排序方式： 共有135条查询结果，搜索用时 93 毫秒
21.
Romain Teyssier 《地球物理与天体物理流体动力学》2013,107(3-4):199-225
We propose to extend the well-known MUSCL-Hancock scheme for Euler equations to the induction equation modeling the magnetic field evolution in kinematic dynamo problems. The scheme is based on an integral form of the underlying conservation law which, in our formulation, results in a “finite-surface” scheme for the induction equation. This naturally leads to the well-known “constrained transport” method, with additional continuity requirement on the magnetic field representation. The second ingredient in the MUSCL scheme is the predictor step that ensures second order accuracy both in space and time. We explore specific constraints that the mathematical properties of the induction equations place on this predictor step, showing that three possible variants can be considered. We show that the most aggressive formulations reach the same level of accuracy than the other ones, at a lower computational cost. More interestingly, these schemes are compatible with the Adaptive Mesh Refinement (AMR) framework. It has been implemented in the AMR code RAMSES. It offers a novel and efficient implementation of a second order scheme for the induction equation. The scheme is then adaptated to solve for the full MHD equations using the same methodology. Through a series of test problems, we illustrate the performances of this new code using two different MHD Riemann solvers (Lax–Friedrich and Roe) and the need of the Adaptive Mesh Refinement capabilities in some cases. Finally, we show its versatility by applying it to the ABC dynamo problem and to the collapse of a magnetized cloud core. 相似文献
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A numerical investigation to illustrate the consequences of hydraulic connections between granular and fractured-rock aquifers 总被引：1，自引：1，他引：0
Natural or artificial hydraulic connections between a granular aquifer in contact with a fractured-rock aquifer can have significant physical and chemical impacts at both a local and a regional scale. In this study, numerical simulations are conducted in order to illustrate the hydrogeological consequences of such hydraulic relationships. The numerical investigation, based on a conceptual model, focuses on the effects of the hydraulic connections when conducting a pumping test in a well that is set into a granular confined aquifer overlying a fractured-rock aquifer which presents a few fractures directly connected to the granular aquifer. It is illustrated that when interpreting the pumping test with the conventional methods consisting of plotting the drawdown versus time, a bias is introduced on the estimation of the transmissivity of the granular aquifer due to groundwater flowing from the fractured-rock aquifer via connecting fractures. However, it is underlined that plotting drawdown log-derivative versus time helps to diagnose the existence of these hydraulic relationships and therefore avoids committing a bias on the transmissivity estimation of the granular aquifer. Numerical simulation results also illustrate that hydraulic connections between the two aquifers can have significant impacts on the hydrogeochemical signature of the granular aquifer under investigation. 相似文献
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Michael Wiederkehr Romain Bousquet Martin A. Ziemann Alfons Berger Stefan M. Schmid 《International Journal of Earth Sciences》2011,100(5):1029-1063
This study monitors regional changes in the crystallinity of carbonaceous matter (CM) by applying Micro-Raman spectroscopy
to a total of 214 metasediment samples (largely so-called Bündnerschiefer) dominantly metamorphosed under blueschist- to amphibolite-facies
conditions. They were collected within the northeastern margin of the Lepontine dome and easterly adjacent areas of the Swiss
Central Alps. Three-dimensional mapping of isotemperature contours in map and profile views shows that the isotemperature
contours associated with the Miocene Barrow-type Lepontine metamorphic event cut across refolded nappe contacts, both along
and across strike within the northeastern margin of the Lepontine dome and adjacent areas. Further to the northeast, the isotemperature
contours reflect temperatures reached during the Late Eocene subduction-related blueschist-facies event and/or during subsequent
near-isothermal decompression; these contours appear folded by younger, large-scale post-nappe-stacking folds. A substantial
jump in the recorded maximum temperatures across the tectonic contact between the frontal Adula nappe complex and surrounding
metasediments indicates that this contact accommodated differential tectonic movement of the Adula nappe with respect to the
enveloping Bündnerschiefer after maximum temperatures were reached within the northern Adula nappe, i.e. after Late Eocene
time. 相似文献
