvert. Le but de cette étude est de déterminer l'origine de Dinophysis. Des campagnes en mer sur le plateau continental Aquitain ont permis d'identifier une zone propice au développement de Dinophysis au large de Capbreton. Les épisodes à Dinophysis dans le bassin d'Arcachon se produisent suite à des vents d'Ouest qui induisent des courants vers le Sud d'après la littérature. L'étude des données hydrodynamiques acquises pendant les campagnes met en évidence un processus complexe et nouveau suite aux vents d'Ouest: de forts courants le long de la côte vers le Nord capables de transporter Dinophysis de Capbreton jusqu'au Bassin d'Arcachon. Un travail de modélisation a permis de reproduire ce courant et d'étudier son mécanisme particulier lié coin Sud-Est du Golfe de Gascogne
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Logvinov, Evgeny. "Two responses of a uniformly stratified flow over a sloping bottom to a spatially varying downwelling favorable wind". Thesis, Online version of original thesis, 2008. http://hdl.handle.net/1912/2500.

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Più fonti

Libri sul tema "Downwelling"

Chance, Kelly, e Randall V. Martin. Modeling Radiative Transfer. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780199662104.003.0009.

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Basic concepts and definitions of radiative transfer modeling are introduced. The applicability of single scattering to aerosol retrievals is demonstrated. A two-stream formulation of radiative transfer is introduced. The two streams, upwelling and downwelling radiation, are selected to angularly represent average atmospheric properties: Relatively simple, two-stream calculations form the basis for much practical calculation, particularly of hemispherical fluxes in stratified atmospheres. Following this development, the most usual method for replacing the general integrodifferential equations obtained when setting up a scattering scenario by a system of linear equations is demonstrated.

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Ruxton, Graeme D., William L. Allen, Thomas N. Sherratt e Michael P. Speed. Countershading. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780199688678.003.0004.

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Countershading is a coloration pattern where the exterior surfaces most exposed to light, typically dorsal surfaces, are more darkly coloured than those oriented away from light, typically ventral surfaces. Countershading is widely discussed as a camouflage defence, although other functions—such as thermoregulation, abrasion resistance, and protection from ultraviolet light—may also select for countershading. In terms of camouflage, countershading is thought to work by up to six distinct mechanisms. We discuss several key examples of countershading and counterillumination that give insight into some of this complexity, before reviewing the evidence for the effectiveness of each of the six mechanisms. These include relatively simple effects, such as background matching dorsal surfaces against dark oceanic depths when viewed from above and ventral surfaces against downwelling light when viewed from below, but also more complex mechanisms, such as the concealment of cues to three-dimensional shape created by an animal’s self-cast shadows. Following this are sections on the evolution and genetics of countershading, before the chapter concludes with ecological considerations and suggestions for future research.

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Capitoli di libri sul tema "Downwelling"

Mohan, Ram K., Andrew D. Short, Gillian Cambers, M. MacLeod, J. A. G. Cooper, David Hopley, Vincent May et al. "Coastal Upwelling and Downwelling". In Encyclopedia of Coastal Science, 306–8. Dordrecht: Springer Netherlands, 2005. http://dx.doi.org/10.1007/1-4020-3880-1_88.

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Barua, Dilip K. "Coastal Upwelling and Downwelling". In Encyclopedia of Earth Sciences Series, 1–5. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-48657-4_88-2.

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Barua, Dilip K. "Coastal Upwelling and Downwelling". In Encyclopedia of Earth Sciences Series, 600–604. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-319-93806-6_88.

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Stathopoulos, V., e C. Matsoukas. "Long-Term Memory and Multifractality of Downwelling Longwave Flux at Stations Worldwide". In Perspectives on Atmospheric Sciences, 1193–98. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-35095-0_172.

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Frank, Tamara M., e Edith A. Widder. "UV Light in the Deep-Sea: In Situ Measurements of Downwelling Irradiance in Relation to the Visual Threshold Sensitivity of UV-Sensitive Crustaceans". In Zooplankton: sensory ecology and physiology, 185–93. London: Routledge, 2021. http://dx.doi.org/10.1201/9780203733615-13.

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"downwelling". In Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik, 409. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-41714-6_43318.

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Carder, Kendall L., e David K. Costello. "Optical Effects of Large Particles". In Ocean Optics. Oxford University Press, 1994. http://dx.doi.org/10.1093/oso/9780195068436.003.0017.

