Дисертації з теми "Covariance turbulente"

Une symetrie fondamentale, la covariance d'echelle, est mise en evidence experimentalement sur un corpus de flammes turbulentes appartenant au regime des flammelettes. Elle implique l'existence d'une courbe unique caracterisant le plissement d'une flamme par la turbulence et integrant dans une meme description toutes nos flammes qu'elles soient faiblement ou fortement plissees. Une consequence directe de ce resultat est la possibilite de definir de maniere deterministe, la construction echelle par echelle d'une flamme par un ecoulement turbulent. La notion de transition d'un objet euclidien vers un objet fractal est ainsi introduite ; elle permet, mieux que la geometrie fractale, de decrire la forme d'une flamme turbulente. Toujours experimentalement, une deuxieme etude a permis de montrer sur nos fronts l'existence d'une intermittence geometrique ; par le biais de l'autosimilarite etendue, les exposants d'echelle ont ete mesures. Nous sommes ainsi parvenu, par voie geometrique, a des resultats comparables a ceux existant en turbulence mais decoulant de mesures de vitesse ; ceci signifie que le phenomene d'intermittence releverait d'une generalite plus grande que l'hydrodynamique pure. Enfin, une derniere etude suggere l'eventuelle utilisation de la flamme comme marqueur de l'ecoulement

La methode des covariances est generalement utilisee pour la mesure des flux turbulents par moyen aeroporte. Cependant elle necessite des equipements sophistiques pour calculer la vitesse verticale de l'air. On propose une methode dissipative-inertielle bien connue pour calculer les flux lorsque les mesures avion sont realisees a basse altitude. Ceci necessite la seule connaissance des caracteristiques du domaine inertiel pour la vitesse et les scalaires. La methode est validee en comparant les flux calcules par la methode dissipative avec les flux calcules par la methode des covariances. L'accord entre les deux est tres bon. Il est ensuite montre comment le taux de dissipation d'energie cinetique turbulente peut etre facilement calcule en utilisant une seule mesure dynamique simple. Ceci permet la mesure a l'aide d'un avion legerement equipe. La deuxieme partie du travail a porte sur l'etude de la variabilite spatiale des flux turbulents calcules par les deux methodes et l'incertitude associee a leur determination. La variabilite spatiale des flux augmente lorsqu'on diminue la longueur d'integration (l#p) et l'erreur evolue suivant une loi voisine de 1/l#p. Les estimations des flux par la methode dissipative-inertielle montrent une plus grande stabilite que celles obtenues par la methode des covariances. Elle peut etre utilisee sur des echantillons plus courts

Le climat et l'activité humaine sont étroitement liés. Les émissions de gaz à effet de serre (GES) impactent la dynamique climatique et la qualité de l'air, affectant des millions de personnes dans le monde. La surveillance efficace des GES est essentielle pour des décisions politiques éclairées, mais elle est complexe en raison de la variabilité des sources et puits, ainsi que du transport atmosphérique. Les réseaux de surveillance abordent cette variabilité en déployant des capteurs dans des lieux géographiques divers, échantillonnant en continu sur le temps.Les zones urbaines sont des points d'émission clés. Cependant, directement surveiller les changements de GES sur > 5 km2 avec des sources variées et des zones végétalisées manque d'une méthode standard. La méthode de covariance turbulente (eddy covariance, EC) offre une surveillance directe et continue du flux net de GES. L'EC basée sur les ondelettes fonctionne sur les mêmes principes mais ne nécessite pas de stationnarité, laissant plus de données exploitables pour l'analyse, ce qui est particulièrement bénéfique dans les environnements urbains complexes.Démêler les composantes anthropiques et biogéniques d'un flux net de CO2 est reconnu comme un problème clé à résoudre dans les zones urbanisées. Les modèles écosystémiques conventionnels utilisés pour partitionner la productivité primaire brute (GPP) et la respiration de l'écosystème (Reco) ne sont pas appropriés pour les zones urbanisées. La partition directe en utilisant des corrélations haute fréquence entre les gaz traceurs peut aider à surmonter les limitations des méthodes de partitionnement standard.Bien que l'EC reste la norme pour les études locales, l'estimation des flux de surface à plus grande échelle implique souvent d'assimiler des mesures de concentration de fond à des estimations antérieures à l'aide de modèles de transport. Les méthodes d'inversion utilisant les données de flux de tour sont encore rares et il serait intéressant de les tester dans les zones urbanisées.L'objectif de cette thèse était d'évaluer l'EC basée sur les ondelettes combinée à des méthodes d'inversion bayésiennes pour la cartographie des flux de CO2. Au cours de la thèse, j'ai découvert une nouvelle méthode de partitionnement direct qui a été utilisée pour améliorer l'inversion globale dans la zone suburbaine du plateau de Saclay.Dans le premier article de la thèse, nous avons proposé la nouvelle méthode de partitionnement direct basée sur l'analyse en quadrants des flux décomposés en fréquence de CO2 et de vapeur d'eau. Nous avons montré que cette méthode pouvait fournir des estimations impartiales de GPP et Reco. Nous avons également constaté que l'EC basée sur les ondelettes a gardé jusqu'à ~30% plus des données exploitables.Dans le deuxième article, nous avons utilisé une grande tour équipée d'analyseurs à haute précision mais lents. Malgré des fréquences d'acquisition plus lentes, l'atténuation était limitée à ~20 % par une plus faible contribution de hautes fréquences à cette hauteur. Les résultats encouragent une collaboration entre les réseaux atmosphériques et écosystémiques.Dans le troisième article, nous avons combiné la méthode de partitionnement proposée dans le premier article avec les instruments d'une tour atmosphérique du deuxième article. Le flux de CO2 partionné en biogéniques et anthropiques ont été assimilé dans des estimations spatialisées des flux à quelques km2. Les cartes de flux obtenues offrent l'avantage de reposer sur des mesures de flux directes à l'échelle du paysage et peuvent être utilisées pour informer les inversions à grande échelle à des échelles plus larges.Les résultats centrés sur la région parisienne fournissent des bases pour les mesures de flux à l'échelle du paysage et à definir des stratégies de surveillance des émissions. Ces avancées contribuent à la compréhension et à la résolution des défis environnementaux aux échelles temporelles et spatiales où les décisions sont prises
Climate and human activity are closely linked. Greenhouse gas (GHGs) emissions impact climate dynamics and air quality, affecting millions globally. Effective GHG monitoring is essential for informed policy decisions, yet it is complex due to spatial and temporal variability of sources and sinks, and atmospheric transport. Monitoring networks address this variability by deploying sensors across diverse geographic locations sampling continuously over time.Urban areas are key emission points, driving climate change. However, monitoring direct GHG changes over >5 km2 with varied sources and vegetated areas lacks a standard method. Eddy Covariance (EC) offers direct, continuous GHG net flux monitoring. Wavelet-based EC operates on the same principles as the standard method but calculates covariance using frequency decomposed time series. This approach does not require stationarity, leaving more data available for analysis, particularly beneficial in complex urban environments where non-stationary fluxes are common.Disentangling anthropogenic and biogenic components of a net CO2 flux is recognised as a key issue yet to be resolved in urbanised areas. Conventional ecosystem models used to partition gross primary productivity (GPP) and ecosystem respiration (Reco) are not appropriate for urbanised areas. Direct partitioning using high-frequency correlations between tracer gases may help overcoming the limitations of standard partitioning methods.While Eddy Covariance remains standard for local studies, estimating larger-scale surface fluxes often involves assimilating background concentration measurements to prior estimations using transport models. The progress in satellite imagery and detailed inventories provides a new basis that helps improve these methods. However, inversion methods using tower flux data are still sparse and would be interesting to test in urbanised areas.The objective of this PhD was to evaluate wavelet-based EC combined with Bayesian inversion methods for CO2 flux mapping. During the course of the PhD I discovered a new direct partitioning method that was used with a combination of CH4 and CO to improve the overall inversion in the suburban area of the Saclay plateau.In the first paper of the PhD, we hypothesised that decomposing concentration and wind signals by frequency can capture individual gusts within each frequency, typically mixed in the original signal. We leveraged this feature to propose a new parameter-free direct partitioning method based on quadrant analysis of CO2 and water vapour frequency decomposed fluxes. We showed that this method could indeed provide unbiased estimates of GPP and Reco at a crop and a forest ecosystem site near Paris. We also found that wavelet eddy covariance further saved up to 30% of the non-stationary data in these sites.In the second paper, we proposed using tall towers equipped with high-precision but slow analysers for measuring fluxes. Despite slower acquisition frequencies, attenuation was limited to 20 % by a lower contribution of high frequencies at this height. Results encourage further collaboration between atmospheric and ecosystem networks for in-situ measurements.In the third paper, we combined the partitioning method proposed in the first paper with the flux from the second paper, including now more gases measured to partition CO2 fluxes in biogenic and anthropogenic components and assimilate them in previous spatially-explicit estimations of fluxes at few km2. The obtained flux maps offer the advantage of relying on direct flux measurements at the landscape scale and may be used to informing large-scale inversions at broader scales.Results focused on the Parisian region provide valuable insights for flux measurements at the landscape scale and beyond, and contributing to emission monitoring strategies. These advancements contribute to understanding and addressing environmental challenges at the temporal and spatial scales where decisions are made

