bluuebunny/crossref_metadata_2025_split huggingface dataset:
First Detection of Kilometer‐Scale Density Irregularities in the Martian Ionosphere
Authors: Fowler C. M. , Bonnell J. W. , Xu S. , Benna M. , Elrod M. , McFadden J. , Mitchell D. L. , Espley J. , Andersson L. , Ergun R. E. , Lillis R. , Jakosky B. 
Published: November 2020

AbstractPlasma instabilities have been studied for many decades in the terrestrial ionosphere via remote and in‐situ measurement techniques. The study of these kilometer‐scale instabilities has provided crucial insight into coupling between the neutral atmosphere and ionosphere. A special high‐time cadence observation mode developed for the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has demonstrated for the first time that kilometer‐scale density fluctuations exist at Mars. Density and associated magnetic fluctuations are observed to occur both in and out of phase with each other, suggesting that multiple instability mechanisms are active, similar to Earth. The unique solar wind interaction with Mars and its localized crustal magnetic fields appears to play an important role in the formation of these irregularity events, which form preferentially during meridionally pointing magnetic field within the ionosphere. This is in contrast to Earth where the strong dipole magnetic field dominates in the terrestrial ionosphere.
Aseismic Deformation During the 2014 Mw 5.2 Karonga Earthquake, Malawi, From Satellite Interferometry and Earthquake Source Mechanisms
Authors: Zheng Whyjay , Oliva Sarah Jaye , Ebinger Cynthia , Pritchard Matthew E. 
Published: November 2020

AbstractAseismic deformation has been suggested as a mechanism to release the accumulated strain in rifts. However, the fraction and the spatial distribution of the aseismic strain are poorly constrained during amagmatic episodes. Using Sentinel‐1 interferograms, we identify the surface deformation associated with the 2014 Mw5.2 Karonga earthquake, Malawi, and perform inversions for fault geometry. We also analyze aftershocks and find a variety of source mechanisms within short timescales. A significant discrepancy in the earthquake depth determined by geodesy (3–6 km) and seismology (11–13 km) exists, although both methods indicate Mw5.2. We propose that the surface deformation is caused by aseismic slip from a shallow depth. This vertical partitioning from seismic to aseismic strain is accommodated by intersecting dilatational faults in the shallow upper crust and sedimentary basin, highlighting the importance of considering aseismic deformation in active tectonics and time‐averaged strain patterns, even in rifts with little volcanism.
Revealing the Dynamical Transition of Anisotropy Behind the HOST by Koopman Analysis
Authors: Li Licheng , Zuo Hongchao , Chen Bolong , Guo Yang , Ma Mengmeng , Dong Longxiang 
Published: November 2020

AbstractThe hockey‐stick transition (HOST), which is depicted by the “local and global shear” assumption, about the turbulence kinetic energy with the averaged flow intensity is noticed widely. However, the intrinsic mechanism of averaged flow influences turbulence kinetic energy via shear and buoyancy is missing. In this research, we deploy the Koopman operator to expose invariant subspaces of the Ri series to identify the quasiperiodic coherent structures from the single tower observation. Analysis of turbulence fluxes and anisotropy demonstrates the mechanism, that is, horizontal kinetic energy coupled with vertical downward flux, whereby anisotropy evolution is changed. Examining the anisotropy invariants changing with kinetic energy reveals a dynamical transition that determines the threshold of HOST. Moreover, the mechanism about how the shear and vertical momentum influences the transition point of HOST is at first given by a group of a quadratic relationship when the anisotropy crossed over the transition point.
Multipoint Conjugate Observations of Dayside ULF Waves During an Extended Period of Radial IMF
Authors: Shi X. , Hartinger M. D. , Baker J. B. H. , Ruohoniemi J. M. , Lin D. , Xu Z. , Coyle S. , Kunduri B. S. R. , Kilcommons L. M. , Willer A. 
Published: November 2020

