bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements
Authors: McCormick J. C. , Cohen M. B. , Gross N. C. , Said R. K. 
Published: March 2018

AbstractThe D region of the ionosphere (60–90 km altitude) is highly variable on timescales from fractions of a second to many hours, and on spatial scales up to many hundreds of kilometers. Very low frequency (VLF) and low‐frequency (LF) (3–30 kHz and 30–300 kHz) radio waves are guided to global distances by reflections from the ground and the D region. Therefore, information about its current state is encoded in received VLF/LF signals. VLF transmitters have been used in the past for D region studies, with ionospheric disturbances manifesting as perturbations in amplitude and/or phase. The return stroke of lightning is an impulsive VLF radiator, but unlike VLF transmitters, lightning events are distributed broadly in space allowing for much greater spatial coverage of the D region compared to VLF transmitter‐based remote sensing in addition to the broadband spectral advantage over the narrowband transmitters. The challenge is that individual lightning‐generated waveforms, or “sferics,” vary due to the lightning current parameters and uncertainty in the time/location information, in addition to D region ionospheric variability. These factors make it difficult to utilize the VLF/LF emissions from lightning in a straightforward manner. We describe a technique to recover the time domain and amplitude/phase spectra for both Bϕ and Br with high fidelity and consider the utility of our technique with ambient and varied ionospheric conditions. We demonstrate a technique to simulate sferics and infer a parameterized ionosphere with the Wait and Spies parameters (h
and β) offering all of the tools needed for a global measurement.
A Statistical Study of Spatial Variation of Relativistic Electron Precipitation Energy Spectra With Polar Operational Environmental Satellites
Authors: Shekhar S. , Millan R. M. , Hudson M. K. 
Published: March 2018

AbstractThe mechanisms that drive relativistic electron precipitation (REP) from the radiation belts can be better understood with a better knowledge of the particle energies involved. National Oceanic and Atmospheric Administration Polar Operational Environmental Satellites, being a network of multiple satellites, can provide multiple point spectral data over a long time period, including the Van Allen Probe's era. The number of energy channels is limited, but the particle detectors on Polar Operational Environmental Satellites have a narrow field of view allowing an investigation of bounce loss cone particles. We use the ratio of count rates in the E3 (>300 keV) and the P6 (>700 keV) channels as a parameter to define spectral hardness. Using this parameter, the spatial variation of spectral hardness of REP events was investigated. It was found that very soft events were mostly found in the dusk‐midnight‐early morning magnetic local time sectors and L∼ 5–7 while the hardest events were located in the postnoon sector peaking at L∼ 4–5. The hardest events peaked at lower L shells, and less than 20% were coincident with low‐energy (30–80 keV) proton precipitation. Further, around 70% of nightside REP coincident with proton precipitation was associated with stretched magnetic field lines indicating that curvature scattering may have been an important driver. Around 62% of nightside REP coincident with proton precipitation associated with relaxed magnetic field lines, suggesting a mechanism other than magnetic field curvature scattering, was highly energetic.
Deformation of the Pacific/North America Plate Boundary at Queen Charlotte Fault: The Possible Role of Rheology
Authors: ten Brink U. S. , Miller N. C. , Andrews B. D. , Brothers D. S. , Haeussler P. J. 
Published: March 2018

AbstractThe Pacific/North America (PA/NA) plate boundary between Vancouver Island and Alaska is similar to the PA/NA boundary in California in its kinematic history and the rate and azimuth of current relative motion, yet their deformation styles are distinct. The California plate boundary shows a broad zone of parallel strike slip and thrust faults and folds, whereas the 49‐mm/yr PA/NA relative plate motion in Canada and Alaska is centered on a single, narrow, continuous ~900‐km‐long fault, the Queen Charlotte Fault (QCF). Using gravity analysis, we propose that this plate boundary is centered on the continent/ocean boundary (COB), an unusual location for continental transform faults because plate boundaries typically localize within the continental lithosphere, which is weaker. Because the COB is a boundary between materials of contrasting elastic properties, once a fault is established there, it will probably remain stable. We propose that deformation progressively shifted to the COB in the wake of Yakutat terrane's northward motion along the margin. Minor convergence across the plate boundary is probably accommodated by fault reactivation on Pacific crust and by an eastward dipping QCF. Underthrusting of Pacific slab under Haida Gwaii occurs at convergence angles >14°–15° and may have been responsible for the emergence of the archipelago. The calculated slab entry dip (5°–8°) suggests that the slab probably does not extend into the asthenosphere. The PA/NA plate boundary at the QCF can serve as a structurally simple site to investigate the impact of rheology and composition on crustal deformation and the initiation of slab underthrusting.
An Integrated Study of the Eolian Dust in Pelagic Sediments From the North Pacific Ocean Based on Environmental Magnetism, Transmission Electron Microscopy, and Diffuse Reflectance Spectroscopy
Authors: Zhang Qiang , Liu Qingsong , Li Jinhua , Sun Youbin 
Published: March 2018