För att ta reda på användbarheten av en specialkonstruerad lättviktsanemometer när det gälleratt beräkna turbulenta flöden, har mätdata från instrumentet använts i den så kallade inertialdissipationsmetoden. Resultatet har jämförts med direkta flödesberäkningar från enljudanemometer enligt turbulenta utbytesmetoden, vilka antas vara korrekta. Resultatanalyshar utförts från mätningar på höjderna 8, 16 och 20 m. Lättviktssanemometern (inertialdissipationsmetoden) visade sig stämma bra överens med ljudanemometern (turbulentautbytesmetoden) under nära neutrala förhållanden och vid höga vindhastigheter. Resultatenvisar ett inflytande av havsvågor och den bör därför användas vid uppbyggande sjö för attundvika detta. I rapporten presenteras en rekommendation med nödvändiga korrektioner föranvändning av lättviktsanemometern till turbulenta flödesberäkningar enligt inertialdissipationsmetoden.
In order to evaluate a combined cup anemometer/wind vane profile instrument, measurementsfrom the instrument has been used in the so called inertial-dissipation method to derive itsability to measure turbulent fluxes. The result was compared to data from a sonic anemometercalculated with eddy-correlation method, which is assumed to be correct. Analysis of theresult was made from measurements at levels 8, 16 and 20 m. The profile instrument (inertialdissipationmethod) agreed well with the sonic anemometer (eddy-correlation method) duringnear neutral conditions and at high wind speed. The profile instrument also proved to be mostaccurate at conditions of growing sea, otherwise the result was affected by waves. In thereport there is also a recommendation for specific corrections when the profile instrument isused for calculating turbulent fluxes according to the inertial-dissipation method.

