bluuebunny/crossref_metadata_2025_split huggingface dataset:
Benchmarking iSALE and CTH Shock Physics Codes to In Situ High‐Velocity Impact Experiments Into Fe‐Ni Targets
Authors: Alexander A. M. , Marchi S. , Chocron S. , Walker J. 
Published: August 2022

AbstractCratering is a prominent evolutionary process on asteroids. Crater morphologies, regolith generation, bulk fracturing and projectile implantation are all examples of asteroidal surface evolution resulting from impact processes. The characterization of these processes on metal‐rich bodies has become a priority due to the upcoming NASA Psyche mission, poised to study the likely metal‐rich 225‐km main belt asteroid, (16) Psyche. Small‐scale impact experiments into metals (e.g., iron, aluminum, copper, steel) have shown that crater morphologies into these materials are different than rocky targets—exhibiting notable distinctive features such as raised, sharp rims, and deeper cavities. In this work, we determine strength constants for different metals used in prior impact experiments, namely manufactured Fe‐Ni materials and the Gibeon iron meteorite at 77 K. These parameters have been used as inputs for the Johnson and Cook (1983) strength model in a suite of numerical simulations reproducing impact experiments. Using the Johnson and Cook strength model and our laboratory‐derived material constants, we find that it is possible to closely match small‐scale experimental crater diameters and depths using iSALE and CTH shock physics codes.
Atmospheric N Deposition Significantly Enhanced Soil N2O Emission From Eastern China Forests
Authors: Cen Xiaoyu , Li Mingxu , Xu Li , Zhu Jianxing , He Nianpeng 
Published: August 2022

AbstractNitrous oxide (N2O) is an influential greenhouse gas (GHG) and an unregulated ozone‐depleting substance. The extent to which N2O emissions from natural forest soils have been enhanced by high atmospheric nitrogen (N) deposition in China during past decades is unclear; however, assessing land‐related N2O emissions for 2060 national “carbon neutrality” goal is urgent. In this study, we proposed a “gray box” conceptual model and deduced a linear relationship between soil N2O emissions and N deposition on a large scale. On this basis, we created a “process‐augmented data‐driven” approach using which we combined experimental N addition data from 38 Chinese forests with N deposition observation data to estimate regional soil N2O emissions. We found that the N2O emission budget of eastern China forest soils averaged 0.24 ± 0.07 TgN yr−1 from 1996 to 2015; of this, ∼36% (0.087 TgN yr−1) was directly induced by N deposition. Soil N2O emission rates (RN2O) fluctuated slightly after 2006, and the RN2Os of different ecoregions were significantly different (p < 0.001). Soil factors and N‐deposition‐related factors dominated the spatial variation of RN2O. Our findings provide country‐specific and ecoregion‐specific emission factors for national GHG inventories in China. Our approach bridges the gap between site‐level experiments and demand for regional N2O emissions, and is applicable for estimating N2O emissions in other countries/regions. Meanwhile, more N addition experiments are needed to comprehensively understand N cycling processes and extend the predictive capability of the approach.
Rotational Discontinuities in the Magnetopause of an Open Magnetosphere
Authors: Ma Yonghui , Wang Shu , Shen Chao , Ren Nian , Chen Tao , Shao Peng , E Peng , Bogdanova Y. V. , Burch J. L. 
Published: August 2022

AbstractIn this paper, we analyze the fine structure of rotational discontinuities (RDs) in the magnetopause of an open magnetosphere using four‐point magnetic field measurements recorded by the Magnetospheric MultiScale mission. An RD is commonly observed within the magnetopause when reconnection occurs in the magnetopause. Furthermore, an RD usually occurs closer to the magnetosheath side of the magnetopause. The magnetic structure of RD is usually much thinner than 110 km. The magnetic field rotation maxima and magnetic strength minima are within the RD. The radius of curvature of the magnetic field lines reaches a minimum in the RD (∼83–1,491 km). In addition, the radius of curvature of the magnetic field lines of the RD is usually much larger than the thickness of the magnetic structure of the RD, indicating that the magnetic field lines almost lie in the RD. Generally, a field‐aligned current dominates in the RD.
Joint Cluster/Ground‐Based Studies in the First 20 Years of the Cluster Mission
Authors: Fear R. C. 
Published: August 2022

