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111.
Ola M. Johannessen Alexander Korablev Victoria Miles Martin W. Miles Knut E. Solberg 《Surveys in Geophysics》2011,32(4-5):387-396
Recent observations of ocean temperature in several Greenland fjords suggest that ocean warming can cause large changes in the outlet glaciers in these fjords. We have observed the Helheim outlet-glacier front in the Sermilik Fjord over the last three decades using satellite images, and the vertical fjord temperature and salinity during three summer expeditions, 2008?C2010. We show that the subsurface water below 250 m depth is the warm saline Atlantic Water from the Irminger Sea penetrating into the fjord and exposing the lower part of the Helheim glacier to warm water up to 4°C. Lagged correlation analysis spanning the 30-year time series, using the subsurface Atlantic Water temperature off the coast as a proxy for the variability of the subsurface warm Atlantic Water in the fjord, indicates that 24% of the Helheim ice-front movement can be accounted for by ocean temperature. A strong correlation (?C0.75) between the ice-front position and the surface air temperature from a nearby meteorological station suggests that the higher air temperature causes melting and subsequent downward percolation of meltwater through crevasses leading to basal lubrication; the correlation accounts for 56% of the ice-front movement. The precise contribution of air temperature versus ocean temperature however, remains an open question, as more oceanographic and meteorological measurements are needed close to the glacier terminus. 相似文献
112.
Knut–Andreas Lie Stein Krogstad Ingeborg Skjelkv?le Ligaarden Jostein Roald Natvig Halvor M?ll Nilsen B?rd Skaflestad 《Computational Geosciences》2012,16(2):297-322
Accurate geological modelling of features such as faults, fractures or erosion requires grids that are flexible with respect
to geometry. Such grids generally contain polyhedral cells and complex grid-cell connectivities. The grid representation for
polyhedral grids in turn affects the efficient implementation of numerical methods for subsurface flow simulations. It is
well known that conventional two-point flux-approximation methods are only consistent for K-orthogonal grids and will, therefore, not converge in the general case. In recent years, there has been significant research
into consistent and convergent methods, including mixed, multipoint and mimetic discretisation methods. Likewise, the so-called
multiscale methods based upon hierarchically coarsened grids have received a lot of attention. The paper does not propose
novel mathematical methods but instead presents an open-source Matlab? toolkit that can be used as an efficient test platform for (new) discretisation and solution methods in reservoir simulation.
The aim of the toolkit is to support reproducible research and simplify the development, verification and validation and testing
and comparison of new discretisation and solution methods on general unstructured grids, including in particular corner point
and 2.5D PEBI grids. The toolkit consists of a set of data structures and routines for creating, manipulating and visualising
petrophysical data, fluid models and (unstructured) grids, including support for industry standard input formats, as well
as routines for computing single and multiphase (incompressible) flow. We review key features of the toolkit and discuss a
generic mimetic formulation that includes many known discretisation methods, including both the standard two-point method
as well as consistent and convergent multipoint and mimetic methods. Apart from the core routines and data structures, the
toolkit contains add-on modules that implement more advanced solvers and functionality. Herein, we show examples of multiscale
methods and adjoint methods for use in optimisation of rates and placement of wells. 相似文献
113.
ABSTRACTEvaluation of a recession-based “top-down” model for distributed hourly runoff simulation in macroscale mountainous catchments is rare in the literature. We evaluated such a model for a 3090 km2 boreal catchment and its internal sub-catchments. The main research question is how the model performs when parameters are either estimated from streamflow recession or obtained by calibration. The model reproduced observed streamflow hydrographs (Nash-Sutcliffe efficiency up to 0.83) and flow duration curves. Transferability of parameters to the sub-catchments validates the performance of the model, and indicates an opportunity for prediction in ungauged sites. However, the cases of parameter estimation and calibration excluding the effects of runoff routing underestimate peak flows. The lower end of the recession and the minimum length of recession segments included are the main sources of uncertainty for parameter estimation. Despite the small number of calibrated parameters, the model is susceptible to parameter uncertainty and identifiability problems.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR A. Carsteanu 相似文献
114.
