Articles de revues sur le sujet « Nuages convectifs »
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Cornet, Céline, Eric Defer, Didier Ricard, Céline Cheymol, Adrien Deschamps et Laurène Gillot. « La mission spatiale C³IEL pour l'étude des nuages convectifs ». La Météorologie, no 125 (2024) : 002. http://dx.doi.org/10.37053/lameteorologie-2024-0023.
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Coquillat, Sylvain, Véronique Pont, Mickaël Pardé, Michaël Kreitz, Dominique Lambert, Ronan Houel, Didier Ricard, Eric Gonneau, Pierre de Guibert et Serge Prieur. « Découverte d'une anomalie électrique dans des orages méditerranéens ». La Météorologie, no 120 (2023) : 046. http://dx.doi.org/10.37053/lameteorologie-2023-0016.
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L'analyse de 561 jours d'orage sur 6 années de données de l'imageur d'éclair 3D Saetta a permis d'identifier des nuages convectifs en région Corse présentant une structure électrique anormale et apparaissant par flux de sud de poussières désertiques africaines. L'explication physique des processus électriques apporte les bases pour comprendre ce que l'imageur permet de déduire sur la structure électrique des cellules orageuses. Des hypothèses microphysiques et radiatives conduisant à un faible contenu en gouttelettes d'eau surfondue à l'origine de cette électrisation anormale sont explorées en s'appuyant sur l'analyse du contexte en aérosols et des conditions météorologiques environnantes. The analysis of 561 days of thunderstorms over 6 years of data from the 3D lightning imager Saetta has allowed to identify convective clouds in Corsica region with an abnormal electrical structure and appearing by southern flow of African desert dust. The physical explanation of the electrical processes brings the basis to understand what the imager allows to deduce about the electrical structure of thunderstorm cells. Microphysical and radiative hypotheses leading to a low content of supercooled droplets at the origin of this abnormal electrification are explored by relying on the analysis of the aerosol context and the surrounding meteorological conditions.
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Ventre, Axel, Gabriel Hausknost, Serge Soula, Sylvain Coquillat, Janusz Mlynarczyk et Alex Hermant. « Mécanismes physiques d'un éclair nuage-air ascendant au-dessus d'un orage méditerranéen ». La Météorologie, no 124 (2024) : 035. http://dx.doi.org/10.37053/lameteorologie-2024-0011.
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Dans la nuit du 1er novembre 2022, une décharge lumineuse a été photographiée au-dessus d'un orage méditerranéen, à 90 km au sud de Nice. L'analyse de deux photographies et d'une vidéo montre qu'elle se compose d'un canal lumineux ascendant émergeant du sommet du nuage à 11,8 km d'altitude, se développant jusqu'à 14,2 km et surmonté de filaments bleus jusqu'à 17,2 km. Elle est associée à un éclair qui démarre par une puissante décharge nuageuse positive à 6 km d'altitude, avec un pic d'intensité électrique de 25 kA. Au cours de cet éclair, le canal lumineux est identifié comme un traceur négatif émergeant du nuage, suivi par trois arcs lumineux reliés à la région de charge négative inférieure d'un dipôle nuageux positif. Cet éclair est produit après une poussée convective et une occurrence d'éclairs positifs au sein de la même région orageuse. La polarité et les conditions de déclenchement de cette décharge ascendante présentent des similitudes avec celles des jets géants. On the night of November 1, 2022, a luminous discharge was photographed above a Mediterranean thunderstorm, 90 km south of Nice (France). The analysis of two photographs and a video shows that it consists of an ascending light channel emerging from the top of the cloud at an altitude of 11.8 km, expanding up to 14.2 km and surmounted by blue filaments up to 17.2 km. It is associated with a lightning flash which starts with a powerful positive cloud discharge at 6 km altitude with a peak current of 25 kA. During this flash, the light channel above the cloud is identified as a negative leader emerging from the cloud, followed by three light arcs connected to the lower negative charge region of a positive cloud dipole. The flash is produced after a convective surge and an occurrence of positive lightning flashes within the same storm region. The polarity and triggering conditions of this upward discharge have similarities with those of giant jets.
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Weckwerth, Tammy M., Hanne V. Murphey, Cyrille Flamant, Janine Goldstein et Crystalyne R. Pettet. « An Observational Study of Convection Initiation on 12 June 2002 during IHOP_2002 ». Monthly Weather Review 136, no 7 (1 juillet 2008) : 2283–304. http://dx.doi.org/10.1175/2007mwr2128.1.
