bluuebunny/crossref_metadata_2025_split huggingface dataset:
A statistical study of magnetospheric ion composition along the geomagnetic field using the Cluster spacecraft forLvalues between 5.9 and 9.5
Authors: Sandhu J. K. , Yeoman T. K. , Fear R. C. , Dandouras I. 
Published: February 2016

AbstractUsing ion density data obtained by the CODIF (ion Composition and Distribution Function analyser) instrument on board the Cluster spacecraft, for the interval spanning 2001–2005, an empirical model describing the average ion mass distribution along closed geomagnetic field lines is determined. The empirical model describes the region spanning 5.9≤L< 9.5, with dependences onLshell and magnetic local time included, and represents ions in the energy range of 0.025 to 40 keV/charge. The data reduction process involves the identification and rejection of CODIF data contaminated by penetrating energetic radiation belt particles, found to frequently occur forL< 5.9. Furthermore, a comparison of data with observations of the cold plasma population in the region provides evidence that the CODIF data set is representative of the full plasma population. The variations in average ion mass along the field lines were modeled using a power law form, which maximizes toward the magnetic equatorial plane, with observed power law index values ranging between approximately −2.0 and 0.0. The resulting model illustrates some key features of the average ion mass spatial distribution, such as an average ion mass enhancement at lowLin the evening sector, indicating the transport of high‐latitude heavy ion outflows to the closed inner magnetosphere.
Data‐adaptive detection of transient deformation in geodetic networks
Authors: Walwer Damian , Calais Eric , Ghil Michael 
Published: February 2016

AbstractThe recent development of dense and continuously operating Global Navigation Satellite System (GNSS) networks worldwide has led to a significant increase in geodetic data sets that sometimes capture transient‐deformation signals. It is challenging, however, to extract such transients of geophysical origin from the background noise inherent to GNSS time series and, even more so, to separate them from other signals, such as seasonal redistributions of geophysical fluid mass loads. In addition, because of the very large number of continuously recording GNSS stations now available, it has become impossible to systematically inspect each time series and visually compare them at all neighboring sites. Here we show that Multichannel Singular Spectrum Analysis (M‐SSA), a method derived from the analysis of dynamical systems, can be used to extract transient deformations, seasonal oscillations, and background noise present in GNSS time series. M‐SSA is a multivariate, nonparametric, statistical method that simultaneously exploits the spatial and temporal correlations of geophysical fields. The method allows for the extraction of common modes of variability, such as trends with nonconstant slopes and oscillations shared across time series, without a priori hypotheses about their spatiotemporal structure or their noise characteristics. We illustrate this method using synthetic examples and show applications to actual GPS data from Alaska to detect seasonal signals and microdeformation at the Akutan active volcano. The geophysically coherent spatiotemporal patterns of uplift and subsidence thus detected are compared to the results of an idealized model of such processes in the presence of a magma chamber source.
Semi‐brittle flow of granitoid fault rocks in experiments
Authors: Pec Matej , Stünitz Holger , Heilbronner Renée , Drury Martyn 
Published: February 2016

