bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prompt enhancement of the Earth's outer radiation belt due to substorm electron injections
Authors: Tang C. L. , Zhang J.‐C. , Reeves G. D. , Su Z. P. , Baker D. N. , Spence H. E. , Funsten H. O. , Blake J. B. , Wygant J. R. 
Published: December 2016

AbstractWe present multipoint simultaneous observations of the near‐Earth magnetotail and outer radiation belt during the substorm electron injection event on 16 August 2013. Time History of Events and Macroscale Interactions during Substorms A in the near‐Earth magnetotail observed flux‐enhanced electrons of 300 keV during the magnetic field dipolarization. Geosynchronous orbit satellites also observed the intensive electron injections. Located in the outer radiation belt, RBSP‐A observed enhancements of MeV electrons accompanied by substorm dipolarization. The phase space density (PSD) of MeV electrons at L*~5.4 increased by 1 order of magnitude in 1 h, resulting in a local PSD peak of MeV electrons, which was caused by the direct effect of substorm injections. Enhanced MeV electrons in the heart of the outer radiation belt were also detected within 2 h, which may be associated with intensive substorm electron injections and subsequent local acceleration by chorus waves. Multipoint observations have shown that substorm electron injections not only can be the external source of MeV electrons at the outer edge of the outer radiation belt (L*~5.4) but also can provide the intensive seed populations in the outer radiation belt. These initial higher‐energy electrons from injection can reach relativistic energy much faster. The observations also provide evidence that enhanced substorm electron injections can explain rapid enhancements of MeV electrons in the outer radiation belt.
Cohesion versus friction in controlling the long‐term strength of a self‐healing experimental fault
Authors: Weiss J. , Pellissier V. , Marsan D. , Arnaud L. , Renard F. 
Published: December 2016

AbstractThe Coulomb's failure criterion, which postulates that failure occurs along a fault plane when the applied shear stress overcomes a resistance made of two parts of different nature, cohesion, and friction, remains the standard conceptual framework of faulting mechanics. More recently, rate‐and‐state friction laws became the main modeling tool of the seismic cycle. These laws implicitly assume that only frictional resistance sets the fault strength and its evolution. We therefore raise the question of the role of cohesion and related healing/sealing mechanisms on fault mechanics. We designed an original laboratory experiment based on a model material, an ice thin layer sitting on top of a water tank and mechanically deformed at various rates with a circular Couette‐like geometry. This allowed sliding along the fault plane over arbitrarily large slip distances, and analyzing the competition between faulting and cohesion‐healing rates, whereas frictional resistance, resulting from the fault roughness, is limited in magnitude. We show that cohesion‐healing plays an essential role in the time evolution of the interface strength under constant loading rate. In particular, the magnitudes of shear stress fluctuations are observed to be temperature and velocity weakening. The present experiment shares several properties similar to that of active faults during seismic cycles, suggesting that cohesive healing could control some of these features: scale invariance properties, Gutenberg‐Richter law of rupture event size distribution, Omori's law of energy dissipation, at least after major ruptures, time asymmetry in energy dissipation, and periods of creep under high shear stress alternating with major earthquake‐like ruptures.
3‐D velocity structure in southern Haiti from local earthquake tomography
Authors: Douilly Roby , Ellsworth William L. , Kissling Edi , Freed Andrew M. , Deschamps Anne , Mercier de Lépinay Bernard 
Published: December 2016

AbstractWe investigate 3‐D local earthquake tomography for high‐quality travel time arrivals from aftershocks following the 2010 M7.0 Haiti earthquake on the Léogâne fault. The data were recorded by 35 stations, including 19 ocean bottom seismometers, from which we selected 595 events to simultaneously invert for hypocenter location and 3‐D Vp and Vs velocity structures in southern Haiti. We performed several resolution tests and concluded that clear features can be recovered to a depth of 15 km. At 5 km depth we distinguish a broad low‐velocity zone in the Vp and Vs structure offshore near Gonave Island, which correlate with layers of marine sediments. Results show a pronounced low‐velocity zone in the upper 5 km across the city of Léogâne, which is consistent with the sedimentary basin location from geologic map. At 10 km depth, we detect a low‐velocity anomaly offshore near the Trois Baies fault and a NW‐SE directed low‐velocity zone onshore across Petit‐Goâve and Jacmel, which is consistent with a suspected fault from a previous study and that we refer to it in our study as the Petit‐Goâve‐Jacmel fault. These observations suggest that low‐velocity structures delineate fault structures and the sedimentary basins across the southern peninsula, which is extremely useful for seismic hazard assessment in Haiti.
Influence of gouge thickness and grain size on permeability of macrofractured basalt
Authors: Wang G. , Mitchell T. M. , Meredith P. G. , Nara Y. , Wu Z. 
Published: December 2016

