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  • Articles  (50,489)
  • Wiley  (50,489)
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  • Articles  (50,489)
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  • 101
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    Understanding Instrumental Stokes Leakage in Murchison Widefield Array Polarimetry (2014)
    Wiley
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    Publication Date: 2014-12-14
    Description: This paper offers an electromagnetic, more specifically array theory, perspective on understanding strong instrumental polarization effects for planar low-frequency “aperture arrays” with the Murchison Widefield Array (MWA) as an example. A long-standing issue that has been seen here is significant instrumental Stokes leakage after calibration, particularly in Stokes Q at high frequencies. A simple model that accounts for inter-element mutual coupling is presented which explains the prominence of Q leakage seen when the array is scanned away from zenith in the principal planes. On these planes, the model predicts current imbalance in the X (E-W) and Y (N-S) dipoles and hence the Q leakage. Although helpful in concept, we find that this model is inadequate to explain the full details of the observation data. This finding motivates further experimentation with more rigorous models that account for both mutual coupling and embedded element patterns. Two more rigorous models are discussed: the “full” and “average” embedded element patterns. The viability of the “full” model is demonstrated by simulating current MWA practice of using a Hertzian dipole model as a Jones matrix estimate. We find that these results replicate the observed Qleakage to approximately 2 to 5%. Finally, we offer more direct indication for the level of improvement expected from upgrading the Jones matrix estimate with more rigorous models. Using the “average” embedded pattern as an estimate for the “full” model, we find that Q leakage of a few percent is achievable.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 102
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    Bayesian inversion of time-lapse seismic data for the estimation of static reservoir properties and dynamic property changes (2014)
    Wiley
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    Publication Date: 2014-12-16
    Description: ABSTRACT Seismic conditioning of static reservoir model properties such as porosity and lithology has traditionally been faced as a solution of an inverse problem. Dynamic reservoir model properties have been constrained by time-lapse seismic data. Here, we propose a methodology to jointly estimate rock properties (such as porosity) and dynamic property changes (such as pressure and saturation changes) from time-lapse seismic data. The methodology is based on a full Bayesian approach to seismic inversion and can be divided into two steps. First we estimate the conditional probability of elastic properties and their relative changes; then we estimate the posterior probability of rock properties and dynamic property changes. We apply the proposed methodology to a synthetic reservoir study where we have created a synthetic seismic survey for a real dynamic reservoir model including pre-production and production scenarios. The final result is a set of point-wise probability distributions that allow us to predict the most probable reservoir models at each time step and to evaluate the associated uncertainty. Finally we also show an application to real field data from the Norwegian Sea, where we estimate changes in gas saturation and pressure from time-lapse seismic amplitude differences. The inverted results show the hydrocarbon displacement at the times of two repeated seismic surveys.
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
    Topics: Geosciences , Physics
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  • 103
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    Revision of the EPICA Dome C CO2 record from 800 to 600 kyr before present (2014)
    Wiley
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    Publication Date: 2014-12-16
    Description: The EPICA Dome C (EDC) ice core has allowed for the reconstruction of atmospheric CO 2 concentrations for the last 800,000 years. Here, we revisit the oldest part of the EDC CO 2 record using different air extraction methods and sections of the core. For our established cracker system, we found an analytical artifact, which increases over the deepest 200 m and reaches 10.1 ± 2.4 ppm in the oldest/deepest part. The governing mechanism is not yet fully understood, but it is related to insufficient gas extraction in combination with ice relaxation during storage and ice structure. The corrected record presented here resolves partly the issue with a different correlation between CO 2 and Antarctic temperatures found in this oldest part of the records, however, this anomaly still persists. In addition we provide here an update of 800,000 years atmospheric CO 2 history including recent studies covering the last glacial cycle.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 104
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    A cautionary note on the use of EESC-based regression analysis for ozone trend studies (2014)
    Wiley
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    Publication Date: 2014-12-16
    Description: Equivalent effective stratospheric chlorine (EESC) construct of ozone regression models attributes ozone changes to EESC changes using a single value of the sensitivity of ozone to EESC over the whole period. Using space-based total column ozone (TCO) measurements, and a synthetic TCO time series constructed such that EESC does not fall below its late 1990s maximum, we demonstrate that the EESC-based estimates of ozone changes in the polar regions (70–90°) after 2000 may, falsely, suggest an EESC-driven increase in ozone over this period. An EESC-based regression of our synthetic “failed Montreal Protocol with constant EESC" time series suggests a positive TCO trend that is statistically significantly different from zero over 2001–2012 when in fact no recovery has taken place. Our analysis demonstrates that caution needs to be exercised when using explanatory variables, with a single fit coefficient, fitted to the entire data record, to interpret changes in only part of the record.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 105
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    Issue Information (2014)
    Wiley
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    Publication Date: 2014-12-16
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 106
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    Field-aligned Currents' Scale Analysis Performed with the Swarm Constellation (2014)
    Wiley
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    Publication Date: 2014-12-16
    Description: We present a statistical study of the temporal and spatial scale characteristics of different field-aligned current (FAC) types derived with the Swarm satellite formation. We divide FACs into two classes: small-scale, up to some ten kilometer, which arecarried predominantly by kinetic Alfvén waves, and large-scale FACs with sizes of more than 150 km. For determining temporal variability we consider measurements at the same point, the orbital crossovers near the poles, but at different times. Fromcorrelation analysis we obtain a persistent period of small-scale FACs of order 10 s, while large-scale FACs can be regarded stationary for more than 60 s. For the first time we investigate the longitudinal scales. Large-scale FACs are different on dayside and nightside. On the nightside the longitudinal extension is on average 4 times the latitudinal width, while on the dayside, in particular in the cusp region, latitudinal and longitudinal scales are comparable.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 107
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    Predicting the long-term fate of buried organic carbon in colluvial soils (2014)
    Wiley
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    Publication Date: 2014-12-16
    Description: A significant part of the soil organic carbon that is eroded in uplands is deposited and buried in colluvial settings. Understanding the fate of this deposited soil organic carbon (SOC) is of key importance for the understanding of the role of (accelerated) erosion in the global C cycle: the residence time of the deposited carbon will determine if, and for how long, accelerated erosion due to human disturbance will induce sequestration of SOC from the atmosphere to the soil. Experimental studies may provide useful information, but, given the time scale under consideration, the response of the colluvial SOC can only be simulated using numerical models which need careful calibration using field data. In this study, we present a depth explicit SOC model (ICBM-DE) including soil profile evolution due to sedimentation to simulate the long-term C dynamics in colluvial soils. The SOC profile predicted by our model is in good agreement with field observations. The C burial efficiency (the ratio of current C content of the buried sediments to the original C content at the time of sedimentation) of deposited sediments exponentially decreases with time and gradually reached an equilibrium value. This equilibrium C burial efficiency is positively correlated with the sedimentation rate. The sedimentation rate is crucial for the long-term dynamics of the deposited SOC as it controls the time that buried sediments spend at a given soil depth, thereby determining its temporal evolution of C input and decomposition rate during the burial process: C input and decomposition rate vary with depth due to the vertical variation of root distribution and soil environmental factors such as (but not limited to) humidity, temperature and aeration. The model demonstrates that, for the profiles studied, it takes ca. 300 yr for the buried SOC to lose half of its C load. It would also take centuries for the SOC accumulated in colluvial soils over the past decades due to soil redistribution under mechanized agriculture to be released to the atmosphere after the application of soil conservation measures such as conservation tillage.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 108
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    Coherent Time Reversal Microwave Imaging for the Detection and Localization of Breast Tissue Malignancies (2014)
    Wiley
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    Publication Date: 2014-12-16
    Description: This paper deals with coherent processing of time reversal operator for microwave imaging in the frequency-domain. In frequency-domain time-reversal imaging approach, images obtained for different frequency bins over ultrawideband are incoherently processed. In highly dense and cluttered medium the signal subspace over each narrow frequency bin varies from that obtained using the complete ultrawideband. As a result, the detection and localization from non-coherent imaging approach is often inconclusive. In order to improve the stability of time-reversal microwave imaging, we propose coherent processing using novel focusing matrix approach. The proposed focusing matrix makes possible the time-reversal imaging technique to coherently process each frequency bin to yield a consistent signal subspace. The performance of coherent focusing is investigated when combined with time-reversal robust capon beamformer (TR-RCB). We have used numerical experiments on breast cancer detection using FDTD employing anatomically realistic numerical breast phantoms that contain varying amounts of dense fibro-glandular tissue content. The imaging results indicate that the proposed Coherent-TR-RCB (C-TR-RCB) could overcome the limitations of time-reversal imaging in a highly heterogeneous and cluttered medium.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 109
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    Design and Numerical Verification of Plasmonic Cross Antennas to Generate Localized Circularly Polarized Light for All-Optical Magnetic Recording (2014)
    Wiley
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    Publication Date: 2014-12-16
    Description: All-optical magnetic recording with localized circularly polarized light is studied for realizing ultra-fast and high-density magnetic recording. We design plasmonic cross antennas with bit-patterned media and evaluate the Stokes parameters. Using our proposed method, the magnetic recording speed is about 100,000 times faster than that for conventional methods and the recording density becomes over 2Tbit/inch 2 .
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 110
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    Unifying the relative hindered velocity in suspensions and emulsions of non-deformable particles (2014)
    Wiley
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    Publication Date: 2014-12-15
    Description: Although the relative velocity of a single crystal or bubble in a quiescent fluid (melt) is well-characterized, the interplay of crystals/bubbles in multiparticle systems and its effect on their settling/rising velocity is poorly quantified. We propose a theoretical model for the hindered velocity of non-Brownian emulsions and suspensions of non-deformable fluid and solid particles in the creeping flow regime. The model is based on three sets of correction; two on the drag coefficient experienced by each particle to account for both return flow and Smoluchowski effects, and a correction on the rheology to account for non-local interactions introduced as a mean-field effective viscosity. Our model is tested against new and published experimental data over a wide range of particle volume fraction and viscosity ratio between the fluids. We find an excellent agreement between our model and experiments. The model is then applied to show that hindered settling can increase mineral residence time by up to an order of magnitude in convecting magma chambers.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 111
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    Cosmic ray event of AD 774-775 shown in quasi-annual 10Be data from the Antarctic Dome Fuji ice core (2014)
    Wiley
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    Publication Date: 2014-12-15
    Description: 14 C content in tree rings and 10 Be concentration records in polar ice core provide information about past cosmic ray intensities. The AD 774–775 cosmic ray event has been identified by 14 C measurement in several tree rings from all over the world. Although the quasi-decadal 10 Be Dome Fuji data in the Antarctic ice core also shows a sharp peak around AD 775, annual 10 Be variations in the Dome Fuji core or in other cores have not been revealed. We have measured quasi-annual 10 Be concentrations from approximately AD 763–794 in the Dome Fuji ice core, and detected a clear increase (~80% above the baseline) in 10 Be concentration around AD 775. However, an accurate height of this increase is not straightforwardly estimated due to the background variation in 10 Be concentration. The 10 Be increase can be due to the same cosmic ray event as shown in the 14 C content in AD 774–775.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 112
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    Gravity waves simulated by high-resolution Whole Atmosphere Community Climate Model (2014)
    Wiley
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    Publication Date: 2014-12-15
    Description: For the first time a mesoscale-resolving whole atmosphere general circulation model (GCM) has been developed, using the NCAR Whole Atmosphere Community Climate Model (WACCM) with ~0.25° horizontal resolution and 0.1 scale height vertical resolution above the middle stratosphere (higher resolution below). This is made possible by the high accuracy and high scalability of the spectral element dynamical core from the High-Order Method Modeling Environment (HOMME). For the simulated January-February period, the latitude-height structure and the magnitudes of the temperature variance compare well with those deduced from SABER observations. The simulation reveals the increasing dominance of gravity waves (GWs) at higher altitudes through both the height dependence of the kinetic energy spectra, which display a steeper slope (~-3) in the stratosphere and an increasingly shallower slope above, and the increasing spatial extent of GWs (including a planetary-scale extent of a concentric GW excited by a tropical cyclone) at higher altitudes. GW impacts on the large-scale flow is evaluated in terms of zonal mean zonal wind and tides: with no GW drag parameterized in the simulations, forcing by resolved GWs does reverse the summer mesospheric wind, albeit at an altitude higher than climatology, and only slows down the winter mesospheric wind without closing it. The hemispheric structures and magnitudes of diurnal and semidiurnal migrating tides compare favorably with observations.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 113
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    3-D Simulations of the Southern Polar Giant Impact Hypothesis for the Origin of the Martian Dichotomy. (2014)
    Wiley
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    Publication Date: 2014-12-15
    Description: We demonstrate via numerical simulations that the impact of a ~ lunar-sized body with Mars is capable of creating a hemispherical magma ocean that upon cooling and solidification resulted in the formation of the southern highlands and thus the Martian dichotomy. The giant impact may have contributed a significant amount of iron to the Martian core and generated a deep thermal anomaly that led to the onset and development of the volcanism in the southern highlands. Our model predicts several mantle plumes converging to the South Pole from the equatorial regions as well as new plumes forming in the equatorial region and also an absence of significant large-scale volcanism in the northern lowlands. The core heat flux evolution obtained from our numerical models is consistent with the decline of the magnetic field. We argue that such a scenario is more consistent with a range of observations than a northern giant impact (excavating the Borealis basin) for the formation of the Martian dichotomy.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 114
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    Greenland ice sheet annual motion insensitive to spatial variations in subglacial hydraulic structure (2014)
    Wiley
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    Publication Date: 2014-12-15
    Description: We present ice velocities observed with global positioning systems and TerraSAR-X/TanDEM-X in a land-terminating region of the south-west Greenland ice sheet (GrIS) during the melt-year 2012–2013, to examine the spatial pattern of seasonal and annual ice motion. We find that whilst spatial variability in the configuration of the subglacial drainage system controls ice motion at short timescales, this configuration has negligible impact on the spatial pattern of the proportion of annual motion which occurs during summer. Whilst absolute annual velocities vary substantially, the proportional contribution of summer motion to annual motion does not. These observations suggest that in land-terminating margins of the GrIS, subglacial hydrology does not significantly influence spatial variations in net summer speedup. Furthermore, our findings imply that not every feature of the subglacial drainage system needs to be resolved in ice sheet models.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 115
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    δ15N in laminated marine sediments provide a proxy for mixing between the California Undercurrent and the California Current: A proof of concept (2014)
    Wiley
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    Publication Date: 2014-12-15