AbstractField studies and seismic data show that semi‐brittle flow of fault rocks probably is the dominant deformation mechanism at the base of the seismogenic zone at the so‐called frictional‐viscous transition. To understand the physical and chemical processes accommodating semi‐brittle flow, we have performed an experimental study on synthetic granitoid fault rocks exploring a broad parameter space (temperature, T = 300, 400, 500, and 600°C, confining pressure, Pc ≈ 300, 500, 1000, and 1500 MPa, shear strain rate,
≈ 10−3, 10−4, 10−5, and 10−6 s−1, to finite shear strains, γ = 0–5). The experiments have been carried out using a granular material with grain size smaller than 200 µm with a little H2O added (0.2 wt %). Only two experiments (performed at the fastest strain rates and lowest temperatures) have failed abruptly right after reaching peak strength (τ ~ 1400 MPa). All other samples reach high shear stresses (τ ~ 570–1600 MPa) then weaken slightly (by Δτ ~ 10–190 MPa) and continue to deform at a more or less steady state stress level. Clear temperature dependence and a weak strain rate dependence of the peak as well as steady state stress levels are observed. In order to express this relationship, the strain rate‐stress sensitivity has been fit with a stress exponent, assuming γ̇ ∝ τn and yields high stress exponents (n ≈ 10–140), which decrease with increasing temperature. The microstructures show widespread comminution, strain partitioning, and localization into slip zones. The slip zones contain at first nanocrystalline and partly amorphous material. Later, during continued deformation, fully amorphous material develops in some of the slip zones. Despite the mechanical steady state conditions, the fabrics in the slip zones and outside continue to evolve and do not reach a steady state microstructure below γ = 5. Within the slip zones, the fault rock material progressively transforms from a crystalline solid to an amorphous material. We present and interpret the experimental results both in terms of sliding friction and viscous flow, and we discuss the possible effect that the formation of nanocrystalline and amorphous layers may have on earthquake nucleation.
Relating permeability and electrical resistivity in fractures using random resistor network models
Authors: Kirkby Alison , Heinson Graham , Krieger Lars 
Published: February 2016

AbstractWe use random resistor network models to explore the relationship between electrical resistivity and permeability in a fracture filled with an electrically conductive fluid. Fluid flow and current are controlled by both the distribution and the volume of pore space. Therefore, the aperture distribution of fractures must be accurately modeled in order to realistically represent their hydraulic and electrical properties. We have constructed fracture surface pairs based on characteristics measured on rock samples. We use these to construct resistor networks with variable hydraulic and electrical resistance in order to investigate the changes in both properties as a fault is opened. At small apertures, electrical conductivity and permeability increase moderately with aperture until the fault reaches its percolation threshold. Above this point, the permeability increases by 4 orders of magnitude over a change in mean aperture of less than 0.1 mm, while the resistivity decreases by up to a factor of 10 over this aperture change. Because permeability increases at a greater rate than matrix to fracture resistivity ratio, the percolation threshold can also be defined in terms of the matrix to fracture resistivity ratio, M. The value of M at the percolation threshold, MPT, varies with the ratio of rock to fluid resistivity, the fault spacing, and the fault offset. However, MPT is almost always less than 10. Greater M values are associated with fractures above their percolation threshold. Therefore, if such M values are observed over fluid‐filled fractures, it is likely that they are open for fluid flow.
Elastic softening in Fe7C3 with implications for Earth's deep carbon reservoirs
Authors: Liu Jiachao , Li Jie , Ikuta Daijo 
Published: February 2016

AbstractIron carbide Fe7C3 has recently emerged as a potential host of reduced carbon in Earth's mantle and a candidate component of the inner core, but the equation of state of Fe7C3 is still uncertain, partly because the nature of pressure‐induced magnetic transitions in Fe7C3 and their elastic effects remain controversial. Here we report the compression curve of hexagonal Fe7C3 in neon medium with dense pressure sampling and in comparison with pure iron in the same loading. The results revealed elastic softening between 7 GPa and 20 GPa, which can be attributed to noncollinear alignment of spin moments in a state between the ferromagnetic and paramagnetic phases, as expected for Invar‐type alloys. The volume reduction associated with the softening would enhance the stability of Fe7C3 in the deeper part of the upper mantle and transition zone. As a result of subsequent spin crossover at higher pressures, Fe7C3 at inner core conditions likely occurs as the nonmagnetic phase, which remains a candidate for the major component of the Earth's central sphere.
Dynamic friction in sheared fault gouge: Implications of acoustic vibration on triggering and slow slip
Authors: Lieou Charles K. C. , Elbanna Ahmed E. , Carlson Jean M. 
Published: February 2016