AbstractFractures allow crystalline rocks to store and transport fluids, but fracture permeability can also be influenced significantly by the existence or absence of gouge and by stress history. To investigate these issues, we measured the water permeability of macrofractured basalt samples unfilled or infilled with gouge of different grain sizes and thicknesses as a function of hydrostatic stress and also under cyclic stress conditions. In all experiments, permeability decreased with increasing effective pressure, but unfilled fractures exhibited a much greater decrease than gouge‐filled fractures. Macrofractures filled with fine‐grained gouge had the lowest permeabilities and exhibited the smallest change with pressure. By contrast, the permeability changed significantly more in fractures filled with coarser‐grained gouge. During cyclic pressurization, permeability decreased with increasing cycle number until reaching a minimum value after a certain number of cycles. Permeability reduction in unfilled fractures is accommodated by both elastic and inelastic deformation of surface asperities, while measurements of the particle size distribution and compaction in gouge‐filled fractures indicate only inelastic compaction. In fine‐grained gouge this is accommodated by grain rearrangement, while in coarser‐grained gouge it is the result of both grain rearrangement and comminution. Overall, sample permeability is dominated by the gouge permeability, which decreases with increasing thickness and is also sensitive to the grain size and its distribution. Our results imply that there is a crossover depth in the crust below which the permeability of well‐mated fractures (e.g., joints) becomes lower than that of gouge‐filled fractures (e.g., shear faults).
Earthquake impact on iron isotope signatures recorded in mineral spring water
Authors: Schuessler Jan A. , Kämpf Horst , Koch Ulrich , Alawi Mashal 
Published: December 2016

AbstractWe investigated the iron isotope signatures of dissolved Fe in the water of the Wettinquelle mineral spring (Bad Brambach, Germany) by time series sampling covering seismically active periods related to tectonic activity near the Eger Rift system in central Europe. Our objective was to test whether Fe isotopes trace earthquake‐induced abiotic and biotic changes in the fluid/rock interaction of the deep, fissured, granitic aquifer. We found that the dissolved Fe isotope signatures in spring water are distinct from the granitic source signature (δ56Fe = +0.09‰). Particularly, we discovered that water δ56Fe values are remarkably stable (−0.01 ± 0.11‰, 2SD, n = 4) before and during a strong seismic swarm period in 2000 (local magnitudes ML > 3), while O2 and H2 concentrations in water decrease and dissolved Fe content increases. Later, recurring events of lower δ56Fe values down to −0.3‰ are observed in the period from 2001 to 2003 with intermittent seismic events (1 < ML < 3.2). The observations indicate a time lag between tectonic forcing and Fe isotope response. The role of abiotic fluid/rock interaction and Fe‐utilizing bacteria identified in the mineral spring water on Fe isotope fractionation is discussed. We explain recurring changes toward isotopically lighter values by a combination of Fe dissolution from deep granite and admixture of isotopically light Fe generated by a complex combination of abiotic and biotic processes operating in the aquifer when disturbed by swarm earthquakes events. We propose a conceptual model scenario of earthquake‐triggered changes in biogeochemical processes.
On the response of MODIS cloud coverage to global mean surface air temperature
Authors: Yue Qing , Kahn Brian H. , Fetzer Eric J. , Wong Sun , Frey Richard , Meyer Kerry G. 
Published: December 2016

