Articles de revues : « Lagrangian dispersal models »

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Kim, Moonil, Seonghun Lee, Songhee Lee, Koong Yi, Hyung-Sub Kim, Sanghoon Chung, Junmo Chung, Hyun Seop Kim et Tae Kyung Yoon. « Seed Dispersal Models for Natural Regeneration : A Review and Prospects ». Forests 13, n^o 5 (23 avril 2022) : 659. http://dx.doi.org/10.3390/f13050659.

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Natural regeneration in forest management, which relies on artificial planting, is considered a desirable alternative to reforestation. However, there are large uncertainties regarding the natural regeneration processes, such as seed production, seed dispersal, and seedling establishment. Among these processes, seed dispersal by wind must be modeled accurately to minimize the risks of natural regeneration. This study aimed to (1) review the main mechanisms of seed dispersal models, their characteristics, and their applications and (2) suggest prospects for seed dispersal models to increase the predictability of natural regeneration. With improving computing and observation systems, the modeling technique for seed dispersal by wind has continued to progress steadily from a simple empirical model to the Eulerian-Lagrangian model. Mechanistic modeling approaches with a dispersal kernel have been widely used and have attempted to be directly incorporated into spatial models. Despite the rapid development of various wind-dispersal models, only a few studies have considered their application in natural regeneration. We identified the potential attributes of seed dispersal modeling that cause high uncertainties and poor simulation results in natural regeneration scenarios: topography, pre-processing of wind data, and various inherent complexities in seed dispersal processes. We suggest that seed dispersal models can be further improved by incorporating (1) seed abscission mechanisms by wind, (2) spatiotemporally complex wind environments, (3) collisions with the canopy or ground during seed flight, and (4) secondary dispersal, long-distance dispersal, and seed predation. Interdisciplinary research linking climatology, biophysics, and forestry would help improve the prediction of seed dispersal and its impact on natural regeneration.

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Reynolds, A. M. « Incorporating Sweeps and Ejections into Lagrangian Stochastic Models of Spore Trajectories Within Plant Canopy Turbulence : Modeled Contact Distributions Are Heavy-Tailed ». Phytopathology® 102, n^o 11 (novembre 2012) : 1026–33. http://dx.doi.org/10.1094/phyto-01-12-0002.

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The turbulent dispersal of fungal spores within plant canopies is very different from that within atmospheric boundary-layers and closely analogous to dispersal within turbulent mixing-layers. The process is dominated by the presence of large coherent flow structures, high-velocity downdrafts (sweeps) and updrafts (ejections), that punctuate otherwise quiescent flow. Turbulent dispersion within plant canopies is best predicted by Lagrangian stochastic (particle-tracking) models because other approaches (e.g., diffusion models and similarity theory) are either inappropriate or invalid. Nonetheless, attempts to construct such models have not been wholly successful. Accounting for sweeps and ejections has substantially worsened rather than improved model agreement with experimental dispersion data. Here we show how this long-standing difficulty with the formulation of Lagrangian stochastic models can be overcome. The new model is shown to be in good agreement with data from a carefully controlled, well-documented wind-tunnel study of scalar dispersion within plant canopy turbulence. Equally good agreement with this data is obtained using Thomson's (1987) Gaussian model. This bolsters confidence in the application of this simple model to the prediction of spore dispersal within plant canopy turbulence. Contact distributions—the probability distribution function for the distance of viable fungal spore movement until deposition—are predicted to have “heavy” inverse power-law tails. It is known that heavy-tailed contact distributions also characterize the dispersal of spores which pass through the canopy turbulence and enter into the overlying atmospheric boundary-layer. Plant disease epidemics due to the airborne dispersal of fungal spores are therefore predicted to develop as accelerating waves over a vast range of scales—from the within field scale to intercontinental scales. This prediction is consistent with recent analyses of field and historical data for rusts in wheat. Such plant disease epidemics are shown to be governed by space-fractional diffusion equations and by Lévy flights.

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Rühs, Siren, Victor Zhurbas, Inga M. Koszalka, Jonathan V. Durgadoo et Arne Biastoch. « Eddy Diffusivity Estimates from Lagrangian Trajectories Simulated with Ocean Models and Surface Drifter Data—A Case Study for the Greater Agulhas System ». Journal of Physical Oceanography 48, n^o 1 (janvier 2018) : 175–96. http://dx.doi.org/10.1175/jpo-d-17-0048.1.

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AbstractThe Lagrangian analysis of sets of particles advected with the flow fields of ocean models is used to study connectivity, that is, exchange pathways, time scales, and volume transports, between distinct oceanic regions. One important factor influencing the dispersion of fluid particles and, hence, connectivity is the Lagrangian eddy diffusivity, which quantifies the influence of turbulent processes on the rate of particle dispersal. Because of spatial and temporal discretization, turbulence is not fully resolved in modeled velocities, and the concept of eddy diffusivity is used to parameterize the impact of unresolved processes. However, the relations between observation- and model-based Lagrangian eddy diffusivity estimates, as well as eddy parameterizations, are not clear. This study presents an analysis of the spatially variable near-surface lateral eddy diffusivity estimates obtained from Lagrangian trajectories simulated with 5-day mean velocities from an eddy-resolving ocean model (INALT01) for the Agulhas system. INALT01 features diffusive regimes for dynamically different regions, some of which exhibit strong suppression of eddy mixing by mean flow, and it is consistent with the pattern and magnitude of drifter-based eddy diffusivity estimates. Using monthly mean velocities decreases the estimated diffusivities less than eddy kinetic energy, supporting the idea that large and persistent eddy features dominate eddy diffusivities. For a noneddying ocean model (ORCA05), Lagrangian eddy diffusivities are greatly reduced, particularly when the Gent and McWilliams parameterization of mesoscale eddies is employed.

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Theuerkauf, Martin, Anna Kuparinen et Hans Joosten. « Pollen productivity estimates strongly depend on assumed pollen dispersal ». Holocene 23, n^o 1 (16 juillet 2012) : 14–24. http://dx.doi.org/10.1177/0959683612450194.

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Past plant abundance may be reconstructed from pollen data if dispersal distances of pollen and pollen productivities of each taxon are known. Using surface sediment samples from small and medium sized, closed and near circular lakes from lowland Central Europe, we tested the validity of three pollen dispersal models by comparing empirical pollen data from each lake with simulated pollen data derived from applying various pollen dispersal models to vegetation data from rings situated up to 100 km from each site. Pollen assemblages simulated with a Lagrangian stochastic (LS) model best fit real pollen assemblages, simulations with the commonly used Prentice model on pollen dispersal underestimated the amount of pollen arriving from distances larger than 10 km and overestimated the differences in dispersal distances between lighter ( Pinus) and heavier ( Fagus, Picea) pollen grains. The LS model appeared to provide more appropriate simulations. Pollen productivity estimates (PPEs) calculated for the data set showed that the choice of the dispersal model has great impact on the results. If derived with the Prentice model, PPEs for Fagus and Picea are three times higher than with the LS model. Studies on pollen productivities thus need to consider the apparent limitations of the Prentice model. We suggest an alternative approach, which uses simulations instead of the extended R-value model, to calculate PPEs. The approach is flexible in the use of dispersal functions and produced consistent results for two independent data sets from small and medium sized lakes.

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Stephens, S. A., N. Broekhuizen, A. B. Macdiarmid, C. J. Lundquist, L. McLeod et R. Haskew. « Modelling transport of larval New Zealand abalone (Haliotis iris) along an open coast ». Marine and Freshwater Research 57, n^o 5 (2006) : 519. http://dx.doi.org/10.1071/mf06020.

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The dispersal and transport of larval New Zealand abalone Haliotis iris was simulated using coupled two-dimensional hydrodynamic and Lagrangian particle-trajectory models. The aim was to estimate pelagic larval dispersal potential along the open coast, as a starting point from which basic management questions can be made for this recreationally and commercially important species. Larval dispersal was simulated from representative spawning sites under a range of representative hydrodynamic conditions, including wave-induced circulation cells. Larval presence over near-shore reef habitat declined as the energy of the flow field and corresponding larval dispersal and transport increased. Thus, spawning during high-energy conditions will promote dispersal and transport but reduce successful recruitment on near-shore reefs. This indicates that seeding of the adjacent coast is likely to be sporadic, with existing populations necessarily being somewhat self-recruiting. Results suggest that an ideal management system would ensure that adult populations were maintained at intervals of 10–30 km along the coast to maintain larval supply to areas in between. Dispersal characteristics were specific to the release site, and the simulations suggest that marine reserves can be positioned to accordingly achieve desired functions: for example, optimal choices can be made for seeding areas, recruitment or self-maintaining areas.

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Seredyn, Tomasz, Adam Dziubiński et Piotr Jaśkowski. « CFD Analysis of the Fluid Particles Distribution by Means of Aviation Technique ». Transactions on Aerospace Research 2018, n^o 1 (1 mars 2018) : 67–97. http://dx.doi.org/10.2478/tar-2018-0006.

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Abstract The article describes a computational study, using CFD models, of droplet spray dispersal in the wake of a ‘Turbo Kruk’ airplane up to 500 m downstream. The CFD Reynolds-averaged Navier-Stokes (RANS) models use a Lagrangian (droplet phase) and Eulerian (fluid phase) procedure to predict the droplet trajectories trough the turbulent aircraft wake. The methods described in the work have the potential to improve current models for aerial spraying and will help in the development of new spraying procedures. In this study, the CFD models are used to describe the phenomenon of sprays released from atomizers mounted on the plane. A parametric study of the aircraft model examines the effects of crosswind on the aircraft’s vortex structures and the resulting droplet trajectories. The study shows, that such influence is underestimated in the current models. A comparison of the present results to AGDISP predictions is provided.

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Rupolo, Volfango. « A Lagrangian-Based Approach for Determining Trajectories Taxonomy and Turbulence Regimes ». Journal of Physical Oceanography 37, n^o 6 (1 juin 2007) : 1584–609. http://dx.doi.org/10.1175/jpo3038.1.

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Abstract The use of the ratio between the acceleration and velocity time scales y = Ta/Tυ to separate Lagrangian trajectories in homogeneous classes is proposed. In fact, when analyzing subsurface floats data in the Atlantic Ocean and surface drifters data in the world’s ocean basins, it is observed that trajectories having different values of y are characterized by different shapes, correlation, and dispersal properties. In particular, trajectories having similar values of the acceleration and velocity time scales clearly show the influence of eddies and are characterized by an oscillating velocity correlation function. It is shown here that this trajectory screening is a useful procedure to rationalize the analysis of real Lagrangian trajectories and to avoid a mixture of different regimes, when averaging quantities. The mean statistical quantities computed averaging on quasi-homogeneous datasets put in evidence the role of the coherent structures in the dispersion properties, both in time and in the main oceanic current systems. These results are discussed in the context of the parameterization of eddy diffusivity in general circulation models.

