bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reconstructed Solar‐Induced Fluorescence: A Machine Learning Vegetation Product Based on MODIS Surface Reflectance to Reproduce GOME‐2 Solar‐Induced Fluorescence
Authors: Gentine P. , Alemohammad S. H. 
Published: March 2018

AbstractSolar‐induced fluorescence (SIF) observations from space have resulted in major advancements in estimating gross primary productivity (GPP). However, current SIF observations remain spatially coarse, infrequent, and noisy. Here we develop a machine learning approach using surface reflectances from Moderate Resolution Imaging Spectroradiometer (MODIS) channels to reproduce SIF normalized by clear sky surface irradiance from the Global Ozone Monitoring Experiment‐2 (GOME‐2). The resulting product is a proxy for ecosystem photosynthetically active radiation absorbed by chlorophyll (fAPARCh). Multiplying this new product with a MODIS estimate of photosynthetically active radiation provides a new MODIS‐only reconstruction of SIF called Reconstructed SIF (RSIF). RSIF exhibits much higher seasonal and interannual correlation than the original SIF when compared with eddy covariance estimates of GPP and two reference global GPP products, especially in dry and cold regions. RSIF also reproduces intense productivity regions such as the U.S. Corn Belt contrary to typical vegetation indices and similarly to SIF.
An Electron‐Scale Current Sheet Without Bursty Reconnection Signatures Observed in the Near‐Earth Tail
Authors: Wang Rongsheng , Lu Quanming , Nakamura Rumi , Baumjohann Wolfgang , Huang Can , Russell Christopher T. , Burch J. L. , Pollock Craig J. , Gershman Dan , Ergun R. E. , Wang Shui , Lindqvist P. A. , Giles Barbara 
Published: March 2018

AbstractObservations of a current sheet as thin as the electron scale are extremely rare in the near‐Earth magnetotail. By measurement from the novel Magnetospheric Multiscale mission in the near‐Earth magnetotail, we identified such an electron‐scale current sheet and determined its detailed properties. The electron current sheet was bifurcated, with a half‐thickness of nine electron inertial lengths, and was sandwiched between the Hall field. Because of the strong Hall electric field, the super‐Alfvénic electron bulk flows were created mainly by the electric field drift, leading to the generation of the strong electron current. Inevitably, a bifurcated current sheet was formed since the Hall electric field was close to zero at the center of the current sheet. Inside the electron current sheet, the electrons were significantly heated while the ion temperature showed no change. The ions kept moving at a low speed, which was not affected by this electron current sheet. The energy dissipation was negligible inside the current sheet. The observations indicate that a thin current sheet, even as thin as electron scale, is not the sufficient condition for triggering bursty reconnection.
Migration of Deep Low‐Frequency Tremor Triggered by Teleseismic Earthquakes in the Southwest Japan Subduction Zone
Authors: Kurihara Ryo , Obara Kazushige , Takeo Akiko , Maeda Takuto 
Published: March 2018

AbstractDeep low‐frequency tremor triggered by teleseismic surface waves is concentrated in several locations along the ambient tremor source region in the Nankai subduction zone, southwest Japan. We systematically investigated triggered tremor in northern Kii and western Shikoku, at 71 teleseismic earthquakes by applying a matched filter technique. We detected 9 and 17 events of triggered tremor in northern Kii and western Shikoku, respectively. In addition, we observed tremor migration episodes, whose directions were always along‐dip. In northern Kii, seven episodes showed downward migration at a speed of 5–20 km/hr. In western Shikoku, six episodes migrated at a speed of 10–100 km/hr, in which five episodes showed upward migration. Migration of the triggered tremor suggests that dynamic stress perturbation from distant earthquakes may trigger propagating creep events caused by fluid.
Apparent Splitting of S Waves Propagating Through an Isotropic Lowermost Mantle
Authors: Parisi Laura , Ferreira Ana M. G. , Ritsema Jeroen 
Published: March 2018

