Dissertations / Theses on the topic 'Eddy heat flux'

This thesis examines the link between airborne flux estimates of CO$ sb2$, sensible heat, and water vapor, and surface parameters retrieved by remote sensing. Chapter 1 analyses the relationship between surface temperature and vegetation indices, obtained from the Advanced Very High Resolution Radiometer on board of NOAA-9 and -10 satellites, and fluxes of sensible heat, latent heat, and CO$ sb2$, estimated from aircraft. Linear relationships between CO$ sb2$ and the Normalized Difference Vegetation Index (NDVI) or the Simple Ratio vegetation index (SR) are found on a daily basis, but a highly nonlinear relationship appears for the seasonal variation. Latent Heat fluxes showed the poorest correlations with surface parameters. A seasonal linear relationship appeared between sensible heat and NDVI. Local extreme flux values due to the intermittency of boundary layer dynamics largely contribute to lower the correlations; such variations are the reason for the difficulties in relating fluxes obtained from single overpasses and over short distances to fixed points at the surface. This problem is further examined in Chapter 2, in which conditional sampling of airborne flux estimates is used to characterize the turbulent structures that are carrying flux, and their link to the surface. The analysis confirms that few extreme events may carry a significant fraction of the flux. Missing or hitting one of these structures may translate into very large oscillations on the flux estimate that are often not directly coupled to surface characteristics. A much clearer surface 'signature' emerges when measurements are taken within the surface layer, since the reorganization of turbulent structures that takes place with increasing height will result in a merging of the signature that came from different sources at the surface. This helps to explain some of the poor correlations obtained in Chapter 1 and reinforces the need for a better understanding of the distributions of these tu

In this study eddy covariance was used to measure sensible heat, latent heat, and carbon dioxide fluxes for the months of August, September, and October of 2009 within the roughness sublayer (RSL) of the urban center of Portland, OR. Vehicle traffic and solar radiation were also measured for the month of October. Flux measurements were compared with measurements from other urban areas as a test of reasonableness. CO₂ fluxes were nearly always positive and were strongly correlated with the weekday diurnal traffic cycle. CO₂ fluxes averaged 6.6 μmol/m^²s, which is less than other published measurements in urban areas. Sensible and latent heat fluxes followed the expected diurnal profile associated with solar radiation. Average sensible heat flux decreased as the season changed from summer to fall, moving from an average of 39 W/m^² in August to 12 W/m^² in October. A corresponding increase in latent heat flux was observed during this period, changing from an average of 10 W/m^² in August to 17 W/m^² in October. Heat flux behavior and amplitude was consistent with other urban measurements, though amplitude varies considerably from city to city. Stationarity was shown to positively influence measured CO₂ fluxes, but to have little effect on measured heat fluxes. Preliminary comparisons of October sensible heat and CO₂ fluxes to an inventory-based estimate of vehicle emissions indicate that eddy covariance measurements underestimate the true fluxes by 50%.

La circulation atmosphérique en Afrique de l'Ouest est caractérisée par des vents de sud-ouest (mousson) pendant la saison humide et par des vents de nord-est (harmattan) pendant la saison sèche. Cette alternance des saisons est due aux variations de pression liée à l'état des surfaces (rugosité, albédo, végétation) en réaction au forçage solaire. Ces mêmes états de surface génèrent une variabilité de flux turbulents de surface et des circulations secondaires qui rendent complexes les analyses des mesures effectuées sur place en vue de documenter les interactions surface-atmosphère. La modélisation fine échelle (LES) couramment utilisée dans l'étude de la couche limite atmosphérique est requise pour pouvoir palier à ces difficultés en raison de sa capacité à prendre en compte les flux turbulents en 3D et sur topographie complexe. Notre site d'étude est le bassin versant d'ARA située au Nord du Bénin dans un contexte Soudanien avec des propriétés de surface variables. Une analyse climatique est effectuée sur la base des observations de radiosondage, de radar UHF et de stations au sol afin d'extraire des données composites représentatives des saisons sèche et humide. Ces données composites ont servi par la suite à forcer le modèle Méso-NH dans sa version LES. Pour pouvoir caractériser les échelles de longueur des flux turbulents de surface relatives aux saisons sèche et humide, les données standard de forçage de surface de Méso-NH que sont le relief GTOPO30 (1km de résolution) et la végétation ECOCLIMAP (1km de résolution) ont été respectivement remplacer par le SRTM (90m de résolution) et les données de SPOT/HRV (20m de résolution) reéchantillonné à 90m de résolution. A l'aide d'outils statistiques comme la variographie 2D et le suivi Lagrangien, il ressort que la variabilité spatiale de la chaleur sensible H est gouvernée par le couple vent-relief tandis que celle de la chaleur latente E est difficile à mettre en lien sur végétation hétérogène (SPOT/HRV) en saison sèche. En saison humide, la variabilité spatiale du champ H dépend du vent tandis que celle du champ E dépend de la végétation. Cette étude révèle dans tous les cas que les échelles caractéristiques de ces deux champs diffèrent dans les mêmes conditions de forçage de surface et atmosphérique
West Africa atmosphere circulation is characterized by south-westerly wind (monsoon regime) during the wet season and north-easterly wind (harmattan regime) during the dry season. This alternation of wind regime is due to surface pressure variability linked to surface heterogeneities. Surface heterogeneities generate surface flux variability, secondary circulation and make complex analysis when trying to document surface-atmosphere feedbacks. LES modelling usually used for boundary-layer studies due to its potential to take into account 3D turbulence over complex topography, is used here to overcome these difficulties. Our site of interest is located in north of Benin characterized by Soudanian climate and heterogeneous surface properties. Climate analysis are first performed with radiosoundings, UHF radar, and EC station data in order to extract composite profile representing dry and wet season.. These composite profiles are then used to force atmosphere part of the Méso-NH LES model. To characterize turbulent fluxes length scales relative to dry and wet season, standard surface forcing data with Méso-NH like GTOPO30 orography (1km ) and ECOCLIMAP vegetation (1km) are respectively replaced by SRTM (90m) and SPOT/HRV vegetation data (20m) resampled to 90m. Along with statistical tools like 2D variography and Lagrangian, we notice that during dry season on heterogeneous vegetation, sensible heat flux H is more driven by wind and orography while we not able to discuss the latent heat flux E case. During wet season with the same surface forcing, it appears that H is driven by wind while E is more dependent to vegetation variability. Our study concludes in all case that H and E are not characterized by the same length scale

