The 14th international workshop on wave hindcasting and forecasting and the 5th coastal hazards symposium     

Øyvind Breivik  Jose Henrique Alves  Diana Greenslade  Kevin Horsburgh  Val Swail 《Ocean Dynamics》2017,67(3-4):551-556

Following the 14th International Workshop on Wave Hindcasting and Forecasting and 5th Coastal Hazards Symposium in November 2014 in Key West, Florida, a topical collection has appeared in recent issues of Ocean Dynamics. Here, we give a brief overview of the 16 papers published in this topical collection as well as an overview of the widening scope of the conference in recent years. A general trend in the field has been towards closer integration between the wave and ocean modelling communities. This is also seen in this topical collection, with several papers exploring the interaction between surface waves and mixed layer dynamics and sea ice.  相似文献   

Numerical simulation of upwelling currents in pockmarks,and data from the Inner Oslofjord,Norway   总被引：5，自引：3，他引：2  

Øyvind Hammer  Karen E. Webb  Davy Depreiter 《Geo-Marine Letters》2009,29(4):269-275

The deflection of oceanic or tidal currents into pockmarks has been studied by both general three-dimensional computational fluid dynamics simulations and acoustic measurements in a number of pockmarks in the Inner Oslofjord, Norway. The modeling demonstrates upstream convergence of flow lines, followed by upwelling over the pockmark. This upwelling is an effect of deflected regional currents, not of expulsion of fluids or gas from the seafloor, and is sufficiently strong to prevent the settling of fine particles. The field measurements, although noisy at low vertical velocities, are consistent with the hypothesis of upwelling. The reduction in sedimentation rate inferred over the pockmarks (relative to that of the flat surrounding seabed) can explain the maintenance, or even deepening of pockmarks in the absence of fluid or gas seepage. The current pattern may also have consequences for the marine biology of pockmarks.  相似文献   

A Hamilton–Jacobi Framework for Modeling Folds in Structural Geology     

Øyvind Hjelle  Steen A. Petersen 《Mathematical Geosciences》2011,43(7):741-761

A novel mathematical framework for modeling folds in structural geology is presented. All the main fold classes from the classical literature: parallel folds, similar folds, and other fold types with convergent and divergent dip isogons are modeled in 3D space by linear and non-linear first-order partial differential equations. The equations are derived from a static Hamilton–Jacobi equation in the context of isotropic and anisotropic front propagation. The proposed Hamilton–Jacobi framework represents folded geological volumes in an Eulerian context as a time of arrival field relative to a reference layer. Metric properties such as distances, gradients (dip and strike), curvature, and their spatial variations can then be easily derived and represented as three-dimensional continua covering the whole geological volume. The model also serves as a basis for distributing properties in folded geological volumes.  相似文献   

Arguing for climate policy through the linguistic construction of narratives and voices: the case of the South-African green paper “National Climate Change Response”     

Kjersti Fløttum  Øyvind Gjerstad 《Climatic change》2013,118(2):417-430

The purpose of the present paper is to examine a selection of macro- and micro-linguistic features (at text and sentence/word level respectively) of the South-African Green Paper “National Climate Change Response” from 2010. Our overarching assumption is that the Green Paper needs to handle competing interests, beliefs and voices in a narrative structure favouring specific courses of action. How does the government portray the complex natural and societal phenomenon of climate change, and how does it take into account the many and often competing national and international views and interests which come into play? Our hypothesis is that the Green Paper constructs a narrative and that it relates to a number of voices other than that of the authors, through linguistic markers of polyphony, such as negation, sentence connectives, adverbs and reported speech. Thus we propose a narrative and polyphonic analysis of the Green Paper, at the level of the text as a whole (macro-level) but also with attention to linguistic constructions of polyphony or “multi-voicedness” (micro-level). We find that the narrative-polyphonic properties of the Green Paper contribute to a strategy for building consensus on climate change policy. The South African government assumes the role of main hero in its own climate change “story”, and there are subtle forms of interaction with different and typically non-identified voices, such as concessive constructions and presuppositions. These results support our overarching interpretation of the whole document as striving to impose a South African consensus on the issue of climate change.  相似文献   

A Numerical Framework for Modeling Folds in Structural Geology   总被引：1，自引：1，他引：0  

Øyvind Hjelle  Steen A. Petersen  Are Magnus Bruaset 《Mathematical Geosciences》2013,45(3):255-276