AbstractThe global surface temperature change (ΔTs) mediated cloud cover response is directly related to cloud‐climate feedback. Using satellite remote sensing data to relate cloud and climate requires a well‐calibrated, stable, and consistent long‐term cloud data record. The Collection 5.1 (C5) Moderate Resolution Imaging Spectroradiometer (MODIS) cloud observations have been widely used for this purpose. However, the MODIS data quality varies greatly with the surface type, spectral region, cloud type, and time periods of study, which calls for additional caution when applying such data to studies on cloud cover temporal trends and variability. Using 15 years of cloud observations made by Terra and Aqua MODIS, we analyze the ΔTs‐mediated cloud cover response for different cloud types by linearly regressing the monthly anomaly of cloud cover (ΔC) with the monthly anomaly of global Ts. The Collection 6 (C6) Aqua data exhibit a similar cloud response to the long‐term counterpart simulated by advanced climate models. A robust increase in altitude with increasing ΔTs is found for high clouds, while a robust decrease of ΔC is noticed for optically thick low clouds. The large differences between C5 and C6 results are from improvements in calibration and cloud retrieval algorithms. The large positive cloud cover responses with data after 2010 and the strong sensitivity to time period obtained from the Terra (C5 and C6) data are likely due to calibration drift that has not been corrected, suggesting that the previous estimate of the short‐term cloud cover response from the these data should be revisited.
Tropospheric ozonesonde profiles at long‐term U.S. monitoring sites: 2. Links between Trinidad Head, CA, profile clusters and inland surface ozone measurements
Authors: Stauffer Ryan M. , Thompson Anne M. , Oltmans Samuel J. , Johnson Bryan J. 
Published: December 2016

AbstractMuch attention has been focused on the transport of ozone (O3) to the western U.S., particularly given the latest revision of the National Ambient Air Quality Standard to 70 parts per billion by volume (ppbv) of O3. This makes quantifying the contributions of stratosphere‐to‐troposphere exchange, local pollution, and pollution transport to this region essential. To evaluate free‐tropospheric and surface O3 in the western U.S., we use self‐organizing maps to cluster 18 years of ozonesonde profiles from Trinidad Head, CA. Three of nine O3 mixing ratio profile clusters exhibit thin laminae of high O3 above Trinidad Head. The high O3 layers are located between 1 and 6 km above mean sea level and reside above an inversion associated with a northern location of the Pacific subtropical high. Ancillary data (reanalyses, trajectories, and remotely sensed carbon monoxide) help identify the high O3 sources in one cluster, but distinguishing mixed influences on the elevated O3 in other clusters is difficult. Correlations between the elevated tropospheric O3 and surface O3 at high‐altitude monitors at Lassen Volcanic and Yosemite National Parks, and Truckee, CA, are marked and long lasting. The temporal correlations likely result from a combination of transport of baseline O3 and covarying meteorological parameters. Days corresponding to the high O3 clusters exhibit hourly surface O3 anomalies of +5–10 ppbv compared to a climatology; the positive anomalies can last up to 3 days after the ozonesonde profile. The profile and surface O3 links demonstrate the importance of regular ozonesonde profiling at Trinidad Head.
Deep convection in elliptical and polygonal eyewalls of tropical cyclones
Authors: Kuo Hung‐Chi , Cheng Wei‐Yi , Yang Yi‐Ting , Hendricks Eric A. , Peng Melinda S. 
Published: December 2016

AbstractIn observations, tropical cyclones with cyclonically rotating elliptical eyewalls are often characterized by wave number 2 (WN2) deep convection located at the edge of the major axis. A simple modeling framework is used to understand this phenomenon, where a nondivergent barotropic model (NBM) is employed to represent the elliptical vortex in the free atmosphere, and an asymmetric slab boundary layer (SBL) model is used to simulate the frictional boundary layer (BL) underneath the free atmosphere. The interaction is one way in that the overlying cyclonic flow drives the BL, but the BL pumping does not feed back to the overlying flow. The nonlinear‐balanced pressure field from the NBM drives the winds in the SBL model, which then causes BL convergence and pumping near the eyewall. The strong updrafts at the edge of the major axis for the elliptic vortex in the BL are induced by the larger convergent radial wind from the asymmetric distribution of the pressure fields of the free atmosphere with noncircular vortex. The large radial inflow maintains the supergradient wind at the edge of the elliptical vortex. The results emphasize the cyclonic rotation of the WN2 feature of strong updrafts at the top of the BL from the local shock‐like BL radial wind structure. Similar radial profiles and strong BL top updrafts occur at the edges of higher‐order polygonal eyewalls with the magnitude of the peak updraft decreasing as the wave number structure of the vortex increases.
Major fraction of black carbon is flushed from the melting New Hampshire snowpack nearly as quickly as soluble impurities
Authors: Lazarcik James , Dibb Jack E. , Adolph Alden C. , Amante Jacqueline M. , Wake Cameron P. , Scheuer Eric , Mineau Madeleine M. , Albert Mary R. 
Published: December 2016