The study of vegetation‒atmosphere exchanges is today of great interest in order to understand and model plant responses to environmental conditions and their potential influence on global climate change. A special attention is usually given to carbon dioxide (CO2) fluxes and, in general, natural ecosystems such as forests received more attention. In the present work we investigated vegetation‒atmosphere interactions over vineyards, focusing on the annual carbon budget and turbulent transport processes driving exchanges of mass and energy. Vineyard is a complex ecosystem with distributed sources/sinks of scalars (water vapour, carbon dioxide, heat), where vines and soil surface combine to give the overall flux of the canopy. In Northern Italy vineyard inter-row is often grassed, playing then an important role in the whole carbon budget. In this context, the partitioning of net ecosystem CO2 exchange (NEE) into soil and vine components deserves a special attention. We monitored vineyard NEE applying the eddy covariance (EC) method for three years, while soil CO2 flux measurements have been carried on using soil chambers (transparent and dark). In 2015, the annual carbon budget of the vineyard was about ‒ 80 g C m‒2 y‒1, however the largest part of carbon assimilation was due to grassed soil compartment (‒ 60 g C m‒2 y‒1). The interannual variability of seasonal carbon budget showed to be high and significantly affected by heat waves and drought spells in summer. During the growing season of 2014, characterized by plenty of rainfall, NEE reached its maximum value of about ‒ 250 g C m‒2. The organization in rows of the vineyard determines a peculiar turbulent transport dynamics within the canopy. However, the morphological structure of the vineyard is greatly variable over the year, shifting from an empty canopy during vine dormancy to dense foliage in summer. We investigated the influence of foliage development on turbulence statistics deploying a vertical array of sonic anemometers. Turbulent flow showed to be greatly influenced by canopy structure. Without leaves, turbulent regime is typical of a rough‒wall boundary layer flow, whereas at full foliage development it assumes the features of a mixing‒layer flow, even if the inflection point at canopy top is weak, due to sparseness of the vineyard. Coherent structures involved in momentum transport and their temporal scales have been also investigated, showing the increasing importance of sweeps throughout the growing season. The average duration of dominating coherent structures was in the order of 6 ‒ 10 s and no clear influence by canopy structure evolution was detected. The research demonstrated the importance of long‒term monitoring of vegetation‒atmosphere exchanges, and also the complexity of turbulent transport dynamics in the canopy space. However, only a thorough comprehension of this mechanics could lead to a solid interpretation of the role of vegetation in fundamental biogeochemical cycles.
Lo studio delle interazioni tra vegetazione e atmosfera è oggi un tema di grande interesse nell’ottica di migliorare la comprensione della risposta delle piante alle variabili ambientali e la modellizzazione del loro ruolo nel cambiamento climatico globale. Particolare attenzione è di solito rivolta ai flussi di anidride carbonica (CO2) e, in genere, gli ecosistemi naturali come le foreste hanno ricevuto una maggiore attenzione. In questa ricerca sono state studiate le interazioni vegetatione-atmosfera su una coltura agraria importante per il bacino mediterraneo, quale il vigneto, focalizzandosi sul monitoraggio del bilancio annuale di carbonio e approfondendo lo studio della meccanica del trasporto turbulento che è alla base degli scambi di energia e materia. Il vigneto è un sistema complesso con diverse sorgenti e sink di scalari (vapore d’acqua, anidride carbonica, calore), in cui le due principali componenti, vite e suolo, compongono il flusso totale della canopy in un rapporto che varia nel corso dell’anno. Nei vigneti del Nord Italia, l’interfila è solitamente non lavorata e inerbita, giocando un ruolo importante nel bilancio del carbonio del sistema. In questo contesto, risulta cruciale la ripartizione dello scambio netto di CO2 dell’ecosistema (Net Ecosystem Exchange, NEE) nelle componenti suolo e vite. Nel corso di questa indagine, la NEE di un vigneto è stata monitorata per tre anni utilizzando la tecnica micrometeorologica dell’ eddy covariance (EC), mentre la misura dei flussi di CO2 al suolo è stata effettuata con camere (a cupola trasparente e oscura). Nel 2015, il bilancio annuale di carbonio del vigneto è stato di circa ‒ 80 g C m‒ 2 a‒ 1, dimostrando quindi la capacità di agire da sink, ma la maggior parte dell’assimilazione è risultata legata al suolo inerbito (‒ 60 g C m‒2 a‒1). In ogni caso, il sistema ha dimostrato un’elevata variabilità interannuale del bilancio del carbonio stagionale, in cui ondate di calore e periodi di siccità estivi hanno giocato un ruolo primario. Nella stagione 2014, caratterizzata da un regime di precipitazione abbondante, la NEE ha raggiunto il valore massimo di circa ‒ 250 g C m‒2. L’organizzazione del vigneto in filari determina una particolare dinamica del trasporto turbolento dentro canopy. Inoltre, la struttura morfologica del vigneto è altamente variabile durante il corso dell’anno, passando da una canopy praticamente vuota nel periodo di dormienza della vite a una situazione dove il fogliame è denso e concentrato nelle file al culmine della stagione vegetativa. L’influenza dello sviluppo della densità fogliare sulle statistiche della turbolenza è stato studiato installando un profilo verticale di anemometri ad ultrasuoni. Il flusso turbolento è risultato fortemente influenzato dalla struttura della canopy. Senza foglie, il regime turbolento è caratteristico di un flusso di parete, mentre con lo sviluppo completo del fogliame assume le proprietà tipiche di un flusso con mixing‒layer, sebbene il flesso al limite superiore della canopy sia poco accentuato, a causa della bassa densità fogliare del vigneto. Infine, è stata condotta un’analisi specifica delle strutture coerenti coinvolte nel trasporto di quantità di moto e sulle loro scale temporali. L’importanza di eventi discendenti che trasportano aria più veloce del flusso medio (sweeps) è aumentata nel corso della stagione. La durata media delle strutture coerenti dominanti è stato nell’ordine di 6 ‒ 10 s e, in questo caso, non è stata riscontrata nessuna chiara correlazione con lo sviluppo della struttura della canopy. Lo studio ha messo in evidenza l’importanza del monitoraggio a lungo termine degli scambi tra vegetazione e atmosfera, ma anche la complessità dei fenomeni di trasporto turbolento che li caratterizzano. Tuttavia, solo la piena comprensione della meccanica di questi processi può portare alla corretta interpretazione del ruolo della vegetazione nei cicli biogeochimici più fondamentali.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
This thesis quantifies the net change of CO2 (NEE) in an irrigated rice crop cultivation in RS (Brazil). The research is part of the project CT-HIDRO, which presents as main purpose the description of surface conditions for different ecosystems in the country. Data were gathered during the cultivation period, from October 2003 to March 2004. During this time, the average air temperature and the incident radiation were suitable for the development of the culture in such an area. The turbulent flows, calculated by the eddy covariance method, overestimated the NEE value, probably due to the low estimate of breathing tax, because, during some night-times, sensor registered little turbulence. Moreover, other factor could have interfered in the result of the flows, for instance, the time in which the flows are calculated. The Webb correction was applied in the curve of NEE, and a value smaller than 1% was found. Such result didn't modify the previous result significantly. The behavior of CO2 flow during the whole analyzed period showed a maximum of -0,47mgCO2 m−2 s −1 in January 2004, what demonstrates the largest absorption of CO2 from the atmosphere by the plant during the day and a smaller liberation at night, due to the development phase in which the plant is. In this case, the Webb correction was also little emphasized, not interfering in the obtained result. The curves that demonstrate the three phases of development of the rice presented a larger absorption of CO 2 during the reproductive phase. The behavior of the flow of CO 2 showed a negative flow during the day, when the plant absorbs CO2 from the atmosphere, and a positive flow during the night, when the inverse process occurs, what was waited for. The latent heat flow presented larger diary average values from January to February, always with positive values, consequence of the rice crop irrigation. Two days with high values of flow of latent heat were obtained, what motivated the analysis of the energy balance. The closing of the energy balance was not reached in both days. A possible reason for that could be the low estimate of flows when the eddy covariance method was applied.
Este trabalho quantifica a troca líquida de CO2 (NEE) em uma área de cultivo de arroz irrigado no RS, como parte do projeto CT-HIDRO, projeto este que tem como finalidade descrever condições de superfície para diferentes ecossistemas do país. Os dados utilizados foram coletados durante o período de cultivo, entre outubro de 2003 e março de 2004. Neste período a temperatura média do ar e a radiação incidente são adequadas para o desenvolvimento da cultura nesta região. Os fluxos turbulentos, calculados pelo método de covariância de vórtices (eddy covariance), superestimaram o valor da NEE, provavelmente devido, a subestimativa da taxa de respiração, pois em alguns períodos noturnos os sensores registraram pouca turbulência. Além disso, outro fator que pode interferir no resultado dos fluxos, como por exemplo, o intervalo em que os fluxos são calculados. Foi aplicada a correção de Webb na curva de NEE e encontrou-se um valor menor que 1%, fato este que não modificou significativamente o resultado encontrado. O comportamento do fluxo de CO 2 durante todo o período analisado, mostrou um pico de -0,47mgCO2 m−2 s −1 , em janeiro de 2004, o que demonstra a maior captura de CO2 da atmosfera pela planta durante o dia e uma menor liberação à noite, devido a fase de desenvolvimento em que a planta se encontra. Neste caso, a correção de Webb também foi pouco acentuada, não interferindo no resultado obtido. As curvas que demonstram as três fases de desenvolvimento do arroz mostraram claramente uma maior absorção de CO 2 durante a fase reprodutiva. O comportamento do fluxo de CO 2 mostra um fluxo negativo durante à dia, quando a planta absorve CO2 da atmosfera e um fluxo positivo durante à noite quando ocorre o processo inverso, o que era esperado. O fluxo de calor latente apresentou maiores valores médios diários entre os meses de janeiro e fevereiro, apresentando sempre valores positivos, conseqüência da irrigação do campo de arroz. Obtivemos dois dias com valores elevados de fluxo de calor latente, o que fez com que analisássemos o balanço de energia. O fechamento do balanço de energia não foi alcançado em ambos os dias. Uma possível razão para isto pode ser o devido à subestimativa dos fluxos quando aplicado o método de covariância de vórtices.

Conselho Nacional de Desenvolvimento Científico e Tecnológico
The dynamics process of the atmosphere near Earth ground is controled by two main forcings, termical and machanics. These process are reponsible for the atmospheric flow variability in this layer, and this variability characterizes the atmospheric turbulence. The presence of turbulence phenomena drives to distinguish it from the rest of atmosphere, such layer is commom called Atmospheric Boundary Layer (ABL). So, the importance of studying ABL is the fact of that turbulence represents an effective transport process near the ground surface. Adequate treating of the experimental data gives more truthful so qualitative as quantitavie when we are interpreting and understading these transports. This is very impportant for suitable trustful charaterizing the turbulent fluxes. This dissertation shows an overview about some basics turbulent data treatment techics. The dataset, colected experimentaly and separed into 27 minutes window samples, were subjected to simple mean, running mean through digital recursive filter e and linear detrending. Our focus are the implications of applying this technics and how each of this acts in turbulent time series of temperature and vertical velocity of the wind data, showing and discussing about the results in the estimating fluxes of sensible heat by Eddy Covariance method and also spectral densities estimates of temperature and vertical wind velocity. The main goal of the study done in this dissertation, was identifying that applying corrections on fase lag, not considered in older digital recursive filter (FDR as proposed by McMillen 1988) and, present into the model (FFDR proposed by Franceschi e Zardi 2003) leads for trusties estimatives, mainly for turbulent temperature spectra, which are the hardest ones for minimizing the non statinarity effects. Clearly, observing the graphical results of temperature spectra, we see that those low frequencies were better removed than the others technics, giving to spectral shape the classics espected shape.
A dinâmica da atmosfera próxima á superfície é regida por dois forçantes principais, um mecânico e outro térmico. Esses processos são responsáveis pela variabilidade dos escoamentos na baixa atmosfera e, é essa variabilidade que caracteriza a turbulência atmosférica. A presença do fenômeno de turbulência, permite distinguir uma camada do restante da atmosfera, esta é chamada de Camada Limite Atmosférica ( CLA). A importância de estudos nessa camada, está relacionada com o fato da turbulência representar um processo efetivo de transporte próximo à superfície. O tratamento adequado dos dados experimentais permite maior contabilidade, tanto qualitativa quanto quantitativas, na interpretação e entendimento desse transporte, ou seja, é necessário para uma adequada caracterização dos fluxos turbulentos. Nesta dissertação são investigadas algumas, das principais técnicas básicas, no tratamento de dados e condicionamento em séries temporais turbulentas. Os dados, experimentalmente coletados e separados em conjuntos de amostras com 27 minutos, são submetidos aos tratamentos com técnicas de média simples, média instantânea através de filtros digitais recursivos e remoção linear de tendência. Obeserva-se as implicações da aplicação destas técnicas, como cada uma delas age nas séries temporais turbulentas de temperatura e velocidade vertical do vento, apresentando e discutindo os resultados dessa aplicação, nas estimativas dos fluxos turbulentos de calor sensível através do método de Covariância dos Vórtices (MCV), e também das densidades espectrais de temperatura e velocidade vertical. Um dos grandes benefícios do estudo feito nessa dissertação, foi identificar que a correção do atraso de fase, que não era levada em consideração nos modelos de filtros digitais anteriores (FDR proposto por McMillen 1988) e, presente no modelo (FFDR Franceschi e Zardi 2003) conduz à estimativas satisfatórias, principalmente para espectros de temperatura turbulenta, que são os mais difíceis de se minimizar os efeitos de não estacionariedade. Ficou claro, observando nos resultados gráficos dos espectros, que a remoção de baixas freqüências nos espectros de temperatura, os deixou com o perfil típico de especros clássicamente esperados.

