<p>High-latitude watersheds have been regarded as a carbon sink with soil carbon accumulating at low temperature. This sink is now believed to turn into a source, acting as positive feedback to climate warming. However, thawing permafrost soils would allow more water to percolate down to deeper soil layers where some of the carbon could be “consumed” in weathering and exported as bicarbonate to the sea. Using a hydrological mixing model showed that this could counterbalance the predicted positive feedback resulting from thawing soils.</p><p>Vegetation-covered riparian zones in headwater areas appear to have a significant role for the dissolved constituent fluxes. Higher concentrations of weathering products are found in taiga and tundra rivers with larger areas of forest and peat cover in the watershed. These landscape elements can thus be regarded as “hot spots” of river loading with dissolved constituents.</p><p>Comparing a regulated and an unregulated river tested the hypothesis that damming leads to a depletion of major elements also in oligotrophic river systems as a consequence of changes in landscape elements. A loss of upper soils and vegetation through inundation prevents the contact of surface waters with vegetated soil, and consequently reduces weathering fluxes. The hypothesis that the lower fluxes of dissolved silica (DSi) in the regulated river could also be explained by biological uptake was then tested using a model, and budget calculations indicate a significant reduction as a result of regulation. About 10% of this reduction can be attributed to the flooding of the fluvial corridor and the rest to diatom blooms in the reservoirs. A more detailed study of landscape elements for the headwaters of the river Luleälven showed that only 3% of the surface area has been inundated by reservoirs but ca. 37% of the deciduous forest. Such a significant loss of hot spots may indeed explain the observed lower DSi fluxes in the regulated watersheds of northern Sweden.</p>

As part of the ONR sponsored Coupled Boundary Layer/Air-Sea Transfer (CBLAST) experiment, data from the NOAA WP-3D research aircraft measurements into major Hurricanes in the 2002-2004 seasons are analyzed to investigate the structure of the boundary layer. The turbulent fluxes of momentum and enthalpy are derived using the eddy correlation method. For the first time, the momentum and enthalpy fluxes were directly measured in the boundary layer of a hurricane with wind speeds up to 30 m/s. A new bulk parameterization of the momentum and enthalpy flux is developed. The vertical structure of turbulence and fluxes are presented for the entire boundary layer in the rain free region between the outer rainbands. The turbulent kinetic energy budget was estimated for the hurricane boundary layer between the outer rainbands. The universal spectra and cospectra of the wind velocity, temperature and humidity are also derived. A case study on the effects of roll vortices on the turbulent fluxes is conducted, which confirmed the existence of the boundary layer rolls and gave the first estimate of their modulation of the momentum and sensible heat flux. The CBLAST data provided an invaluable perspective on the evaluation and development of the boundary layer parameterization suited for the hurricane models. Studies on entrainment processes above of the mixed layer and turbulent transport processes induced by the inflow are recommended in the future.

High-latitude watersheds have been regarded as a carbon sink with soil carbon accumulating at low temperature. This sink is now believed to turn into a source, acting as positive feedback to climate warming. However, thawing permafrost soils would allow more water to percolate down to deeper soil layers where some of the carbon could be “consumed” in weathering and exported as bicarbonate to the sea. Using a hydrological mixing model showed that this could counterbalance the predicted positive feedback resulting from thawing soils. Vegetation-covered riparian zones in headwater areas appear to have a significant role for the dissolved constituent fluxes. Higher concentrations of weathering products are found in taiga and tundra rivers with larger areas of forest and peat cover in the watershed. These landscape elements can thus be regarded as “hot spots” of river loading with dissolved constituents. Comparing a regulated and an unregulated river tested the hypothesis that damming leads to a depletion of major elements also in oligotrophic river systems as a consequence of changes in landscape elements. A loss of upper soils and vegetation through inundation prevents the contact of surface waters with vegetated soil, and consequently reduces weathering fluxes. The hypothesis that the lower fluxes of dissolved silica (DSi) in the regulated river could also be explained by biological uptake was then tested using a model, and budget calculations indicate a significant reduction as a result of regulation. About 10% of this reduction can be attributed to the flooding of the fluvial corridor and the rest to diatom blooms in the reservoirs. A more detailed study of landscape elements for the headwaters of the river Luleälven showed that only 3% of the surface area has been inundated by reservoirs but ca. 37% of the deciduous forest. Such a significant loss of hot spots may indeed explain the observed lower DSi fluxes in the regulated watersheds of northern Sweden.