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Abstract The International H2O Project (IHOP_2002) was designed to sample the three-dimensional time-varying moisture field to better understand convective processes. Numerous research and operational water vapor measuring systems and retrievals, via in situ and remote sensing techniques, were operated in the U.S. Southern Great Plains from 13 May to 25 June 2002. This was done in combination with more traditional observations of wind and temperature. Convection initiation (CI) sampling strategies were designed to optimally employ the array of ground-based and airborne sensors to observe the processes leading to the development of deep, moist convection. This case study examines several clear-air features and their impact on CI on 12 June 2002. The supercells that developed produced damaging winds and hail. The clear-air, preconvective features included (i) a mesoscale low pressure region, (ii) a dryline, (iii) an old outflow boundary, (iv) the intersection of (ii) and (iii), (v) internal gravity waves, and (vi) horizontal convective rolls. A unique combination of instruments was positioned to sample the preconvective environment on 12 June 2002. The Lidar pour l’Etude des Interactions Aérosols Nuages Dynamique Rayonnement et du Cycle de l’Eau (LEANDRE II) water vapor differential absorption lidar (DIAL), the airborne Electra Doppler Radar (ELDORA), and the Navy Research Laboratory (NRL) P3 aircraft in situ measurements provided information on the moisture and vertical velocity distribution within the boundary layer. Radiosondes, dropsondes, wind profilers, and an Atmospheric Emitted Radiance Interferometer (AERI) provided temperature, moisture, and wind profiling information. Although other ground-based sensors (i.e., S-band dual-polarization Doppler radar, Mobile Integrated Profiling System) were 50–150 km west of the CI area, they were useful for illustrating the boundary layer kinematics and reflectivity fields. Results suggest that the mesolow and mesoscale boundaries, respectively, acted to enhance the low-level moisture advection and convergence in the CI region. While internal gravity waves were present and appeared to modulate water vapor along the old outflow boundary, they did not play an obvious role in CI in this case. Horizontal convective rolls were observed beneath the new storms that initiated and may have helped to focus the CI in this case.
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Cai, Weihua, Zhifeng Zheng, Changye Huang, Yue Wang, Xin Zheng et Hongna Zhang. « Lattice Boltzmann simulation of Rayleigh-Benard convection in enclosures filled with Al2O3-water nanofluid ». Thermal Science 22, Suppl. 2 (2018) : 535–45. http://dx.doi.org/10.2298/tsci171023038c.
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In order to clarify the controversies for the role of nanoparticles on heat transfer in natural convection, lattice Boltzmann method is used to investigate Rayleigh-Benard convection heat transfer in differentially-heated enclosures filled with Al2O3-water nanofluids. The results for streamline and isotherm contours, vertical velocity, and temperature profiles as well as the local and average Nusselt number are discussed for a wide range of Rayleigh numbers and nanoparticle volume fractions (0 ? ? ? 5%). The results show that with the increase of Rayleigh number and nanoparticles loading, Nuave increases. It is suggested that the addition of nanoparticles can enhance the heat transfer in Rayleigh-Benard convection.
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Scialom, G., et Y. Lemaître. « Vertical Moistening by AMMA Mesoscale Convective Systems ». Journal of Atmospheric and Oceanic Technology 28, no 5 (1 mai 2011) : 617–39. http://dx.doi.org/10.1175/2010jtecha1486.1.
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Abstract The apparent heat source Q1 and the apparent moisture sink Q2 are crucial parameters for precipitating systems studies because they allow for the evaluation of their contribution in water and energy transport and infer some of the mechanisms that are responsible for their evolution along their lifetime. In this paper, a new approach is proposed to estimate Q2 budgets from radar observations within precipitating areas at the scale of the measurements, that is, either convective scale or mesoscale, depending on the selected retrieval zone. This approach relies upon a new analysis of the radar reflectivity based on the concept of the traditional velocity–azimuth display (VAD) analysis. From the following five steps, Q2 is deduced from velocity and reflectivity fields: (i) mixing ratio retrieval using empirical relations, (ii) radial wind analysis using the VAD analysis, (iii) radar reflectivity analysis using a new analysis called reflectivity–azimuth display (RAD), (iv) retrieval of mixing ratio derivatives, and (v) Q2 retrieval. The originality and the main interest of the present approach with respect to previous studies rely on the fact it uses radar data alone and is based on a relatively low-cost analysis, allowing future systematic application on large datasets. In the present paper, this analysis is described and its robustness is evaluated and illustrated on three cases observed during the African Monsoon Multidisciplinary Analyses (AMMA) special observing period (SOP) field experiment (15 June–15 September) by means of the Recherche sur les Orages et Nuages par un Système Associé de Radars Doppler (RONSARD) radar. Results are analyzed in terms of the convective or stratiform character of observed precipitation.
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Cazelles, B., et D. Fontvieille. « Modélisation d'un écosystème lotique pollué par une charge organique : prise en compte de l'hydrodynamique et des mécanismes de transport ». Revue des sciences de l'eau 2, no 2 (12 avril 2005) : 183–209. http://dx.doi.org/10.7202/705028ar.