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Nilsson, Jenny A. U., Kristofer Döös, Paolo M. Ruti, Vincenzo Artale, Andrew Coward et Laurent Brodeau. « Observed and Modeled Global Ocean Turbulence Regimes as Deduced from Surface Trajectory Data ». Journal of Physical Oceanography 43, n^o 11 (1 novembre 2013) : 2249–69. http://dx.doi.org/10.1175/jpo-d-12-0193.1.

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Abstract A large-scale tool for systematic analyses of the dispersal and turbulent properties of ocean currents and the subsequent separation of dynamical regimes according to the prevailing trajectories taxonomy in a certain area was proposed by Rupolo. In the present study, this methodology has been extended to the analysis of model trajectories obtained by analytical computations of the particle advection equation using the Lagrangian open-source software package Tracing the Water Masses of the North Atlantic and the Mediterranean (TRACMASS), and intercomparisons have been made between the surface velocity fields from three different configurations of the global Nucleus for European Modelling of the Ocean (NEMO) ocean/sea ice general circulation model. Lagrangian time scales of the observed and synthetic trajectory datasets have been calculated by means of inverse Lagrangian stochastic modeling, and the influence of the model field spatial and temporal resolution on the analyses has been investigated. In global-scale ocean modeling, compromises are frequently made in terms of grid resolution and time averaging of the output fields because high-resolution data require considerable amounts of storage space. Here, the implications of such approximations on the modeled velocity fields and, consequently, on the particle dispersion, have been assessed through validation against observed drifter tracks. This study aims, moreover, to shed some light on the relatively unknown turbulent properties of near-surface ocean dynamics and their representation in numerical models globally and in a number of key regions. These results could be of interest for other studies within the field of turbulent eddy diffusion parameterization in ocean models or ocean circulation studies involving long-term coarse-grid model experiments.

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Reynolds, Andy M., et Don R. Reynolds. « Aphid aerial density profiles are consistent with turbulent advection amplifying flight behaviours : abandoning the epithet ‘passive’ ». Proceedings of the Royal Society B : Biological Sciences 276, n^o 1654 (9 septembre 2008) : 137–43. http://dx.doi.org/10.1098/rspb.2008.0880.

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Seminal field studies led by C. G. Johnson in the 1940s and 1950s showed that aphid aerial density diminishes with height above the ground such that the linear regression coefficient, b , of log density on log height provides a single-parameter characterization of the vertical density profile. This coefficient decreases with increasing atmospheric stability, ranging from −0.27 for a fully convective boundary layer to −2.01 for a stable boundary layer. We combined a well-established Lagrangian stochastic model of atmospheric dispersal with simple models of aphid behaviour in order to account for the range of aerial density profiles. We show that these density distributions are consistent with the aphids producing just enough lift to become neutrally buoyant when they are in updraughts and ceasing to produce lift when they are in downdraughts. This active flight behaviour in a weak flier is thus distinctly different from the aerial dispersal of seeds and wingless arthropods, which is passive once these organisms have launched into the air. The novel findings from the model indicate that the epithet ‘passive’ often applied to the windborne migration of small winged insects is misleading and should be abandoned. The implications for the distances traversed by migrating aphids under various boundary-layer conditions are outlined.

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Ospina-Alvarez, A., S. de Juan, J. Alós, G. Basterretxea, A. Alonso-Fernández, G. Follana-Berná, M. Palmer et IA Catalán. « MPA network design based on graph theory and emergent properties of larval dispersal ». Marine Ecology Progress Series 650 (17 septembre 2020) : 309–26. http://dx.doi.org/10.3354/meps13399.

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Despite the recognised effectiveness of networks of marine protected areas (MPAs) as a biodiversity conservation instrument, MPA network design frequently disregards the importance of connectivity patterns. In the case of sedentary marine populations, connectivity stems not only from the stochastic nature of the physical environment that affects dispersal of early life stages, but also from the spawning stock attributes that affect reproductive output (e.g. passive eggs and larvae) and survivorship. Early life stages are virtually impossible to track in the ocean. Therefore, numerical ocean current simulations coupled with egg and larval Lagrangian transport models remain the most common approach for the assessment of marine larval connectivity. Inferred larval connectivity may differ depending on the type of connectivity considered; consequently, the prioritisation of sites for the conservation of marine populations might also differ. Here, we introduce a framework for evaluating and designing MPA networks based on the identification of connectivity hotspots using graph theoretic analysis. As a case study, we used a network of open-access areas and MPAs off Mallorca Island (Spain), and tested its effectiveness for the protection of the painted comber Serranus scriba. Outputs from network analysis were used to (1) identify critical areas for improving overall larval connectivity, (2) assess the impact of species’ biological parameters in network connectivity and (3) explore alternative MPA configurations to improve average network connectivity. Results demonstrate the potential of graph theory to identify non-trivial egg/larval dispersal patterns and emerging collective properties of the MPA network, which are relevant for increasing protection efficiency.

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Brett, Genevieve Jay, Larry Pratt, Irina Rypina et Peng Wang. « Competition between chaotic advection and diffusion : stirring and mixing in a 3-D eddy model ». Nonlinear Processes in Geophysics 26, n^o 2 (5 avril 2019) : 37–60. http://dx.doi.org/10.5194/npg-26-37-2019.

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Abstract. The importance of chaotic advection relative to turbulent diffusion is investigated in an idealized model of a 3-D swirling and overturning ocean eddy. Various measures of stirring and mixing are examined in order to determine when and where chaotic advection is relevant. Turbulent diffusion is alternatively represented by (1) an explicit, observation-based, scale-dependent diffusivity, (2) stochastic noise, added to a deterministic velocity field, or (3) explicit and implicit diffusion in a spectral numerical model of the Navier–Stokes equations. Lagrangian chaos in our model occurs only within distinct regions of the eddy, including a large chaotic “sea” that fills much of the volume near the perimeter and central axis of the eddy and much smaller “resonant” bands. The size and distribution of these regions depend on factors such as the degree of axial asymmetry of the eddy and the Ekman number. The relative importance of chaotic advection and turbulent diffusion within the chaotic regions is quantified using three measures: the Lagrangian Batchelor scale, the rate of dispersal of closely spaced fluid parcels, and the Nakamura effective diffusivity. The role of chaotic advection in the stirring of a passive tracer is generally found to be most important within the larger chaotic seas, at intermediate times, with small diffusivities, and for eddies with strong asymmetry. In contrast, in thin chaotic regions, turbulent diffusion at oceanographically relevant rates is at least as important as chaotic advection. Future work should address anisotropic and spatially varying representations of turbulent diffusion for more realistic models.

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Pullar, D. « Incorporating level set methods in Geographical Information Systems (GIS) for land-surface process modeling ». Advances in Geosciences 4 (9 août 2005) : 17–22. http://dx.doi.org/10.5194/adgeo-4-17-2005.

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Abstract. Land-surface processes include a broad class of models that operate at a landscape scale. Current modelling approaches tend to be specialised towards one type of process, yet it is the interaction of processes that is increasing seen as important to obtain a more integrated approach to land management. This paper presents a technique and a tool that may be applied generically to landscape processes. The technique tracks moving interfaces across landscapes for processes such as water flow, biochemical diffusion, and plant dispersal. Its theoretical development applies a Lagrangian approach to motion over a Eulerian grid space by tracking quantities across a landscape as an evolving front. An algorithm for this technique, called level set method, is implemented in a geographical information system (GIS). It fits with a field data model in GIS and is implemented as operators in map algebra. The paper describes an implementation of the level set methods in a map algebra programming language, called MapScript, and gives example program scripts for applications in ecology and hydrology.

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Hinrichsen, Hans-Harald, Christoph Petereit, Anders Nissling, Isa Wallin, Didzis Ustups et Ann-Britt Florin. « Survival and dispersal variability of pelagic eggs and yolk-sac larvae of central and eastern baltic flounder (Platichthys flesus) : application of biophysical models ». ICES Journal of Marine Science 74, n^o 1 (25 octobre 2016) : 41–55. http://dx.doi.org/10.1093/icesjms/fsw163.

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A hydrodynamic model coupled with a Lagrangian particle tracking technique was utilized to simulate spatially and temporally resolved long-term environmentally related (i) size of habitat suitable for reproduction, (ii) egg/yolk-sac larval survival, (iii) separation of causes of mortality, and (iv) connectivity between spawning areas of Baltic flounder with pelagic eggs. Information on reproduction habitat requirements and mortality sources were obtained from field or laboratory studies. In our modelling study we only quantified physical processes generating heterogeneity in spatial distribution of eggs and yolk-sac larvae, as e.g. predation is not accounted for. The spatial extent of eggs and larvae represented as modelled particles is primarily determined by oxygen and salinity conditions. The reproduction habitat most suitable was determined for the Gdansk Deep, followed by the Bornholm Basin. Relatively low habitat suitability was obtained for the Arkona Basin and the Gotland Basin. The model runs also showed yolk-sac larval survival to be to a large extent affected by sedimentation. Eggs initially released in the Arkona Basin and Bornholm Basin are strongly affected by sedimentation compared with those released in the Gdansk Deep and Gotland Basin. Highest relative survival of eggs occurred in the Gdansk Deep and in the Bornholm Basin. Relatively low survival rates in the Gotland Basin were attributable to oxygen-dependent mortality. Oxygen content had almost no impact on survival in the Arkona Basin. For all spawning areas mortality caused by lethally low temperatures was only evident after severe winters. Buoyancy of eggs and yolk-sac larvae in relation to topographic features appear as a barrier for the transport of eggs and yolk-sac larvae and potentially limits the connectivity of early life stages between the different spawning areas.

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Lipták, Ľudovít, Eva Fojcíková, Monika Krpelanová, Viera Fabová et Peter Čarný. « The ESTE Decision Support System for Nuclear and Radiological Emergencies : Atmospheric Dispersion Models ». Atmosphere 12, n^o 2 (3 février 2021) : 204. http://dx.doi.org/10.3390/atmos12020204.

