bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Variational Merging Approach to the Spatial Description of Environmental Variables
Authors: Ulloa Jacinto , Samaniego Esteban , Campozano Lenin , Ballari Daniela 
Published: March 2018

AbstractHigh‐resolution images of environmental variables are highly valuable sources of information in research and environmental management. Obtaining spatially continuous information from ground observations is challenging due to the wide variety of factors that affect classical interpolation methods. While geostatistical methods have produced noteworthy results, they generally rely on important assumptions and strongly depend on the availability of observed data. In turn, satellite‐based or model‐based gridded images generally represent the global spatial structure of environmental variables but are subject to bias. With the objective of exploiting the benefits of both sources of information, we propose a new mathematical formulation to merge observed data with gridded images of environmental variables using partial differential equations in a variational setting. With a convenient functional, formed as the sum of two competing terms, two simultaneous goals are achieved: to improve the description of the spatial structure in maps generated by simple deterministic interpolation methods and to increase the reliability of satellite‐based or model‐based images. Either satellite‐based or model‐based information is included in a regularity term to provide the global spatial structure, while in situ data are included in a fidelity term. The resulting maps can be considered a merging of interpolated in situ data with satellite or model imagery. The method is first evaluated using simulated images generated by geostatistical simulation and then applied to actual temperature and precipitation data in selected regions in the Tropical Andes. The results indicate that the method is capable of generating realistic maps while performing well in terms of validation.
Time Series Forecasting of Air Quality Based On Regional Numerical Modeling in Hong Kong
Authors: Liu Tong , Lau Alexis K. H. , Sandbrink Kai , Fung Jimmy C. H. 
Published: March 2018

AbstractBased on prevailing numerical forecasting models (Community Multiscale Air Quality [CMAQ] model , Comprehensive Air Quality Model with Extensions, and Nested Air Quality Prediction Modeling System) and observations from monitoring stations in Hong Kong, we employ a set of autoregressive integrated moving average (ARIMA) models with numerical forecasts (ARIMAX) to improve the forecast of air pollutants including PM2.5, NO2, and O3. The results show significant improvements in multiple evaluation metrics for daily (1–3 days) and hourly (1–72 hr) forecast. Forecasts on daily 1‐hr and 8‐hr maximum O3are also improved. For instance, compared with CMAQ, applying CMAQ‐ARIMA reduces average root‐mean‐square errors (RMSEs) at all stations for daily average PM2.5, NO2, and O3in the next 3 days by 14.3–21.0%, 41.2–46.3%, and 47.8–49.7%, respectively. For hourly forecasts in the next 72 hr, reductions in RMSEs brought by ARIMAX using CMAQ are 18.2% for PM2.5, 32.1% for NO2, and 36.7% for O3. Large improvements in RMSEs are achieved for nonrural PM2.5and rural NO2using ARIMAX with three numerical models. Dynamic hourly forecast shows that ARIMAX can be applied for forecast of 7‐ to 72‐hr PM2.5, 4‐ to 72‐hr NO2, and 4‐ to 6‐hr O3. Besides applying ARIMAX for NO2, we recommend a mixed forecast strategy to ARIMAX for normal values of PM2.5and O3and employ numerical models for outputs above 75th percentile of historical observations. Our hybrid ARIMAX method can combine the advantage of ARIMA and numerical modeling to assist real‐time air quality forecasting efficiently and consistently.
Regional Regime‐Based Evaluation of Present‐Day General Circulation Model Cloud Simulations Using Self‐Organizing Maps
Authors: Schuddeboom Alex , McDonald Adrian J. , Morgenstern Olaf , Harvey Mike , Parsons Simon 
Published: March 2018