A numerical framework for modeling folds in structural geology is presented. This framework is based on a novel and recently published Hamilton–Jacobi formulation by which a continuum of layer boundaries of a fold is modeled as a propagating front. All the fold classes from the classical literature (parallel folds, similar folds, and other fold types with convergent and divergent dip isogons) are modeled in two and three dimensions as continua defined on a finite difference grid. The propagating front describing the fold geometry is governed by a static Hamilton–Jacobi equation, which is discretized by upwind finite differences and a dynamic stencil construction. This forms the basis of numerical solution by finite difference solvers such as fast marching and fast sweeping methods. A new robust and accurate scheme for initialization of finite difference solvers for the static Hamilton–Jacobi equation is also derived. The framework has been integrated in simulation software, and a numerical example is presented based on seismic data collected from the Karama Block in the North Makassar Strait outside Sulawesi.  相似文献   

Numerical simulation of flow and aquaculture organic waste dispersion in a curved channel     

Alfatih Ali  Øyvind Thiem  Jarle Berntsen 《Ocean Dynamics》2013,63(9-10):1073-1082

The dispersion and deposition of particulate organic matter from a fish cage located in an idealized curved channel with a 90° bend are studied for different horizontal grid resolutions. The model system consists of a three-dimensional, random-walk particle tracking model coupled to a terrain-following ocean model. The particle tracking model is a Lagrangian particle tracking simulator which uses the local flow field, simulated by the ocean model, for advection of the particles and random walk to simulate the turbulent diffusion. The sinking of particles is modeled by imposing an individual particle settling velocity. As the homogeneous water flows through the bend in the channel, the results show that a cross-channel secondary circulation is developed. The motion of this flow is similar to a helical motion where the water in the upper layers moves towards the outer bank and towards the inner bank in the lower layers. The intensity of the secondary circulation will depend on the viscosity scheme and increases as the horizontal grid resolution decreases which significantly affects the distribution of the particles on the seabed. The presence of the secondary circulation leads to that most of the particles that settle, settle close to the inner bank of the channel.  相似文献   

Accuracy and efficiency of stencils for the eikonal equation in earth modelling     

Tor Gillberg  ?yvind Hjelle  Are Magnus Bruaset 《Computational Geosciences》2012,16(4):933-952

Motivated by the needs for creating fast and accurate models of complex geological scenarios, accuracy and efficiency of three stencils for the isotropic eikonal equation on rectangular grids are evaluated using a fast marching implementation. The stencils are derived by direct modelling of the wave front, resulting in new and valuable insight in terms of improved upwind and causality conditions. After introducing a method for generalising first-order upwind stencils to higher order, a new second-order diagonal stencil is presented. Similarly to the multistencil fast marching approach, the diagonal stencil makes use of nodes in the diagonal directions, whereas the traditional Godunov stencil uses solely edge-connected neighbours. The diagonal stencil uses nodes close to each other, reaching upwind, to get a more accurate estimate of the angle of incidence of the arriving wave front. Although the stencils are evaluated in a fast marching setting, they can be adapted to other efficient eikonal solvers. All first- and second-order stencils are evaluated in a range of tests. The first test case models a folded structure from the Zagros fold belt in Iran. The other test cases are constructed to investigate specific properties of the examined stencils. The numerical investigation considers convergence rates and CPU times for non-constant and constant speed first-arrival computations. In conclusion, the diagonal stencil is the most efficient and accurate of the three alternatives.  相似文献   

Application of a Large-Eddy Simulation Database to Optimisation of First-Order Closures for Neutral and Stably Stratified Boundary Layers     

