Download or read book Spatial Characteristics of Coherent Turbulent Structures and Exchange Processes in the Atmospheric Surface Layer Within and Above an Orchard Canopy written by Changan Zhang and published by . This book was released on 1991 with total page 450 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Precipitation Scavenging And Atmosphere Surface Exchange written by Stephen Schwartz and published by CRC Press. This book was released on 1992-06-01 with total page 616 pages. Available in PDF, EPUB and Kindle. Book excerpt: This three-volume set contains selected papers arising from a conference held in 1991 on precipitation and air pollution. The first volume addresses the precipitation scavenging process; the second deals with atmosphere-surface exchange processes; and the third covers air pollution and deposition.

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1993 with total page 814 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Organized Turbulence Structures and Associated Transport Processes in the Lower Atmospheric Layer Within and Above a Plant Canopy written by Weigang Gao and published by . This book was released on 1990 with total page 396 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Boundary Layer Meteorology 25th Anniversary Volume 1970 1995 written by John R. Garratt and published by Springer Science & Business Media. This book was released on 1996-09-30 with total page 434 pages. Available in PDF, EPUB and Kindle. Book excerpt: The journal Boundary-Layer Meteorology was started in 1970 and has become the premier vehicle for the publication of research papers in its field. Dr R.E. Munn served as Editor-in-Chief until recently. The special 25th Anniversary volume, on which this book is based, was compiled from review and other articles solicited and selected as a `Festschrift' to honour Ted Munn's achievement as editor of the journal over that time. Articles by leading contributors to the field include reviews of field studies (Askervein, HEXOS, Cabauw) and their impacts; numerical modelling (large-eddy simulation of the surface layer, frontal structures); analyses and critical discussions (of the von Karman constant, bulk aerodynamic formulations, air-sea interaction, vegetation canopies); and reviews or previews of progress in our understanding of the atmospheric boundary layer, turbulence simulation, Lagrangian descriptions of turbulent diffusion and remote sensing of the boundary layer. The collection provides an excellent perspective on the state of the subject and where it is headed. It should provide fascinating and stimulating reading for researchers and students of boundary-layer meteorology and related areas.

