Dissertations / Theses: 'Atmospheric boundary layer budget'

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Wittebol, Laura A. 1973. "Refinement of the nocturnal boundary layer budget method for quantifying agricultural greenhouse gas emissions." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115843.

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Measuring greenhouse gas (GHG) emissions directly at the farm scale is most relevant to the agricultural sector and has the potential to eliminate some of the uncertainty arising from scaling up from plot or field studies or down from regional or national levels. The stable nighttime atmosphere acts as a chamber within which sequentially-measured GHG concentration profiles determine the flux of GHGs. With the overall goal of refining the nocturnal boundary layer (NBL) budget method to obtain reliable flux estimates at a scale representative of the typical eastern Canadian farm (approximately 1 km2), fluxes of CO2, N2O, and CH4 were measured at two agricultural farms in Eastern Canada. Field sites in 1998 and 2002 were located on an experimental farm adjacent to a suburb southwest of the city of Ottawa, ON, a relatively flat area with corn, hay, and soy as the dominant crops. The field site in 2003 was located in the rural community of Coteau-du-Lac, QC, about 20 km southwest of the island of Montreal, a fairly flat area bordered by the St. Lawrence River to the south, consisting mainly of corn and hay with a mixture of soy and vegetable crops. A good agreement was obtained between the overall mean NBL budget-measured CO2 flux at both sites, near-in-time windy night eddy covariance data and previously published results. The mean NBL-measured N2O flux from all wind directions and farming management was of the same order of magnitude as, but slightly higher than, previously published baseline N2O emissions from agroecosystems. Methane fluxes results were judged to be invalid as they were extremely sensitive to wind direction change. Spatial sampling of CO 2, N2O, and CH4 around the two sites confirmed that [CH4] distribution was particularly sensitive to the nature of the emission source, field conditions, and wind direction. Optimal NBL conditions for measuring GHG fluxes, present approximately 60% of the time in this study, consisted of a very stable boundary layer in which GHG profiles converged at the top of the layer allowing a quick determination of the NBL flux integration height. For suboptimal NBL conditions consisting of intermittent turbulence where GHG profiles did not converge, a flux integration method was developed which yielded estimates similar to those obtained during optimal conditions. Eighty percent of the GHG flux in optimal NBL conditions corresponded to a footprint-modelled source area of approximately 2 km upwind, slightly beyond the typical length of a farm in Coteau-du-Lac. A large portion (50%) of the flux came from within 1 km upwind of the measurement site, showing the influence of local sources. 'Top-down' NBL-measured flux values were compared with aggregated field, literature and IPCC flux values for four footprint model-defined areas across both sites, with results indicating that in baseline climatic and farm management conditions, with no apparent intermittent NBL phenomena, the aggregated flux was a good approximation of the NBL-measured flux.

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Mathieu, Nathalie. "A study of atmospheric properties and their impact on the use of the nocturnal boundary layer budget technique for trace gas measurement /." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82291.

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While most micrometeorological measurement techniques are only suitable for windy conditions, the Nocturnal Boundary Layer Technique can be used to measure trace gas flux during calm, clear nights as the nighttime stability enables gas emitted at the ground to accumulate. The difference between two measurements over the whole depth of this layer is believed to integrate emissions from a large area representative of, in this study, an agricultural farm. A tethersonde and infrared gas analyzer attached to a blimp carrying a bag sampling system monitored atmospheric variables for each ascent during two summer field campaigns. A mini-SODAR was installed in the field to obtain the wind flowfield. Strong accumulation was observed under low level jets suggesting that this feature acts as a good lid for trace gases. An average background vertical motion different from zero seemed to have more influence on gas propagation than did intermittent turbulence. On at least one night, a density current created by the nearby St-Lawrence River was observed to influence measurements.

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Wittebol, Laura. "Refinement and verification of the nocturnal boundary layer budget method for estimating greenhouse gas emissions from Eastern Canadian agricultural farms." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66706.

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Measuring greenhouse gas (GHG) emissions directly at the farm scale is most relevant to the agricultural sector and has the potential to eliminate some of the uncertainty arising from scaling up from plot or field studies or down from regional or national levels. The stable nighttime atmosphere acts as a chamber within which sequentially-measured GHG concentration profiles determine the flux of GHGs. With the overall goal of refining the nocturnal boundary layer (NBL) budget method to obtain reliable flux estimates at a scale representative of the typical eastern Canadian farm (approximately 1 km2), fluxes of CO2, N2O, and CH4 were measured at two agricultural farms in Eastern Canada. Field sites in 1998 and 2002 were located on an experimental farm adjacent to a suburb southwest of the city of Ottawa, ON, a relatively flat area with corn, hay, and soy as the dominant crops. The field site in 2003 was located in the rural community of Coteau-du-Lac, QC, about 20 km southwest of the island of Montreal, a fairly flat area bordered by the St. Lawrence River to the south, consisting mainly of corn and hay with a mixture of soy and vegetable crops. A good agreement was obtained between the overall mean NBL budget-measured CO2 flux at both sites, near-in-time windy night eddy covariance data and previously published results. The mean NBL-measured N2O flux from all wind directions and farming management was of the same order of magnitude as, but slightly higher than, previously published baseline N2O emissions from agroecosystems. Methane fluxes results were judged to be invalid as they were extremely sensitive to wind direction change. Spatial sampling of CO2, N2O, and CH4 around the two sites confirmed that [CH4] distribution was particularly sensitive to the nature of the emission source, field conditions, and wind direction. Optimal NBL conditions for measuring GHG fluxes, present approximately 60% of the t
Les don nées sur les émissions des gaz à effet de serre (GES) obtenues au niveau des fermes entières agricoles sont pertinentes au secteur agricole et ont le potentiel d'éliminer une partie de l'incertitude qui se produit quant à l'extrapolation du niveau de la parcelle jusqu'au niveau du champ. La couche limite nocturne (CLN) agit comme une chambre virtuelle dans laquelle on fait plusieurs ascensions pour déterminer les fluxes de GES. Dans le but géneral de raffiner la méthode du budget de la CLN afin d'obtenir de plus fiables estimées au niveau de la ferme typique (environ 1 kilomètre carré), les fluxes de CO2, N2O, et CH4 ont été mesurés sur deux fermes agricoles dans l'est du Canada. En 1998 et 2002, les sites d'étude se trouvaient sur une ferme près d'une banlieue au sud-ouest d'Ottawa (Ontario), où le terrain est relativement plat et les principales cultures sont le maïs, le foin et le soya. En 2003, le site d'étude se situait dans la communauté rurale de Coteau-du-Lac (Québec), environ 20 km au sud-ouest de Montréal. Bordé par le fleuve St-Laurent au sud, ce terrain est plat et on y cultive surtout le maïs, le foin et un mélange de soya et de légumes. Le flux moyen de CO2 mesuré aux deux sites par la méthode du budget de la CLN correspondait bien avec celui mesuré par la technique de la covariance des fluctuations et aussi avec ce qui est rapporté dans la littérature. Considérant toutes les directions de vent et toutes les pratiques agricoles, la moyenne des flux de N2O mesurés par la technique de NBL était du même ordre de grandeur, quoiqu'un peu plus élevée, que ce qui est rapporté dans la littérature pour les émissions de base de N2O des écosystèmes agricoles. Les résultats pour le CH4 ont été jugés non-valides car l'échantillonage concurrente des trois gaz aux alentours des deux sites a confirmé que le CH4 était particulièrement sensible à la

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Clendon, Penelope Catherine. "Summertime surface mass balance and atmospheric processes on the McMurdo Ice Shelf, Antarctica." Thesis, University of Canterbury. Geography, 2009. http://hdl.handle.net/10092/2630.

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The aim of this research was to demonstrate the relationship between variations in summertime surface mass balance of the McMurdo Ice Shelf and atmospheric processes. The approach encompassed a broad range of techniques. An existing energy balance mass balance model was adapted to deal with debris-covered ice surfaces and modified to produce distributed output. Point based surface energy and mass balance for two key surfaces of the ice shelf were linked to different synoptic types that were identified using a manual synoptic classification. The distributed model was initialised with distributed parameters derived from satellite remote sensing and forced with data from a regional climate model. Patterns of summertime surface mass balance produced by the distributed model were assessed against stake measurements and with respect to atmospheric processes. During the summers of 2003-2004 and 2004-2005 an automatic weather station (AWS) was operated on bare and debris-covered ice surfaces of the McMurdo Ice shelf, Antarctica. Surface mass balance was calculated using the energy balance model driven by the data from the AWS and additional data from permanent climate stations. Net mass balance for the measurement period was reproduced reasonably well when validated against directly measured turbulent fluxes, stake measurements, and continuously measured surface height at the AWS. For the bare ice surface net radiation provided the major energy input for ablation, whereas sensible heat flux was a second heat source. Ablation was by both melt (70%) and sublimation (30%). At the debris-covered ice site investigated, it is inferred that the debris cover is sufficient to insulate the underlying ice from ablation. Synoptic weather situations were analysed based on AVHRR composite images and surface pressure charts. Three distinct synoptic situations were found to occur during the summers, these were defined as Type A, low pressure system residing in the Ross Sea Embayment; Type B, anticyclonic conditions across region; and Type C, a trough of low pressure extending into the Ross Sea Embayment. A dependence of surface energy fluxes and mass balance on synoptic situation was identified for the bare ice surface. The distributed model was found to produce spatial patterns of mass balance which compared well with stake measurements. Mass balance patterns show that the McMurdo Ice Shelf was generally ablating in the west, and accumulating in the east during summer. Areas of enhanced ablation were found which were likely to be caused by the surface conditions and topographic effects on the wind field. The mean summertime surface mass balance across the entire ice shelf for the 2003-2004 and 2004-2005 summers were –2.5 mm w.e. and –6.7 mm w.e. respectively. The differences between the two summers are inferred to be a result of more frequent type A conditions occurring during the summer of 2004-2005.

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Styles, Julie Maree, and julie styles@oregonstate edu. "Inverse Modelling of Trace Gas Exchange at Canopy and Regional Scales." The Australian National University. Research School of Biological Sciences, 2003. http://thesis.anu.edu.au./public/adt-ANU20030905.040030.