    Description: Measurements of particulate δ 15 N in coastal marine laminated sediments provide a high-resolution proxy for fluctuations in the intensity of denitrification in the water column. In the Eastern Tropical North Pacific oxygen minimum zone, this denitrification signal is transported northward by the California Undercurrent, thus serving as a tracer of ocean circulation. This is verified through comparisons between salinity in the thermocline off Southern California (Santa Monica Basin) and the difference between δ 15 N sed within age equivalent sediments from a southern (Pescadero Slope) and northern (Santa Monica Basin) site. Trends in this parameter, Δ δ 15 N sed , relate to Pacific Decadal Oscillation (PDO) phase changes between 1900 and 1990. We hypothesize that the decline in Δ δ 15 N sed during warm PDO phases is due to a strengthening of the California Undercurrent transporting 15  N-enriched nitrate from the ETNP northward. The deviation from this trend after 1990 suggests recent changes in circulation and/or California Current water nutrient biogeochemistry.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 116
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    Mechanical properties and processes of deformation in shallow sedimentary rocks from subduction zones: An experimental study (2014)
    Wiley
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    Publication Date: 2014-12-15
    Description: To better constrain the mechanical behavior of sediments accreted to accretionary prism, we conducted triaxial mechanical tests on natural samples from the Miura-Boso paleo-accretionary prism (Japan) in drained conditions with confining pressures up to 200 MPa as well as post-experiments P-wave velocity (V p ) measurements. During experiments, deformation is principally non-coaxial and accommodated by two successive modes of deformation, both associated with strain-hardening and velocity-strengthening behavior: (1) compaction-assisted shearing, distributed in a several mm-wide shear zone and (2) faulting, localized within a few tens of µm-wide, dilatant fault zone. Deformation is also associated with (1) a decrease in Young's modulus all over the tests, (2) anomalously low V p in the deformed samples compared to their porosity and (3) an increase in sensitivity of V p to effective pressure. We interpret this evolution of the poroelastic properties of the material as reflecting the progressive breakage of intergrain cement and the formation of microcracks along with macroscopic deformation. When applied to natural conditions, these results suggest that the deformation style (localized vs distributed) of shallow (z 〈 a few km) sediments is mainly controlled by the variations in stress/strain rate during the seismic cycle and is therefore independent of the porosity of sediments. Finally, we show that the effect of strain, through cement breakage and microcracks formation, may lower V p for effective pressure up to 40 MPa. As a consequence, the low V p anomalies observed in Nankai accretionary prisms by seismic imaging between 2 and 4km depth [ Kitajima and Saffer , 2012] could reflect sediment deformation rather than porosity anomalies. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 117
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    Effects of Climate Oscillations on Wind Resource Variability in the United States (2014)
    Wiley
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    Publication Date: 2014-12-15
    Description: Natural climate variations in the United States wind resource are assessed by using cyclostationary empirical orthogonal functions (CSEOFs) to decompose wind reanalysis data. Compared to approaches that average climate signals or assume stationarity of the wind resource on interannual timescales, the CSEOF analysis isolates variability associated with specific climate oscillations, as well as their modulation from year to year. Contributions to wind speed variability from the modulated annual cycle (MAC) and the El Niño-Southern Oscillation (ENSO) are quantified, and information provided by the CSEOF analysis further allows the spatial variability of these effects to be determined. The impacts of the MAC and ENSO on the wind resource are calculated at existing wind turbine locations in the United States, revealing variations in the wind speed of up to 30% at individual sites. The results presented here have important implications for predictions of wind plant power output and siting.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 118
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    Thermodynamic calculations of the polybaric melting phase relations of spinel lherzolite (2014)
    Wiley
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    Publication Date: 2014-12-17
    Description: This study presents a new thermodynamic model for the calculation of phase relations during the melting of anhydrous spinel lherzolite at pressures of 1–2.5 GPa. The model is based on the total energy minimization algorithm for calculating phase equilibria within multicomponent systems and the thermodynamic configuration of Ueki and Iwamori [2013]. The model is based on a SiO 2 – Al 2 O 3 – FeO–Fe 3 O 4 –MgO–CaO system that includes silicate melt, olivine, clinopyroxene, orthopyroxene, and spinel as possible phases. The molar Gibbs free energy of the melt phase is modeled quasi-empirically, and the thermodynamic parameters for silicate melt end-member components are calibrated with a polybaric calibration database. The temperatures and pressures used in this newly compiled calibration dataset are 1230–1600 ∘ C and 0.9–3 GPa, corresponding to the stability range of spinel lherzolite. The modeling undertaken during this study reproduces the general features of experimentally determined melting phase relations of spinel lherzolite at 1–2.5 GPa, including the solidus temperature, the melt composition, the chemical reaction during melting and the degree of melting. This new thermodynamic modeling also reproduces phase relations of various bulk compositions from fertile to deplete spinel lherzolite and can be used in the modeling of polybaric mantle melting within various natural settings. Comparing the results derived from this new modeling with those produced using previous models indicates that the new approach outlined here, involving a combination of total energy minimization and the direct calibration of melt thermodynamic parameters at pressure and temperature conditions corresponding to mantle melting with a relatively simple melt thermodynamic equation, can accurately model polybaric melting phase relations. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 119
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    Issue Information (2014)
    Wiley
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    Publication Date: 2014-12-16
    Description: Cover. Evolving and increasingly hazardous radiation levels in space. (top) ACE dose rates (red) are based on fits to CRIS spectra [ O'Neill , 2006]; CRaTER measurements (green) from the zenith-facing D1/D2 detectors are used as proxies for lens dose rates behind 0.3 g/cm2 Al shielding Schwadron et al . [2012]. The sunspot number predictions (the lower black and blue dashed lines) show two cases based on a Gleissberg-like and a Dalton-like minimum, the results of which are similar. The dose predictions (solid blue line and the upper black and blue dashed lines) are from a sunspot-based model of the heliospheric magnetic field and the correlated variation in modulation of GCRs. The ACE data, CRaTER data, and model results are projected to the lunar surface. (bottom) Same as the top panel, but for a longer time span. See pp. 622–632.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
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  • 120
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    Relationship between sunshine duration and air temperature and contemporary global warming (2014)
    Wiley
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    Publication Date: 2014-12-17
    Description: ABSTRACT The purpose of this paper is to describe the variability of sunshine duration and air temperature and to assess the relationship between these variables. The paper is based on daily means of air temperature and daily sunshine duration totals from the 1884–2012 period. The variability analyses of these variables for the whole period is supplemented by additional trend analyses for two separate time periods described in the literature as dimming (1958–1985) and brightening (1985–2012). All the data come from the Jagiellonian University Research Station in Krakow. In Krakow, there is a decrease in the number of sunshine hours in the 1950s to 1980s period followed by an increase in the last two decades of the 20th century. The long-term course of air temperature in Krakow confirms the results obtained in other places in the world and exhibits increasing warming of the climate. The temperature increase is visible in each month but is highest in winter (exceeding 1.5 °C per 100 years). Therefore, it may be assumed that the increase in air temperature, which has been particularly strong since the 1980s, showed the full effect of global warming in the brightening period that was previously masked by global dimming as shown in the sunshine duration records. The time course of air temperature for the whole study period (1884–2012) shows a statistically significant positive linear trend. The present warming is influenced probably by the air-quality improvement (brightening period) and an increase in sunshine duration in the years 1980–2012.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
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  • 121
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    Long-term changes in summer temperature anomaly patterns in Japan since the early 20th century (2014)
    Wiley
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    Publication Date: 2014-12-17
    Description: The relationship between long-term variations in summer temperature in Japan since the early 20th century and the large-scale atmospheric circulation field was analysed. The combined influence of various circulation predictors on temperature variations was analysed via a multicomponent canonical correlation analysis (CCA). The positive phase of the first CCA mode is related to a positive temperature anomaly across Japan, characterized by a weak blocking high over the Okhotsk Sea, and a strong North Pacific subtropical high (NPSH) over Japan. The positive phase of the second CCA mode corresponds to a positive temperature anomaly in southwestern Japan, and a negative anomaly in northern Japan, characterized by an anticyclonic circulation anomaly over eastern China and a cyclonic anomaly over the northwestern Pacific. By investigating the temporal changes in CCA scores, we detected an abrupt increase in the first CCA score in the early 1910s and a long-term increasing trend in the second CCA score since the early 20th century. The abrupt increase in the first CCA score indicates an abrupt increase in temperature throughout Japan. By investigating changes in the circulation field associated with this abrupt warming, we determined that intensification of zonal flow over the Okhotsk Sea was responsible. The increasing trend of the second CCA score indicates an increase in the regional difference in summer temperatures between northern and southwestern Japan. After investigating changes in the circulation field before and after the mid-20th century, we suggest that the southwestward shift of the NPSH and the weakening of anticyclonic circulation anomalies over the northwestern Pacific were responsible for this increase in the regional temperature difference.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
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    Wind forcing controls on river plume spreading on a tropical continental shelf (2014)
    Wiley
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    Publication Date: 2014-12-17
    Description: The Berau Continental Shelf is located close to the Equator in the Indonesian Archipelago, hosting a complex of coral reefs along its oceanic edge. The Berau coral reefs have a very high biodiversity, but the area is under serious risk due to river-derived nutrients and sediments. The region is characterized by weak winds, moderate tides and almost absent Coriolis forcing. Existing knowledge about river plume behaviour in tropical environments is limited. The aim of this paper is to investigate the influence of the subtle physical forcing on the dynamics of the Berau river plume. A three-dimensional model (ECOMSED) was calibrated with observational data. The model was forced by freshwater input from the Berau river distributaries, tides at the open boundaries and measured hourly wind. The model reproduces the freshwater dynamics on the shelf adequately and highlights that the river plume spreads symmetrically for river forcing only. Tides cause vertical mixing and suppress the cross-shelf spreading of the river plume. However, the spreading of the river plume over the shelf is mainly controlled by the weak monsoonal winds, resulting in a seasonal development. During the Southeast Monsoon, the southerly winds push the plume northeastward and cause a stratified water column in the northern part of the continental shelf. Northerly winds during the Northwest Monsoon disperse the plume to the south, promoting a vertically well-mixed water column. The results can be used to predict the possible impact of land-use changes in the steadily developing Berau region on coral reef health. This article is protected by copyright. All rights reserved.
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    Kinetics and thermodynamics of reversible disproportionation–comproportionation in redox triad oxoammonium cations – nitroxyl radicals – hydroxylamines (2014)
    Wiley
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    Publication Date: 2014-12-06
    Description: Kinetics and equilibrium of the acid-catalyzed disproportionation of cyclic nitroxyl radicals R 2 NO • to oxoammonium cations R 2 NO + and hydroxylamines R 2 NOH is defined by redox and acid–base properties of these compounds. In a recent work ( J. Phys. Org. Chem . 2014, 27, 114-120), we showed that the kinetic stability of R 2 NO • in acidic media depends on the basicity of the nitroxyl group. Here, we examined the kinetics of the reverse comproportionation reaction of R 2 NO + and R 2 NOH to R 2 NO • and found that increasing in – I -effects of substituents greatly reduces the overall equilibrium constant of the reaction K 4 . This occurs because of both the increase of acidity constants of hydroxyammonium cations K 3H+ and the difference between the reduction potentials of oxoammonium cations E R2NO+/R2NO• and nitroxyl radicals E R2NO•/R2NOH . pH dependences of reduction potentials of nitroxyl radicals to hydroxylamines E 1/3Σ and bond dissociation energies D(O–H) for hydroxylamines R 2 NOH in water were determined. For a wide variety of piperidine- and pyrrolidine-1-oxyls values of p K 3H+ and E R2NO+/R2NO• correlate with each other, as well as with the equilibrium constants K 4 and the inductive substituent constants σ I . The correlations obtained allow prediction of the acid–base and redox characteristics of redox triads R 2 NO • –R 2 NO + –R 2 NOH. Copyright © 2014 John Wiley & Sons, Ltd. The overall equilibrium constant K 4 of disproportionation of nitroxyl radicals 1 depend on the difference of their pH-dependent reduction potentials to hydroxyammonium cations 3 H + and reduction potentials of oxoammonium cations 2 to 1 : E 1 / 3 Σ  −  E 2 / 1  = ( RT / F )ln K 4 . – I -Effects of substituents R and heterocycle contraction increase the rate constant of comproportionation k − 2 , acidity constants of protonated nitroxyl radicals K 1 H+ and hydroxylamines K 3 H+ , thus reducing the constant K 4  =  k 2  /  (k − 2  ×  K 1 H+  ×  K 3 H+ ) in the studied series of compounds a–i by more than seven orders of magnitude.
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    Electronic ISSN: 1099-1395
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    Dimethyl Sulfide in the Amazon Rain Forest (2014)
    Wiley
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    Publication Date: 2014-12-09
    Description: Surface-to-atmosphere emissions of dimethyl sulfide (DMS) may impact global climate through the formation of gaseous sulfuric acid, which can yield secondary sulfate aerosols and contribute to new particle formation. While oceans are generally considered the dominant source of DMS, a shortage of ecosystem observations prevents an accurate analysis of terrestrial DMS sources. Using mass spectrometry, we quantified ambient DMS mixing ratios within and above a primary rainforest ecosystem in the central Amazon Basin in real-time (2010–2011) and at high vertical resolution (2013–2014). Elevated but highly variable DMS mixing ratios were observed within the canopy, showing clear evidence of a net ecosystem source to the atmosphere during both day and night in both the dry and wet seasons. Periods of high DMS mixing ratios lasting up to 8 hours (up to 160 ppt) often occurred within the canopy and near the surface during many evenings and nights. Daytime gradients showed mixing ratios (up to 80 ppt) peaking near the top of the canopy as well as near the ground following a rain event. The spatial and temporal distribution of DMS suggests that ambient levels and their potential climatic impacts are dominated by local soil and plant emissions. A soil source was confirmed by measurements of DMS emission fluxes from Amazon soils as a function of temperature and soil moisture. Furthermore, light and temperature dependent DMS emissions were measured from seven tropical tree species. Our study has important implications for understanding terrestrial DMS sources and their role in coupled land-atmosphere climate feedbacks.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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    The effect of stratospheric sulfur from Mount Pinatubo on tropospheric oxidizing capacity and methane (2014)
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    Publication Date: 2014-12-09
    Description: The eruption of Mount Pinatubo in 1991 injected a large amount of SO 2 into the stratosphere, which formed sulfate aerosols. Increased scattering and absorption of UV radiation by the enhanced stratospheric SO 2 and aerosols decreased the amount of UV radiation reaching the troposphere, causing changes in tropospheric photochemistry. These changes affected the oxidizing capacity of the atmosphere and the removal rate of CH 4 in the years following the eruption. We use the three-dimensional chemistry transport model TM5 coupled to the aerosol microphysics module M7 to simulate the evolution of SO 2 and sulfate aerosols from the Pinatubo eruption. Their effect on tropospheric photolysis frequencies and concentrations of OH and CH 4 are quantified for the first time. We find that UV attenuation by stratospheric sulfur decreased the photolysis frequencies of both ozone and NO 2 by about 2% globally, decreasing global OH concentrations by a similar amount in the first two years after the eruption. SO 2 absorption mainly affects OH primary production by ozone photolysis, while aerosol scattering also alters OH recycling. The effect of stratospheric sulfur on global OH and CH 4 is dominated by the effect of aerosol extinction, while SO 2 absorption contributes by 12.5% to the overall effect in the first year after the eruption. The reduction in OH concentrations causes an increase in the CH 4 growth rate of 4 and 2 ppb/yr in the first and second year after the eruption, respectively, contributing 11 Tg to the 27 Tg observed CH 4 burden change in late 1991 and early 1992.
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    Adaptive observation in the South China Sea using CNOP approach based on a 3-D ocean circulation model and its adjoint model (2014)
    Wiley
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    Publication Date: 2014-12-09
    Description: This study investigates the effect of adaptive (or targeted) observation on improving the mid-range (30 days) forecast skill of ocean state of the South China Sea (SCS). A region associated with the South China Sea Western Boundary Current (SCSWBC) is chosen as the “target” of the adaptive observation. The Conditional Nonlinear Optimal Perturbation (CNOP) approach is applied to a 3-dimensional ocean model and its adjoint model for determining the sensitive region. Results show that the initial errors in the sensitive region determined by the CNOP approach have significant impacts on the forecast of ocean state in the target region; thus, reducing these initial errors through adaptive observation can lead to a better 30-day prediction of ocean state in the target region. Our results suggest that implementing adaptive observation is an effective and cost-saving way to improve an ocean model's forecast skill over the SCS. This article is protected by copyright. All rights reserved.
