bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wake Potential and Wake Effects on the Ionospheric Plasma Density Measurements With Sounding Rockets
Authors: Paulsson J. J. P. , Spicher A. , Clausen L. B. N. , Moen J. I. , Miloch W. J. 
Published: October 2018

AbstractA new method is developed to systematically study variations in the electrostatic potential around a spinning spacecraft in flowing plasma. We argue that the main modulation of this potential is due to wake leading to different depletions in electron and ion densities. This wake potential can be calculated with the help of electric currents measured by Langmuir probes mounted on a boom system and the assumption of Boltzmann‐distributed electrons. The wake position is determined with the electric field measurements. We apply this method to data from the Investigation of Cusp Irregularities 3 ionospheric sounding rocket and find the observed wake to be larger than expected from the flow velocity and the Mach cone formation, which can be explained by the presence of booms. By using the wake potential to filter the rocket data, we show that this method is robust during highly dynamic plasma conditions and that it can be used to improve the quality of plasma density measurements and reduce the wake effects.
Crustal Magmatism and Deformation Fabrics in Northeast Japan Revealed by Ambient Noise Tomography
Authors: Chen Kai‐Xun , Gung Yuancheng , Kuo Ban‐Yuan , Huang Tzu‐Ying 
Published: October 2018

AbstractMapping both isotropic and anisotropic velocity structures of the crust provides insight into the dominant mechanisms that produce the deformation. We performed ambient noise tomography for shear velocity Vs in the Tohoku region, Japan, where plate kinematics remains simple as the Pacific plate is subducting under the Okhotsk plate. Cross‐correlation functions were retrieved from Hi‐net recordings and phase velocities of 3–16 s were measured, followed by a one‐step, wavelet‐based multiscale inversion for both Vs and its azimuthal anisotropy. The isotropic model shows that high Vs anomalies underlie the Cretaceous aged Kitakami and Abukuma Mountains from shallow crust to lower crust. Low Vs is found to track the active volcanoes with the strongest anomalies concentrated at roughly 10 km depth, which we interpret as the shallow magma reservoirs of the Quaternary magmatic system. The resolved azimuthal anisotropy exhibits a switch of anisotropy in the upper crust from island‐parallel to a random or suppressed state in 5–15 km depth interval and back to island‐parallel. The island‐parallel fast direction may map the structural fabrics of the crustal deformation, and the spatial correlation between velocity and anisotropy patterns suggests that continuous volcanic activities and magma ponding disrupt the otherwise consistent fabrics in the upper crust. Below 20 km depth, the anisotropy turns to convergence‐parallel, which may result from shearing either imposed by the return flow in the mantle wedge or frozen‐in from the last stage of extension of the continental margin that opened the Sea of Japan.
Regional Short‐Term Forecasting of Ionospheric TEC and Scintillation
Authors: Grzesiak Marcin , Cesaroni Claudio , Spogli Luca , De Franceschi Giorgiana , Romano Vincenzo 
Published: October 2018

AbstractWe describe a novel empirical technique for the regional, short‐term (from seconds to minutes) forecasting of both TEC (total electron content) and scintillation indices on Global Navigation Satellite System signals. To provide TEC‐forecasted values, the method exploits the continuity equation in the conservative form, while the continuity equation with source term added is used in the case of scintillation forecasting. The performance of the model is investigated, resulting to be satisfactory when applied at equatorial latitudes in Brazil and during postsunset hours, when scintillation phenomena are more likely to occur. Five days affected by strong amplitude scintillation events (S4 > 0.7) are used to test the model performance and evaluate the model accuracy. In addition, the performance of the amplitude scintillation forecasting is evaluated by leveraging on larger statistics. On the average, the forecasting accuracy, in terms of standard deviation of the distributions of the differences between forecasted and actual values, is about 5% for TEC and 15–20% for scintillation parameters.
Complexity of Marine CO2 System Highlighted by Seasonal Asymmetries
Authors: Woosley Ryan J. 
Published: October 2018