Download or read book Dissertation Abstracts International written by and published by . This book was released on 1992 with total page 850 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Turbulence Statistics and Coherent Structures Within and Above Plant Canopies written by Jie Qiu and published by . This book was released on 1994 with total page 302 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Characterization and Modeling of Atmospheric Flow Within and Above Plant Canopies written by Livia Souza Freire Grion and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The turbulent flow within and above plant canopies is responsible for the exchange of momentum, heat, gases and particles between vegetation and the atmosphere. Turbulence is also responsible for the mixing of air inside the canopy, playing an important role in chemical and biophysical processes occurring in the plants environment. In the last fifty years, research has significantly advanced the un- derstanding of and ability to model the flow field within and above the canopy, but important issues remain unsolved. In this work, we focus on (i) the estimation of turbulent mixing timescales within the canopy from field data; and (ii) the development of new computationally efficient modeling approaches for the coupled canopy-atmosphere flow field.The turbulent mixing timescale represents how quickly turbulence creates a well- mixed environment within the canopy. When the mixing timescale is much smaller than the timescale of other relevant processes (e.g. chemical reactions, deposition), the system can be assumed to be well-mixed and detailed modeling of turbulence is not critical to predict the system evolution. Conversely, if the mixing timescale is comparable or larger than the other timescales, turbulence becomes a controlling factor for the concentration of the variables involved; hence, turbulence needs to be taken into account when studying and modeling such processes. In this work, we used a combination of ozone concentration and high-frequency velocity data measured within and above the canopy in the Amazon rainforest to characterize turbulent mixing. The eddy diffusivity parameter (used as a proxy for mixing efficiency) was applied in a simple theoretical model of one-dimensional diffusion, providing an estimate of turbulent mixing timescales as a function of height within the canopy and time-of-day. Results showed that, during the day, the Amazon rainforest is characterized by well-mixed conditions with mixing timescales smaller than thirty minutes in the upper-half of the canopy, and partially mixed conditions in the lower half of the canopy. During the night, most of the canopy (except for the upper 20%) is either partially or poorly mixed, resulting in mixing timescales of up to several hours. For the specific case of ozone, the mixing timescales observed during the day are much lower than the chemical and deposition timescales, whereas chemical processes and turbulence have comparable timescales during the night. In addition, the high day-to-day variability in mixing conditions and the fast increase in mixing during the morning transition period indicate that turbulence within the canopy needs to be properly investigated and modeled in many studies involving plant-atmosphere interactions.Motivated by the findings described above, this work proposes and tests a new approach for modeling canopy flows. Typically, vertical profiles of flow statistics are needed to represent canopy-atmosphere exchanges in chemical and biophysical processes happening within the canopy. Current single-column models provide only steady-state (equilibrium) profiles, and rely on closure assumptions that do not represent the dominant non-local turbulent fluxes present in canopy flows. We overcome these issues by adapting the one-dimensional turbulent (ODT) model to represent atmospheric flows from the ground up to the top of the atmospheric boundary layer (ABL). The ODT model numerically resolves the one-dimensional diffusion equation along a vertical line (representing a horizontally homogeneous ABL column), and the presence of three-dimensional turbulence is added through the effect of stochastic eddies. Simulations of ABL without canopy were performed for different atmospheric stabilities and a diurnal cycle, to test the capabilities of this modeling approach in representing unsteady flows with strong non-local transport. In addition, four different types of canopies were simulated, one of them including the transport of scalar with a point source located inside the canopy. The comparison of all simulations with theory and field data provided satisfactory results. The main advantages of using ODT compared to typical 1D canopy-flow models are the ability to represent the coupled canopy-ABL flow with one single modeling approach, the presence of non-local turbulent fluxes, the ability to simulate transient conditions, the straightforward representation of multiple scalar fields, and the presence of only one adjustable parameter (as opposed to the several adjustable constants and boundary conditions needed for other modeling approaches).The results obtained with ODT as a stand-alone model motivated its use as a surface parameterization for Large-Eddy Simulation (LES). In this two-way coupling between LES and ODT, the former is used to simulate the ABL in a case where a canopy is present but cannot be resolved by the LES (i.e., the LES first vertical grid point is above the canopy). ODT is used to represent the flow field between the ground and the first LES grid point, including the region within and just above the canopy. In this work, we tested the ODT-LES model for three different types of canopies and obtained promising results. Although more work is needed in order to improve first and second-order statistics within the canopy (i.e. in the ODT domain), the results obtained for the flow statistics in the LES domain and for the third order statistics in the ODT domain demonstrate that the ODT-LES model is capable of capturing some important features of the canopy-atmosphere interaction. This new surface superparameterization approach using ODT provides a new alternative for simulations that require complex interactions between the flow field and near-surface processes (e.g. sand and snow drift, waves over water surfaces) and can potentially be extended to other large-scale models, such as mesoscale and global circulation models.