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    Moored observations of synoptic and seasonal variability in the East Greenland Coastal Current (2014)
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    Publication Date: 2014-12-09
    Description: We present a year-round assessment of the hydrographic variability within the East Greenland Coastal Current on the Greenland shelf from five synoptic crossings and four years of moored hydrographic data. From the five synoptic sections the current is observed as a robust, surface intensified flow with a total volume transport of 0.66 ± 0.18 Sv and a freshwater transport of 42 ± 12 mSv. The moorings showed heretofore unobserved variability in the abundance of Polar and Atlantic water masses in the current on synoptic scales. This is exhibited as large vertical displacement of isotherms (often greater than 100 m). Seasonally, the current is hemmed into the coast during the fall by a full depth Atlantic Water layer that has penetrated onto the inner shelf. The Polar Water layer in the current then thickens through the winter and spring seasons increasing the freshwater content in the current; the timing implies that this is probably driven by the seasonally varying export of freshwater from the Arctic and not the local runoff from Greenland. The measured synoptic variability is enhanced during the winter and spring period due to a lower halocline and a concurrent enhancement in the along-coast wind speed. The local winds force much of the high-frequency variability in a manner consistent with downwelling, but variability distinct from downwelling is also visible. This article is protected by copyright. All rights reserved.
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    Multimodel simulations of Arctic Ocean sea surface height variability in the period 1970–2009 (2014)
    Wiley
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    Publication Date: 2014-12-09
    Description: The performance of several numerical ocean models is assessed with respect to their simulation of sea surface height (SSH) in the Arctic Ocean, and the main patterns of SSH variability and their causes over the past 40 years (1970-2009) are analyzed. In comparison to observations, all tested models broadly reproduce the mean SSH in the Arctic and reveal a good correlation with both tide gauge data and SSH anomalies derived from satellite observations. Although the models do not represent the positive Arctic SSH trend observed over the last two decades, their interannual-to-decadal SSH variability is in reasonable agreement with available measurements. Focusing on results from one of the models for a detailed analysis it is shown that the decadal-scale SSH variability over shelf areas and deep parts of the Arctic Ocean have pronounced differences that are determined mostly by salinity variations. A further analysis of the three time periods 1987-1992, 1993-2002 and 2003-2009, corresponding to the transition times between cyclonic and anticyclonic regimes of the atmospheric circulation over the Arctic, revealed an unusual increase of SSH in the Amerasian basin during 2003-2009. Results from this model support the recent finding that the increase is caused mainly by changes in freshwater content brought about by the freshwater export through the Canadian Arctic Archiplago and increased Ekman pumping in the Amerasian basin and partly by lateral freshwater transport changes, leading to a re-distribution of low-salinity shelf water. Overall we show that present day models can be used for investigating the reasons for low-frequency SSH variability in the region. This article is protected by copyright. All rights reserved.
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    A neural network-based four-band model for estimating the total absorption coefficients from the global oceanic and coastal waters (2014)
    Wiley
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    Publication Date: 2014-12-09
    Description: In this study, a neural network-based four-band model (NNFM) for the global oceanic and coastal waters has been developed in order to retrieve the total absorption coefficients a ( λ ). The applicability of the quasi-analytical algorithm (QAA) and NNFM models is evaluated by five independent datasets. Based on the comparison of a ( λ ) predicted by these two models with the field measurements taken from the global oceanic and coastal waters, it was found that both the QAA and NNFM models had good performances in deriving a ( λ ), but that the NNFM model works better than the QAA model. The results of the QAA model-derived a ( λ ), especially in highly turbid waters with strong backscattering properties of optical activity, was found to be lower than the field measurements. The QAA and NNFM models-derived a ( λ ) could be obtained from the MODIS data after atmospheric corrections. When compared with the field measurements, the NNFM model decreased by a 0.86 to 24.15% uncertainty (root mean square relative error) of the estimation from the QAA model in deriving a ( λ ) from the Bohai, Yellow, and East China seas. Finally, the NNFM model was applied to map the global climatological seasonal mean a (443) for the time range of July, 2002 to May, 2014. As expected, the a (443) value around the coastal regions was always larger than the open ocean around the equator. Viewed on a global scale, the oceans at a high latitude exhibited higher a (443) values than those at a low latitude. This article is protected by copyright. All rights reserved.
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    Thermal variations in the South China Sea associated with the eastern and central Pacific El Niño events and their mechanisms (2014)
    Wiley
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    Publication Date: 2014-12-09
    Description: In this study, we investigate the interannual variability of the sea surface temperature (SST) in the South China Sea (SCS) associated with two types of El Niño, namely, the eastern Pacific (EP) El Niño and the central Pacific (CP) El Niño. First, double warm peaks can occur during both types of El Niño events in the SCS. However, the strong warm basin mode can only develop in the EP El Niño, while the warm semi-basin mode exists during the CP El Niño. Associated with an anomalous positive (negative) net surface heat flux in the EP (CP) El Niño, along with a shallower thermocline with weaker (stronger) northeasterly wind anomalies, the SST anomalies become warmer (cooler) in the developing autumn. Over the background of cooling SST in autumn of CP El Niño, therefore, only a weak warming can occur in the subsequent years, which is limited in the western boundary area under the forcing of warm ocean advection. Second, the SST oscillation periods are different in these two types of El Niño. The SST evolution in the EP El Niño is negative-positive with a quasi-biennial oscillation, but that in the CP El Niño is positive-negative-positive-negative with an annual oscillation. It seems that the double cooling in the CP El Niño is phase-locked to the late autumn season. This article is protected by copyright. All rights reserved.
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    Comprehensive study of emission source contributions for tropospheric ozone formation over East Asia (2014)
    Wiley
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    Publication Date: 2014-12-09
    Description: Emission source contributions of tropospheric ozone (O 3 ) were comprehensively investigated by using the higher-order decoupled direct method (HDDM) for sensitivity analysis and the ozone source apportionment technology (OSAT) for mass balance analysis in the comprehensive air-quality model with extensions (CAMx). The response of O 3 to emissions reductions at various levels in mainland China, Korea, and Japan were estimated and compared with results calculated by the brute force method (BFM) where one model parameter is varied at a time. Emissions were assessed at three receptor sites in Japan that experienced severe pollution events in May 2009. For emissions from China, HDDM assessed O 3 response with a bias of only up to 3 ppbv (a relative error of 4.5%) even for a 50% reduction, but failed to assess a more extreme reduction. OSAT was reasonably accurate at 100% reduction, with a −4 ppbv (−7%) bias, but was less accurate at moderate ranges of reduction (⊔50-70%). For emissions from Korea and Japan, HDDM captured the nonlinear response at all receptor sites and at all reduction levels to within 1% in all but one case; however, the bias of OSAT increased with the increasing reduction of emissions. One possible reason for this is that OSAT does not account for NO titration. To address this, a term for potential ozone (PO; O 3 and NO 2 together) was introduced. Using of PO instead of O 3 improved the performance of OSAT, especially for emissions reductions from Korea and Japan. The proposed approach with PO refined the OSAT results and did not degrade HDDM performance.
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    Theoretical investigations on 4,4′,5,5′-tetranitro-2,2′-1H,1′H-2,2′-biimidazole derivatives as potential nitrogen-rich high energy materials (2014)
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    Publication Date: 2014-12-09
    Description: The ―NH 2 , ―NO 2 , ―NHNO 2 , ―C(NO 2 ) 3 and ―CF(NO 2 ) 2 substitution derivatives of 4,4′,5,5′-tetranitro-2,2′-1H,1′H-2,2′-biimidazole were studied at B3LYP/aug-cc-pVDZ level of density functional theory. The crystal structures were obtained by molecular mechanics (MM) methods. Detonation properties were evaluated using Kamlet–Jacobs equations based on the calculated density and heat of formation. The thermal stability of the title compounds was investigated via the energy gaps ( ∆E LUMO − HOMO ) predicted. Results show that molecules T5 ( D  = 10.85 km·s −1 , P  = 57.94 GPa) and T6 ( D  = 9.22 km·s −1 , P  = 39.21 GPa) with zero or positive oxygen balance are excellent candidates for high energy density oxidizers (HEDOs). All of them appear to be potential explosives compared with the famous ones, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocane (HMX, D  = 8.96 km·s −1 , P  = 35.96 GPa) and hexanitrohexaazaisowurtzitane (CL-20, D  = 9.38 km·s −1 , P  = 42.00 GPa). In addition, bond dissociation energy calculation indicates that T5 and T6 are also the most thermally stable ones among the title compounds. Copyright © 2014 John Wiley & Sons, Ltd. The ―NH 2 , ―NO 2 , ―NHNO 2 , ―C(NO 2 ) 3 and ―CF(NO 2 ) 2 substitution derivatives of 4,4',5,5'-tetranitro-2,2'-1H,1'H- 2,2'-biimidazole were studied at B3LYP/aug-cc- pVDZ level of density functional theory. The crystal structures were obtained by molecular mechanics methods. The thermal stability of the title compounds was investigated via the energy gaps (ΔELUMO-HOMO) predicted. Results show that 4,4',5,5'-tetranitro-2,2'- 1H,1'H- 2,2'-biimidazole-1,1'-ditrinitromethyl amino (T5), (D = 10.85 km s –1 , P = 57.94 GPa) and 4,4',5,5'-tetranitro-2,2'-1H,1'H-2,2'- biimidazole-1,1'-difluorodinitromethylamino (T6) (D = 9.22 km s –1 , P = 39.21 GPa) with zero or positive oxygen balance, are excellent candidates for high energy density oxidizers.
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    Proton transfer reactions of N-aryl triazolium salts: unusual ortho-substituent effects (2014)
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    Publication Date: 2014-12-09
    Description: Previous studies of the C(3)-hydrogen/deuterium exchange reactions of the triazolium ion conjugate acids of triazolyl N-heterocyclic carbenes revealed a change of mechanism under acidic conditions with N1-protonation to a dicationic salt. Interestingly, the data suggested an increase in p K a N1 in the presence of a N -pentafluorophenyl substituent relative to other N -aryl substituents with hydrogens or methyl substituents rather than fluorines at the ortho -positions. To probe the presence of an apparent donor effect of a N -pentafluorophenyl substituent, which differs from the more common electron withdrawing effect of this group, we have studied the analogous deuterium exchange reactions of four triazolium salts with heteroatoms or heteroatom substituents in the 2-position and/or 6-position of the N -aryl ring. These include triazolium salts with N -2,4,6-tribromophenyl , N -2,6-dichlorophenyl , N -2-pyridyl and N -2-pyrimidinyl substituents. The log k ex – p D profiles for , and were found to show similar trends at lower p D s as for the previously studied N -pentafluorophenyl triazolium salt, hence supporting the presence an apparent donor effect on p K a N1 . Surprisingly, the log k ex – p D profile for N -pyridyl salt uniquely showed acid catalysis at lower p D s. We propose herein that this data is best explained by invoking an intramolecular general base role for the N -(2-pyridyl) substituent in conjunction with N1-protonation on the triazolium ring. Finally, the second order rate constants for deuteroxide ion catalysed C(3)-H/D exchange ( k DO , M −1  s −1 ), which could be obtained from data at p D s 〉1.5, were used to provide estimates of C(3)-carbon acid p K a C3 values for the four triazolium salts . Copyright © 2014 John Wiley & Sons, Ltd. We have studied the C(3)-H/D exchange reactions in D 2 O of four triazolium salts with heteroatoms or heteroatom substituents in the 2-position and/or 6-position of the N -aryl ring. The log k ex – p D rate profiles in each case are consistent with a change in mechanism at p D 〈 1.5 as a result of N 1-deuteronation of the triazole ring. In addition, formal acid catalysis of deuterium exchange was uniquely observed for the N -pyridyltriazolium salt providing evidence for a possible intramolecular proton transfer reaction involving the pyridyl substituent.
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    Rice Growth Monitoring using Simulated Compact Polarimetric C-band SAR (2014)
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    Publication Date: 2014-12-06
    Description: In this study, a set of nine compact polarimetric (CP) images were simulated from polarimetric RADARSAT-2 data acquired over a test site containing two types of rice field in Jiangsu province, China. The types of rice field in the test site were (1) transplanted hybrid rice fields, and (2) direct-sown japonica rice fields. Both types have different yields and phenological stages. As a first step, the two types of rice field were distinguished with 94% and 86% accuracy respectively through analyzing CP SAR observations and their behavior in terms of scattering mechanisms during the rice growth season. The focus was then on phenology retrieval for each type of rice field. A decision tree (DT) algorithm was built to fulfill the precise retrieval of rice phenological stages, in which seven phenological stages were discriminated. The key criterion for each phenological stage was composed of 1–4 CP parameters, some of which were firstly used for rice phenology retrieval and found to be very sensitive to rice phenological changes. The retrieval results were verified at parcel level for a set of 12 stands of rice and up to nine observation dates per stand. This gave an accuracy of 88-95%. Throughout the phenology retrieval process, only simulated CP data was used, without any auxiliary data. These results demonstrate the potential of CP SAR for rice growth monitoring applications.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
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    Tectonic control on the petrophysical properties of foredeep sandstone in the Central Apennines, Italy (2014)
    Wiley
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    Publication Date: 2014-11-06
    Description: Petrophysical properties of rocks and their applicability at larger scale are a challenging topic in Earth sciences. Petrophysical properties of rocks are severely affected by: boundary conditions, rock fabric/microstructure, and tectonics that require a multi-scale approach to be properly defined. Here we: (1) report laboratory measurements of density, porosity, permeability and P-wave velocities at increasing confining pressure conducted on Miocene foredeep sandstones (Frosinone Fm.); (2) compare the laboratory results with larger-scale geophysical investigations; (3) discuss the effect of thrusting on the properties of sandstones. At ambient pressure, laboratory porosity varied from 2.2% to 13.8% and P-wave velocities (Vp) from 1.5 km/s to 2.7 km/s. The P-wave velocity increased with confining pressure, reaching between 3.3 km/s to 4.7 km/s at 100 MPa. In situ Vp profiles, measured using sonic logs, matched the ultrasonic laboratory measurement well. The permeability varied between 1.4 × 10 -15  m 2 to 3.9 × 10 -15  m 2 and was positively correlated with porosity. The porosity and permeability of samples taken at various distances to the Olevano-Antrodoco fault plane progressively decreased with distance while P-wave velocity increased. At about 1 km from the fault plane, the relative variations reached 43%, 65% and 20% for porosity, permeability and P-wave velocity, respectively. This suggests that tectonic loading changed the petrophysical properties inherited from sedimentation and diagenesis. Using field constraints and assuming overburden-related inelastic compaction in the proximity of the fault plane, we conclude that the fault reached the mechanical condition for rupture in compression at differential stress of 64.8 MPa at a depth of 1500 m.