AbstractThe complexities of the marine carbon cycle continue to be uncovered. In this issue, Fassbender et al. (2018, https://doi.org/10.1029/2017GB005855) combined measured surface ocean partial pressure of carbon dioxide (pCO2) with model predictions of increases in dissolved inorganic carbon to explore seasonal pCO2 changes. They find that when seasonal cycles of other variables (temperature, salinity, total alkalinity, and dissolved inorganic carbon) are maintained to climatological means, seasonal amplitudes of pCO2 are affected asymmetrically. Thus, even ignoring other natural or climate change factors, the assumption that the seasonal cycle of pCO2 will be preserved may not be valid. Fassbender et al. (2018) intentionally ignore the influence of other variables such as a global warming signal in order to hone in explicitly on carbon system dynamics. The results show that when studying CO2 fluxes, especially into the future, the full seasonal cycle must be investigated, as what happens at one time of year may not translate to the rest of the year. Practically, this means that in order to fully understand the marine carbon cycle and its control over atmospheric CO2 levels, there is an urgent need for more surface pCO2 data covering more months of the year particularly in the polar oceans that are highly seasonally biased.
Submarine Deep‐Water Lava Flows at the Base of the Western Galápagos Platform
Authors: Anderson Molly , Wanless V. Dorsey , Schwartz Darin M. , McCully Emma , Fornari Daniel J. , Jones Max P. , Soule S. Adam 
Published: October 2018

AbstractTo investigate the initial phases of magmatism at the leading edge of the upwelling mantle plume, we mapped, photographed, and collected samples from two long, deep‐water lava flows located at the western base of the Galápagos Platform using the remotely operated vehicle Hercules. Lavas were recovered from four areas on the seafloor west of Fernandina volcano, including the western flow fronts of two deep‐water flows, heavily sedimented terrain between the two flows, and the eastern, shallower end of one flow. The sediment cover and morphologies are distinct between the western flow fronts and the eastern region based on seafloor imagery, suggesting that the long lava flows are not a single eruptive unit. Major and trace element concentrations reveal both tholeiitic and alkalic compositions and support the interpretation that multiple eruptive units comprise the deep‐water flows. Alkalic lavas have higher [La/Sm]N ratios (2.05–2.12) and total alkali contents (5.18–5.40) compared to tholeiitic lavas, which have [La/Sm]N ratios ranging from 1.64 to 1.68 and total alkali contents ranging from 3.07 to 4.08 wt%. Radiogenic isotope ratios are relatively homogeneous, suggesting a similar mantle source. We use petrologic models to assess three alternative mechanisms for the formation of the alkalic magmas: (1) high‐pressure crystallization of clinopyroxene, (2) mixing of high silica and mafic magmas, and (3) variable extents of melting of the same mantle source. Our modeling indicates that the alkalic samples form from lower extents of melting compared to the tholeiitic lavas and suggests that the deep‐water alkalic lavas are analogous to the initial, preshield building phase observed south of Hawaii and at the base of Loihi Seamount.
Saturn's Innermost Radiation Belt Throughout and Inward of the D‐Ring
Authors: Kollmann P. , Roussos E. , Kotova A. , Regoli L. , Mitchell D. G. , Carbary J. , Clark G. , Krupp N. , Paranicas C. 
Published: October 2018

AbstractCassini discovered Saturn's innermost radiation belt during the end of its mission. The belt is populated with relativistic protons, probably up to the trapping limit of ≈20 GeV. It extends from Saturn's dense atmosphere into and throughout the D‐ring. The A–C rings separate this belt entirely from the previously known radiation belts, suggesting that the innermost radiation belt is populated entirely via cosmic ray albedo neutron decay. We find that the proton pitch angle distributions are consistent with being shaped by losses to the D‐ring and the upper atmosphere rather than, for example, wave‐particle interactions. This supports that the main loss process of this new radiation belt is energy loss in neutral material, different from Saturn's other radiation belts. This property constrains the overall scale height of Saturn's exosphere to <700 km and the average D‐ring water molecule column density to being about 1 order of magnitude below the Enceladus gas torus.
Ring Shadowing Effects on Saturn's Ionosphere: Implications for Ring Opacity and Plasma Transport
Authors: Hadid L. Z. , Morooka M. W. , Wahlund J.‐E. , Moore L. , Cravens T. E. , Hedman M. M. , Edberg N. J. T. , Vigren E. , Waite J. H. , Perryman R. , Kurth W. S. , Farrell W. M. , Eriksson A. I. 
Published: October 2018