AbstractGround‐based facilities make an important contribution to our understanding of the magnetospheric system. Coordination with ground‐based facilities has been embedded within the Cluster mission since before launch, and this has given rise to a large number of studies which have exploited data from both Cluster and one or more of the diverse range of ground‐based instrumentation that have been available during the mission timespan. In this paper, we review the advances that have been made to our understanding of the magnetosphere‐ionosphere system, in which insight has been enhanced by combining ground‐based observations with observations from Cluster. Topics covered span from the bow shock to the magnetotail and down to the aurora.
Study of the Electron‐Scale Magnetic Peaks in the Magnetotail Current Sheet Observed by the Magnetospheric Multiscale Mission
Authors: Chen Y. Q. , Wang G. Q. , Wu M. Y. , Xiao S. D. , Zhang T. L. 
Published: August 2022

AbstractElectron‐scale magnetic holes have been revealed to widely exist in many plasma environments in the last decade, playing an important role in transporting particles and dissipating energies. Recently, electron‐scale magnetic peaks (ESMPs) have also been reported to exist in the terrestrial magnetosheath and the solar wind at 1 AU. Here, we report the existence of ESMPs in the terrestrial magnetotail current sheet for the first time based on observations of the Magnetospheric Multiscale (MMS) mission. We find a clear bipolar signature in the electron velocity inside one ESMP, suggesting the existence of an electron vortex inside it. The current in the ESMP is mainly contributed by electrons. We also find that they prefer to occur near the neutral sheet with a northward component of the magnetic field, suggesting that they prefer to occur during the dipolarization process. Our observation results suggest that both ion and electron mirror instabilities are not the generation mechanism of these ESMPs. Their role and generation mechanism in the magnetotail current sheet are unclear and need further investigation.
Strong Correspondence in Evapotranspiration and Carbon Dioxide Fluxes Between Different Eddy Covariance Systems Enables Quantification of Landscape Heterogeneity in Dryland Fluxes
Authors: Cunliffe Andrew M. , Boschetti Fabio , Clement Robert , Sitch Stephen , Anderson Karen , Duman Tomer , Zhu Songyan , Schlumpf Mikael , Litvak Marcy E. , Brazier Richard E. , Hill Timothy C. 
Published: August 2022

AbstractThe eddy covariance method is widely used to investigate fluxes of energy, water, and carbon dioxide at landscape scales, providing important information on how ecological systems function. Flux measurements quantify ecosystem responses to environmental perturbations and management strategies, including nature‐based climate‐change mitigation measures. However, due to the high cost of conventional instrumentation, most eddy covariance studies employ a single system, limiting spatial representation to the flux footprint. Insufficient replication may be limiting our understanding of ecosystem behavior. To address this limitation, we deployed eight lower‐cost eddy covariance systems in two clusters around two conventional eddy covariance systems in the Chihuahuan Desert of North America for a period of 2 years. These dryland settings characterized by large temperature variations and relatively low carbon dioxide fluxes represented a challenging setting for eddy covariance. We found very good closure of energy and water balance across all systems (within ±9% of unity). We found very good correspondence between the lower‐cost and conventional systems' fluxes of sensible heat (with concordance correlation coefficient (CCC) of ≥0.87), latent energy (evapotranspiration; CCC ≥ 0.89), and useful correspondence in the net ecosystem exchange ((NEE); with CCC ≥ 0.4) at the daily temporal resolution. Relative to the conventional systems, the low‐frequency systems were characterized by a higher level of random error, particularly in the NEE fluxes. Lower‐cost systems can enable wider deployment affording better replication and sampling of spatiotemporal variability at the expense of greater measurement noise that might be limiting for certain applications. Replicated eddy covariance observations may be useful when addressing gaps in the existing monitoring of critical and underrepresented ecosystems and for measuring areas larger than a single flux footprint.
Stochastic Modeling Approach to Identify Uncertainties of Karst Conduit Networks in Carbonate Aquifers
Authors: Banusch S. , Somogyvári M. , Sauter M. , Renard P. , Engelhardt I. 
Published: August 2022