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This thesis deals with the estimation of plant-atmosphere trace gas exchange and isotopic discrimination from atmospheric concentration measurements. Two space scales were investigated: canopy and regional. The canopy-scale study combined a Lagrangian model of turbulent dispersal with ecophysiological principles to infer vertical profiles of fluxes of CO2, H2O and heat as well as carbon and oxygen isotope discrimination during CO2 assimilation, from concentration measurements within a forest. The regional-scale model used a convective boundary layer budget approach to infer average regional isotopic discrimination and fluxes of CO2 and sensible and latent heat from the evolution during the day of boundary layer height and mean concentrations of CO2 and H2O, temperature and carbon and oxygen isotope composition of CO2. For the canopy study, concentrations of five scalar quantities, CO2, 13CO2, C18O16O, H2O and temperature, were measured at up to nine heights within and above a mixed fir and spruce forest in central Siberia over several days just after snow melt in May 2000. Eddy covariance measurements of CO2, H2O and heat fluxes were made above the canopy over the same period, providing independent verification of the model flux estimates. Photosynthesis, transpiration, heat exchange and isotope discrimination during CO2 assimilation were modelled for sun and shade leaves throughout the canopy through a combination of inversion of the concentration data and principles of biochemistry, plant physiology and energy balance. In contrast to the more usual inverse modelling concept where fluxes are inferred directly from concentrations, in this study the inversion was used to predict unknown parameters within a process-based model of leaf gas and energy exchange. Parameters relating to photosynthetic capacity, stomatal conductance, radiation penetration and turbulence structure were optimised by the inversion to provide the best fit of modelled to measured concentration profiles of the five scalars. Model results showed that carbon isotope discrimination, stomatal conductance and intercellular CO2 concentration were depressed due to the low temperatures experienced during snow melt, oxygen isotope discrimination was positive and consistent with other estimates, radiation penetrated further than simple theoretical predictions because of leaf clumping and penumbra, the turbulence coherence was lower than expected and stability effects were important in the morning and evening. For the regional study, five flights were undertaken over two days in and above the convective boundary layer above a heterogeneous pine forest and bog region in central Siberia. Vertical profiles of CO2 and H2O concentrations, temperature and pressure were obtained during each flight. Air flask samples were taken at various heights for carbon and oxygen isotopic analysis of CO2. Two budget methods were used to estimate regional surface fluxes of CO2 and plant isotopic discrimination against 13CO2 and C18O16O, with the first method also used to infer regional sensible and latent heat fluxes. Flux estimates were compared to ground-based eddy covariance measurements. Model results showed that afternoon estimates for carbon and oxygen isotope discrimination were close to those expected from source water isotopic measurements and theory of isotope discrimination. Estimates for oxygen isotope discrimination for the morning period were considerably different and could be explained by contrasting influences of the two different ecosystem types and non-steady state evaporative enrichment of leaf water.

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Puhales, Franciano Scremin. "Parametrização do transporte de energia cinética turbulenta na camada limite convectiva." Universidade Federal de Santa Maria, 2011. http://repositorio.ufsm.br/handle/1/3899.

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In this work a parameterization for the transport terms of the turbulent kinetic energy (TKE) budget equation, valid for a convective boundary layer (CBL) is presented. This is a hard task to acomplish from experimental data, especially because of the difficulty associated to the measurements of pressure turbulent fluctuations, which are necessary to determine the pressure correlation TKE transport term. Thus, employing a large eddy symulation (LES), all terms of the TKE budget equation were determined for a CBL. From these data, polynomials that describe the TKE transport terms vertical profiles were adjusted for a CBL. The found polynomial fits are a good description of the LES data, and from them it is shown that a simple formulation that directly relates the transport terms to the TKE magnitude has advantages on other parameterizations commonly used in CBL numerical models. Furthermore, the present study shows that the TKE turbulent transport term dominates over the TKE transport by pressure perturbations and that for most of the CBL these two terms have apposite signs. The simulation consists of a full diurnal PBL cycle utilizing, at the surface, a forcing obtained from experimental data, so that the numerical experiment represents a more realistic case than a idealized CBL.
Neste trabalho, uma parametrização para os termos de transporte da equação de balanço de energia cinética turbulenta (ECT), válida para uma camada limite convectiva (CLC), é apresentada. Esta é uma tarefa complicada de ser realizada a partir de dados experimentais, especialmente devido a dificuldade associada às medidas das flutuações de pressão, que são necessárias para a determinação do termo de correlação de pressão. Desta forma, empregando a simulação dos grandes turbilhões (LES, do inglês Large Eddy Simulation), todos os termos da equação de balanço de ECT foram determinados para a CLC. A partir desses dados, foram ajustados polinômios que descrevem os perfis verticais dos termos de transporte para a CLC. Os polinômios obtidos fornecem uma boa descrição dos dados da simulação LES, e em função deles é mostrado que uma formulação simples, que se relaciona com os termos de transporte a partir da ECT, apresenta vantagens em relação a outras paramametrizações comumente empregadas em modelos numéricos para a CLC. Além disso, o presente estudo mostra que o termo de transporte turbulento domina sobre o transporte devido a flutuações de pressão, e que para a maior parte da extensão vertical CLC estes dois termos tem sinais opostos. A simulação consiste em um ciclo diário da CLP, utilizando como forçante de superfície dados obtidos experimentalmente, assim o experimento numérico representa um caso mais realista que uma simulação de CLC estacionária.

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Ayet, Alex. "Flux de quantité de mouvement à l'interface air-mer : approche théorique du couplage entre turbulence et vagues de vent On the Impact of Long Wind-Waves on Near-Surface Turbulence and Momentum Fluxes, in Boundary-Layer Meteorology volume 174, March 2020 Scalewise return to isotropy in stratified boundary layer flows, in JGR Atmospheres 125 (16), August 2020 Scaling laws for the length scale of energy‐containing eddies in a sheared and thermally stratified atmospheric surface layer, in Geophysical Research Letters 47(23), December 2020." Thesis, Brest, 2020. http://www.theses.fr/2020BRES0038.

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Malgré de nombreuses études, le lien de causalité entre vent et vagues fait toujours l’objet de controverses : cela est dû entre autres au caractère multi-échelle d'une surface océanique réaliste, et à la présence de déferlements, qui modifient radicalement sa topologie. Dans cette thèse, ces deux questions sont abordées sous un angle théorique, à travers un modèle phénoménologique, qui relie les propriétés spectrales et moyennées de la turbulence proche de paroi en utilisant la géométrie de tourbillons attachés à celle-ci. La première partie de la thèse revisite ce modèle phénoménologique en questionnant ses hypothèses sous-jacentes et révèle, en particulier, des incohérences dans les modèles utilisés pour décrire le terme de redistribution d'énergie entre composantes turbulentes (modèle de Rotta). Le modèle phénoménologique est ensuite utilisé pour étudier le couplage entre vagues de vent longues (de l'ordre de 10m) et turbulence. Les résultats démontrent que la déformation des tourbillons attachés induite par cette interaction pourrait expliquer une partie de la variabilité des flux de quantité de mouvement à un vent moyen donné. Finalement, le couplage entre la turbulence et les vagues courtes et déferlantes est abordé en définissant une sous-couche rugueuse dans laquelle les propriétés des tourbillons attachés sont définies par la vitesse des fronts déferlants dominants pour un vent donné. Ces deux études posent les bases d'un nouveau paradigme, permettant d'étudier le couplage multi-échelle entre le spectre turbulent et le spectre des vagues. Celui-ci pourrait permettre de mieux prendre en compte l'influence de paramètres environnementaux sur les flux de quantité de mouvement et de chaleur. Il ouvre ainsi de nouvelles perspectives pour les études théoriques et pour l’exploration des données expérimentales
Despite numerous works, the causal link between wind and waves is still a controversial subject. This is due, among others, to the multi-scale nature of a realistic ocean surface and to wave breaking, which changes its topology. In this thesis, such problems are studied from a theoretical perspective, using a phenomenological model linking the spectral and averaged properties of wall-bounded turbulence through the geometry attached eddies.The first part of the thesis revisits this phenomenological model by questioning its underlying assumptions and, in particular, reveals inconsistencies in the models used for the energy redistribution between turbulence components (the Rotta model). The phenomenological model is then used to study the coupling between long wind-waves (of order 10m) and turbulence. Results indicate that the deformation of attached eddies, induced by this interaction, could explain some of the variability in momentum fluxes for a given mean wind. Finally, the study of the coupling between turbulence and short breaking waves is approached by defining a roughness sublayer, in which the properties of the attached eddies depend solely on the speed of the dominant breaking fronts for a given wind. These two studies from the basis of a new paradigm to study the multi-scale coupling between the turbulent and wave spectra. This would allow accounting for the influence of environmental parameters on momentum and heat fluxes, and opens new paths both from a theoretical perspective and for the analysis of experimental data

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Blay, Carreras Estel. "Transitional periods of the atmospheric boundary layer." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/277380.

