Statistical downscaling of daily precipitation over Sweden using GCM output   总被引：3，自引：2，他引：1  

Fredrik Wetterhall  András Bárdossy  Deliang Chen  Sven Halldin  Chong-yu Xu 《Theoretical and Applied Climatology》2009,96(1-2):95-103

A classification of Swedish weather patterns (SWP) was developed by applying a multi-objective fuzzy-rule-based classification method (MOFRBC) to large-scale-circulation predictors in the context of statistical downscaling of daily precipitation at the station level. The predictor data was mean sea level pressure (MSLP) and geopotential heights at 850 (H850) and 700 hPa (H700) from the NCEP/NCAR reanalysis and from the HadAM3 GCM. The MOFRBC was used to evaluate effects of two future climate scenarios (A2 and B2) on precipitation patterns on two regions in south-central and northern Sweden. The precipitation series were generated with a stochastic, autoregressive model conditioned on SWP. H850 was found to be the optimum predictor for SWP, and SWP could be used instead of local classifications with little information lost. The results in the climate projection indicated an increase in maximum 5-day precipitation and precipitation amount on a wet day for the scenarios A2 and B2 for the period 2070–2100 compared to 1961–1990. The relative increase was largest in the northern region and could be attributed to an increase in the specific humidity rather than to changes in the circulation patterns.  相似文献   

Effects of groundwater extraction from crystalline hard rock on water chemistry in an acid forested catchment at Gårdsjön,Sweden     

Fredrik Mossmark  Hans Hultberg  Lars O. Ericsson 《Applied Geochemistry》2007

Atmospheric deposition of S in Sweden has decreased by some 80% over the last 15 a, resulting in a general reduction of SO₄ concentrations in ground and surface water. This project, however, shows that artificial hydrological alteration in an acid wetland can reverse this trend and increase acidity and SO₄ concentrations. The experiment involved the monitoring of two catchments in relatively virgin conditions. In one of the catchments, an experiment with intensive groundwater extraction from the bedrock was carried out. During the experiment, the runoff from the catchment decreased by 50%. Furthermore, the extraction of groundwater resulted in increased seasonal aeration of the centrally located wetland, leading to oxidation of reduced S bound to the soil layers of the wetland. The S changed to solute SO₄, with a subsequent SO₄ surge. Thus, the experiment resulted in an induced acidification of the wetland and runoff waters. The extraction of groundwater significantly increased the recharge of water from the overburden, glacial till and organic soils to groundwater in the bedrock, which in turn reduced the retention time in the bedrock aquifer. These changes resulted in the chemical signature of the groundwater in the bedrock becoming similar to those of the wetland. The findings revealed deterioration in the water quality in the bedrock due to increased concentrations of dissolved organic C and SO₄, as well as a decrease in pH.  相似文献   

Towards the modelling of pedestrian wind speed using high-resolution digital surface models and statistical methods     

Lars Johansson  Shiho Onomura  Fredrik Lindberg  Jonathan Seaquist 《Theoretical and Applied Climatology》2016,124(1-2):189-203

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Sand dunes and valley fills from Preboreal glacial-lake outburst floods in south-eastern Norway – beyond the aeolian paradigm     

Louise Hansen  Georgios Tassis  Fredrik Høgaas 《Sedimentology》2020,67(2):810-848

A major glacial-lake outburst flood in the Glomma valley, south-eastern Norway, took place during the final decay of the Scandinavian Ice Sheet. A combined morphological, geophysical and sedimentological study provides new insight into the variety of processes and deposits of the flood. The studied succession, some tens of metres in thickness, comprises the fill of a major flood basin that developed during hydraulic ponding. Large-scale sand dunes and bars accumulated downstream of locations with expanding flow. Most notable are 10 m high, concentric dune ridges that accumulated downstream of a topographical constriction hosting a high-velocity flow. Flow expansion at the outlet generated intense turbulence and scouring. The sand-loaded eddies helped feeding the semi-stationary dune ridges that grew vertically and downflow under high aggradation rates. Internal structures vary but reflect an overall shift in sedimentation from prevailing supercritical flow to overall subcritical flow conditions at high flood levels. Loading by water and sediment caused large-scale, synsedimentary deformation, increasing local accommodation space. Fast-falling flood levels caused stronger flow locally, while mud and fine sand settled in stagnant pools. The fall caused a significant drop in hydrostatic pressure. This triggered a release of excess pore pressure causing massive dewatering and fluidisation. Water-escape structures include numerous (sub)vertical pipes. The present study shows that outburst flood-generated, large-scale dunes can develop in well-sorted, fine sand and are thereby easily confused with aeolian deposits. Several dune fields in south-eastern Norway are here reinterpreted as the product of at least two major flood events. Sandy dune fields with similar characteristics elsewhere in Scandinavia should likely also be reinterpreted, and the role of outburst floods during the final deglaciation of Scandinavia has seemingly been underestimated. The study emphasises the importance of ponding, flow expansion, sorting, rapidly changing pressure conditions and deformation for outburst flood-related sedimentation.  相似文献   

Water column monitoring near oil installations in the North Sea 2001-2004     

Hylland K  Tollefsen KE  Ruus A  Jonsson G  Sundt RC  Sanni S  Røe Utvik TI  Johnsen S  Nilssen I  Pinturier L  Balk L  Barsiene J  Marigòmez I  Feist SW  Børseth JF 《Marine pollution bulletin》2008,56(3):414-429