AbstractLong‐lasting Pc5 ultralow frequency (ULF) waves spanning the dayside and extending from L ∼ 5.5 into the polar cap region were observed by conjugate ground magnetometers. Observations from MMS satellites in the magnetosphere and magnetometers on the ground confirmed that the ULF waves on closed field lines were due to fundamental toroidal standing Alfvén waves. Monochromatic waves at lower latitudes tended to maximize their power away from noon in both the morning and afternoon sectors, while more broadband waves at higher latitudes tended to have a wave power maximum near noon. The wave power distribution and MMS satellite observations during the magnetopause crossing indicate surface waves on a Kelvin‐Helmholtz (KH) unstable magnetopause coupled with standing Alfvén waves. The more turbulent ion foreshock during an extended period of radial interplanetary magnetic field (IMF) likely plays an important role in providing seed perturbations for the growth of the KH waves. These results indicate that the Pc5 waves observed on closed field lines and on the open field lines of the polar cap were from the same source.
Evaluation and Projection of Surface Wind Speed Over China Based on CMIP6 GCMs
Authors: Wu Jie , Shi Ying , Xu Ying 
Published: November 2020

AbstractSurface wind speed has great impacts on the economy, environment, and society around the world. Based on 24 global climate models (GCMs) from Coupled Model Intercomparison Project Phase 6 (CMIP6), this paper assesses the historical surface wind speed over China, and quantifies the advancements of CMIP6 over CMIP5. In addition, future changes of surface wind speed under the Shared Socioeconomic Pathway scenarios of 1‐2.6, 2‐4.5, and 5‐8.5 (SSP1‐2.6, SSP2‐4.5, and SSP5‐8.5) are also provided, by using 18 out of the 24 models with all three scenarios. Results show that multimodel ensemble mean of CMIP6 can well capture the spatial distributions of the annual, summer, and winter surface wind speed and generally performs better than both the median of the individual CMIP6 GCMs and multimodel ensemble mean of CMIP5 in monthly, seasonal, and annual wind climatology. However, CMIP6 GCMs fail to reproduce the observed decreasing trends, in terms of magnitude and/or sign. Meanwhile, the annual cycle of the surface wind speed simulated by CMIP6 GCMs falsely demonstrates the maximum in winter instead of spring. In the context of global warming, surface wind speed is projected to decrease in most parts of China in the middle and late 21st century under the three scenarios. Moreover, the trends of wind speed averaged over China will decrease significantly in both annual and winter under all three scenarios, but it will increase significantly in summer under SSP5‐8.5.
Long‐Term Trends in Acid Precipitation and Watershed Elemental Export From an Alpine Catchment of the Colorado Rocky Mountains, USA
Authors: Crawford John T. , Hinckley Eve‐Lyn S. , Neff Jason C. 
Published: November 2020

AbstractAcid deposition associated with precipitation is an ecological problem that has affected watersheds in industrialized parts of North America and Europe, but remote landscapes, such as the Colorado Rocky Mountains, have also been impacted. The deposition of strong acids, including nitric and sulfuric acids, has decreased substantially over the past 30 years at Niwot Ridge, a high‐alpine watershed of Colorado. The pH of precipitation has followed these declines and has increased to ~5.5. Meanwhile, NH4+, another important constituent of acid/base balance, and a fertilizing nutrient, has more than doubled in precipitation between 1984 and 2017. A statistical model of long‐term water chemistry concentrations and loads revealed a variety of trends in watershed export of acids and bases, some of which were unexpected, and remain unexplained. For example, despite declining sulfate deposition, sulfate export has increased. On the other hand, watershed nitrate export has remained constant despite decreases in atmospheric deposition, while watershed NH4+ export has increased, albeit minimally, relative to total nitrogen export. Watershed pH and alkalinity appear to have stabilized in response to decreased acid precipitation, which may be explained by geochemical processes, such as carbonate weathering. Overall, in this high‐alpine watershed, atmospheric deposition is trending toward preindustrial conditions, and there is a need to conduct targeted, process‐based studies to determine the mechanisms underlying these trends. The unexpected watershed responses that we identify here require a new framework for understanding acid precipitation recovery.
Changes of Light Components and Impacts on Interannual Variations of Photosynthesis in China Over 2000–2017 by Using a Two‐Leaf Light Use Efficiency Model
Authors: Yan H. , Wang S. Q. , Wang J. B. , Shugart H. H. 
Published: November 2020