Tracer methods are commonly used for estimation of soil water and groundwater recharge flux especially in arid and semiarid regions. These tracer methods are based on the solute profile shape (distribution of concentration with depth) and peak position. For soils of semi-arid to sub-humid climates, vertical water movement may seasonally vary in direction due to climate conditions and vegetative demands. The first objective of this thesis was to show that TDR (time domain reflectometry) can be a useful tool for estimation of soil water fluxes using tracer methods. The second objective was to study the effects of repeated cycles of directionally-varying flow upon solute profile shape and position used by tracer methods under controlled laboratory conditions. Three soil columns with a KCl tracer and Beaver Creek sand were used for this study. Rain and evaporative systems were used to cause the downward and upward soil water movements in the column, respectively. Soil moisture content and solute concentration were measured using TDR.<p> The result for the first objective was that the peak migration and the soil water balance methods gave similar average upward and downward soil water fluxes. This result indicates that the TDR method can be recommended for determination of soil water fluxes with tracer methods in fields or in laboratory studies for sufficient time and depth.<p> In the second objective, three different seasonal flow regimes were studied using the sand columns, and each flow regime simulated climatic seasons that might occur in the field. Several apparent and statistical parameters were used to evaluate the change of the solute profile shape and position under cycling conditions of the three different flow regimes. These parameters showed that the solute profile shape and position clearly changed under the three different repeated regimes of downward and upward seasonal flows. It was concluded that climate (seasonality) can have significant impacts on the estimation of soil water fluxes using tracer methods. The result from this investigation shows that the profile shape and position after a number of cycles (years of fluctuations) can provide a description of the previous climatic effects on the concentration profile. Therefore, the profile shape can be used as an indicator of the flow regime that has affected the solute profile shape. Moreover, if a reference of a solute profile is available (a solute profile before a period of time), it is easier to determine the flow regime affected the profile shape and position by determining the change of the profile shape and position using statistical parameters presented in this thesis.

As space exploration has advanced, time spent in space has increased. With the building of the International Space Station and plans for exploration missions to the Moon and Mars, astronauts will be staying in space for longer periods of time. With these increased stays in space comes an increase in fire safety concerns. One area of fire safety interest is flammability. While current flammability test procedures are in place, they are all performed on the ground and may not be representative of flammability in microgravity. In addition to this, limited research into the severity of skin burn injury in a microgravity environment has been performed. <p>An apparatus was designed to be flown on a low gravity parabolic aircraft flight to assess the flammability of cotton and 50% cotton/50% polyester fabrics and the resulting skin burn injury that would occur if these fabrics were to ignite. The apparatus, modelled after a Canadian General Standards Board standard flammability test, was also used on the ground for experiments in 1-g. Variables examined in the tests include gravity level, fabric type, air gap size, oxygen concentration, apparatus orientation, ignition source, and method used to secure the specimen. Flame spread rates, heat fluxes, and skin burn predictions determined from test results were compared. <p>Results from test in 1-g indicated that the orientation of the apparatus had a large effect on flame spread rate, heat flux and predicted skin burn times. Flame spread rates and heat fluxes were highest when the fabric was held in the vertical orientation, which resulted in the lowest predicted times to produce skin burns. Flame spread rates and heat fluxes were considerably lower in microgravity than in 1-g, which resulted in higher predicted times to produce skin burns.

As space exploration has advanced, time spent in space has increased. With the building of the International Space Station and plans for exploration missions to the Moon and Mars, astronauts will be staying in space for longer periods of time. With these increased stays in space comes an increase in fire safety concerns. One area of fire safety interest is flammability. While current flammability test procedures are in place, they are all performed on the ground and may not be representative of flammability in microgravity. In addition to this, limited research into the severity of skin burn injury in a microgravity environment has been performed. <p>An apparatus was designed to be flown on a low gravity parabolic aircraft flight to assess the flammability of cotton and 50% cotton/50% polyester fabrics and the resulting skin burn injury that would occur if these fabrics were to ignite. The apparatus, modelled after a Canadian General Standards Board standard flammability test, was also used on the ground for experiments in 1-g. Variables examined in the tests include gravity level, fabric type, air gap size, oxygen concentration, apparatus orientation, ignition source, and method used to secure the specimen. Flame spread rates, heat fluxes, and skin burn predictions determined from test results were compared. <p>Results from test in 1-g indicated that the orientation of the apparatus had a large effect on flame spread rate, heat flux and predicted skin burn times. Flame spread rates and heat fluxes were highest when the fabric was held in the vertical orientation, which resulted in the lowest predicted times to produce skin burns. Flame spread rates and heat fluxes were considerably lower in microgravity than in 1-g, which resulted in higher predicted times to produce skin burns.