AbstractGlobal clusters are derived by applying the self‐organizing map technique to the Moderate Resolution Imaging Spectroradiometer cloud top pressure‐cloud optical thickness joint histograms. These cloud clusters are then used to classify Cloud Feedback Model Intercomparison Project Observation Simulator Package output from the HadGEM3 (Global Atmosphere version 7) atmosphere‐only climate model. Discrepancies in the Global Atmosphere version 7 representation of particular clusters can be established by examining the two sets of cluster's occurrence rate and radiative effect. The overall differences in the occurrence rates show major discrepancies in several of the clusters, resulting in a shift from five dominant clusters in Moderate Resolution Imaging Spectroradiometer (above 10% occurrence rate) to two dominant clusters in the model. A comparison of the geographic distributions of occurrence rate shows that the differences are strongly regional and unique to each cluster. While comparisons of the global mean longwave and shortwave cloud radiative effect (CRE) show strong agreement, examination of the CRE of individual cloud types reveals larger errors that highlight the role of compensating errors in masking model deficiencies. CRE data for each of the clusters is further partitioned into regions. This establishes that the bias associated with a cluster is highly variable globally, with no clusters showing consistent biases across all regions. Therefore, regional level phenomena likely play an important role in the creation of these errors.
Ash Metrics for European and Trans‐Atlantic Air Routes During the Eyjafjallajökull Eruption 14 April to 23 May 2010
Authors: Prata A. J. , Kristiansen N. , Thomas H. E. , Stohl A. 
Published: March 2018

AbstractMetrics for the risk associated with the threat that airborne volcanic ash particles pose to commercial jet aircraft are presented using simulations based on a Lagrangian particle transport and dispersion model driven by satellite measurements for the Eyjafjallajökull volcanic eruption, Iceland, for the period 14 April to 23 May 2010. The study utilizes a four‐dimensional data set of simulated ash concentrations together with European and trans‐Atlantic air routes to determine metrics corresponding to the total mass intercepted (defined as the dose), the mass interception rate (the dose rate), and the concentration (the exposure) over time (the dosage) that a jet aircraft encounters along the air route. The methodology can be used as a logistical and flight planning tool in a forecast mode and also in hindcast mode to assess the extent of airline fleet exposure to ash following an eruption, thereby providing operators with information useful for flight safety.
Constructional Volcanic Edifices on Mercury: Candidates and Hypotheses of Formation
Authors: Wright Jack , Rothery David A. , Balme Matthew R. , Conway Susan J. 
Published: March 2018

AbstractMercury, a planet with a predominantly volcanic crust, has perplexingly few, if any, constructional volcanic edifices, despite their common occurrence on other solar system bodies with volcanic histories. Using image and topographical data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, we describe two small (<15‐km diameter) prominences with shallow summit depressions associated with volcanically flooded impact features. We offer both volcanic and impact‐related interpretations for their formation, and then compare these landforms with volcanic features on Earth and the Moon. Though we cannot definitively conclude that these landforms are volcanic, the paucity of constructional volcanic edifices on Mercury is intriguing in itself. We suggest that this lack is because volcanic eruptions with sufficiently low eruption volumes, rates, and flow lengths, suitable for edifice construction, were highly spatiotemporally restricted during Mercury's geological history. We suggest that volcanic edifices may preferentially occur in association with late‐stage, postimpact effusive volcanic deposits. The European Space Agency/Japan Aerospace Exploration Agency BepiColombo mission to Mercury will be able to investigate further our candidate volcanic edifices; search for other, as‐yet unrecognized edifices beneath the detection limits of MESSENGER data; and test our hypothesis that edifice construction is favored by late‐stage, low‐volume effusive eruptions.
Climate Forcing of Ripple Migration and Crest Alignment in the Last 400 kyr in Meridiani Planum, Mars
Authors: Fenton Lori K. , Carson Helen C. , Michaels Timothy I. 
Published: March 2018

AbstractThe plains ripples of Meridiani Planum are the first paleo‐aeolian bedforms on Mars to have had their last migration episode constrained in time (to ~50–200 ka). Here we test how variations in orbital configuration, air pressure, and atmospheric dust loading over the past 400 kyr affect bedform mobility and crest alignment. Using the National Aeronautics and Space Administration Ames Mars Global Climate Model, we ran a series of sensitivity tests under a number of different conditions, seeking changes in wind patterns relative to those modeled for present‐day conditions. Results indicate that enhanced sand drift potential in Meridiani Planum correlates with (1) high axial obliquity, (2) a longitude of perihelion (Lp) near southern summer solstice, and (3) a greater air pressure. The last pulse of westward plains ripple migration likely occurred during the most recent obliquity (relative) maximum, from 111 to 86 ka. At Lp coinciding with southern summer solstice, the Mars Global Climate Model produced a westward resultant drift direction, consistent with the observed north‐south plains ripple crest alignment. However, smaller superposed ripples, aligned NNE‐SSW, are consistent with a strengthened northern summer Hadley return flow, occurring when Lp coincided with northern summer solstice. The superposed NNE‐SSW ripples likely formed as the axial obliquity decreased during the last relative maximum and Lp swung toward northern summer, from 86 to 72 ka. The timeline of bedform activity supports the proposed sequence of CO2 sequestration in the south polar residual cap over the past 400 kyr.
Paleopole Reconstruction of Martian Magnetic Field Anomalies
Authors: Thomas Paul , Grott Matthias , Morschhauser Achim , Vervelidou Foteini 
Published: March 2018