L'impact des modifications climatiques et de l'augmentation de la démographie sur le cycle de l'eau et de l'énergie dans la région ouest africaine passe par la quantification des échanges entre les différents couverts de la surface continentale et l'atmosphère. Toutefois, la compréhension du rôle des interactions entre la surface et l'atmosphère dans la dynamique de la mousson ouest africaine est limitée par le manque d'observations dans cette région. Cette thèse porte sur l'étude des flux turbulents, en particulier l'évapotranspiration réelle, en climat soudanien. Les deux couverts étudiés sont une forêt claire (site de Bellefoungou) et une mosaïque de culture/jachère (site de Nalohou), situés dans la région du Nord – Bénin. On dispose de quatre années de mesures (2007 à 2010). Les sites d'étude font partie de l'observatoire hydro – météorologique AMMA – CATCH.Les données de flux turbulents de l'atmosphère ont été mesurées avec la technique d'eddy covariance. La partition énergétique des flux a été examinée à travers la fraction évaporative (EF) et le rapport de Bowen (β) aux échelles diurne, saisonnière et inter-annuelle. Des caractéristiques de surface (conductance de surface et aérodynamique) et le coefficient de découplage ont été calculés pour interpréter la dynamique de l'évapotranspiration réelle.L'analyse des résultats est basée sur un découpage du cycle saisonnier suivant quatre phases du cycle de la mousson : la saison sèche, la saison humide, les phases d'humidification et d'assèchement de l'atmosphère. Aux échelles diurne et saisonnière, on montre que le taux d'évapotranspiration réelle de la forêt est toujours supérieur à celui de la mosaïque de culture/jachère quelle que soit la saison. L'évapotranspiration réelle demeure non nulle en saison sèche sur le site de Nalohou malgré les conditions de surface peu favorables à ce processus. En saison humide, après le saut de mousson, la partition énergétique des flux atteint un régime stationnaire avec une moyenne égale à 0,75 à Bellefoungou et 0,70 à Nalohou pour les 4 années étudiées. Le rapport de Bowen pris dans le même ordre est environ de 0,4 et 0,6 traduisant ainsi, en dépit des conditions humides, la part non négligeable du flux de chaleur sensible sur les deux couverts végétaux. La différence de rugosité entre les deux couverts végétaux entraîne une conductance aérodynamique nettement supérieure à Bellefoungou par rapport à Nalohou. On montre également que la végétation du site de Nalohou est plus efficace en transpiration pendant la saison humide que celle du site de Bellefoungou. A l'échelle inter-annuelle, on n'a pas pu mettre en évidence une relation entre flux de chaleur latente et pluviométrie pour les quatre années étudiées qui sont toutes des années excédentaires. Cependant nous avons observé que le rayonnement net explique la majeure partie de la variabilité inter-annuelle des flux turbulents.Enfin, nous avons également montré avec le coefficient de découplage que la surface soudanienne et l'atmosphère restent couplées toute l'année. Ce fonctionnement de l'interface surface – atmosphère reflète le rôle majeur que jouent les conditions de surface dans la variabilité saisonnière de l'évapotranspiration réelle. Les résultats issus de cette étude donnent une première estimation des flux de chaleur latente et de chaleur sensible sur une forêt claire et une mosaïque de culture/jachère en climat soudanien. Ils sont d'une importance capitale pour la paramétrisation et la validation des modèles de surface ainsi que pour la quantification robuste de la ressource en eau disponible en surface pour l'agriculture, principale activité génératrice de revenus des populations locales
Assessing the impact of climate and anthropic changes on the water and energy cycles, mainly rely on the quantification of the transfer between the various land covers and the atmosphere. Nevertheless the land – atmosphere interactions in the West African monsoon dynamic is not yet well understood because of the lack of observations in this region. This thesis focuses on the analysis of the sensible and latent heat fluxes under Sudanian climate. The two studied land covers are a clear forest (Bellefoungou) and a cultivated area (Nalohou), located in northern Benin, during four years (2007-2010). The study sites are a part of the hydro – meteorological AMMA – CATCH observatory.Turbulent fluxes were measured with the eddy covariance technique.The flux partitioning was investigated through the evaporative fraction (EF) and the Bowen ratio (β) at diurnal, seasonal and inter-annual scales. Surface characteristics (surface and aerodynamical conductance) and the decoupling factor were calculated to interpret the dynamic of the actual evapotranspiration.The analysis was performed according to four different stages of the monsoon cycle: dry and wet seasons drying and moistening intermediate stages. At diurnal and seasonal scales, actual evapotranspiration was always higher on the forest than on the cultivated area. It remained non zero during the dry season at Nalohou despite surface conditions which were not favorable to this process. During the wet season, after the monsoon onset, EF remained steady with a mean seasonal value of 0.75 at Bellefoungou and 0.70 at Nalohou for the four studied years. The Bowen ratio was 0.4 and 0.6 respectively, thus the sensible heat flux was significant on the two contrasted vegetation covers during the wet season. The contrasted roughness length of the two vegetation covers led to a highest aerodynamic conductance at the clear forest site. The mixed of crop/fallow was shown to be more efficient than the clear forest regarding wet season transpiration. At the inter-annual scale, no relationship can be evidenced between evapotranspiration and annual rainfall for the studied period (2007-2010), which was rather rainy. Nevertheless, the net radiation explains the main part of turbulent fluxes inter-annual variation.Finally, complete surface atmosphere decoupling was never observed. This property of the surface – atmosphere interface underlines the key role of the surface conditions in the actual evapotranspiration. Our results provide a first estimate of the latent and sensible heat fluxes over a clear forest and a mixed crop/fallow under sudanian climate. They are relevant to land surface models parametrisation or evaluation and to a robust quantification of the water resources for agriculture, the main economic activity in this region