AbstractSeasonal snowpacks accumulate impurities derived from atmospheric aerosols and trace gases throughout the winter and release them during snowmelt. Previous field and laboratory studies have shown that a snowpack can lose up to 80% of the soluble ion burden in the first 20% of the melt, an event commonly known as an ionic pulse. Other studies have concluded that particulate impurities (e.g., black carbon (BC)) concentrate in surface layers during melt which can have important implications for snowpack albedo. However, model and field studies have indicated that meltwater scavenging efficiency of BC in melting snowpacks is still an area of uncertainty. To quantify BC melt dynamics and the release of soluble impurities, we collected and analyzed near‐daily chemical profiles in the snowpack at three sites during two winters in New Hampshire, United States of America. We observe an ionic pulse and a pulse of BC from the snowpack at the onset of melt; up to 62% of BC leaves within the first 24% of the melt. Surface concentrations of BC are higher than seasonal medians at the end of the winter season, but surface enhancements do not appear to be closely linked to decreases in snow‐water equivalence caused by melting.
Land surface temperature over global deserts: Means, variability, and trends
Authors: Zhou Chunlüe , Wang Kaicun 
Published: December 2016

AbstractLand surface air temperature (LSAT) has been a widely used metric to study climate change. Weather observations of LSAT are the fundamental data for climate change studies and provide key evidence of global warming. However, there are very few meteorological observations over deserts due to their uninhabitable environment. This study fills this gap and provides independent evidence using satellite‐derived land surface temperatures (LSTs), benefiting from their global coverage. The frequency of clear sky from MODerate Resolution Imaging Spectroradiometer (MODIS) LST data over global deserts was found to be greater than 94% for the 2002–2015 period. Our results show that MODIS LST has a bias of 1.36°C compared to ground‐based observations collected at 31 U.S. Climate Reference Network (USCRN) stations, with a standard deviation of 1.83°C. After bias correction, MODIS LST was used to evaluate existing reanalyses, including ERA‐Interim, Japanese 55‐year Reanalysis (JRA‐55), Modern‐Era Retrospective Analysis for Research and Applications (MERRA), MERRA‐land, National Centers for Environmental Prediction (NCEP)‐R1, and NCEP‐R2. The reanalyses accurately reproduce the seasonal cycle and interannual variability of the LSTs, but their multiyear means and trends of LSTs exhibit large uncertainties. The multiyear averaged LST over global deserts is 23.5°C from MODIS and varies from 20.8°C to 24.5°C in different reanalyses. The MODIS LST over global deserts increased by 0.25°C/decade from 2002 to 2015, whereas the reanalyses estimated a trend varying from −0.14 to 0.10°C/decade. The underestimation of the LST trend by the reanalyses occurs for approximately 70% of the global deserts, likely due to the imperfect performance of the reanalyses in reproducing natural climate variability.
The substorm cycle as reproduced by global MHD models
Authors: Gordeev E. , Sergeev V. , Tsyganenko N. , Kuznetsova M. , Rastäetter L. , Raeder J. , Tóth G. , Lyon J. , Merkin V. , Wiltberger M. 
Published: December 2016