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The ESTE system is running in nuclear crisis centers at various levels of emergency preparedness and response in Slovakia, the Czech Republic, Austria, Bulgaria, and Iran (at the Bushehr Nuclear Power Plant, monitored by the International Atomic Energy Agency (IAEA)). ESTE is a decision-support system that runs 24/7 and serves the crisis staff to propose actions to protect inhabitants against radiation in case of a nuclear accident. ESTE is also applicable as a decision-support system in case of a malicious act with a radioactive dispersal device in an urban or industrial environment. The dispersion models implemented in ESTE are the Lagrangian particle model (LPM) and the Puff trajectory model (PTM). We describe model approaches as implemented in ESTE. The PTM is applied in ESTE for the dispersion calculation near the point of release, up to 100 km from the point of a nuclear accident. The LPM for general atmospheric transport is applied for short-range, meso-scale and large-scale dispersion, up to dispersion on the global scale. Additionally, a specific micro-scale implementation of the LPM is applied for urban scale dispersion modeling. The dispersion models of ESTE are joined with radiological-consequences models to calculate a complete spectrum of radiological parameters—effective doses, committed doses, and dose rates by various irradiation pathways and by various radionuclides. Finally, radiation protective measures, like sheltering, iodine prophylaxis, or evacuation, evaluated on the base of predicted radiological impacts, are proposed. The dispersion and radiological models of the state-of-the-art ESTE systems are described. The results of specific analyses, like the number of particles applied, the initial spatial distribution of the source, and the height of the bottom reference layer, are presented and discussed.

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Teske, Milton E., Harold W. Thistle et Bradley K. Fritz. « Modeling Aerially Applied Sprays : An Update to AGDISP Model Development ». Transactions of the ASABE 62, n^o 2 (2019) : 343–54. http://dx.doi.org/10.13031/trans.13129.

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Abstract. AGDISP (AGricultural DISPersal) models the release of aerially applied sprays with a Lagrangian-based droplet tracking algorithm initialized by user inputs (aircraft description, spray boom nozzle locations, drop size distribution, spray material properties, release height, and meteorology). The model offers an extensive set of output plots and toolbox options (deposition, spray block, stream, and multiple application assessments) to predict the downwind behavior of released sprays and assess their potential environmental impact. The model is used in risk analysis, operational planning, post-operation analysis, and training, particularly by the USDA Forest Service (FS) and its cooperators, including the U.S. Environmental Protection Agency (USEPA), the U.S. Fish and Wildlife Service, the U.S. Department of Defense, and various other state and private entities. This article updates the further development of the model since 2003, including the implementation of a quadratic droplet evaporation model and its behavior as Reynolds number approaches zero, a more accurate time step algorithm tied to droplet settling velocity, an optical canopy model, a Gaussian model for far-field extension (downwind to 20 km), an Eulerian model for tracking volatile active spray material, and the Tier 1 ground and orchard assessments previously developed by the Spray Drift Task Force (SDTF). Keywords: Aerial application, AGDISP, Model, Spray drift.

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Reynolds, A. M. « Exponential and Power-Law Contact Distributions Represent Different Atmospheric Conditions ». Phytopathology® 101, n^o 12 (décembre 2011) : 1465–70. http://dx.doi.org/10.1094/phyto-01-11-0001.

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It is well known that the dynamics of plant disease epidemics are very sensitive to the functional form of the contact distribution—the probability distribution function for the distance of viable fungal spore movement until deposition. Epidemics can take the form of a constant-velocity travelling wave when the contact distribution is exponentially bounded. Fat-tailed contact distributions, on the other hand, lead to epidemic spreads that accelerate over time. Some empirical data for contact distributions can be well represented by negative exponentials while other data are better represented by fat-tailed inverse power laws. Here we present data from numerical simulations that suggest that negative exponentials and inverse power laws are not competing candidate forms of the contact distribution but are instead representative of different atmospheric conditions. Contact distributions for atmospheric boundary-layers with stabilities ranging from strongly convective (a hot windless day time scenario) to stable stratification (a cold windy night time scenario) but without precipitation events are calculated using well-established state-of-the-art Lagrangian stochastic (particle tracking) dispersal models. Contact distributions are found to be well represented by exponentials for strongly convective conditions; a –3/2 inverse power law for convective boundary-layers with wind shear; and by a –2/3 inverse power law for stably stratified conditions.

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Dehkharghani, Amin, Nicolas Waisbord, Jörn Dunkel et Jeffrey S. Guasto. « Bacterial scattering in microfluidic crystal flows reveals giant active Taylor–Aris dispersion ». Proceedings of the National Academy of Sciences 116, n^o 23 (16 mai 2019) : 11119–24. http://dx.doi.org/10.1073/pnas.1819613116.

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The natural habitats of planktonic and swimming microorganisms, from algae in the oceans to bacteria living in soil or intestines, are characterized by highly heterogeneous fluid flows. The complex interplay of flow-field topology, self-propulsion, and porous microstructure is essential to a wide range of biophysical and ecological processes, including marine oxygen production, remineralization of organic matter, and biofilm formation. Although much progress has been made in the understanding of microbial hydrodynamics and surface interactions over the last decade, the dispersion of active suspensions in complex flow environments still poses unsolved fundamental questions that preclude predictive models for microbial transport and spreading under realistic conditions. Here, we combine experiments and simulations to identify the key physical mechanisms and scaling laws governing the dispersal of swimming bacteria in idealized porous media flows. By tracing the scattering dynamics of swimming bacteria in microfluidic crystal lattices, we show that hydrodynamic gradients hinder transverse bacterial dispersion, thereby enhancing stream-wise dispersion ∼100-fold beyond canonical Taylor–Aris dispersion of passive Brownian particles. Our analysis further reveals that hydrodynamic cell reorientation and Lagrangian flow structure induce filamentous density patterns that depend upon the incident angle of the flow and disorder of the medium, in striking analogy to classical light-scattering experiments.

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Kuneš, Petr, Vojtěch Abraham, Barbora Werchan, Zuzana Plesková, Karel Fajmon, Eva Jamrichová et Jan Roleček. « Relative pollen productivity estimates for vegetation reconstruction in central-eastern Europe inferred at local and regional scales ». Holocene 29, n^o 11 (15 juillet 2019) : 1708–19. http://dx.doi.org/10.1177/0959683619862026.

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Understanding pollen-vegetation relationships is crucial for accurate land-cover and climate reconstructions, yet important parameters for quantifying past vegetation abundance are mostly unknown for large parts of Europe harbouring temperate thermophilous ecosystems. We collected pollen and vegetation data in central-eastern Europe, a region covered by patchy cultural landscapes of high biodiversity to estimate relative pollen productivity (RPP) for important pollen-equivalent taxa. Our study area was situated in the south-western part of the White Carpathians (Czechia–Slovakia borderland), where we collected 40 modern moss pollen samples scattered over 250 km2 and mapped vegetation within 100 m around each pollen site. Additional vegetation data were compiled from Forest management plans, Natura 2000 habitat mapping and floristic inventories over the entire area. We calculated RPP (referenced to Poaceae) by testing two approaches: the extended R-value (ERV) model by estimating relevant source area of pollen and the REVEALS-based productivity using regional scale vegetation estimates. Two models were applied to depict pollen dispersal: Lagrangian stochastic and the Gaussian plume (Prentice) models. We estimated RPP for 16 taxa using the ERV model and an additional nine taxa using REVEALS. Both approaches found Plantago lanceolata-type to be a high pollen producer, Quercus medium-to-high, Asteraceae subf. Cichorioideae, Anthemis-type, Ranunculus acris-type and Rubiaceae low-to-medium and Brassicaceae and Senecio-type as low pollen producers. Results for other, mainly tree taxa, significantly differed in both approaches mainly due to largely uneven representation in both local and regional vegetation. In comparison with other studies, our data demonstrate a high variability in the estimated RPPs which could be influenced by climatic conditions or potentially vegetation structure. We suggest that the accuracy of RPP estimates could be enhanced by comparing modern pollen data with large-scale vegetation data in the future.

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Laín, Santiago. « Evaluación de los enfoques euleriano y lagrangianopara modelar la fase dispersa en flujos turbulentosno uniformes cargados con partículas ». INGENIERÍA Y COMPETITIVIDAD 10, n^o 1 (9 juin 2011) : 9–20. http://dx.doi.org/10.25100/iyc.v10i1.2477.

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El presente artículo considera flujos turbulentos no uniformes tipo chorro cargados con partículas. Estos flujos se encuentran frecuentemente en la industria y se caracterizan por altos valores de anisotropía de la velocidad fluctuante de las partículas, mucho mayor que la de la fase portadora. Dado que los enfoques euleriano y lagrangiano clásicos para la descripción de la fase dispersa son incapaces de estimar correctamente esa anisotropía, en este trabajo se introducen dos modelos eulerianos extendidos para la fase de las partículas; uno de ellos es algebraico (el modelo algebraico de esfuerzos, APS) y el otro es diferencial (el modelo de esfuerzos de Reynolds, PRS). El desempeño de ambos modelos y de un modelo lagrangiano clásico se evalúa con respecto a mediciones experimentales disponibles en la literatura. El modelo PRS proporciona resultados que concuerdan con los experimentos para todas las variables medidas, incluyendo la anisotropía de la velocidad fluctuante de las partículas. Las ecuaciones diferenciales que describen la fase dispersa se descomponen en sus términos básicos y se analizan separadamente. En el caso de partículas de gran inercia, se demuestra que el modelado de los términos de interacción es crucial ya que éstos gobiernan los equilibrios existentes en las ecuaciones eulerianas que describen la fase dispersa

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NASCIMENTO, A. L., J. C. CARVALHO et W. D. JACONDINO. « Pollutants Dispersion in a Pre-Residual and Stable Layer Environment Using a Lagrangean Random-Speed Model ». Anuário do Instituto de Geociências - UFRJ 42, n^o 1 (25 mars 2019) : 32–40. http://dx.doi.org/10.11137/2019_1_32_40.

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Reynolds, A. M. « Stokes number effects in Lagrangian stochastic models of dispersed two-phase flows ». Journal of Colloid and Interface Science 275, n^o 1 (juillet 2004) : 328–35. http://dx.doi.org/10.1016/j.jcis.2004.02.039.

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Hofmann, Eileen E., A. G. Edward Haskell, John M. Klinck et Cathy M. Lascara. « Lagrangian modelling studies of Antarctic krill (Euphausia superba) swarm formation ». ICES Journal of Marine Science 61, n^o 4 (1 janvier 2004) : 617–31. http://dx.doi.org/10.1016/j.icesjms.2004.03.028.