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L'article décrit la partie hydrophysique d'un modèle écologique de simulation des transferts de carbone organique dans un cours d'eau pollué par le rejet d'une porcherie. Cette partie est constituée d'un modèle hydrodynamique inspiré du modèle de Saint-Venant, couplé à un modèle de transport basé sur l'équation classique de convection-diffusion. Ces modèles sont appliqués à un écoulement unidirectionnel, non uniforme et non stationnaire. Les équations de ces deux modèles sont résolues par une méthode aux différences finies utilisant des schémas implicites. L'ajustement des paramètres est réalisé à partir de résultats d'expériences de traçage à la rhodamine. Appliqués au carbone organique dissous de l'Albenche, les modèles montrent l'extrême étalement des nuages dû aux seuls phénomènes physiques. L'une des interprétations possibles de l'écart entre les valeurs expérimentales et les valeurs calculées au niveau de la station aval, peut être l'importance de la consommation du carbone par les biocoenoses benthiques.
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Shah, Zahir, Anwar Saeed, Imran Khan, Mahmoud M. Selim, Ikramullah et Poom Kumam. « Numerical modeling on hybrid nanofluid (Fe3O4+MWCNT/H2O) migration considering MHD effect over a porous cylinder ». PLOS ONE 16, no 7 (1 juillet 2021) : e0251744. http://dx.doi.org/10.1371/journal.pone.0251744.
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The free convective hybrid nanofluid (Fe3O4+MWCNT/H2O) magnetized non-Darcy flow over a porous cylinder is examined by considering the effects constant heat source and uniform ambient magnetic field. The developed coupled PDEs (partial differential equations) are numerically solved using the innovative computational technique of control volume finite element method (CVFEM). The impact of increasing strength of medium porousness and Lorentz forces on the hybrid nanofluid flow are presented through contour plots. The variation of the average Nusselt number (Nuave) with the growing medium porosity, buoyancy forces, radiation parameter, and the magnetic field strength is presented through 3-D plots. It is concluded that the enhancing medium porosity, buoyancy forces and radiation parameter augmented the free convective thermal energy flow. The rising magnetic field rises the temperature of the inner wall more drastically at a smaller Darcy number. An analytical expression for Nusselt number (Nuave) is obtained which shows its functional dependence on the pertinent physical parameters. The augmenting Lorentz forces due to the higher estimations of Hartmann retard the hybrid nanoliquid flow and hence enhance the conduction.
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Miller, Paul W., et Thomas L. Mote. « A Climatology of Weakly Forced and Pulse Thunderstorms in the Southeast United States ». Journal of Applied Meteorology and Climatology 56, no 11 (novembre 2017) : 3017–33. http://dx.doi.org/10.1175/jamc-d-17-0005.1.
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AbstractWeakly forced thunderstorms (WFTs), convection forming in the absence of a synoptic forcing mechanism and its associated shear regime, are the dominant convective mode during the warm season in the southeast United States. This study uses 15 yr (2001–15) of warm-season (May–September) composite reflectivity images from 30 WSR-88D sites in the southeastern United States to detect WFTs and pulse thunderstorms, defined as WFTs associated with a severe weather event. Thunderstorms were identified as regions of contiguous reflectivities greater than or equal to 40 dBZ using connected neighborhoods labeling. Ward’s clustering was then performed upon the duration, size, strength, initiation time, and solidity of the approximately 1 900 000 thunderstorms. Of the 10 clusters of morphologically similar storms, five groups, containing 885 496 thunderstorms, were designated as WFTs. In line with previous work, WFT development mirrors landscape features, such as the Appalachian Mountains and Mississippi Delta. However, the large sample size also reveals more subtle nuances to the spatial distribution, such as decreases over river valleys and increases along the Atlantic fall line. The most active pulse thunderstorm region, the Blue Ridge Mountains, was displaced from the overall WFT maximum: the Florida Peninsula and Gulf Coast. Most pulse thunderstorms were associated with larger moisture values, particularly in the midlevels, which supported larger and longer-lasting WFT complexes. Synoptically, two distinct modes of variability yielded WFT-favorable environments: the intrusion of the Bermuda high from the east and the expansion of high pressure over the southern Great Plains from the west.
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Sheng He. « Exploring Medium and Low-Temperature Convective Geothermal Resources Through Controlled Source Audio Magnetotelluric Mothod ». Journal of Electrical Systems 20, no 7s (4 mai 2024) : 46–57. http://dx.doi.org/10.52783/jes.3248.
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Medium and low-temperature convective geothermal resources are a crucial component of China's geothermal wealth, primarily concentrated in the eastern coastal regions. To maximize the utilization of these resources, geophysical surveys are essential, with controlled source audio magnetotelluric(CSAMT) being a prominent and effective method employed in geothermal resource assessments. This study focuses on applying CSAMT to survey specific geothermal sites, including the Xiu Yan Gou Tang Hot Spring, Fengcheng Gou Tang Hot Spring, and Hai Cheng Xi Huang di Geothermal Field. The results obtained through this method provide detailed insights into the distribution of both deep and shallow thermal storage spaces within these fields, shedding light on the intricate thermal circulation systems associated with them. These findings serve as a reliable foundation for planning and executing further geothermal resource development projects. CSAMT emerges as a comprehensive tool for understanding the nuances of medium and low-temperature convective geothermal resources.