AbstractThe crust of Mars shows strong remanent magnetization, which was likely acquired during the early phases of planetary evolution when a core dynamo still operated. The direction of the field responsible for magnetizing the crust holds clues to the working of the dynamo and the rotational dynamics of the planet. By analyzing individual crustal magnetic field anomalies and with the aid of additional assumptions, the field orientations can be reconstructed. We have implemented an Equivalent Source Dipole method to determine the main field orientation during magnetization, assuming that the considered anomalies are unidirectionally magnetized without making specific assumptions about the source geometry. The available data are fit in a least squares sense, and the method yields confidence intervals for the admissible paleopole locations. The method was applied to six crustal magnetic field anomalies, two of which require a south pole in the northern hemisphere, while three indicate a south pole in the southern hemisphere. This implies that polar reversals took place at least once in Martian history. Furthermore, one of the investigated anomalies requires a south pole at equatorial to midlatitudes, indicating that a significant amount of true polar wander must have occurred on Mars. Finally, tests with synthetic data indicate that admissible paleopole locations typically spread across at least 25% of the planet, which may partially explain the scatter found in previously published paleopole studies.
Quantifying the Effects of Snowpack on Soil Thermal and Carbon Dynamics of the Arctic Terrestrial Ecosystems
Authors: Lyu Zhou , Zhuang Qianlai 
Published: March 2018

AbstractSnow insulation effects modify soil and carbon dynamics in northern middle to high latitudes (45°–90°N). This study incorporates these effects by introducing a snow model into an existing soil thermal model in a biogeochemistry modeling framework, the Terrestrial Ecosystem Model. The coupled model is used to quantify snow insulation effects on carbon and soil thermal dynamics in 45°–90°N region for the historical period (2003–2010) and the future period (2017–2099) under two climate scenarios. The revised model captures the snow insulation effects and improves the estimates of soil thermal dynamics and the land freeze‐thaw as well as terrestrial ecosystem carbon dynamics. Historical mean cold‐season soil temperature at 5 cm depth driven with satellite‐based snow data is 6.4°C warmer in comparison with the original model simulation. Frozen area in late spring is estimated to shrink mainly over eastern Siberia, in central to eastern Europe, and along southern Canada in November. During each nongrowing season in the historical period, 0.41 Pg more soil C is released due to warmer soil temperature estimated using the new model. During 2003–2010, the revised model estimates that the region accumulated 0.86 Pg less C due to weaker gross primary production, leading to a regional C loss at 0.19 PgC/year. The revised model projects that the region will lose 38–51% permafrost area by 2100 and continue to be a C source under the low‐emission scenario (Representative Concentration Pathway 2.6) but to be gradually transitioning into a weak sink in the latter half of the 21st century under the high‐emission scenario (Representative Concentration Pathway 8.5).
Sediment Fingerprinting Suggests Differential Suspended Particulate Matter Formation and Transport Processes Across Hydrologic Regimes
Authors: Rose L. A. , Karwan D. L. , Aufdenkampe A. K. 
Published: March 2018

