Numerical studies of large-amplitude internal waves shoaling and breaking at shelf slopes     

Øyvind Thiem  Jarle Berntsen 《Ocean Dynamics》2009,59(6):937-952

Hydro carbon fields beyond the shelf break are presently being explored and developed, which has increased the scientific focus in this area. Measurements from the slopes reveal large variability in temperature and velocity, and some of the observed events are due to interactions between large-amplitude oscillations of the thermocline and the topography. The present study focuses on the strong currents that are generated near the seabed during shoaling and breaking of internal waves along shelf slopes. The parameter regime used is similar to the one for the Nordic Seas. The results show that, during shoaling of large internal waves along (gentle) slopes, the energy is transferred towards smaller scales and strong velocities (over 1 m s^− 1) can be generated. To resolve all scales involved is still not feasible, and therefore, the model results are sensitive to the grid size and the subgrid scale closure.  相似文献   

Effects of the bottom boundary condition in numerical investigations of dense water cascading on a slope     

Jarle Berntsen  Guttorm Alendal  Helge Avlesen  Øyvind Thiem 《Ocean Dynamics》2018,68(4-5):553-573

The flow of dense water along continental slopes is considered. There is a large literature on the topic based on observations and laboratory experiments. In addition, there are many analytical and numerical studies of dense water flows. In particular, there is a sequence of numerical investigations using the dynamics of overflow mixing and entrainment (DOME) setup. In these papers, the sensitivity of the solutions to numerical parameters such as grid size and numerical viscosity coefficients and to the choices of methods and models is investigated. In earlier DOME studies, three different bottom boundary conditions and a range of vertical grid sizes are applied. In other parts of the literature on numerical studies of oceanic gravity currents, there are statements that appear to contradict choices made on bottom boundary conditions in some of the DOME papers. In the present study, we therefore address the effects of the bottom boundary condition and vertical resolution in numerical investigations of dense water cascading on a slope. The main finding of the present paper is that it is feasible to capture the bottom Ekman layer dynamics adequately and cost efficiently by using a terrain-following model system using a quadratic drag law with a drag coefficient computed to give near-bottom velocity profiles in agreement with the logarithmic law of the wall. Many studies of dense water flows are performed with a quadratic bottom drag law and a constant drag coefficient. It is shown that when using this bottom boundary condition, Ekman drainage will not be adequately represented. In other studies of gravity flow, a no-slip bottom boundary condition is applied. With no-slip and a very fine resolution near the seabed, the solutions are essentially equal to the solutions obtained with a quadratic drag law and a drag coefficient computed to produce velocity profiles matching the logarithmic law of the wall. However, with coarser resolution near the seabed, there may be a substantial artificial blocking effect when using no-slip.  相似文献   

Mesozoic marine reptiles from Spitsbergen and their ecosystems     

Lene L. Delsett  Patrick S. Druckenmiller   yvind Hammer  Krzysztof Hryniewicz  Espen M. Knutsen  Maayke J. Koevoets  Hans A. Nakrem  Aubrey J. Roberts  Jrn H. Hurum 《Geology Today》2019,35(1):20-25

In the Mesozoic seas, the apex predators were reptiles. From the Arctic archipelago of Svalbard, the Spitsbergen Mesozoic Research Group has excavated numerous well preserved marine reptile skeletons in order to understand the biology of these animals and the environment they lived in. The work of eleven field seasons has made this one of the largest and most productive palaeontological research projects in the high Arctic world‐wide. The initial eight seasons focused on one of the richest occurrences of Late Jurassic—earliest Cretaceous (c. 150–139 Ma) marine reptiles in the world, and nearly sixty specimens have been collected, together with a diverse assemblage of invertebrates, some of which are associated with methane seeps. The last three seasons were spent investigating events further back in time, as Spitsbergen preserves the remains from some of the first marine reptile radiations in the wake of the most devastating extinction in the history of the Earth, at the Permian–Triassic boundary (c. 252 Ma).  相似文献   

A REGIONAL INVENTORY OF ROCK GLACIERS AND ICE‐CORED MORAINES IN NORWAY     

KARIANNE S. LILLEØREN  BERND ETZELMÜLLER 《Geografiska Annaler: Series A, Physical Geography》2011,93(3):175-191

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Bianchi type-I universe models with nonlinear viscosity     

Nouraddin Mostafapoor  Øyvind Grøn 《Astrophysics and Space Science》2013,343(1):423-434