The energy exchange in the soil-snow-vegetation-atmospheresystem was studied to improve the quantitative knowledge of thegoverning processes. The lack of such knowledge contributes tothe uncertainty in the applicability of many existing modelsindependent of the temporal or spatial scale. The theoreticalbackground and available methods for measurements and numericalsimulations were reviewed. Numerical simulation models andavailable data sets representing open land and boreal forestwere evaluated in both diurnal and seasonal time-scales.Surface heat fluxes, snow depth, soil temperatures andmeteorological conditions were measured at an agriculturalfield in central Sweden over two winters, 1997-1999. Twoone-dimensional simulation models of different complexity wereused to simulate the heat and water transfer in thesoil-snow-atmosphere system and compared with the measurements.Comparison of simulated and observed heat fluxes showed thatparameter values governing the upper boundary condition weremore important than the formulation of the internal mass andheat balance of the snow cover. The models were useful toevaluate the lack of energy balance closure in the observedsurface heat fluxes, which underlined the importance ofimproved accuracy in eddy correlation measurements of latentflow during winter conditions.

The representation of boreal forest in the land surfacescheme used within a weather forecast model was tested with athree-year data set from the NOPEX forest site in centralSweden. The formulation with separate energy balances forvegetation and the soil/snow beneath tree cover improvedsimulation of the seasonal and diurnal variations of latent andsensible heat flux compared with an older model version.Further improvements of simulated surface heat fluxes could beexpected if the variation of vegetation properties within andbetween years and a new formulation of the boundary conditionsfor heat flux into the soil is included.

Keywords: Surface energy balance, Snow, Boreal forest,SVAT models, Eddy-correlation Measurements, Latent heat flux,Sensible heat flux, Net radiation, Soil temperature,Aerodynamic roughness, Surface resistance