AbstractObservations of shear wave anisotropy are key for understanding the mineralogical structure and flow in the mantle. Several researchers have reported the presence of seismic anisotropy in the lowermost 150–250 km of the mantle (i.e., D
layer), based on differences in the arrival times of vertically (SV) and horizontally (SH) polarized shear waves. By computing waveforms at a period > 6 s for a wide range of 1‐D and 3‐D Earth structures, we illustrate that a time shift (i.e., apparent splitting) between SV and SH may appear in purely isotropic simulations. This may be misinterpreted as shear wave anisotropy. For near‐surface earthquakes, apparent shear wave splitting can result from the interference of S with the surface reflection sS. For deep earthquakes, apparent splitting can be due to the S wave triplication in D
, reflections off discontinuities in the upper mantle, and 3‐D heterogeneity. The wave effects due to anomalous isotropic structure may not be easily distinguished from purely anisotropic effects if the analysis does not involve full waveform simulations.
Inverse Method for Static Stress Drop and Application to the 2011 Mw9.0 Tohoku‐Oki Earthquake
Authors: Xie Zhoumin , Cai Yongen 
Published: March 2018

AbstractSeismic stress drop is a fundamental parameter for the investigation of earthquake mechanism. In general, it is indirectly predicted by fault slip based on the dislocation source model or seismic moment; inversion for the stress change on faults has not received the deserved attention. In this study, we propose a finite element method to invert the stress drop on fault, constrained by the observed coseismic deformation. Rupture termination and displacement on fault are automatically predicted from the model. Applying the method to the 2011 Mw9.0 Tohoku‐Oki earthquake, we find that the fault consists of two asperities with maximum shear stress drops of 11.7 and 10.1 MPa, respectively. The predicted maximum horizontal and vertical displacements on the hanging wall at the Japan Trench are 55.2 and 10.8 m, respectively, in good agreement with observation. The predicted total static moments of the mainshock and the Mw7.9 aftershock, 29 min after the mainshock, are 4.48 × 1022 and 1.46 × 1021 Nm, corresponding to moment magnitudes of Mw9.0 and Mw8.0, respectively, again in excellent agreement with the observationally determined Mw9.0 and Mw7.9 by the U.S. Geological Survey.
Phase Transitions in Orthoenstatite and Subduction Zone Dynamics: Effects of Water and Transition Metal Ions
Authors: Xu Jingui , Zhang Dongzhou , Fan Dawei , Zhang Jin S. , Hu Yi , Guo Xinzhuan , Dera Przemyslaw , Zhou Wenge 
Published: March 2018

AbstractSynchrotron‐based high‐pressure and temperature single‐crystal X‐ray diffraction experiments were conducted on two hydrous orthoenstatite samples (oEn#1: Mg1.004Si0.996O3, ~619 ppm water; oEn#2: Mg0.947Ni0.055Si0.998O3, ~696 ppm water) to ~34 GPa and 700 K, using resistively heated diamond anvil cells. The α‐opx (Pbca space group)→β‐opx (P21/c space group) phase transition of oEn#1 occurs at 12.90(2) GPa, and the β‐opx phase persists to 34.25(1) GPa. The α‐β transition of oEn#2 occurs at 13.50(1) GPa, and a new isosymmetric β‐opx→β‐opxII transition takes place at 29.80(4) GPa. The β‐opxII phase is preserved down to 24.53(3) GPa during decompression. The transition to the monoclinic β‐opxII phase is interpreted as a result of incorporation of Ni2+ into the orthoenstatite structure. Fitting the third‐order Birch‐Murnaghan thermal equation of state to the single‐crystal P‐V‐T data yields the thermoelastic parameters of the α‐ and β‐opx phases for both orthoenstatite samples. This study is the first attempt to determine the thermal equation of state of the β‐opx phase. Our results suggest that several hundred ppm of water has negligible effects on the bulk modulus of orthoenstatite but notably enhances the thermal expansion. The potential effects of metastable orthoenstatite on subduction zone dynamics are discussed, and the possible contributions of displacive phase transitions to enhancement of the transformational faulting mechanism of the deep‐focus earthquakes in subducted slabs are considered. The presence of metastable orthoenstatite within cold slabs could promote slab stagnation above the 660‐km discontinuity.
A Mineral Magnetic Approach to Determine Paleo‐Firing Temperatures in the Neolithic Settlement Site of Mursalevo‐Deveboaz (SW Bulgaria)
Authors: Jordanova Neli , Jordanova Diana , Kostadinova‐Avramova Maria , Lesigyarski Deyan , Nikolov Vassil , Katsarov Georgi , Bacvarov Krum 
Published: March 2018