Fisheries have been vital to coastal communities around the North Sea for centuries, but this semi-enclosed sea also receives large amounts of waste. It is therefore important to monitor and control inputs of contaminants into the North Sea. Inputs of effluents from offshore oil and gas production platforms (produced water) in the Norwegian sector have been monitored through an integrated chemical and biological effects programme since 2001. The programme has used caged Atlantic cod and blue mussels. PAH tissue residues in blue mussels and PAH bile metabolites in cod have confirmed exposure to effluents, but there was variation between years. Results for a range of biological effects methods reflected exposure gradients and indicated that exposure levels were low and caused minor environmental impact at the deployment locations. There is a need to develop methods that are sufficiently sensitive to components in produced water at levels found in marine ecosystems.  相似文献   

Ethoxyresorufin-O-deethylase activity and fixed wavelength fluorescence detection of PAHs metabolites in bile in turbot (Scophthalmus maximus L.) Exposed to a dispersed topped crude oil in a Continuous Flow System     

Lionel Camus  Endre Aas  Jan Fredrik Brseth 《Marine environmental research》1998,46(1-5)

Long term effects of sublethal concentrations of oil on the marine environment have become of general concern. Cytochrome P4501A activity (EROD) in liver and fixed wavelength fluorescence detection of PAHs metabolites (FF) have in this study been used as biomarkers for dispersed oil exposure on a long term period of juvenile turbot (Scophthalmus maximus L.). A Continuous Flow System was used to carry out the study. The fish were continuously exposed to 0.125, 0.5 or 2.0 mg litre⁻¹ dispersed topped crude oil for 6, 15, 24 h, 4 and 21 days followed by a 9 days recovery period in clean seawater. No induction of the cytochrome P4501A was measured. A maximum level in bile metabolites (4- to 5-fold) was recorded after 24 h of exposure revealing thereby a detoxification process, but a decline occurred from day 4 to day 21. This study demonstrated that FF detection of PAHs metabolites in bile could be a more sensitive biomarker than EROD activity in a long term exposure to sublethal concentration of oil.  相似文献   

Evaluation of image analysis methods used for quantification of particle angularity     

Solomon Tafesse  Joanne M. Robison Fernlund  Wenjuan Sun  Fredrik Bergholm 《Sedimentology》2013,60(4):1100-1110

Angularity is an important parameter in the characterization of particle morphology that is used to interpret the transport history of particles in sedimentary deposits. In the past, visual classification using silhouette charts was widely used to determine particle angularity, but this approach is subjective and time‐consuming. With advances in modern image analysis techniques and low‐cost software packages, it is possible to rapidly quantify particle angularity more objectively than using visual classification methods. This study re‐examines the performance of three existing image analysis methods and one new image analysis procedure, applied to six rock and sediment samples that were visually different in angularity. To facilitate comparison between the angularity results, measurements were reduced to rankings for each aggregate sample. These results show that the four image analysis methods rank the angularity of the samples differently, and that none rank the mean angularity index in the same order as the angularity ranking using visual classification. Therefore, further research is needed to develop an image analysis method that can quantify the angularity of sedimentary particles more precisely.  相似文献   

A Holocene sea‐level curve and revised isobase map based on isolation basins from near the southern tip of Norway          下载免费PDF全文

Anders Romundset  Ola Fredin  Fredrik Høgaas 《Boreas: An International Journal of Quaternary Research》2015,44(2):383-400

We report a new Holocene relative sea‐level curve based on the stratigraphy in five closely located isolation basins near Lista in southernmost Norway. The results detail the progress and timing of the mid‐Holocene Tapes transgression, the peak of which in this region represents the highest postglacial sea level, as well as the rate of land emergence since then. One additional cored basin is situated above the marine limit. All the basins have bedrock sills that were levelled using a differential GPS. Isolation and ingression boundaries were identified by macrofossil analysis and radiocarbon dated on terrestrial plant remains. In most cases several dates were obtained from each transition. Relative sea level rose with a mean rate of 7 mm a^?1 during the last part of the Tapes transgression 8600?8200 cal. a BP and then gradually slowed to a mean rate of 1 mm a^?1 from 8200?7000 cal. a BP. Mean sea level reached ～5 m higher than the present level when the transgression culminated. Land emergence took place after this, first slowly at a mean rate of 0.4 mm a^?1 until ～3900 cal. a BP before it increased to 2.6 mm between 3900 and 3400 cal. a BP. Since then it has slowly decreased until today and has been ～0.2 mm a^?1 for the last 2000 years. Based on the new curve we present updated Tapes isobases for the region that are displaced by ～20 km in relation to the existing model. From one basin we also report a 5–10 cm thick layer of sorted, sandy gravel, embedded in a more than 5‐m‐thick deposit of homogeneous shallow‐marine mud. The gravel was deposited ～5500 cal. a BP, which is the same age as a tsunami deposit previously mapped in Shetland. As several typical characteristics of tsunami facies deposits are lacking, the origin of the gravel layer remains inconclusive.  相似文献   

A forest history for the last 10 900 years at the site Storasjö, southern Sweden: implications from beetle assemblages     

Fredrik Olsson  Geoffrey Lemdahl 《第四纪科学杂志》2010,25(8):1211-1221

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Macroscopic diffusivity in concrete determined by computational homogenization     

Filip Nilenius  Fredrik Larsson  Karin Lundgren  Kenneth Runesson 《国际地质力学数值与分析法杂志》2013,37(11):1535-1551

Effective moisture and chloride ion diffusivity coefficients for concrete are determined by computational homogenization, where concrete is modeled on the mesoscale as a heterogenous three‐phase composite material. By imposing moisture and chloride ion gradients on a representative volume element, effective macroscale properties are obtained through finite element analysis. A parametric study of the effects of the ballast content was carried out. The numerical results correspond well with an estimate of the Hashin–Shtrikman type available in the literature. The computational homogenization strategy proposed here also includes the interfacial transition zone, and its influence on the effective diffusivity coefficients is assessed. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献