Download or read book American Doctoral Dissertations written by and published by . This book was released on 1991 with total page 724 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Measurement and Modeling of Canopy Microclimate and Fluxes in Mediterranean Agricultural Systems written by Eric Richard Kent and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Estimates of crop water-use are important for water resources planning, irrigation scheduling, and efficient use of water. Surface renewal methods for measuring sensible heat flux in conjunction with an energy-budget residual approach can provide relatively inexpensive crop evapotranspiration information. Surface renewal is usually calibrated against the more expensive eddy covariance method to correct for an often-observed linear bias in sensible heat flux. Factors contributing to this bias have been hypothesized or demonstrated, including sensor frequency response, multiple ramp scales, micro-advection, and uneven heating of air within a canopy. Measurements were taken in a vineyard to test multiple surface renewal methods, determine importance of several factors contributing to the linear bias between eddy covariance and surface renewal sensible heat flux measurements, and characterize vertically varying temperature ramp characteristics associated with coherent turbulence structures. Single-layer surface renewal assuming uniform canopy heating, as used in most previous studies, performed well with low bias. Temperature ramps were found to be largely intermittent, with fewer ramps being observed lower in the canopy, and canopy heating rates that were non-uniform, which contributes significantly to the alpha calibration. Corrections for uneven heating rates using multi-layer surface renewal schemes decreased sensible heat fluxes and largely offset the effect of thermocouple frequency response compensation which increased fluxes. The use of a larger ramp scale in the surface renewal estimates, as developed by Shapland et al. (2012a,b), resulted in much lower fluxes, even when compensating for uneven canopy heating and sensor frequency response. This research contributes to a better understanding of surface renewal methodologies and their uncertainties, and contributes to more accurate evapotranspiration estimates. Canopy-microlimate is important for plant physiological processes including photosynthesis, transpiration, plant stresses, and phenology. Modeling canopy-microclimate is relevant to a variety of orchard applications including disease and pest modeling, frost prediction, and evapotranspiration modeling. UCD-ACASA (Pyles et al, 2000) is a higher-order-closure soil-plant-atmosphere transfer model used to simulate canopy turbulence, micro-climate, and fluxes of momentum, water vapor, carbon dioxide, and energy. It can be driven at the field scale by above-canopy measurements or at larger scales coupled to a regional weather or climate model. Most past work has focused on top-of-the-canopy fluxes, and indicated generally good performance. The third chapter of this dissertation compares one model version's simulation of vertically-varying within-canopy micro-climate and fluxes in a walnut orchard with a set of vertical profile measurements taken during the Canopy Horizontal Array Turbulence Study (Patton et al, 2011). Vertical profiles of within- and above-canopy air temperature, humidity, wind speed, sensible heat flux and momentum flux were examined under different atmospheric stability conditions and both before and after leaf-out in the orchard. Significant differences in model-measurement agreement were found for the canopy before and after leaf-out.

Download or read book Turbulence Within and Above an Urban Canopy written by Mathias W. Rotach and published by . This book was released on 1991 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Meteorological and Geoastrophysical Abstracts written by and published by . This book was released on 1992 with total page 632 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Physics Briefs written by and published by . This book was released on 1994 with total page 1146 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Determination of Turbulent Structures in the Atmospheric Surface Layer written by Jacobus Leonardus Josephus Schols and published by . This book was released on 1984 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In chapter V the present results are discussed and suggestions for future research are presented.

Download or read book The Determination of Turbulent Structures in the Atmospheric Surface Layer written by Jacobus Leonardus Josephus Schols and published by . This book was released on 1984 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Turbulence Variance Characteristics in the Unstable Atmospheric Boundary Layer Above Flat Pine Forest written by Jun Asanuma and published by . This book was released on 1996 with total page 446 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical Modeling of Atmospheric Boundary Layer Flow Over Forest Canopy written by Konstantin Gavrilov and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work is dedicated to the investigation of the interaction between an Atmospheric Boundary Layer and a canopy (representing a forest cover). We have focused our attention to the complex problem of the generation and transformation of turbulent vortices over homogeneous, heterogeneous and sparse canopy. This problem has been studied using Large Eddy Simulation (LES) approach and High Performance Computing (HPC) technique.The numerical results reproduced correctly all the main characteristics of this flow, as reported in the literature: the formation of a first generation of coherent structures aligned transversally with the wind flow direction, the reorganization and the deformation of these vortex tubes into horse-shoe structures. The results obtained with the introduction of a discontinuity in the canopy (reproducing a clearing or a fuel break in a forest) are compared with the experimental data collected in a wind tunnel. In this case, the results confirmed the existence of a strong turbulence activity inside the canopy at a distance equal to 8 times the height of the canopy, referenced in the literature as the Enhance Gust Zone (EGZ) characterized by a local peak of the skewness factor. Then, the process of passive scalar transport from a forest canopy into a clear atmosphere is studied for two cases, i.e., when the concentration held by the forest canopy is either constant or variable. While this difference has little influence on the concentration patterns, results show that it has an important influence on the concentration magnitude as well as on the dynamics of the total concentration in the atmosphere.