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The atmospheric boundary layer is the part of the troposphere influenced by the presence of the surface, and where most weather phenomena occur. During the day, with fair weather conditions, a convective boundary layer exists. In contrast, during the night, a stable boundary layer appears. It is important to note that the evolution from a convective boundary layer to a stable boundary layer and vice versa happens through two transitional processes. Due to its complexity and the rapid variability, there is a lack of studies about the morning or afternoon/evening transitions. This thesis wants to solve some of the uncertainties related with the morning and afternoon/evening transition of the atmospheric boundary layer. It is based on observations from the project Boundary-Layer Late Afternoon and Sunset Turbulence (BLLAST) and numerical simulation experiments developed with mixed-layer and large-eddy simulation models. In this thesis, we develop an analysis focused on the role played by the residual layer during the morning transition and by the large-scale subsidence on the evolution of the boundary layer. DALES numerical experiments that include the residual layer are capable of modeling the observed sudden increase of the boundary-layer depth during the morning transition and the subsequent evolution of the boundary layer. These simulations show a large increase in the entrainment buoyancy flux when the residual layer is incorporated into the mixed layer. We also examine how the inclusion of the residual layer above a shallow convective boundary layer modifies the turbulent kinetic energy budget. Large-scale subsidence mainly acts when the boundary layer is fully developed and, for the studied day, it is necessary to consider this in order to reproduce the afternoon observations. Finally, we also investigate how CO2 stored the previous night in the residual layer plays a fundamental role in the evolution of the CO2 mixing ratio during the following day. Moreover, we hypothesize that during the evening transition a delay exists between the instant when the buoyancy flux goes to zero and the time when the local gradient of the virtual potential temperature changes sign contradict the assumption in which are base the gradient-based turbulence models. The results from this work confirm and quantify a flux-gradient delay. Specifically, the observed values of the delay are between approximately 30 and 80 min. The existence of the delay and its duration can be explained by considering the convective time and the competition of forces associated with the classical Rayleigh-Bénard problem. This combined theory predicts that the last eddy formed should produce a delay when the sensible heat flux changes sign during the evening transition. It appears that this last eddy is decelerated through the action of turbulent momentum and thermal diffusivity, and that the delay is related to the convective turnover time. Observations indicate that, as horizontal shear becomes more important, the delay time apparently increases to values greater than the convective turnover time. Finally, we study the existence and characteristics of Lifted Temperature Minimum (LTM) during the evening transition. The study shows that LTM can be detected in calm conditions already during day¿night transition, several hours earlier than the usual time of occurrence reported by previous works. These conditions are fulfilled when weak synoptic forcing exists and the local flow shifts from valley to mountain breeze in a relatively complex orography. Under these special conditions, turbulence becomes a crucial parameter to determine the ideal conditions for observing LTM. Additionally, the correlation of longwave radiation measured at 0.8 m and estimated at the ground varies when the LTM is observed. Therefore, LTM is also related to a change in the atmospheric radiative characteristics under calm conditions.
La capa límit atmosfèrica és la part de la troposfera influenciada per la presència de la superfície terrestre, i on es produeixen la majoria dels fenòmens meteorològics. Durant el dia, en condicions de bon temps, es forma una capa límit convectiva. En canvi, durant la nit, apareix una capa límit estable. L'evolució d'una capa límit convectiva a una capa límit estable i viceversa passa a través de dos processos de transició. A causa de la seva complexitat i la ràpida variació, hi ha una manca d'estudis sobre les transicions del dia a la nit o viceversa. Aquesta tesi vol resoldre algunes de les incerteses relacionades amb les transicions de la capa límit atmosfèrica. La tesi es basa en les observacions obtingudes durant la campanya Boundary-Layer Late Afternoon and Sunset Turbulence i simulacions numèriques desenvolupades amb dos models: un model de capa de mescla i un model de tipus large-eddy simulation. Primerament, es desenvolupa una anàlisi centrada en el paper de la capa residual durant la transició entre la nit i el dia i en el paper de la subsidència en l'evolució de la capa límit. Les simulacions que inclouen la capa residual són capaces de modelar l’augment sobtat de l’alçada de la capa límit durant aquesta transició i també la posterior evolució de la capa límit. Aquestes simulacions mostren un gran augment del flux que entra des de la atmosfera lliure quan la capa residual s'incorpora a la capa convectiva. També s’analitza els efectes de considerar la capa residual en el balanç d'energia cinètica turbulenta. La subsidència actua principalment quan la capa límit està totalment desenvolupada i , pel dia seleccionat, cal tenir-la en compte per tal de reproduir les observacions durant la tarda. Finalment, també investiguem com el diòxid de carboni (CO2) emmagatzemat a la capa residual juga un paper fonamental en l'evolució del CO2 durant el dia. En segon lloc, s'analitza el fet de que durant la transició del dia a la nit hi ha una demora entre el moment en què el flux de flotació esdevé zero i el moment en què el gradient de la temperatura potencial virtual canvia de signa. Aquest fet contradiu el supòsit en què estan basats els models de simulació. Els resultats d'aquest treball confirmen i quantifiquen aquest demora. Específicament, els valors observats de la demora són aproximadament d'entre 30 i 80 min. L'existència de la demora i la seva durada es pot explicar a través del temps convectiu i de les forces associades amb el problema de Rayleigh-Bénard. La teoria proposada considera que l'últim remolí format abans de cessament del flux de superfície produeix el retard en el canvi de signe del gradient del flux de calor. Alhora aquest últim remoli es pot frenar a través de l'acció de la viscositat i la difusivitat tèrmica, i el retard està relacionat amb el temps que dura el recorregut del remolí. Les observacions indiquen que, com més important és el cisallament de vent horitzontal, el temps de retard aparentment augmenta a valors més grans que el temps convectiu. Finalment , s'estudia l'existència i característiques d'un Mínim Elevat de Temperatura (LTM) durant la transició entre el dia i la nit. L'estudi mostra que el LTM es pot detectar en condicions de calma durant aquesta transició hores abans de l'hora d’observació descrita en els treballs anteriors. Aquestes condicions de calma es compleixen quan les forces sinòptiques són febles i el vent local canvia de direcció en una orografia relativament complexa (durant el dia prové de la vall i durant la nit de la muntanya). En aquestes condicions especials, la turbulència es converteix en un paràmetre fonamental per determinar les condicions ideals per a l'observació de LTM. A més, la correlació de la radiació d'ona llarga mesurada a 0,8 m i estimada a terra varia quan s'observa el LTM. Per tant, el LTM també està relacionada amb un canvi de les característiques radiatives de l’atmosfera en condicions de calma.

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Pennells, Jonathan Stephen. "Atmospheric boundary layer impacts on wind farms." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/19660/.

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Increasing demand for renewable energy sources has meant that wind power is becoming a more crucial source of energy, leading to larger wind farms. It is currently unknown whether wind farms impact the boundary layer. This thesis aims to improve our understanding of the impact from wind farms. To do this, numerical simulations are carried out in BLASIUS and WRF with an existing Wind Farm Parametrisation (WFP) being implemented in BLASIUS. Neutral boundary layer simulations are carried out in BLASIUS, with different velocities, height and capping inversion strengths. It is found that decreases in boundary layer height increase the impact from the wind farm, where the height is between 715 m and 992 m for turbines with a hub height of 95 m. Increases in velocity increase the vertical advection of horizontal momentum upstream of the turbines and greater deceleration of momentum in the wind farm. Non-dimensional analysis found jumps in the inversion layer above the wind farm for Fr < 1, and increases in the pressure perturbations for low Z flows. Comparisons are made between BLASIUS and a linear model for wind farms in neutral boundary layers. The drag term in the linear model is overestimated and should be modified to account for the logarithmic velocity profile near the surface. The assumptions made in the linear model do not inhibit its representation of the velocity and pressure perturbations within the boundary layer. The impact of a wind farm on a sea breeze is investigated using WRF simulations. It is found that a wind farm at the coast does not impact the propagation of the sea breeze but does impact the land breeze. This is due to the turbulent boundary layer which the wake is in, causing a fast decay of the wake. The land breeze propagates through the wind farms and is directly impacted.

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Lazeroms, Werner. "Turbulence modelling applied to the atmospheric boundary layer." Doctoral thesis, KTH, Turbulens, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-166806.

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Turbulent flows affected by buoyancy lie at the basis of many applications, both within engineering and the atmospheric sciences. A prominent example of such an application is the atmospheric boundary layer, the lowest layer of the atmosphere, in which many physical processes are heavily influenced by both stably stratified and convective turbulent transport. Modelling these turbulent flows correctly, especially in the presence of stable stratification, has proven to be a great challenge and forms an important problem in the context of climate models. In this thesis, we address this issue considering an advanced class of turbulence models, the so-called explicit algebraic models.In the presence of buoyancy forces, a mutual coupling between the Reynolds stresses and the turbulent heat flux exists, which makes it difficult to derive a fully explicit turbulence model. A method to overcome this problem is presented based on earlier studies for cases without buoyancy. Fully explicit and robust models are derived for turbulence in two-dimensional mean flows with buoyancy and shown to give good predictions compared with various data from direct numerical simulations (DNS), most notably in the case of stably stratified turbulent channel flow. Special attention is given to the problem of determining the production-to-dissipation ratio of turbulent kinetic energy, for which the exact equation cannot be solved analytically. A robust approximative method is presented to calculate this quantity, which is important for obtaining a consistent formulation of the model.The turbulence model derived in this way is applied to the atmospheric boundary layer in the form of two idealized test cases. First, we consider a purely stably stratified boundary layer in the context of the well-known GABLS1 study. The model is shown to give good predictions in this case compared to data from large-eddy simulation (LES). The second test case represents a full diurnal cycle containing both stable stratification and convective motions. In this case, the current model yields interesting dynamical features that cannot be captured by simpler models. These results are meant as a first step towards a more thorough investigation of the pros and cons of explicit algebraic models in the context of the atmospheric boundary layer, for which additional LES data are required.