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Abstract A two-dimensional Lagrangian particle model was developed to examine the spatial distribution of Antarctic krill (Euphausia superba). The time-dependent location of particles, which represent krill individuals, is determined by random diffusion, foraging activity, and movement induced by the presence of neighbours. Foraging activity is based on prescribed food conditions and is such that krill swim slower and turn more frequently in areas of high food concentration. The presence or absence of neighbours either disperses krill, if the local concentrations become too dense, or coalesces krill, if concentrations become too dilute, respectively. Predation on krill is included and affects swarm characteristics by removing individuals. Sensitivity studies indicate that the rate of krill swarm formation and the total number of swarms formed are determined primarily by foraging response and nearest neighbour sensing distance. Simulations using food distributions that are representative of those encountered at boundaries, such as fronts, mesoscale eddies, or the sea ice edge, show that foraging activity can produce rapid swarm formation. Results from other krill swarm models show that attraction between individuals is the primary mechanism producing krill swarms. However, the parameterizations for krill interactions used in those models and that used in this model differ, thereby implying different biological dynamics. Thus, parameterization of the basic interactions in krill swarm models remains to be defined.

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Hu, Y., et E. Gutheil. « Transported Joint Probability Density Function Modeling of Turbulent Dilute Spray Flows ». Eurasian Chemico-Technological Journal 16, n^o 2-3 (8 avril 2014) : 227. http://dx.doi.org/10.18321/ectj186.

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A transported joint probability density function (PDF) model for turbulent spray flows is presented, where a one-point one-time statistical description of the gas-phase mixture fraction and the gas velocity is used. This approach requires the closure of the molecular mixing, which is achieved through use of the extended interaction-by-exchange-with-the-mean (IEM) model and a simplified Langevin model for the closure of the gas velocity both of which are extended through additional terms accounting for spray evaporation. These equations require the solution of the turbulent time scales and the mean pressure field through a Eulerian description. The numerical approach includes a Lagrangian Monte Carlo method for the solution of modeled joint PDF equation with a Eulerian finite-volume algorithm to determine the turbulent time scale and the mean pressure field. For the dispersed liquid phase, Lagrangian equations are used to describe the droplet heating, evaporation, and motion in the framework of a discrete droplet model. The convective droplet evaporation model is employed, and the infinite conductivity model with consideration of non-equilibrium effects based on the Langmuir-Knudsen law is used. The droplet turbulent dispersion is modeled with two different Lagrangian stochastic models. The resulting spray evolution equations are solved by a Lagrangian discrete droplet method using the point source approximation for a dilute spray. The numerical results are compared with experimental data of Gounder et al. [1], where the experimental set B of the acetone spray flows SP2 and SP6 are simulated. Comparison of numerical and experimental results includes droplet size, liquid volume flux as well as the mean and fluctuating velocities. Generally, good agreement is achieved, although the radial droplet dispersion is somewhat under-predicted by the computations. The droplet fluctuating velocities show sensitivity to the different dispersion models.

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Souhar, Otmane, Alexis Marceau et Benjamin Loubet. « Modelling and inference of maize pollen emission rate with a Lagrangian dispersal model using Monte Carlo method ». Journal of Agricultural Science 158, n^o 5 (juillet 2020) : 383–95. http://dx.doi.org/10.1017/s0021859620000763.

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AbstractThis work explores the uncertainty of the inferred maize pollen emission rate using measurements and simulations of pollen dispersion at Grignon in France. Measurements were obtained via deposition of pollen on the ground in a canopy gap; simulations were conducted using the two-dimensional Lagrangian Stochastic Mechanistic mOdel for Pollen dispersion and deposition (SMOP). First, a quantitative evaluation of the model's performance was conducted using a global sensitivity analysis to analyse the convergence behaviour of the results and scatter diagrams. Then, a qualitative study was conducted to infer the pollen emission rate and calibrate the methodology against experimental data for several sets of variable values. The analysis showed that predicted and observed values were in good agreement and the calculated statistical indices were mostly within the range of acceptable model performance. Furthermore, it was revealed that the mean settling velocity and vertical leaf area index are the main variables affecting pollen deposition in the canopy gap. Finally, an estimated pollen emission rate was obtained according to a restricted setting, where the model studied includes no deposition on leaves, no resuspension and with horizontal pollen fluctuations either taken into account or not. The estimated pollen emission rate obtained was nearly identical to the measured quantity. In conclusion, the findings of the current study show that the described methodology could be an interesting approach for accurate prediction of maize pollen deposition and emission rates and may be appropriate for other pollen types.

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Smouse, Peter E., Stefano Focardi, Paul R. Moorcroft, John G. Kie, James D. Forester et Juan M. Morales. « Stochastic modelling of animal movement ». Philosophical Transactions of the Royal Society B : Biological Sciences 365, n^o 1550 (27 juillet 2010) : 2201–11. http://dx.doi.org/10.1098/rstb.2010.0078.

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Modern animal movement modelling derives from two traditions. Lagrangian models, based on random walk behaviour, are useful for multi-step trajectories of single animals. Continuous Eulerian models describe expected behaviour, averaged over stochastic realizations, and are usefully applied to ensembles of individuals. We illustrate three modern research arenas. (i) Models of home-range formation describe the process of an animal ‘settling down’, accomplished by including one or more focal points that attract the animal's movements. (ii) Memory-based models are used to predict how accumulated experience translates into biased movement choices, employing reinforced random walk behaviour, with previous visitation increasing or decreasing the probability of repetition. (iii) Lévy movement involves a step-length distribution that is over-dispersed, relative to standard probability distributions, and adaptive in exploring new environments or searching for rare targets. Each of these modelling arenas implies more detail in the movement pattern than general models of movement can accommodate, but realistic empiric evaluation of their predictions requires dense locational data, both in time and space, only available with modern GPS telemetry.

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Minier, Jean-Pierre, Sergio Chibbaro et Stephen B. Pope. « Guidelines for the formulation of Lagrangian stochastic models for particle simulations of single-phase and dispersed two-phase turbulent flows ». Physics of Fluids 26, n^o 11 (novembre 2014) : 113303. http://dx.doi.org/10.1063/1.4901315.

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Takeyasu, Kimika, Yusuke Uchiyama, Xu Zhang, Kosei Matsushita et Satoshi Mitarai. « A Numerical Analysis on Coral Larval Networks across Reef Areas on the Northwest Coast of Okinawa Main Island, Japan ». IOP Conference Series : Earth and Environmental Science 945, n^o 1 (1 décembre 2021) : 012030. http://dx.doi.org/10.1088/1755-1315/945/1/012030.

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Abstract Coral bleaching has recently occurred extensively over the world’s oceans, primarily due to high water temperatures. Mesophotic corals that inhabit at depths of approximately 30–150 m are expected to survive during bleaching events and to reseed shallow water corals afterward. In particular, in Okinawa, Japan, mesophotic coral ecosystems (MCEs) have been reported to serve as a refuge to preserve genotypic diversities of bleaching-sensitive corals. Connectivity of larval populations between different habitats is a key element that determines the area to be conserved for desirable coral ecosystems. Coral larvae generally behave passively to the surrounding currents and are transported by the advective and dispersive effects of ambient ocean currents. Thus, numerical ocean circulation models enable us to quantify connectivity with detailed spatiotemporal network structures. Our aim in this study is to quantify the short-distance and vertical connectivity of coral larvae in reef areas on the northwest coast of Okinawa Main Island. For the reason that both short-distance and vertical larval transport are influenced by complex nearshore topography, a very high-resolution 3-D circulation model is required. Therefore, we developed a quadruple nested high-resolution synoptic ocean model at a lateral spatial resolution of 50 m, coupled with an offline 3-D Lagrangian particle-tracking model. After validation of the developed model, short-distance horizontal coral connectivity across reef areas on the northwest coast was successfully evaluated. Furthermore, a series of Lagrangian particle release experiments were conducted to identify the vertical coral migration and 3-D connectivity required for the preservation of MCEs. The model revealed that coral larvae released from the semi-enclosed areas tended to remain near the source area, whereas they were diffused and dispersed gradually with time. The mesophotic corals were dispersed vertically to the deeper zone below the mixed layer, while upward transport occurred to induce the mesophotic corals to emerge near the surface, under the influence of the surface mixed layer. The model results solidly indicated significant connectivity between MCEs and shallow coral ecosystems.

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Lonin, Serguei, et Jairo Guillermo Vásquez A. « Hidrodinámica y distribución de coliformes en el Golfo de Urabá ». Boletín Científico CIOH, n^o 23 (23 décembre 2005) : 76–89. http://dx.doi.org/10.26640/22159045.140.

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Los coliformes fecales se observaron en las campañas de CORPOURABÁ para distintas épocas del año en zonas del Golfo de Urabá, relativamente lejanas de las posibles fuentes costeras, teniendo en cuenta que el tiempo de degradación de la microflora patógena es de orden de horas. El objetivo de este trabajo fue determinar la extensión de las zonas de contaminación por coliformes, originadas por las principales fuentes puntuales en los ríos y zonas urbanas. Con el fin de estudiar la dinámica de los coliformes en el golfo, fue aplicado el modelo hidrodinámico ECOMSED. El transporte de la sustancia fue simulado tanto en sistema lagrangeano, como euleriano. Con lo primero, fue identificado el alcance hasta donde se dispersa la sustancia de cada fuente particular; con lo segundo fue posible establecer los patrones resultantes de contaminación bajo distintas condiciones climáticas del año.

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van Wachem, Berend, Thomas Curran et Fabien Evrard. « Fully Correlated Stochastic Inter-Particle Collision Model for Euler–Lagrange Gas–Solid Flows ». Flow, Turbulence and Combustion 105, n^o 4 (6 février 2020) : 935–63. http://dx.doi.org/10.1007/s10494-020-00111-7.

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AbstractIn Lagrangian stochastic collision models, a fictitious particle is generated to act as a collision partner, with a velocity correlated to the velocity of the real colliding particle. However, most often, the fluid velocity seen by this fictitious particles is not accounted for in the generation of the fictitious particle velocity, leading to a de-correlation between the fictitious particle velocity and the local fluid velocity, which, after collision, leads to an unrealistic de-correlation of the real particle velocity and the fluid velocity as seen by the particle. This de-correlation, in turn, causes a spurious decrease of the particle kinetic energy, even though the collisions are assumed perfectly elastic. In this paper, we propose a new model in which the generated fictitious particle velocity is correctly correlated to both the real particle velocity and the local fluid velocity at the particle, hence preventing the spurious loss of the total particle kinetic energy. The model is suitable for small inertial particles. Two algorithms for integrating the collision frequency are also compared to each other. The models are validated using large eddy simulation (LES) of mono-dispersed particle-laden stationary homogeneous isotropic turbulence. Simulations are conducted with spherical particles with different turbulent Stokes number, $$St_t = [0.75 - 5.8]$$ S t t = [ 0.75 - 5.8 ] , and volume fractions, $$\alpha _p = [0.014 - 0.044]$$ α p = [ 0.014 - 0.044 ] , and are compared to the results of the LES using a deterministic discrete particle simulation model.