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Yann Rolland Romain Darnault Régis Braucher Didier Bourlès Carole Petit Stéphane Bouissou ASTER Team 《地球表面变化过程与地形》2020,45(2):393-410
Estimating the extent and age of the last glacial maxima as well as the chronology of glacial recessions in various environmental contexts is key to source-to-sink studies and paleoclimate reconstructions. The Argentera-Mercantour massif is located at the transition between the Alps and the Mediterranean Sea, therefore, its deglaciation chronology can be compared to the sediment budget of the Var River basin. Based on 13 new cosmic-ray exposure (CRE) beryllium-10 (10Be) datings performed on moraines and polished crystalline bedrocks and 22 reassessed 10Be CRE ages from similar altitude nearby steep basement surfaces, and from a lake sediment core, we can constrain the deglaciation chronology of the Argentera-Mercantour massif. These data allow for the first time to fully reconstruct the deglaciation history at the scale of the entire massif in agreement with a major glacier recession at c. 15 ka, at the onset of Bølling transition between the Oldest and Older Dryas. Main deglaciation of the upper slopes [2700–2800 m above sea level (a.s.l.)] occurred after the Last Glacial Maximum (LGM) at 20.8–18.6 ka, followed by the main deglaciation of the lower slopes (2300 m a.s.l.) at 15.3–14.2 ka. Finally, the flat polished surfaces above 2600 m a.s.l. and the zones confined within narrow lateral valleys were likely affected by progressive ice melting of remaining debris covered glaciers and moraine erosion following the Younger Dryas re-advance stage between 12 and 8–9 ka. At lower elevations, the Vens Lake located at 2300 m a.s.l., allows evidence of the onset of lake sedimentation at c. 14 ka and a transition towards a vegetated environment that mainly occurred before 8 ka. Moraine final stabilization at 5 ka might reflect denudation acceleration during the Holocene humid phase. This contribution reveals a glacier–climate relationship more sensitive to warming phases in the southern Alps highlighted by a major decrease of glaciers after c. 15 ka. This major deglaciation is correlated with a 2.5-fold decrease of sediment discharge of rivers into the Mediterranean Sea. © 2019 John Wiley & Sons, Ltd. 相似文献
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Assessment of groundwater recharge processes through karst vadose zone by cave percolation monitoring 
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下载免费PDF全文 Amaël Poulain Arnaud Watlet Olivier Kaufmann Michel Van Camp Hervé Jourde Naomi Mazzilli Gaëtan Rochez Romain Deleu Yves Quinif Vincent Hallet 《水文研究》2018,32(13):2069-2083
Recharge processes of karst aquifers are difficult to assess given their strong heterogeneity and the poorly known effect of vadose zone on infiltration. However, recharge assessment is crucial for the evaluation of groundwater resources. Moreover, the vulnerability of karst aquifers depends on vadose zone behaviour because it is the place where most contamination takes place. In this work, an in situ experimental approach was performed to identify and quantify flow and storage processes occurring in karst vadose zone. Cave percolation monitoring and dye tracing were used to investigate unsaturated zone hydrological processes. Two flow components (diffuse and quick) were identified and, respectively, account for 66% and 34% of the recharge. Quickflow was found to be the result of bypass phenomenon in vadose zone related to water saturation. We identify the role of epikarst as a shunting area, most of the storage in the vadose zone occurring via the diffuse flow component in low permeability zones. Relationship between rainfall intensity and transit velocity was demonstrated, with 5 times higher velocities for the quick recharge mode than the diffuse mode. Modelling approach with KarstMod software allowed to simulate the hybrid recharge through vadose zone and shows promising chances to properly assess the recharge processes in karst aquifer based on simple physical models. 相似文献
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This article provides an ex post analysis of the compliance of the Parties to the Kyoto Protocol during the first commitment period (2008–2012) based on the final data for national GHG emissions and exchanges in carbon units that became available at the end of 2015. On the domestic level, among the 36 countries that fully participated in the Kyoto Protocol, only nine countries emitted higher levels of GHGs than committed and therefore had to resort to flexibility mechanisms. On the international level – i.e. after the use of flexibility mechanisms – all Annex B Parties are in compliance. Countries implemented different compliance strategies: purchasing carbon units abroad, stimulating the domestic use of carbon credits by the private sector and incentivizing domestic emission reductions through climate policies.
