Water mass exchange, pathways and the mesoscale eddy field in the Lofoten Basin of the Norwegian Sea

The Lofoten Basin situated in the Norwegian Sea, plays a central role in redistributing and modifying the warm Atlantic Water carried poleward with the Norwegian Atlantic Current. Increased residence time of the warm Atlantic Water in this region, leads to a large cooling and the largest surface heat losses in the Nordic Seas. This thesis studies the exchange of Atlantic Water with the Lofoten Basin using observations and numerical models, and Lagrangian and Eulerian approaches. A key focus is the study of the mass and heat exchange with the basin outlined by the 3000-m isobath. Surface drifters are analyzed to study the surface circulation in the Nordic Seas and to estimate the water mass exchange with the Lofoten Basin. Fields from Eulerian models and trajectories from Lagrangian simulations at multiple levels are further used to study the processes leading to the exchange, by delineating the mean and eddy component of the flows. Analyses aimed to quantify the mesoscale eddy properties, their interaction with the ambient, heat and vorticity budgets, and to assess the importance of eddies relative to the ambient flow and other submesoscale processes in the mass and heat exchange with the Lofoten Basin. The geographical origins of the water masses having largest interaction with the basin are identified, and these sites are studied in detail to investigate the processes behind the exchange. The thesis also investigates the fate of water masses in the basin to study how their properties evolve with time, and compare this with other regions. The first main finding, obtained from surface drifter observations, indicates an increased exchange of Atlantic Water across the southern sector of the Lofoten Basin. The drifters show a meandering motion between the eastern and western branches of the Norwegian Atlantic Current towards the basin, and Eulerian simulations suggest that the inflow is primarily related to a mean component of the flow. The warm waters experience long residence times and large temperature losses in the basin. In contrast with earlier literature, there is less evidence of near-surface exchange with the waters carried by the slope current along the continental slope off Norway. However, the net heat transport into the basin is dominated by eddy fluxes. Furthermore, the divergence of eddy heat fluxes obtained from Eulerian calculations on the continental slope is large, and particularly enhanced at depths of about 400 m. It is therefore suggested that the flow from the south dominates the near-surface exchange of Atlantic Water with the basin, but eddy fluxes from the slope region are important at deeper levels. Lagrangian simulations of particles deployed at several depths reveal variations in the vertical structure of the inflows to the Lofoten Basin. Of the water parcels that are cooled most (more than 1^oC) while in the basin, those at the surface mainly enter from the south, and those at deeper levels (about 500 m) come from the slope. The inflows also have a seasonal variability. In winter, cooling and vertical mixing result in weak stratification and distribute the particles vertically, while strong stratification in summer limits their vertical excursions from their deployment depths. During winter, water masses close to the surface therefore tend to sink and give weaker inflows (less particles) close to the surface and stronger inflows (more particles) at deeper levels (100-300 m). The eddy activity in the basin and on the continental slope is quantified. Eddy signals extracted from Lagrangian trajectories, using multivariate wavelet ridge analysis, show that water masses in coherent vortices experience larger changes in their water properties (such as temperature and density) than water masses in the ambient flow, with enhanced warming in cyclones and enhanced cooling in anticyclones. There is also evidence of upwelling in the cyclones and downwelling in the anticyclones. The change of water properties and net vertical displacement is most pronounced in the Lofoten Basin. The anticyclones have a longer lifetime, more circular shape and larger radius than the cyclones. However, the eddies only cover a small portion of the Nordic Seas (about 6%) and the ambient flow and filaments around eddies therefore play an important role in balancing the Lofoten Basin heat and vorticity budgets. Ridge analysis confirms the role of eddy activity at deeper levels on the slope, and further reveals that the anticyclonic eddies generated on the slope bring warm water into the basin. Energetics and energy-conversion rates calculated from mooring observations from the upper slope, supported by volume-averaged calculations from an Eulerian model, are consistent with the Lagrangian and Eulerian analyses. Estimated baroclinic conversion rates imply that potential energy is extracted from the mean flow to eddies. The role of filaments in the upper layers, the link between the generation of eddies on the slope and their exchange with the LB at deeper layers, and contribution of these eddies and filaments to the Lofoten Basin heat and vorticity budgets merit further studies