QC 20150522

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Findell, Kirsten L. (Kirsten Lynn). "Atmospheric controls on soil moisture-boundary layer interactions." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/44509.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001.
Includes bibliographical references (leaves 163-168).
This thesis addresses the question of how the early morning atmospheric thermodynamic structure affects the interaction between the soil moisture state and the growth and development of the boundary layer (BL), leading to the triggering of convection. It is concluded that in mid-latitudes, for matters of convective triggering and response to land surface conditions, the critical portion of the atmospher~approximately1 to 3 km above the ground surface is independent of geographic location and local synoptic setting. As long as the low levels of the troposphere are relatively humid but not extremely close to saturation, a negative feedback between soil moisture and rainfall is likely when the early morning temperature lapse rate in this region is dry adiabatic; a positive feedback is likely when it is moist adiabatic; and when there is a temperature inversion in this region, deep convection cannot occur, independent of the soil moisture. Additionally, when the low levels of the troposphere are extremely dry or very close to saturation, the occurrence of convection is determined solely by the atmospheric conditions. Essential characteristics of the temperature structure of the early-morning atmosphere are captured by a new thermodynamic measure, the Convective Triggering Potential (CTP), developed to distinguish between soundings favoring rainfall over dry soils from those favoring rainfall over wet soils. Many measures of atmospheric humidity are effective at separating atmospherically-controlled cases from cases where the land surface conditions can influence the likelihood for convection, but Hi low, a variation of a humidity index, proved most effective. A one-dimensional model of the planetary boundary layer (BL) and surface energy budget has been modified to allow the growing BL to entrain air from an observed atmospheric sounding. The model is used to analyze the impact of soil saturation on BL development and the triggering of convection in different atmospheric settings. Results from this 1D model and from the three-dimensional Fifth-Generation Penn State/NCAR Mesoscale Model (MM5) show a small but significant positive soil moisture-rainfall feedback in Illinois. This is consistent with an analysis of the distribution of early morning sounding values of CTP and Hi low from Illinois, though wind effects important in the MM5 simulations are not captured by the CTP-HIhow framework. From the MM5 simulations, it is concluded that the land surface condition can impact the potential for convection only when the atmosphere is not already predisposed to convect or not to convect. This atmospheric predisposition can be determined by analyzing the CTP, the Hi low, and the vertical profile of the winds. Analyses of Hi low scatter plots from radiosonde stations across the contiguous 48 United States reveal that positive feedbacks are likely in much of the eastern half of the country. The only area showing a potential negative feedback is in the Dryline and Monsoon Region of the arid southwest. Land surface conditions are unlikely to impact convective triggering in the rest of the western half of the country. Use of the lD BL model at four additional stations confirms that HilowTP-Hi low framework used in this nationwide analysis is valid for regions far removed from Illinois, where it was originally developed.
by Kirsten Lynn Findell.
Ph.D.

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Svensson, Andreas. "Humidity Structures in the Marine Atmospheric Boundary Layer." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-302863.

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The turbulence structure over the sea was studied with the emphasis on humidity. The data sets used came from the island of Östergarnsholm outside Gotland in the Baltic Sea. The study included spectral and quadrant analyses of the wind, temperature and humidity parameters from one measuring level. The wave state of the sea was deduced from data from a wave rider buoy anchored 4 km from the site.Two turbulence instruments for humidity were compared, the MIUU instrument (hot wire) and an open pass infrared gas analyser from LI-COR. The comparison showed that the LI-COR instrument resolved the high frequency fluctuations of the humidity better. The unstable cospectra of the sensible and latent heat fluxes were studied and categorised. It was found that many cospectra have two or more maxima. The higher frequency maxima gained influence when the stratification became near neutral.The quadrant analyses showed that the structures of humidity flux were similar to those of the heat flux. The sources of the flux were studied using different ratios. The ratio between events of moist updrafts and dry downdrafts were extensively studied. It was shown that the events of moist updrafts were more dominating during swell than during growing sea. When the results of the spectral and quadrant analyses were combined, it was shown that the smaller sized eddies of heat dominate the events of warm updrafts and that the large eddies dominate the cold downdrafts. The bulk transfer number for moisture, the Dalton number (CE), was found to be almost constant with stratification for unstable runs. The mean value was calculated to (1.0±0.3)·10-3.
Målet för denna studie var turbulensstrukturer över hav med särskild tonvikt på fuktigheten. I denna studie har använts observationer från en mast på ön Östergarns-holm, strax öster om Gotland. Arbetet innefattar spektral- och kvadrantanalys av vind, temperatur och fuktighet från en mätnivå. Havets aktuella tillstånd mättes med en vågboj förtöjd 4 km från masten. Två turbulensinstrument för fuktighet jämfördes, MIUU-instrumentet (varmtråds-instrument) och ett instrument från företaget LI-COR som mäter infraröd absorption. Jämförelsen visade att LI-COR-instrumentet löser upp de högfrekventa fuktighets-fluktuationerna bättre. Instabila cospektra för sensibelt och latent värmeflöde studerades och kategoriserades. Det visade sig att många cospektra hade två eller flera maxima. Det högfrekventa maximumet fick ökad betydelse när skiktningen blev nära neutral. Kvadrantanalyserna visade att strukturerna för värme- och fuktighetsflödet är liknande. Källan för flödena studerades med hjälp av olika kvoter. Av särskilt intresse var kvoten mellan tillfällen med fuktiga uppvindar och torra nedvindar. Det visade sig att tillfällen med fuktiga uppvindar var mer dominerande vid dyning än vid upp-byggande vågor. När resultaten från spektral- och kvadrantanalysen kombinerades, visade det sig att de små virvlarna med värme dominerar vid tillfällen med varma uppvindar och att de stora virvlarna dominerar vid kalla nedvindar. Utbyteskoefficienten CE för fuktighet, även kallad Dalton-talet, är nästan konstant för de instabila fallen. Medelvärdet av CE beräknades till (1,0±0,3)·10-3.

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Lee-Thorp, Andrew Michael. "The atmospheric boundary layer above the Agulhas current." Master's thesis, University of Cape Town, 1996. http://hdl.handle.net/11427/19455.

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This thesis describes the atmospheric boundary layer above the Agulhas Current using shipboard meteorological measurements and rawinsonde ascents. The juxtaposition of the warm Agulhas Current and cool shelf waters is shown to have far-reaching effects on the overlying atmosphere. Air-sea fluxes of momentum, sensible and latent heat and resultant boundary layer characteristics demonstrate high horizontal inhomogeneity. The results suggest that this inhomogeneity is permanent. The spatial heat flux gradient is reflected in the overlying atmosphere by a transition in stability of the boundary layer and potential cumulus formation from the cool shelf to the warm current. For airflow perpendicular to the Agulhas Current an internal boundary layer was observed to develop at the inshore sea surface temperature front. Onshore-moving air accumulated a significant quantity of moisture during its trajectory over the current. When airflow is parallel to the current an atmospheric moisture front exists along the axis of the inshore sea surface temperature front. The mean thermodynamic structure of the atmosphere was investigated. An inversion capped the boundary layer whilst a second, higher-level subsidence inversion was found which acts to limit the vertical development of cumulus clouds and therefore the redistribution of heat and moisture above the boundary layer. The results presented in this thesis are useful in two ways. The Agulhas Current has frequently been linked to South African climate. This is the first dedicated study which quantifies and characterizes the atmospheric boundary layer in this region. Secondly, maritime airmasses are dramatically modified above the Agulhas Current. The resultant large horizontal inhomogeneity, its vertical extent and permanence suggest that its inclusion is vital to any successful climate model. Atmospheric general circulation models have been criticized for not taking into account regions of strong horizontal inhomogeneity. The results of this thesis support this argument and highlight the need for similar studies. Bibliography: pages 116-123.

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Holloway, Simon. "Remote sensing measurements of the atmospheric boundary layer : development of a nocturnal boundary layer temperature LiDAR." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/remote-sensing-measurements-of-the-atmospheric-boundary-layer-development-of-a-nocturnal-boundary-layer-temperature-lidar(3de0f22b-8165-4c22-b38e-296062b37940).html.

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A LiDAR instrument to monitor the evolution of the urban boundary layer capping inversion over Manchester has been developed from a previous instrument. This LiDAR uses a frequency-tripled Nd:YAG laser, operating at low pulse energy but high repetition frequency. Rotational Raman scattering of this laser light is parsed into two channels by narrowband interference filters, before detection by photomultiplier tubes operating in photon-counting mode. The receiving telescope was refocused to operate in the boundary layer, and an interference filter was replaced following modelling work. The calibrations of this instrument use locally-launched sondes to determine corrections due to operating in the near-field region of the receiving telescope. The LiDAR receiver was thoroughly calibrated under laboratory conditions to construct a lookup table. Locally-launched sondes were used to correct for mirror shading by instrument components, as well as constrain the overlap function of the BLT. A temperature resolution of better than 0.4K arising from Poisson noise was achieved for data collected for the mean temperature profile measured over the course of a night, with temperature inversions being identifiable down to a height of 500m. A total temperature error of less than 3K was achieved by taking the whole-night mean, which is significantly less than the size of the smallest identified temperature inversion (7.6Â±2K). The LiDAR instrument data was compared with locally-launched sondes to validate the collected data, agreeing with the sonde measurements to within the uncertainty of the instrument. A WRF model temperature output was compared to both the BLT and sonde data and found to poorly capture the boundary layer temperature profile. The inversion strength was always underestimated by several K, and when the inversion height is below 300m the model underestimates the inversion height by 100-500m.

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Perry, Felicity Mary. "Quantification of coherent structures in the atmospheric boundary layer." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496522.

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Öhlund, Olof. "Wind Turbine Sound Propagation in the Atmospheric Boundary Layer." Licentiate thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-224205.

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Wind turbines have grown both in size and number in the past decades. The taller turbines has made it possible to place them in forest areas which is fortunate for a country like Sweden with lots of forest. An issue with wind turbines is the sound they produce. The sound mainly comes from the rotor blades when they pass through the air. The sound heard some distance away from the turbine is sometimes masked by ambient background noise such as wind induced sound in the vegetation, but this is not always the case. Noise concerns among some people living in the vicinity of wind turbines are sometimes raised. Sound propagation models are used to predict the wind turbine sound level at certain distance. It is important that these models are accurate. Sound propagation is greatly influenced by the meteorological conditions. These conditions change over the day and year and vary a lot depending on the terrain conditions. In the past, large meteorological propagation effects have been found for sound sources close to the ground. Higher elevated sources like wind turbines have not been studied as much. One reason for this is that wind turbines are a relatively new sound source. In this thesis the meteorological influence on the wind turbine sound propagation is studied. Continuous simultaneous acoustic and meteorological measurements are performed at two different wind turbine sites during two years to capture all variations in the weather. The two sites are covered by forest, one is flat and the other has shifting terrain. The sites are representative for many locations in Sweden and around the world. The differences between the measured and expected wind turbine sound levels are established for different meteorological categories. The median of all deviations within each meteorological category is then compared. During no snow cover conditions the variation of the median under different meteorological conditions is 6 dBA and during snow cover the variation of the median is 14 dBA. The variations are due to the combined effect of refraction, ground conditions and terrain shape. The deviations from an expected value are seen for all octave bands from 63 Hz to 1000 Hz but are found to most distinct at low frequencies of around 125Hz. Meteorological effects starts to be important somewhere between 400 m and 1000 m from wind turbines.The characteristic "swish" sound from wind turbines are also studied in this thesis. The swish sound or as it is also called, the amplitude modulated sound, is found to be more common under some meteorological conditions such as temperature inversions and downwind conditions. A metric for detection of amplitude modulation duration and strength is proposed. Amplitude modulation, is according to some, the reason why wind turbine sound is perceived as more annoying than other typical environmental sounds at the same sound level. The swishes probably increase the probability to hear the wind turbine sound in presence of other background noise.