This study investigates the relocation behaviours of out-movers of deprived areas in the region of Stockholm, Sweden. The research is motivated by the concerns raised by deprived and segregated neighbourhoods in relation to a social fragmentation and an unsuccessful socio-economic inclusion of all citizens. Some researches affirm that the out-movers of deprived neighbourhoods tend to be more integrated than the stayers or the individual moving in such neighbourhoods. And if some studies are concerned about their prospective, they have been restricted to their destinations’ socio-economic features and dismissed any spatial approach.This study aims to analyse flows’ direction and features as well as the areas of destination such as to identify processes of selective migration and how socio-spatial disparities are (re)produced. A specific attention is given to counter-urban movements and their possible correlation to “preservation” objectives: The possible migration of lower classes toward peripheries in order to access a better living environment and avoid a forced economic selective migration toward the urban most deprived neighbourhoods.Descriptive and inferential statistics with binary logistic regressions enabled to put into exergue the selective migration among movers, between the counter-urban and the others but also among counter-urban. If most movers remain in the urban core and in an almost deprived area, a substantial proportion seeks to combine to a move “up” the social ladder (a better suited neighbourhood), a “downward” migration on the urban hierarchy (a move toward the peripheries). And the regression confirms that among this population, a segment is statically significantly disadvantaged and remains in rental after the move.Scholars should consider such evidences by including a spatial dimension to their studies on segregation, neighbourhood sorting processes and selective migration. And most importantly, the results of this study invite them to reassess the traditional life-style and life-cycle explanations of counter-urbanisation in favour of an economic driven migration.

Tracer methods are commonly used for estimation of soil water and groundwater recharge flux especially in arid and semiarid regions. These tracer methods are based on the solute profile shape (distribution of concentration with depth) and peak position. For soils of semi-arid to sub-humid climates, vertical water movement may seasonally vary in direction due to climate conditions and vegetative demands. The first objective of this thesis was to show that TDR (time domain reflectometry) can be a useful tool for estimation of soil water fluxes using tracer methods. The second objective was to study the effects of repeated cycles of directionally-varying flow upon solute profile shape and position used by tracer methods under controlled laboratory conditions. Three soil columns with a KCl tracer and Beaver Creek sand were used for this study. Rain and evaporative systems were used to cause the downward and upward soil water movements in the column, respectively. Soil moisture content and solute concentration were measured using TDR.<p> The result for the first objective was that the peak migration and the soil water balance methods gave similar average upward and downward soil water fluxes. This result indicates that the TDR method can be recommended for determination of soil water fluxes with tracer methods in fields or in laboratory studies for sufficient time and depth.<p> In the second objective, three different seasonal flow regimes were studied using the sand columns, and each flow regime simulated climatic seasons that might occur in the field. Several apparent and statistical parameters were used to evaluate the change of the solute profile shape and position under cycling conditions of the three different flow regimes. These parameters showed that the solute profile shape and position clearly changed under the three different repeated regimes of downward and upward seasonal flows. It was concluded that climate (seasonality) can have significant impacts on the estimation of soil water fluxes using tracer methods. The result from this investigation shows that the profile shape and position after a number of cycles (years of fluctuations) can provide a description of the previous climatic effects on the concentration profile. Therefore, the profile shape can be used as an indicator of the flow regime that has affected the solute profile shape. Moreover, if a reference of a solute profile is available (a solute profile before a period of time), it is easier to determine the flow regime affected the profile shape and position by determining the change of the profile shape and position using statistical parameters presented in this thesis.