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Wenxin Ma, Jun Pan, Sheng He,. « Exploring Medium and Low-Temperature Convective Geothermal Resources in Eastern China Through Acoustic-Emission Geomagnetic Bathymetry ». Journal of Electrical Systems 20, no 4s (8 avril 2024) : 416–31. http://dx.doi.org/10.52783/jes.1927.
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Medium and low-temperature convective geothermal resources are a crucial component of China's geothermal wealth, primarily concentrated in the eastern coastal regions. To maximize the utilization of these resources, geophysical surveys are essential, with acoustic-emission geomagnetic bathymetry being a prominent and effective method employed in geothermal resource assessments. This study focuses on applying acoustic-emission geodetic bathymetry to survey specific geothermal sites, including the Xiu Yan Gou Tang Hot Spring, Fengcheng Gou Tang Hot Spring, and Hai Cheng Xi Huang di Geothermal Field. The results obtained through this method provide detailed insights into the distribution of both deep and shallow thermal storage spaces within these fields, shedding light on the intricate thermal circulation systems associated with them. These findings serve as a reliable foundation for planning and executing further geothermal resource development projects. Acoustic-emission geomagnetic bathymetry emerges as a comprehensive tool for understanding the nuances of medium and low-temperature convective geothermal resources.
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Kubicki, Agnès, et Pierre-Antoine Bois. « Structure double diffusive des équations de la convection en air humide saturé avec application à l'air nuageux ». Comptes Rendus de l'Académie des Sciences - Series IIB - Mechanics-Physics-Astronomy 328, no 4 (avril 2000) : 317–22. http://dx.doi.org/10.1016/s1287-4620(00)00129-0.
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Cintineo, John L., Michael J. Pavolonis, Justin M. Sieglaff, Anthony Wimmers, Jason Brunner et Willard Bellon. « A Deep-Learning Model for Automated Detection of Intense Midlatitude Convection Using Geostationary Satellite Images ». Weather and Forecasting 35, no 6 (décembre 2020) : 2567–88. http://dx.doi.org/10.1175/waf-d-20-0028.1.
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AbstractIntense thunderstorms threaten life and property, impact aviation, and are a challenging forecast problem, particularly without precipitation-sensing radar data. Trained forecasters often look for features in geostationary satellite images such as rapid cloud growth, strong and persistent overshooting tops, U- or V-shaped patterns in storm-top temperature (and associated above-anvil cirrus plumes), thermal couplets, intricate texturing in cloud albedo (e.g., “bubbling” cloud tops), cloud-top divergence, spatial and temporal trends in lightning, and other nuances to identify intense thunderstorms. In this paper, a machine-learning algorithm was employed to automatically learn and extract salient features and patterns in geostationary satellite data for the prediction of intense convection. Namely, a convolutional neural network (CNN) was trained on 0.64-μm reflectance and 10.35-μm brightness temperature from the Advanced Baseline Imager (ABI) and flash-extent density (FED) from the Geostationary Lightning Mapper (GLM) on board GOES-16. Using a training dataset consisting of over 220 000 human-labeled satellite images, the CNN learned pertinent features that are known to be associated with intense convection and skillfully discriminated between intense and ordinary convection. The CNN also learned a more nuanced feature associated with intense convection—strong infrared brightness temperature gradients near cloud edges in the vicinity of the main updraft. A successive-permutation test ranked the most important predictors as follows: 1) ABI 10.35-μm brightness temperature, 2) ABI GLM flash-extent density, and 3) ABI 0.64-μm reflectance. The CNN model can provide forecasters with quantitative information that often foreshadows the occurrence of severe weather, day or night, over the full range of instrument-scan modes.
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Tahiananirina, Razafindralambo Hasina, RAZAFIMANDIMBY Honoré, Rabeharisoa Jean Marc et RATIARISON Adolphe. « Change In Statistical Distribution Of Annual Accumulations Of Convective Precipitation In The Lower Betsiboka Valley ». International Journal of Progressive Sciences and Technologies 41, no 2 (30 novembre 2023) : 588. http://dx.doi.org/10.52155/ijpsat.v41.2.5704.
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In this article, we examine how the global warming of the atmosphere affects the annual convective precipitation accumulations in the lower Betsiboka valley. We specifically delve into a lesser-discussed yet equally crucial aspect of climate change, the change in statistical distribution. The statistical analyses unequivocally revealed significant breaks in statistical distributions, occurring between 1985 and 1987. This led us to adjust the empirical distributions both before and after the observed break using Gaussian models. By grasping these nuances of climate change, we can gain a deeper understanding of the challenges that lie ahead and develop strategies to mitigate the negative effects while capitalizing on the opportunities that come our way.
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Cai, Huaqing, Wen-Chau Lee, Tammy M. Weckwerth, Cyrille Flamant et Hanne V. Murphey. « Observations of the 11 June Dryline during IHOP_2002—A Null Case for Convection Initiation ». Monthly Weather Review 134, no 1 (1 janvier 2006) : 336–54. http://dx.doi.org/10.1175/mwr2998.1.