In this paper we study the evolution of spatially homogeneous and anisotropic Bianchi type-I Universe models with the cosmological constant, Λ, and filled with nonlinear viscous fluid. The dynamical equations for these models are obtained and solved for some special cases. We calculate the statefinder parameters for the models and display them in the s-r-plane.  相似文献   

The Ritland impact structure,southwestern Norway     

F. RIIS  E. KALLESON  H. DYPVIK  S. O. KRØGLI  O. NILSEN 《Meteoritics & planetary science》2011,46(5):748-761

Abstract– The Ritland structure is a newly discovered impact structure, which is located in southwestern Norway. The structure is the remnant of a simple crater 2.5 km in diameter and 350 m deep, which was excavated in Precambrian gneissic rocks. The crater was filled by sediments in Cambrian times and covered by thrust nappes of the Caledonian orogen in the Silurian–Devonian. Several succeeding events of uplift, erosion, and finally the Pleistocene glaciations, disclosed this well‐preserved structure. The erosion has exposed brecciated rocks of the original crater floor overlain by a thin layer of melt‐bearing rocks and postimpact crater‐filling breccias, sandstones, and shales. Quartz grains with planar deformation features occur frequently within the melt‐bearing unit, confirming the impact origin of the structure. The good exposures of infilling sediments have allowed a detailed reconstruction of the original crater morphology and its infilling history based on geological field mapping.  相似文献   

A new approach for reconstructing glacier variability based on lake sediments recording input from more than one glacier     

Kristian Vasskog  Øyvind Paasche  Atle Nesje  John F. Boyle  H.J.B. Birks 《Quaternary Research》2012,77(1):192-204

We explore the possibility of building a continuous glacier reconstruction by analyzing the integrated sedimentary response of a large (440 km²) glacierized catchment in western Norway, as recorded in the downstream lake Nerfloen (N61°56’, E6°52’). A multi-proxy numerical analysis demonstrates that it is possible to distinguish a glacier component in the ~ 8000-yr-long record, based on distinct changes in grain size, geochemistry, and magnetic composition. Principal Component Analysis (PCA) reveals a strong common signal in the 15 investigated sedimentary parameters, with the first principal component explaining 77% of the total variability. This signal is interpreted to reflect glacier activity in the upstream catchment, an interpretation that is independently tested through a mineral magnetic provenance analysis of catchment samples. Minimum glacier input is indicated between 6700–5700 cal yr BP, probably reflecting a situation when most glaciers in the catchment had melted away, whereas the highest glacier activity is observed around 600 and 200 cal yr BP. During the local Neoglacial interval (~ 4200 cal yr BP until present), five individual periods of significantly reduced glacier extent are identified at ~ 3400, 3000–2700, 2100–2000, 1700–1500, and ~ 900 cal yr BP.  相似文献   

POPULATION AND RESOURCES IN TWO TYPES OF RURAL LANDSCAPE     

HENNING MØRCH M.Sc. 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):89-92

Mørch, Henning: Population and resources in two types of rural landscape—Denmark 1860, 1900, and 1960. Geografisk Tidsskrift 80: 88–92. Copenhagen, June 1980.

An investigation on the basis of simple, linear regression of the relationship between size of population and physical resources in two types of landscape—moraine and outwash plain—Denmark 1860–1960.  相似文献   

Advances in search and rescue at sea   总被引：2，自引：0，他引：2  

Øyvind Breivik  Arthur Addoms Allen  Christophe Maisondieu  Michel Olagnon 《Ocean Dynamics》2013,63(1):83-88

A topical collection on “Advances in Search and Rescue at Sea” has appeared in recent issues of Ocean Dynamics following the latest in a series of workshops on “Technologies for Search and Rescue and other Emergency Marine Operations” (2004, 2006, 2008, and 2011), hosted by IFREMER in Brest, France. Here, we give a brief overview of the history of search and rescue at sea before we summarize the main results of the papers that have appeared in the topical collection.  相似文献   

An EC 14026 pulsator in a reflection binary     

M. D. Reed  D. M. Terndrup  R. Østensen  S. Geier  J. Gilker  P. G. Beck  P. Degroote  J. Vanautgaerden  C. Waelkens 《Astrophysics and Space Science》2010,328(1-2):83-86

During our campaign of acquiring follow-up photometric data to resolve short period pulsating sdB (EC14026 or V361 Hya) stars, we obtained data on the known pulsator KUV 04421+1416 and discovered that it is also in a reflection-effect binary. Here we present preliminary results of the pulsation analysis and provide some constraints on the companion, which is most likely an MV star. This makes KUV 04421+1416 only the second known system with an EC14026-type pulsator in a reflection-effect binary.  相似文献