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    Changes of summer precipitation in China: The dominance of frequency and intensity and linkage with changes in moisture and air temperature (2014)
    Wiley
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    Publication Date: 2014-11-06
    Description: Using observed precipitation and the NCEP-NCAR reanalysis, the changes in the metrics of the summer precipitation in China, the dominance of frequency and intensity of daily extreme precipitation, and the linkage with changes in moisture and air temperature are explored. Results show that over the recent 50 years, total summer rainfall increased over the southeast and the west and decreased over the northeast. The changes in the frequency, identified with the 95% threshold and Poisson regression, and rainfall extremes show similar spatial patterns. The relative importance of the changes in frequency and intensity in the variability and changes in extreme precipitation is estimated. It is shown that, while the interannual variability of the rainfall amount is dominated by the frequency change in almost all stations, the long-term change of rainfall amount can be dominated by both frequency and intensity, depending on the station. The change in the rainfall total is linked to changes in atmospheric moisture and temperature. Results show that the variability and change of the rainfall total can be dominated by changes in both moisture and air temperature, and the relative importance depends on the region.
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    Estimating the global oceanic net freshwater flux from Argo and comparing it with satellite-based freshwater flux products (2014)
    Wiley
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    Publication Date: 2014-11-06
    Description: Following the idea that analysis of in-situ information in the salt budget could be used as a surrogate for global “ocean rain gauge”, the annual mean oceanic net freshwater flux (E-P) was estimated from the Argo profiles and the wind stress data on a global scale. The comparison between the independent E-P estimation from Argo and the E-P product sets, including the combination of precipitation from TRMM, GPCP, CMAP and evaporation from OAFlux, GSSTF3 and IFREMER and E-P set from NEWS formed from satellite, generally show similar spatial patterns, particularly on the larg scale. However, there are differences among the different satellite-based E-P estimates and between satellite estimates and independent in-situ estimates. Based on the pattern correlation and the RMSD, the evaporation and precipitation from OAFlux and TRMM agrees best with the E-P estimated from the independent Argo-based estimates.
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    Variations of stratospheric water vapor over the past three decades (2014)
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    Publication Date: 2014-11-06
    Description: We examine variations in water vapor in air entering the stratosphere through the tropical tropopause layer (TTL) over the past three decades in satellite data and in a trajectory model. Most of the variance can be explained by three processes that affect the TTL: the quasi-biennial oscillation, the strength of the Brewer-Dobson circulation, and the temperature of the tropical troposphere. When these factors act in phase, significant variations in water entering the stratosphere are possible. We also find that volcanic eruptions, which inject aerosol into the TTL, affect the amount of water entering the stratosphere. While there is clear decadal variability in the data and models, we find little evidence for a long-term trend in water entering the stratosphere through the TTL over the past 3 decades.
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    Contrasting mountain and piedmont dynamics of sediment discharge associated with groundwater storage variation in the Biobío River (2014)
    Wiley
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    Publication Date: 2014-12-06
    Description: Supply and transport of sediment in catchments involve processes with fundamental consequences for river management, land use and the prediction of climate-driven sediment fluxes. In the present study we addressed spatial variability in the water routes through the surface and subsurface of a catchment and the suspended sediment discharge ( Q s ) over a mountain–piedmont system. We analyzed daily suspended sediment concentration ( C s ) and water discharge ( Q ) measurements at stations located in different topographic settings (mountain and piedmont) in the Biobío River basin (southern-central Andes, 37-39°S). In steep catchments, the Q vs. Q s relationship has a marked seasonal hysteresis. In the piedmont, Q s is proportional to Q , with no seasonal hysteresis. The contrast in the hysteresis pattern between catchments with different topographies is explained by differences in the routing of rainfall-derived water. In the piedmont, most of the rainfall is converted into surface runoff because the water table is near the surface. In the mountains, groundwater storage results in large seasonal variations in the proportion of Q that flows at the surface and transports sediment from the hillslopes, producing hysteresis. By separating the total Q into two components (direct discharge, Q d and baseflow, Q b ), we observed the response of Q s to the fraction of water that quickly leaves the catchment after a rainfall event ( Q d ). Similar results between the mountain and piedmont and the absence of hysteresis simplify the behavior of Q s into a linear relationship with Q d over the entire catchment and lead usto propose that sediment mobilization to the river along the Biobío catchment is primarily controlled by overland flow. Our findings highlight the importance of an adequate hydrological model for understanding the erosion and transport processes of a catchment, and which can be applied to other natural and modeled mountain–piedmont systems.
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    The offset-midpoint travel-time pyramid for P-wave in 2D transversely isotropic media with a tilted symmetry axis (2014)
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    Publication Date: 2014-12-09
    Description: ABSTRACT For pre-stack phase-shift migration in homogeneous isotropic media, the offset-midpoint travel time is represented by the double-square-root equation. The travel time as a function of offset and midpoint resembles the shape of Cheops’ pyramid. This is also valid for transversely isotropic media with a vertical symmetry axis. In this study, we extend the offset-midpoint travel-time pyramid to the case of 2D transversely isotropic media with a tilted symmetry axis. The P-wave analytical travel-time pyramid is derived under the assumption of weak anelliptical property of the tilted transverse isotropy media. The travel-time equation for the dip-constrained transversely isotropic model is obtained from the depth-domain travel-time pyramid. The potential applications of the derived offset-midpoint travel-time equation include pre-stack Kirchhoff migration, anisotropic parameter estimation, and travel-time calculation in transversely isotropic media with a tilted symmetry axis.
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
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    Increasing the effectiveness of electrical resistivity tomography using γ11n configurations (2014)
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    Publication Date: 2014-12-09
    Description: ABSTRACT A new array type, i.e., the γ 11n arrays, is introduced in this paper, in which the sequence of the current (C) and potential (P) electrodes is CPCP, and the distance between the last two electrodes is n times the distance between the first two ones and that of the second one and the third one. These arrays are called quasinull arrays because they are—according to their array and behaviour—between the traditional and null arrays. It is shown by numerical modelling that, in detecting small-effect inhomogeneity, these configurations may be more effective than the traditional ones, including the optimized Stummer configuration. Certain γ 11n configurations—especially the γ 112 , γ 113, and γ 114 —produced better results both in horizontal and vertical resolution investigations. Based on the numerical studies, the γ 11n configurations seem to be very promising in problems where the anomalies are similar to the numerically investigated ones, i.e., they can detect and characterize, e.g., tunnels, caves, cables, tubes, abandoned riverbeds, or discontinuity, in a clay layer with greater efficacy than those of the traditional configurations. γ 11n measurements need less data than traditional configurations; therefore, the time demand of electrical resistivity tomography measurements can be shortened by their use.
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    Retrieval of super-virtual refraction by cross-correlation (2014)
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    Publication Date: 2014-12-09
    Description: ABSTRACT Topography and severe variations of near-surface layers lead to travel-time perturbations for the events in seismic exploration. Usually, these perturbations could be estimated and eliminated by refraction technology. The virtual refraction method is a relatively new technique for retrieval of refraction information from seismic records contaminated by noise. Based on the virtual refraction, this paper proposes super-virtual refraction interferometry by cross-correlation to retrieve refraction wavefields by summing the cross-correlation of raw refraction wavefields and virtual refraction wavefields over all receivers located outside the retrieved source and receiver pair. This method can enhance refraction signal gradually as the source–receiver offset decreases. For further enhancement of refracted waves, a scheme of hybrid virtual refraction wavefields is applied by stacking of correlation-type and convolution-type super-virtual refractions. Our new method does not need any information about the near-surface velocity model, which can solve the problem of directly unmeasured virtual refraction energy from the virtual source at the surface, and extend the acquisition aperture to its maximum extent in raw seismic records. It can also reduce random noise influence in raw seismic records effectively and improve refracted waves’ signal-to-noise ratio by a factor proportional to the square root of the number of receivers positioned at stationary-phase points, based on the improvement of virtual refraction's signal-to-noise ratio. Using results from synthetic and field data, we show that our new method is effective to retrieve refraction information from raw seismic records and improve the accuracy of first-arrival picks.
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    Full-Wave Multiscale Anisotropy Tomography in Southern California (2014)
    Wiley
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    Publication Date: 2014-12-09
    Description: Understanding the spatial variation of anisotropy in the upper mantle is important for characterizing the lithospheric deformation and mantle flow dynamics. In this study, we apply a full-wave approach to image the upper-mantle anisotropy in Southern California using 5954 SKS splitting data. Three-dimensional sensitivity kernels combined with a wavelet-based model parameterization are adopted in a multiscale inversion. Spatial resolution lengths are estimated based on a statistical resolution matrix approach, showing a finest resolution length of ~25 km in regions with densely-distributed stations. The anisotropic model displays structural fabric in relation to surface geologic features such as the Salton Trough, the Transverse Ranges and the San Andreas Fault. The depth variation of anisotropy does not suggest a lithosphere-asthenosphere decoupling. At long-wavelengths, the fast directions of anisotropy are aligned with the absolute plate motion inside the Pacific and North American plates.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
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    Seismic interferometry by tangent-phase correction (2014)
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    Publication Date: 2014-12-09
    Description: ABSTRACT We present a modified interferometry method based on local tangent-phase analysis, which corrects the cross-correlated data before summation. The approach makes it possible to synthesize virtual signals usually vanishing in the conventional seismic interferometry summation. For a given pair of receivers and a set of different source positions, a plurality of virtual traces is obtained at new stationary projected points located along the signal wavefronts passing through the real reference receiver. The position of the projected points is estimated by minimizing travel times using wavefront constraint and correlation-signal tangent information. The method uses mixed processing, which is partially based on velocity-model knowledge and on data-based blind interferometry. The approach can be used for selected events, including reflections with different stationary conditions and projected points with respect to those of the direct arrivals, to extend the interferometry representation in seismic exploration data where conventional illumination coverage is not sufficient to obtain the stationary-phase condition. We discuss possible applications in crosswell geometry with a velocity anomaly and a time lapse.
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    AEROSOL TRANSPORT OVER THE WESTERN MEDITERRANEAN BASIN: EVIDENCE OF THE CONTRIBUTION OF FINE PARTICLES TO DESERT DUST PLUMES OVER ALBORÁN ISLAND. (2014)
    Wiley
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    Publication Date: 2014-12-09
    Description: Eight months (June 2011-January 2012) of aerosol property data were obtained at the remote site of Alborán Island (35.95 ° N, 3.03 ° W) in the western Mediterranean basin. The aim of this work is to assess the aerosol properties according to air-mass origin and transport over this remote station with a special focus on air mass transport from North Africa. For air masses coming from North Africa, different aerosol properties showed strong contributions from mineral dust lifted from desert areas. Nevertheless, during these desert dust intrusions, some atmospheric aerosol properties are clearly different from pure mineral dust particles. Thus, Angström exponent α(440–870) presents larger values than those reported for pure desert dust measured close to dust source regions. These results combine with α(440,670)-α(670,870) ≥ 0.1 and low single scattering albedo (ω(λ)) values, especially at the largest wavelengths. Most of the desert dust intrusions over Alborán can be described as a mixture of dust and anthropogenic particles. The analyses support that our results apply to North Africa desert dust air masses transported from different source areas. Therefore, our results indicate a significant contribution of fine absorbing particles during desert dust intrusions over Alborán arriving from different source regions. The aerosol optical depth (AOD) data retrieved from sun-photometer measurements have been used to check MODIS retrievals, and they show reasonable agreement, especially for North African air masses.
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    Aircraft type dependency of contrail evolution (2014)
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    Publication Date: 2014-12-09
    Description: The impact of aircraft type on contrail evolution is assessed using a large-eddy simulation (LES) model with Lagrangian ice microphysics. Six different aircraft ranging from the small regional airliner Bombardier CRJ to the largest aircraft Airbus A380 are taken into account. Differences in wake vortex properties and fuel flow lead to considerable variations in the early contrail geometric depth and ice crystal number. Larger aircraft produce contrails with more ice crystals (assuming that the number of initially generated ice crystals per kg fuel is constant). These initial differences are reduced in the first minutes, as the ice crystal loss during the vortex phase is stronger for larger aircraft. In supersaturated air, contrails of large aircraft are much deeper after 5 minutes than those of small aircraft. A parametrization for the final vertical displacement of the wake vortex system is provided, depending only on the initial vortex circulation and stratification. Cloud resolving simulations are used to examine whether the aircraft-induced initial differences have a long-lasting mark. These simulations suggest that the synoptic scenario controls the contrail-cirrus evolution qualitatively. However, quantitative differences between the contrail-cirrus properties of the various aircraft remain over the total simulation period of six hours. The total extinctions of A380-produced contrails are about 1.5 to 2.5 times higher than those from contrails of a Bombardier CRJ.
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    Quantifying the heat flux regulation of metropolitan land-use/land-cover components by coupling remote sensing-modelling with in situ measurement (2014)
    Wiley
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    Publication Date: 2014-12-09
    Description: Quantifying the effects of urban land-use/land-cover with regard to surface radiation and heat-flux regulation is important to ecological planning and heat stress mitigation. To retrieve the spatial pattern of heat fluxes in the Beijing metropolitan area, China, a remote sensing–based energy balance model was calibrated with synchronously measured energy fluxes including net radiation, latent heat flux (LE), and sensible heat flux (H). Our model calibration approach avoided the uncertainties due to subjective judgments in previous empirical parameterization methods. The land surface temperature (LST), H, and Bowen ratio (β) of Beijing were found to increase along the outskirt-suburban-urban gradient, with strong spatial variation. LST and H were negatively correlated with vegetation fraction cover (VFC). For example, the modern high-rise residential areas with relatively higher VFC had lower H and β than the traditional low-rise residential areas. Our findings indicate thermal dissipation through vegetation transpiration might play an important role in urban heat regulation. Notably, the thermal-dissipating strength of vegetation (calculated as LE/VFC) declined exponentially with increased VFC. For the purpose of heat stress regulation, we recommend upgrading the traditional low-rise residential areas to modern high-rise residential areas and focusing urban greenery projects in areas whose VFC 〈 0.1, where the heat-regulating service by urban vegetation could be twice as effective as in other places.
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    Forecasting Space Weather Events for a Neighboring World (2014)
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    Publication Date: 2014-12-06
    Description: Shortly after NASA's Mars Atmosphere and Volatile EvolutioN mission (MAVEN) spacecraft entered Mars’ orbit on Sept 21, 2014, scientists glimpsed the Martian atmosphere's response to a front of solar energetic particles (SEPs) and an associated coronal mass ejection (CME). In response to some solar flares and CMEs, streams of SEPs burst from the solar atmosphere and are further accelerated in the interplanetary medium between the Sun and the planets. These particles deposit their energy and momentum into anything in their path, including the Martian atmosphere and MAVEN particle detectors.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
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    Satellite Based Augmentation Systems – A Novel and Cost Effective Tool For Ionospheric and Space Weather Studies (2014)
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    Publication Date: 2014-12-06
    Description: Satellite Based Augmentation Systems (SBASes) are designed to provide additional accuracy and robustness to existing satellite-based radio navigation systems for all phases of a flight. However, similar to navigation systems such as GPS which has proven its worth for the investigation of the ionosphere, the SBASes do have certain advantages. In the present paper, we propose and demonstrate SBAS applicability to ionospheric and space weather research in a novel and cost-effective way. The recent commissioning of the Indian SBAS, named GPS Aided Geo Augmented Navigation (GAGAN), covering the equatorial and low-latitude regions centered around the Indian longitudes provides the motivation for this approach. Two case studies involving different ionospheric behavior over low-latitude regions vindicate the potential of SBAS over extended areas.