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Abstract The detailed analysis of the three-dimensional structure of a dryline observed over the Oklahoma panhandle during the International H2O Project (IHOP_2002) on 11 June 2002 is presented. High-resolution observations obtained from the National Center for Atmospheric Research Electra Doppler Radar (ELDORA), S-band dual-polarization Doppler radar (S-Pol), water vapor differential absorption lidar (DIAL) Lidar pour l'Etude des Interactions Aérosols Nuages Dynamique Rayonnement et du Cycle de l'Eau (LEANDRE II; translated as Lidar for the Study of Aerosol–Cloud–Dynamics–Radiation Interactions and of the Water Cycle) as well as Learjet dropsondes are used to reveal the evolution of the dryline structure during late afternoon hours when the dryline was retreating to the northwest. The dryline reflectivity shows significant variability in the along-line direction. Dry air was observed to overrun the moist air in vertical cross sections similar to a density current. The updrafts associated with the dryline were 2–3 m s−1 and were able to initiate boundary-layer-based clouds along the dryline. The formation of this dryline was caused by high equivalent potential temperature air pushing northwestward toward a stationary front in the warm sector. Middle-level clouds with radar reflectivity greater than 18 dBZe near the dryline were detected by ELDORA. A roll boundary, which was associated with larger convergence and moisture content, was evident in the S-Pol data. It is found that the instability parameters most favorable for convection initiation were actually associated with the roll boundary, not the dryline. A storm was initiated near the roll boundary probably as a result of the combination of the favorable instability parameters and stronger upward forcing. It is noted that both the 11 June 2002 dryline and the roll boundary presented in this paper would not be identified if the special datasets from IHOP_2002 were not available. Although all model runs [fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5), Meso Eta, and Rapid Update Cycle (RUC)] suggested deep convection over the Oklahoma panhandle and several cloud lines were observed near the dryline, the dryline itself did not initiate any storms. The reasons why the dryline failed to produce any storm inside the IHOP_2002 intensive observation region are discussed. Both synoptic-scale and mesoscale conditions that were detrimental to convection initiation in this case are investigated in great detail.
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Derbal, Djamila, Mohamed Bouzit et Fayçal Bouzit. « Effect of the inclination angle of finned cylinder over a BFS on the MHD behavior in the presence of a nanofluid ». Metallurgical and Materials Engineering 28, no 2 (12 mars 2022) : 203–21. http://dx.doi.org/10.30544/760.
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The present numerical study is based on the forced magnetohydrodynamic (MHD) convection of a ferrofluid through a backward facing step (BFS). A cylinder with two fixed fins and fixed dimensions is implanted inside fluid. The dimensionless governing equations have been solved using the multigrid finite element method. Several parameters were considered, such as the Hartmann number 0≤ Ha ≤100, the magnetic field inclination angle 0°≤ ɣ ≤90°, the Reynolds number 10≤ Re ≤200, the nanoparticle volume fraction 0%≤ φ ≤10%, and the fins inclination angle 0°≤ a ≤180°. The results have shown that the presence of the fins improves the heat transfer, especially at the position a = 90° where the Nuave number increases with a ratio of 113% for Re = 200.
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Droegemeier, Kelvin K. « Transforming the sensing and numerical prediction of high-impact local weather through dynamic adaptation ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 367, no 1890 (16 décembre 2008) : 885–904. http://dx.doi.org/10.1098/rsta.2008.0211.
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Mesoscale weather, such as convective systems, intense local rainfall resulting in flash floods and lake effect snows, frequently is characterized by unpredictable rapid onset and evolution, heterogeneity and spatial and temporal intermittency. Ironically, most of the technologies used to observe the atmosphere, predict its evolution and compute, transmit or store information about it, operate in a static pre-scheduled framework that is fundamentally inconsistent with, and does not accommodate, the dynamic behaviour of mesoscale weather. As a result, today's weather technology is highly constrained and far from optimal when applied to any particular situation. This paper describes a new cyberinfrastructure framework, in which remote and in situ atmospheric sensors, data acquisition and storage systems, assimilation and prediction codes, data mining and visualization engines, and the information technology frameworks within which they operate, can change configuration automatically, in response to evolving weather. Such dynamic adaptation is designed to allow system components to achieve greater overall effectiveness, relative to their static counterparts, for any given situation. The associated service-oriented architecture, known as Linked Environments for Atmospheric Discovery (LEAD), makes advanced meteorological and cyber tools as easy to use as ordering a book on the web. LEAD has been applied in a variety of settings, including experimental forecasting by the US National Weather Service, and allows users to focus much more attention on the problem at hand and less on the nuances of data formats, communication protocols and job execution environments.
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Ren, Jiyun, Zunlong Jin, Xiaole Huang, Srdjan Belošević, Aleksandar Milićević, Ivan Tomanović, Lei Deng et Defu Che. « A lattice Boltzmann method for two-phase nanofluid under variable non-uniform magnetic fields ». Journal of Applied Physics 132, no 17 (7 novembre 2022) : 174703. http://dx.doi.org/10.1063/5.0118137.