AbstractArcheological remains from the Neolithic period in SE Europe are characterized by the presence of massive burnt daub relics sintered at high temperatures. These findings raised the hypothesis of deliberate house burning as a strategy for ensuring the survival of place and the development of social memory in Neolithic society. Although highly discussed in the archeological community, analytical data on the ancient firing temperatures achieved during burning Neolithic houses are missing except an empirical study determining firing temperatures according to the color of burned clay. The Neolithic site Mursalevo‐Deveboaz (Bulgaria) is one of the largest known settlements consisting of more than 70 houses. Rock‐magnetic analyses are applied for characterization of iron oxides produced during firing, and the firing temperatures were estimated using the magnetic susceptibility method. Results on a collection of 445 samples show the presence of very fine grained magnetite/maghemite and hematite. Magnetic data are supported by elemental analysis, reflectance spectroscopy, and scanning electron microscopy. The data suggest an increase in the magnetic grain size from superparamagnetic toward single domain with increasing firing temperature. Firing temperature estimates for 148 samples of different color vary between 680 and 1,140°C. Comparing the magnetic properties of iron oxides identified and literature data on solution‐combustion synthesis of iron oxides allowed a mechanism behind the extreme firing of Neolithic houses to be suggested. Our study proposes for the first time that combustion synthesis of iron oxides could explain the extreme house burning in many Neolithic settlements achieved through intentional addition of wood, dung and urine.
Hamiltonian Monte Carlo Inversion of Seismic Sources in Complex Media
Authors: Fichtner Andreas , Simutė Saule 
Published: March 2018

AbstractWe present a probabilistic seismic point source inversion, taking into account 3‐D heterogeneous Earth structure. Our method rests on (1) reciprocity and numerical wavefield simulations in complex media and (2) Hamiltonian Monte Carlo sampling that requires only a small amount of test models to provide reliable uncertainty information on the timing, location, and mechanism of the source. Using spectral element simulations of 3‐D, viscoelastic, anisotropic wave propagation, we precompute receiver side strain tensors in time and space. This enables the fast computation of synthetic seismograms for any hypothetical source within the volume of interest, and thus a Bayesian solution of the inverse problem. To improve efficiency, we developed a variant of Hamiltonian Monte Carlo sampling. Taking advantage of easily computable derivatives, numerical examples indicate that Hamiltonian Monte Carlo can converge to the posterior probability density with orders of magnitude less samples than the derivative‐free Metropolis‐Hastings algorithm, which we use for benchmarking. Exact numbers depend on observational errors and the quality of the prior. We apply our method to the Japanese Islands region where we previously constrained 3‐D structure of the crust and upper mantle using full‐waveform inversion with a minimum period of 15 s.
Unusual Magnetic Properties of Sedimentary Pyrrhotite in Methane Seepage Sediments: Comparison With Metamorphic Pyrrhotite and Sedimentary Greigite
Authors: Horng Chorng‐Shern 
Published: March 2018

AbstractInterpretation of the paleomagnetic and environmental signals carried by magnetic iron sulfide minerals depends on the ability to diagnose their magnetic properties and to recognize their origin. Greigite (Fe3S4) and hexagonal pyrrhotite (with variable composition between Fe9S10 and Fe11S12) often form authigenically in sulfidic and methanic sedimentary environments, whereas monoclinic pyrrhotite (Fe7S8) occurs widely in igneous and metamorphic rocks so that erosion of such rocks can give rise to deposition of detrital pyrrhotite in sediments. In this study, low‐ and high‐field, and low‐, room temperature, and high‐temperature magnetization data are presented to demonstrate that these magnetic iron sulfide minerals have contrasting magnetic properties that enable their identification, particularly when assisted by mineralogical characterizations. The results presented here should have wide applicability in sedimentary magnetic studies.
The Elastic Anisotropy Change Near the 410‐km Discontinuity: Predictions From Single‐Crystal Elasticity Measurements of Olivine and Wadsleyite
Authors: Zhang Jin S. , Bass Jay D. , Schmandt Brandon 
Published: March 2018