AbstractFriction and deformation in granular fault gouge are among various dynamic interactions associated with seismic phenomena that have important implications for slip mechanisms on earthquake faults. To this end, we propose a mechanistic model of granular fault gouge subject to acoustic vibrations and shear deformation. The grain‐scale dynamics is described by the Shear‐Transformation‐Zone theory of granular flow, which accounts for irreversible plastic deformation in terms of flow defects whose density is governed by an effective temperature. Our model accounts for stick‐slip instabilities observed at seismic slip rates. In addition, as the vibration intensity increases, we observe an increase in the temporal advancement of large slip events, followed by a plateau and gradual decrease. Furthermore, slip becomes progressively slower upon increasing the vibration intensity. The results shed important light on the physical mechanisms of earthquake triggering and slow slip and provide essential elements for the multiscale modeling of earthquake ruptures. In particular, the results suggest that slow slip may be triggered by tremors.
Enhanced soil moisture drying in transitional regions under a warming climate
Authors: Cheng Shanjun , Huang Jianping 
Published: February 2016

AbstractWe analyzed global trends of soil moisture for the period 1948–2010 using the Global Land Data Assimilation System data set. Soil moisture was dominated by negative trends, with pronounced drying over East Asia and the Sahel. Spatial analysis according to climatic region revealed that the most obvious drying occurred over transitional regions between dry and wet climates. The noticeable drying first took place in the humid transitional regions and extended to the dry transitional regions, beginning in the 1980s. The variability of soil moisture was notably related to the changes in precipitation and temperature, but with different roles. For the global average, precipitation had a dominant effect on the variability of soil moisture at interannual to decadal time scales, but temperature was the main cause of the long‐term trend of soil moisture on the whole. The enhanced soil drying in the transitional regions was primarily caused by global warming, which is illustrated by regression analysis and the land surface model.
Paleoseawater density reconstruction and its implication for cold‐water coral carbonate mounds in the northeast Atlantic through time
Authors: Rüggeberg Andres , Flögel Sascha , Dullo Wolf‐Christian , Raddatz Jacek , Liebetrau Volker 
Published: February 2016

AbstractCarbonate buildups and mounds are impressive biogenic structures throughout Earth history. In the recent NE Atlantic, cold‐water coral (CWC) reefs form giant carbonate mounds of up to 300 m of elevation. The expansion of these coral carbonate mounds is paced by climatic changes during the past 2.7 Myr. Environmental control on their development is directly linked to controls on its main constructors, the reef‐building CWCs. Seawater density has been identified as one of the main controlling parameter of CWC growth in the NE Atlantic. One possibility is the formation of a pycnocline above the carbonate mounds, which is increasing the hydrodynamic regime, supporting elevated food supply, and possibly facilitating the distribution of coral larvae. The potential to reconstruct past seawater densities from stable oxygen isotopes of benthic foraminifera has been further developed: a regional equation gives reliable results for three different settings,peak interglacials(e.g., Holocene),peak glacials(e.g., Last Glacial Maximum), andintermediatesetting (between the two extremes). Seawater densities are reconstructed for two different NE Atlantic CWC carbonate mounds in the Porcupine Seabight indicating that the development of carbonate mounds is predominantly found at a seawater density range between 27.3 and 27.7 kg m−3(σΘnotation). Comparable to recent conditions, we interpret the reconstructed density range as a pycnocline serving as boundary layer, on which currents develop, carrying nutrition and possibly coral larvae. The close correlation of CWC reef growth with reconstructed seawater densities through the Pleistocene highlights the importance of pycnoclines and intermediate water mass dynamics.
On the reconstruction of ocean circulation and climate based on the “Gardar Drift”
Authors: Langehaug H. R. , Mjell T. L. , Otterå O. H. , Eldevik T. , Ninnemann U. S. , Kleiven H. F. 
Published: February 2016