QC 20100614

This thesis consists of analysis of three different data sets: (i) Aircraft-based eddy correlation data collected above irrigated and non-irrigated agricultural land in Southern California during the California Ozone Deposition Experiment (CODE) summer 1991; (ii) micrometeorological tower data, collected over grape and cotton canopies as part of CODE; (iii) aircraft-based eddy correlation flux data above two grid sites in the Canadian boreal forest during the Boreal Ecosystem-Atmosphere Study (BOREAS), spring and summer of 1994 and 1996.
Results from the CODE aircraft data document composition and size of the dominant structures, which transport heat and gases (H2O, CO 2 and ozone) over water stressed and non-water stressed surfaces, and the relative frequency with which structures carrying only a single scalar, or given combinations of scalars, were encountered along the flight paths. Interpretation of results provides further evidence for the existence of a second (nonphysiological) sink for ozone. The relative preponderance of structures that carry moisture, carbon dioxide and ozone simultaneously, particularly in the gradient-up mode, reflects the importance of vegetation as co-located source/sink for these scalars. The detrending procedures described in this study may help to define a more effective separation between local and mesoscale events in biosphere-atmosphere interaction.
Results from the CODE tower data indicates a single vegetated ozone sink for the grape site, but a vegetated as well as a non-vegetated sink for the cotton site. For both sites, structures simultaneously transporting significant flux contributions of CO2, H2O, heat and ozone dominate during unstable conditions. During stable conditions, unmixed single flux structures dominated over cotton but not over grape. The results of this study contribute empirical evidence about the relationship between ozone uptake and the physical and physiological state of vegetation, as well as the limitations placed on eddy scales in simulation models.
Results from the BOREAS aircraft data shows a decoupling between the surface and the atmosphere, where the patterns of vegetation, greenness and surface temperature may be quite dissimilar to those of the fluxes of sensible heat, latent heat and---to a lesser degree---CO2. Reasons for this lie in the extraordinary boundary layer conditions, high vapour pressure deficit, moist soil and hot canopies, and the response of the vegetation to these conditions. Analysis of the coherent structure compositions to some extent permits the characterization of the different sources and sinks. Overall, this study shows the importance of understanding the various interacting components of soil, vegetation and atmosphere when attempting to design process-based models for predictions in 'micrometeorologiacally' complex ecosystems.

Resumo: Considerando a importância da compreensão da dinâmica espaço temporal dos componentes do balanço de energia (BE) em escala regional para o gerenciamento de recursos hídrico e o manejo agrícola, o objetivo principal desta tese foi construir e analisar uma série temporal dos componentes do BE adequada às condições de clima subtropical úmido do Estado do Rio Grande do Sul. Para tanto, inicialmente foi avaliada a adequação de modelos de estimativa de BE para o Estado. Nesta etapa foram utilizados produtos MODIS e dados de referência medidos em uma torre micrometeorológica instalada em Cruz Alta – RS, usando valores instantâneos para um período de estudo de 2009 a 2011. Na sequência foi avaliada a adequação dos modelos em representar a variabilidade espacial dos componentes do BE. Nesta etapa foram usados produtos MODIS, dados de reanálise ERA Interim, dados de referência da torre micrometeorológica e dados de estações meteorológicas do INMET, para o mesmo período de estudo. Na última etapa do trabalho foi construída a série temporal dos componentes do BE usando o modelo METRIC, a qual abrangeu um período de 14 anos, de 2002 a 2016. Os resultados demonstraram que os três modelos analisados apresentam coerência com as medidas de referência, sendo as maiores limitações apresentadas pelo modelo SEBAL, as quais se atribui principalmente às condições ecoclimáticas do Estado e a baixa resolução espacial das imagens. Na análise da variabilidade espacial, o modelo METRIC apresentou maior consistência nos resultados e proporcionou maior número de dias com resultados válidos, sendo assim apontado como o mais apto para realização do restante do estudo. A série temporal construída possibilitou a compreensão dos padrões de distribuição espaço temporal dos componentes do BE no estado do Rio Grande do Sul. Há uma marcada sazonalidade nos componentes do BE, com maiores valores no verão e menores no inverno. G (fluxo de calor no solo) é o componente de menor magnitude e sua distribuição espacial e temporal é determinada pela distribuição de Rn (saldo de radiação). Já os componentes LE (fluxo de calor latente) e H (fluxo de calor sensível), são os que mostram magnitude maior e apresentam padrões de distribuição espacial e temporal coerentes com as condições climáticas e com os tipos de uso e cobertura na área de estudo. Observase um padrão inverso, com um gradiente de LE no sentido noroeste para sudeste e para o componente H, no sentido sudeste para noroeste. Sendo estas informações de grande importância para gerenciamento de recursos hídricos em escala regional, para estudos de zoneamento agrícola.
Abstract: Given the importance of understanding the temporal and spatial dynamics of of the energy balance (EB) components in a regional scale for the management of water resources and agricultural, the main objective of this thesis was to construct and analyze a time series of the components of BE appropriate to the subtropical humid climate conditions of the State of Rio Grande do Sul. In order to reach the objective initially, the adequacy of the models for the humid climate conditions was evaluated, in this step we used MODIS data and reference data measured in a micrometeorological tower installed in Cruz Alta - RS. The analyzes performed with instantaneous values and the study period was from 2009 to 2011. The next step evaluate the spatial variability of the BE components, the data used were the MODIS products, ERA Interim reanalysis data, reference data of the micrometeorological tower and INMET meteorological stations, for the same study period. In the last stage the time series of the BE components was constructed from the METRIC model. The period series was 14 years from 2002 to 2016.The results showed that the three models analyzed were consistent with the reference measurements, with the greatest limitations presented by the SEBAL model, which are mainly attributed to the state's eco-climatic conditions and the low spatial resolution of the images In the analysis of the spatial variability, the METRIC model presented greater consistency in the results and provided greater number of days with valid results, this model thus indicated as the most suitable for the rest of the study. The time series constructed allowed us to understand the temporal distribution patterns of BE components in the state of Rio Grande do Sul. There is a marked seasonality in the BE components, with higher values in summer and lower in winter. G is the smallest magnitude component and its spatial and temporal distribution is determined by the Rn distribution. On the other hand, the LE and H components are those that show higher magnitude and present spatial and temporal distribution patterns consistent with the climatic conditions and the types of use and coverage in the study area. An inverse pattern is observed, with a LE gradient from north-west to south-east and for H-component, from southeast to northwest.