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In this study, a new lattice Boltzmann scheme is developed for the two-phase CuO–H2O nanomagnetic fluid (ferrofluid) under a non-uniform variable magnetic field. It introduces the second-order external force term including both MHD (magnetohydrodynamic) and FHD (ferrohydrodynamic) into the lattice Boltzmann equation. The square cavity and a heat source inside the circular cavity with natural convections of nanofluid are investigated, respectively. The effects of Rayleigh number ( Ra), the volume fraction of nanoparticles ( φ), Hartmann number ( Ha) generated by MHD, and magnetic number ( MnF) generated by FHD on the nanofluid flow and heat transfer properties, as well as the total entropy generation ( Stot) have been examined. The two-phase lattice Boltzmann model has demonstrated that it is more accurate in predicting the heat transfer of nanofluid than the single-phase model. Consequently, the results calculated by the single-phase and the two-phase methods show the opposite trends. It indicates that nanoparticles could enhance heat transfer with maximum values of 1.78% or deteriorate heat transfer with maximum values of 14.84%. The results of the circular cavity show that Ha could diminish the flow intensity, whereas MnF could enhance it. The average Nusselt number ( Nuave) on the heat source decreases with the augments of Ha and MnF but increases with Ra. An optimal volume fraction φ = 1% for heat transfer is obtained except for Ra = 104. Stot achieves the maximum value at Ha = 40 when Ra = 105. It increases with a rise of Ra but reduces with an increment of φ.
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Fereidooni, Jalil. « Free convection analysis for a nanofluid in a wavy porous domain subject to shape of nanoparticle and internal heat generation ». International Journal of Modern Physics B, 17 juin 2023. http://dx.doi.org/10.1142/s0217979224501947.
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Natural convection takes up the attention of researchers due to its expansive industrial and engineering utilizations i.e., heat exchangers and electronic cooling. In this work, free convection of Cu-H2O nanoliquid flow and heat transfer (HT) in porous circular wavy domain under the internal heat generation has been perused by finite element method (FEM). The shape factor of nanomaterials is also considered. The influences of active factors like Rayleigh number Ra, nanofluid concentration, wavy wall’s contraction ratio A, number of undulations D, and shape factor of nanomaterials m are explored on flow and HT specifications. Moreover, the correlations for average Nusselt number Nuave have been attained with regard to impressive parameters of current study. Findings show that Nuave soars with soaring nanofluid concentration and nanoparticles’ shape factor. Further, the outcomes characterize that Nuave may lessen up to 15.11% and 9.95% by detracting A from 0.1 to 0.3 and by mounting D from 4 to 12, respectively.
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Al-damook, Amer, et Itimad D. J. Azzawi. « MHD Natural Convection of Water in An L-Shaped Container Filled with An Aluminium Metal Foam ». Journal of Heat Transfer, 11 octobre 2022. http://dx.doi.org/10.1115/1.4055942.
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Abstract The current research employed computational simulation to assess magnetohydrodynamics (MHD) natural convection in an L-shaped container with metal foam, which has a variety of engineering applications such as electronic systems, heat exchangers, solar collectors and nuclear energy. As a result, the originality of this study is employing numerical simulation together with response surface methodology (RSM) to investigate the optimal natural convection in an L-shape container filled with metal foam with and without MHD. The influence of varied aspect ratios (AR), tilted angles of the container (θ), Hartmann number (Ha) and porosities (F) on the cooling rate concerning average Nusselt number (Nuave), Nusselt number enhancement (NNE), surface temperature (Ts) and entropy generation (S) were evaluated. According to the findings of this study, no effect of the MHD and θ on the Nuave, Ts and S except for porosity of 0.9. Furthermore, the Nuave enhances while the Ts and S reduce as the aspect ratio of horizontal (ARh), vertical (ARv), and Darcy number (Da) increases. The multi-objective optimisation methodology for the highest desirability is accomplished as ARv, ARh and Da are 0.9, 0.9 and 10-1 respectively. In this case, the maximum increase in NNE was 26.7 times with the greatest reductions in Ts and S being 59% and 97% respectively compared to the unfavourable design data. Thus, this combination investigation of the CFD and RSM yields a novel approach and valuable recommendations for the optimum cooling L-shaped container design.
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Sheikholeslami, M., et Houman B. Rokni. « Magnetohydrodynamic CuO–Water Nanofluid in a Porous Complex-Shaped Enclosure ». Journal of Thermal Science and Engineering Applications 9, no 4 (19 avril 2017). http://dx.doi.org/10.1115/1.4035973.