AbstractDiffuse radiation produces a higher light use efficiency (LUE) than does direct radiation. However, light components and their impacts on interannual variations of photosynthesis in China have not been intensively studied. We estimated gross primary production (GPP) from a two‐leaf LUE model that incorporates a diffuse radiation effect and compared it with a big‐leaf LUE model that ignores the diffuse radiation impact. The results show that a dimming occurred in China—the estimated annual photosynthetically active radiation (PAR) declined by −1.79 MJ m−2 yr−1. However, the diffuse fraction and diffuse PAR increased over this interval. Both GPP models simulated an increasing trend of GPP in China from 2000 to 2017. The big‐leaf GPP model underestimated the increasing trend of GPP from the two‐leaf GPP model by 6.4%. The diffuse fraction change during the dimming exerted an embedded positive impact relative to the big‐leaf GPP trend in China.To evaluate the impact of total PAR versus its components on GPP, annual anomaly percentage (Ap) of GPP shows that the big‐leaf GPP model had a positive correlation between Ap of GPP and PAR across China. Considering the diffuse radiation impact, Ap of two‐leaf GPP was negatively correlated with PAR in southern China, which had a higher leaf area index (2.02) and a greater diffuse fraction (0.63). Strong diffuse radiation effects in southern China produced GPP anomalies in opposition to the direction of the PAR changes. These findings highlight the distinctive impact of light components on interannual variations of plant photosynthesis.
Global Patterns and Climate Controls of Terrestrial Ecosystem Light Use Efficiency
Authors: Tang Shuchang , Wang Xuhui , He Mingzhu , Huang Ling , Zhang Yuan , Yang Hui , Piao Shilong 
Published: November 2020

AbstractLight use efficiency (LUE) is a critical parameter, on which we rely to quantify the vegetation's capability to harvest solar energy and thus the photosynthesis carbon uptake. However, our understanding on its magnitude, global pattern, and climatic drivers remains uncertain. In this study, we investigated global mean annual LUE during 1980–2013 based on state‐of‐the‐art estimates from scaled‐up eddy covariance measurements (data‐driven models) and 10 process‐based models used in Global Carbon Project. We found comparable global LUE estimates from data‐driven models (0.90 ± 0.25 g C MJ−1) and process‐based models (0.73 ± 0.22 g C MJ−1), with individual model estimates ranging from 0.49 to 0.98 g C MJ−1. While both types of models agreed on highest LUE over the tropical evergreen forests, discrepancies remained over middle and high latitudes of the Northern Hemisphere, which probably resulted from different response of LUE to climatic factors. Spatial analyses revealed that LUE variations were more driven by temperature and precipitation than by solar radiation. While the response of LUE to precipitation was almost always positive globally, the response of LUE to temperature was only positive in part of the nontropical regions. Process‐based models showed that precipitation strongly regulated the response of LUE to temperature, which shifted from negative to positive when mean annual precipitation was larger than 1,000 mm yr−1. Our results provide converging global LUE estimates and highlight the need to take fully account of interactive effects of climatic factors in regulating LUE and thus the response of photosynthesis to climate change.
Fate of Dissolved Organic Carbon in Antarctic Surface Environments During Summer
Authors: Samui Gautami , Antony Runa , Thamban Meloth 
Published: November 2020

AbstractWhile the role of supraglacial environments such as the cryoconite holes and surface snow in cycling of carbon and nutrients has gained momentum in the last decade, little has been done to assess how interactions with sunlight and microbes control the dissolved organic matter cycling in these environments. In this study, the cryoconite holes, which are subjected to different light conditions, were monitored in the coastal Antarctica during the summer in order to determine how the geochemistry of these environments varied through the melt season. Additionally, mesocosm experiments were conducted to understand the impact of photochemical and microbial activities on dissolved organic carbon (DOC) and ionic constituents in the snow and cryoconite holes. In situ measurements of primary and bacterial production carried out in the surface snow and cryoconite holes showed that the primary production rates were higher than the bacterial production rates. Both photochemical and microbial processes resulted in changing the concentration of DOC, carboxylate, and nitrate ions in these environments. Sunlight‐induced production of biologically labile compounds, such as acetate and formate, and photochemical degradation of oxalate were also observed. Microbial activity had the opposite effect, resulting in an increase in oxalate and decrease in acetate and formate concentrations. Consequences of these combined processes would determine the fate of DOC and associated nutrients in the Antarctic supraglacial environments and potentially influence the local productivity within these systems.
Initiation of the Western Pacific Warm Pool at the Middle Miocene Climate Transition?
Authors: Sosdian S. M. , Lear C. H. 
Published: November 2020