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Haggagy, Mahmoud El-Nouby Adam [Verfasser], and Helmut [Akademischer Betreuer] Mayer. "A sodar-based investigation of the atmospheric boundary layer." Freiburg : Universität, 2003. http://d-nb.info/115653271X/34.

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Boppe, Ravi Shankar. "Quasi-coherent structures in the marine atmospheric boundary layer." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09292009-020027/.

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Haggagy, Mahmoud El-Nouby Adam. "A sodar based investigation of the atmospheric boundary layer /." [S.l. : s.n.], 2003. http://www.gbv.de/dms/goettingen/367276976.pdf.

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Edwards, Kathleen A. "The marine atmospheric boundary layer during Coastal Waves 96 /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p3035915.

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Potvin, Guy. "The application of RASS in urban boundary layer meteorology." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0019/NQ44556.pdf.

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MacKenzie, Angus Robert. "'Small system' modelling of the polluted planetary boundary layer." Thesis, University of Essex, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235597.

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Sullivan, Zachary S. "Karst Landscape Influence on the Planetary Boundary Layer Atmosphere." TopSCHOLAR®, 2016. http://digitalcommons.wku.edu/theses/1638.

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Karst landscapes cover approximately 20% of the ice-free land area worldwide. The soluble nature of the bedrock within a karst landscape allows for the formation of caverns, joints, fissures, sinkholes, and underground streams, which affect the hydrological behavior of the region. Currently, the Noah Land-Surface Model (Noah- LSM), coupled with the Weather Research and Forecasting (WRF) model, does not provide a representation of the physical behavior of a karst terrain. Previous research has attempted to model karst behavior through soil moisture and land cover/land use changes to determine the influence this unique landscape may have on atmospheric phenomenon. This highlights the need to study the potential influence that karst landscapes may have on model simulations. For this study, several factors were taken into account while studying karst and meteorology: the verification of a current operational forecasting model against observational data over five years (2007 to 2011), the formation of a karstlike soil type for use within an operational forecasting model, and model behavior once this karst-like soil type was added to the operational forecasting model. The verification of a currently operational forecasting model, the North American Mesoscale (NAM), indicated that, overall, the karst regions may exhibit an influence on local winds (greater error) and precipitation (frequency and forecasting). When developing a realistic karst-like soil proxy for use in the Noah-LSM, hydraulic conductivity values show a variation ranging from around 10-7 and 10-5 m s-1 for the karst bedrock within Tennessee and Kentucky. Sandy loam and clay soils were used, along with bedrock parameters, to determine an average soil parameter type for the epikarst bedrock located within this region. The model study demonstrated that the addition of karst highlighted the potential influence on precipitation distribution and energy fluxes, through RMSD and R2 values taken at a 95% confidence interval.

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Walsh, David J. "Multispectral NOAA Marine Atmospheric Boundary Layer (MABL) estimates during VOCAR." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA283702.

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Nilsson, Erik Olof. "Fluxes and Mixing Processes in the Marine Atmospheric Boundary Layer." Doctoral thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-195875.

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Atmospheric models are strongly dependent on the turbulent exchange of momentum, sensible heat and moisture (latent heat) at the surface. Oceans cover about 70% of the Earth’s surface and understanding the processes that control air-sea exchange is of great importance in order to predict weather and climate. In the atmosphere, for instance, hurricane development, cyclone intensity and track depend on these processes. Ocean waves constitute an obvious example of air-sea interaction and can cause the air-flow over sea to depend on surface conditions in uniquely different ways compared to boundary layers over land. When waves are generated by wind they are called wind sea or growing sea, and when they leave their generation area or propagate faster than the generating wind they are called swell. The air-sea exchange is mediated by turbulent eddies occurring on many different scales. Field measurements and high-resolution turbulence resolving numerical simulations have here been used to study these processes. The standard method to measure turbulent fluxes is the eddy covariance method. A spatial separation is often used between instruments when measuring scalar flux; this causes an error which was investigated for the first time over sea. The error is typically smaller over ocean than over land, possibly indicating changes in turbulence structure over sea. Established and extended analysis methods to determine the dominant scales of momentum transfer was used to interpret how reduced drag and sometimes net upward momentum flux can persist in the boundary layer indirectly affected by swell. A changed turbulence structure with increased turbulence length scales and more effective mixing was found for swell. A study, using a coupled wave-atmosphere regional climate model, gave a first indication on what impact wave mixing have on atmosphere and wave parameters. Near surface wind speed and wind gradients was affected especially for shallow boundary layers, which typically increased in height from the introduced wave-mixing. A large impact may be expected in regions of the world with predominant swell. The impact of swell waves on air-sea exchange and mixing should be taken into account to develop more reliable coupled Earth system models.

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Hepplewhite, C. L. "Radiometric observation of the atmospheric boundary layer : the ROSSA project." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329921.

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Bozier, Karen Elizabeth. "Observations of the atmospheric boundary layer using a Doppler lidar." Thesis, University of Salford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395665.

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Lewis, Huw Wyn. "The dynamics of the atmospheric boundary layer over steep terrain." Thesis, University of Leeds, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434204.

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Cropley, Ford. "Coherent vortical structures in the atmospheric boundary layer near ground." Thesis, Cranfield University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281042.

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Flagg, David D. (David Douglas). "A time-varying subsidence parameterization for the atmospheric boundary layer." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33725.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005.
Includes bibliographical references (p. 46-49).
This study examines the effect of a time-varying parameterization for subsidence in the atmospheric boundary layer (ABL) on a one-dimensional coupled land-atmosphere model. Measurements of large-scale divergence in the ABL are scarce and often marred by error, providing the motivation to model this important physical process and estimate its values from indirect but related observations. Constant parameterizations of-large- scale divergence and/or subsidence velocity are adequate for periods within a characteristic synoptic time scale, but longer studies require a parameterization that yields to local atmospheric change. After confirming the potential significance of subsidence in the ABL, this experiment investigates two key areas: (1) the ability to model subsidence change as a response to estimated time-varying model error and (2) the net improvement and potential benefits of this enhancement. This study indicates a consistent reduction of root-mean-square error scores for the time-varying subsidence (divergence) parameter scheme versus a constant parameterization for the 2 m specific humidity measurement, with negligible change to the 2 m temperature measurement.
(cont.) Model error does not improve explicitly, in spite of the presumed improvement to model physics. However, the unknown nature of the model error precludes an accurate diagnose of change, thus leaving the root-mean-square-error scores as the principal tool of evaluation and hence the justifying the potential usefulness of the time-varying parameterization.
by David D. Flagg.
S.M.

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Tastula, Esa-Matti. "Insights into the Challenges of Modeling the Atmospheric Boundary Layer." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5782.

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This work approaches the topic of modeling the atmospheric boundary layer in four research projects, which are summarized below. i) The diurnal cycles of near-surface meteorological parameters over Antarctic sea ice in six widely used atmospheric reanalyses were validated against observations from Ice Station Weddell. The station drifted from February through May 1992 and provided the most extensive set of meteorological observations ever collected in the Antarctic sea ice zone. For the radiative and turbulent surface fluxes, both the amplitude and shape of the diurnal cycles varied considerably among different reanalyses. Near-surface temperature, specific humidity, and wind speed in the reanalyses all featured small diurnal ranges, which, in most cases, fell within the uncertainties of the observed cycle. A skill score approach revealed the superiority of the ERA-Interim reanalysis in reproducing the observed diurnal cycles. An explanation for the shortcomings in the reanalyses is their failure to capture the diurnal cycle in cloud cover fraction, which leads to errors in other quantities as well. Apart from the diurnal cycles, NCEP-CFSR gave the best error statistics. ii) The accuracy of prediction of stable atmospheric boundary layers depends on the parameterization of the surface layer which is usually derived from the Monin-Obukhov similarity theory. In this study, several surface-layer models in the format of velocity and potential temperature Deacon numbers were compared to observations from CASES-99, Cardington, and Halley datasets. The comparisons were hindered by a large amount of scatter within and among datasets. Tests utilizing R2 demonstrated that the Quasi-Normal Scale Elimination (QNSE) theory exhibits the best overall performance. Further proof of this was provided by 1D simulations with the Weather Research and Forecasting (WRF) model. iii) The increasing number of physics parameterization schemes adopted in numerical weather forecasting models has resulted in a proliferation of inter-comparison studies in recent years. Many of these studies concentrated on determining which parameterization yields results closest to observations rather than analyzing the reasons underlying the differences. In this work, the performance of two 1.5-order boundary layer parameterizations was studied, the QNSE and Mellor-Yamada-Janjić (MYJ) schemes, in the Weather Research and Forecasting (WRF) model. The objectives were to isolate the effect of stability functions on the near-surface values and vertical profiles of virtual temperature, mixing ratio and wind speed. The results demonstrate that the QNSE stability functions yield better error statistics for 2-m virtual temperature but higher up the errors related to QNSE are slightly larger for virtual temperature and mixing ratio. A surprising finding is the sensitivity of the model results to the choice of the turbulent Prandtl number for neutral stratification (Prt0): in the Monin-Obukhov similarity function for heat, the choice of Prt0 is sometimes more important than the functional form of the similarity function itself. There is a stability-related dependence to this sensitivity: with increasing near-surface stability, the relative importance of the functional form increases. In near-neutral conditions, QNSE exhibits too strong vertical mixing attributed to the applied turbulent kinetic energy subroutine and the stability functions including the effect of Prt0. iv) In recent years, many eddy-diffusivity mass flux (EDMF) planetary boundary layer (PBL) parameterizations have been introduced. Yet, most validations are based on idealized setups and/or single column models. To address this gap, this study focused on the effect the mass flux part has on the performance in the QNSE-EDMF PBL scheme in the WRF model by comparing the results to observations from the CASES-97 field campaign. In addition, two refined versions, one introducing the parameterized clouds to the WRF radiation scheme, and the second adding a different entrainment formulation, were evaluated. The introduction of mass flux reduced errors in the average moisture profile but virtual temperature and wind speed profiles did not change as much. The turbulent flux profiles for modeled virtual potential temperature were little affected, with consistent reasonable agreement with observations, if one allows for biases in the observed data and modeled surface fluxes. However, the water vapor flux divergences from QNSE tend to be more negative than observed, while including the mass flux part tends to make the divergences more positive, the latter at least partially due to deeper model PBLs resulting from excessive model surface virtual temperature fluxes. Further, both virtual potential temperature and water vapor flux profiles display spurious spikes attributed to the way the non-local and local terms interact in the model. The influence of the mass flux schemes extends to 60 – 100-km scale circulation features, which were greatly modified by both the inclusion of mass flux and the new entrainment formulation. Adding mass flux based clouds to the radiation calculation improved the time and space averaged modeled incoming shortwave flux. The choice of the representation for entrainment/detrainment often affected the results to the same extent as adding mass flux did.