冰水介质间的热传递过程广泛存在于海冰与冰川的生消演化中。对冰水间传热过程的研究有助于理解冰脊固结与冰川融化过程的内在机理。分别采用浸没试验与基于有限差分法的数值模型对热传递过程进行研究,并通过量纲分析对测试结果进行深入讨论。试验过程中分别采用不同初始温度与初始厚度的试样,并测试冰温与冰厚的变化情况。试验数据显示,在瞬态热传导过程中冰内存在明显的温度梯度,且在试验初期呈非线性分布而在中后期呈准线性分布。试样的平均温度表现出试验初期的快速升高与中后期的缓慢提升两个阶段。当试样具有较低初始温度或较高的厚度时需要更长的时间达到环境温度。冰厚的变化也同样出现快速增长与缓慢提升的两个阶段。当试样初始冰温较低或初始厚度较大时,冰厚增长量显著提高。分析结果表明,影响冰温变化的决定因素是由Fourier所表示的导热与内能之间的比值而非初始条件。冰厚的最终增长率则由表示相变的Stefan数与表示热对流的Biot数两者之间差值所决定。 相似文献
115.
Food security for a growing world population is high on the list of grand sustainability challenges, as is reducing the pace of biodiversity loss in landscapes of food production. Here we shed new insights on areas that harbor place specific social memories related to food security and stewardship of biodiversity. We call them bio-cultural refugia. Our goals are to illuminate how bio-cultural refugia store, revive and transmit memory of agricultural biodiversity and ecosystem services, and how such social memories are carried forward between people and across cohorts. We discuss the functions of such refugia for addressing the twin goals of food security and biodiversity conservation in landscapes of food production. The methodological approach is first of its kind in combining the discourses on food security, social memory and biodiversity management. We find that the rich biodiversity of many regionally distinct cultural landscapes has been maintained through a mosaic of management practices that have co-evolved in relation to local environmental fluctuations, and that such practices are carried forward by both biophysical and social features in bio-cultural refugia including; genotypes, artifacts, written accounts, as well as embodied rituals, art, oral traditions and self-organized systems of rules. Combined these structure a diverse portfolio of practices that result in genetic reservoirs—source areas—for the wide array of species, which in interplay produce vital ecosystem services, needed for future food security related to environmental uncertainties, volatile financial markets and large scale conflicts. In Europe, processes related to the large-scale industrialization of agriculture threaten such bio-cultural refugia. The paper highlights that the dual goals to reduce pressures from modern agriculture on biodiversity, while maintaining food security, entails more extensive collaboration with farmers oriented toward ecologically sound practices. 相似文献
116.
Evidence of shelf-water transfer from temperature, salinity, and 228Ra/226Ra sampling from the nuclear submarine USS L. Mendel Rivers SCICEX cruise in October, 2000 demonstrates the heterogeneity of the Arctic Ocean with respect to halocline ventilation. This likely reflects both time-dependent events on the shelves and the variety of dispersal mechanisms within the ocean, including boundary currents and eddies, at least one of which was sampled in this work. Halocline waters at the 132 m sampling depth in the interior Eurasian Basin are generally not well connected to the shelves, consonant with their ventilation within the deep basins, rather than on the shelves. In the western Arctic, steep gradients in 228Ra/226Ra ratio and age since shelf contact are consistent with very slow exchange between the Chukchi shelf and the interior Beaufort Gyre. These are the first radium measurements from a nuclear submarine. 相似文献
117.
Sonia Leonard Meg Parsons Knut Olawsky Frances Kofod 《Global Environmental Change》2013,23(3):623-632
Indigenous peoples offer alternative knowledge about climate variability and change based on their own locally developed knowledges and practices of resource use. In this article we discuss the role of traditional ecological knowledge in monitoring and adapting to changing environmental conditions. Our case study documents a project to record the seasonal knowledge of the Miriwoong people in northern Australia. The study demonstrates how indigenous groups’ accumulate detailed baseline information about their environment to guide their resource use and management, and develop worldviews and cultural values associated with this knowledge. We highlight how traditional ecological knowledge plays a critical role in mediating indigenous individuals and communities’ understandings of environmental changes in the East Kimberley region of north-west Australia, and how these beliefs may influence future decision-making about how to go about adapting to climate change at a local level. 相似文献
118.