AbstractAcross the middle Miocene, Earth's climate underwent a major cooling and expansion of the Antarctic ice sheet. However, the associated response and development of the tropical climate system is not fully understood, in part because this is influenced by both global climate and also low‐latitude tectonic gateways and paleoceanography. Here we use combined δ18O and Mg/Ca of planktic foraminifera to reconstruct the thermal history and changes in hydrology from the Indo‐Pacific region from 16.5 to 11.5 Ma. During the warmth of the early middle Miocene, our records indicate a dynamic ocean‐atmosphere system in the Indo‐Pacific region, with episodes of saltier and warmer tropical surface waters associated with high pCO2 and retreat of the Antarctic ice sheet. We show that across the Middle Miocene Climate Transition (MMCT) surface ocean temperatures in the Indo‐Pacific cooled by ~2°C, synchronous with the advance of the Antarctic ice sheet. The associated cooling in the Southern Ocean appears to have started earlier and was stronger. Further, we show that western Pacific Ocean warmed and eastern tropical Indian Ocean freshened following the MMCT, likely caused by the constriction of the Indonesian Seaway and reduced connectivity between the Pacific and Indian Oceans following Antarctic glaciation. The MMCT therefore represented a key phase in the evolution of the West Pacific Warm Pool and associated tropical climate dynamics.
The Role of Tectonic Plate Thickness and Mantle Conductance in Determining Regional Vulnerability to Extreme Space Weather Events: Possible Enhancement of Magnetic Source Fields by Secondary Induction in the Asthenosphere
Authors: Simpson Fiona , Bahr Karsten 
Published: November 2020

AbstractDuring magnetic storms, solar‐magnetosphere‐ionosphere‐Earth interactions give rise to geomagnetically induced currents (GICs) in man‐made technological conductors such as power grids, gas pipelines, and railway networks with potentially damaging outcomes. Generally, electrically conductive regions of the Earth are assumed to be less at risk to GICs than resistive ones, since induced electric fields associated with GICs are linearly related to given magnetic source fields via Earth's impedance. Here, we show that magnetic source fields associated with storms can be enhanced by secondary electromagnetic (EM) induction in Earth's electrically conductive asthenosphere and that this previously neglected effect can give rise to larger electric fields close to the lithosphere‐asthenosphere boundary in regions where the conductance of the asthenosphere is higher. Our analysis of data from the 30 October 2003 “Halloween” and 8 September 2017 storms shows that the magnitudes of electric fields from both storms are affected by lithospheric plate thickness and asthenosphere conductance (conductivity‐thickness product) and that they are 5 times larger in southern Sweden (>5 V/km for the 30 October 2003 “Halloween” storm) than in central Scotland. Our results provide insight into why Sweden experienced a storm‐related power outage in 2003, whereas Scotland did not.
Real‐Time Imaging Reveals Distinct Pore‐Scale Dynamics During Transient and Equilibrium Subsurface Multiphase Flow
Authors: Spurin Catherine , Bultreys Tom , Rücker Maja , Garfi Gaetano , Schlepütz Christian M. , Novak Vladimir , Berg Steffen , Blunt Martin J. , Krevor Samuel 
Published: November 2020

AbstractMany subsurface fluid flows, including the storage of CO2 underground or the production of oil, are transient processes incorporating multiple fluid phases. The fluids are not in equilibrium meaning macroscopic properties such as fluid saturation and pressure vary in space and time. However, these flows are traditionally modeled with equilibrium (or steady‐state) flow properties, under the assumption that the pore‐scale fluid dynamics are equivalent. In this work, we used fast synchrotron X‐ray tomography with 1 s time resolution to image the pore‐scale fluid dynamics as the macroscopic flow transitioned to steady state. For nitrogen or decane, and brine injected simultaneously into a porous rock, we observed distinct pore‐scale fluid dynamics during transient flow. Transient flow was found to be characterized by intermittent fluid occupancy, whereby flow pathways through the pore space were constantly rearranging. The intermittent fluid occupancy was largest and most frequent when a fluid initially invaded the rock. But as the fluids established an equilibrium the dynamics decreased to either static interfaces between the fluids or small‐scale intermittent flow pathways, depending on the capillary number and viscosity ratio. If the fluids were perturbed after an equilibrium was established, by changing the flow rate, the transition to a new equilibrium was quicker than the initial transition. Our observations suggest that transient flows require separate modeling parameters. The time scales required to achieve equilibrium suggest that several meters of an invading plume front will have flow properties controlled by transient pore‐scale fluid dynamics.
Impact of Sub‐core‐scale Heterogeneity on Meter‐Scale Flow and Brine Displacement in Drainage by CO2
Authors: Moreno Z. , Rabinovich A. 
Published: November 2020