AbstractThe characterization of the karst conduit network is an essential task to understand the complex flow system within karst aquifers. However, this task is challenging and often associated with uncertainty. Equivalent porous media approaches for modeling flow in karst aquifers fall short of capturing the hydraulic effect of individual karst features, while process‐oriented karst evolution models imply major computational efforts. In this study, we apply the Stochastic Karst Simulator (SKS) developed by Borghi et al. (2012) to generate karst conduit networks at a regional scale of a highly karstified carbonate aquifer located in the Eastern Mediterranean region and extensively used for water supply. The SKS generates conduit network geometries reasonably quick, using a mathematical proxy that mimics conduit evolution. The conduit simulation is based on a conceptual model of the genesis of the aquifer, consisting of different karstification phases. The stochastic approach of the algorithm enables us to generate an ensemble of conduit network realizations and to represent the uncertainties of these simulations in a Karst Probability Map. With only soft input information to constrain conduit evolution, multiple equivalent realizations yield similar resulting network geometries, indicating a robust approach. The presented methodology is numerically efficient, and its input can be easily adjusted. Subsequently, the resulting stochastic spatial distribution of conductivities can be employed for the parametrization of regional karst groundwater models.
The Longest Baseline Record of Vegetation Dynamics in Antarctica Reveals Acute Sensitivity to Water Availability
Authors: Colesie Claudia , Pan Yueming , Cary S. Craig , Gemal Emma , Brabyn Lars , Kim Jeong‐Hoon , Green T. G. Allan , Lee Charles K. 
Published: August 2022

AbstractAgainst a changing climate, the development of evidence‐based and progressive conservation policies depends on robust and quantitative baseline studies to resolve habitat natural variability and rate of change. Despite Antarctica's significant role in global climate regulation, climate trend estimates for continental Antarctica are ambiguous due to sparse long‐term in situ records. Here, we present the longest, spatially explicit survey of Antarctic vegetation by harmonizing historic vegetation mapping with modern remote sensing techniques. In 1961, E. D. Rudolph established a permanent survey plot at Cape Hallett, one of the most botanically diverse areas along the Ross Sea coastline, harboring all known types of non‐vascular Antarctic vegetation. Following a survey in 2004 using ground‐based photography, we conducted the third survey of Rudolph's Plot in 2018 using near‐ground remote sensing and methodologies closely mirroring the two historic surveys to identify long‐term changes and trends. Our results revealed that the vegetation at Cape Hallett remained stable over the past six decades with no evidence of transformation related to a changing climate. Instead, the local vegetation shows strong seasonal phenology, distribution patterns that are driven by water availability, and steady perennial growth of moss. Given that East Antarctica is at the tipping point of drastic change in the near future, with biological change having been reported at certain locations, this record represents a unique and potentially the last opportunity to establish a meaningful biological sentinel that will allow us to track subtle yet impactful environmental change in terrestrial Antarctica in the 21st century.
EMIRS Observations of the Aphelion‐Season Mars Atmosphere
Authors: Smith Michael D. , Badri Khalid , Atwood Samuel A. , Edwards Christopher S. , Christensen Philip R. , Wolff Michael J. , Bertrand Tanguy , Forget François , Al Tunaiji Eman , Wolfe Christopher , Smith Nathan , Anwar Saadat 
Published: August 2022

