排序方式： 共有69条查询结果，搜索用时 15 毫秒
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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
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A short-term predictive system for surface currents from a rapidly deployed coastal HF radar network
Donald Barrick Vicente Fernandez Maria I. Ferrer Chad Whelan Øyvind Breivik 《Ocean Dynamics》2012,62(5):725-740
In order to address the need for surface trajectory forecasts following deployment of coastal HF radar systems during emergency-response situations (e.g., search and rescue, oil spill), a short-term predictive system (STPS) based on only a few hours data background is presented. First, open-modal analysis (OMA) coefficients are fitted to 1-D surface currents from all available radar stations at each time interval. OMA has the effect of applying a spatial low-pass filter to the data, fills gaps, and can extend coverage to areas where radial vectors are available from a single radar only. Then, a set of temporal modes is fitted to the time series of OMA coefficients, typically over a short 12-h trailing period. These modes include tidal and inertial harmonics, as well as constant and linear trends. This temporal model is the STPS basis for producing up to a 12-h current vector forecast from which a trajectory forecast can be derived. We show results of this method applied to data gathered during the September 2010 rapid-response demonstration in northern Norway. Forecasted coefficients, currents, and trajectories are compared with the same measured quantities, and statistics of skill are assessed employing 16 24-h data sets. Forecasted and measured kinetic variances of the OMA coefficients typically agreed to within 10–15%. In one case where errors were larger, strong wind changes are suspected and examined as the cause. Sudden wind variability is not included properly within the STPS attack we presently employ and will be a subject for future improvement. 相似文献
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Swail Val Alves Jose-Henrique Breivik Øyvind Brown Jennifer Greenslade Diana 《Ocean Dynamics》2019,69(4):513-517
Following the 1st International Workshop on Waves, Storm Surges and Coastal Hazards, which incorporated the 15th session of the long-standing the International Workshop on Wave Hindcasting and Forecasting, in September 2017 in Liverpool, United Kingdom, a topical collection has appeared in recent issues of Ocean Dynamics. Here, we give a brief overview of the 15 papers published in this topical collection as well as an overview of the widening scope of the conference in recent years. The continuing trend towards closer integration between the wave and ocean modeling communities is reflected in this workshop, culminating in the renaming of the workshop, while maintaining the connection with the three-decade long history of the wave workshop. This is also seen in this topical collection, with several papers exploring wave-generated storm surge, wave-tide contributions to coastal flooding, forcing a global ocean model with fluxes from a wave model and interaction between surface waves and sea ice.
相似文献56.
Joanna Staneva Victor Alari Øyvind Breivik Jean-Raymond Bidlot Kristian Mogensen 《Ocean Dynamics》2017,67(1):81-101
The effect of wind waves on water level and currents during two storms in the North Sea is investigated using a high-resolution Nucleus for European Modelling of the Ocean (NEMO) model forced with fluxes and fields from a high-resolution wave model. The additional terms accounting for wave-current interaction that are considered in this study are the Stokes-Coriolis force, the sea-state-dependent energy and momentum fluxes. The individual and collective role of these processes is quantified and the results are compared with a control run without wave effects as well as against current and water-level measurements from coastal stations. We find a better agreement with observations when the circulation model is forced by sea-state-dependent fluxes, especially in extreme events. The two extreme events, the storm Christian (25–27 October 2013), and about a month later, the storm Xaver (5–7 December 2013), induce different wave and surge conditions over the North Sea. Including the wave effects in the circulation model for the storm Xaver raises the modelled surge by more than 40 cm compared with the control run in the German Bight area. For the storm Christian, a difference of 20–30 cm in the surge level between the wave-forced and the stand-alone ocean model is found over the whole southern part of the North Sea. Moreover, the modelled vertical velocity profile fits the observations very well when the wave forcing is accounted for. The contribution of wave-induced forcing has been quantified indicating that this represents an important mechanism for improving water-level and current predictions. 相似文献
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Bonaduce Antonio Staneva Joanna Grayek Sebastian Bidlot Jean-Raymond Breivik Øyvind 《Ocean Dynamics》2020,70(12):1547-1569
Ocean Dynamics - The contribution of sea-state-induced processes to sea-level variability is investigated through ocean-wave coupled simulations. These experiments are performed with a... 相似文献
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Brit Thyberg Jens JahrenTurid Winje Knut BjørlykkeJan Inge Faleide Øyvind Marcussen 《Marine and Petroleum Geology》2010
Late Cretaceous mudstones from two wells located in the northern North Sea and the Norwegian Sea have been examined with respect to quartz cement. Two different types of quartz cement (Type 1 and Type 2) have been identified using SEM/EDS/CL-analysis of drill-bit cuttings at depths 2370–2670 m (80–85 °C). Type 1 appears as relatively large aggregates (30–100 μm) of depth/temperature related crypto- or microcrystalline to macrocrystalline irregular quartz cement formed by local re-crystallization of biogenic silica. The CL-responses of Type 1 quartz cement give a clear indication of an authigenic origin. Type 2 quartz cement represents relatively high amounts of extremely fine-grained micro-sized (1–3 μm) crystals embedded as discrete, short chains or small clusters/nests within the illitized clay matrix. The CL-responses of micro-quartz crystals indicate an authigenic origin. The micro-quartz is most probably sourced from silica released during the smectite to illite dissolution–precipitation reaction. The petrographic evidence indicates that most of the silica released by the smectite to illite reaction has not been exported out of the mudstones. The silica released produce a subtle inter-connected micro-quartz network interlocked with aggregates of micro-quartz and authigenic clay crystals. This micro-quartz cementation process causes a significant and sharp change in the mudstone stiffness at the onset of the chemical compaction regime. This is indicated by an abrupt increase in well log velocity (Vp) and change in seismic facies close to 2500 m (80/85 °C). 相似文献
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Øyvind Marcussen Tom Erik MaastNazmul H. Mondol Jens JahrenKnut Bjørlykke 《Marine and Petroleum Geology》2010
Rock physical properties, like velocity and bulk density, change as a response to compaction processes in sedimentary basins. In this study it is shown that the velocity and density in a well defined lithology, the shallow marine Etive Formation from the northern North Sea increase with depth as a function of mechanical compaction and quartz cementation. Physical properties from well logs combined with experimental compaction and petrographic analysis of core samples shows that mechanical compaction is the dominant process at shallow depth while quartz cementation dominates as temperatures are increased during burial. At shallow depths (<2000–2500 m, 70–80 °C) the log derived velocities and densities show good agreement with results from experimental compaction of loose Etive sand indicating that effective stress control compaction at these depths/temperatures. This indicates that results from experimental compaction can be used to predict reservoir properties at burial depths corresponding to mechanical compaction. A break in the velocity/depth gradient from about 2000 m correlates with the onset of incipient quartz cementation observed from petrographic data. The gradient change is caused by a rapid grain framework stiffening due to only small amounts of quartz cement at grain contacts. At temperatures higher than 70–80 °C (2000–2500 m) the velocities show a strong correlation with quartz cement amounts. Porosity reduction continues after the onset of quartz cementation showing that sandstone diagenesis is insensitive to effective stress at temperatures higher than 70–80 °C. The quartz cement is mainly sourced from dissolution at stylolites reflected by the fact that no general decrease in intergranular volume (IGV) is observed with increasing burial depth. The IGV at the end of mechanical compaction will be important for the subsequent diagenetic development. This study demonstrates that mechanical compaction and quartz cementation is fundamentally different and this needs to be taken into consideration when analyzing a potential reservoir sandstone such as the Etive Formation. 相似文献