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Gavrilov, Konstantin. "Numerical modeling of atmospheric boundary layer flow over forest canopy." Thesis, Aix-Marseille 2, 2011. http://www.theses.fr/2011AIX22007/document.

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Ce travail de recherche concerne l’interaction entre une couche limite atmosphérique et une canopée (représentant un couvert forestier). J’ai étudié le problème complexe de production et d’évolution de grosses structures turbulentes au dessus de couverts homogènes et hétérogènes, moyennement denses. J’ai abordé ce problème en mettant en œuvre les outils de la simulation numérique des grosses structures (LES) et du calcul haute performance (HPC). Les résultats numériques obtenus, reproduisent correctement les principales caractéristiques de cet écoulement, telles qu’elles sont rapportées dans la littérature : la formation d’une première génération de structures cohérentes en rouleaux, orientées transversalement par rapport à la direction de l’écoulement principal, puis la réorganisation et la déformation de ces structures qui évoluent vers une forme en fer à cheval. Les résultats obtenus au dessus d’un couvert discontinu (représentant une clairière ou une coupure de combustible dans une forêt), ont été comparés avec des données expérimentales collectées dans une soufflerie. Ceux-ci confirment l’existence d’un niveau élevé de turbulence au sein même du couvert végétal à une distance égale à 8 fois la hauteur de canopée. Cette zone, (appelée « Enhance Gust Zone » dans la littérature), est par ailleurs caractérisée par l’existence d’un pic local du facteur de dissymétrie (« skewness factor »).Le transport d’un contaminant passif émis par le feuillage a été également étudié, dans deux configurations, en supposant que la concentration à la surface du feuillage pouvait être considérée comme constante (source infinie) ou variable (source finie) en fonction du temps. Les résultats montrent un impact significatif de cette hypothèse sur la dynamique et le niveau des concentrations relevées dans l’atmosphère
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

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33

Bruno, Olimpia. "Turbulence models in the atmospheric boundary layer under convective conditions." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/6579/.

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In this work a modelization of the turbulence in the atmospheric boundary layer, under convective condition, is made. For this aim, the equations that describe the atmospheric motion are expressed through Reynolds averages and, then, they need closures. This work consists in modifying the TKE-l closure used in the BOLAM (Bologna Limited Area Model) forecast model. In particular, the single column model extracted from BOLAM is used, which is modified to obtain other three different closure schemes: a non-local term is added to the flux- gradient relations used to close the second order moments present in the evolution equation of the turbulent kinetic energy, so that the flux-gradient relations become more suitable for simulating an unstable boundary layer. Furthermore, a comparison among the results obtained from the single column model, the ones obtained from the three new schemes and the observations provided by the known case in literature ”GABLS2” is made.

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Andrae, Ulf. "Turbulence structures in a non-stationary marine atmospheric boundary layer." Thesis, Uppsala universitet, Meteorologiska institutionen, 1996. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-392332.

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The vertical structure in the coastal marine atmosphere has been investigated using data from aircraft measurements performed along the Blekinge coast. The present data are from the third of October 1990. The main feature is fairly homogeneous horizontal conditions and a subceeing boundary layer which lowers from 600 meters down to about 50 meters during the day. The turbulence were found to be in a decreasing state. The turbulence parameters were normalized using normal stationary scaling, in order to compare with other results.

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Harris, Brad G. "Analysis of lateral boundary effects on inner domain of COAMPS." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Sep%5FHarris.pdf.

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Thesis (M.S. in Meteorology and Physical Oceanography and M.S. in Applied Mathematics)--Naval Postgraduate School, Sept. 2004.
Thesis advisor(s): Douglas K. Miller, Beny Neta. Includes bibliographical references (p. 83). Also available online.

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Paunova, Irena T. "Explicit numerical study of aerosol-cloud interactions in boundary layer clouds." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100670.

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Aerosol-cloud interactions, the mechanisms by which aerosols impact clouds and precipitation and clouds impact aerosols as they are released upon droplet evaporation, are investigated by means of explicit high-resolution (3 km) numerical simulations with the Mesoscale Compressible Community (MC2) model. This model, which is non-hydrostatic and compressible, was extended by including separate continuity equations for dry and activated multi-modal aerosol, and for chemical species. The sources and sinks include: particle activation, solute transfer between drops, generation of extra soluble material in clouds via oxidation of dissolved SO2, and particle regeneration. The cloud processes are represented by an advanced double-moment bulk microphysical parameterization.
Three summertime cases have been evaluated: a marine stratus and a cold frontal system over the Bay of Fundy near Nova Scotia, formed on 1 Sep 1995 and extensively sampled as a part of the Radiation, Aerosol, and Cloud Experiment (RACE); and a continental stratocumulus, formed over the southern coast of Lake Erie on 11 July 2001. The marine stratus and the frontal system have been examined for the effects of aerosol on cloud properties and thoroughly evaluated against the available observations. The frontal system and the continental stratocumulus have been evaluated for the effects of cloud processing on the aerosol spectrum.
The marine stratus simulations suggest a significant impact of the aerosol on cloud properties. A simulation with mechanistic activation and a uni-modal aerosol showed the best agreement with observations in regards to cloud-base and cloud-top height, droplet concentration, and liquid water content. A simulation with a simple activation parameterization failed to simulate essential bulk cloud properties: droplet concentration was significantly underpredicted and the vertical structure of the cloud was inconsistent with the observations. A simulation with a mechanistic parameterization and a bi-modal aerosol, including a coarse mode observed in particle spectra below cloud, showed high sensitivity of droplet concentration to the inclusion of the coarse mode. There was a significant reduction in droplet number relative to the simulation without the coarse mode. A similar change occurred in the precipitating system preceding the stratus formation, resulting in an enhancement of precipitation in the weaker (upstream) part of the system while the precipitation in the more vigorous (downstream) part of the system remained almost unaffected.
Aerosol processing via collision-coalescence and aqueous chemistry in the non-drizzling stratocumulus case suggests that impact of the two mechanisms is of similar magnitude and can be as large as a 3-5 % increase in particle mean radius. A more detailed analysis reveals that the impact of chemical processing is oxidant-limited; beyond times when the oxidant (H 2O2) is depleted (∼ 40 minutes), the extent of processing is determined by supply of fresh oxidant from large-scale advection (fresh gaseous emissions are not considered). Aerosol processing via drop collision-coalescence alone suggests, as expected, sensitivity to the strength of the collection process in clouds. Larger particle growth, up to 5-10 %, is observed in the case of the frontal clouds, which exhibit stronger drop collection compared to that in the stratocumulus case. The processed aerosol exerted a measurable impact on droplet concentrations and precipitation production in the frontal clouds. For the case modeled here, contrary to expectations, the processed spectrum (via physical processing) produced higher droplet concentration than the unprocessed spectrum. The reasons explaining this phenomenon and the resulting impact on precipitation production are discussed.
The current work illustrates the complexity of the coupled system at the cloud system scales, revealed earlier at much smaller large eddy scales. If future parameterizations of the regional effect of aerosols on clouds are to be developed, careful consideration is required of the many of feedbacks in the boundary layer.

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Taylor, Alexander Charles. "Dispersion by time-varying atmospheric boundary layers." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/3602.

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The periods of time-varying turbulence in the atmospheric boundary layer, i.e.\ the morning and evening transitions, are often overlooked or highly idealised by dispersion models. These transitions make up a significant portion of the diurnal cycle and are known to affect the spread of pollution due to the properties of turbulence in the residual and stable layers, resulting in phenomena such as lofting, trapping, and fumigation.\\ Two main simulation techniques are presented for the purpose of modelling the dispersion of passive tracers in both convective and evening transitional boundary layers: Lagrangian stochastic (LS) modelling for 1D, inhomogeneous, non-stationary turbulence; and large-eddy simulation (LES) with a particle model tracing pollutant paths using a combination of the resolved flow velocities and a random displacement model to represent sub-grid scale motions.\\ In the convective boundary layer, LS models more accurately representing the state of turbulence, and including the effect of skewness, are shown to produce dispersion results in closer agreement with LES. By considering individual particle trajectories, a reflective top boundary in LS models is shown to produce un-physical, sharp changes in velocity and position. By applying a correction to the vertical velocity variance based on representing the stable potential temperature gradient above the boundary layer, particles are contained within the boundary layer in a physically accurate way. \\ An LS model for predicting dispersion in time-varying, skewed turbulence is developed and tested for various particle releases in transitional boundary layers with different rates of decay, showing an improvement in accuracy compared with previous LS models. Further improvement is made by applying a correction to the vertical velocity variance to represent the effect of a positive potential temperature gradient developing over the course of the transition. Finally, a developing stable boundary layer is shown to have a significant trapping effect on particles released near the surface. \\

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Shuai, Hua. "Characteristics of Coherent Structures in Marine Atmospheric Surface Layer." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36931.