AbstractRecently, Gordeev et al. (2015) suggested a method to test global MHD models against statistical empirical data. They showed that four community‐available global MHD models supported by the Community Coordinated Modeling Center (CCMC) produce a reasonable agreement with reality for those key parameters (the magnetospheric size, magnetic field, and pressure) that are directly related to the large‐scale equilibria in the outer magnetosphere. Based on the same set of simulation runs, here we investigate how the models reproduce the global loading‐unloading cycle. We found that in terms of global magnetic flux transport, three examined CCMC models display systematically different response to idealized 2 h north then 2 h south interplanetary magnetic field (IMF) Bz variation. The LFM model shows a depressed return convection and high loading rate during the growth phase as well as enhanced return convection and high unloading rate during the expansion phase, with the amount of loaded/unloaded magnetotail flux and the growth phase duration being the closest to their observed empirical values during isolated substorms. Two other models exhibit drastically different behavior. In the BATS‐R‐US model the plasma sheet convection shows a smooth transition to the steady convection regime after the IMF southward turning. In the Open GGCM a weak plasma sheet convection has comparable intensities during both the growth phase and the following slow unloading phase. We also demonstrate potential technical problem in the publicly available simulations which is related to postprocessing interpolation and could affect the accuracy of magnetic field tracing and of other related procedures.
Low‐Frequency CH Stretch Vibrations of Free Alkoxide Ions
Authors: Oomens Jos , Berden Giel , Morton Thomas Hellman 
Published: December 2016

AbstractCH stretches in hydrocarbon cations often shift to lower frequencies relative to neutral molecules, because they do not have sufficient electrons to give every bond an electron pair. A parallel effect in negatively charged species has not been previously observed. Here we show that CH bond weakening occurs in alkoxide anions as a consequence of hyperconjugation. The reasoning differs somewhat from the case of positively charged ions, but the net effect is the same: to lower CH stretching frequencies by hundreds of wavenumbers.
Carboxylation of Terminal Alkynes with Carbon Dioxide Catalyzed by an In Situ Ag2O/N‐Heterocyclic Carbene Precursor System
Authors: Yuan Ye , Chen Cheng , Zeng Cheng , Mousavi Bibimaryam , Chaemchuen Somboon , Verpoort Francis 
Published: December 2016

AbstractA carboxylation of terminal alkynes with carbon dioxide (CO2) at ambient conditions was developed in situ using a series of N‐heterocyclic carbene (NHC) precursors and Ag2O. The unique structure of NHCs largely increases the solubility of active Ag species and meanwhile activates CO2 by forming the NHC–CO2 adduct. This novel catalytic system demonstrated quite low Ag loading, very high activities, wide substrate generality and excellent tolerance for a variety of functionalities. In addition, avoiding cumbersome synthesis procedures, processing, and reserving of the photosensitive Ag complex, this system could be stored and operated as straightforward as the inorganic Ag salt catalysts.
Explicit Water Molecules Play a Key Role in the Mechanism of Rhodium‐Substituted Human Carbonic Anhydrase
Authors: Piazzetta Paolo , Marino Tiziana , Russo Nino , Salahub Dennis R. 
Published: December 2016

AbstractThe efficient conversion of carbon dioxide into useful products is a prime challenge to modern chemistry. An alternative route to address this challenge based on a rhodium‐substituted human carbonic anhydrase is described that can be considered the first cofactor‐independent reductase. This artificial enzyme is able to convert CO2 into formic acid, with potential applications in renewable energy. Our quantum mechanical investigation (QM/QM′ method), which considers the entire catalytic pocket (390 atoms), provides evidence that the catalytic process is governed by an energetically favored σ‐bond‐metathesis mechanism and the rate‐limiting step is the release of formic acid (11.7 kcal mol−1). Water molecules are found to play an active role during the chemical process by contributing to reduce dramatically the energy of the rate‐limiting step and favoring an efficient regeneration of the catalyst.
Methods for the Trace Oxygen Removal from Methane‐Rich Gas Streams
Authors: Peppel Tim , Seeburg Dominik , Fulda Gerhard , Kraus Markus , Trommler Ulf , Roland Ulf , Wohlrab Sebastian 
Published: December 2016

AbstractOxygen removal to very low residual contents in methane‐rich gas streams and carbon dioxide as co‐component (simulated biogas) was achieved via three different methods at various temperatures, namely, by reduction with hydrogen admixtures on Pt/γ‐Al2O3catalysts, by oxygen absorption affinity of YBaCo4O7+δ, and by the catalytic reaction with methane on both the materials, respectively. The three methods have characteristic advantages and disadvantages which are discussed in the context of existing methods for gas treatments focused on oxygen removal. Finally, the advantage of dielectric radio‐frequency heating on the powdered functional materials is suggested as alternative to conventional routes.