AbstractEolian dust is a major terrigenous component in North Pacific Ocean pelagic sediments and is an important recorder of Asian terrestrial environmental evolution and Northern Hemisphere atmospheric circulation. In order to extract and quantify wind‐borne mineral signals and develop a reliable eolian dust proxy for pelagic sediments, we investigated sediments from Ocean Drilling Program Hole 885A, North Pacific Ocean, by integrating results from environmental magnetism, transmission electron microscopy, and diffuse reflectance spectroscopy (DRS). Our results indicate that ferrimagnetic and antiferromagnetic minerals coexist in the sediments. The former includes biogenic magnetite, nano‐sized single domain (titano) magnetite inclusions embedded in silicate hosts, submicron vortex state magnetite, and ultrafine superparamagnetic maghemite. The latter includes hematite and goethite. Our results indicate that magnetic properties can be used to determine an overall trend of increased eolian dust inputs, with additional significant influence from biogenic and volcanogenic components. In contrast, a newly proposed parameter RelHm+Gt (combined hematite and goethite concentration) obtained from DRS measurements extracts precisely the eolian signal and precludes other components. Our DRS results indicate that hematite/goethite and siliceous fractions deposited at Hole 885A were jointly delivered to the North Pacific Ocean from Asian dust sources. Therefore, we suggest that RelHm+Gt is a reliable eolian dust proxy for pelagic sediments in this region.
Along‐Trench Structural Variations of the Subducting Juan de Fuca Plate From Multichannel Seismic Reflection Imaging
Authors: Han Shuoshuo , Carbotte Suzanne M. , Canales Juan Pablo , Nedimović Mladen R. , Carton Hélène 
Published: March 2018

AbstractTo characterize the along‐strike structural variations of the Juan de Fuca (JdF) Plate as it enters the Cascadia subduction zone, we present prestack time migrated multichannel seismic reflection images of the JdF Plate along a 400‐km‐long trench‐parallel transect extending from 44.3°N to 47.8°N. Beneath the 1.8–3.0‐km‐thick sediment cover, our data reveal basement topographic anomalies associated with a 1.2‐km‐high seamount and in the vicinity of propagator wakes (390–540‐m relief). Weak Moho reflections are imaged beneath the propagator wakes and coincide with reduced Vp in the lower crust and/or uppermost mantle. The inferred locations of propagator wakes in the downgoing plate collocate with some of the boundaries of episodic tremor and slip events. We propose that the structural and hydration heterogeneities associated with these features could lead to anomalous plate interface properties and contribute to episodic tremor and slip segmentation. Intracrustal reflections with apparent dips (20°–30°) consistent with subduction bending normal faults change near 45.8°N, from northward dipping reflections confined to the middle crust in the north to antithetic reflections through the crust in the south, coinciding with a Vp reduction in the lower crust. These observations indicate more extensive faulting deformation and associated hydration of the JdF Plate south of 45.8°N, which likely results from variations of slab dip and resistance to subduction across 46°N. Basement offsets and abrupt depth/amplitude changes in Moho reflections are imaged beneath the four major WNW trending strike‐slip faults that cross the Cascadia deformation front, providing strong evidence of a lower plate origin for these faults.
A Critical Appraisal of the “Day” Diagram
Authors: Roberts Andrew P. , Tauxe Lisa , Heslop David , Zhao Xiang , Jiang Zhaoxia 
Published: March 2018