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Two important problems facing the ocean optics research community in the coming decade concern optical model closure and inversion (see Chapter 3). We obtain model closure if we can describe the measured light environment by combining elementary measurements of the optical properties of the medium with radiative transfer theory. If we can accurately deduce the concentration of various constituents from a combination of measures of the submarine light field and inverse model calculations, we term this process model inversion. The most elementary measurements of the optical properties of the sea are those that are independent of the geometry of the light field, the inherent optical properties (Preisendorfer, 1961). Optical properties that are dependent on the geometry of the light field are termed apparent optical properties (AOP). Models of the submarine light field typically relate apparent optical properties to inherent optical properties (see Chapter 2). Examples include the relationship between the AOP irradiance reflectance R and a combination of inherent optical properties (backscattering coefficient bb and absorption coefficient a), and the relationship between the AOP downwelling diffuse attenuation coefficient kd and a combination of the absorption coefficient, backscattering coefficient, and downwelling average cosine μd (e.g., Gordon et al., 1975; Morel and Prieur, 1977; Smith and Baker, 1981; Morel, 1988; Kirk, 1984a). Under some circumstances these relationships work well enough that the absorption coefficient can be derived indirectly. This is important since measurement of the absorption coefficient by direct means has been difficult. Derived values for the absorption coefficient by model inversion methods are not easily verified by independent measurements, however, because of the difficulty of measuring the absorption coefficient. Model closure and model inversion both become more tenuous when the following phenomena are present: 1. Transpectral or inelastic scattering such as fluorescence (e.g., Gordon, 1979; Carder and Steward, 1985; Mitchell and Kiefer, 1988a; Spitzer and Dirks, 1985; Hawes and Carder, 1990) or water Raman scattering (Marshall and Smith, 1990; Stavn, 1990; Stavn and Weidemann, 1988a,b; Peacock et al, 1990; Chapter 12 this volume). 2. Particles that are large relative to the measurement volume for inherent optical property meters such as beam transmissometers, light-scattering photometers, fluorometers, and absorption meters.

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Walker, James C. G. "How to Solve a Nonlinear System". In Numerical Adventures with Geochemical Cycles. Oxford University Press, 1991. http://dx.doi.org/10.1093/oso/9780195045208.003.0006.

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In a linear system the expressions, yp, for rates of change are linear functions of the dependent variables, y. More complicated functions of y do not appear, not even products of the dependent variables like y1 * y2. But most theoretical problems in Earth system science involve nonlinearities. For example, the rate at which a chemical reaction consumes species 1 may be proportional to the product of the concentrations of species 1 and the species 2 with which it is reacting, y1 * y2. In this chapter I shall describe and solve a simple nonlinear system involving the reaction between dissolved oxygen and organic carbon in the deep sea. I shall show how the nonlinear system can be represented by a linear system, provided that changes in the dependent variables are made in sufficiently small increments. Such increments are kept small by stepping forward in time with small steps. The time step can be adjusted automatically during the calculation so as to keep the increments small enough but no smaller than necessary. Steps that are too large cause errors or even instability, and steps that are too small waste time. The representation of a nonlinear system by its linear equivalent (for small increments) calls on algebraic manipulations that can be tedious and a prolific source of mistakes in complicated systems. This algebra can be avoided, however, by letting the computer perform the equivalent manipulations numerically. I shall demonstrate how to do this, finishing the chapter with a program that can solve coupled nonlinear systems directly from the equations for the rates of change of the dependent variables, automatically adjusting the time step to small values when the rates of change are large and to large values when the rates of change are small. Figure 4-1 shows a simple model of the processes that control the oxygen balance of the deep sea. Dissolved oxygen in surface seawater equilibrates with the atmosphere. Downwelling currents carry dissolved oxygen into the deep sea, where most of it reacts (metabolically) with organic matter carried into the deep sea in the form of settling particles of biological origin.

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KING, S. "Mantle Downwellings and the Fate of Subducting Slabs: Constraints from Seismology, Geoid Topography, Geochemistry, and Petrology". In Treatise on Geophysics, 325–70. Elsevier, 2007. http://dx.doi.org/10.1016/b978-044452748-6/00122-x.