<p>Spatial variability of the Earth's surface has a considerable impact on the atmosphere at all scales and understanding the mechanisms involved in land-atmosphere interactions is hindered by the scarcity of appropriate observations. A measurement gap exists between traditional point sensors and large aircraft and satellite-based sensors in collecting measurements of atmospheric quantities. Point sensors are capable of making long time series of measurements, but cannot make measurements of spatial variability. Large aircraft and satellites make measurements over large spatial areas, but with poor spatial and temporal resolution. A helicopter-based platform can make measurements on scales relevant for towers, especially close to the Earth's surface, and can extend these measurements to account for spatial variability. Thus, the Duke University Helicopter Observation Platform (HOP) is designed to fill the existing measurement gap. </p><p>Because measurements must be made in such a way that they are as uncontaminated by the platform itself as much as is possible, it is necessary to quantify the aerodynamic envelope of the HOP. The results of an analytical analysis of the location of the main rotor wake at various airspeeds are shown. Similarly, the results of a numerical analysis using the commercial Computational Fluid Dynamics software Fluent are shown. The optimal flight speed for the sampling of turbulent fluxes is found to be around 30 m/s. At this airspeed, the sensors located in front of the nose of the HOP are in advance of the wake generated by the main rotor. This airspeed is also low enough that the region of high pressure due to the stagnation point on the nose of the HOP does not protrude far enough forward to affect the sensors. Measurements of differential pressures, variables and turbulent fluxes made while flying the HOP at different airspeeds support these results. No systematic effects of the platform are seen at airspeeds above about 10 m/s.</p><p>Processing of HOP data collected using the current set of sensors is discussed, including the novel use of the Empirical Mode Decomposition (EMD) to detrend and filter the data. The EMD separates the data into a finite number of Impirical Mode Functions (IMFs), each of which is unique and orthogonal. The basis is determined by the data itself, so that it need not be known a priori, and it is adaptive. The EMD is shown to be an ideal tool for the filtering and detrending of HOP data using data gathered during the Cloud and Land Surface Interaction Campaign (CLASIC). </p><p>The ability of the HOP to accurately measure atmospheric profiles of potential temperature is demonstrated. During experiments conducted in the marine boundary layer (MBL) and the convective boundary layer (CBL), HOP profiles are evaluated using profiles from an elastic backscatter lidar. The HOP and the lidar agree on the height of the boundary layer in both cases, and the HOP effectively locates other atmospheric structures.</p><p>Atmospheric sensible and latent heat fluxes, turbulence kinetic energy (TKE) and horizontal momentum fluxes are also measured, and the resulting information is used to provide context to tower-based data collected concurrently. A brief comparison made over homogeneous ocean conditions yields good results. A more exhaustive evaluation is made using short HOP flights made over an orchard during the Canopy Horizontal Turbulence Study (CHATS).</p> / Dissertation

This study investigated the concentrations of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in the particulate and dissolved phase, as well as concentrations of PAHs in the sediment in Kaohsiung Harbor lagoon. Sources of PAHs in the water column were determined by isomer ratios, hierarchical cluster analysis (HCA) and principal components analysis (PCA). The net and annual fluxes of PAHs were calculated after a lagoon-wide water sampling campaign and compared with those found in a previous study (Fang, 2007) in which data from only one water sampling station was used. ¡@¡@In rain season, total PAH concentrations ranged from 21.6 to 36.2 ng/L for water samples, with dissolved and particulate phase concentrations ranged from 15.5 to 27.2 ng/L and from 3.4 to 8.6 ng/L, respectively. In dry season, total PAH concentrations ranged from 13.2 to 31.5 ng/L for water samples, with dissolved and particulate phase concentrations ranged from 8.0 to 21.1 ng/L and from 5.3 to 10.5 ng/L, respectively. Total PAH concentrations were found higher in rain season than in dry season. The highest total PAH concentration in dry season was observed in Chianjen River estuary. Relatively high PAH concentrations were also observed in these southern stations of Kaohsiung Harbor because of their location near Dalin industrial park. Total PAH concentrations ranged from 81.7 to 2279 ng/g for sediment samples, with average of 895 ng/g. The correlations between PAH concentrations and organic carbons, water temperature, salinity and suspended particles were also examined in this study. PAH concentration in dissolved phase was negatively correlated with water temperature (p<0.05). PAH concentration in sediment was positively correlated with organic carbons (p<0.05), and negatively correlated with median diameter (p<0.01). The logKoc¡ÐlogKow relationship in rain and dry season was compared with literature. It was found that the logKoc values were higher than those reported in literature, suggesting that soot particles might play an important role in the transport and distribution of PAHs in the study area. In rain season, PAHs in dissolved phase were mainly from pyrogenic origins; while mainly from petrogenic origins in particulate phase. In contrast, in dry season, PAHs in dissolved phase were mainly from petrogenic origins; while mainly from pyrogenic origins in particulate phase. In addition, it was found, relatively, that petrogenic pollution was introduced maily from the northern area of the lagoon. In rain season, total PCB concentrations ranged from 1.1 to 2.7 ng/L for water samples, with dissolved and particulate phase concentrations ranged from 0.42 to 2.1 ng/L and from 0.24 to 1.4 ng/L, respectively. In dry season, total PCB concentrations ranged from 0.54 to 1.3 ng/L for water samples, with dissolved and particulate phase concentrations ranged from 0.20 to 0.74 ng/L and from 0.32 to 0.76 ng/L, respectively. The direction of net fluxes of PAHs in this study are from water to air (net volatilization) in summer. In winter, however, the absorptive PAH fluxes obtained for four to six-ring PAH, such as fluoranthrene, chrysene + triphenylene and benzo[a]anthracene, indicating that PAHs were absorbed into surface waters. According to our results, it was suggested that the results from previous study (Fang, 2007) might underestimate the net fluxes of Pyrene and total fluxes in dry season. The annual fluxes of PAHs estimated in this study were 212 mg/m2 /year and 5.7 kg of PAHs were emitted annually from the harbor lagoon surface waters to the ambient atmosphere.