Texte intégralRésumé :
Steady nanofluid convective flow in a porous cavity is investigated. Darcy and Koo–Kleinstreuer–Li (KKL) models are considered for porous media and nanofluid, respectively. The solutions of final equations are obtained by control volume-based finite element method (CVFEM). Effective parameters are CuO–water volume fraction, number of undulations, and Rayleigh and Hartmann numbers for porous medium. A correlation for Nuave is presented. Results depicted that heat transfer improvement reduces with the rise of buoyancy forces. Influence of adding nanoparticle augments with augment of Lorentz forces. Increasing Hartmann number leads to decrease in temperature gradient.
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Hosseinjani, Ali Akbar, et Amir H. Roohi. « Immersed boundary method for MHD unsteady natural convection around a hot elliptical cylinder in a cold rhombus enclosure filled with a nanofluid ». SN Applied Sciences 3, no 2 (février 2021). http://dx.doi.org/10.1007/s42452-021-04221-3.
Texte intégralRésumé :
AbstractIn this study, the numerical investigation of the natural convection heat transfer around a hot elliptical cylinder inside a cold rhombus enclosure filled with a nanofluid in the presence of a uniform magnetic field is conducted. An immersed boundary method as a computational tool has been extended and applied to solve the problem. The influence of various parameters such as cylinder diameters (a, b), Hartmann number (Ha = 0, 50 and 100), nanofluid volume fraction ($$\varphi = 0 , 2.5\% and 5\%$$ φ = 0 , 2.5 % a n d 5 % ), and Rayleigh number (Ra = 103, 104, 105, 106, and 107) has been studied. Streamlines and isotherms contours as well as average Nusselt number have been specified for different modes. An equation for the average Nusselt number as a function of mentioned parameters is presented in this paper. The results show that at lower Ra numbers of Ra = 103 and 104, the magnetic field effect is negligible. However, at higher Rayleigh numbers, the average Nusselt number (Nuave) decreases with the increasing Ha number. The maximum decrease in Nuave at Ra = 105, 106 and 107are calculated −8.15%, −23.4% and −27.3%, respectively. An asymmetry-unsteady flow is observed at $${\text{Ra}} = 10^{7}$$ Ra = 10 7 for Ha = 0. However, at higher Ha numbers a steady-symmetrical flow is formed.
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Maboa, Relotilwe, Kowiyou Yessoufou, Solomon Tesfamichael et Yegnanew A. Shiferaw. « Sizes of atmospheric particulate matters determine the outcomes of their interactions with rainfall processes ». Scientific Reports 12, no 1 (19 octobre 2022). http://dx.doi.org/10.1038/s41598-022-22558-6.
Texte intégralRésumé :
AbstractEnvironmental sustainability remains at risk, given the coupled trends of economic development with air pollution. The risk is even greater in the water-stressed world, given the potential suppression effects of air pollutants on rain formation. Here, since these suppression effects remain debated, we tested the hypothesis that air pollutants suppress rainfall in the water-stressed South Africa. This was done by fitting generalized linear models to a 21-year historical dataset of rainfall and air pollutants. We found that some gaseous pollutants and PM10 show a significant negative correlation with rainfall, perhaps due to the temperature inversion they cause, which might prevent the upward rise of humid air and convective clouds to grow high enough to produce rain. Surprisingly, as opposed to PM10, we found a rather positive significant effect of PM2.5. Altogether, our study supports the hypothesis of rain prevention by pollutants but provides some nuances that are dependent on the size of air particle matters. To achieve environmental sustainability while growing the economy, we can only rely on emission purification technologies to strike this trade-off.
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Irshad, Kashif, Amjad Ali Pasha, Mohammed K. Al Mesfer, Mohd Danish, Manoj Kumar Nayak, Ali Chamkha et Ahmed M. Galal. « Second law and thermal analyses of non-Newtonian nanofluid double-diffusive natural convection within a two-hot-baffles-equipped C-shaped domain impacted by magnetic field ». International Journal of Numerical Methods for Heat & ; Fluid Flow, 7 novembre 2023. http://dx.doi.org/10.1108/hff-02-2023-0089.
Texte intégralRésumé :
Purpose The entropy and thermal behavior analyses of non-Newtonian nanofluid double-diffusive natural convection inside complex domains may captivate a bunch of scholars’ attention because of the potential utilizations that they possess in modern industries, for example, heat exchangers, solar energy collectors and cooling of electronic apparatuses. This study aims to investigate the second law and thermal behavior of non-Newtonian double-diffusive natural convection (DDNC) of Al2O3-H2O nanofluid within a C-shaped cavity emplacing two hot baffles and impacted by a magnetic field. Design/methodology/approach For the governing equations of the complicated and practical system with all considered parameters to be solved via a formidable numerical approach, the finite element method acts as an approach to achieving the desired solution. This method allows us to gain a detailed solution to the studied geometry. Findings This investigation has been executed for the considered parameters of range, such as power-law index, baffle length, Lewis number, buoyancy ratio, Hartmann number and Rayleigh number. The main results reveal that isothermal and concentration lines are significantly more distorted, indicating intensified concentration and temperature distributions because of the growth of baffle length (L). Nuave decreases by 8.4% and 0.8% while it enhances by 49.86% and 33.87%, respectively, because of growth in the L from 0.1 to 0.2 and 0.2 to 0.3. Originality/value Such a comprehensive study on the second law and thermal behavior of DDNC of Al2O3-H2O nanofluid within a C-shaped cavity emplacing two hot baffles and impacted by magnetic field has not yet been carried out.