In the context of the European iSCAPE project (Improving the Smart Control of Air Pollution in Europe) an experiment was set up in order to test photocatalytic coatings effectiveness in reducing the concentration of pollutants. Further analysis on various aspects of the urban environment have been possible thanks to the experiment. The measurements collected during the experimental field campaign have been used to study the differences in the atmospheric phenomena due to the different morphology of two street canyons. Data in time periods characterized by non-synoptic conditions have been selected and then compared. The first part of the study is dedicated to the characterization of the mean flow. Subsequently, turbulent fluxes have been studied for both canyons with the Eddy Covariance method, in order to appreciate the different behaviour of the two canyons. In the end, the data collected have been elaborated with the Quadrant Analysis. This latest study has made possible to compare the results obtained by the measurements in a real urban canopy layer with the results obtained in a controlled environment and in a vegetated canopy layer. The study has examined the intensity of sweep and ejection effects in an urban canopy layer. The results show that in both canyons sweep effects prevail for the downwind case. Instead, for an upwind flow the dominant effects are those of ejection. For parallel wind directions the two canyons behave differently, due to their different morphology. Furthermore, the intensity of both effects is not as strong as in the perpendicular cases. The behaviour of the fluctuations of CO2 and H2O concentration with respect to the temperature fluctuations has been compared to the results obtained in a vegetated canopy layer. The analysis has shown that in the downwind and parallel cases the trends are in agreement with the ones obtained in the vegetated environment. For an upwind flow, however, the expected trends are not found.

Les échanges de chaleur et de quantité de mouvement à l'interface-océan atmosphère jouent un rôle majeur dans la formation et la dynamique des masses d'air et d'eau. Malgré des décennies de recherche, nous avons encore besoin d'améliorer nos connaissances sur ces échanges, et plus spécifiquement nos connaissances sur les flux turbulents, qui sont des variables clés dans les modèles météorologiques et de climat. Dans ces modèles, les processus turbulents sont des processus sous-maille, non-résolus explicitement, ainsi les flux turbulents doivent être modélisés, au travers de paramétrisations, qui sont pour la plupart réalisées à partir de la théorie des similitudes de Monin-Obukhov [1954]. Cependant, d'une part, l'utilisation d'un modèle implique que les coefficients doivent être ajustés. D'autre part, le modèle lui-même peut demander des améliorations. Malheureusement, l'obtention d'estimations de flux avec une bonne précision est un gros défi, à cause des effets intrusifs de la plate-forme sur la mesure, de la précision limité des instruments et des capacités d'échantillonnages propres de chaque instrument.Notre étude porte sur l'estimation des flux turbulents en mer à partir de mesures réalisées avec la nouvelle plate-forme OCARINA (trimaran autonome) lors des campagnes STRASSE 2012 et AMOP 2014. Nous analysons les caractéristiques de la turbulence dans la couche limite de surface, nous estimons les flux turbulents par différentes méthodes, et nous comparons les valeurs des flux en fonction des conditions environnementales, en prenant en compte l'état de mer
Exchanges of heat and momentum at the air-sea interface play a major role in the formation and the dynamics of water and air masses. In spite of decades of research, we still need to improve our knowledge of these exchanges, and more specifically our knowledge of turbulent fluxes, which are key variables in meteorological and climate models. In these models, sub-grid turbulent processes, thus turbulent fluxes also have to be modeled, which is mostly done with the Monin-Obukhov (1954, MOS hereafter) similarity theory. However, on the one hand, the use of a model implies that coefficients have to be adjusted. On the other hand, the model itself may require improvements. Unfortunately, obtaining flux estimates that have a good accuracy is a challenging effort, because of the intrusive effect of the platform, the limited accuracy the instruments, and because the instruments have their own sampling volume.Our study focuses on the estimation of turbulent fluxes at sea from measurements made with the new OCARINA platform (autonomous trimaran) during two campaigns : STRASSE 2012 and AMOP 2014. We analyze the characteristics of turbulence in the surface boundary layer, we estimate the turbulent fluxes by different methods, and compare the values of fluxes depending on environmental conditions, taking into account the sea state

Les échanges de chaleur et de quantité de mouvement à l'interface-océan atmosphère jouent un rôle majeur dans la formation et la dynamique des masses d'air et d'eau. Malgré des décennies de recherche, nous avons encore besoin d'améliorer nos connaissances sur ces échanges, et plus spécifiquement nos connaissances sur les flux turbulents, qui sont des variables clés dans les modèles météorologiques et de climat. Dans ces modèles, les processus turbulents sont des processus sous-maille, non-résolus explicitement, ainsi les flux turbulents doivent être modélisés, au travers de paramétrisations, qui sont pour la plupart réalisées à partir de la théorie des similitudes de Monin-Obukhov [1954]. Cependant, d'une part, l'utilisation d'un modèle implique que les coefficients doivent être ajustés. D'autre part, le modèle lui-même peut demander des améliorations. Malheureusement, l'obtention d'estimations de flux avec une bonne précision est un gros défi, à cause des effets intrusifs de la plate-forme sur la mesure, de la précision limité des instruments et des capacités d'échantillonnages propres de chaque instrument.Notre étude porte sur l'estimation des flux turbulents en mer à partir de mesures réalisées avec la nouvelle plate-forme OCARINA (trimaran autonome) lors des campagnes STRASSE 2012 et AMOP 2014. Nous analysons les caractéristiques de la turbulence dans la couche limite de surface, nous estimons les flux turbulents par différentes méthodes, et nous comparons les valeurs des flux en fonction des conditions environnementales, en prenant en compte l'état de mer
Exchanges of heat and momentum at the air-sea interface play a major role in the formation and the dynamics of water and air masses. In spite of decades of research, we still need to improve our knowledge of these exchanges, and more specifically our knowledge of turbulent fluxes, which are key variables in meteorological and climate models. In these models, sub-grid turbulent processes, thus turbulent fluxes also have to be modeled, which is mostly done with the Monin-Obukhov (1954, MOS hereafter) similarity theory. However, on the one hand, the use of a model implies that coefficients have to be adjusted. On the other hand, the model itself may require improvements. Unfortunately, obtaining flux estimates that have a good accuracy is a challenging effort, because of the intrusive effect of the platform, the limited accuracy the instruments, and because the instruments have their own sampling volume.Our study focuses on the estimation of turbulent fluxes at sea from measurements made with the new OCARINA platform (autonomous trimaran) during two campaigns : STRASSE 2012 and AMOP 2014. We analyze the characteristics of turbulence in the surface boundary layer, we estimate the turbulent fluxes by different methods, and compare the values of fluxes depending on environmental conditions, taking into account the sea state