This study investigates the upper ocean circulation along the west Australian coast, based on recent observations (WOCE ICM6, 1994/96) and numerical output from the 1/6 degree Parallel Ocean Program model (POP11B 1993/97). Particularly, we identify the source regions of the Leeuwin Current, quantify its mean and seasonal variability in terms of volume, heat and salt transports, and examine its heat balance (cooling mechanism). This also leads to further understanding of the regional circulation associated with the Leeuwin Undercurrent, the Eastern Gyral Current and the southeast Indian Subtropical Gyre. The tropical and subtropical sources of the Leeuwin Current are understood from an online numerical particle tracking. Some of the new findings are the Tropical Indian Ocean source of the Leeuwin Current (in addition to the Indonesian Throughflow/Pacific); the Eastern Gyral Current as a recirculation of the South Equatorial Current; the subtropical source of the Leeuwin Current fed by relatively narrow subsurface-intensified eastward jets in the Subtropical Gyre, which are also a major source for the Subtropical Water (salinity maximum) as observed in the Leeuwin Undercurrent along the ICM6 section at 22 degrees S. The ICM6 current meter array reveals a rich vertical current structure near North West Cape (22 degrees S). The coastal part of the Leeuwin Current has dominant synoptic variability and occasionally contains large spikes in its transport time series arising from the passage of tropical cyclones. On the mean, it is weaker and shallower compared to further downstream, and it only transports Tropical Water, of a variable content. The Leeuwin Undercurrent carries Subtropical Water, South Indian Central Water and Antarctic Intermediate Water equatorward between 150/250 to 500/750 m. There is a poleward flow just below the undercurrent which advects a mixed Intermediate Water, partially associated with outflows from the Red Sea and Persian Gulf. Narrow bottom-intensified currents are also observed. The 5-year mean model Leeuwin Current is a year-round poleward flow between 22 degrees S and 34 degrees S. It progressively deepens, from 150 to 300 m depth. Latitudinal variations in its volume transport are a response to lateral inflows/outflows. It has double the transport at 34 degrees S (-2.2 Sv) compared to at 22 degrees S (-1.2 Sv). These model estimates, however, may underestimate the transport of the Leeuwin Current by 50%. Along its path, the current becomes cooler (6 degrees C), saltier (0.6 psu) and denser (2 kg m -3). At seasonal scales, a stronger poleward flow in May-June advects the warmest and freshest waters along the west Australian coast. This advection is apparently spun up by the arrival of a poleward Kelvin wave in April, and reinforced by a minimum in the equatorward wind stress during July. In the model heat balance, the Leeuwin Current is significantly cooled by the eddy heat flux divergence (4 degrees C out of 6 degrees C), associated with mechanisms operating at submonthly time scales. However, exactly which mechanisms it is not yet clear. Air-sea fluxes only account for ~30% of the cooling and seasonal rectification is negligible. The eddy heat divergence, originating over a narrow region along the outer edge of the Leeuwin Current, is responsible for a considerable warming of a vast area of the adjacent ocean interior, which is then associated with strong heat losses to the atmosphere. The model westward eddy heat flux estimates are considerably larger than those associated with long lived warm core eddies detaching from the Leeuwin Current and moving offshore. This suggests that these mesoscale features are not the main mechanism responsible for the cooling of the Leeuwin Current. We suspect instead that short lived warm core eddies might play an important role.