Igor N. Esau  Øyvind Byrkjedal 《Boundary-Layer Meteorology》2007,125(2):207-225

Large-eddy simulation (LES) is a well-established numerical technique, resolving the most energetic turbulent fluctuations in the planetary boundary layer. By averaging these fluctuations, high-quality profiles of mean quantities and turbulence statistics can be obtained in experiments with well-defined initial and boundary conditions. Hence, LES data can be beneficial for assessment and optimisation of turbulence closure schemes. A database of 80 LES runs (DATABASE64) for neutral and stably stratified planetary boundary layers (PBLs) is applied in this study to optimize first-order turbulence closure (FOC). Approximations for the mixing length scale and stability correction functions have been made to minimise a relative root-mean-square error over the entire database. New stability functions have correct asymptotes describing regimes of strong and weak mixing found in theoretical approaches, atmospheric observations and LES. The correct asymptotes exclude the need for a critical Richardson number in the FOC formulation. Further, we analysed the FOC quality as functions of the integral PBL stability and the vertical model resolution. We show that the FOC is never perfect because the turbulence in the upper half of the PBL is not generated by the local vertical gradients. Accordingly, the parameterised and LES-based fluxes decorrelate in the upper PBL. With this imperfection in mind, we show that there is no systematic quality deterioration of the FOC in the strongly stable PBL provided that the vertical model resolution is better than 10 levels within the PBL. In agreement with previous studies, we found that the quality improves slowly with the vertical resolution refinement, though it is generally wise not to overstretch the mesh in the lowest 500 m of the atmosphere where the observed, simulated and theoretically predicted stably stratified PBL is mostly located. The submission to a special issue of the “Boundary-Layer Meteorology” devoted to the NATO advanced research workshop “Atmospheric Boundary Layers: Modelling and Applications for Environmental Security”.  相似文献   

Preparation of a Synthetic Titanite Glass Calibration Material for In Situ Microanalysis by Direct Fusion in Graphite Electrodes: A Preliminary Characterisation by EPMA and LA-ICP-MS   总被引：1，自引：2，他引：1  

Magne Ødegård  Øyvind Skår  Henrik Schiellerup  Norman J. Pearson 《Geostandards and Geoanalytical Research》2005,29(2):197-209

This paper describes a technique for the preparation of a titanite (CaTiSiO₅) glass calibration material for use in in situ microanalysis of major, minor, and trace elements in geological materials. The starting composition was a titanite matrix doped with minor and trace elements at ∼ 200 μg g^-1. The elements Sc, Y, REEs, Th and U were added in the form of nitrates in solution, and the elements V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Hf and W were added as solid oxides. The synthetic titanite glass was produced by direct fusion by resistance heating in graphite electrodes at 1600-1700 °C, and quenched in air. Backscattered electron images indicate good homogeneity, with no signs of separate phases or vesicles, and analysis of the major elements Ca, Ti and Si by electron microprobe showed relative standard deviations between 0.5 and 0.7%, based on six independent measurements. Deviations from nominal concentrations for Ca, Si and Ti were measured to -1.2, -3.3 and -0.8%, respectively. The homogeneity of the trace elements in the glass was assessed by LA-ICP-MS analyses, using NIST SRM 610, 612 and 616 as external calibrators, and Ca as the internal standard element. Determinations were made both with a quadrupole mass spectrometer and a sector field instrument, and both raster and spot modes of analysis were used. For the majority of doped elements, precision was better than 10%, and relative deviations from nominal values were, with few exceptions, between 5 and 10%.  相似文献   

Glacier Mass Balance in Southern Norway Modelled by Circulation Indices and Spring-Summer Temperatures ad 1781–2000     

Øyvind Nordli  Øyvind Lie  Atle Nesje  Rasmus E. Benestad 《Geografiska Annaler: Series A, Physical Geography》2005,87(3):431-445

By stepwise regression analysis the accumulation, ablation, and equilibrium line altitude (ELA) were modelled by circulation indices and spring‐summer temperature on six Norwegian glaciers (Ålfotbreen, Nigardsbreen, Rembesdalsskåka, Storbreen, Hellstugubreen and Gråsubreen). The circulation indices were derived from a gridded monthly mean sea level pressure (MSLP) data set, whereas temperature series were derived from instrumental and proxy data. Analyses showed that accumulation on the western glaciers was strongly related to western airflow perpendicular to the main mountain range releasing precipitation on the glaciers. No other airflow variable significantly improved the regression. For the continental glaciers, circulating air in connection with low pressure systems was also found to be important. This may explain the lack of synchronicity in the glaciers' development in southern Norway during the Holocene. Accumulation was better modelled using the MSLP data set than by using the North Atlantic Oscillation (NAO) index as predictor. The decadal variations of accumulation, ablation, and ELA were analysed by a Gaussian low pass filter. The well‐known abundant accumulation on Norwegian glaciers during the early 1990s turned out to be unprecedented during the entire series (since 1781), whereas the accumulation of the 1960s has not been lower since the early 19th century according to model results. Ablation increased significantly from the mid‐19th century to the 1930s. The ablation maximum during the 1930s has not yet been exceeded. Also the 1930s show extremely high ELA values.  相似文献