AbstractSediment‐based reconstructions of bottom water velocity at the Gardar Drift are commonly interpreted to reflect changes in the eastern Nordic Seas overflows. Here we investigate the relationship between changes in the water that overflows through the Faroe Shetland Channel and downstream bottom velocity at the location of the Gardar Drift as represented in a 500 year long simulation with the Bergen Climate Model. We identify a region in our simulation proximal to the geographical location of the northern Gardar Drift where 76% of the variance in bottom velocity can be explained by changes in the volume transport and density of the Faroe Shetland Channel overflow. By contrast, Labrador Sea Water changes do not appear to play a significant role in the bottom flow over the Gardar Drift. Our findings support the assumption in the paleo literature that reconstructions of bottom water velocity at the Gardar Drift reflect past changes in the eastern Nordic Seas overflows. However, our results suggest that velocity changes downstream are not a simple metric for the strength of the overflow, rather overflow density plays the largest role.
Lithospheric structure of Central Europe: Puzzle pieces from Pannonian Basin to Trans‐European Suture Zone resolved by geophysical‐petrological modeling
Authors: Alasonati Tašárová Zuzana , Fullea Javier , Bielik Miroslav , Środa Piotr 
Published: February 2016

AbstractWe have analyzed the thermochemical structure of the mantle in Central Europe, a complex area with a highly heterogeneous lithospheric structure reflecting the interplay of contraction, strike slip, subduction, and extension tectonics. Our modeling is based on an integrative 3‐D approach (LitMod) that combines in a self‐consistent manner concepts and data from thermodynamics, mineral physics, geochemistry, petrology, and solid Earth geophysics. This approach minimizes uncertainties of the estimates derived from modeling of various data sets separately. To further constrain our 3‐D model we have made use of the vast geophysical and geological data (2‐D and 3‐D, shallow/crustal versus deep lithospheric experiments) based on experiments performed in Central Europe in the past decades. Given the amount and the different nature/resolution of the available constraints, one of the most challenging tasks of this study was to consistently combine them, finding a trade‐off between all local and regional data sets available in a way that (i) preserves as many structural details as possible and (ii) summarizes those data sets into a single robust regional model. The resulting P/T‐dependent mantle densities are in LitMod 3‐D calculated based on a given mineralogical composition. They therefore provide more reliable estimates compared to pure gravity models, which enhance modeling of the crustal structures. Our results clearly indicate presence of several lithospheric domains characterized by distinct features, Pannonian Basin being one of the most outstanding ones. It has the thinnest crust and lithosphere in the area modeled, characterized by relatively fertile composition.
Dispersion and dissolution of a buoyancy driven gas plume in a layered permeable rock
Authors: Woods Andrew W. , Norris Simon 
Published: February 2016

AbstractUsing a series of simplified models, we explore the controls on the migration, dispersion and eventual dissolution of a plume of hydrogen gas which may, in principle, rise under buoyancy through a layered permeable rock if released from a Geological Disposal Facility (GDF). We show that the presence of low permeability shale barriers causes the gas to spread laterally as it rises. Averaging over the length scale of the barriers, we use expressions for the Darcy velocity of the gas to describe the dispersion of a tracer and illustrate the effect with a new experiment using a baffled Hele‐Shaw cell. While the plume is flowing, a large volume of gas may build up beneath the barriers. If the gas flux subsequently wanes, much of the gas will drain upward through the formation and spread on the upper impermeable boundary of the formation. However, a significant capillary‐trapped wake of gas may develop beneath each barrier. Owing to the low solubility of hydrogen in water and assuming relatively slow groundwater flow rates, this trapped hydrogen may require a period of tens to hundreds of thousands of years to dissolve and form a cloud of hydrogen rich water. Although simplified, these models provide a framework to assess the possible travel times and pathways of such a gas plume.
The implication of nonradiative energy fluxes dominating Greenland ice sheet exceptional ablation area surface melt in 2012
Authors: Fausto Robert S. , van As Dirk , Box Jason E. , Colgan William , Langen Peter L. , Mottram Ruth H. 
Published: February 2016