AbstractWe present new results obtained by the Radio and Plasma Wave Science Langmuir probe on board Cassini during the Grand Finale. The total direct current sampled by the Langmuir probe at negative bias voltage is used to study the effect of the ring shadows on the structure of the Kronian topside ionosphere. The D and C rings and the Cassini Division are confirmed to be optically thin to extreme ultraviolet solar radiation. However, different responses from the opaque A and B rings are observed. The edges of the A ring shadow are shown to match the A ring boundaries, unlike the B ring, which indicates variable responses to the B ring shadow. We show that the variable responses are due to the ionospheric plasma, more precisely to the longer chemical lifetime of H+ compared to
and
, suggesting that the plasma is transported from the sunlit region to the shadowed one in the ionosphere.
Warm Arctic, Increased Winter Sea Ice Growth?
Authors: Petty Alek A. , Holland Marika M. , Bailey David A. , Kurtz Nathan T. 
Published: October 2018

AbstractWe explore current variability and future projections of winter Arctic sea ice thickness and growth using data from climate models and satellite observations. Winter ice thickness in the Community Earth System Model's Large Ensemble compares well against thickness estimates from the Pan‐Arctic Ice Ocean Modeling and Assimilation System and CryoSat‐2, despite some significant regional differences—for example, a high thickness bias in Community Earth System Model's Large Ensemble in the western Arctic. Differences across the available CryoSat‐2 thickness products hinder more robust validation efforts. We assess the importance of the negative conductive feedback of sea ice growth (thinner ice grows faster) by regressing October atmosphere/ice/ocean conditions against winter ice growth. Our regressions demonstrate the importance of a strong negative conductive feedback process in our current climate, which increases winter growth for thinner initial ice, but indicate that later in the 21st century this negative feedback is overwhelmed by variations in the fall atmosphere/ocean state.
The Heat of the Flow: Thermal Equilibrium in Gravitational Mass Flows
Authors: Fischer Jan‐Thomas , Kaitna Roland , Heil Kilian , Reiweger Ingrid 
Published: October 2018

AbstractFlow behavior and mobility of gravitational mass flows such as rapid‐moving landslides, ice‐rock avalanches, or snow avalanches strongly depend on the material temperature. Flow temperature dependence is particularly pronounced for materials with high homologous temperatures, such as snow or ice under natural conditions. The interplay between mechanisms driving the temperature evolution in flowing geomaterials remain largely unknown. Here we present laboratory experiments in a rotating drum, measuring the temperature evolution of steadily flowing snow at ambient temperatures below freezing. After initial heating the flow reaches thermal equilibrium. To describe the thermal energy balance, we derive an analytical model, taking into account frictional energy dissipation and heat exchange with the ambient medium. The model accurately captures the measured temperature evolution and predicts the observed thermal equilibrium, where ambient cooling compensates frictional heating. It allows to determine heat transfer coefficients and total shear stresses of the flowing material based on measured temperatures.
The Equilibrium Climate Response to Sulfur Dioxide and Carbonaceous Aerosol Emissions From East and Southeast Asia
Authors: Grandey Benjamin S. , Yeo Lik Khian , Lee Hsiang‐He , Wang Chien 
Published: October 2018

AbstractWe investigate the equilibrium climate response to East and Southeast Asian emissions of carbonaceous aerosols and sulfur dioxide, a precursor of sulfate aerosol. Using the Community Earth System Model with the Community Atmosphere Model version 5.3, we find that anthropogenic aerosol emissions from East and Southeast Asia exert a global mean net radiative effect of −0.49 ± 0.04 W/m2. Approximately half of this cooling effect can be attributed to anthropogenic sulfur dioxide emissions. The aerosol emissions drive widespread cooling across the Northern Hemisphere. Strong suppression of precipitation occurs over East and Southeast Asia, indicating that anthropogenic aerosol emissions may impact water resources locally. However, in contrast to previous research, we find no clear evidence of remote effects on precipitation over Australia and West Africa. We recommend further investigation of possible remote effects.
Assessing Quasi‐Periodicities in Jovian X‐Ray Emissions: Techniques and Heritage Survey
Authors: Jackman C. M. , Knigge C. , Altamirano D. , Gladstone R. , Dunn W. , Elsner R. , Kraft R. , Branduardi‐Raymont G. , Ford P. 
Published: October 2018