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BARATA, Jorge. « On the modeling of droplet transport, dispersion and evaporation in turbulent flows ». Combustion Engines 122, n^o 3 (1 juillet 2005) : 42–55. http://dx.doi.org/10.19206/ce-117399.

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The present paper presents a numerical study on evaporating droplets injected through a turbulent cross-stream. Several models have been used with more or less success to describe similar phenomena, but much of the reported work deals only with sprays in stagnant surroundings. The ultimate goal of this study is to develop an Eulerian/Lagragian approach to account for turbulent transport, dispersion, evaporation and coupling between both processes in practical spray injection systems, which usually include air flows in the combustion chamber like swirl, tumble and squish in I.C. engines or crossflow in gas turbines. In this work a method developed to study isothermal turbulent dispersion is extended to the case of an array of evaporating droplets through a crossflow, and the performance of two different evaporation models widely used is investigated. The convection terms were evaluated using the hybrid or the higher order QUICK scheme. The dispersed phase was treated using a Lagrangian reference frame. The differences between the two evaporation models and its applicability to the present flow are analysed in detail. During the preheating period of the Chen and Pereira [1] model the droplets are transported far away from the injector by the crossflow, while with the Sommerfeld [2] formulation for evaporation the droplet has a continuous variation of the diameter. This result has profound implications on the results because the subsequent heat transfer and turbulent dispersion is extremely affected by the size of the particles (or droplets). As a consequence, droplet diameter, temperature and mass fraction distributions were found to be strongly dependent on the evaporation model used. So, a new formulation that takes into account also the transport of the evaporating droplets needs to be developed if practical injection systems are to be simulated. Also, in order to better evaluate and to improve the vaporization models more detailed measurements of three-dimensional configurations are required.

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Bourqui, M. S., A. Yamamoto, D. Tarasick, M. D. Moran, L. P. Beaudoin, I. Beres, J. Davies et al. « A new real-time Lagrangian diagnostic system for stratosphere-troposphere exchange : evaluation during a balloon sonde campaign in eastern Canada ». Atmospheric Chemistry and Physics Discussions 11, n^o 10 (18 octobre 2011) : 27967–8011. http://dx.doi.org/10.5194/acpd-11-27967-2011.

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Abstract. A new real-time Lagrangian diagnostic system for stratosphere-troposphere exchange (STE) developed for Environment Canada (EC) has been delivering daily archived data since 20 July 2010. The STE calculations are performed globally following the Lagrangian approach proposed in Bourqui (2006) using medium-range, high-resolution operational global weather forecasts. Following every weather forecast, trajectories are started from a dense three-dimensional grid covering the globe, and are calculated for six days of the forecast. All trajectories crossing either the dynamical tropopause (±2 PVU) or the 380 K isentrope and having a residence time greater than 12 h are archived, and also used to calculate several diagnostics. This system provides daily global STE forecasts that can be used to guide field campaigns, among other applications. The archived data set offers unique high-resolution information on transport across the tropopause for both extra-tropical hemispheres and the tropics. This will be useful for improving our understanding of STE globally, and as a reference for the evaluation of lower-resolution models. This new data set is evaluated here against measurements taken during a balloon sonde campaign with daily launches from three stations in eastern Canada (Montreal, Egbert, and Walsingham) for the period from 12 July to 4 August 2010. The campaign found an unexpectedly high number of observed stratospheric intrusions: 79% (38%) of the profiles appear to show the presence of stratospheric air below 500 hPa (700 hPa). An objective identification algorithm developed for this study is used to identify layers in the balloon-sonde profiles affected by stratospheric air and to evaluate the Lagrangian STE forecasts. We find that the predictive skill for the overall intrusion depth is excellent for intrusions penetrating down to 300 and 500 hPa, while it becomes negligible for intrusions penetrating below 700 hPa. Nevertheless, the statistical representation of these deep intrusions is reasonable, with an average bias of 24%. Evaluation of the skill at representing the detailed structures of the stratospheric intrusions shows good predictive skill down to 500 hPa, reduced predictive skill between 500 and 700 hPa, and none below. A significant low statistical bias of about 30% is found in the layer between 500 to 700 hPa. However, analysis of missed events at one site, Montreal, shows that 70% of them coincide with candidate clusters of trajectories that pass through Montreal, but that are too dispersed to be detected in the close neighbourhood of the station. This allows us to expect a negligible bias throughout the troposphere in the spatially averaged STE frequency derived from this data set, for example in climatological maps of STE mass fluxes.

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Bourqui, M. S., A. Yamamoto, D. Tarasick, M. D. Moran, L. P. Beaudoin, I. Beres, J. Davies et al. « A new global real-time Lagrangian diagnostic system for stratosphere-troposphere exchange : evaluation during a balloon sonde campaign in eastern Canada ». Atmospheric Chemistry and Physics 12, n^o 5 (13 mars 2012) : 2661–79. http://dx.doi.org/10.5194/acp-12-2661-2012.

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Abstract. A new global real-time Lagrangian diagnostic system for stratosphere-troposphere exchange (STE) developed for Environment Canada (EC) has been delivering daily archived data since July 2010. The STE calculations are performed following the Lagrangian approach proposed in Bourqui (2006) using medium-range, high-resolution operational global weather forecasts. Following every weather forecast, trajectories are started from a dense three-dimensional grid covering the globe, and are calculated forward in time for six days of the forecast. All trajectories crossing either the dynamical tropopause (±2 PVU) or the 380 K isentrope and having a residence time greater than 12 h are archived, and also used to calculate several diagnostics. This system provides daily global STE forecasts that can be used to guide field campaigns, among other applications. The archived data set offers unique high-resolution information on transport across the tropopause for both extra-tropical hemispheres and the tropics. This will be useful for improving our understanding of STE globally, and as a reference for the evaluation of lower-resolution models. This new data set is evaluated here against measurements taken during a balloon sonde campaign with daily launches from three stations in eastern Canada (Montreal, Egbert, and Walsingham) for the period 12 July to 4 August 2010. The campaign found an unexpectedly high number of observed stratospheric intrusions: 79% (38%) of the profiles appear to show the presence of stratospheric air below than 500 hPa (700 hPa). An objective identification algorithm developed for this study is used to identify layers in the balloon-sonde profiles affected by stratospheric air and to evaluate the Lagrangian STE forecasts. We find that the predictive skill for the overall intrusion depth is very good for intrusions penetrating down to 300 and 500 hPa, while it becomes negligible for intrusions penetrating below 700 hPa. Nevertheless, the statistical representation of these deep intrusions is reasonable, with an average bias of 24%. Evaluation of the skill at representing the detailed structures of the stratospheric intrusions shows good predictive skill down to 500 hPa, reduced predictive skill between 500 and 700 hPa, and none below. A significant low statistical bias of about 30% is found in the layer between 500 to 700 hPa. However, analysis of missed events at one site, Montreal, shows that 70% of them coincide with candidate clusters of trajectories that pass through Montreal, but that are too dispersed to be detected in the close neighbourhood of the station. Within the limits of this study, this allows us to expect a negligible bias throughout the troposphere in the spatially averaged STE frequency derived from this data set, for example in climatological maps of STE mass fluxes. This first evaluation is limited to eastern Canada in one summer month with a high frequency of stratospheric intrusions, and further work is needed to evaluate this STE data set in other months and locations.

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BINI, M., et W. P. JONES. « Large-eddy simulation of particle-laden turbulent flows ». Journal of Fluid Mechanics 614 (16 octobre 2008) : 207–52. http://dx.doi.org/10.1017/s0022112008003443.

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A large-eddy-based methodology for the simulation of turbulent sprays is discussed. The transport equations for the spatially filtered gas phase variables, in which source terms accounting for the droplet effects are added, are solved together with a probabilistic description of the liquid phase. The probabilistic approach for the liquid phase is based on the transport equation for the spatially filtered joint probability density function of the variables required in order to describe the state of the liquid phase. In this equation, unclosed terms representing the filtered Lagrangian rates of change of the variables describing the spray are present. General modelling ideas for subgrid-scale (SGS) effects are proposed. The capabilities of the approach and the validity of the closure models, with particular with respect to the SGS dispersion, are investigated through application to a dilute particle-laden turbulent mixing layer. It is demonstrated that the formulation is able to reproduce very closely the measured properties of both the continuous and dispersed phases. The large-eddy simulation (LES) results are also found to be entirely consistent with the experimentally observed characteristics of droplet–gas turbulence interactions. Consistent with direct numerical simulation (DNS) studies of isotropic turbulence laden with particles where the entire turbulence spectrum is found to be modulated by the presence of particles, the present investigation, which comprises the effects of particle transport upon the large-scale vortical structures of a turbulent shear flow, highlights what appears to be a selective behaviour; few large-scale frequencies gain energy whereas the remaining modes are damped.

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Feng, Meiyan, Shenghong Huang et Guofu Lian. « An Anti-Clustering Model for Stability Enhancement of a 3D Moving Particle Semi-Implicit Method and Two-Phase Coupling between MPS and Euler Grids ». Water 13, n^o 7 (24 mars 2021) : 887. http://dx.doi.org/10.3390/w13070887.