AbstractThe “Day” diagram (Day et al., 1977,https://doi.org/10.1016/0031-9201(77)90108-X) is used widely to make inferences about the domain state of magnetic mineral assemblages. Based on theoretical and empirical arguments, the Day diagram is demarcated into stable “single domain” (SD), “pseudo single domain” (“PSD”), and “multidomain” (MD) zones. It is straightforward to make the necessary measurements for a sample and to plot results within the “domain state” framework based on the boundaries defined by Day et al. (1977,https://doi.org/10.1016/0031-9201(77)90108-X). We discuss 10 issues that limit Day diagram interpretation, including (1) magnetic mineralogy, (2) the associated magnetocrystalline anisotropy type, (3) mineral stoichiometry, (4) stress state, (5) surface oxidation, (6) magnetostatic interactions, (7) particle shape, (8) thermal relaxation, (9) magnetic particle mixtures, and (10) definitional/measurement issues. In most studies, these variables are unknowns and cannot be controlled for, so that hysteresis parameters for single bulk samples are nonunique and any data point in a Day diagram could result from infinite combinations of relevant variables. From this critical appraisal, we argue that the Day diagram is fundamentally ambiguous for domain state diagnosis. Widespread use of the Day diagram has also contributed significantly to prevalent but questionable views, including underrecognition of the importance of stable SD particles in the geological record and reinforcement of the unhelpful PSD concept and of its geological importance. Adoption of approaches that enable correct domain state diagnosis should be an urgent priority for component‐specific understanding of magnetic mineral assemblages and for quantitative rock magnetic interpretation.
Investigating the Mechanisms Associated With the Evolutions of Twin Extratropical Cyclones Over the Northwest Pacific Ocean in Mid‐January 2011
Authors: Fu Shen‐Ming , Sun Jian‐Hua , Li Wan‐Li , Zhang Yuan‐Chun 
Published: March 2018

AbstractTwin extratropical cyclones that appeared over the northwest Pacific Ocean in mid‐January 2011 experienced significantly different transitions: the northern cyclone dissipated rapidly, whereas the southern cyclone developed into an extreme example of an explosive (i.e., rapidly deepening) extratropical cyclone. This event was reasonably reproduced by the fifth‐generation Mesoscale Model, and its associated mechanisms were investigated using piecewise potential vorticity inversion and the Zwack‐Okossi vorticity budget. Main results are as follows. (i) The extratropical cyclone‐included twin cyclone event showed a Fujiwhara effect, during which the two cyclones orbited cyclonically about a midpoint, approached each other, and finally merged. The twin cyclone interactions enhanced the northern cyclone, but weakened the southern cyclone, by inducing warm advection and cold advection, respectively. (ii) Although upper level tropopause folding contributed the most to deepening of the twin cyclones, significant differences in their deepening rates were due predominantly to the contrast between lower level temperature advection and precipitation‐related latent heating. (iii) Stronger upper tropospheric positive absolute‐vorticity advection and warm advection associated with an upper level jet, and larger latent heating, made geostrophic vorticity of the southern cyclone increase more rapidly than that of the northern cyclone. (iv) Explosive deepening of the southern cyclone showed insensitive responses to its relative configuration with the upper level jet, whereas its rotation enhancement was faster when the cyclone was embedded within the upper level jet. (v) The upper level forcing had a greater influence on the large‐scale flow associated with the twin cyclones, whereas the middle‐level and lower level forcings were more dominant close to the cyclone core regions.
Investigation of a Generalized Nonlinear Form of the Complementary Principle for Evaporation Estimation
Authors: Liu Xiaomang , Liu Changming , Brutsaert Wilfried 
Published: March 2018