This thesis develops a one-dimensional version of a new data driven model of turbulence that uses the KL expansion to provide a spectral solution of the turbulent flow field based on analysis of Particle Image Velocimetry (PIV) turbulent data. The analysis derives a 2nd order random field over the whole flow domain that gives better turbulence properties in areas of non-uniform flow and where flow separates than the present models that are based on the Navier-Stokes Equations. These latter models need assumptions to decrease the number of calculations to enable them to run on present day computers or super-computers. These assumptions reduce the accuracy of these models. The improved flow field is gained at the expense of the model not being generic. Therefore the new data driven model can only be used for the flow situation of the data as the analysis shows that the kernel of the turbulent flow field of undular hydraulic jump could not be related to the surface waves, a key feature of the jump. The kernel developed has two parts, called the outer and inner parts. A comparison shows that the ratio of outer kernel to inner kernel primarily reflects the ratio of turbulent production to turbulent dissipation. The outer part, with a larger correlation length, reflects the larger structures of the flow that contain most of the turbulent energy production. The inner part reflects the smaller structures that contain most turbulent energy dissipation. The new data driven model can use a kernel with changing variance and/or regression coefficient over the domain, necessitating the use of both numerical and analytical methods. The model allows the use of a two-part regression coefficient kernel, the solution being the addition of the result from each part of the kernel. This research highlighted the need to assess the size of the structures calculated by the models based on the Navier-Stokes equations to validate these models. At present most studies use mean velocities and the turbulent fluctuations to validate a models performance. As the new data driven model gives better turbulence properties, it could be used in complicated flow situations, such as a rock groyne to give better assessment of the forces and pressures in the water flow resulting from turbulence fluctuations for the design of such structures. Further development to make the model usable includes; solving the numerical problem associated with the double kernel, reducing the number of modes required, obtaining a solution for the kernel of two-dimensional and three-dimensional flows, including the change in correlation length with time as presently the model gives instant realisations of the flow field and finally including third and fourth order statistics to improve the data driven model velocity field from having Gaussian distribution properties. As the third and fourth order statistics are Reynolds Number dependent this will enable the model to be applied to PIV data from physical scale models. In summary, this new data driven model is complementary to models based on the Navier-Stokes equations by providing better results in complicated design situations. Further research to develop the new model is viewed as an important step forward in the analysis of river control structures such as rock groynes that are prevalent on New Zealand Rivers protecting large cities.

学位授与大学：京都大学 ; 取得学位: 博士(工学) ; 学位授与年月日: 2007-09-25 ; 学位の種類: 新制・課程博士 ; 学位記番号: 工博第2843号 ; 請求記号: 新制/工/1418 ; 整理番号: 25528
The unsteady buffeting forces and the gust response prediction of bridges in the atmospheric turbulent flows is recently attracted more attention due to uncertainties in both experiment and analytical theory. The correction functions such as the aerodynamic admittance function and the spatial coherence function have been supplemented to cope with limitations of the quasi-steady theory and strip one so far. Concretely, so-called single-variate quasi-steady aerodynamic admittance functions as the transfer functions between the wind turbulence and induced buffeting forces, as well as coherence of wind turbulence has been widely applied for the gust response prediction. Recent literatures, however, pointed out that the coherence of force exhibits higher than that of turbulence. These correction functions, in the other words, contain their uncertainties which are required to be more understanding. Proper orthogonal decomposition (POD), known as the Karhunen-Loeve decomposition has been applied popularly in many engineering fields. Main advantage of the POD is that the multi-variate correlated random fields/processes can be decomposed and described in such simplified way as a combination of limited number of orthogonally low-order dominant eigenvectors (or turbulent modes) which is convenient and applicable for order-reduced representation, simulation of the random fields/processes such as the turbulent fields, turbulent-induced force fields and stochastic response prediction as well. The POD and its proper transformations based on either zero-time-lag covariance matrix or cross spectral one of random fields/processes have been branched by either the covariance proper transformation (CPT) in the time domain or the spectral proper transformation (SPT) in the frequency domain. So far, the covariance matrix-based POD and its covariance proper transformation in the time domain has been used almost in the wind engineering topics due to its simplification in computation and interpretation. In this research, the unsteady buffeting forces and the gust response prediction of bridges with emphasis on the POD applications have been discussed. Investigations on the admittance function of turbulent-induced buffeting forces and the coherence one of the surface pressure as well as the spatial distribution and correlation of the unsteady pressure fields around some typically rectangular cylinders in the different unsteady flows have been carried out thanks to physical measurements in the wind tunnel. This research indicated effect of the bluff body flow and the wind-structure interaction on the higher coherence of buffeting forces than the coherence of turbulence, thus this effect should be accounted and undated for recent empirical formulae of the coherence function of the unsteady buffeting forces. Especially, the multi-variate nonlinear aerodynamic admittance function has been proposed in this research, as well as the temporo-spectral structure of the coherence functions of the wind turbulence and the buffeting forces has been firstly here using the wavelet transform-based coherence in order to detect intermittent characteristics and temporal correspondence of these coherence functions. In POD applications, three potential topics in the wind engineering field have been discussed in the research: (i) analysis and identification, modeling of unsteady pressure fields around model sections; (ii) representation and simulation of multi-variate correlated turbulent fields and (iii) stochastic response prediction of structures and bridges. Especially, both POD branches and their proper transformations in the time domain and the frequency one have been used in these applications. It found from these studies that only few low-order orthogonal dominant modes are enough accuracy for representing, modeling, simulating the correlated random fields (turbulence and unsteady surface pressure, unsteady buffeting forces), as well as predicting stochastic response of bridges in the time and frequency domains. The gust response prediction of bridges has been formulated in the time domain at the first time in this research using the covariance matrix-based POD and its covariance proper transformation which is very promising to solve the problems of the nonlinear and unsteady aerodynamics. Furthermore, the physical linkage between these low-order modes and physical causes occurring on physical models has been interpreted in some investigated cases.
Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第13372号
工博第2843号
新制||工||1418(附属図書館)
25528
UT51-2007-Q773
京都大学大学院工学研究科社会基盤工学専攻
(主査)教授 松本 勝, 教授 河井 宏允, 准教授 白土 博通
学位規則第4条第1項該当

Sur la rive sud de la Méditerranée, les zones de relief sont le siège d’une intensification des activités agricoles, leurs structurations permettant la captation des eaux de ruissellement. Les enjeux sont l’adaptation à une demande alimentaire croissante et le maintien des populations locales. Au regard de ces pressions anthropiques, conjuguées avec les changements climatiques attendus, il est nécessaire de développer des outils d’aide à la décision pour une gestion optimale de ces agrosystèmes. Dans ce contexte, la quantification des échanges d’énergie et d’eau à l’interface sol - végétation - atmosphère est primordiale, car ils sont étroitement liés aux rendements agricoles, et ils représentent les deux tiers du bilan hydrologique en région semi-arides. Cependant, peu de travaux ont été menés sur ce type de relief caractérisé par des structurations collinaires. La présente étude vise à observer et caractériser les échanges d’énergie et de masse à l’interface sol - végétation - atmosphère, à l’intérieur d’un petit bassin versant agricole à structuration collinaire. Afin de s’assurer de la cohérence des observations mises en œuvre, nous avons recours à deux méthodes indépendantes qui sont le bilan d’énergie et le bilan hydrique, et dont la comparaison à différentes échelles spatiotemporelles se fait via l’évapotranspiration réelle. Pour le bilan d’énergie, nous considérons des techniques de mesures éprouvées en conditions de relief montagneux : les mesures par covariances turbulentes et par scintillométrie. L’analyse des conditions environnementales a montré que le site d’étude est soumis à un forçage de vent externe, avec deux directions de vent dominantes qui induisent des écoulements ascendant et descendant sur les deux versants face au vent. Par suite, les plans d’écoulements capturés par covariances turbulentes sont fortement corrélés à l’inclinaison topographique capturée par MNT, avec des tendances à l’horizontalité selon les conditions de couverture végétale et d’écoulement (ascendant ou descendant). Dans un troisième temps, les corrections d’inclinaison sur les mesures par covariances turbulentes sont significatives, et les flux convectifs sont très variables selon l’écoulement. Cette dernière tendance s’observe aussi pour le rayonnement net, les analyses des variables intermédiaires suggérant une variation de la température de surface en lien avec une variation de la chaleur sensible. Par suite, nous avons comparé les estimations locales par covariances turbulentes et celles intégrées par scintillométrie. Les résultats montrent une surestimation par scintillométrie, expliquée par une caractérisation inadéquate de la hauteur de mesure. Pour finir, la comparaison entre bilan d’énergie et bilan hydrique suggère qu’il est nécessaire d’affiner ce dernier. Estimations énergétiques et hydriques permettent néanmoins de caractériser la dynamique saisonnière de l’état hydrique des cultures, avec des apports en eau suffisants en début de cycle, mais de possibles stress en pleine croissance ou en fin de cycle. L’ensemble de ces travaux montre la cohérence des mesures de flux collectées dans des conditions environnementales particulières, ces mesures pouvant être utilisées pour des travaux ultérieurs de modélisation. Au regard des résultats obtenus, en particulier des variations de flux convectifs selon les conditions d’écoulement, il s’avère en effet nécessaire de reconsidérer les paramétrages actuels des coefficients d’échanges turbulents, afin de les adapter aux effets de couplage entre topographie et direction du vent