AbstractWe present a model of the single‐crystal elasticity of olivine with ~9–10 mol% Fe based on all available single‐crystal velocity measurements. A set of finite strain equations of state that account for thermoelastic effects is used for fitting the individual elastic moduli at various pressure‐temperature conditions. The same analysis is applied to reanalyze the experimentally determined single‐crystal elastic moduli of hydrous and anhydrous Fe‐bearing wadsleyite. Based on the obtained thermoelastic parameters of individual elastic moduli, we then calculated various elastic anisotropy indices of olivine and wadsleyite and extrapolated them to the pressure‐temperature conditions expected in the Earth's mantle. The results suggest that the elastic anisotropy in the Earth's upper transition zone (410–520 km depth) is likely below the seismic detection limit if it originates primarily from the lattice preferred orientation of wadsleyite crystals. On the other hand, the elastic anisotropy of olivine is still relatively high (~19–25%) at 410 km depth. Thus, if a mantle flow field induces lattice preferred orientation of olivine and wadsleyite near 410 km depth, a reduction of elastic anisotropy is expected across the 410‐km discontinuity.
A 400‐Year Ice Core Melt Layer Record of Summertime Warming in the Alaska Range
Authors: Winski Dominic , Osterberg Erich , Kreutz Karl , Wake Cameron , Ferris David , Campbell Seth , Baum Mark , Bailey Adriana , Birkel Sean , Introne Douglas , Handley Mike 
Published: March 2018

AbstractWarming in high‐elevation regions has societally important impacts on glacier mass balance, water resources, and sensitive alpine ecosystems, yet very few high‐elevation temperature records exist from the middle or high latitudes. While a variety of paleoproxy records provide critical temperature records from low elevations over recent centuries, melt layers preserved in alpine glaciers present an opportunity to develop calibrated, annually resolved temperature records from high elevations. Here we present a 400‐year temperature proxy record based on the melt layer stratigraphy of two ice cores collected from Mt. Hunter in Denali National Park in the central Alaska Range. The ice core record shows a sixtyfold increase in water equivalent total annual melt between the preindustrial period (before 1850 Common Era) and present day. We calibrate the melt record to summer temperatures based on weather station data from the ice core drill site and find that the increase in melt production represents a summer warming rate of at least 1.92 ± 0.31°C per century during the last 100 years, exceeding rates of temperature increase at most low‐elevation sites in Alaska. The Mt. Hunter melt layer record is significantly (p < 0.05) correlated with surface temperatures in the central tropical Pacific through a Rossby wave‐like pattern that enhances high temperatures over Alaska. Our results show that rapid alpine warming has taken place in the Alaska Range for at least a century and that conditions in the tropical oceans contribute to this warming.
Evolution of Precipitation Structure During the November DYNAMO MJO Event: Cloud‐Resolving Model Intercomparison and Cross Validation Using Radar Observations
Authors: Li Xiaowen , Janiga Matthew A. , Wang Shuguang , Tao Wei‐Kuo , Rowe Angela , Xu Weixin , Liu Chuntao , Matsui Toshihisa , Zhang Chidong 
Published: March 2018

AbstractEvolution of precipitation structures are simulated and compared with radar observations for the November Madden‐Julian Oscillation (MJO) event during the DYNAmics of the MJO (DYNAMO) field campaign. Three ground‐based, ship‐borne, and spaceborne precipitation radars and three cloud‐resolving models (CRMs) driven by observed large‐scale forcing are used to study precipitation structures at different locations over the central equatorial Indian Ocean. Convective strength is represented by 0‐dBZ echo‐top heights, and convective organization by contiguous 17‐dBZ areas. The multi‐radar and multi‐model framework allows for more stringent model validations. The emphasis is on testing models' ability to simulate subtle differences observed at different radar sites when the MJO event passed through. The results show that CRMs forced by site‐specific large‐scale forcing can reproduce not only common features in cloud populations but also subtle variations observed by different radars. The comparisons also revealed common deficiencies in CRM simulations where they underestimate radar echo‐top heights for the strongest convection within large, organized precipitation features. Cross validations with multiple radars and models also enable quantitative comparisons in CRM sensitivity studies using different large‐scale forcing, microphysical schemes and parameters, resolutions, and domain sizes. In terms of radar echo‐top height temporal variations, many model sensitivity tests have better correlations than radar/model comparisons, indicating robustness in model performance on this aspect. It is further shown that well‐validated model simulations could be used to constrain uncertainties in observed echo‐top heights when the low‐resolution surveillance scanning strategy is used.
On Which Microphysical Time Scales to Use in Studies of Entrainment‐Mixing Mechanisms in Clouds
Authors: Lu Chunsong , Liu Yangang , Zhu Bin , Yum Seong Soo , Krueger Steven K. , Qiu Yujun , Niu Shengjie , Luo Shi 
Published: March 2018