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As a Lagrangian gridless particle method, the MPS (Moving Particle Semi-implicit) method has a wide engineering application. However, for complex 3D flows, unphysical pressure oscillations often occur and result in the failure of simulations. This paper compares the stability enhancement methods proposed by different researchers to develop a 3D, stable MPS method. The results indicate that the proposed methods are incapable of eliminating the particle clustering that leads to instability as the main source in coarser particle spacing cases. An anti-clustering model, referring to the SPH (Smoothed Particle Hydrodynamics) artificial viscosity model, is proposed to further reduce instability. Combining various proposed methods and models, several typical examples are simulated comparatively. The results are compared with those of the VOF (Volume of Fluid) model using commercial software to validate the accuracy and stability of the combination of the proposed methods and models. It is concluded that (1) 3D cases that adopt a high-order Laplacian model and high-order source terms in PPE are more accurate than those adopting the low-order operators; (2) the proposed anti-clustering model can produce a tuned interparticle force to prevent particle clustering and introduce no additional viscosity effects in the flow of the normal state, which plays a very positive role for further stability enhancement of MPS; (3) particle resolution significantly maintains simulation accuracy given the stable algorithms by the combination of stability enhancement methods. The 3D MPS method is coupled with the Euler grid (FLUENT V17 software, ANSYS, Pittsburgh, PA, USA) in two phases. In particular, the 3D MPS algorithm is used to calculate the liquid-phase change from the continuous to the dispersed, and the finite volume method based on the Euler grid is adopted to measure the corresponding gas-phase motion. The atomization of the liquid jet under static air flow is calculated and compared with the results of the VOF method, which can capture the continuous interface.

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Uhlmann, Markus, et Agathe Chouippe. « Clustering and preferential concentration of finite-size particles in forced homogeneous-isotropic turbulence ». Journal of Fluid Mechanics 812 (11 janvier 2017) : 991–1023. http://dx.doi.org/10.1017/jfm.2016.826.

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We have performed interface-resolved direct numerical simulations of forced homogeneous-isotropic turbulence in a dilute suspension of spherical particles in the Reynolds number range $Re_{\unicode[STIX]{x1D706}}=115{-}140$. The solid–fluid density ratio was set to $1.5$, gravity was set to zero and two particle diameters were investigated corresponding to approximately $5$ and $11$ Kolmogorov lengths. Note that these particle sizes are clearly outside the range of validity of the point-particle approximation, as has been shown by Homann & Bec (J. Fluid Mech., vol. 651, 2010, pp. 81–91). At the present parameter points the global effect of the particles upon the fluid flow is weak. We observe that the dispersed phase exhibits clustering with moderate intensity. The tendency to cluster, which was quantified in terms of the standard deviation of Voronoï cell volumes, decreases with the particle diameter. We have analysed the relation between particle locations and the location of intense vortical flow structures. The results do not reveal any significant statistical correlation. Contrarily, we have detected a small but statistically significant preferential location of particles with respect to the ‘sticky points’ proposed by Goto & Vassilicos (Phys. Rev. Lett., vol. 100 (5), 2008, 054503), i.e. points where the fluid acceleration field is acting such as to increase the local particle concentration in one-way coupled point-particle models under Stokes drag. The presently found statistical correlation between the ‘sticky points’ and the particle locations further increases when focusing on regions with high local concentration. Our results suggest that small finite-size particles can be brought together along the expansive directions of the fluid acceleration field, as previously observed only for the simplest model for sub-Kolmogorov particles. We further discuss the effect of density ratio and collective particle motion upon the basic Eulerian and Lagrangian statistics.

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Kharlamov, Sergey N., Mehran Janghorbani et Vsevolod V. Zaykovskiy. « TRANSPORTATION OF CUTTINGS BY DRILLING MUD IN HORIZONTAL WELLS. PART 1. MODELING THE STRUCTURE OF DISPERSED CURRENTS ». Bulletin of the Tomsk Polytechnic University Geo Assets Engineering 334, n^o 10 (31 octobre 2023) : 34–48. http://dx.doi.org/10.18799/24131830/2023/10/4433.

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Link for citation: Kharlamov S.N., Mehran Janghorbani, Zaykovskiy V.V. Transportation of cuttings by drilling mud in horizontal wells. Part 1. Modeling the structure of dispersed currents. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 10, рр. 34-48. In Rus. The relevance of the research is associated with the development of technical solutions for drilling wells with horizontal endings, in which cleaning the annulus from particles of drilled cuttings in hydraulic transport conditions seems technologically and economically efficient compared to other, for example, mechanical methods. The purpose of the article is to develop a computational methodology/approach to a detailed forecast and deep understanding of the physical mechanism of the influence of hydraulic transport on the well cleaning intensity. Moreover, the strategy of such a study is focused on the choice of flow conditions/rheological parameters of the model, in which the obtained detailed theoretical information on the evolution of the dynamic flow structure should be used in the development of design methods and the formulation of recommendations to engineering personnel for emergency warnings. The object of this study is a new class of viscous currents of dispersed media induced by external and internal forces, characteristic of the functioning of special equipment that ensures the movement of drilling mud with complex rheology in the well through an eccentric annular annulus. Results. The given article is the first part of the study devoted to solving complex problems accompanying the hydraulic transfer of rheologically complex mixtures through wells with an extended horizontal section and their cleaning from drilling cuttings. The first part presents the data on reasonable modeling of hydrodynamics of viscous dispersed mixture within the framework of reference to full equations describing laws of mass conservation, impulse for detection of peculiarities, determination of flow regularities in eccentric area of annular annulus, as well as search for ways of intensification of cleaning under conditions of real drilling. It is assumed that the viscous-inertial-gravitational flow of a liquid of the Herschel–Bulkly type with solid particles (sand) is carried out in conditions of laminar-turbulent, straight-flow and twisted (by the method of a movable wall) flow developing in the space. It is noted that the formation of modes with active and conservative action of external and internal forces allows efficient cleaning of the annulus. System of defining equations of mathematical model of hydrodynamics and mass transfer is analyzed for possibility of taking into account changes in nonlinearity of thermophysical properties, resistance to disturbances at boundaries of flow area and phase separation. It is noted that the prediction of molar processes is carried out within the framework of modern statistical models of the RANS method and the Euler–Lagrangian approach to describing the movement of heterogeneous media implemented in the ANSYS CFD software. It was shown that at the real drilling conditions, the mathematical model is successful in determining the spectrum of local and integral parameters of hydrodynamics and mass transfer in a wide range of changes in drilling conditions, which make it possible to understand the effects of particle sedimentation on the lower wall, the dynamics of vortex separation and the transfer of particles to the low-Reynolds region with a suspended state of the mixture structure and the inertial zone of the flow core. It is noted that the intensity of hydraulic transport downstream is significantly influenced by the conditions of phase entry, rheological characteristics of the mud. The calculations established the flow areas with satisfactory agreement of dynamic characteristics of the flow according to the proposed model with available experimental data, for example, shear stress at the wall, radial distributions of the components of the fluid velocity vector along the length of the well at different angles of deviation of its borehole from the vertical. Moreover, the results of this article should be taken into account when describing the data of the second part, as an addition to the study of hydraulic transport according to the proposed technique of real drilling of horizontal wells with optimal rheological properties of the mud.

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Kharlamov, Sergey N., Mehran Janghorbani et Artem G. Chernov. « Transportation of cuttings by drilling mud in horizontal wells. Part 2. Numerical results of drilling at optimal rheological properties of mud ». Bulletin of the Tomsk Polytechnic University Geo Assets Engineering 334, n^o 11 (30 novembre 2023) : 7–24. http://dx.doi.org/10.18799/24131830/2023/11/4468.

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The relevance. Ensuring technological equipment operation efficiency when drilling wells with an arbitrary orientation of their wellbores. In particular, the search for productive hydrocarbon reservoirs requires drilling deeper wells with extended horizontal sections, for which the removal of the cuttings bed is the key problem of modern drilling. The aim. Study the features and establish the patterns of cuttings movement through the annulus eccentric space formed by a drill string and well walls under various modes (in-situ) and drilling conditions within the framework of modern mathematical models of hydrodynamics, numerical algorithms and approaches implemented in ANSYS CFD. Optimize the parameters that determine drilling, such as an inclination angle, mass-average velocity and morphology of the inlet rheologically complex viscous flow to form the maximum allowable drilling velocity for various combinations of mud effective viscosity and mixture flow rate. Give practical recommendations for engineers to reduce time, costs and material resources for maintenance and optimization of well cleaning. The object. A well with an eccentric core and an extended horizontal section operating in modes and conditions close to real drilling. The methods. Complex of physical and mathematical analysis and numerical modeling of hydrodynamics and mass transfer in homogeneous and heterogeneous continuous media. The media were widely tested on the class of internal rheological complex flows, the verification of which was carried out under appropriate conditions, performed by other authors when solving problems of drilling and cleaning wells. The results. The paper presents the results of a numerical study of hydrodynamics of a dispersed flow of a rheological complex viscous mixture of a drilling fluid with the properties of a Herschel–Bulkley type fluid and sand particles in wells with an arbitrary generatrix of its wellbore in an eccentric space. The results are required to clarify the features that accompany direct-flow and swirling flow (the moving wall method), identify the patterns in such modes, accounting for which allows for effective cleaning of the annulus. The calculations were performed within the framework of modern mathematical models of the RANS-method and the Euler–Lagrangian approach to describing the motion of heterogeneous media, implemented in the ANSYS CFD software and efficient numerical algorithms for determining intra- and interfacial processes of mass and momentum transfer in mixtures. The authors have determined that when drilling a vertical section, the most effective parameter in terms of cleaning control is the effective viscosity of the mud; the most problematic configurations for cleaning are wells with sloping sections at angles close to the vertical. When drilling a horizontal section, the eccentricity of the drill string creates “the dead” zone of flow and complicates cleaning. This zone should be removed by creating swirling flow conditions through relatively weak rotation of a drill string (30–60 rpm). When drilling inclined sections, it is necessary to reduce a solution viscosity (preferably to the level of fresh water) and increase the flow rate (in this case, to 2 m/s or higher). When drilling a horizontal section, a mud with a viscosity close to fresh water is recommended at flow rates of about 2 m/s (or 640 gpm) at the well inlet and a maximum drilling velocity of 9 m/h.

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Schilling, Hayden T., Stefanos Kalogirou, Christina Michail et Periklis Kleitou. « Testing passive dispersal as the key mechanism for lionfish invasion in the Mediterranean Sea using Lagrangian particle tracking ». Biological Invasions, 7 novembre 2023. http://dx.doi.org/10.1007/s10530-023-03187-0.

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AbstractThe expansion of lionfish Pterois miles across the Mediterranean Sea since its introduction via the Suez Canal has been rapid, but the mechanisms by which the expansion occurred have not been fully tested. By using a series of Lagrangian particle tracking simulations and high-resolution hydrodynamic models, we tested the hypothesis that passive dispersal of larvae could explain the east to west expansion of lionfish. By sequentially modelling the annual dispersal of larvae, from the first observation in Lebanon in 2012 and then modelling dispersal of larval from the simulated settlement sites, we showed that passive dispersal driven by ocean currents largely explained the observed expansion of lionfish until 2020. The spread of lionfish was likely restricted by environmental conditions when the population reached the central Mediterranean and the particle tracking simulations diverged from observations. The results emphasize the potential contribution of computational models in understanding the dispersal of non-indigenous and range expanding species in response to changing environmental conditions, identifying high risk areas, and guiding targeted surveillance, early detection, and informing management strategies for such species. Given that many non-indigenous species in the Mediterranean are introduced through a consistent pathway (the Suez Canal), the incorporation of interdisciplinary approaches and high-resolution biophysical models can provide fundamental knowledge for management action prioritization.