River, lakes and   streams account for more carbon dioxide emissions than all other freshwater   reservoirs together. However, there is still lack of knowledge of the   physical processes that control the efficiency of the air-water exchange of   CO2 in these aquatic systems. In the more turbulent water sections   of a river, the gas transfer is thought to be governed by the river’s   morphology such as bottom topography, slope and stream flow. Whiles for wider   sections of the river, the gas transfer could potentially be influenced by   atmospheric forcing (e.g. Wind speed). The main purpose of this project is to   study the fluxes of carbon dioxide and how (wind speed and stream discharge)   influence the CO2 fluxes in the river. In this study, direct and   continuous measurements of CO2 emission was conducted for the   first time in a controlled boreal river in Kattstrupeforsen (Sweden) from   18th April to 10th May 2018. A unique measurement setup which combines eddy   covariance techniques, general meteorology and in situ water variables (for   high accuracy emission measurements) was used. The results show that   in the late winter, an   upward directed CO2 fluxes measured in the river was approximately   2.2 μmol m−2 s−1. This value agrees with many other small and   large rivers where CO2 fluxes has been studied. The river can be   said to serve as source of CO2 to the atmosphere in the day due to   the dominant upward fluxes recorded during the daytime. The results also show   that carbon dioxide fluxes increase with increasing wind speed notably at   wind speed above 2 m s-1. There   was no relation between CO2 fluxes and stream discharge. This   indicates that wind speed could be one principal factor for air- river gas   exchange. The findings in this work on river gas exchange will provide   a basis for a regional estimate and be applicable for many river systems on a   global scale.

2018-07-09

Les sols agricoles sont la principale source du gaz à effet de serre N₂O. Ces émissions sont caractérisées par une variabilité spatiale et temporelle considérable, ce qui rend très difficile leur quantification. L’UR SOLS étudie depuis 2008 les émissions de N₂O dans une zone agricole du Centre de la France. Spécifiquement, nous avons étudié au laboratoire l’effet de la température sur ces émissions et développé une méthode permettant l’estimation des émissions de N₂O à l’échelle du paysage. De façon surprenante, nous avons observé que les émissions de N₂O n’augmentent pas systématiquement avec la température. L’indicateur Q₁₀ est apparu, pour les émissions de N₂O, variable avec le temps. L’utilisation de l’acétylène, inhibiteur de la réduction de N2O, a révélé que les processus biologiques de production et de consommation de N₂O répondent différemment à la température. Les émissions de N₂O mesurées au champ à l’aide de différentes techniques ont permis d’obtenir des résultats cohérents, avec des moyennes de 43 μg N- N₂O m⁻² h⁻¹ pour la méthode par eddy covariance, 37 μg N- N₂O m⁻² h⁻¹ pour la méthode de fast-box et 71 μg N- N₂O m⁻² h⁻¹ pour la méthode des chambres automatiques sur un blé fertilisé. Des méthodes d’attribution des flux ont été développées pour déterminer de façon exhaustive les variations spatiales et temporelles des émissions de N₂O avec élaboration de cartes originales d’émissions à l’échelle du paysage. L’ensemble de ces résultats pourra être utilisé pour le développement de modèles de fonctionnement des écosystèmes. Ils vont contribuer à quantifier les émissions de N₂O aux échelles adaptées pour les inventaires et les stratégies d’atténuation
The greenhouse gas N₂O is mainly emitted by soils. Soil emissions are characterized by considerable spatial and temporal variabilities that make their quantification very difficult. While soil N₂O emissions are studied on an agricultural area in the Central France by the UR SOLS since 2008, we specifically studied in the laboratory the effect of temperature on these emissions and also developed a method for upscaling N₂O emissions from the plot to the landscape scales. Surprisingly, N₂O emissions were observed not to increase with temperature. Q₁₀ values, describing N₂O emission sensitivity to temperature, were observed to change over time. The use of acetylene for inhibiting N₂O reduction has revealed that the biological processes involved in the N₂O production and its consumption respond differently to temperature variations. N2O fluxes measured in the field using several methods covering different scales of the landscape gave consistent results. The mean measured N₂O fluxes were 43 μg N- N₂O m⁻² h⁻¹ for the eddy covariance mast, 37 μg N- N₂O m⁻² h⁻¹ for the fast-box over a similar area, while it was 71 μg N- N₂O m⁻² h⁻¹ by the automatic chambers over a fertilized wheat field. Flux attribution methods were developed to determine both the spatial and temporal variability of the N₂O flux over a 1-km landscape, resulting in original maps of N₂O emissions at the landscape scale. All these results could be further used for developing ecosystem models. Both these ecosystems models and the methodologies hereby proposed for upscaling N₂O emissions will help in soil N₂O emission quantification at large scales, relevant to the inventories and mitigation strategies