This thesis examines the development and validation of Canadian Land Surface Scheme (CLASS) for various wetland landscapes individually, along with an evaluation of modelled results over a heterogeneous surface with airborne observations. A further statistical analysis of the effects of land surface classification procedures over the study area and their influence on modelled results is performed. CLASS is tested over individual wetland types: bog, fen and marsh in a stand-alone (non-GCM coupled) mode. Atmospheric conditions are provided for the eight site locations from tower measured data, while each surface is parameterized within the model from site specific measurements. Resulting model turbulent and radiative flux output is then statistically evaluated against observed tower data. Findings show that while CLASS models vascular dominated wetland areas (fen and marsh) quite well, non-vascular wetlands (bogs) are poorly represented, even with improved soil descriptions. At times when the water table is close to the surface, evaporation is greatly overestimated, whereas lowered water tables generate a vastly underestimated latent heat flux. Because CLASS does not include a moisture transfer scheme applicable for non-vascular vegetation, the description of this vegetation type as either a vascular plant or bare soil appears inappropriate.
CLASS was then tuned for a specific bog location found in the Hudson Bay Lowland (HBL) during the Northern Wetlands Study (NOWES). With bog surfaces better described within the model, testing of CLASS over a highly heterogeneous 169 km2 HBL region is then undertaken. The model is first modified for lake and pond surfaces and then separate runs for bog, fen, lake and tree/shrub categories is undertaken. Using a GIS, the test region under which airborne flux measurements are available is divided into 104 grid cells and proportions of each surface type are calculated within each cell. Findings indicate that although the modelled grid average radiation and flux values are reasonably well reproduced (4% error for net radiation, 10% for latent heat flux and 30% for sensible heat flux), spatial agreement between modelled and observed grid cells is disappointing. (Abstract shortened by UMI.)

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.