Overall, the countries party to the Protocol surpassed their aggregate commitment by an average 2.4 GtCO2e yr–1. Of the possible explanations for this overachievement, ‘hot-air’ was estimated at 2.2 GtCO2e yr–1, while accounting rules for land use, land-use change and forestry (LULUCF) further removed 0.4 GtCO2e yr–1 from the net result excluding LULUCF. The hypothetical participation of the US and Canada would have reduced this overachievement by a net 1 GtCO2e yr–1. None of these factors – some of which may be deemed illegitimate – would therefore on its own have led to global non-compliance, even without use of the 0.3 GtCO2e of annual emissions reductions generated by the Clean Development Mechanism. The impact of domestic policies and ‘carbon leakage’ – neither of which is quantitatively assessed here – should not be neglected either.
Policy relevance
Given the ongoing evolution of the international climate regime and the adoption of the Paris Agreement in December 2015, we believe that there is a need to evaluate the results of the first commitment period of the Kyoto Protocol. To our knowledge there has been no overarching quantitative ex post assessment of the Kyoto Protocol based on the final emissions data for 2008–2012, which became available in late 2015. This article attempts to fill this gap, focusing on the domestic and international compliance of the Parties to the Kyoto Protocol in the first commitment period. 相似文献
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Relay zone evolution: a history of repeated fault propagation and linkage,central Corinth rift,Greece 下载免费PDF全文
下载免费PDF全文 Established models indicate that, before being breached, relay zones along rift borders can evolve either by lengthening and rotating during progressive overlap of growing fault segments (isolated fault model), or, by simply rotating without lengthening before breaching (coherent fault model). The spatio‐temporal distribution of vertical motions in a relay zone can thus be used to distinguish fault growth mechanisms. Depositional relay zones that develop at sea level and accommodate both deposition on the ramp itself as well as transfer of sediments from the uplifting footwall into the hangingwall depocentres and provide the most complete record of vertical motions. We examine the development of a depositional relay ramp on the border of the active Corinth rift, Greece to reconstruct fault interaction in time and space using both onshore and offshore (2D seismic lines) data. The Akrata relay zone developed over a period of ca. 0.5 Myr since the Middle Pleistocene between the newly forming East Helike Fault (EHF) that propagated towards the older, more established Derveni Fault (DF). The relay zone captured the Krathis River, which deposited prograding Gilbert‐type deltas on the sub‐horizontal ramp. Successive oblique faults record progressive linkage and basinward migration of accommodation along the ramp axis, whereas marine terraces record diachronous uplift in their footwalls. Although early linkage of the relay zone occurs, continuous propagation and linkage of the EHF onto the static DF is recorded before final beaching. Rotation on forced folds above the upward and laterally propagating normal faults at the borders of the relay zone represents the ramp hinges. The Akrata relay zone cannot be compared directly to a simple fault growth model because (1) the relay zone connects two fault segments of different generations; (2) multiple linkages during propagation was facilitated by the presence of pre‐existing crustal structures, inherited from the Hellenide fold and thrust belt. The linkage of the EHF to the DF contributed to the westward and northward propagation of the southern rift border. 相似文献
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Hydrogeology Journal - Adequate groundwater management requires models capable of representing the heterogeneous nature of aquifers. A key point is the theoretical knowledge of flow behaviour in... 相似文献
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