AbstractJupiter's auroral X‐rays are rather mysterious, with an unknown driver, and several previous reports of individual cases of quasi‐periodic emission. In this work we revisit heritage X‐ray data sets from the 1990s to 2015 and apply robust significance testing of emerging quasi‐periodicities, seeking to understand the robustness and regularity of previously reported quasi‐periodic emissions. Our analysis incorporates the use of the Rayleigh test as an alternative to Lomb‐Scargle analysis or Fast Fourier Transforms, where Rayleigh is particularly suited to a time‐tagged data set of sparse counts such as is common for jovian X‐ray data. Furthermore, the analysis techniques that we present (including Rayleigh testing and Monte Carlo simulation) can be applied to any time‐tagged data set. The code to conduct such analysis is released as supplementary information to accompany this paper. The five most significant (p value <0.01) quasi‐periods from Jupiter's northern auroral region have periods ranging from ~8.0 to 45.96 min, and the two most significant (p value <0.01) quasi‐periods from the south have periods of ~14.1 and ~34.9 min. The selection of a restrictive hot spot source region seems to be critical for detecting quasi‐periodic emission, suggesting that the site of pulsations may be spatially localized. Periods vary from one Jupiter rotation to the next in one long observation, and the north and south are shown to pulse independently in another conjugate observation. These results have important implications for understanding the driver of jovian X‐ray emission.
Multiinstrument Studies of Thermospheric Weather Above Alaska
Authors: Conde M. G. , Bristow W. A. , Hampton D. L. , Elliott J. 
Published: October 2018

AbstractWe describe how space weather impacts thermospheric winds above Alaska, using an array of ground and space‐based instrumentation. Forcing of the thermosphere is observed using coherent (Super Dual Auroral Radar Network) and incoherent (Poker Flat Incoherent Scatter Radar) radars to measure ion convection, plus ground and space‐based imagers to map auroral precipitation. The primary emphasis in this work is to determine the neutral thermospheric wind response at F region heights to these drivers, using an array of ground‐based all‐sky imaging Fabry‐Perot spectrometers that record Doppler spectra of optical emissions at 630‐nm wavelength, originating from a height of around 240 km. Line‐of‐sight winds are derived from Doppler shifts and, because each instrument only directly measures this one component, considerable postprocessing must be applied to infer the full three‐component vector velocity field. Several techniques for doing so are identified, and a detailed description is presented of the hybrid algorithm used here. Results show that thermospheric winds at these latitudes respond strongly to magnetospheric drivers associated with the aurora over length scales down 100 km or less, and on time scales as short as 15 min. These scales are considerably smaller than those resolved by previous observations, or those captured in semiempirical models such as the Horizontal Wind Model or global‐scale first principle models such as the Thermospheric Global Circulation Model and its relatives. Divergence and vorticity commonly occur in the observed horizontal wind fields, over regions spanning hundred of kilometers across and with magnitudes exceeding 0.5 × 10−3 s−1.
Solar Dependence of Equatorial F Region Irregularities Observed by COSMIC Radio Occultations
Authors: Yu Tao , Miyoshi Yasunobu , Xia Chunliang , Zuo Xiaomin , Yan Xiangxiang , Yang Na , Sun Yangyi , Yue Xinan , Mao Tian 
Published: October 2018

AbstractWith an improved method for retrieving the equatorial F region irregularities (EFIs) from radio occultation measurements, a huge amount of S4 index profiles from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites is employed to study the solar cycle variation of global EFIs during the period of 2007 to 2017. This full solar cycle data show that impacts of the solar activity on the occurrence rates and heights of EFIs are notable and complex. The occurrence rates of EFIs at higher altitude (greater than 500 km) increase with increasing the solar activity. The mean heights (
) and heights standard deviation (σh) of EFIs at higher altitudes do not show clearly the solar activity dependence. On the other hand, the occurrence rates of EFIs at entire altitudes (from 150 to 800 km) do not have clear relation with the solar activity. The
and σh of EFIs at entire altitudes increase with increasing the solar activity. Moreover, the dependence of the occurrence rates of EFIs on the solar activity are the strongest in the equinoxes, weaker in winter and weakest in summer. The electric fields and corresponding seasonal variation can account for the EFIs occurrence and height variation versus solar activities, and the EFIs at low altitudes seem to be related to the seed associated with atmospheric gravity wave.
Muon Tomography Applied to a Dense Uranium Deposit at the McArthur River Mine
Authors: Schouten Douglas , Ledru Patrick 
Published: October 2018