本論文主要通過衛星遙感觀測資料和海洋數值模式的方法，來研究南海海洋上層對颱風西馬侖（2006）的回應過程，以及南海水平方向的渦度熱通量的年變化過程。
通過衛星海表溫度資料和氣候態海洋溫度資料反演颱風西馬侖引起的混合層加深的問題。反演結果顯示，2006年11月3日，對應海表溫度降低了4.4度，混合層則由颱風前的43.2米加深了104.5米，該結果與一維混合層模型(GOTM)的類比結果一致。此外，颱風引起的海表面溫度梯度可用來計算斜壓地轉流場和渦度。負渦度顯示了反氣旋斜壓迴圈在混合層底部最強，在50米水深處地轉流速可達到0.2米每秒。2006年11月3日，颱風西馬侖在最大的海表溫度降低的附近，向西南方向轉彎，此時行進速度比較緩慢(1.7 米每秒)進而導致在亞臨界條件弗勞德數(颱風的平移速度與第一斜壓相速度的比值)為0.6，在颱風尾區因缺少慣性重力波從而促進了海表溫度冷卻和混合層加深。通過比較Argo浮標觀測資料和氣候態資料的溫度剖面，混合層加深程度估算的誤差在10米以內。
三維海洋數值模型ROMS 用來研究颱風期間海洋物理動力和生態回應。海表溫度類比值同衛星觀測值比對得到的相關係數高達84%以上，表明ROMS基本上可以模擬在颱風期間南海的海表面溫度變化情況。但是深入研究發現由於垂向混合強度不夠，模式結果低估了海表面溫度冷卻和混合層加深，混合層深度被低估。通過增加波致混合效應(Bv)改進KPP混合方案，可以提高海表面溫度冷卻和混合層加深的模擬精度。類比結果顯示在颱風尾區，葉綠素的大規模爆發則發生在颱風經過的1周以後。透光層葉綠素濃度由颱風前的0.1 mg m⁻³ 增加到11月9日的1.9 mg m⁻³。衛星觀測顯示在颱風尾區，葉綠素濃度在11月16日仍高達0.85 mg m⁻³。
高度計的海表面高度異常值與海表面溫度的衛星觀測資料可以用來計算南海渦度熱通量。南海表層渦度熱通量的年變化趨勢表明，在南海西邊的熱通量表現出北向輸送特徵，其強度甚至與黑潮延伸區域的強熱通量相當。渦熱通量在冬季最強，熱量由南海南部流入，並且從呂宋海峽流出，甚至通過臺灣海峽進入東海海域。冬季熱通量的輻合帶主要分佈在南海東部近呂宋海峽附近海域和越南東南海域，而夏季主要集中在越南東南海域。研究表明，冬季和夏季的海表面渦度熱通量對海洋上層熱收支平衡的調整有顯著影響。
This dissertation focuses on the investigation of the upper ocean response to typhoon Cimaron (2006) and annual variations of horizontal eddy fluxes in the South China Sea (SCS) through the methods both of satellite remote sensing and numerical ocean modeling.
The mixed layer deepening induced by typhoon Cimaron is derived based on satellite observed sea surface temperature (SST) and climatological temperature profiles in the SCS. Corresponding to the SST drop of 4.4ÅC on November 3, 2006, the mixed-layer deepened by 104.5 m relative to the undisturbed depth of 43.2 m, which is consistent with the simulation results from the one-dimensional mixed-layer model (GOTM). Furthermore, baroclinic geostrophic velocity and vorticity are calculated from the surface temperature gradient caused by the typhoon. The negative vorticity, associated with the typhoon cooling, indicated an anti-cyclonic baroclinic circulation strongest at the base of the mixed-layer, and at the depth of 50 m, the geostrophic speed reached as high as 0.2 m s⁻¹. Typhoon Cimaron proceeded slowly (1.7 m s⁻¹) when it was making a southwestward turn on November 3, 2006, resulting in a subcritical condition with a Froude number (the ratio of typhoon translation speed to first baroclinic mode speed) of 0.6 around the maximum SST drop location and facilitating high SST cooling and mixed-layer deepening due to absence of inertial-gravity waves in the wake of the typhoon. Comparison of Argo buoy data with the climatological temperature suggests that the average uncertainty in the mixed-layer deepening estimation caused by the difference between Argo and climatological temperature profiles is less than 10 m.
The physical dynamic and biological responses to typhoon Cimaron are investigated through a three-dimensional ocean model, the Regional Ocean Modeling System (ROMS). The correlation between simulated sea surface temperature (SST) and the satellite observations is over 84%, which indicates ROMS can generally simulate the sea surface temperature in the South China Sea during typhoon process. However, detailed analysis shows that the ROMS model underestimates the sea surface temperature cooling and mixed layer deepening because of insufficient mixing in the modeling. The wave-induced mixing term (Bv) added into the nonlocal K-Profile Parameterization (KPP) scheme can increase the simulation accuracy of surface temperature cooling and mixed layer depth deepening in response to the typhoon forcing. The simulation results show that the blooming of phytoplankton in the wake of storm appeared one week later after typhoon’s passage. The concentration of chlorophyll is 0.1 mg m⁻³ at pre-typhoon time and increase to 1.9 mg m⁻³ on November 9. Satellite Observation indicates the concentration of chlorophyll in wake of typhoon Cimaron was also in a high value of 0.85 mg m⁻³ on November 16.
The eddy heat flux in the SCS is derived from the satellite data including the altimeter surface height anomalies and optimally interpolated sea surface temperature. The long term heat flux shows a northward heat transport on the west side of the SCS, comparable to that in other strong flux regions such as the Kuroshio extension. The eddy flux becomes the strongest in winter with the inflow flux in the south and the outflow through the Luzon, and the eddy heat can flux through the Taiwan Strait into the East China Sea. The convergence of the flux indicates that heat accumulation in the eastern SCS close to Luzon Strait in winter and also to southeast of Vietnam in winter and summer. The eddy heat flux is more significant in adjusting the ocean upper layer heat budget flux in winter and summer.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Sun, Yujuan.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2013.
Includes bibliographical references (leaves 101-111).
Abstracts also in Chinese.
Abstract --- p.ii
摘要 --- p.v
Acknowledgements --- p.vii
Table of Contents --- p.viii
List of Tables --- p.x
List of figures --- p.xi
Chapter 1. --- Introduction --- p.1
Chapter 1.1 --- Ocean responses to typhoons (or tropical storms and hurricanes) --- p.4
Chapter 1.2 --- Eddy Heat Transport --- p.9
Chapter 2. --- The one-dimension remote sensing model (the mixed-layer deepening) --- p.11
Chapter 2.1 --- Introduction --- p.11
Chapter 2.2 --- Data and Methodology --- p.11
Chapter 2.3 --- Results --- p.16
Chapter 2.4 --- One-dimensional mixed-layer model --- p.17
Chapter 2.5 --- Discussions --- p.20
Chapter 2.5.1 --- Horizontal baroclinic pressure gradient and vorticity --- p.20
Chapter 2.5.2 --- Effects of subsurface temperature variation on the mixed-layer deepening --- p.22
Chapter 2.6 --- Summary --- p.28
Chapter 3. --- Three-dimensional numerical ocean model --- p.29
Chapter 3.1 --- Model description --- p.29
Chapter 3.1.1 --- Physical model --- p.30
Chapter 3.1.2 --- Biological model --- p.34
Chapter 3.2 --- Model setting --- p.40
Chapter 3.2.1 --- Initial and lateral boundary conditions --- p.41
Chapter 3.2.3 --- Bio-module setting --- p.47
Chapter 3.3 --- Model result validation --- p.51
Chapter 3.3.1 --- Satellite observations --- p.51
Chapter 3.3.2 --- Validations of observations and simulations --- p.54
Chapter 3.4 --- Model results analysis --- p.56
Chapter 3.4.1 --- Ocean temperature --- p.56
Chapter 3.4.2 --- Ocean current --- p.62
Chapter 3.4.3 --- bio-results of simulation --- p.70
Chapter 3.4.4 --- Effect of the wave-induced mixing --- p.77
Chapter 3.5 --- summary --- p.83
Chapter 4. --- Annual Variations of Horizontal Eddy Heat Flux in the South China Sea --- p.84
Chapter 4.1 --- Introduction --- p.84
Chapter 4.2 --- Methodology and data --- p.86
Chapter 4.3 --- Results --- p.89
Chapter 4.4 --- Summary --- p.96
Chapter 5. --- Conclusion --- p.97
Chapter 6. --- Future work --- p.100
Bibliography --- p.101

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.

