1,720,990 research outputs found
Potential-temperature variance budget in a saturated coastal-fog environment
Full text linkIn this work, we explore the intricacies of the potential-temperature variance budget in coastal fog. We propose an improvement to the theoretical framework of the budget, whereby we include the heat exchange due to water-phase changes. We then show this framework's consistency with a real-world case study from the Coastal Fog (C-FOG) Research Program. Results show that the presence of intermittent energy bursts is driven by the sudden turbulent injection of heat into the environment caused by the condensation of water vapour, and the improved theoretical framework proves satisfactory in detailing the observed process. The heat excess is transported vertically, creating a two-term balance of high-order moments. A bulk parametrization of this balance is also proposed to provide a simplified representation of the phase-change process and suggest that it could be used for operational purposes. Finally, the length-scales of the processes are evaluated from the parametrizations. The analysis indicates that the scales of the phase change of water vapour are consistent with the buoyancy production and Taylor scales.We propose an improvement to the theoretical framework of the potential-temperature variance theta ' 2 {\theta}<^>{\prime 2} budget under fog conditions, whereby we include the heat exchange due to water-phase changes, which is responsible for sudden, localized turbulent injections of heat into the environment (see figure). The heat excess is transported vertically, creating a two-term balance of high-order moments that we parametrize using the aerodynamic formulations of the sensible and latent heat fluxes. Finally, the length-scales of the processes are evaluated, indicating that the phase change of water vapour is consistent with the buoyancy-production and Taylor scales. imag
Large-eddy simulation analyses of heated urban canyon facades
Full text linkThermal convective flows are common phenomena in real urban canyons and strongly affect the mechanisms of pollutant removal from the canyon. The present contribution aims at investigating the complex interaction between inertial and thermal forces within the canyon, including the impacts on turbulent features and pollutant removal mechanisms. Large-eddy simulations reproduce infinitely long square canyons having isothermal and differently heated facades. A scalar source on the street mimics the pollutant released by traffic. The presence of heated facades triggers convective flows which generate an interaction region around the canyon-ambient interface, characterised by highly energetic turbulent fluxes and an increase of momentum and mass exchange. The presence of this region of high mixing facilitates the pollutant removal across the interface and decreases the urban canopy drag. The heating-up of upwind facade determines favourable convection that strengthens the primary internal vortex and decreases the pollutant concentration of the whole canyon by 49% compare to the isothermal case. The heating-up of the downwind facade produces adverse convection counteracting the wind-induced motion. Consequently, the primary vortex is less energetic and confined in the upper-canyon area, while a region of almost zero velocity and high pollution concentration (40% more than the isothermal case) appears at the pedestrian level. Finally, numerical analyses allow a definition of a local Richardson number based on in-canyon quantities only and a new formulation is proposed to characterise the thermo-dynamics regimes
Misure e dati per comprendere i fenomeni
No full textIl concetto di misura si è più volte evoluto. Oggi, ciò che quantifichiamo attraverso un numero è il risultato di un procedimento che comprende aspetti di mera "misurazione in campo", di modellistica computazionale e interpretazione fisica. Un lavoro complesso per il quale servono scienza, rete e organizzazione
Characteristic Scales for Turbulent Exchange Processes in a Real Urban Canopy
Full text linkAn experimental field campaign is designed to unveil mechanisms responsible for turbulent exchange processes when mechanical and thermal effects are entwined. The focus is an urban street canyon with a mean aspect ratio H/W of 1.65 in the business centre of a mid-size Italian city (H is the mean building height and W is the mean canyon width). The exchange processes can be characterized by time scales and time-scale ratios specific to either mechanical or thermal process. Time scales describe the mixing caused by momentum and heat exchange within different canyon layers, while their rates are surrogates of their efficacy. Given that homogeneous mixing does not always occur within the canyon, several time scales are estimated at different levels, showing that mechanical and thermal processes may both contribute to enhance mixing. By computing mechanical time scales, it is found that the fastest mixing occurs at the canyon rooftop level for perpendicular or oblique wind directions, while slow mixing occurs for parallel directions. Thermal processes are faster than the mechanical ones and are particularly efficient for perpendicular wind directions. By calculating the time-scale ratios, exchange processes are found to facilitate mixing for most wind directions and to regulate the pollutant-concentration variability in the canyon. This variability can be associated with the local-circulation regime, demarcated as thermally driven or inertially driven using a buoyancy parameter, i.e., the ratio between thermal and inertial forcings. Using this approach, a generalization of the results is proposed, enabling the extension of the current investigation to different street-canyon aspect ratios