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Ma, Yongxing, Yongsheng Wu, Nicholas W. Jeffery, Rachel Horwitz, Jinshan Xu, Ed Horne et Ryan R. E. Stanley. « Simulating dispersal in a complex coastal environment : the Eastern Shore Islands archipelago ». ICES Journal of Marine Science, 14 décembre 2023. http://dx.doi.org/10.1093/icesjms/fsad193.

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Abstract The Eastern Shore Islands (ESI) archipelago on the Scotian Shelf supports a rich variety of biogenic habitats and associated diversity of coastal species. The unique and complex geometry of the ESI coastline has a significant impact on circulation and, correspondingly, influences the dispersal of nearshore organisms. For many coastal areas, the ability to accurately resolve the dispersal processes is contingent on the availability of oceanographic models that can resolve fine-scale coastal boundary conditions, including coastlines and bathymetric features. We applied a high-resolution ocean circulation model and Lagrangian particle tracking in the ESI to simulate dispersal of nearshore organisms. Our results revealed predominant southwest–northeast transport that was associated with a nearshore reversal flow. While transport among different zones of the study region is mainly determined by residual currents over the long term, tidal currents dominate patterns of particle dispersal over shorter time scales. An analysis of Lagrangian coherent structures found that they were consistently associated with the mouths of bays, demonstrating that the islands and associated oceanographic processes promote self-retention. These results highlight how complex coastlines and associated oceanographic processes promote retention and underline the need to resolve these fine-scale physical and oceanographic features when estimating biophysical dispersal in the coastal environment.

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Demmer, Jonathan, Simon P. Neill, Olga Andres, Shelagh K. Malham, Trevor Jones et Peter Robins. « Larval dispersal from an energetic tidal channel and implications for blue mussel (Mytilus edulis) shellfisheries ». Aquaculture International, 16 août 2022. http://dx.doi.org/10.1007/s10499-022-00948-x.

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AbstractComplex coastal currents control early-stage larval dispersal from intertidal populations, and late-stage settlement patterns, but are often poorly resolved in larval dispersal models. Generally, there is high uncertainty in the timing of larval spawning, which markedly affects larval dispersal. In this study, we describe the physical parameters that induce spawning events in the blue mussel, Mytilus edulis, using a variation of the Condition Index (which relates the mass of meat to the mass of the shell) as a proxy. We developed a high-resolution Eulerian coastal hydrodynamic model, coupled with a Lagrangian particle tracking model, to quantify the potential dispersal of early-stage mussel larvae based on differing spawning dates obtained from field data. Our results showed that (1) the timings of larval spawning cannot be explained solely by ‘thermal shocks’ in the sea or air temperatures (i.e. fluctuations in temperature causing stress); (2) larger spawning events generally occurred during neap tides; (3) the simulated larval dispersal was largely but not always predicted by averaged current pathways (calculated over two weeks period); and (4) simulated self-recruitment was low at sites associated with strong tidal currents. These results have important implications for shellfisheries stock management and sustainability. Specific to this study, simulated mussels from shellfishery beds off North Wales dispersed more than 25 km in one week and so could feasibly contribute to the wider population throughout the northern part of the Irish Sea.

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Reynolds, Andy M. « Incorporating terminal velocities into Lagrangian stochastic models of particle dispersal in the atmospheric boundary layer ». Scientific Reports 8, n^o 1 (15 novembre 2018). http://dx.doi.org/10.1038/s41598-018-34924-4.

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Fu, Lin-Tao. « Effect of the local wind reduction zone on seed dispersal from a single shrub element on sparsely vegetated land ». AoB PLANTS 13, n^o 4 (21 mai 2021). http://dx.doi.org/10.1093/aobpla/plab025.

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Abstract Accurate predictions of seed dispersal kernels are crucial for understanding both vegetation communities and landscape dynamics. The influences of many factors, including the physical properties of seeds, the time-averaged wind speed and the wind turbulence, on seed dispersal have been studied. However, the influence of local wind speed reduction around a single shrub element (e.g. a small patch of scrub) on seed dispersal is still not well understood. Here, the spatial distribution of the wind intensity (represented by the wind friction speed u*) around a single shrub element is described, with an emphasis on the variation in the streamwise direction, and assuming that the time-averaged lateral and vertical speeds are equal to zero. The trajectories of the seeds were numerically simulated using a Lagrangian stochastic model that includes the effects of wind turbulence and particle inertia. The patterns of seed deposition with and without the effect of local wind reduction were compared. The variation in seed deposition with changing wind intensity, release height and shrub porosity were also simulated. The simulation results revealed that the local wind reduction increased seed deposition in nearby regions and therefore decreased seed deposition in the regions farther away. Local wind reduction had a greater impact on short-distance dispersal than on long-distance dispersal. Moreover, the dispersal in the circumferential direction decreased once the motion of a seed moving in the streamwise direction was reduced due to the local wind reduction. As the wind intensity and release height increased, the effect of local wind reduction on seed dispersal weakened. Seed dispersal was both wider and farther as the shrub porosity increased. These results may help explain the disagreement between the mechanistic models and the fitting curves in real cases. In addition, the results of this study may improve the currently used mechanistic models by either increasing their flexibility in case studies or by helping explain the variations in the observed distributions.

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Villastrigo, Adrián, Víctor Orenes-Salazar, Antonio José García-Meseguer, Juana María Mirón-Gatón, Baptiste Mourre, Andrés Millán et Josefa Velasco. « Oceanic currents maintain the genetic structure of non-marine coastal taxa in the western Mediterranean Sea ». npj Biodiversity 2, n^o 1 (20 novembre 2023). http://dx.doi.org/10.1038/s44185-023-00028-0.

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AbstractCoastal habitats are amongst the most dynamic on Earth, due to their simultaneous exposure to terrestrial, oceanic and atmospheric processes. Coastal taxa are therefore often ecologically specialised and adapted to withstand frequent shifts in sea level, wave exposure, temperature or salinity. This specialisation often resulting in significant cryptic diversity. Previous molecular studies have suggested that genetic differentiation in non-marine coastal organisms may be influenced by oceanic currents and fronts, but the extent to which such processes affect dispersal and evolution of such taxa remains unclear. Here we explore whether population genetic structure in two supralittoral rockpool beetle species (genus Ochthebius) can be predicted from the general circulation pattern of the marine currents and associated oceanic fronts. We simulated dispersal using a Lagrangian particle tracking model and compared this with population genetic structure inferred from COI (mitochondrial) and wingless (nuclear) genes applying linear models and Mantel tests. We show that a biophysical model based on oceanic currents and fronts in the western Mediterranean Sea is a much better predictor of observed population genetic structure than isolation by distance in both species. Our results show that oceanic processes, besides shaping contemporary population connectivity in fully marine organisms, also exert a meaningful influence on terrestrially-derived coastal taxa such as supralittoral rockpool beetles — the first time this mode of dispersal has been demonstrated in an insect.

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Torri, Marco, Stefania Russo, Federico Falcini, Biagio De Luca, Simone Colella, Gianluca Volpe, Raffaele Corrado et al. « Coupling Lagrangian simulation models and remote sensing to explore the environmental effect on larval growth rate : The Mediterranean case study of round sardinella (Sardinella aurita) early life stages ». Frontiers in Marine Science 9 (20 janvier 2023). http://dx.doi.org/10.3389/fmars.2022.1065514.

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The relationship between environmental conditions and early life-history traits of Sardinella aurita are investigated using material collected in two sites of the Central Mediterranean Sea. Individual mean daily growth during the planktonic phase has been determined by using otolith microstructure analysis, while Lagrangian simulation models allowed to estimate the daily position in space and time of each specimen from the hatching to the catch. Generalized Additive Mixed Models (GAMMs) have been implemented to explore the impact of environmental conditions at time t, t-1 day and t-2 days on the mean daily growth rate occurring at time t. Spatial analysis evidenced a wide dispersion of eggs and larvae in the coastal area of both sampling sites in correspondence to relatively warmer and chlorophyll-a enriched waters. Lagrangian simulations detected a complementary larval dispersal pathway able to transport larvae to a known retention area. Temperature at time t was the most important driver affecting the mean daily larval growth, followed by the food availability. On the other hand, models performed on lagged environmental covariates (t-1 and t-2) did not show any significant effect on the growth rate at time t. In addition to the sub-linear positive correlation between temperature and mean daily larval growth, model highlighted a decrease in the otolith core width at higher temperature that can be linked to an earlier stage of ontogeny at hatching. This study provided a useful methodological approach that takes advantage of available remote sensing data to perform ecological studies in support to fisheries management.

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Cao, Zhixuan, Marcus Bursik, Qingyuan Yang et Abani Patra. « Simulating the Transport and Dispersal of Volcanic Ash Clouds With Initial Conditions Created by a 3D Plume Model ». Frontiers in Earth Science 9 (23 septembre 2021). http://dx.doi.org/10.3389/feart.2021.704797.

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Volcanic ash transport and dispersion (VATD) models simulate atmospheric transport of ash from a volcanic source represented by parameterized concentration of ash with height. Most VATD models represent the volcanic plume source as a simple line with a parameterized ash emission rate as a function of height, constrained only by a total mass eruption rate (MER) for a given total rise height. However, the actual vertical ash distribution in volcanic plumes varies from case to case, having complex dependencies on eruption source parameters, such as grain size, speed at the vent, vent size, buoyancy flux, and atmospheric conditions. We present here for the first time the use of a three-dimensional (3D) plume model based on conservation laws to represent the ash cloud source without any prior assumption or simplification regarding plume geometry. By eliminating assumed behavior associated with a parameterized plume geometry, the predictive skill of VATD simulations is improved. We use our recently developed volcanic plume model based on a 3D smoothed-particle hydrodynamic Lagrangian method and couple the output to a standard Lagrangian VATD model. We apply the coupled model to the Pinatubo eruption in 1991 to illustrate the effectiveness of the approach. Our investigation reveals that initial particle distribution in the vertical direction, including within the umbrella cloud, has more impact on the long-range transport of ash clouds than does the horizontal distribution. Comparison with satellite data indicates that the 3D model-based distribution of ash particles through the depth of the volcanic umbrella cloud, which is much lower than the observed maximum plume height, produces improved long-range VATD simulations. We thus show that initial conditions have a significant impact on VATD, and it is possible to obtain a better estimate of initial conditions for VATD simulations with deterministic, 3D forward modeling of the volcanic plume. Such modeling may therefore provide a path to better forecasts lessening the need for user intervention, or attempts to observe details of an eruption that are beyond the resolution of any potential satellite or ground-based technique, or a posteriori creating a history of ash emission height via inversion.