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    Impacts of Urbanization on Indian Summer Monsoon Rainfall Extremes (2014)
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    Publication Date: 2014-12-09
    Description: ABSTRACT Urban areas have different climatology with respect to their rural surroundings. Though urbanization is a worldwide phenomenon, it is especially prevalent in India, where urban areas have experienced an unprecedented rate of growth over the last 30 years. Here we take up an observational study to understand the influence of urbanization on the characteristics of precipitation (specifically extremes) in India. We identify 42 urban regions, and compare their extreme rainfall characteristics with those of surrounding rural areas. We observe that, on an overall scale, the urban signatures on extreme rainfall are not prominently and consistently visible, but they are spatially non uniform. Zonal analysis reveals significant impacts of urbanization on extreme rainfall in central and western regions of India. An additional examination, to understand the influences of urbanization on heavy rainfall climatology, is carried with station level data using a statistical method, quantile regression. This is performed for the most populated city of India, Mumbai, in pair with a nearby non–urban area, Alibaug; both having similar geographic location. The derived extreme rainfall regression quantiles reveal the sensitivity of extreme rainfall events to the increased urbanization. Overall the study identifies the climatological zones in India, where, increased urbanization affects regional rainfall pattern and extremes, with a detailed case study of Mumbai. This also calls attention to the need of further experimental investigation, for the identification of the key climatological processes, in different regions of India, affected by increased urbanization.
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    The Victoria mode in the North Pacific linking extratropical SLP variations to ENSO (2014)
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    Publication Date: 2014-12-09
    Description: The Victoria mode (VM) represents the second dominant mode (EOF2) of North Pacific variability, independent of the Pacific Decadal Oscillation (PDO), and is defined as the EOF2 of SST anomalies (SSTAs) in the North Pacific poleward of 20°N. The present study indicates that the VM is closely linked to the development of El Niño–Southern Oscillation (ENSO). The VM may effectively act as an ocean bridge (or conduit) through which the extratropical atmospheric variability in the North Pacific influences ENSO. The VM can trigger the onset of ENSO via the following two dominant processes: 1) surface air–sea coupling associated with the VM in the subtropical/tropical Pacific and 2) evolution of subsurface ocean temperature anomalies along the equator associated with the VM. These two processes may force sufficient surface warming to occur in the central–eastern equatorial Pacific from spring to summer, which in turn initiates an ENSO event. The VM influence on ENSO relies on a basin-scale air–sea interaction dynamic, as opposed to more local-scale dynamics typically associated with the seasonal footprinting mechanism (SFM) or Pacific meridional mode (PMM). The majority of VM events are followed by ENSO events. These ENSO events triggered by VM include El Niño Modoki (EM) as well as conventional El Niño. There is no evidence that the VM tends to be more conducive to the initialization of EM than conventional El Niño.
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    Homogeneous and unimolecular gas-phase thermal decomposition kinetics of methyl benzoylformate: experimental and theoretical study (2014)
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    Publication Date: 2014-12-09
    Description: The kinetics of the gas-phase thermal decomposition of the α-ketoester methyl benzoylformate was carried out in a static system with reaction vessel deactivated with allyl bromide, and in the presence of the free radical inhibitor propene. The rate coefficients were determined over the temperature range of 440–481 °C and pressures from 32 to 80 Torr. The reaction was found to be homogenous, unimolecular and obey a first-order rate law. The products are methyl benzoate and CO. The temperature dependence of the rate coefficient gives the following Arrhenius parameters: log 10 k (s −1 ) = 13.56 ± 0.31 and E a (kJ mol −1 ) = 232.6 ± 4.4. Theoretical calculations of the kinetic and thermodynamic parameters are in good agreement with the experimental values using PBE1PBE/6-311++g(d,p). A theoretical Arrhenius plot was constructed at this level of theory, and the good agreement with the experimental Arrhenius plot suggests that this model of transition state may describe reasonably the elimination process. These results suggest a concerted non-synchronous semi-polar three-membered cyclic transition state type of mechanism. The most advanced coordinate is the bond breaking C δ+ --- δ- OCH 3 with an evolution of 66.7%, implying this as the limiting factor of the elimination process. Copyright © 2014 John Wiley & Sons, Ltd. Kinetic of the gas-phase thermal decomposition of methyl benzoylformate was carried at 440–481 °C and 32–80 Torr. The product formation suggests both experimentally and theoretically a three-membered cyclic transition state mechanism.
    Print ISSN: 0894-3230
    Electronic ISSN: 1099-1395
    Topics: Chemistry and Pharmacology , Physics
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    Preferential burial of permafrost-derived organic carbon in Siberian-Arctic shelf waters (2014)
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    Publication Date: 2014-11-23
    Description: The rapidly changing East Siberian Arctic Shelf (ESAS) receives large amounts of terrestrial organic carbon (OC) from coastal erosion and Russian-Arctic rivers. Climate warming increases thawing of coastal Ice Complex Deposits (ICD) and can change both the amount of released OC, as well as its propensity to be converted to greenhouse gases (fueling further global warming) or to be buried in coastal sediments. This study aimed to unravel the susceptibility to degradation, and transport and dispersal patterns of OC delivered to the ESAS. Bulk and molecular radiocarbon analyses on surface particulate matter (PM), sinking PM and underlying surface sediments illustrate the active release of old OC from coastal permafrost. Molecular tracers for recalcitrant soil OC showed ages of 3.4-13 14 C-ky in surface PM and 5.5-18 14 C-ky in surface sediments. The age difference of these markers between surface PM and surface sediments is larger (i) in regions with low OC accumulation rates, suggesting a weaker exchange between water column and sediments, and (ii) with increasing distance from the Lena River, suggesting preferential settling of fluvially-derived old OC nearshore. A dual-carbon end-member mixing model showed that (i) contemporary terrestrial OC is dispersed mainly by horizontal transport while being subject to active degradation, (ii) marine OC is most affected by vertical transport and also actively degraded in the water column, and (iii) OC from ICD settles rapidly and dominates surface sediments. Preferential burial of ICD-OC released into ESAS coastal waters might therefore lower the suggested carbon cycle climate feedback from thawing ICD permafrost. This article is protected by copyright. All rights reserved.
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    Issue Information (2014)
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    Publication Date: 2014-11-23
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    The Seasonal evolution of sea ice floe size distribution (2014)
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    Publication Date: 2014-11-23
    Description: The Arctic sea ice cover undergoes large changes over an annual cycle. In winter and spring the ice cover consists of large, snow-covered plate-like ice floes, with very little open water. By the end of summer the snow cover is gone and the large floes have broken into a complex mosaic of smaller, rounded floes surrounded by a lace of open water. This evolution strongly affects the distribution and fate of the solar radiation deposited in the ice-ocean system and consequently the heat budget of the ice cover. In particular, increased floe perimeter can result in enhanced lateral melting. We attempt to quantify the floe evolution process through the concept of a floe size distribution that is modified by lateral melting and floe breaking. A time series of aerial photographic surveys made during the SHEBA field experiment is analyzed to determine evolution of the floe size distribution from spring through summer. Based on earlier studies, we assume the floe size cumulative distribution could be represented by a power law D -α where D is the floe diameter. The exponent α as well as the number density of floes N tot are estimated from measurements of total ice area and perimeter. As summer progressed, there was an increase in α as the size distribution shifted towards smaller floes and the number of floes increased. Lateral melting causes the distribution to deviate from a power law for small floe sizes. This article is protected by copyright. All rights reserved.
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    Responses of the ocean planktonic ecosystem to finite-amplitude perturbations (2014)
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    Publication Date: 2014-11-23
    Description: The responses of the ocean planktonic ecosystem to finite-amplitude perturbations are investigated using an ocean planktonic ecosystem model. Through changing the higher predation rate on zooplankton, multiple equilibria of the model, namely “high-nutrient” and “low-nutrient” states, are obtained under certain parameter values. Based on these states, the perturbations with maximum nonlinear growth are determined using the conditional nonlinear optimal perturbation (CNOP) method. The linear and nonlinear evolutions of the CNOP perturbation are compared. The results show that the nonlinear evolution of the perturbation leads to predator–prey oscillations with larger amplitude than the linear evolution. Besides, after the perturbation amplitude exceeds a critical value, the nonlinear evolution of the perturbation will induce the linearly stable ecosystem state to lose the stability and become nonlinearly unstable. This implies that nonlinear processes have important impacts on the stability of the ecosystem. Specifically, we identify the nonlinear processes related to zooplankton grazing to impact the stability most for the high-nutrient state, while for the low-nutrient state the main nonlinear process affecting the stability is the uptake process. These results help to improve our understanding of the sensitivity of the oceanic ecosystem model to finite-amplitude perturbations and the underlying nonlinear stability properties. This article is protected by copyright. All rights reserved.
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    Influence of summertime mesoscale convective systems on the heat balance and surface mixed-layer dynamics of a large Amazonian hydroelectric reservoir (2014)
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    Publication Date: 2014-11-23
    Description: We evaluated the impacts of summertime mesoscale convective systems (MCS) on the heat balance and diel surface mixed layer (SML) dynamics of the Brazilian Amazon's Tucuruí Hydroelectric Reservoir (THR). We used a synergistic approach that combines in situ data, remote sensing data and three-dimensional (3D) modeling to investigate the typical behavior of the components of the heat balance and the SML dynamics. During the study period (the austral summer of 2012-2013), 22 days with MCS activity were identified. These events occurred approximately every 4 days, and they were most frequent during January (50% of the observations). An analysis of local meteorological data showed that when MCS occur, the environmental conditions at THR change significantly ( p-value 〈 0.01). The net longwave flux, which was the heat balance component most strongly impacted by MCS, increased more than 32% on days with MCS activity. The daily integrated heat balance became negative (-54 W m -2 ) on MCS days, while the balance was positive (19 W m -2 ) on non MCS days. In response to the changes in the heat balance, the SML dynamics changed when a MCS was over the THR. The SML depth was typically 28% higher on the days with MCS (~1.6 m) compared with the days without MCS (~1.3 m). The results indicate that MCS are one of the main meteorological disturbances driving the heat balance and the mixing dynamics of Amazonian hydroelectric reservoirs during the summer. These events may have implications for the water quality and greenhouse gas emissions of Amazonian reservoirs. This article is protected by copyright. All rights reserved.
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    CO2 and CH4 isotope compositions and production pathways in a tropical peatland (2014)
    Wiley
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    Publication Date: 2014-11-29
    Description: While it is widely recognized that peatlands are important in the global carbon cycle, there is limited information on belowground gas production in tropical peatlands. We measured porewater methane (CH 4 ) and carbon dioxide (CO 2 ) concentrations and δ 13 C isotopic composition and CH 4 and CO 2 production rates in peat incubations from the Changuinola wetland in Panama. Our most striking finding was that CH 4 was depleted in 13 C (-94‰ in porewater and produced at -107‰ in incubated peat) relative to CH 4 found in most temperate and northern wetlands, potentially impacting the accuracy of approaches that use carbon isotopes to constrain global mass balance estimates. Fractionation factors between CH 4 and CO 2 showed that hydrogenotrophic methanogenesis was the dominant CH 4 production pathway, with up to 100% of the CH 4 produced via this route. Far more CO 2 than CH 4 (7 to 100 X) was measured in porewater, due in part to loss of CH 4 through ebullition or oxidation and to the production of CO 2 from pathways other than methanogenesis. We analyzed data on 58 wetlands from the literature to determine the dominant factors influencing the relative proportions of CH 4 produced by hydrogenotrophic and acetoclastic methanogenesis and found that a combination of environmental parameters including pH, vegetation type, nutrient status and latitude are correlated to the dominant methanogenic pathway. Methane production pathways in tropical peatlands do not correlate with these variables in the same way as their more northerly counterparts and thus may be differently affected by climate change.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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    Temperature sensitivity as an explanation of the latitudinal pattern of green-up date trend in Northern Hemisphere vegetation during 1982–2008 (2014)
    Wiley
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    Publication Date: 2014-11-29
    Description: ABSTRACT The vegetation green-up date (GUD) is widely expected to advance to an earlier date in the year in response to increasing spring temperature. However, although it is well known that climatic warming has been more intensive at higher latitudes than at lower latitudes in the Northern Hemisphere, it is not known whether this greater climatic warming at higher latitudes has led to a greater advance of vegetation GUD during the past few decades. We have first determined GUD from the satellite-derived greenness vegetation index for all the vegetated land between 30 and 75°N from 1982 to 2008, and then investigated the latitudinal pattern of the inter-annual trend of GUD and its relation to pre-season temperature. The results show a generally greater GUD advance in lower latitudes, in spite of the faster increase in pre-season temperature in higher latitudes. We find that 88% of the latitudinal variability in the GUD trend can be explained by the sensitivity of the GUD response to pre-season temperature. The GUD change has also resulted in a northward shift of GUD isolines by 1°–4° between 50 and 65°N during the period. These findings highlight the sensitivity of vegetation response to temperature in shaping the spatial pattern of spring phenological change and suggest that temperate ecosystems may experience greater phenological change if the current latitudinal pattern of climatic warming continues.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
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    Intensified anticyclonic anomaly over the western North Pacific during El Niño decaying summer under a weakened Atlantic thermohaline circulation (2014)
    Wiley
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    Publication Date: 2014-11-29
    Description: It has been well documented that there is an anticyclonic anomaly over the western North Pacific (WNPAC, hereafter) during El Niño decaying summer. This El Niño − WNPAC relationship is greatly useful for the seasonal prediction of summer climate in the WNP and East Asia. In this study, we investigate the modification of the El Niño–WNPAC relationship induced by a weakened Atlantic thermohaline circulation (THC) in a water-hosing experiment. The results suggest that the WNPAC during the El Niño decaying summer, as well as the associated precipitation anomaly over the WNP, is intensified under the weakened THC. On the one hand, this intensification is in response to the increased amplitude and frequency of El Niño events in the water-hosing experiment. On the other hand, this intensification is also because of greater climatological humidity over the western to central North Pacific under the weakened THC. We suggest that the increase of climatological humidity over the western to central North Pacific during summer under the weakened THC is favourable for enhanced interannual variability of precipitation, and therefore favourable for the intensification of the WNPAC during El Niño decaying summer. This study suggests a possible modulation of the ENSO–WNP summer monsoon relationship by the low frequency fluctuation of Atlantic sea surface temperature (SST). The results offer an explanation for the observed modification of the multidecadal fluctuation of El Niño–WNPAC relationship by the Atlantic multidecadal oscillation (AMO).
    Print ISSN: 0148-0227
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    Low time resolution analysis of polar ice cores cannot detect impulsive nitrate events (2014)
    Wiley
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    Publication Date: 2014-11-29
    Description: Ice cores are archives of climate change and possibly large solar proton events (SPEs). Wolff et al . [2012] used a single event, a nitrate peak in the GISP2-H core, which McCracken et al . [2001a] time associated with the poorly quantified 1859 Carrington event, to discredit SPE-produced, impulsive nitrate deposition in polar ice. This is not the ideal test case. We critique the Wolff et al. analysis and demonstrate that the data they used cannot detect impulsive nitrate events because of resolution limitations. We suggest re-examination of the top of the Greenland ice sheet at key intervals over the last two millennia with attention to fine resolution and replicate sampling of multiple species. This will allow further insight into polar depositional processes on a sub-seasonal scale, including atmospheric sources, transport mechanisms to the ice sheet, post-depositional interactions, and a potential SPE association.