This work took place a procedure for processing the data fluxes measured by a system eddy covariance in an experimental site with representative vegetation of the Pampa biome in conjunction with measures of a meteorological station for the period 2013-11-20 to 2015-09-07. From this set of data was performed an analysis of the seasonality of surface energy fluxes and meteorological variables. The results showed that the application of different methods of corrections for the calculation of energy fluxes produces fluxes with different quality levels in relation to the energy balance closure (EBC). The slope varies up to 20% due to different combinations of corrections applied in the processing of data for calculating the average within a 30 minute interval. The correction options that showed greater sensibility were the time constant and the method of removing the turbulent fluctuations. By the diagnosis EBC has found that the change of IRGA closed path to open path improved to about 12% of the EBC, indicating a deficiency of IRGA closed path. It was also verified that the soil term (flow and storage) increased by ~ 4% EBC, indicating its importance for the natural pasture energy balance. Due to non-closure of the energy balance observed in most studies, and this also, a new method of post-closure of the energy balance was proposed, simple but careful because it is based on the quality of classification of energy fluxes (H and LE). The objective of the method is to generate a corrected series of fluxes, it is important for the calibration and validation surface models. In relation to energy partition, evapotranspiration (ET) was the predominant component, with a Fev = 61% of the available radiation and β = 51%. It varies from ~ 4 mm d-1 in the summer to ~ 1 mm d-1 in winter and is mainly controlled by atmospheric forcing (Rn, DPV, Tar) which determined its seasonal variation. In winter, its reduction was also associated with low photosynthetic activity of the vegetation. The daytime average albedo of natural grasslands of Rio Grande do Sul was 18%, with little seasonal variation. Finally, it is here suggested the inclusion of the procedures carried out in this work for the processing of data from the experimental sites SULFLUX.
Neste trabalho realizou-se um procedimento para o processamento dos dados de fluxos medidos por um sistema de covariância dos vórtices turbulentos em um sítio experimental com vegetação representativa do bioma Pampa, em conjunto com medidas de uma estação meteorológica para o período de 20/11/2013 a 07/09/2015. A partir deste conjunto de dados foi realizada uma análise da sazonalidade dos fluxos superficiais de energia e das variáveis meteorológicas. Os resultados mostraram que a aplicação de diferentes métodos de correções para o cálculo dos fluxos de energia produz fluxos com diferentes níveis de qualidade em relação ao fechamento do balanço de energia (FBE). O coeficiente angular (CA) variou até 20% em razão das diferentes combinações de correções aplicadas no processamento dos dados para o cálculo das médias num intervalo de 30 minutos. As opções de correção que mostraram maior sensibilidade foram a constante de tempo e o método de remoção das flutuações turbulentas. Pelo diagnóstico do FBE constatou-se que a mudança de IRGA caminho fechado para caminho aberto melhorou cerca de 12% o FBE, indicando alguma deficiência do IRGA caminho fechado. Também foi verificado que o termo de solo (fluxo e armazenamento) aumentou ~4% o FBE, indicando sua importância para o balanço de energia de pastagem natural. Em virtude do não fechamento do balanço de energia observado na maioria dos estudos, e neste também, foi proposto um novo método de pós-fechamento do balanço de energia, simples, mas criterioso, pois se baseia na classificação de qualidade dos fluxos de energia (H e LE). O objetivo do método é gerar uma série de fluxos corrigidas, importante para a calibração e validação de modelos de superfície. Em relação à partição da energia, a evapotranspiração (ET) foi a componente predominante, com uma Fev = 61% da radiação disponível e β = 51%. Ela variou de ~4 mm d-1 no verão para ~1 mm d-1 no inverno, sendo controlada principalmente pelas forçantes atmosféricas (Rn, DPV, Tar) que determinaram a sua variação sazonal. No inverno, a sua redução foi associada também a baixa atividade fotossintética da vegetação. O albedo médio diurno da pastagem natural do Rio Grande do Sul foi 18%, com pouca variação sazonal. Por fim, fica sugerido aqui a inserção dos procedimentos realizados neste trabalho para o processamento de dados dos sítios experimentais da SULFLUX.

碩士
國立中興大學
環境工程學系
93
The Eddy Covariance System (EC) is now generally acknowledged that can used routinely for direct measurements of fluxes of momentum, heat, and trace gases in the Atmosphere Surface Layer (ASL). In this study we done an experiment on rice paddy at Wufong (24°01´ N, 120°41´ E) for one month (2005/4/4 to 2005/5/4) with EC. We also made vertical temperature and relative humidity profiles in the daytime during experiment period with the tethersonde. Then we compare with latent heat and sensible heat flux with different method, EC, Bowen Ratio Method, and Integral Businger Equation (IBE) Method. We found that the energy was imbalanced with EC. The energy gaps (1- [(LE +H) /(Rn-G-S) ]) are about 35.2 % during daytime and 28.0 % full-time. Using corrections, including with WPL term (Webb, 1980) and Double / Triple Rotation (Aubinet et al., 2000), for reducing the imbalance. After corrections the energy gaps in the daytime were became 27.4 % after correcting, and 20.1 % full-time. When we collect enough data about the real energy balance between the ecosystem on land and ASL with EC routinely. We can use these data to research, proof and improve the simulations of atmosphere, environment, ecosystem, etc. in the future. According to these data, we can have good applications of climate changes, hydrology circulation, remote sensing technology, etc. And we can increase the accuracy of regional weather forecast in the future.

碩士
國立中興大學
環境工程學系所
94
This study is to measure urban surface heat fluxes, especially emphasizing on turbulent heat flux in the atmospheric surface layer using eddy covariance system. The turbulent heat fluxes were measured at 50 m height above ground level on a tower standing on the roof of the Civil and Environmental Building (24°12'' N, 120°67''E) in National Chung-Hsing University, Taichung, Taiwan, for almost four months (2006/2/11~ 2006/6/1). It is found the surface energy budget was imbalanced, the turbulent heat flux was 28.05 % lower than the available surface heat flux during the study period. Corrections are made to reduce the energy gap, including coordinate system rotation, WPL correction, urban albedo correction, advected term correction, and long-wave radiational cooling term correction. After all the above corrections, the energy closure gap is reduced to 4.08 % using two-axis rotation correction, and to 5.68 % using three-axis rotation correction. That is, the result of the two-axis rotational correction is close to the true energy balance. The average urban albedo is determined to be 0.202 estimated within the radius of 1.4 km from the tower site. The peaks of the diurnal CO2 flux were observed at 8 AM and 6 PM, and the peaks of weekly CO2 flux were observed on Monday and Friday. In addition, flux from the east was higher than other wind direction. Therefore, it is suggested that the CO2 flux was mainly from the nearby traffic source, Kuo-Kuang Road.

Le réchauffement climatique affecte fortement les régions nordiques du Canada où le dégel du pergélisol discontinu à sa limite sud est accompagné du mouvement de la limite des arbres vers le nord en zone de pergélisol continu. Ces altérations faites aux paysages de la Taïga des Plaines sont le point de départ de plusieurs rétroactions puisque les changements apportés aux caractéristiques de la surface (au niveau de l’albédo, l’humidité du sol et la rugosité de la surface) vont à leur tour entraîner des modifications biophysiques et éventuellement influencer l’augmentation ou la diminution subséquente des températures et de l’humidité de l’air. Seulement, il y a un nombre important de facteurs d’influence qu’il est difficile de projeter toutes les boucles rétroactives qui surviendront avec les présents changements climatiques en régions nordiques. Dans le but de caractériser les échanges d’eau et d’énergie entre la surface et l’atmosphère de trois sites des Territoires du Nord-Ouest subissant les conséquences de l’augmentation des températures de l’air, la méthode micro-météorologique de covariance des turbulences fut utilisée en 2013 aux sites de Scotty Creek (forêt boréale et tourbière nordique en zone de pergélisol sporadique-discontinu), de Havikpak Creek (forêt boréale nordique en zone de pergélisol continu) et de Trail Valley Creek (toundra arctique en zone de pergélisol continu). En identifiant les procédés biotiques et abiotiques (ex. intensité lumineuse, disponibilité en eau, etc.) d’évapotranspiration aux trois sites, les contrôles par l’eau et l’énergie furent caractérisés et permirent ainsi de projeter une augmentation de la limitation en eau, mais surtout en énergie du site de Trail Valley Creek. La répartition de l’énergie projetée est semblable à celle de Havikpak Creek, avec une augmentation de la proportion du flux de chaleur sensible au détriment de celui latent suite aux modifications des caractéristiques de la surface (albédo, rugosité et humidité du sol). L’augmentation relative du flux d’énergie sensible laisse présager une boucle rétroactive positive de l’augmentation des températures de l’air à ce site. Ensuite, en comparant des données modelées de la hauteur de la couche limite planétaire et des données provenant de profils atmosphériques d’Environnement Canada entre les trois sites, les changements de hauteur de cette couche atmosphérique furent aussi projetés. Trail Valley Creek pourrait connaître une hausse de la hauteur de sa couche limite planétaire avec le temps alors que Scotty Creek connaîtrait une diminution de celle-ci. Ces changements au niveau des couches atmosphériques liés à la répartition des flux d’énergie dans les écosystèmes se répercuteraient alors sur le climat régional de façon difficile à déterminer pour l’instant. Les changements apportés désignent une boucle rétroactive positive des températures de l’air à Trail Valley Creek et l’inverse à Scotty Creek. Les deux axes d’analyse arrivent donc aux mêmes conclusions et soulignent aussi l’importance de l’influence mutuelle entre le climat et les caractéristiques spécifiques des écosystèmes à la surface.
Along the southern margin of permafrost, the boreal forest is underlain by ice-rich and relatively warm permafrost which is converted into permafrost-free peatlands and lake ecosystems due to warmer temperatures and increased thaw rates. At the same time, in the continuous permafrost zone the tree-line of the boreal forest is advancing northward into what is currently Arctic tundra. Both land cover changes in the Taiga Plains ecozone are affecting the magnitude of complex feedback loops, including regional biophysical feedbacks through altered net water vapor and heat exchanges caused by changes in land surface albedo, hydrology and surface roughness. Changes affecting the ecosystems are numerous and it is currently hard to estimate the direction (positive or negative) and magnitude of the resulting biophysical feedbacks. To improve our understanding of implications arising from land cover changes, the energy and water exchanges between surface and atmosphere at three sites in the Northwest Territories, Canada are characterized: Scotty Creek (boreal forest-peatland landscape with sporadic permafrost), Havikpak Creek (boreal forest with continuous permafrost) and Trail Valley Creek (tundra with continuous permafrost). The results of this study are based on measurements of water vapor and heat fluxes obtained with the eddy covariance technique, in addition to supporting ancillary measurements (e.g., net radiation, ground heat flux). For the growing season of 2013, biotic and abiotic controls (ex. light intensity, water availability, etc.) of evapotranspiration at the three sites were identified and analyzed leading to a projected increase in water and energy limitation for Trail Valley Creek. This limitation can be explained by increased energy repartition to sensible heat than to latent heat, following alterations of the land surface as the treeline moves towards the arctic tundra landscape. The relative increase in the sensible heat flux is an indication for an amplified positive feedback of rising air temperature. A comparison of modeled planetary boundary layer heights with Environment Canada atmospheric profiles for the sites leads to the same projection of a positive air temperature feedback. As the treeline moves north, at Trail Valley Creek, an increase of its planetary boundary layer is expected and the opposite phenomenon is expected at Scotty Creek. Albedo, hydrology and surface roughness will be modified, affecting energy partitioning and atmospheric layers which in turn will influence climate. The two methods have led to the same conclusion and highlight the importance of mutual influence between climate and land surface characteristics.