AbstractThis article reports on the first application of muon tomography (a novel method for imaging density contrasts underground using cosmic rays) for imaging dense uranium deposits within the Athabasca Basin in Canada. We present a qualitative assessment of the radiographic imaging and 3‐D density inversion of a uranium deposit using muon tomography. The muon tomography survey summarized in this article was performed at the McArthur River mine. We demonstrate the validity of muon tomographic imaging with data acquired at a depth of about 600 m underground. The statistical significance of the uranium deposit signature in the muon data was larger than 5 standard deviations, and the corresponding 3‐D density inversion compared well with drill assay data from the deposit.
Fully Dynamic Spontaneous Rupture Due to Quasi‐Static Pore Pressure and Poroelastic Effects: An Implicit Nonlinear Computational Model of Fluid‐Induced Seismic Events
Authors: Jin Lei , Zoback Mark D. 
Published: October 2018

AbstractFluid perturbations play a pivotal role in triggering earthquakes. However, the role of fluid in the coseismic rupture process remains largely unknown. To this end, we develop a 2‐D fully dynamic spontaneous rupture model for fluid‐induced earthquakes. The effect of fluid in the preseismic quasi‐static regime is modeled as either pore pressure diffusion or fully coupled poroelasticity, using our Jin and Zoback (2017, https://doi.org/10.1002/2017JB014892) computational model. The two approaches lead to radically different predictions on the time of earthquake nucleation. Correspondingly, the evolved fluid pressure or poroelastic stress on the fault, together with the spatially altered density of the fluid‐saturated hosting rock, is passed to the dynamic regime. Under the assumption of an undrained coseismic fluid‐solid system, we discretize the fully dynamic Cauchy equation of motion subjected to an exact fault contact constraint using a split‐node finite element method in space and an implicit Newmark family finite difference method in time. Within each time step, a fully implicit Newton‐Raphson scheme is implemented iteratively for linearizing the fully discrete equations. Within each Newton iteration, a physics‐based and nonstationary preconditioner is designed to accelerate the convergence of the selected generalized minimal residual method iterative linear solver. The effect of fluid is highlighted throughout the discretization and computational procedures. Finally, by conducting a numerical experiment, we illustrate that a fully coupled poroelastic model can lead to significantly different predictions on coseismic rupture behaviors and wavefields compared to a decoupled model. Our computational model can also serve as one of the earliest full‐physics modeling tool for fluid‐induced earthquakes.
Ambient Noise Monitoring of Seismic Velocity Around the Longmenshan Fault Zone From 10 Years of Continuous Observation
Authors: Liu Zhikun , Huang Jinli , He Ping , Qi Juanjuan 
Published: October 2018

AbstractWe present 10‐year continuous seismic velocity changes from 2007 to 2017 around the Longmenshan fault zone, where the 2008Mw7.9 Wenchuan earthquake and the 2013Mw6.6 Lushan earthquake occurred. We collected continuous waveforms recorded by 20 broadband stations covering the entire Longmenshan fault zone and used three‐component ambient noise correlation techniques to measure the velocity changes in four different period bands. Our results show that a significant drop, 0.04–0.06%, occurred in the coseismic velocity at the time of the Wenchuan earthquake, near the rupture zone for the period bands of 1–3 and 3–8 s. In addition, only one fourth of the coseismic velocity drop has been recovered 9 years after the earthquake. We also observed a subtle velocity drop, 0.0066%, delayed by ~100 days relative to the time of the mainshock in the period bands of 6–15 s. In the source region of the Lushan earthquake, we detected a weak but reliable coseismic velocity change of ~0.01% in the period band of 1–3 s. The physical mechanism of the seismic velocity change could involve the damage in the shallow subsurface layer (<3 km), the damage in the fault zone at depth (~10 km), and the postseismic slip along the deep rupture zone up to ~20 km. The uncommonly slow postseismic velocity recovery indicates the slow healing of the Longmenshan fault zone after the Wenchuan earthquake, which may be associated with the low rate of stress loading onto the fault zone.