AbstractThe commonly used time scales in entrainment‐mixing studies are examined to seek the most appropriate one, based on aircraft observations of cumulus clouds from the RACORO campaign and numerical simulations with the Explicit Mixing Parcel Model. The time scales include the following: τevap, the time for droplet complete evaporation; τphase, the time for saturation ratio deficit (S) to reach 1/e of its initial value; τsatu, the time for S to reach −0.5%; and τreact, the time for complete droplet evaporation or S to reach −0.5%. It is found that the proper time scale to use depends on the specific objectives of entrainment‐mixing studies. First, if the focus is on the variations of liquid water content (LWC) and S, then τreact for saturation, τsatu and τphase are almost equivalently appropriate, because they all represent the rate of dry air reaching saturation or of LWC decrease. Second, if one focuses on the variations of droplet size and number concentration, τreact for complete evaporation and τevap are proper because they characterize how fast droplets evaporate and whether number concentration decreases. Moreover, τreact for complete evaporation and τevap are always positively correlated with homogeneous mixing degree (ψ); thus, the two time scales, especially τevap, are recommended for developing parameterizations. However, ψ and the other time scales can be negatively, positively, or not correlated, depending on the dominant factors of the entrained air (i.e., relative humidity or aerosols). Third, all time scales are proportional to each other under certain microphysical and thermodynamic conditions.
Impact of Synoptic‐Scale Factors on Rainfall Forecast in Different Stages of a Persistent Heavy Rainfall Event in South China
Authors: Zhang Murong , Meng Zhiyong 
Published: March 2018

AbstractThis study investigates the stage‐dependent rainfall forecast skills and the associated synoptic‐scale features in a persistent heavy rainfall event in south China, Guangdong Province, during 29–31 March 2014, using operational global ensemble forecasts from the European Centre for Medium‐Range Weather Forecasts. This persistent rainfall was divided into two stages with a better precipitation forecast skill in Stage 2 (S2) than Stage 1 (S1) although S2 had a longer lead time. Using ensemble‐based sensitivity analysis, key synoptic‐scale factors that affected the rainfall were diagnosed by correlating the accumulated precipitation of each stage to atmospheric state variables in the middle of respective stage. The precipitation in both stages was found to be significantly correlated with midlevel trough, low‐level vortex, and particularly the low‐level jet on the southeast flank of the vortex and its associated moisture transport. The rainfall forecast skill was mainly determined by the forecast accuracy in the location of the low‐level jet, which was possibly related to the different juxtapositions between the direction of the movement of the low‐level vortex and the orientation of the low‐level jet. The uncertainty in rainfall forecast in S1 was mainly from the location uncertainty of the low‐level jet, while the uncertainty in rainfall forecast in S2 was mainly from the width uncertainty of the low‐level jet with the relatively accurate location of the low‐level jet.
Inconsistent Responses of Hot Extremes to Historical Land Use and Cover Change Among the Selected CMIP5 Models
Authors: Li Xing , Chen Haishan , Wei Jiangfeng , Hua Wenjian , Sun Shanlei , Ma Hedi , Li Xiao , Li Jingping 
Published: March 2018

AbstractLand use and cover change (LUCC) is an important anthropogenic forcing of the climate system. Previous studies have demonstrated that LUCC significantly impacts both mean and extreme temperatures. In this study, we explored the multimodel performance of simulating LUCC‐induced asymmetric effects on the different percentiles of maximum temperatures (Tmax) as well as the possible reasons for these effects using results from the fifth phase of the Coupled Model Intercomparison Project (CMIP5). Four state‐of‐art Earth system models (which provide the necessary data) are selected for investigating this issue. In general, all the cases of the model from the Geophysical Fluid Dynamics Laboratory show robust asymmetric responses between the 90th (TX90P) and 10th percentiles (TX10P) of Tmax, mainly due to cropland expansions, especially over India, the Sahel, and some parts of North America. However, weak and insignificant responses are shown for both the TX90P and TX10P in other models. The different changes in the Tmax variability among the models are primarily responsible for the occurrence of asymmetric features. Furthermore, by decomposing the Tmax changes over three typical regions, we analyze the potential causes for the inconsistencies among these models' results and find two crucial processes, that is, the repartitioning of the turbulent heat fluxes and the changes of the diurnal cycle variability due to LUCC. Whether these processes are pronounced determines the occurrence of the asymmetric Tmax responses. Overall, this study provides a critical clue for reducing the uncertainties of the LUCC effects on temperature extremes, which should be evaluated against observations.