AbstractSediment fingerprinting techniques are increasingly used to characterize the sources and transport processes of particulate materials in surface waters. However, consensus on the use of biologically labile compounds such as organic carbon and nitrogen for sediment fingerprinting remains elusive. We used multiple biogeochemical characteristics of suspended particulate material (SPM) to characterize the differences in formation and transport processes of these materials during storm events ranging in size from small seasonal rainfall events to hurricanes and tropical storms in a small mid‐Atlantic watershed. During storms, particle surface area, percent organic C, percent organic N, percent Fe, and percent Al of SPM decreased with increasing discharge; these contents were lowest during the extreme events Hurricane Sandy, Hurricane Irene, and Tropical Storm Lee. Conversely, SPM C:N values during these storms were among the highest of all samples, and C:N generally increased with discharge. End‐member mixing analysis indicated that organic matter and metal contents of SPM collected during high event flows were well described by materials collected from erosional source areas throughout the watershed, while SPM collected during low event flows fell outside of the end‐member mixing space. This suggests that physical transport processes govern SPM export primarily from surface and fluvial areas during high flows, while in‐stream biogeochemical processes become increasingly important contributors to SPM at lower flows.
Orbitally Forced Hyperstratification of the Oligocene South Atlantic Ocean
Authors: Liebrand Diederik , Raffi Isabella , Fraguas Ángela , Laxenaire Rémi , Bosmans Joyce H. C. , Hilgen Frederik J. , Wilson Paul A. , Batenburg Sietske J. , Beddow Helen M. , Bohaty Steven M. , Bown Paul R. , Crocker Anya J. , Huck Claire E. , Lourens Lucas J. , Sabia Luciana 
Published: March 2018

AbstractPelagic sediments from the subtropical South Atlantic Ocean contain geographically extensive Oligocene ooze and chalk layers that consist almost entirely of the calcareous nannofossil Braarudosphaera. Poor recovery and the lack of precise dating of these horizons in previous studies has limited the understanding of the number of acmes, their timing and durations, and therefore their likely cause. Here we present a high‐resolution, astronomically tuned stratigraphy of Braarudosphaera oozes (29.5–27.9 Ma) from Ocean Drilling Program Site 1264 in the southeastern Atlantic Ocean. We identify seven episodes with highly abundant Braarudosphaera. Four of these acme events coincide with maxima and three with minima in the ~110 and 405‐kyr paced eccentricity cycles. The longest lasting acme event corresponds to a pronounced minimum in the ~2.4‐Myr eccentricity cycle. In the modern ocean, Braarudosphaera occurrences are limited to shallow marine and neritic settings, and the calcified coccospheres of Braarudosphaera are probably produced during a resting stage in the algal life cycle. Therefore, we hypothesize that the Oligocene acmes point to extensive and episodic (hyper) stratified surface water conditions, with a shallow pycnocline that may have served as a virtual seafloor and (partially/temporarily) prevented the coccospheres from sinking in the pelagic realm. We speculate that hyperstratification was either extended across large areas of the South Atlantic basin, through the formation of relatively hyposaline surface waters, or eddy contained through strong isopycnals at the base of eddies. Astronomical forcing of atmospheric and/or oceanic circulation could have triggered these conditions through either sustained rainfall over the open ocean and adjacent land masses or increased Agulhas Leakage.
Diagenetic Attenuation of Carbon Isotope Excursion Recorded by Planktic Foraminifers During the Paleocene‐Eocene Thermal Maximum
Authors: Kozdon Reinhard , Kelly D. Clay , Valley John W. 
Published: March 2018

AbstractEarth surface temperatures warmed by ~5 °C during an ancient (~56 Ma) global warming event referred to as the Paleocene‐Eocene thermal maximum (PETM). A hallmark of the PETM is a carbon isotope excursion (CIE) signaling the release of massive amounts of 13C‐depleted carbon into the ocean‐atmosphere system, but substrate‐specific differences in the CIE magnitude are a source of uncertainty for estimating the mass of carbon emitted. Here we report that secondary ion mass spectrometry (SIMS)‐based in situ measurements of δ13C in minute (7 μm) domains of planktic foraminifer shells (Ocean Drilling Program Site 865, central Pacific Ocean) yield a CIE that is ~2‰ larger than that delineated by conventional “whole‐shell” δ13C values for this same PETM record. SIMS‐based measurements on diagenetic crystallites yield δ13C values (~2.8‰) that fall between those of pre‐CIE and CIE planktic foraminifer shells, indicating that the crystallites are an amalgamated blend of pre‐CIE and CIE carbonates. This suggests that diagenesis shifts the whole‐shell δ13C compositions of pre‐CIE and CIE foraminifers found in samples straddling the base of the PETM interval toward the intermediate δ13C composition of the crystallites, thereby dampening the amplitude of the isotopic excursion. The diagenetic process envisioned would be most consequential for carbonate‐rich PETM records that have suffered chemical erosion of pre‐CIE carbonate. Given that the domains targeted for SIMS analysis may not be pristinely preserved, we consider the 4.6‰ excursion in our SIMS‐based δ13C record to be a conservative estimate of the full CIE for surface ocean dissolved inorganic carbon.
Varactor‐Tunable Frequency Selective Surface With an Appropriate Embedded Bias Network
Authors: Lin Baoqin , Guo Jianxin , Chu Peng , Li Nan , Wu Lan , Liu Xiangwen 
Published: March 2018