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Hosseinzadeh, Kh, Elham Montazer, Mohammad Behshad Shafii et D. D. Ganji. « Heat transfer hybrid nanofluid (1-Butanol/MoS2–Fe3O4) through a wavy porous cavity and its optimization ». International Journal of Numerical Methods for Heat & ; Fluid Flow ahead-of-print, ahead-of-print (23 décembre 2020). http://dx.doi.org/10.1108/hff-07-2020-0442.
Texte intégralRésumé :
Purpose The purpose of this paper is to investigate natural convection in a porous wavy-walled enclosure that is including a cylinder cavity in the middle of it and filled with a hybrid nanofluid contains 1-Butanol as the base fluid and MoS2–Fe3O4 hybrid nanoparticles. Design/methodology/approach The domain of interest is bounded by constant temperature horizontal corrugated surfaces and isothermal vertical flat surfaces. The numerical outputs are explained in the type of isotherms, streamline and average Nusselt number with variations of the Rayleigh number, Hartmann number, nanoparticle shape factor and porosity of the porous medium. For solving the governing equations, the finite element method has been used. Findings The results show that Nuave is proportional to Rayleigh and nanoparticle shape factor directly as well as it has an inverse relation with Hartmann and porosity. The obtained results reveal that the shape factor parameter has a significant effect on the heat transfer performance, which shows a 55.44% contribution on the average Nusselt number. Originality/value As a novelty, to maximize the heat transfer performance in a corrugated walls enclosure, the optimal parameters have intended by using the response surface and Taguchi methods. Additionally, an accurate correlation for the average Nusselt number is developed with sensibly great precision.
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Lee, Y. J., P. S. Lee et S. K. Chou. « Enhanced Thermal Transport in Microchannel Using Oblique Fins ». Journal of Heat Transfer 134, no 10 (7 août 2012). http://dx.doi.org/10.1115/1.4006843.
Texte intégralRésumé :
Sectional oblique fins are employed, in contrast to continuous fins in order to modulate the flow in microchannel heat sinks. The breakage of a continuous fin into oblique sections leads to the reinitialization of the thermal boundary layer at the leading edge of each oblique fin, effectively reducing the boundary layer thickness. This regeneration of entrance effects causes the flow to always be in a developing state, thus resulting in better heat transfer. In addition, the presence of smaller oblique channels diverts a small fraction of the flow into adjacent main channels. The secondary flows created improve fluid mixing, which serves to further enhance heat transfer. Both numerical simulations and experimental investigations of copper-based oblique finned microchannel heat sinks demonstrated that a highly augmented and uniform heat transfer performance, relative to the conventional microchannel, is achievable with such a passive technique. The average Nusselt number, Nuave, for the copper microchannel heat sink which uses water as the working fluid can increase as much as 103%, from 11.3 to 22.9. Besides, the augmented convective heat transfer leads to a reduction in maximum temperature rise by 12.6 °C. The associated pressure drop penalty is much smaller than the achieved heat transfer enhancement, rendering it as an effective heat transfer enhancement scheme for a single-phase microchannel heat sink.
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« Influences of CAPE on Hail Production in Simulated Supercell Storms ». Journal of the Atmospheric Sciences 79, no 1 (janvier 2022) : 179–204. http://dx.doi.org/10.1175/jas-d-21-0054.1.
Texte intégralRésumé :
Abstract Lasting updrafts are necessary to produce severe hail; conventional wisdom suggests that extremely large hailstones require updrafts of commensurate strength. Because updraft strength is largely controlled by convective available potential energy (CAPE), one would expect environments with larger CAPE to be conducive to storms producing larger hail. By systematically varying CAPE in a horizontally homogeneous initial environment, we simulate hail production in high-shear, high-instability supercell storms using Cloud Model 1 and a detailed 3D hail growth trajectory model. Our results suggest that CAPE modulates the updraft’s strength, width, and horizontal wind field, as well as the liquid water content along hailstones’ trajectories, all of which have a significant impact on final hail sizes. In particular, hail sizes are maximized for intermediate CAPE values in the range we examined. Results show a non-monotonic relationship between the hailstones’ residence time and CAPE due to changes to the updraft wind field. The ratio of updraft area to southerly wind speed within the updraft serves as a proxy for residence time. Storms in environments with large CAPE may produce smaller hail because the in-updraft horizontal wind speeds become too great, and hailstones are prematurely ejected out of the optimal growth region. Liquid water content (LWC) along favorable hailstone pathways also exhibits peak values for intermediate CAPE values, owing to the horizontal displacement across the midlevel updraft of moist inflow air from differing source levels. In other words, larger CAPE does not equal larger hail, and storm-structural nuances must be examined.