Review on heatwaves: a risk perspective
Full text linkCurrent anthropogenic climate change is increasing the occurrence and magnitude of heatwaves causing closely interconnected and interdependent risks across multiple domains, such as environmental and human health, water and food security, etc. The following systematic literature review synthesizes the state of the art concerning risks related to heatwaves by analyzing 1459 publications. Since risks arise from the interaction of hazard, exposure, and vulnerability, publications were first classified by risk components and then further categorized by research fields: healthcare, society, ecosystem, agriculture, infrastructure, and heritage. The analysis allowed the identification of gaps in the current research with implications for policies and practical applications of risk assessments. First, only 3.1% of the revised literature integrates all three components in risk assessments. Second, most of the literature provides average risks over several heatwave events, thus neglecting critical factors like heatwave magnitude and duration. Third, the absence of standardized indices for identifying and classifying heatwaves hinders effective comparisons of results within the same field. It is recommended that future studies in the same field adopt a common methodology and that the above gaps are taken into account as this would enable building more robust and coherent scientific evidence while reducing ambiguities and uncertainties in risk estimates. Decisionmakers may otherwise struggle to develop effective heatwave adaptation and mitigation strategies if risk assessments are inconsistent or unreliable, and fail to account for risk interdependencies across different domains. More research is needed to develop quantitative frameworks that estimate heatwave risks by summing contributions from each affected domain. This is particularly important, as most of the papers reviewed only focused on healthcare (61.1%) or ecosystems (16.3%). However, we acknowledge that this literature review may have excluded some relevant studies, such as those in the heritage field, due to the specific search string applied in our methodology
Anabatic flow along a uniformly heated slope studied through large-eddy simulation
Full text linkAnabatic flows are common phenomena in the presence of sloping terrains, which significantly affect the dynamics and the exchange of mass and momentum in the low-atmosphere. Despite this, very few studies in the literature have tackled this topic. The present contribution addresses this gap by utilising high-resolved large-eddy simulations for investigating an anabatic flow in a simplified configuration, commonly used in laboratory experiments. The purpose is to analyse the complex thermo-fluid dynamics and the turbulent structures arising from the anabatic flow near the slope. In such a flow, three main dynamic layers are identified and reported: the conductive layer close to the surface, the convective layer where the most energetic motion develops, and the outer region, which is almost unperturbed. The analysis of instantaneous fields reveals the presence of thermal plumes, which are stable turbulent structures enhancing vertical transport and mixing of momentum and temperature. Such structures are generated by thermal instabilities in the conductive layer that trigger the rise of the plumes above them. Their evolution along the slope is described, identifying three regions responsible for the plumes generation, stabilisation, and merging. To the best of the authors’ knowledge, this is the first numerical experiment describing the along-slope behaviour of the thermal plumes in the convective layer
Convezione atmosferica
Full text linkLa convezione è una forma di trasporto di energia e materia caratteristica dei fluidi, attribuita all'azione del campo gravitazionale terrestre in risposta ad una variazione di densità del fluido. In atmosfera la convezione è sinonimo di moti verticali d’aria, sotto opportune condizioni di riscaldamento del suolo e stratificazione termica (stabilità) dell’atmosfera. I moti convettivi comportano spostamenti verticali delle masse d’aria, con la possibilità di formare nubi di carattere cumuliforme sia di natura precipitativi che non. In questo articolo entreremo nell'ambito della convezione atmosferica spiegandone la fisica e la dinamica, descrivendo in particolare le condizioni in cui i moti convettivi possono svilupparsi. Successivamente ci dedicheremo alla trattazioni delle nubi che si possono originare in seguito alla convezione, partendo dai cumuli di bel tempo fino ad arrivare ai cumulonembi temporaleschi
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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