    Print ISSN: 0148-0227
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    Why Logarithmic? A Note on the Dependence of Radiative Forcing on Gas Concentration (2014)
    Wiley
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    Publication Date: 2014-11-29
    Description: Line-by-line radiative transfer computations show that the logarithmic dependence of radiative forcing on gas concentration not only applies to broadband irradiation fluxes such as in the well-known case of the CO 2 forcing, but also applies to the spectral radiance change due to both CO 2 and other gases, such as H 2 O. That the logarithmic relationship holds for monochromatic radiance requires an explanation beyond the conventional ideas based on the spectroscopic features of the gas absorption lines. We show that the phenomenon can be explained by an Emission Layer Displacement Model , which describes the radiance response to gas perturbation under normal atmospheric conditions such as temperature linearly varying with height and gas concentration exponentially decaying with height.
    Print ISSN: 0148-0227
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    What are the intermediates that could react in the interstellar ices? (2014)
    Wiley
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    Publication Date: 2014-11-29
    Description: Interstellar chemical reactivity forms complex organic molecules implying different intermediates. In this mini review, reactions arising in/on interstellar ices are presented. These ices are a place where molecules are formed and where they can evolve under thermal and nonthermal effects. We present in this paper different intermediates that have been detected in experimental simulations of interstellar ices. Ionic, neutral, and radical intermediates have been characterized by different means allowing the building of an ice chemical network explaining their formation. Copyright © 2014 John Wiley & Sons, Ltd. Jean-Baptiste Bossa studied Chemistry at Aix-Marseille University in France. He received his PhD in Chemistry from Aix-Marseille University in 2010 under the supervision of Prof Thierry Chiavassa. He is currently the principal investigator of a research project founded by the Marie Skłodowska-Curie actions and conducted at both Leiden University (the Netherlands) and the University of Cologne (Germany). His research interests are in the field of laboratory astrophysics.
    Print ISSN: 0894-3230
    Electronic ISSN: 1099-1395
    Topics: Chemistry and Pharmacology , Physics
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    Carbon-cycle extremes during the 21st century in CMIP5 models: future evolution and attribution to climatic drivers (2014)
    Wiley
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    Publication Date: 2014-12-02
    Description: Climate extremes such as droughts and heatwaves affect terrestrial ecosystems and may alter local carbon budgets. However, it still remains uncertain to what degree extreme impacts in the carbon cycle influence the carbon cycle-climate feedback both today and the near future. Here, we analyze spatiotemporally contiguous negative extreme anomalies in gross primary production (GPP) and net ecosystem production (NEP) in model output of the Coupled Model Intercomparison Project Phase 5 (CMIP5) ensemble and investigate their future development and attribution to climatic drivers. We find that relative to the overall increase in global carbon uptake, negative extremes in GPP and NEP lose importance towards the end of the 21st century. This effect can be related to elevated CO 2 concentrations and higher amounts of available water at the global scale, partially mitigating the impacts of droughts and heatwaves, respectively. Overall, based on CMIP5 models we hypothesize that terrestrial ecosystems might be more resilient against future climate extremes than previously thought. Future work will have to further scrutinize these results considering that various biological and biogeochemical feedbacks are not yet integrated within earth system models.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
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    Laboratory Experiments of Forced Plumes in a Density-Stratified Crossflow and Implications for Volcanic Plumes (2014)
    Wiley
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    Publication Date: 2014-12-02
    Description: The mass eruption rate feeding a volcanic plume is commonly estimated from its maximum height. Winds are known to affect the column dynamics causing bending and hence reducing the maximum plume height for a given mass eruption rate. However, the quantitative predictions including wind effects on mass eruption rate estimates are not well constrained. To fill this gap, we present a series of new laboratory experiments on forced plumes rising in a density-stratified crossflow. We identify three dynamical regimes corresponding to increasing effect of wind on the plume rise. The transition from one regime to another is governed by two dimensionless velocity scales defined as a function of source and environmental parameters. The results are found consistent with the conditions of historical eruptions and provide new empirical relationships to estimate mass eruption rate from plume height in windy conditions, leading to valuable tools for eruption risk assessment.
    Print ISSN: 0094-8276
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    Sharp spatially constrained inversion with applications to transient electromagnetic data (2014)
    Wiley
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    Publication Date: 2014-12-02
    Description: ABSTRACT Time-domain electromagnetic data are conveniently inverted by using smoothly varying 1D models with fixed vertical discretization. The vertical smoothness of the obtained models stems from the application of Occam-type regularization constraints, which are meant to address the ill-posedness of the problem. An important side effect of such regularization, however, is that horizontal layer boundaries can no longer be accurately reproduced as the model is required to be smooth. This issue can be overcome by inverting for fewer layers with variable thicknesses; nevertheless, to decide on a particular and constant number of layers for the parameterization of a large survey inversion can be equally problematic. Here, we present a focusing regularization technique to obtain the best of both methodologies. The new focusing approach allows for accurate reconstruction of resistivity distributions using a fixed vertical discretization while preserving the capability to reproduce horizontal boundaries. The formulation is flexible and can be coupled with traditional lateral/spatial smoothness constraints in order to resolve interfaces in stratified soils with no additional hypothesis about the number of layers. The method relies on minimizing the number of layers of non-vanishing resistivity gradient, instead of minimizing the norm of the model variation itself. This approach ensures that the results are consistent with the measured data while favouring, at the same time, the retrieval of horizontal abrupt changes. In addition, the focusing regularization can also be applied in the horizontal direction in order to promote the reconstruction of lateral boundaries such as faults. We present the theoretical framework of our regularization methodology and illustrate its capabilities by means of both synthetic and field data sets. We further demonstrate how the concept has been integrated in our existing spatially constrained inversion formalism and show its application to large-scale time-domain electromagnetic data inversions.
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
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    Effect of temperature on rates of ammonium uptake and nitrification in the western coastal Arctic during winter, spring, and summer (2014)
    Wiley
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    Publication Date: 2014-12-03
    Description: Biogeochemical rate processes in the Arctic are not currently well constrained and there is very limited information on how rates may change as the region warms. Here we present data on the sensitivity of ammonium (NH 4 + ) uptake and nitrification rates to short-term warming. Samples were collected from the Chukchi Sea off the coast of Barrow, Alaska during winter, spring, and summer and incubated for 24 hours in the dark with additions of 15 NH 4 + at -1.5, 6, 13, and 20 °C. Rates of NH 4 + uptake and nitrification were measured in conjunction with bacterial production. In all seasons, NH 4 + uptake rates were highest at temperatures similar to current summertime conditions, but dropped off with increased warming, indicative of psychrophilic (i.e. cold-loving) microbial communities. In contrast, nitrification rates were less sensitive to temperature and were higher in winter and spring compared to summer. These findings suggest that as the Arctic coastal ecosystem continues to warm, NH 4 + assimilation may become increasingly important, relative to nitrification, although the magnitude of NH 4 + assimilation would be still be lower than nitrification.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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    Why the spring North Pacific Oscillation is a predictor of typhoon activity over the Western North Pacific (2014)
    Wiley
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    Publication Date: 2014-12-03
    Description: ABSTRACT In this study, we investigated the impact of the spring North Pacific Oscillation (NPO) on typhoon frequency over the Western North Pacific (WNP, north of the equator and west of dateline). To reduce the statistical uncertainty, all the data we used have been excluded the El Nino/Southern Oscillation signals. We found that the spring NPO positively correlated with the annual typhoon number over the WNP (hereafter TNWNP) during the period 1968–2010, with a correlation coefficient of 0.62 (above the 99% significance level). When the Northern Low and Southern High pattern over the north Pacific weakens, the TNWNP tends to increase. A positive phase of spring NPO is associated with the tropical circulation and sea surface temperature (SST) anomalies in the North Pacific, which may lead to unfavorable dynamical and thermal conditions for typhoon genesis over the WNP during JJAS. The negative anomaly of SST over the WNP, associated with the positive spring NPO anomaly, is connected to the tropical atmospheric circulations from spring to summer via good oceanic seasonal persistence and air–sea interaction. Thus, the spring NPO-related variability of the tropical atmospheric circulation as well as the SST can affect typhoon activity over the WNP. In addition, the spring NPO can also be adopted as a predictor for the summer rainfall in South China, since the spring NPO can modulate the WNP SST and western Pacific subtropical high from spring to summer.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
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    Observed high-latitude GNSS disturbances during a less-than-minor geomagnetic storm (2014)
    Wiley
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    Publication Date: 2014-12-03
    Description: This paper presents the effects of a weak geomagnetic storm event on January 17, 2013. While the Kp index reached a maximum of only 4, this event still caused severe disturbances for GNSS-based positioning services at high latitudes. We present data from the Norwegian Mapping Authority's Real Time Ionospheric Monitor (RTIM), based on a dense network of geodetic receivers, and scintillation indices from scintillation receivers located in Norway. In northern parts of Norway, the Centimeter positioning service (CPOS) was severely disturbed for hours. Service monitoring measurements showed that the effect was significantly worse for a receiver far away from the nearest network reference station.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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    Ionosphere data assimilation capabilities for representing the high-latitude geomagnetic storm event in September 2011 (2014)
    Wiley
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    Publication Date: 2014-12-04
    Description: Severe geomagnetic storms have a strong impact on space communication and satellite navigation systems. Forecasting the appearance of geomagnetically induced disturbances in the ionosphere is one of the urgent goals of the space weather community. The challenge is that the processes governing the distribution of the crucial ionospheric parameters has a rather poor quantitative description and the models, built using the empirical parameterisations, have limited capabilities for operational purposes. On the other hand, data assimilation techniques are becoming more and more popular for nowcasting the state of the large-scale geophysical systems. We present an example of an ionospheric data assimilation system performance assessment during a strong geomagnetic event, which took place on 26 September 2011. The first-principle model has assimilated slant total electron content measurements from a dense network of ground stations, provided by the Norwegian Mapping Authority. The results have shown satisfactory agreement with independent data and demonstrate that the assimilation model is accurate to about 2–4 TEC units, and can be used for operational purposes in high-latitude regions. The operational system performance assessment is the subject of future work.
    Print ISSN: 0148-0227
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    Statistical Downscaling of Rainfall Changes in Hawai‘i based on the CMIP5 Global Model Projections (2014)
    Wiley
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    Publication Date: 2014-12-05
    Description: Seasonal mean rainfall projections for Hawai‘i are given based on statistical downscaling of the latest CMIP5 global model results for two future representative concentration pathways (RCP4.5 and RCP8.5). The spatial information content of our statistical downscaling (SD) method is improved over previous efforts through the inclusion of spatially extensive, high quality monthly rainfall data set and the use of improved large-scale climate predictor information. Predictor variables include moisture transport in the middle atmosphere (700 hPa), vertical temperature gradients, and geopotential height fields of the 1000 and 500 hPa layers. The results allow for the first time to derive a spatially interpolated map with future rainfall change estimates for the main Hawaiian Islands. The statistical downscaling was applied to project wet (November-April) and dry (May-October) season rainfall anomalies for the mid and late 21 st century. Overall, the statistical downscaling gives more reliable results for the wet season than the dry season. The wet season results indicate a pronounced dipole structure between windward-facing mountain slopes and the leeward side of most of the islands. The climatically wet regions on the windward slopes of the mountain regions are expected to become wetter or remain stable in their seasonal precipitation amounts. On the climatically dry leeward sides Kaua‘i, O‘ahu Maui and Hawai‘i Island, future precipitation exhibits the strongest drying trends. The projected future rainfall anomaly pattern is associated with a circulation anomaly that resembles a shift in the position or strength of the subtropical high and the average location of extratropical troughs. These new results suggest that a negative trend dominates the area-averaged changes in the statistical downscaling over the Hawaiian Islands. However, the islands are expected to experience a greater contrast between the wet and dry regions in future.
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    Quantifying the energy dissipation of overriding plate deformation in three-dimensional subduction models (2014)
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    Publication Date: 2014-12-05
    Description: In a subduction system the force and the energy required to deform the overriding plate are generally thought to come from the negative buoyancy of the subducted slab and its potential energy, respectively. Such deformation might involve extension and backarc basin formation, or shortening and mountain building. How much of the slab's potential energy is consumed during overriding plate deformation remains unknown. In this work, we present dynamic three-dimensional laboratory experiments of progressive subduction with an overriding plate to quantify the force ( F OPD ) that drives overriding plate deformation and the associated energy dissipation rate (Φ OPD ), and we compare them with the negative buoyancy ( F BU ) of the subducted slab and its total potential energy release rate (Φ BU ), respectively. We varied the viscosity ratio between the plates and the sub-lithospheric upper mantle with η SP /η UM  = 157-560, and the thickness of the overriding plate with T OP  = 0.5-2.5 cm (scaling to 25-125 km in nature). The results show that F OPD / F BU has average values of 0.5-2.0%, with a maximum of 5.3% and Φ OPD /Φ BU has average values of 0.05-0.30%, with a maximum of 0.41%. The results indicate that only a small portion of the negative buoyancy of the slab and its potential energy are used to deform the overriding plate. Our models also suggest that the force required to deform the overriding plate is of comparable magnitude to the ridge push force. Furthermore, we show that in subduction models with an overriding plate bending dissipation at the subduction zone hinge remains low (3-15% during steady-state subduction).
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    Effects of rupture complexity on local tsunami inundation: Implications for probabilistic tsunami hazard assessment by example (2014)
    Wiley
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    Publication Date: 2014-12-05
    Description: We investigated the influence of earthquake source complexity on the extent of inundation caused by the resulting tsunami. We simulated 100 scenarios with collocated sources of variable slip on the Hikurangi subduction-interface in the vicinity of Hawke's Bay and Poverty Bay in New Zealand and investigated the tsunami effects on the cities of Napier and Gisborne. Rupture complexity was found to have a first order effect on flow depth and inundation extent for local tsunami sources. The position of individual asperities in the slip distribution on the rupture interface control to some extent how severe inundation will be. However, predicting inundation extent in detail from investigating the distribution of slip on the rupture interface proves difficult. Assuming uniform slip on the rupture interface in tsunami models can underestimate the potential impact and extent of inundation. For example, simulation of an M W 8.7 to M W 8.8 earthquake with uniform slip reproduced the area that could potentially be inundated by equivalent non-uniform slip events of M W 8.4. De-aggregation, to establish the contribution of different sources with different slip distributions to the probabilistic hazard, cannot be performed based on magnitude considerations alone. We propose two predictors for inundation severity based on the offshore tsunami wave field using the linear wave equations in an attempt to keep costly simulations of full inundation to a minimum.
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    Crustal and Upper Mantle Velocity Structure in the Vicinity of the Eastern Tennessee Seismic Zone Based Upon Radial P-Wave Transfer Functions (2014)
    Wiley
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    Publication Date: 2014-12-05
    Description: Teleseismic transfer function analysis is used to investigate crust and upper mantle velocity structure in the vicinity of the active eastern Tennessee seismic zone (ETSZ). The ETSZ is associated with the New York – Alabama (NY-AL) magnetic lineament, a prominent aeromagnetic anomaly indicative of Grenville-age, basement structure. Radial component, P-wave transfer functions for ten short-period stations operated by the Center for Earthquake Research and Information (CERI) are inverted for velocity structure. Velocity profiles are also determined for three broadband stations by converting the instrument response to that of an S-13 short-period seismometer. Distinct differences in the velocity profiles are found for stations located on either side of the NY-AL magnetic lineament; velocities west of the lineament are lower than velocities to the east of the lineament in the upper 10 km and in the depth range 30 to 50 km. A gradational Moho boundary is found beneath several stations located in the Valley and Ridge province. A Moho boundary is absent at four Valley and Ridge stations located east of the magnetic lineament and south of 35.5°N.