Dimensional reduction of a fractured medium for a two-phase flow

We consider a porous medium containing a single fracture, and identify the aperture to length ratio as the small parameter ɛ with the fracture permeability and the fracture porosity scaled as exponents of ɛ. We consider a two-phase flow where the flow is governed by the mass balance and the Darcy law. Using formal asymptotic approach, we derive a catalogue of reduced models as the vanishing limit of ɛ. Our derivation provides new models in a hybrid-dimensional setting as well as models which exhibit two-scale behaviour. Several numerical examples confirm the theoretical derivations and provide additional insight.publishedVersio

“Premierløytnant Bielke”: A Mobile Game for Teaching and Learning History

Developments in mobile phone technology, together with an increased research interest in utilizing computer games to facilitate teaching and learning, are an important catalyst for the emergence of the area of mobile, location-based computer games in schools. This article describes both the design process and an evaluation of Premierløytnant Bielke, a mobile, location-based game for teaching and learning history using mobile phones. We argue that by using the surroundings and milieu that are local to the students in a playful context, we can support the construction of meaning related to the subject of history in a way that is both engaging and worthwhile.publishedVersio

Testing of CO2 Specifications With Respect to Corrosion and Bulk Phase Reactions

AbstractCaptured anthropogenic CO2 contains impurities that might react and form solids and separate corrosive phases when the impurity concentrations exceed the limit where the impurity combination becomes thermodynamically unstable. A number of tentative CO2 specifications and recommendations for the maximum acceptable impurity concentrations have been published. The recommendations include impurity combinations and impurity levels that are not found in the published CO2 specifications for pipelines that are or have been in operation. The lack of field experience and the lack of published lab data that support these specifications are a concern.The most referred recommendations have been challenged in the present work. Experiments were performed with dense phase CO2 containing 300 ppmv water, 350 ppmv O2, 100 ppmv SO2, 100 ppmv NO2 and 100 ppmv H2S. The CO2 and the impurities were continuously injected in the test autoclaves and the consumption rate of the impurities was measured. The experiments showed that the carbon steel corroded and that elemental sulfur formed together with a liquid phase containing sulfuric and nitric acid.The paper discusses the experimental technique and the results obtained in four autoclave experiments. The paper also discusses how the lack of fundamental data and understanding makes it difficult to predict corrosion rates and define a safe operation window for transport of dense phase CO2 originating from different sources with different contaminants

Do people prefer offshore to onshore wind energy? The role of ownership and intended use.

Global investments in offshore wind energy are expected to escalate over the coming decades, fueled by improvements in technology, declining costs, and increasing political support. The complexity, scale, and location of these developments make international ownership and export of electricity more feasible. We examine how the general public's acceptance of wind energy will be affected by a political shift in focus from onshore to nearshore or offshore locations, from local or national dominance of ownership to international dominance, and from meeting local or national needs to meeting international ones. We use a nationwide choice experiment with 1612 individuals in Norway to reveal the preferences for these attributes and apply a mixed logit regression model to estimate the willingness to pay to avoid certain outcomes. We show that, although respondents prefer offshore and nearshore locations to onshore ones, they are even more concerned with maintaining local or national control both through ownership and intended use of the added electricity. Although the preferences for national ownership are strong for both nearshore and offshore alternatives, the preference for meeting national needs becomes less important when wind energy developments are located farther off the coast. Three wind energy scenarios are used to further investigate these preferences: 1) international consortium for offshore wind energy, 2) national alliances for nearshore wind energy, and 3) local energy communities for onshore wind energy. We also discuss how a shift to nearshore and offshore wind energy can be enabled by paying greater attention to people's concerns over national control of wind energy resources.Do people prefer offshore to onshore wind energy? The role of ownership and intended use.publishedVersio