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Wind speed data of multi-heights have been examined to investigate the spatial and temporal characteristics of coherent structures in the near neutral marine atmospheric surface layer. With Taylor's hypothesis, the temporal velocity signals have been transformed to spatial fluctuations and then visualize these spatial velocity fluctuations to identify the coherent structures. It has been confirmed that there exist similar coherent structures in the marine atmospheric surface layer to those in laboratory turbulent boundary layer. These similar coherent structures include ejections, sweeps, shear layers, transverse vortices, and combined events of the shear layers and transverse vortices. Besides these similar coherent structures, there exist the plume and downdraft motions in the unstable marine atmospheric surface layer.

It has been observed that the streamwise spatial length of the ejections and sweeps is 20-250 m and their mean frequency is of order of 0.01-0.001 /s at mean wind speed of 5-12.6 m/s. Between the region of the upstream ejection and downstream sweep motions an inclined shear layer is often seen. The inclined angle of the shear layer has been observed to vary from 30 to 70 degree with the height and length of the the shear layer. The transverse vortices are seen to exist in every region from the wall up to a height of 45 m and their diameter is up to 40 m. The mean frequency of the shear layers and the transverse vortices is of order of 0.001 /s. In the fully developed stage of the combined event of the shear layer and transverse vortex, the shear layer is generally longer and the diameter of the transverse vortex is larger. The mean frequency of the combined event of the shear layers and the transverse vortices is of order of 0.001 /s. The streamwise spatial length of the plume and downdraft motions is generally from 20 m to 50 m.

Analysis indicates that the mean wind speed is a dominant factor in affecting the spatial and temporal characteristics of the coherent structures in the near neutral marine atmospheric surface layer. As the mean wind speed increases, the frequency of the shear related coherent events will increase, while the frequency of the buoyancy related coherent events (plumes and downdrafts) will decrease. The temperature difference between higher level of the surface layer and sea surface is the second main factor in affecting the spatial and temporal characteristics of the coherent structures. As the marine atmospheric surface layer becomes more stable the coherent motions will be suppressed. The effect of the temperature difference on the buoyancy related plume and downdraft motions is more evident than on the other shear related coherent motions.
Master of Science

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Mayer, Jens-Christopher. "Transport processes of reactive trace gases in the atmospheric boundary layer." kostenfrei, 2008. http://opus.ub.uni-bayreuth.de/volltexte/2009/573/.

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Bauduin, Sophie. "Remote sensing of atmospheric boundary layer composition using infrared satellite observations." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/239053.

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Measuring the composition of the planetary boundary layer is essential for monitoring pollutants and for understanding their impact on environment and health. Nadir satellite remote sensing is particularly appealing to sound this part of the atmosphere, but is however challenging because pollutants concentrations are generally weak and confined in a small part of the atmospheric column. Among the sounders currently in orbit, those operating in the thermal infrared have usually their maximum sensitivity in the mid-troposphere, and are thought to be inadequate to measure the near-surface atmospheric composition. Their sensitivity to this part of the atmosphere is indeed generally limited by low temperature contrast (called thermal contrast) between the ground and the air above it. Shortly before the beginning of this PhD, this has however been challenged with different studies, which have shown the possibility to measure air pollution with thermal infrared sounders in case of high thermal contrast conditions. This was especially demonstrated with the measurement of ammonia global distribution using the Infrared Atmospheric Sounding Interferometer (IASI). This work aims at fully exploring the capabilities of thermal infrared sounders to sound the near-surface atmospheric composition. It mainly focuses on the observations of the IASI instrument, and addresses the following questions: where and when is IASI sensitive to the near-surface atmosphere? How large and how variable is the sensitivity to near-surface pollutants? What are the parameters that drive this variability? The answers to these questions are looked at for two pollutants: sulphur dioxide (SO2) and carbon monoxide (CO), and are obtained through a series of different analyses. SO2 is the first constituent on which this work focuses. The retrieval of its near-surface concentration is first of all attempted in an area surrounding the industrial area of Norilsk. This region, well-known for the extraction of heavy metals and its extremely high levels of pollution, encounters large temperature inversions in winter, which trap SO2 close to the ground. By exploiting these (corresponding to high negative thermal contrast), we show that it is possible to retrieve the surface SO2 concentrations in the region. This is done using a simplified version of the optimal estimation method, based on the use of a total measurement error covariance matrix. Further, we show that the surface SO2 concentration retrieval using the ν3 band is limited, in addition to thermal contrast, by the strong water (H2O) absorption, which renders the lowest atmosphere opaque in this spectral range in case of large humidity. Two conditions are therefore shown to be required to monitor near-surface SO2 in the ν3 band: large thermal contrast and low surface humidity. These findings are confirmed with the retrieval of SO2 at global scale, performed using a newly developed retrieval scheme based on the conversion of radiance indexes into SO2 columns using look-up-tables. It is composed of two successive steps: 1) the determination of the altitude of SO2 and the selection of low plumes (below 4 km), 2) for the selected observations, the conversion of radiance indexes into integrated SO2 0–4 km columns. The distributions and time series so obtained are used to better characterise the variability of IASI sensitivity to surface SO2 in the ν3 band at the global scale, and more particularly, in terms of thermal contrast strength and total column of H2O.The characterisation of IASI sensitivity to CO is realised in a second part of the work. Radiative transfer simulations are conducted first to determine the possibility to detect enhancement in CO near-surface concentrations with IASI. The framework of the optimal estimation is then used to investigate the capability of IASI to decorrelate, as a function of thermal contrast, the CO concentration in the low troposphere from that in the high troposphere. Finally, comparisons of IASI CO observations with co-located aircraft and ground-based measurements are shown to confirm with real data how IASI sensitivity to near-surface CO varies in terms of thermal contrast conditions, and to which extent it allows determining the CO abundance in case of high pollution.
Mesurer la composition de la couche limite atmosphérique depuis les satellites est essentiel pour comprendre l’impact des polluants sur l’environnement global et sur la santé. Parmi les sondeurs actuellement en orbite, ceux opérant dans l’infrarouge thermique sont souvent considérés comme inadéquats pour cet objectif, leur sensibilité à l’atmosphère de surface étant généralement limitée par de faibles contrastes de température (appelés contrastes thermiques, TC) entre le sol et l’air au-dessus. Différentes études récentes ont cependant montré la possibilité de mesurer la pollution de l’air avec ce type de sondeur dans des conditions de TC élevé.Ce travail a pour objectif de redéfinir la capacité des sondeurs opérant dans l’infrarouge thermique à mesurer la composition de l’atmosphère de surface. Il se focalise sur les observations de l’instrument IASI (Interféromètre Atmosphérique de Sondage Infrarouge), et tente de répondre, pour les deux polluants que sont le dioxyde de soufre (SO2) et le monoxyde de carbone (CO), aux questions suivantes :Où et quand IASI est-il sensible à l’atmosphère de surface ?Quels sont les paramètres qui influencent cette sensibilité et dans quelle mesure?Dans une première partie, la thèse se focalise sur l’ajustement des concentrations de SO2 de surface pour la région industrielle de Norilsk, connue pour son niveau de pollution élevé. Nous montrons qu’il y est possible de restituer les concentrations de surface de SO2 en hiver, en exploitant les larges inversions de température (TC négatifs) qui s’y développent. Les restitutions reposent sur une version simplifiée de la méthode de l’estimation optimale, utilisant une matrice complète de l’erreur de mesure. En plus du TC, nous montrons que l’ajustement dans la bande ν3 du SO2 est également limité par la forte absorption de la vapeur d’eau (H2O), qui rend les basses couches de l’atmosphère opaques. La nécessité de combiner des TCs élevés et une faible humidité pour permettre la mesure du SO2 en surface est confirmée par une analyse à l’échelle globale, utilisant une méthode basée sur la mesure d’indices de radiance et leur conversion en colonnes de SO2 à l’aide de tables pré-calculées. Composée de 2 étapes, cette méthode identifie et sélectionne d’abord les panaches situés sous 4 km ;elle convertit ensuite les indices de radiance en colonnes de SO2 intégrées entre 0 et 4 km. Les distributions et séries temporelles obtenues sont utilisées pour caractériser, en termes de valeurs de TC et de colonnes totales d’H2O, la variabilité de la sensibilité de IASI au SO2 de surface dans la bande ν3.Dans la seconde partie du travail, des simulations de transfert radiatif sont entreprises pour déterminer la possibilité de détecter avec IASI des augmentations de la concentration de CO dans l’atmosphère de surface. Le formalisme de l’estimation optimale est aussi utilisé pour analyser l’influence du TC sur la capacité de IASI à décorreler les concentrations du CO dans la basse et la haute troposphère. Finalement, des comparaisons entre les concentrations de CO restituées des mesures IASI sous différentes conditions de TC et de pollution et celles mesurées par avions et par des stations au sol complètent la caractérisation.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

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Schindler, Dirk [Verfasser], and Helmut [Akademischer Betreuer] Mayer. "Characteristics of the atmospheric boundary layer over a Scots pine forest." Freiburg : Universität, 2004. http://d-nb.info/1156532760/34.

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42

Ghobadian, Ali. "Prediction of turburlant dispersion of pollutants in the atmospheric boundary layer." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38012.

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43

Breedt, Hendrik Johannes. "Atmospheric boundary layer stability and its application to computational fluid dynamics." Diss., University of Pretoria, 2005. http://hdl.handle.net/2263/66234.