AbstractA generalized nonlinear form of the complementary principle for evaporation estimation was tested against evaporation measurements from seven flux stations in China representing different climatic conditions and ecosystem types. The method was implemented using routine meteorological data and pan evaporation measurements. The results indicate that the generalized nonlinear form with its regular boundary conditions can accurately estimate daily evaporation; its performance was somewhat better when the atmospheric evaporative demand was determined from the Penman equation than from pan evaporation. In addition, two formulations of the generalized nonlinear form, namely, a basic formulation and a more flexible quartic formulation, were compared. The comparisons indicate that the quartic formulation is not necessary and may only be needed possibly to accommodate unusual situations. The results should further advance and facilitate the application of the generalized nonlinear form to estimate daily evaporation; since only routine meteorological data are required as input, the method should be useful to generate long time series and their trends, wherever such data are available.
Effects of Different Stratospheric SO2 Injection Altitudes on Stratospheric Chemistry and Dynamics
Authors: Tilmes Simone , Richter Jadwiga H. , Mills Michael J. , Kravitz Ben , MacMartin Douglas G. , Garcia Rolando R. , Kinnison Douglas E. , Lamarque Jean‐Francois , Tribbia Joseph , Vitt Francis 
Published: March 2018

AbstractStrategically applied geoengineering is proposed to reduce some of the known side effects of stratospheric aerosol modifications. Specific climate goals could be reached depending on design choices of stratospheric sulfur injections by latitude, altitude, and magnitude. Here we explore in detail the stratospheric chemical and dynamical responses to injections at different altitudes using a fully coupled Earth System Model. Two different scenarios are explored that produce approximately the same global cooling of 2°C over the period 2042–2049, a high‐altitude injection case using 24 Tg SO2/year at 30 hPa (≈25‐km altitude) and a low‐altitude injection case using 32 Tg SO2/year injections at 70 hPa (between 19‐ and 20‐km altitude), with annual injections divided equally between 15°N and 15°S. Both cases result in a warming of the lower tropical stratosphere up to 10 and 15°C for the high‐ and low‐altitude injection case and in substantial increases of stratospheric water vapor of up to 2 and 4 ppm, respectively, compared to no geoengineering conditions. Polar column ozone in the Northern Hemisphere is reduced by up to 18% in March for the high‐altitude injection case and up to 8% for the low‐altitude injection case. However, for winter middle and high northern latitudes, low‐altitude injections result in greater column ozone values than without geoengineering. These changes are mostly driven by dynamics and advection. Antarctic column ozone in 2042–2049 does not recover from present‐day (2002–2009) values for both cases.
Effects of Landcover, Soil Property, and Temperature on Covariations of DOC and CDOM in Inland Waters
Authors: Li Jiwei , Yu Qian , Tian Yong Q. , Boutt David F. 
Published: March 2018

AbstractSignificant uncertainty exists in the estimation of dissolved organic carbon (DOC) concentration via remote sensing from colored dissolved organic matter (CDOM) absorption in inland waters pointing to a need for more process‐based understanding of the relationship between CDOM and DOC. In this study, we examine the factors affecting the covariations of DOC and CDOM using controlled experiments combined with field measurements at subbasin scale that have varying environmental and biological conditions. Our analysis reveals that the DOC:CDOM ratio is mainly related to landcover types. Higher DOC:CDOM linear regression slopes observed in evergreen leaf litter leachate suggest that CDOM comprises a smaller fraction of the DOC pool in evergreen sites in comparison to agricultural and deciduous leaf litter leachates. Given the same DOC concentrations, the range of CDOM levels from deciduous forest plant varied 3 times greater than that from other plant types. Results indicate that soil narrows the slope differences in the linear regressions of DOC from CDOM for all plant types (by 19% of evergreen, 18% of agriculture, and 77% of deciduous). Raising soil temperature by 5°C could double the range of DOC concentration and CDOM absorption for all scenarios. We present a mathematical model to estimate DOC concentration in freshwater environment via CDOM variations with reference to land cover and soil effects. The model was able to explain 95% of field measurements of multiple years in four subbasins. This improved understanding is critical for the remote sensing of DOC directly via observations of CDOM.
The Effects of Turbulence and Carbon Amendments on Nitrate Uptake and Microbial Gene Abundances in Stream Sediment
Authors: Tomasek Abigail A. , Barman Tusha D. , Wang Ping , Kozarek Jessica L. , Staley Christopher , Sadowsky Michael J. , Hondzo Miki 
Published: March 2018