The mesoscale eddy field in the Lofoten Basin from high-resolution Lagrangian simulations

Warm Atlantic-origin waters are modified in the Lofoten Basin in the Nordic Seas on their way toward the Arctic. An energetic eddy field redistributes these waters in the basin. Retained for extended periods, the warm waters result in large surface heat losses to the atmosphere and have an impact on fisheries and regional climate. Here, we describe the eddy field in the Lofoten Basin by analyzing Lagrangian simulations forced by a high-resolution numerical model. We obtain trajectories of particles seeded at three levels – near the surface, at 200 m and at 500 m depth – using 2D and 3D velocity fields. About 200 000 particle trajectories are analyzed from each level and each simulation. Using multivariate wavelet ridge analysis, we identify coherent cyclonic and anticyclonic vortices in the trajectories and describe their characteristics. We then compare the evolution of water properties inside cyclones and anticyclones as well as in the ambient flow outside vortices. As measured from Lagrangian particles, anticyclones have longer lifetimes than cyclones (16–24 d compared to 13–19 d), a larger radius (20–22 km compared to 17–19 km) and a more circular shape (ellipse linearity of 0.45–0.50 compared to 0.51–0.57). The angular frequencies for cyclones and anticyclones have similar magnitudes (absolute values of about 0.05f). The anticyclones are characterized by warm temperature anomalies, whereas cyclones are colder than the background state. Along their path, water parcels in anticyclones cool at a rate of 0.02–0.04 ∘Cd−1, while those in cyclones warm at a rate of 0.01–0.02 ∘Cd−1. Water parcels experience a net downward motion in anticyclones and upward motion in cyclones, often found to be related to changes in temperature and density. The along-path changes in temperature, density and depth are smaller for particles in the ambient flow. An analysis of the net temperature and vorticity fluxes into the Lofoten Basin shows that while vortices contribute significantly to the heat and vorticity budgets, they only cover a small fraction of the domain area (about 6 %). The ambient flow, including filaments and other non-coherent variability undetected by the ridge analysis, hence plays a major role in closing the budgets of the basin.publishedVersio

Acceptance of wind power development and exposure – Not-in-anybody’s-backyard

Despite a large stated-preference (SP) literature on wind power externalities, few SP studies employ a case-control approach to examine whether people’s acceptance of new wind power developments and renewable energy initiatives increases or decreases with exposure. Furthermore, the existing studies are inconclusive on this issue. In a case-control discrete choice experiment, we measure the level of acceptance in terms of people’s willingness-to-accept (WTA) for having future land-based wind power developments in Norway; comparing exposed and non-exposed people’s WTA. We find that exposure lowers acceptance. Furthermore, exposed people are also unwilling to pay as much to increase general domestic renewable energy production (from all sources) as non-exposed people, and thus have lower acceptance for such renewable energy policy initiatives. After testing for type of exposure, we argue that the inconclusiveness in the literature of how exposure affects acceptance of wind power developments could be due to the fact that impacts considered differ somewhat across studies.publishedVersio

Acceptance of wind power development and exposure – Not-in-anybody’s-backyard

Despite a large stated-preference (SP) literature on wind power externalities, few SP studies employ a case-control approach to examine whether people’s acceptance of new wind power developments and renewable energy initiatives increases or decreases with exposure. Furthermore, the existing studies are inconclusive on this issue. In a case-control discrete choice experiment, we measure the level of acceptance in terms of people’s willingness-to-accept (WTA) for having future land-based wind power developments in Norway; comparing exposed and non-exposed people’s WTA. We find that exposure lowers acceptance. Furthermore, exposed people are also unwilling to pay as much to increase general domestic renewable energy production (from all sources) as non-exposed people, and thus have lower acceptance for such renewable energy policy initiatives. After testing for type of exposure, we argue that the inconclusiveness in the literature of how exposure affects acceptance of wind power developments could be due to the fact that impacts considered differ somewhat across studies.publishedVersio

Place attachment and preferences for wind energy – A value-based approach

publishedVersio