Les forêts boréales stockent de grandes quantités de carbone organique et jouent un rôle important dans le climat planètaire. Le climat est étroitement associé à la surface terrestre à travers les flux de gaz à effet de serre, d’énergie et de vapeur d’eau. Dans la zone de pergélisol sporadique nord-américaine, l’affaissement du sol attribuable au dégel provoque l’expansion de milieux humides sans pergélisol remplaçant des forêts avec pergélisol. Cependant, l’étendue spatiale de ces changements et leurs conséquences sur le climat sont inconnues. Dans cette étude, j’analyse les flux turbulents d’un paysage comprenant des forêts boréales et des milieux humides dans la partie sud de la Taïga des plaines, T.N.-O., Canada. J’associe ces flux avec la modélisation d’empreintes de flux, des données satellite, des données paléoécologiques, et des projections climatiques afin de caractériser l’impact des changements de la couverture terrestre sur les interactions entre la terre et l’atmosphère. Dans la Taïga des plaines, la perte de forêt boréale attribuable au dégel est d’une importance égale à celle due aux feux de forêt. La perte de forêt modifie les flux turbulents d’énergie à travers des changements dans les propriétés aérodynamiques et écophysiologiques de la surface terrestre. L’accroissement de l’albédo cause de petites réductions dans la somme des flux turbulents de chaleur sensible (H) et de chaleur latente (LE)). La diminution de la rugosité et l’augmentation de l’humidité de la surface augmentent toutefois LE tout en réduisant H, ce qui mènerait à une baisse des températures estivales et à une augmentation de l’humidité de l’air, d’après des simulations réalisées à l’aide d’un modèle de la couche limite planétaire. Contrairement à l’effet biophysique de refroidissement du climat régional dû à la perte de couvert forestier, l’expansion des milieux humides et l’augmentation des émissions de méthane (CH4) provoque un réchauffement du climat. L’expansion des milieux humides dans la partie sud de la Taïga des plaines entraîne une augmentation des émissions de 0.034 g CH4 m-2 a-1. Les taux d’absorption de CO2 caractéristiques de ces paysages sont trop faibles pour neutraliser le réchauffement du climat dû aux émissions de CH4 d’ici la fin du 21ème siècle. Tout en dégelant rapidement, ces paysages boréaux restent des puits de CO2, absorbant 74 g CO2 m-2 a-1. L’expansion des milieux humides n’affecte pas les émissions nettes de CO2, les changements de la productivité primaire brute (PPB) et de la respiration de l’écosystème (RE) étant d’une magnitude similaire. Les répercussions négligeables sur les flux nets de CO2 sont largement compensées par les répercussions climatiques directes d’un réchauffement de la température de l’air. Un scénario de réchauffement élevé mène à un accroissement de RE dépassant significativement l’accroissement de PPB. Dans la Taïga des plaines, le dégel du pergélisol a donc des répercussions climatiques qui s’opposent aux plans biophysiques et biogéochimiques. Dans un climat plus chaud, le dégel modifie la façon dont les paysages interagissent avec le climat, ce qui souligne la nécessité d’intégrer les changements dans la couverture terrestre attribuable au dégel dans les modèles du système Terre.
Boreal forests store large amounts of organic carbon and are an important component of the regional and global climate systems. Climate and land surface are closely coupled through the land-atmosphere exchange of greenhouse gases, such as CO2 and CH4, and of energy and water vapor. In lowlands of the North American sporadic permafrost region, thaw-induced surface subsidence leads to expansion of permafrost-free wetlands at the expense of boreal forests underlain by permafrost. However, the spatial extent of these land cover changes and their implications for land-atmosphere interactions are unknown. In this study, I analyze eddy covariance flux measurements from an organic-rich boreal forest-wetland landscape in the southern Taiga Plains, NT, Canada. I combine these measurements with flux footprint modeling, satellite remote sensing data, paleoecological records, and downscaled climate projections to characterize how thaw-induced land cover change affects land-atmosphere interactions and climate. In the Taiga Plains ecozone, thaw-induced boreal forest loss currently transforms the composition and structure of the boreal zone in North America and is of equal importance for tree cover dynamics as wildfire disturbance. Forest loss modifies landatmosphere energy fluxes through changes in aerodynamic and ecophysiological land surface properties. On the one hand, increasing albedo decreases total turbulent energy fluxes (i.e., sensible (H) and latent heat (LE) flux), and on the other hand decreasing surface roughness and increasing wetness enhances LE at the expense of H. The resulting maximum summer air temperatures and humidity would be substantially colder (1-2 C) and wetter (2 mmol mol-1) in a hypothetical permafrost-free wetland landscape, as indicated by planetary boundary layer model simulations. In contrast to the regional biophysical climate cooling impact of thaw-induced land cover change, wetland expansion and related increases in landscape CH4 emissions induce a net global biogeochemical climate warming impact. At the current rate of wetland expansion in the southern Taiga Plains of 0.26 % yr-1, landscape CH4 emissions increase by 0.034 g CH4 m-2 yr-1. Typical rates of long-term net CO2 uptake in these landscapes are too small to neutralize the associated climate warming effect until the end of the 21st century. The rapidly thawing boreal forest-wetland landscape still acts as a net CO2 sink taking up 74 g CO2 m-2 yr-1. Wetland expansion does not affect landscape-level net CO2 uptake as changes in gross primary productivity (GPP) and ecosystem respiration (ER) are of similar magnitude. The negligible thaw-induced effects on net CO2 fluxes are contrasted by larger direct climate change impacts of warming air temperatures and reduced incoming shortwave radiation. For a high warming scenario (RCP8.5), increases in modeled ER outpace the increasing GPP significantly. For a moderate warming scenario (RCP4.5), ER and GPP increase are of similar magnitude. Thaw-induced land cover change in the Taiga Plains causes thus biophysical and biogeochemical climate impacts of opposite sign and at contrasting scales of impacts (regional vs. global). In an increasingly warmer climate, thawing permafrost alters how boreal landscapes interact with climate highlighting the need to incorporate thaw-induced land cover changes into global Earth system models.