This study documents the temporal and spatial variability of surface wind conditions over the Norwegian county of Finnmark and the coupling of local surface winds to the larger-scale atmospheric circulation, represented by the mean sea level pressure field. At locations along the northern coast, thermally driven offshore winds from the south dominate, especially during the cold season. During the warm season, downward mixing of westerly overlying winds becomes more important as the stability of the boundary layer stratification decreases. In the western part, locations are situated in valleys, resulting in two opposing along-channel dominant wind directions. Seasonal changes in atmospheric conditions are reflected in a reversal of the dominant wind direction, with a component towards the coast during the cold season. At all locations, a clear separation between different prevailing surface wind directions in each season can be achieved based exclusively on local mean sea level geostrophic wind direction. This allows statistical downscaling of the prevailing surface wind conditions from lower-resolution simulations of the surface pressure field and may improve local wind forecasts over complex terrain. 相似文献
119.
Knut METZLER Addi BISCHOFF Richard C. GREENWOOD Herbert PALME Marko GELLISSEN Jens HOPP Ian A. FRANCHI Mario TRIELOFF 《Meteoritics & planetary science》2011,46(5):652-680
Abstract– Northwest Africa (NWA) 869 consists of thousands of individual stones with an estimated total weight of about 7 metric tons. It is an L3–6 chondrite and probably represents the largest sample of the rare regolith breccias from the L–chondrite asteroid. It contains unequilibrated and equilibrated chondrite clasts, some of which display shock‐darkening. Impact melt rocks (IMRs), both clast‐free and clast‐poor, are strongly depleted in Fe,Ni metal, and sulfides. An unequilibrated microbreccia, two different light inclusions and two different SiO2‐bearing objects were found. Although the matrix of this breccia appears partly clastic, it is not a simple mixture of fine‐grained debris formed from the above lithologies, but mainly represents an additional specific lithology of low petrologic type. We speculate that this material stems from a region of the parent body that was only weakly consolidated. One IMR clast and one SiO2‐bearing object show Δ17O values similar to bulk NWA 869, suggesting that both are related to the host rock. In contrast, one light inclusion and one IMR clast appear to be unrelated to NWA 869, suggesting that the IMR clast is contaminated with impactor material. 40Ar‐39Ar analyses of a type 4 chondrite clast yield a plateau age of 4402 ± 7 Ma, which is interpreted to be the result of impact heating. Other impact events are recorded by an IMR clast at 1790 ± 36 Ma and a shock‐darkened clast at 2216 ± 40 Ma, demonstrating that NWA 869 escaped major reset in the course of the event at approximately 470 Ma that affected many L–chondrites. 相似文献
120.
Julia ROSZJAR Knut METZLER Addi BISCHOFF Jean‐Alix BARRAT Thorsten GEISLER Richard C. GREENWOOD Ian A. FRANCHI Stephan KLEMME 《Meteoritics & planetary science》2011,46(11):1754-1773
Abstract– We report on the bulk chemical composition, petrology, oxygen isotopic composition, trace element composition of silicates, and degree of self‐irradiation damage on zircon grains of the eucrite Northwest Africa (NWA) 5073 to constrain its formation and postcrystallization thermal history, and to discuss their implications for the geologic history of its parent body. This unequilibrated and unbrecciated meteorite is a new member of the rare Stannern‐trend eucrites. It is mainly composed of elongated, zoned pyroxene phenocrysts up to 1.2 cm, plagioclase laths up to 0.3 cm in length, and is rich in mesostasis. The latter contains zircon grains up to 30 μm in diameter, metal, sulfide, tridymite, and Ca‐phosphates. Textural observations and silicate compositions, coupled with the occurrence of extraordinary Fe‐rich olivine veins that are restricted to large pyroxene laths, indicate that NWA 5073 underwent a complex thermal history. This is also supported by the annealed state of zircon grains inferred from μ‐Raman spectroscopic measurements along with U and Th data obtained by electron probe microanalyses. 相似文献