AbstractUnderstanding the mechanisms governing nitrate uptake in aquatic ecosystems is paramount in mitigating the impact of increased anthropogenic nitrogen loading on water quality. An experimental laboratory flume with agricultural sediment and carbon‐amended sediment was used to evaluate the effect of turbulent fluid flow above rough sediment on oxygen uptake, nitrate uptake, and sediment bacterial gene abundances. The transport of dissolved oxygen to the sediment scaled with the friction velocity and sediment roughness height. Results demonstrated that nitrate uptake was mediated by turbulence levels, as quantified by friction velocity, above the sediment‐water interface. Facilitated nitrate uptake for amended and unamended sediment occurred under midrange of friction velocities from 0.75 to 1.2 cm/s, which corresponds to Reynolds numbers from 2,010 to 5,200. High turbulence levels in the water column above the sediment with friction velocities larger than 1.40 cm/s or Reynolds numbers larger than 5,500, as well as low turbulence with friction velocities less than 0.65 cm/s or Reynolds numbers less than 1,400, were determined to minimize nitrate uptake by the sediment. Carbon‐amended sediment had approximately 100 times greater nitrate uptake fluxes compared to field‐collected unamended sediment. For unamended sediment experiments, gene abundances significantly increased over the course of the experiments for midrange friction velocities; increases were not observed in the low and high friction velocities. Gene abundances did not significantly increase in any experiments for carbon‐amended sediment. Maintaining optimal turbulence levels could facilitate sustained nitrate uptake and reduce nitrogen loading to higher‐order streams in aquatic ecosystems.
Regional 3‐D Modeling of Ground Electromagnetic Field Due To Realistic Geomagnetic Disturbances
Authors: Ivannikova Elena , Kruglyakov Mikhail , Kuvshinov Alexey , Rastätter Lutz , Pulkkinen Antti 
Published: March 2018

AbstractDuring extreme space weather events the fluctuating geomagnetic field induces an electric field in the conducting Earth. This geoelectric field in turn generates currents in ground‐based technological systems, affecting their operation. Thus, calculation of the geoelectric field is a key step in predicting, assessing, and, potentially, forecasting the space weather impact on critical infrastructure. We present an approach and a tool for the first fully coupled regional three‐dimensional (3‐D) forward modeling of the electromagnetic field from far geospace down to the surface of the Earth. Applying the developed tool to the British Isles, we perform a 3‐D study in order to explore in detail the so‐called coastal effect (i.e., the anomalous behavior of the geoelectric field near the coasts) and to understand the limitations of the thin‐sheet model widely used for estimating this effect. For this purpose we compare the results of 3‐D and thin‐sheet modelings for plane wave source of excitation and different periods of variations. We conclude that for the British Isles the thin sheet is a reasonable approximation for periods longer than a few minutes. However, for shorter periods 3‐D modeling is essential. Another inference from the results of 3‐D modeling for plane wave and realistic sources is that for the British Isles the geoelectric field is distorted by the coastal effect practically everywhere on land. Finally, we compare modeled and observed geomagnetic fields at four observatories in the region during the first day of the Halloween storm in 2003 and discuss the results of this comparison.
Uncertainty Quantification of Medium‐Term Heat Storage From Short‐Term Geophysical Experiments Using Bayesian Evidential Learning
Authors: Hermans Thomas , Nguyen Frédéric , Klepikova Maria , Dassargues Alain , Caers Jef 
Published: March 2018

AbstractIn theory, aquifer thermal energy storage (ATES) systems can recover in winter the heat stored in the aquifer during summer to increase the energy efficiency of the system. In practice, the energy efficiency is often lower than expected from simulations due to spatial heterogeneity of hydraulic properties or non‐favorable hydrogeological conditions. A proper design of ATES systems should therefore consider the uncertainty of the prediction related to those parameters. We use a novel framework called Bayesian Evidential Learning (BEL) to estimate the heat storage capacity of an alluvial aquifer using a heat tracing experiment. BEL is based on two main stages: pre‐ and postfield data acquisition. Before data acquisition, Monte Carlo simulations and global sensitivity analysis are used to assess the information content of the data to reduce the uncertainty of the prediction. After data acquisition, prior falsification and machine learning based on the same Monte Carlo are used to directly assess uncertainty on key prediction variables from observations. The result is a full quantification of the posterior distribution of the prediction conditioned to observed data, without any explicit full model inversion. We demonstrate the methodology in field conditions and validate the framework using independent measurements.