AbstractDuring two exceptionally large July 2012 multiday Greenland ice sheet melt episodes, nonradiative energy fluxes (sensible, latent, rain, and subsurface collectively) dominated the ablation area surface energy budget of the southern and western ice sheet. On average the nonradiative energy fluxes contributed up to 76% of daily melt energy at nine automatic weather station sites in Greenland. Comprising 6% of the ablation period, these powerful melt episodes resulted in 12–15% of the south and west Greenland automatic weather station annual ablation totals. Analysis of high resolution (~5 km) HIRHAM5 regional climate model output indicates widespread dominance of nonradiative energy fluxes across the western ablation area during these episodes. Yet HIRHAM5 still underestimates melt by up to 56% during these episodes due to a systematic underestimation of turbulent energy fluxes typical of regional climate models. This has implications for underestimating future melt, when exceptional melt episodes are expected to occur more frequently.
Response of northern winter polar cap to auroral substorms
Authors: Liou Kan , Sotirelis Thomas 
Published: February 2016

AbstractThe three‐phase substorm sequence has been generally accepted and is often tied to the Dungey cycle. Although previous studies have mostly agreed on the increase and decrease in the polar cap area during an episode of substorm, there are disparate views on when the polar cap starts to contract relative to substorm onset. Here we address this conflict using high‐resolution (~1–3 min) snapshot global auroral images from the ultraviolet imager on board the Polar spacecraft. On the basis of 28 auroral substorm events, all observed in the Northern Hemispheric winter, it is found that the polar cap inflated prior to onset in all events and it attained the largest area ~6 min prior to the substorm expansion phase onset, while the dayside polar cap area remained steady around the onset. The onset of nightside polar cap deflation is found to be attributed to intensifications of aurora on the poleward edge of the nightside oval, mostly in the midnight sector. Although this result supports the loading‐unloading and reconnection substorm models, it is not clear if the initial polar cap deflation and the substorm expansion are parts of the same process.
Fast and slow precipitation responses to individual climate forcers: A PDRMIP multimodel study
Authors: Samset B. H. , Myhre G. , Forster P. M. , Hodnebrog Ø. , Andrews T. , Faluvegi G. , Fläschner D. , Kasoar M. , Kharin V. , Kirkevåg A. , Lamarque J.‐F. , Olivié D. , Richardson T. , Shindell D. , Shine K. P. , Takemura T. , Voulgarakis A. 
Published: February 2016

AbstractPrecipitation is expected to respond differently to various drivers of anthropogenic climate change. We present the first results from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP), where nine global climate models have perturbed CO2, CH4, black carbon, sulfate, and solar insolation. We divide the resulting changes to global mean and regional precipitation into fast responses that scale with changes in atmospheric absorption and slow responses scaling with surface temperature change. While the overall features are broadly similar between models, we find significant regional intermodel variability, especially over land. Black carbon stands out as a component that may cause significant model diversity in predicted precipitation change. Processes linked to atmospheric absorption are less consistently modeled than those linked to top‐of‐atmosphere radiative forcing. We identify a number of land regions where the model ensemble consistently predicts that fast precipitation responses to climate perturbations dominate over the slow, temperature‐driven responses.
Green Catalytic Process for Click Synthesis Promoted by Copper Oxide Nanocomposite Supported on Graphene Oxide
Authors: Reddy V. Hanuman , Reddy Y. V. Rami , Sridhar B. , Reddy B. V. Subba 
Published: February 2016

AbstractThe catalytic activity of graphene oxide supported copper oxide (CuO–GO) has been investigated in Click synthesis of 1,2,3‐triazole derivatives under green reaction conditions. In the context of green approach, water is used as solvent under ligand free and aerobic conditions at room temperature, with low catalyst loading (0.2 mol %) while ensuring the recovery and reusability of the catalyst. The catalyst affords excellent selectivity in formation of the desired products in good to excellent yields. Further, the work‐up procedure adopted here is clean and simple, while recycling the organic solvents that one used for work‐up procedure. It is proposed that the functional groups present on the GO surface are effective for preventing the aggregation of the catalytically active copper oxide species during the reaction. Moreover, the excellent performance of CuO–GO nanocomposite is ascribed to the excellent dispersity of the catalyst in water, hydrophilic nature of the GO for the accumulation of organic substrates in water and the “Breslow effect.”magnified image