AbstractThermal infrared spectra taken by the Emirates Mars Infrared Spectrometer (EMIRS) on‐board the Emirates Mars Mission (EMM) spacecraft are well suited for the retrieval of surface temperatures, the atmospheric temperature profile from the surface to ∼40 km, and the column abundance of dust aerosols, water ice clouds, and water vapor. A constrained linear inversion retrieval routine that includes multiple scattering has been developed and optimized for this purpose. Here, we present a brief overview of the retrieval algorithm and first atmospheric science results from observations taken by EMIRS over the first Earth year of EMM Science Phase operations. These retrievals show extensive water ice clouds, typical for the aphelion season of these observations, and the expected north polar summer maximum and subsequent equatorward transport of water vapor is well documented. An unusually strong and early regional dust storm and its associated thermal response were also observed.
Electron Precipitation Curtains—Simulating the Microburst Origin Hypothesis
Authors: O’Brien T. P. , Lemon C. L. , Blake J. B. 
Published: August 2022

AbstractWe explore the hypothesis that electron precipitation curtains such as those observed by the AeroCube‐6 satellite pair can be produced by electron microbursts. Precipitation curtains are latitudinal structures of stable precipitation that persist for timescales of 10s of seconds or longer. The electrons involved have energies of 10–100s of keV. The microburst formation hypothesis states that a source region in the equatorial region produces a series of very low frequency chorus wave emissions. Each of these emissions in turn produces a microburst of electron precipitation, filling the drift and bounce loss cone on the local field line. Electrons in the drift loss cone remain on the field line and bounce‐phase mix over subsequent bounces while also drifting in azimuth. When observed at downstream azimuths by a satellite equipped with an integral energy sensor, no bounce phase structure remains, or, equivalently, the same time profile is present when two such satellites pass by many seconds apart. The spatial structure that remains reflects the pattern of microburst sources. Statistical studies of where and when curtains occur have indicated that some, but not all, curtains could be caused by microbursts. We use test particle tracing in a dipole magnetic field to show that spatially stationary source regions generating periodic microbursts can produce curtain signatures azimuthally downstream. We conclude that one viable explanation for many of the curtains observed by the AeroCube‐6 pair is the accumulation of drift‐dispersed microburst electron byproducts in the drift loss cone.
Distributed Fiber Optics Measurements of Rock Deformation and Failure in Triaxial Tests
Authors: Salazar Vásquez Antonio , Rabaiotti Carlo , Germanovich Leonid N. , Puzrin Alexander M. 
Published: August 2022

AbstractThe implementation of distributed strain measurement methods in triaxial and uniaxial tests have demonstrated the development of strain localization, even at early stages. This implies that single point measurement methods are location dependent. The use of distributed methods is required not only to improve the interpreted constitutive parameters obtained from triaxial tests, but also to understand the implications of strain localization in the failure process. This work uses optical fibers in triaxial tests. The developed distributed measurement method was implemented on granite, gabbro, and sandstone samples and tested under different confining pressures, reaching 200 MPa on the granite sample. Using a temporal resolution of 0.25 Hz and 5 mm of spatial resolution, the strain evolution at over 300 locations at the sample surface was measured during testing. When compared to point sensing methods, the use of optical fiber greatly increases the number of measurements at the surface of the sample, and their interpolation provides the entire deformation of the sample surface. In all the tests performed, strain localizations were revealed before failure. A three‐dimensional interpretation of a test, combining an optical scan of the sample and the distributed measurements, show good correlation between the fractures and the strain localization.
Mechanical Compliance of Individual Fractures in a Heterogeneous Rock Mass From Production‐Type Full‐Waveform Sonic Data
Authors: Zhou Zhenya , Caspari Eva , Barbosa Nicolás D. , Greenwood Andrew , Holliger Klaus 
Published: August 2022