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    Acoustic and reservoir properties of microporous carbonate rocks: implication of micrite particle size and morphology (2014)
    Wiley
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    Publication Date: 2014-12-05
    Description: This integrated study provides significant insight into parameters controlling the acoustic and reservoir properties of microporous limestones, improving the knowledge of the relationships among petrophysic and microstructural content. Petrophysical properties measured from laboratory and logging tools (porosity, permeability, electrical conductivity and acoustic properties) have been coupled with thin section and SEM observations on the EST205 borehole from the Oxfordian limestone aquifer of the Eastern part of the Paris Basin. A major achievement is the establishment of the link between micrite microtexture types (particle morphology and nature of inter-crystal contacts) and the physical response, introducing a new effective and interesting rock-typing approach for microporous reservoirs. Fluid-flow properties are enhanced by the progressive augmentation of intercrystalline microporosity and associated pore throat diameter, as the coalescence of micrite particles decreases. Concerning acoustic properties, the slow increase of P-wave velocity can be seen as a reflection of crystal size and growing contact cementation leading to a more cohesive and stiffer micrite microtexture. By applying poroelasticity theory on our samples, we show that velocity dispersion can be a very useful tool for data discrimination in carbonates. This dispersion analysis highlights the presence of microcracks in the rocks, and their overall effect on acoustic and transport properties. The presence of microcracks is also confirmed with observations and permeability measurements under high confining pressure. Finally, a possible origin of high porous levels in neritic limestones is a mineralogical transformation of carbonates through freshwater-related diagenesis during subaerial exposure time. Finally, by applying poroelasticity theory on our samples, we show that velocity dispersion can be a very useful tool for data discrimination in carbonates.
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    Effect of the local clay distribution on the effective electrical conductivity of clay-rocks (2014)
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    Publication Date: 2014-12-05
    Description: The “local porosity theory” proposed by Hilfer was revisited to develop a “local clay theory” (LCT) that establishes a quantitative relationship between the effective electrical conductivity and clay distribution in clay-rocks. This theory is primarily based on a “local simplicity” assumption; under this assumption, the complexity of spatial clay distribution can be captured by two local functions, namely, the local clay distribution and the local percolation probability, which are calculated from a partitioning of a mineral map. The local clay distribution provides information about spatial clay fluctuations and the local percolation probability describes the spatial fluctuations in the clay connectivity. This LCT was applied to (a) a mineral map made from a Callovo-Oxfordian mudstone sample and (b) (macroscopic) electrical conductivity measurements performed on the same sample. The direct and inverse modeling show two results. First, the textural and classical model assuming that the electrical anisotropy of clay-rock is mainly controlled by the anisotropy of the sole clay matrix provides inconsistent inverted values. An other textural effect, the anisotropy induced by elongated and oriented non-clayey grains, should be considered. Second, the effective conductivity values depend primarily on the choice of the inclusion-based models used in the LCT. The impact of local fluctuations of clay content and connectivity on the calculated effective conductivity is lower.
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    Non-isothermal viscous sintering of volcanic ash (2014)
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    Publication Date: 2014-12-05
    Description: Volcanic ash is often deposited in a hot state. Volcanic ash containing glass, deposited above the glass transition interval, has the potential to sinter viscously both to itself (particle-particle) and to exposed surfaces. Here, we constrain the kinetics of this process experimentally under non-isothermal conditions using standard glasses. In the absence of external load, this process is dominantly driven by surface relaxation. In such cases the sintering process is rate-limited by the melt viscosity, the size of the particles and the melt-vapour interfacial tension. We propose a polydisperse continuum model that describes the transition from a packing of particles to a dense pore-free melt and evaluate its efficacy in describing the kinetics of volcanic viscous sintering. We apply our model to viscous sintering scenarios for cooling crystal-poor rhyolitic ash using the 2008 eruption of Chaitén volcano as a case example. We predict that moderate linear cooling rates of 〉10 -1  °C.min -1 can result in the common observation of incomplete sintering and the preservation of pore networks.
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    Global ionospheric total electron contents (TECs) during the last two solar minimum periods (2014)
    Wiley
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    Publication Date: 2014-01-11
    Description: [1]  The last solar minimum period was anomalously extended and low in EUV irradiance compared with previous solar minima. It can readily be expected that the thermosphere and ionosphere must be correspondingly affected by this low solar activity. While there have been unanimous reports on the thermospheric changes, being cooler and lower in its density as expected, the ionospheric responses to low solar activity in previous studies were not consistent with each other, probably due to the limited ionospheric observations used for them. In this study, we utilized the measurements of total electron content (TEC) from TOPEX and JASON-1 satellites during the periods of 1992 to 2010, which includes both the last two solar minimum periods, in order to investigate how the ionosphere responded to the extremely low solar activity during the last solar minimum compared with previous solar minimum. Although the global daily mean TECs show negligible differences between the two solar minimum periods, the global TEC maps reveal that there are significant systematic differences ranging from about -30% to +50% depending on local time, latitude and season. The systematic variations of the ionospheric responses seem to mainly result from the relative effects of reduced solar EUV production and reduced recombination rate due to thermospheric changes during the last solar minimum period.
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    Deep water circulation in the Luzon Strait (2014)
    Wiley
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    Publication Date: 2014-01-11
    Description: Deep water circulation in the Luzon Strait, which connects the Pacific deep circulation with the South China Sea throughflow, is investigated using a set of oceanographic observations combined with results from three numerical experiments. Both the in situ observations and the model show a deep water overflow in the Luzon Strait. Their results suggest that the deep Pacific water first flows into the Luzon Strait through the Bashi Channel (1.2 Sv, 1 Sv = 1×10 6 m 3 s -1 ) and the Taltung Canyon (0.4 Sv), then turns southward along the Luzon Trough, and finally enters the South China Sea primarily through two gaps in the Heng-Chun Ridge. Overall, the mean transport of the Luzon Strait overflow is about 1.5 Sv. Results from numerical experiments suggest that strong diapycnal mixing in the South China Sea and Luzon Strait, which sustains the baroclinic pressure gradient across the Luzon Strait, is the primary driving mechanism of the deep circulation in the Luzon Strait.
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    Predicting the Time Derivative of Local Magnetic Perturbations (2014)
    Wiley
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    Publication Date: 2014-01-11
    Description: [1]  Some of the potentially most destructive effects of severe space weather storms are caused by the Geomagnetically Induced Currents. GICs can cause failures of electric transformers and result in wide-spread blackouts. GICs are induced by the time variability of the magnetic field, and are closely related to the time derivative of the local magnetic field perturbation. Predicting dB/dt is rather challenging, since the local magnetic perturbations and their time derivatives are both highly fluctuating quantities, especially during geomagnetic storms. The currently available first-principles based and empirical models cannot predict the detailed minute-scale or even faster time variation of the local magnetic field. On the other hand, Pulkkinen et al. [2013] demonstrated recently that several models can predict with positive skill scores whether the horizontal component of dB/dt at a given magnetometer station will exceed some threshold value in a 20-minute time interval. In this paper we investigate if one can improve the efficiency of the prediction further. We find that the Space Weather Modeling Framework, the best performing among the five models compared by Pulkkinen et al. [2013], shows significantly better skill scores in predicting the magnetic perturbation than predicting its time derivative, especially for large deviations. We also find that there is a strong correlation between the magnitude of dB/dt and the magnitude of the horizontal magnetic perturbation itself. Combining these two results one can devise an algorithm that gives better skill scores for predicting dB/dt exceeding various thresholds in 20-minute time intervals than the direct approach.
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    Changing effect of El Niño on Antarctic iceberg distribution: From canonical El Niño to El Niño Modoki (2014)
    Wiley
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    Publication Date: 2014-01-11
    Description: Earlier studies indicate that during El Niño events the iceberg concentration increases in the east of the Pacific sector and in the west of the Atlantic sector of Southern Ocean, but decreases in the center of the Pacific sector. During La Niña the pattern of the iceberg concentration anomalies in these regions reverses. This iceberg redistribution is explained by anomalous winds and currents around an extensive positive atmospheric pressure anomaly that typically develops in the South-East Pacific during the warm El Niño-Southern Oscillation (ENSO) phase. In this study the results of iceberg observations during two cruises of the r/v “Akademik Fedorov” in Antarctica in January-February of 2008 (La Niña) and 2010 (El Niño) have been used to examine the consistency of changes in the iceberg distribution in the Southern Ocean related to El Niño events. The analysis of these observations has shown that in the Pacific Sector of Antarctica changes in the iceberg distribution between 2008 and 2010 followed the scenario outlined above and thus could be associated with the ENSO phase change. Contrary to earlier observations, the iceberg concentration in the Atlantic sector of Antarctica did not increase during 2010 El Niño. The latter is explained by a non-canonical type of 2010 El Niño, El Niño Modoki and associated atmospheric circulation pattern different from the canonical El Niño. Further analysis has shown that a more frequent occurrence of El Niño Modoki in recent years have resulted in weaker links between El Niño events and the Antarctic iceberg distribution.
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    Global Model of Low Frequency Chorus (fLHR  (2014)
    Wiley
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    Publication Date: 2014-01-11
    Description: [1]  Whistler mode chorus is an important magnetospheric emission, playing a dual role in the acceleration and loss of relativistic electrons in the Earth's outer radiation belt. Chorus is typically generated in the equatorial region in the frequencyrange 0.1 - 0.8 f ce , where f ce is the local electron gyrofrequency. However, as the waves propagate to higher latitudes, significant wave power can occur at frequencies below 0.1 f ce . Since this wave power is largely omitted in current radiation belt models we construct a global model of low frequency chorus, f LHR  〈  f  〈 0.1 f ce , using data from six satellites. We find that low frequency chorus is strongest, with an average intensity of 200 pT 2 , in the pre-noon sector during active conditions at mid latitudes (20 o  〈 | λ m | 〈 50 o ) from 4 〈  L ∗  〈 8. Such mid-latitude, low frequency chorus wave power will contribute to the acceleration and loss of relativistic electrons and should be taken into account in radiation belt models.
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    Mechanisms limiting the growth of aeolian Megaripples (2014)
    Wiley
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    Publication Date: 2014-01-11
    Description: [1]  Megaripples are distinguished from regular ripples by their larger size and bimodal sediment distribution. The interplay between wind, grain size and morphology controls their development, but the exact mechanisms that limit the size of megaripples have been unclear. Using wind tunnel experiments we found two main mechanisms that limit the height of megaripples. The first mechanism is megaripple flattening due to strong enough winds that drive the coarse grains into saltation; the second mechanism is megaripple deflation by impacts of faster saltation grains. In this latter mechanism, the coarse grains are propelled by the impacts of fine saltating grains. The occurrence of both these mechanisms depends on the grain size distribution, and increases with both megaripple height and wind speed. Thus, for a given wind environment and grain size distribution, there exists a limit on the size of megaripples, which is determined by these two mechanisms.
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    Observation of Local and Conjugate Ionospheric Perturbations from Individual Oceanic Lightning Flashes (2014)
    Wiley
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    Publication Date: 2014-01-11
    Description: [1]  Very low frequency (VLF) remote sensing observations of multifaceted local and conjugate ionospheric perturbations from geographically identified and well characterized oceanic lightning discharges are presented for the first time. Lightning-induced electron precipitation (LEP) events are shown to produce disturbances first in the conjugate hemisphere and subsequently in the hemisphere of the causative lightning discharge in agreement with theoretical predictions. A rough threshold peak current of ~100 kA is identified for lightning discharges to generate LEP events for the geomagnetic conditions present during observations. The occurrence of early VLF events and the subsequent duration of their recovery does not seem to fit any simple metric of lightning discharge peak current or proximity to great circle path. Knowledge of the full spectral density of the lightning EMP not just its peak current and the subionospheric mode structure are likely necessary to determine if a specific lightning discharge will generate an early VLF perturbation.
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    Limited magnesium isotope fractionation during metamorphic dehydration in metapelites from the Onawa contact aureole, Maine (2014)
    Wiley
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    Publication Date: 2014-01-12
    Description: Knowledge on the behavior of Mg isotopes during metamorphic dehydration is the prerequisite for applying Mg isotopes as tracers for crustal recycling. Here, we report Mg isotopic compositions of metapelites from the Onawa contact aureole, Maine. Except one sample, all metapelites across the aureole, from the wall-rock regional metamorphic rocks to the partially melted rocks adjacent to the pluton, have similar Mg isotopic compositions (δ 26 Mg = -0.09 to +0.12‰). This observation indicates limited Mg isotope fractionation during metamorphic dehydration and fluid-rock interaction, due to the low Mg concentration in fluids relative to rocks. Our results suggest that Mg isotopic compositions of metapelites can record those of their protoliths and, hence, recycled clastic sedimentary materials may preserve their low-temperature Mg isotopic signatures through subduction zones. Therefore, Mg isotopes may serve as new tracers for crustal recycling, for example, tracing components experienced weathering cycles within granite sources.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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    Splay fault triggering by great subduction earthquakes inferred from finite-element models (2014)
    Wiley
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    Publication Date: 2014-01-14
    Description: [1]  We have investigated the influence that megathrust earthquake slip has on the activation of splay faults using a 2D Finite Element Method (FEM), taking into account the effects of gravity and variations in the frictional strength properties of splay faults. We simulated both landward-dipping and seaward-dipping splay fault geometries, and imposed depth-variable slip distributions of subduction events. Our results indicate that the two types of splay fault exhibit a similar behavior, with variations in frictional properties along the faults affecting only the seismic magnitude. The triggering process is controlled by a critical depth. Megathrust slip concentrated at depths shallower than the critical depth will favor normal displacement, while megathrust slip concentrated at depths deeper than the critical depth is likely to result in reverse motion. Our results thus provide a useful tool for predicting the activation of secondary faults and may have direct implications for tsunami hazard research.
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    Evanescent wave coupling in a geophysical system: Airborne acoustic signals from the Mw 8.1 Macquarie Ridge earthquake (2014)
    Wiley
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    Publication Date: 2014-01-15
    Description: [1]  Atmospheric low frequency sound, i.e., infrasound, from underwater events has not been considered thus far, due to the high impedance contrast of the water-air interface making it almost fully reflective. Here, we report for the first time on atmospheric infrasound from a large underwater earthquake (Mw 8.1) near the Macquarie Ridge, which was recorded at 1,325 km from the epicenter. Seismic waves coupled to hydro-acoustic waves at the ocean floor, after which the energy entered the SOund Fixing And Ranging (SOFAR) channel and was detected on a hydrophone array. The energy was diffracted by a sea mount and an oceanic ridge, which acted as a secondary source, into the water column followed by coupling into the atmosphere. The latter results from evanescent wave coupling and the attendant anomalous transparency of the sea surface for very low frequency acoustic waves.