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In the wind resource and wind turbine suitability industry Computational Fluid Dynamics has gained widespread use to model the airflow at proposed wind farm locations. These models typically focus on the neutrally stratified surface layer and ignore physical process such as buoyancy and the Coriolis force. These physical processes are integral to the accurate description of the atmospheric boundary layer and reductions in uncertainties of turbine suitability and power production calculations can be achieved if these processes are included. The present work focuses on atmospheric flows in which atmospheric stability and the Coriolis force are included. The study uses Monin-Obukhov Similarity Theory to analyse time series data output from a proposed wind farm location to determine the prevalence and impact of stability at the location. The output provides the necessary site data required for the CFD model as well as stability-dependent wind profiles from measurements. The results show non-neutral stratification to be the dominant condition onsite with impactful windfield changes between stability conditions. The wind flows considered in this work are classified as high Reynolds number flows and are based on numerical solutions of the Reynolds-Averaged Navier-Stokes equations. A two-equation closure method for turbulence based on the k __ turbulence model is utilized. Modifications are introduced to standard CFD model equations to account for the impact of atmospheric stability and ground roughness effects. The modifications are introduced by User Defined Functions that describe the profiles, source terms and wall functions required for the ABL CFD model. Two MOST models and two wall-function methods are investigated. The modifications are successfully validated using the horizontal homogeneity test in which the modifications are proved to be in equilibrium by the model�s ability to maintain inlet profiles of velocity and turbulence in an empty domain. The ABL model is applied to the complex terrain of the proposed wind farm location used in the data analysis study. The inputs required for the stability modifications are generated using the available measured data. Mesoscale data are used to describe the inlet boundary conditions. The model is successfully validated by cross prediction of the stabilitydependent wind velocity profiles between the two onsite masts. The advantage of the developed model is the applicability into standard wind industry loading and power production calculations using outputs from typical onsite measurement campaigns. The model is tuning-free and the site-specific modifications are input directly into the developed User Defined Functions. In summary, the results show that the implemented modifications and developed methods are applicable and reproduce the main wind flow characteristics in neutral and non-neutral flows over complex wind farm terrains. In additions, the developed method reduce modelling uncertainties compared against models and measurements that neglect non-neutral stratification.
Dissertation (MEng)--University of Pretoria, 2018.
Mechanical and Aeronautical Engineering
MEng
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44

Liu, Zhong. "Atmospheric boundary layer dynamics near Ross Island and over West Antarctica /." The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487930304687146.

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45

Le, Fevre Julie. "Analysis of boundary layer wind structures associated with land-falling hurricanes." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97234.

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Hurricanes are the most intense form of tropical cyclones and are a major natural hazard affecting millions of people every year. Their intensity, measured in maximum wind speed, is not well forecasted which can lead to an underestimation in the severity of the tropical cyclones and the consequent damage to civil infrastructure, injuries and loss of human life.Part of the problem, as been highlighted by several scientists, is the lack of observations in the boundary layer of hurricanes, particularly over land. This study explores the Velocity Azimuth Display technique with NEXRAD WSR-88D data, adapts it to hurricane boundary layer to retrieve wind profiles and tests its accuracy through comparisons with other observations. This method is applied to two hurricanes and one strong tropical storm that hit the southeast coasts of the United States. The utility of this work is determined through comparisons to model outputs and reanalysis.
Les ouragans constituent un risque naturel majeur qui touche des millions de personnes chaque année. La prévision de leur intensité, la vitesse maximale du vent, n'est pas optimale, pouvant conduire à une sous-estimation de la gravité des cyclones tropicaux, des dégâts, des blessés et des décès.Une partie du problème, soulignée par plusieurs scientifiques, est le manque d'observations dans la couche limite des ouragans, en particulier sur les terres. Cette étude explore la technique de représentation de la vitesse Doppler par rapport à l'azimut avec des données WSR-88D, l'adapte à la couche limite des ouragans pour créer des profils de vent et teste son exactitude grâce à d'autres observations. Cette méthode est appliquée à deux ouragans et une forte tempête tropicale qui ont frappé les côtes sud-est des États-Unis. L'utilité de ce travail est déterminée par comparaison avec des résultats de modèle et des réanalyses.

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Maguire, Andrew J. "Numerical modelling of the stable atmospheric boundary layer overlying a uniform slope." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287633.

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Carlsson, Magnus. "The stable boundary layer over the ice covered Bothnian Bay." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-392449.

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The turbulence structure in a stable boundary layer over ice has been studied. Data from the Bothnian Bay, measured during the BASIS field campaign in February/March 1998, have been used. Turbulence as well as wind- and temperature profiles were measured at three sites. The sites were Umeå at the Swedish East Coast, Kokkola at the Finnish West Coast and the ship R/V Aranda outside the Finnish coast. Turbulence parameters are studied in terms of their stability dependence. At stronger stability σu/u*, σv/u* and σw/u* all increase with stability. At near neutral stratification σw/u* increases with height. A linear dependence of the pressure gradient scale ln(zf/u*) is seen for σw/u* in the interval 0<z/L<0.1. σw/σu first increases and then decreases with stability in agreement with earlier results. From the results it is concluded that the turbulence structure in the stable boundary layer over ice follows the Monin-Obukhov similarity theory. In some of the studied parameters the results from the Umeå site deviate from the other two. Since Umeå has a larger measuring height (10 m) than the other two (2 and 3.5 m) the conclusion is drawn that the surface layer height is lower than 10 m. Data from the Umeå site has been used to study atmospheric phenomena that develop over the marginal ice zone. During two days two phenomena were observed that were triggered by the temperature difference between ice and water - a stable internal boundary layer and an ’ice breeze’ similar to the land breeze. The development of the internal boundary layer has been studied by using an expression for internal boundary layer height. A criterion earlier used to forecast the sea breeze has been shown to be suitable also for the ’ice breeze’.

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Mengesha, Yoseph Gebrekidan. "Atmospheric boundary-layer flow over topography data analysis and representations of topography /." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ39212.pdf.

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廖俊豪 and Chun-ho Liu. "Numerical modelling of atmospheric boundary layer with application to air pollutant dispersion." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31239018.

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Pieterse, Jacobus Erasmus. "CFD investigation of the atmospheric boundary layer under different thermal stability conditions." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80024.

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Thesis (MScEng)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: An accurate description of the atmospheric boundary layer (ABL) is a prerequisite for computational fluid dynamic (CFD) wind studies. This includes taking into account the thermal stability of the atmosphere, which can be stable, neutral or unstable, depending on the nature of the surface fluxes of momentum and heat. The diurnal variation between stable and unstable conditions in the Namib Desert interdune was measured and quantified using the wind velocity and temperature profiles that describe the thermally stratified atmosphere, as derived by Monin- Obukhov similarity theory. The implementation of this thermally stratified atmosphere into CFD has been examined in this study by using Reynoldsaveraged Navier-Stokes (RANS) turbulence models. The maintenance of the temperature, velocity and turbulence profiles along an extensive computational domain length was required, while simultaneously allowing for full variation in pressure and density through the ideal gas law. This included the implementation of zero heat transfer from the surface, through the boundary layer, under neutral conditions so that the adiabatic lapse rate could be sustained. Buoyancy effects were included by adding weight to the fluid, leading to the emergence of the hydrostatic pressure field and the resultant density changes expected in the real atmosphere. The CFD model was validated against measured data, from literature, for the flow over a cosine hill in a wind tunnel. The standard k-ε and SST k-ω turbulence models, modified for gravity effects, represented the data most accurately. The flow over an idealised transverse dune immersed in the thermally stratified ABL was also investigated. It was found that the flow recovery was enhanced and re-attachment occurred earlier in unstable conditions, while flow recovery and re-attachment took longer in stable conditions. It was also found that flow acceleration over the crest of the dune was greater under unstable conditions. The effect of the dune on the flow higher up in the atmosphere was also felt at much higher distances for unstable conditions, through enhanced vertical velocities. Under stable conditions, vertical velocities were reduced, and the influence on the flow higher up in the atmosphere was much less than for unstable or neutral conditions. This showed that the assumption of neutral conditions could lead to an incomplete picture of the flow conditions that influence any particular case of interest.
AFRIKAANSE OPSOMMING: 'n Akkurate beskrywing van die atmosferiese grenslaag (ABL) is 'n voorvereiste vir wind studies met berekenings-vloeimeganika (CFD). Dit sluit in die inagneming van die termiese stabiliteit van die atmosfeer, wat stabiel, neutraal of onstabiel kan wees, afhangende van die aard van die oppervlak vloed van momentum en warmte. Die daaglikse variasie tussen stabiele en onstabiele toestande in die Namib Woestyn interduin is gemeet en gekwantifiseer deur gebruik te maak van die wind snelheid en temperatuur profiele wat die termies gestratifiseerde atmosfeer, soos afgelei deur Monin-Obukhov teorie, beskryf. Die implementering van hierdie termies gestratifiseerde atmosfeer in CFD is in hierdie studie aangespreek deur gebruik te maak van RANS turbulensie modelle. Die handhawing van die temperatuur, snelheid en turbulensie profiele in die lengte van 'n uitgebreide berekenings domein is nodig, en terselfdertyd moet toegelaat word vir volledige variasie in die druk en digtheid, deur die ideale gaswet. Dit sluit in die implementering van zero hitte-oordrag vanaf die grond onder neutrale toestande sodat die adiabatiese vervaltempo volgehou kan word. Drykrag effekte is ingesluit deur die toevoeging van gewig na die vloeistof, wat lei tot die ontwikkeling van die hidrostatiese druk veld, en die gevolglike digtheid veranderinge, wat in die werklike atmosfeer verwag word. Die CFD-model is gevalideer teen gemete data, vanaf die literatuur, vir die vloei oor 'n kosinus heuwel in 'n windtonnel. Die standaard k-ε en SST k-ω turbulensie modelle, met veranderinge vir swaartekrag effekte, het die data mees akkuraat voorgestel. Die vloei oor 'n geïdealiseerde transversale duin gedompel in die termies gestratifiseerde ABL is ook ondersoek. Daar is bevind dat die vloei herstel is versterk en terug-aanhegging het vroeër plaasgevind in onstabiele toestande, terwyl vloei herstel en terug-aanhegging langer gevat het in stabiele toestande. Daar is ook bevind dat vloei versnelling oor die kruin van die duin groter was onder onstabiele toestande. Die effek van die duin op die vloei hoër op in die atmosfeer is ook op hoër afstande onder onstabiele toestande gevoel, deur middel van verhoogte vertikale snelhede. Onder stabiele toestande, is vertikale snelhede verminder, en die invloed op die vloei hoër op in die atmosfeer was veel minder as vir onstabiel of neutrale toestande. Dit het getoon dat die aanname van neutrale toestande kan lei tot 'n onvolledige beeld van die vloei toestande wat 'n invloed op 'n bepaalde geval kan hê.

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Dissertations / Theses on the topic 'Atmospheric boundary layer budget'

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