AbstractIn this work, a varactor‐tunable frequency selective surface (FSS) is proposed; it is based on a common FSS composed of annular ring slot cells, in which four varactors are loaded on each annular ring slot to dynamically tune its resonant frequency in real time. In addition, an appropriate embedded bias network is added to introduce a same direct current bias voltage for each varactor. Numerical simulations demonstrate that the resonant‐frequency of the proposed FSS can be tuned over a 77.2% wide frequency range from 2.73 to 6.16 GHz by altering the capacitance of the varactors from 1.0 to 0.1 pF; moreover, the embedded bias network has little effect on the band‐pass response, and the minimum of the reflection coefficients is less than −24 dB at all times. Finally, one effective experimental validation is carried out. The proposed tunable FSS possesses the merits of wide tuning range and high transmittance; thus, it has great potential applications in the design of tunable radomes or adaptive screening of unwanted wireless transmissions.
Lightning Sferics: Analysis of the Instantaneous Phase and Frequency Inferred From Complex Waveforms
Authors: Liu Zhongjian , Koh Kuang Liang , Mezentsev Andrew , Enno Sven‐Erik , Sugier Jacqueline , Fullekrug Martin 
Published: March 2018

AbstractAnalysis of very low frequency lightning waveforms, or radio sferics, can contribute to research into lower ionosphere perturbations and the corresponding atmospheric chemistry. Lightning waveforms can also be characterized on the basis of their propagation distance from receivers in order to study radio wave propagation. A bank of average waveforms, that is, the waveform bank, <1,000 km with a spatial resolution of 10 km has been produced, based on the lightning waveforms recorded in Europe on 8 August 2014. These average lightning waveforms at different distances exhibit a sequence of consecutive maxima resulting from ionospheric reflections, named sky waves. The spectral waveform bank shows a sequence of consecutive modal maxima at different frequencies depending on distance. The Hilbert transform is applied to produce complex lightning waveforms, which provide additional information to the original real waveforms alone, that is, the instantaneous phase and frequency. The time differences calculated from the instantaneous phases of complex lightning waveforms give the minimum arrival time difference error when compared to other analyzed signal processing methods. The derivative of the instantaneous phase, that is, the instantaneous frequency, represents the amplitude‐weighted average of frequency components at maximum amplitude according to theory and numerical simulation. In real experiments, the instantaneous frequency can be understood as the median value of the real frequency distribution calculated at maximum amplitude. It is found that the instantaneous frequencies at maximum amplitudes are distance dependent. This finding might enable the development of a novel method to determine lightning distances in the future.
TMz/TEz Vector Potentials Due to an Arbitrarily Oriented Dipole in 3‐D Space in the Presence of an Infinite Dielectric Cylinder
Authors: Neese J. W. , Jackson D. R. , Zheng Y. , Thomsen L. A. 
Published: March 2018

AbstractThis manuscript provides a new formulation for the classic electromagnetic scattering problem of a point dipole source in the presence of an infinite lossy dielectric cylinder embedded within a lossy space. The formulation is in terms of the TMz and TEz vector potential components (scalar potentials) Az and Fz for an arbitrary dipole orientation. A new Bessel function identity, apparently derived here for the first time, shows that the new solution is equivalent to the previous dyadic vector wave function solutions that solve for the electric and magnetic fields directly. Expressions for the scattered potential coefficients, for a dipole inside or outside the cylinder, can be reduced to a linear set of two equations that has a simple closed‐form solution. The new potential formulation should find application in the numerical solution of various problems in electromagnetics and geophysics involving tunnels or other structures that can be modeled as cylinders.