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    Evaluation of UT/LS hygrometer accuracy by intercomparison during the NASA MACPEX mission (2014)
    Wiley
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    Publication Date: 2014-01-14
    Description: [1]  Acquiring accurate measurements of water vapor at the low mixing ratios (〈 10 ppm) encountered in the upper troposphere and lower stratosphere has proven to be a significant analytical challenge evidenced by persistent disagreements between high-precision hygrometers. These disagreements have caused uncertainties in the description of the physical processes controlling dehydration of air in the tropical tropopause layer and entry of water into the stratosphere, and have hindered validation of satellite water vapor retrievals. A 2011 airborne intercomparison of a large group of in situ hygrometers onboard the NASA WB-57F high-altitude research aircraft and balloons has provided an excellent opportunity to evaluate progress in the scientific community towards improved measurement agreement. In this work we intercompare the measurements from the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) and discuss the quality of agreement. Differences between values reported by the instruments were reduced in comparison to some prior campaigns, but were non-negligible and on the order of 20% (0.8 ppm). Our analysis suggests that unrecognized errors in the quantification of instrumental background for some or all of the hygrometers are a likely cause. Until these errors are understood, differences at this level will continue to somewhat limit our understanding of cirrus microphysical processes and dehydration in the tropical tropopause layer.
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    Martian Ionospheric Responses to Dynamic Pressure Enhancements in the Solar Wind (2014)
    Wiley
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    Publication Date: 2014-01-14
    Description: [1]  As a weakly magnetized planet, Mars ionosphere/atmosphere interacts directly with the shocked solar wind plasma flow. Even though many numerical studies have been successful in reproducing numerous features of the interaction process, these earlier studies focused mainly on interaction under steady solar wind conditions. Recent observations suggest that plasma escape fluxes are significantly enhanced in response to solar wind dynamic pressure pulses. In this study, we focus on the response of the ionosphere to pressure enhancements in the solar wind. Through modeling of two idealized events using a magnetohydrodynamics model, we find that the upper ionosphere of Mars responds almost instantaneously to solar wind pressure enhancements, while the collision dominated lower ionosphere (below ~150 km) does not have noticeable changes in density. We also find that ionospheric perturbations in density, magnetic field and velocity can last more than an hour after the solar wind returns to the quiet conditions. The topside ionosphere forms complicated transient shapes in response, which may explain unexpected ionospheric behaviors in recent observations. We also find that ionospheric escape fluxes do not correlate directly with simultaneous solar wind dynamic pressure. Rather, their intensities also depend on the earlier solar wind conditions. It takes a few hours for the ionospheric/atmospheric system to reach a new quasi-equilibrium state.
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    Degenerate thermal isomerizations of bicyclo[3.1.1]heptâ2âene: strategy and analysis (2014)
    Wiley
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    Publication Date: 2014-01-14
    Description: Bicyclo[3.1.1]heptâ2âene was first prepared and well identified in 1972. In 1974, the degenerate thermal isomerization involving 1â d â and 3â d âbicyclo[3.1.1]heptâ2âene was approached successfully, as one of the two deuteriumâlabeled structures was selected, heated, and equilibrated. There has been no further study of this degenerate isomerization. Here, a detailed outline of reaction trajectories for d 2 âlabeled bicyclo[3.1.1]heptâ2âenes is given that will establish the four independent kinetic parameters needed for 20 linking paths between six d 2 âspecies. The use of racemates, eliminating chiral separations and dissections, provides degenerate isomerization paths providing this method with general utility. Copyright © 2014 John Wiley & Sons, Ltd. The use of racemic doubly deuteriumâlabeled species can be used to obtain, for the first time, the full set of four unique rate constants for the degenerate rearrangements of d 2 âbicyclo[3.1.1]heptâ2âene. The expectations for deuterium isotope 1 Î effects on 13C NMR chemical shifts are tabulated and show that it can be used to quantify the isotopomers and monitor the reactions as they progress.
    Print ISSN: 0894-3230
    Electronic ISSN: 1099-1395
    Topics: Chemistry and Pharmacology , Physics
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    The influence of structured interfacial water on the photoluminescence of carboxyesterâterminated oligoâpâphenylene ethynylenes (2014)
    Wiley
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    Publication Date: 2014-01-14
    Description: Oligoâ p âphenylene ethynylenes have been shown to be useful for their sensing and biocidal capabilities. In this study, we examine the influence of interfacial water on the photophysical properties of a carboxyesterâsubstituted compound in this class through analysis of the aggregation with ionic surfactants, solvent isotope effects, and classical molecular dynamics simulations. The results of this study reveal that the presence of carboxyester groups leads to highly structured interfacial water and results in quenched fluorescence. In addition, the results indicate that hydrogen bonding is essential for aggregate formation. Copyright © 2014 John Wiley & Sons, Ltd. The influence of Hâbonding with aqueous solvent on the fluorescence of an oligoâpâphenylene ethynylene was explored using a combined experimental and computational approach. Fluorescence spectra and lifetimes were compared in deuterium oxide and water, and complexation with an ionic surfactant revealed striking changes in fluorescence and absorbance spectra. Classical molecular dynamics studies revealed and extended Hâbonding networks are involved in surfactant complexation. The results of this study reveal the importance of the carboxyester moiety and Hâbonding in fluorescent sensors.
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    Paired deformation sources of the Campi Flegrei caldera (Italy) required by recent (1980-2010) deformation history (2014)
    Wiley
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    Publication Date: 2014-01-15
    Description: [1]  We analyse 1980-2010 ground displacements, to discern similarities or differences between Campi Flegrei (CF) inflations and deflations and highlight possible anomalies in particular areas. We show that the deformation pattern can be decomposed into two stationary (constant over time, except for a mere scaling factor) parts; both of them are satisfied by simple deformation sources. A quasi-horizontal elongated crack (oriented NW to SE, and embedded in an elastic layered half-space at a depth of about 3600 m) satisfies large-scale deformation. All source parameters but potency (volume change) are constant over time. Residual deformation is confined to the area of the Solfatara fumarolic field and satisfied by a small spheroid located at about 1900 m in depth. Again, all source parameters but potency are constant over time. The histories of the two sources are somewhat similar but not equal, supporting the existence of a genuine local deformation source at Solfatara against the emergence of a mere distortion of large-scale deformation. Although reality is probably much more complex, our simple model explains 1980-2010 CF deformation within ground-displacement data errors, and is consistent with Solfatara geochemical conceptual models, fumarolic geochemical data, and seismic attenuation imaging of CF. The observation that the CF deformation pattern can be decomposed into two stationary parts is hardly compatible with several recent works which proposed multiple sources with different features acting in different periods, fluid injections implying ample changes of large-scale deformation pattern over time, complex spatial and temporal patterns of distributions of volumetric sources.
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    Magnetosonic wave excitation by ion ring distributions in the Earth's inner magnetosphere (2014)
    Wiley
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    Publication Date: 2014-01-15
    Description: [1]  Combining THEMIS wave and particle observations and a quantitative calculation of linear wave growth rate, we demonstrate that magnetosonic (MS) waves can be locally excited by ion ring distributions in the Earth's magnetosphere when the ion ring energy is comparable to the local Alfven energy. MS waves in association with ion ring distributions were observed by THEMIS A on 24 November 2010 in the afternoon sector, both outside the plasmapause where the wave spectrum varied with f LHR and inside the plasmapause where the wave frequency band remained nearly constant. Our plasma instability analysis in three different regions shows that higher and narrow frequency band MS waves are excited locally outside the plasmapause, and lower and broad frequency band MS waves are excited in the region where the density slightly increases. However, there is no evidence for wave excitation inside the plasmapause, and wave propagation from a distant source is needed to explain their existence. The simulation of the MS wave growth rate spectra during this event agrees reasonably well with the observed wave magnetic field power spectra. We also simulated a MS wave event on 19 October 2011 in the dusk sector, and found that the ion ring distribution with an ion ring energy slightly higher than the local Alfven energy can excite the typical broad band MS waves outside the plasmapause.
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    Magnetic aspect sensitivity of high-latitude E region irregularities measured by the RAX-2 CubeSat (2014)
    Wiley
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    Publication Date: 2014-01-15
    Description: [1]  The second Radio Aurora Explorer (RAX-2) satellite has completed more than 30 conjunction experiments with the AMISR chain of incoherent scatter radars in Alaska, and Resolute Bay, Canada. Coherent radar echoing occurred during four of the passes: three when E region electron drifts exceeded the ion acoustic speed threshold and one during HF heating of the ionosphere by the HAARP heater. In this paper, we present the results for the first three passes associated with backscatter from natural irregularities. We analyze, in detail, the largest drift case because the plasma turbulence was the most intense and because the corresponding ground-to-space bi-static scattering geometry was the most favorable for magnetic aspect sensitivity analysis. A set of data analysis procedures including interference removal, autocorrelation analysis, and the application of a radar beam deconvolution algorithm mapped the distribution of E region backscatter with 3 km resolution in altitude and ∼ 0.1 ∘ in magnetic aspect angle. To our knowledge, these are the highest resolution altitude-resolved magnetic aspect sensitivity measurements made at UHF frequencies in the auroral region. In this paper, we show that, despite the large electron drift speed of ∼ 1500 m/s, the magnetic aspect sensitivity of sub-meter scale irregularities is much higher than previously reported. The root-mean-square of the aspect angle distribution varied monotonically between 0.5-0.1 ∘ for the altitude range 100-110 km. Findings from this single but compelling event suggest that sub-meter scale waves propagating at larger angles from the main E  ×  B flow direction (secondary waves) have parallel electric fields that are too small to contribute to E region electron heating. It is possible anomalous electron heating in the auroral electrojet can be explained by (a) the dynamics of those sub-meter scale waves propagating in the E  ×  B direction (primary waves) or (b) the dynamics of longer wavelengths.
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    Sulfur-bearing phases detected by evolved gas analysis of the Rocknest aeolian deposit, Gale Crater, Mars (2014)
    Wiley
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    Publication Date: 2014-01-16
    Description: [1]  The Sample Analysis at Mars (SAM) instrument suite detected SO 2 , H 2 S, OCS and CS 2 from ~450-800 ºC during evolved gas analysis (EGA) of materials from the Rocknest aeolian deposit in Gale Crater, Mars. This was the first detection of evolved sulfur species from a martian surface sample during in situ EGA. SO 2 (~3-23  μ mol) is consistent with the thermal decomposition of Fe-sulfates or Ca-sulfites, or evolution/desorption from sulfur-bearing amorphous phases. Reactions between reduced sulfur phases such as sulfides and evolved O 2 or H 2 O in the SAM oven are another candidate SO 2 source. H 2 S (~41-109 nmol) is consistent with interactions of H 2 O, H 2 and/or HCl with reduced sulfur phases and/or SO 2 in the SAM oven. OCS (~1-5 nmol) and CS 2 (~0.2-1 nmol) are likely derived from reactions between carbon-bearing compounds and reduced sulfur. Sulfates and sulfites indicate some aqueous interactions, although not necessarily at the Rocknest site; Fe-sulfates imply interaction with acid solutions whereas Ca-sulfites can form from acidic to near-neutral solutions. Sulfides in the Rocknest materials suggest input from materials originally deposited in a reducing environment, or from detrital sulfides from an igneous source. The presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering. The possibility of both reduced and oxidized sulfur compounds in the deposit indicates a non-equilibrium assemblage. Understanding the sulfur mineralogy in Rocknest materials, which exhibit chemical similarities to basaltic fines analyzed elsewhere on Mars, can provide insight in to the origin and alteration history of martian surface materials.
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    Persistent flow acceleration within the interior of the Greenland Ice Sheet (2014)
    Wiley
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    Publication Date: 2014-01-16
    Description: [1]  We present surface velocity measurements from a high-elevation site located 140 km from the western margin of the Greenland Ice Sheet, and ~ 50 km into its accumulation area. Annual velocity increased each year from 51.78 ± 0.01 m yr -1 in 2009 to 52.92 ± 0.01 m yr -1 in 2012 – a net increase of 2.2 %. These data also reveal a strong seasonal velocity cycle of up to 8.1 % above the winter mean, driven by seasonal melt and supraglacial lake drainage. Sole et al. (2013) recently argued that ice motion in the ablation area is mediated by reduced winter flow following the development of efficient subglacial drainage during warmer, faster, summers. Our data complement this analysis and reveal a year-on-year increase in annual velocity above the ELA, where despite surface melt increasing, it is still sufficiently low to hinder the development of efficient drainage under thick ice.
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    Gradual Diffusion and Punctuated Phase Space Density Enhancements of Highly Relativistic Electrons: Van Allen Probes Observations (2014)
    Wiley
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    Publication Date: 2014-01-16
    Description: [1]  The dual-spacecraft Van Allen Probes mission has provided a new window into megaelectron Volt (MeV) particle dynamics in the Earth's radiation belts. Observations (up to E ~10 MeV) show clearly the behavior of the outer electron radiation belt at different time scales: months-long periods of gradual inward radial diffusive transport and weak loss being punctuated by dramatic flux changes driven by strong solar wind transient events. We present analysis of multi-MeV electron flux and phase space density (PSD) changes during March 2013 in the context of the first year of Van Allen Probes operation. This March period demonstrates the classic signatures both of inward radial diffusive energization as well as abrupt localized acceleration deep within the outer Van Allen zone (L ~4.0 ± 0.5). This reveals graphically that both “competing” mechanisms of multi-MeV electron energization are at play in the radiation belts, often acting almost concurrently or at least in rapid succession.
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    A 3400-year lacustrine paleoseismic record from the North Anatolian Fault, Turkey: Implications for bimodal recurrence behavior (2014)
    Wiley
    Details
    Publication Date: 2014-01-16
    Description: [1]  High-resolution physical, geochemical and geochronological analyses on the sedimentary sequence of Yeniçağa Lake, located in a fault-bounded basin along the North Anatolian Fault, reveal fingerprints of paleoearthquakes. A robust sediment chronology, spanning the last 3400 years, is constructed by radiocarbon dating and time-stratigraphical correlation with the precisely dated Sofular Cave speleothem record. Yeniçağa sedimentary sequence contains eleven seismically induced event deposits characterized by siliciclastic-enriched intervals. Some of the event deposits are also associated with implications of sudden lake deepening, which may be related to co-seismic subsidence. The paleoearthquake series having an average recurrence interval of ca. 260 years are interrupted by two possible seismic gaps of ca. 420 and 540 years.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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    Reply to Comment on ‘NAIRAS aircraft radiation model development, dose climatology, and initial validation’ (2014)
    Wiley
    Details
    Publication Date: 2014-01-16
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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    Melt water input from the Bering Glacier Watershed into the Gulf of Alaska (2014)
    Wiley
    Details
    Publication Date: 2014-01-17
    Description: [1]  The annual runoff from the melting of large glaciers and snow fields along the northern perimeter of the Gulf of Alaska is a critical component of marine physical and biological systems; yet, most of this freshwater is not measured. Here we show estimates of melt for the watershed that contains the largest and longest glacier in North America, the Bering Glacier. The procedure combines in-situ observations of snow and ice melt acquired by a long-term monitoring program, multi-spectral satellite observations and nearby temperature measurements. The estimated melt is 40 km 3 per melt season, ± 3.0 km 3 , observed over the decadal period, 2002-2012. As a result of climate change these estimates could increase to 60 km 3 per year by 2050. This technique and the derived melt coefficients can be applied to estimate melt from Alaska to Washington glaciers.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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