碩士
國立臺灣大學
環境工程學研究所
101
Many air quality models developed from the USA have been widely utilized in Taiwan. However, in these modeling systems, many of default surface parameters are set for the topographic and climatic conditions in the USA, which are quite different from those in Taiwan. In addition, the simulation of diffusion patterns of air pollutant is directly affected by the estimation of the atmospheric stability, which can be quantified from the sensible heat flux. In many studies, the utilization of Bowen ratio by using different approaches are commonly used to calculate sensible heat fluxes and further determine the atmospheric stability used in air quality models . However, very few studies discuss the comparison among these approaches by using local measurement. Therefore, the objective of this research is to determine the localized surface parameters suitable in AERMOD for the conditions in Taiwan, to improve the determination of atmospheric stability and the performance of air quality models. To achieve the abovementioned objective, in these researches, the widely used Penman-Monteith (PM) and Priestley –Taylor (EPA) formulas are being conducted to provide the quantitative basis for atmospheric stability. To verify the performance of these approaches, the measurement data collected by using eddy-covariance technique at Guandu grassland is applied in this study. In this study, Penman-Monteith and Priestley –Taylor formulas are applied to the study area, Guandu. The canopy resistance of Penman-Monteith formular is about 100 (sm-1). The Bowen ratio calculated by Penman-Monteith formula has a higher correlation with the Bowen ratio calculated by eddy covariance. The Bowen ratio calculated by Priestley –Taylor formula is only affected by temperature. Then, input two of the Bowen ratios above to the AERMOD and then take the number calculated by eddy covariance as the real value. We found out that the correlation with pollutant concentration using default Bowen Ratio and real pollutant concentration is irrelevant. Furthermore, the pollutant concentration calculated by default Bowen Ration underestimated much more seriously.

Atmospheric convection is sensitive to the nature of the surface and its temperature. Both dry (without cloud) and moist (with cloud) convections depend on the surface temperature. Surface temperature is of critical importance in several practical applications like human comfort and crop cultivation. In the climate change scenario too, variations in the surface temperature take the center stage. Therefore, prediction of surface temperature is important. The evolution of the temperature is governed by the energy equation and the surface temperature by the surface energy balance. Important components of the surface energy balance are radiation (incoming solar radiation, reflected solar radiation, incoming and outgoing longwave radiation), sensible and latent heat fluxes and heat flux into the ground (called ground heat flux). A large number of individual and collective observations have been carried out in the past to understand the atmospheric boundary layer and the surface energy budgets. However a major share of the observations is from mid-latitudes. There have been few experiments carried out in India, for example, MONTBLEX, LASPEX, etc. One common drawback among these experiments is that the data time series is discontinuous and continuous measurements covering an entire season are lacking. Moreover these measurements were not comprehensive and hence did not allowed to calculate complete surface energy balance – in some cases radiation data is not available while in some humidity data. Therefore, continuous time series of sufficient duration and covering all variables needed to look at the seasonal energy balance based on measurements alone is missing in the Indian context. New programmes with the main objective of predicting convection are being planned in India. For example, PROWNAM (Prediction of Regional Weather with Observational Meso-Network and Atmospheric Modeling) is aimed at predicting the short term weather at SHAR and STORM (Severe Thunderstorms – Observations and Regional Modeling) aims to predict the occurrence of severe thunderstorms in the northeastern India. In both these programmes, measurement of all components of surface energy balance is one of the main objectives. However, the minimum configuration and data accuracy requirements for the flux towers, sensitivity of computed fluxes on data accuracy have not been carefully evaluated. This thesis is aimed at filling this gap. As a part of my work, a 10 m high micrometeorological tower was installed in an open area within the Indian Institute of Science (IISc) Air Field. Temperature, relative humidity and wind speed and direction instruments were mounted at two levels, 2 m and 8 m. All components of radiation were measured. Data, sampled every 5 s and averaged for 2 minutes were continuously stored, starting May 2006 onwards. Soil temperature was measured at 4 depths, 5 cm, 10 cm, 15 cm and 20 cm. In addition, a sonic anemometer capable of measuring 3 components of velocity and air temperature was installed at 2 m height, and data was collected for more than a month to enable the calculation of momentum and buoyancy fluxes using the Eddy correlation method (ECM). The present work evaluated the sensitivity of the fluxes for small calibration errors and quantified the minimum data accuracies and configuration needed for flux measurement with the Profile method (PM). After applying corrections, the comparison of fluxes from PM and ECM are in good agreement. The complete long-term surface energy balances is calculated in terms of source and sink. One aspect that emerges from the observation is that the seasonal variation in the sink term is relatively small (150-170 Wm-2) whereas the source term shows much larger variation from 180-250 Wm-2. A method has been implemented by which the ground surface temperature can be estimated by using the subsurface temperature timeseries by the method of Fourier decomposition and using the Fourier heat conduction equation. In addition we can compute the thermal diffusivity of the soil by using the amplitude and phase information of the sub-surface soil time series. The estimated temperatures from this method and one that estimated from radiation method are in good agreement with the maximum difference being less than 0º C.