AbstractThe mechanical fracture compliance is of interest in a number of geoscientific applications. Seismic borehole methods, especially full‐waveform sonic (FWS) data, have indicated their potential to infer the compliance of macroscopic fractures under in situ conditions. These approaches rely on the assumption of a homogeneous background embedding the fractures and, as of yet, compliance estimates for individual fractures are limited to static FWS measurements. In this work, we assess the potential of inferring the compliance of individual fractures from standard, production‐type FWS data in the presence of background heterogeneity. We first perform a comparative test on synthetic data to evaluate three approaches known as the transmission, phase, and group time delay methods. The results indicate that the former two produce adequate compliance estimates for scenarios with a strongly heterogeneous background or a damage zone around the fracture. These two methods are then applied to two FWS data sets acquired before and after a hydraulic stimulation campaign in a crystalline rock, which allows to test them on natural and man‐made fractures. The transmission method turned out to be unsuitable for the considered data due to its reliance on amplitudes. Conversely, the travel time behavior remained stable and the phase time delay method produced robust and consistent estimates. The results for a newly created hydro‐fracture imply the capability of resolving remarkably small compliance values of the order of 10−14 m/Pa. This estimate is one order‐of‐magnitude smaller than that for the natural fracture, which may help to distinguish between these two fracture types.
The Effect of a Weak Asthenospheric Layer on Surface Kinematics, Subduction Dynamics and Slab Morphology in the Lower Mantle
Authors: Cerpa Nestor G. , Sigloch Karin , Garel Fanny , Heuret Arnauld , Davies D. Rhodri , Mihalynuk Mitchell G. 
Published: August 2022

AbstractOn Earth, the velocity at which subducting plates are consumed at their trenches (termed “subduction rate” herein) is typically 3 times higher than trench migration velocities. The subduction rate is also 5 times higher than estimated lower mantle slab sinking rates. Using simple kinematic analyses, we show that if this present‐day “kinematic state” operated into the past, the subducting lithosphere should have accumulated and folded beneath near‐stationary trenches. These predictions are consistent with seismic tomography, which images localized and widened lower‐mantle slab piles. They are, however, at odds with most dynamic‐subduction models, which predict rapid trench retreat and inclined slabs in the mantle transition zone. We test the hypothesis that a weak asthenospheric layer (WAL), between the lithosphere‐asthenosphere boundary and 220 km depth, compatible with geophysical constraints, can remedy the discrepancies between numerical models and observations. The WAL lubricates the base of the lithosphere, increases the subduction rate while reducing trench retreat. As a consequence, simulations featuring a WAL predict slab accumulation at the mantle transition zone, and thicker, folded slabs in the lower mantle. A WAL viscosity only 2–5 times lower than that of the adjacent mantle is sufficient to shift subduction regimes toward a mode of vertical slab sinking and folding beneath near‐stationary trenches, across a wide range of model parameters, producing surface and slab velocities close to those observed at the present‐day. These findings provide support for the existence of a weak asthenosphere beneath Earth's lithosphere, complementing independent evidence from various geophysical data.
Pronounced Seismic Anisotropy in Kanto Sedimentary Basin: A Case Study of Using Dense Arrays, Ambient Noise Seismology, and Multi‐Modal Surface‐Wave Imaging
Authors: Jiang Chengxin , Denolle Marine A. 
Published: August 2022

AbstractMetropolitan Tokyo is subject to significant seismic hazards because it is located near a triple junction of tectonic plates and because it sits atop the soft and thick sediments of the Kanto sedimentary Basin. Numerical simulations of earthquake ground motions rely on accurate velocity models of the basin elastic and anelastic structure, which remains to be improved. Here, we leverage the density of permanent stations of the Metropolitan Seismic Observation network seismic network to construct a high‐resolution radially anisotropic (VSV ≠ VSH) shear wave velocity model of the Kanto basin. We construct surface waves using ambient seismic noise cross correlations. In sedimentary structures, it is common for several surface‐wave modes to arise and to couple in time, so we use local sub‐arrays to extract the phase velocity of the fundamental mode and first overtone of Rayleigh and Love waves at short periods (1–7 s). We find that a strong and negative shear‐wave anisotropy (−5%) is confined to the upper 300 m depth range, and a strong and positive anisotropy (+5%) at greater depths. We interpret them as a result of the vertical cracks from repeated earthquake damage and sediment stratigraphy in the Kanto Basin. Because anisotropy models are not routinely used in physics‐based ground motion prediction, our study motivates the consideration of seismic anisotropy in sedimentary basins for the ground motion of future earthquakes.