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King, S. D. "Mantle Downwellings and the Fate of Subducting Slabs: Constraints from Seismology, Geoid Topography, Geochemistry, and Petrology". In Treatise on Geophysics, 325–70. Elsevier, 2007. http://dx.doi.org/10.1016/b978-044452748-6.00122-x.

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Atti di convegni sul tema "Downwelling"

Pieper, M., D. Manolakis, E. Truslow, T. Cooley, M. Brueggeman, A. Weisner e J. Jacobson. "In-scene LWIR downwelling radiance estimation". In SPIE Optical Engineering + Applications, a cura di John F. Silny e Emmett J. Ientilucci. SPIE, 2016. http://dx.doi.org/10.1117/12.2239138.

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Slegel, David A., e T. D. Dickey. "Characterization Of Downwelling Spectral Irradiance Fluctuations". In 1988 Technical Symposium on Optics, Electro-Optics, and Sensors, a cura di Marvin A. Blizard. SPIE, 1988. http://dx.doi.org/10.1117/12.945710.

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Linnemann, K., P. Gege, S. Rößler, T. Schneider e A. Melzer. "CDOM retrieval using measurements of downwelling irradiance". In SPIE Remote Sensing, a cura di Charles R. Bostater, Stelios P. Mertikas e Xavier Neyt. SPIE, 2013. http://dx.doi.org/10.1117/12.2031250.

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Goforth, Mark A., George W. Gilchrist e Joseph D. Sirianni. "Cloud effects on thermal downwelling sky radiance". In AeroSense 2002, a cura di Xavier P. Maldague e Andres E. Rozlosnik. SPIE, 2002. http://dx.doi.org/10.1117/12.459570.

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Groetsch, Philipp, e Peter Gege. "Determination of sensor depth from downwelling irradiance measurements". In IGARSS 2012 - 2012 IEEE International Geoscience and Remote Sensing Symposium. IEEE, 2012. http://dx.doi.org/10.1109/igarss.2012.6350835.

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Tessendorf, Jerry A. "Downwelling irradiance fluctuations in the small-angle approximation". In Orlando '90, 16-20 April, a cura di Richard W. Spinrad. SPIE, 1990. http://dx.doi.org/10.1117/12.34724.

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Estep, Leland. "Spectral eigenanalysis of up- and downwelling k profiles". In San Diego '92, a cura di Gary D. Gilbert. SPIE, 1992. http://dx.doi.org/10.1117/12.140657.

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Wurst, Nathan P., Joseph Meola e David L. Perry. "Measurement and modeling of longwave infrared directional downwelling spectral radiance". In SPIE Optical Engineering + Applications, a cura di Thomas S. Pagano e John F. Silny. SPIE, 2015. http://dx.doi.org/10.1117/12.2186557.

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Mlynczak, Martin G., Richard P. Cageao, Harri Latvakoski, David P. Kratz, Jeffrey Mast e David G. Johnson. "Observations Of Downwelling Far-Infrared Radiance At Earth’s Surface with FIRST". In Hyperspectral Imaging and Sounding of the Environment. Washington, D.C.: OSA, 2015. http://dx.doi.org/10.1364/hise.2015.ht4b.4.

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Tiwari, Surya Prakash, Y. V. B. Sarma e Burton H. Jones. "Evaluation of downwelling diffuse attenuation coefficient algorithms in the Red Sea". In SPIE Asia-Pacific Remote Sensing, a cura di Robert J. Frouin, Satheesh C. Shenoi e K. H. Rao. SPIE, 2016. http://dx.doi.org/10.1117/12.2222823.

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Rapporti di organizzazioni sul tema "Downwelling"

Voss, Kenneth J. Polarized Downwelling Radiance Distribution Camera System. Fort Belvoir, VA: Defense Technical Information Center, gennaio 2008. http://dx.doi.org/10.21236/ada516872.

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Finkel, R. Evidence for Stratospheric Downwelling Associated with High-Elevation Topography. Office of Scientific and Technical Information (OSTI), gennaio 2009. http://dx.doi.org/10.2172/947744.

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Long, CN, P. Gotseff e EG Dutton. Investigation of the Downwelling LW Differences Between the Niamey AMF Main and Supplementary Sites. Office of Scientific and Technical Information (OSTI), aprile 2008. http://dx.doi.org/10.2172/948029.

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