AbstractStudies of CO2‐brine two‐phase flow are predominantly carried out on core samples or reservoir‐scale domains. In this work we investigate intermediate‐scale flow considering a cubic rock with 1 m3 volume incorporating sub‐core (mm)‐scale heterogeneity. First, a coreflooding experiment is analyzed to estimate subcore permeability spatial distribution and the results are used as input into the meter‐scale model without any upscaling required. High‐resolution numerical simulations are conducted to model CO2 injection into a brine saturated rock. We find significant differences between the meter‐scale rock simulation and core experiment saturation distributions resulting from highly influential boundary effects on the core scale and pronounced gravity impact on the meter scale. A detailed analysis of flow and brine trapping in rock simulations is presented considering different flow models and permeability structures. It is shown that gravity and capillary heterogeneity have substantial impact on the saturation in the deeper regions, which exhibit sufficiently low capillary pressure, and these regions also show increased trapping of brine. Two trapping mechanisms are discussed: Type I which is a result of entry pressure considerations and Type II, which occurs due to lack of CO2 connectivity. The two types of trapping are found to be correlated to the permeability structure. A formula is presented relating between trapping and permeability statistical parameters, that is, variance of log‐permeability and correlation length scale, as well as to the Bond number characterizing the ratio between gravity and capillary effects.
Periodontitis-level butyrate-induced ferroptosis in periodontal ligament fibroblasts by activation of ferritinophagy
Authors: Zhao Yunhe , Li Jiao , Guo Wei , Li Houxuan , Lei Lang 
Published: November 2020

AbstractLoss of periodontal ligament fibroblasts (PDLFs) is one critical issue for regenerating lost periodontal tissues. A wide variety of regulated cell death pathways, such as apoptosis, pyroptosis, and necroptosis have been proposed in the periodontitis development. The aim of the present study was to explore whether long-term periodontitis-level butyrate may trigger ferroptosis, a newly characterized iron-dependent regulated cell death in PDLFs. Here, we showed that long-term treatment of butyrate, an important short-chain fatty acid in the periodontal pocket, induces the cargo receptor nuclear receptor coactivator 4 (NCOA4)-mediated ferritinophagy and ferroptosis in PDLFs. Butyrate-induced iron accumulation, reactive oxygen species (ROS) generation, glutathione depletion and lipid peroxidation in PDLFs, and the butyrate-induced ferroptosis can be blocked by the lipid peroxide scavenger ferrostatin-1. The NCOA4-mediated ferritinophagy is dependent on p38/hypoxia inducible factor-1α (HIF-1α) pathway activation as well as Bromodomain-containing protein (BRD) 4 and cyclin-dependent kinase 9 (CDK9) coordination. These lines of evidence provide a new mechanistic insight into the mechanism of loss of PDLFs during periodontitis development, showing that periodontitis-level butyrate disrupted iron homeostasis by activation of NCOA4-mediated ferritinophagy, leading to ferroptosis in PDLFs.
Observation of nanoscale opto-mechanical molecular damping as the origin of spectroscopic contrast in photo induced force microscopy
Authors: Almajhadi Mohammad A. , Uddin Syed Mohammad Ashab , Wickramasinghe H. Kumar 
Published: November 2020

AbstractInfrared photoinduced force microscopy (IR-PiFM) is a scanning probe spectroscopic technique that maps sample morphology and chemical properties on the nanometer (nm)-scale. Fabricated samples with nm periodicity such as self-assembly of block copolymer films can be chemically characterized by IR-PiFM with relative ease. Despite the success of IR-PiFM, the origin of spectroscopic contrast remains unclear, preventing the scientific community from conducting quantitative measurements. Here we experimentally investigate the contrast mechanism of IR-PiFM for recording vibrational resonances. We show that the measured spectroscopic information of a sample is directly related to the energy lost in the oscillating cantilever, which is a direct consequence of a molecule excited at its vibrational optical resonance—coined as opto-mechanical damping. The quality factor of the cantilever and the local sample polarizability can be mathematically correlated, enabling quantitative analysis. The basic theory for dissipative tip-sample interactions is introduced to model the observed opto-mechanical damping.