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Dukhovskoy, Dmitry S., Steven L. Morey, Eric P. Chassignet, Xu Chen, Victoria J. Coles, Linlin Cui, Courtney K. Harris et al. « Development of the CSOMIO Coupled Ocean-Oil-Sediment- Biology Model ». Frontiers in Marine Science 8 (10 mars 2021). http://dx.doi.org/10.3389/fmars.2021.629299.

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The fate and dispersal of oil in the ocean is dependent upon ocean dynamics, as well as transformations resulting from the interaction with the microbial community and suspended particles. These interaction processes are parameterized in many models limiting their ability to accurately simulate the fate and dispersal of oil for subsurface oil spill events. This paper presents a coupled ocean-oil-biology-sediment modeling system developed by the Consortium for Simulation of Oil-Microbial Interactions in the Ocean (CSOMIO) project. A key objective of the CSOMIO project was to develop and evaluate a modeling framework for simulating oil in the marine environment, including its interaction with microbial food webs and sediments. The modeling system developed is based on the Coupled Ocean-Atmosphere-Wave-Sediment Transport model (COAWST). Central to CSOMIO’s coupled modeling system is an oil plume model coupled to the hydrodynamic model (Regional Ocean Modeling System, ROMS). The oil plume model is based on a Lagrangian approach that describes the oil plume dynamics including advection and diffusion of individual Lagrangian elements, each representing a cluster of oil droplets. The chemical composition of oil is described in terms of three classes of compounds: saturates, aromatics, and heavy oil (resins and asphaltenes). The oil plume model simulates the rise of oil droplets based on ambient ocean flow and density fields, as well as the density and size of the oil droplets. The oil model also includes surface evaporation and surface wind drift. A novel component of the CSOMIO model is two-way Lagrangian-Eulerian mapping of the oil characteristics. This mapping is necessary for implementing interactions between the ocean-oil module and the Eulerian sediment and biogeochemical modules. The sediment module is a modification of the Community Sediment Transport Modeling System. The module simulates formation of oil-particle aggregates in the water column. The biogeochemical module simulates microbial communities adapted to the local environment and to elevated concentrations of oil components in the water column. The sediment and biogeochemical modules both reduce water column oil components. This paper provides an overview of the CSOMIO coupled modeling system components and demonstrates the capabilities of the modeling system in the test experiments.

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Wang, Yixin, Dionysios E. Raitsos, George Krokos, Peng Zhan et Ibrahim Hoteit. « A Lagrangian model-based physical connectivity atlas of the Red Sea coral reefs ». Frontiers in Marine Science 9 (28 octobre 2022). http://dx.doi.org/10.3389/fmars.2022.925491.

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Connectivity, the exchange of individuals and genes among geographically separated marine populations, plays a key role in coral reef biodiversity and resilience. The Red Sea is a semi-enclosed basin with dynamic circulation and abundant coral reefs, making it a natural laboratory for coral reef connectivity research. Previous studies broadly investigated Red Sea connectivity, but were spatially restricted to regional or sparsely-distributed reef sites. Here, using hydrodynamic and particle tracking models, a high-resolution circulation-driven physical connectivity atlas covering every Red Sea coral reef, including seasonality, was simulated and further validated against available in-situ genetic datasets. The simulation was conducted without incorporating larval traits to isolate and quantify the connectivity contributed by circulation. Our validation experiment suggests the importance of circulation in shaping the genetic structure of Red Sea reef species, supporting the Isolation By Circulation (IBC) theory in the Red Sea seascape genetics. The simulated atlas reveals that reefs in the northern Red Sea are better sources and destinations than those in the southern basin, regardless of season. The east-west connections between the southern reefs are identified to be weak. Complex circulation dynamics drive a regional-specific seasonality, e.g., the Farasan Islands reefs are better sources during summer while the nearby Bab-Al-Mandeb strait reefs are better sources during winter. The west-coast reefs are generally winter-intensified sources whereas the east-coast reefs are generally summer-intensified sources. The revealed seasonality of physical connectivity is important for larval dispersal processes as reef species may spawn in different seasons. This physical connectivity atlas provides a reference for designing marine conservation strategies from a circulation perspective and easy-to-access physical connectivity datasets for the future Red Sea seascape genetic studies.

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Hatzonikolakis, Yannis, Sylvaine Giakoumi, Dionysios E. Raitsos, Kostas Tsiaras, Sofia Kalaroni, George Triantaphyllidis et George Triantafyllou. « Quantifying Transboundary Plastic Pollution in Marine Protected Areas Across the Mediterranean Sea ». Frontiers in Marine Science 8 (10 janvier 2022). http://dx.doi.org/10.3389/fmars.2021.762235.

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Micro- and macro-plastics pollution is a growing threat for marine biodiversity, ecosystem functioning, and consequently human wellbeing. Numerical models that consider main sources of plastics and simulate their dispersal characteristics are unique tools for exploring plastic pollution in marine protected areas (MPAs). Here, we used a Lagrangian plastic drift model, taking into account various sizes/types of plastic litter, originating from major land-based sources (coastal cities and rivers), to predict plastic accumulation zones in protected areas of the Mediterranean Sea (i.e., nationally designated MPAs, Natura 2000 sites, and Cetacean Critical Habitats). The model predicted that the size of plastic litters plays a key role in their dispersion and ultimate destination (i.e., larger litter travel longer distances). Most of the studied Mediterranean countries (13 out of 15) had at least one national MPA with over 55% of macroplastics originating from sources beyond their borders. Consequently, in many cases, local efforts to reduce plastic pollution in protected areas would be insufficient, especially for macroplastics management. Transboundary collaboration among Mediterranean countries is critical for implementing successful management plans against plastic pollution in their territorial waters and specifically in MPAs.

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Mériguet, Zoé, Marion Vilain, Alberto Baudena, Chloé Tilliette, Jérémie Habasque, Anne Lebourges-Dhaussy, Nagib Bhairy, Cécile Guieu, Sophie Bonnet et Fabien Lombard. « Plankton community structure in response to hydrothermal iron inputs along the Tonga-Kermadec arc ». Frontiers in Marine Science 10 (4 octobre 2023). http://dx.doi.org/10.3389/fmars.2023.1232923.

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The Western Tropical South Pacific (WTSP) basin has been identified as a hotspot of atmospheric dinitrogen fixation due to the high dissolved iron ([DFe]) concentrations (up to 66 nM) in the photic layer linked with the release of shallow hydrothermal fluids along the Tonga-Kermadec arc. Yet, the effect of such hydrothermal fluids in structuring the plankton community remains poorly studied. During the TONGA cruise (November-December 2019), we collected micro- (20-200 μm) and meso-plankton (>200 μm) samples in the photic layer (0-200 m) along a west to east zonal transect crossing the Tonga volcanic arc, in particular two volcanoes associated with shallow hydrothermal vents (< 500 m) in the Lau Basin, and both sides of the arc represented by Melanesian waters and the South Pacific Gyre. Samples were analyzed by quantitative imaging (FlowCam and ZooScan) and then coupled with acoustic observations, allowing us to study the potential transfer of phytoplankton blooms to higher planktonic trophic levels. We show that micro- and meso-plankton exhibit high abundances and biomasses in the Lau Basin and, to some extent, in Melanesian waters, suggesting that shallow hydrothermal inputs sustain the planktonic food web, creating productive waters in this otherwise oligotrophic region. In terms of planktonic community structure, we identified major changes with high [DFe] inputs, promoting the development of a low diversity planktonic community dominated by diazotrophic cyanobacteria. Furthermore, in order to quantify the effect of the shallow hydrothermal vents on chlorophyll a concentrations, we used Lagrangian dispersal models. We show that chlorophyll a concentrations were significantly higher inside the Lagrangian plume, which came into contact with the two hydrothermal sites, confirming the profound impact of shallow hydrothermal vents on plankton production.

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Demmer, Jonathan, Peter Robins, Shelagh Malham, Matthew Lewis, Aaron Owen, Trevor Jones et Simon Neill. « The role of wind in controlling the connectivity of blue mussels (Mytilus edulis L.) populations ». Movement Ecology 10, n^o 1 (21 janvier 2022). http://dx.doi.org/10.1186/s40462-022-00301-0.

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Abstract Background Larval connectivity between distinct benthic populations is essential for their persistence. Although connectivity is difficult to measure in situ, it can be predicted via models that simulate biophysical interactions between larval behaviour and ocean currents. The blue mussel (Mytilus Edulis L.) is widespread throughout the northern hemisphere and extensively commercialised worldwide. In the Irish Sea, this industry represents ~ 50% of Welsh shellfisheries, where cultivation is mainly based on wild spat. However, the main sources and amount of spat varied interannually (1100 tonnes harvest in 2014 against zero in 2018). The aim of this study is to characterise the structure and dynamics of the blue mussel metapopulation within the northern part of the Irish Sea. Methods We develop a Lagrangian particle tracking model, driven by a high-resolution (from 30 to 5000 m) validated unstructured coastal hydrodynamic model of the Irish Sea, to simulate spatial and temporal variability of larval dispersal and connectivity between distinct mussel populations and potential settlement areas. Results Our results showed that: (1) larvae positioned near the surface were strongly influenced by wind-driven currents suggesting that connectivity networks had the potential to span hundreds of kilometres; (2) in contrast, larvae positioned deeper in the water column were driven by tidal currents, producing intricate spatial patterns of connectivity between mussel beds over tens of kilometres that were consistent over time. Conclusions Dispersal of mussel larvae in the tidally energetic Irish Sea during the April–May spawning season is potentially driven by wind-driven surface currents, as confirmed by fisherman observations of inter-annual variability in wild spat collection. These results have important implications for metapopulation dynamics within the context of climate change and sustainable shellfisheries management (i.e. gain and loss of populations and harvest areas according to wind conditions).

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