bluuebunny/crossref_metadata_2025_split huggingface dataset:
One Drought and One Volcanic Eruption Influenced the History of China: The Late Ming Dynasty Mega‐drought
Authors: Chen Kefan , Ning Liang , Liu Zhengyu , Liu Jian , Yan Mi , Sun Weiyi , Yuan Linwang , Lv Guonian , Li Longhui , Jin Chunhan , Shi Zhengguo 
Published: August 2020

AbstractThe late Ming Dynasty Megadrought (LMDMD) (1637–1643) occurred at the end of Ming Dynasty and is the severest drought event in China in the last millennium. This unprecedented drought contributed significantly to the collapse of the Ming Dynasty in 1644, casting profound impacts on Chinese history. Here, the physical mechanism for the LMDMD is studied. Based on paleoclimate reconstructions, we hypothesize that this drought was initially triggered by a natural drought event starting in 1637 and was then intensified and extended by the tropical volcanic eruption at Mount Parker in 1641. This hypothesis is supported by the case study of the Community Earth System Model‐Last Millennium Experiment archive as well as sensitivity experiments with volcanic forcing superimposed on natural drought events. The volcano‐intensified drought was associated with a decreased land‐ocean thermal contrast, a negative soil moisture response, and a weakening and eastward retreating West Pacific Subtropical High.
First Topology of Electron‐Scale Magnetic Hole
Authors: Liu Y. Y. , Fu H. S. , Zong Q. G. , Wang Z. , Liu C. M. , Huang S. Y. , Chen Z. Z. , Xu Y. , Shi Q. Q. , Yao S. T. 
Published: August 2020

AbstractElectron‐scale magnetic holes (ESMHs) have been widely observed in astrophysical and space plasmas, while their generations, evolutions, and three‐dimensional topologies are still unclear. Here we report two ESMH events detected by the Magnetospheric Multiscale spacecraft in the solar wind and the magnetosheath, respectively. The divergence analysis for the magnetic field indicates that ESMHs have nonlinear field topologies. Then a recently developed reconstruction method, based on the second‐order Taylor expansion, is applied to such ESMHs. Eventually, the first three‐dimensional topologies of ESMHs are obtained. The reconstructed results show that the ESMHs may have complex cross‐section shapes (e.g., saddle‐like shapes) and comparable extension lengths in the parallel and perpendicular directions to the magnetic field, which are inconsistent with the cylinder simplifications for a magnetic hole in previous studies. This work could improve our understandings for the geometric properties and thereby the generations and evolutions of ESMHs.
Subseasonal Forecast Skill for Weekly Mean Atmospheric Variability Over the Northern Hemisphere in Winter and Its Relationship to Midlatitude Teleconnections
Authors: Yamagami Akio , Matsueda Mio 
Published: August 2020

AbstractThis study assesses the subseasonal predictability of the weekly mean geopotential height anomaly at 500 hPa and its relationship to teleconnections over the Northern Hemisphere in winter. The skill over the North Pacific, Canada, and Greenland is higher than over other areas for weeks 3 and 4 forecasts. These peaks correspond to the centers of action for the Pacific–North American (PNA) pattern and the North Atlantic Oscillation (NAO). PNA (NAO phase) predictions are better for El Niño years at lead times of 3–4 weeks (2–4 weeks). The effects of La Niña forcing on PNA and NAO forecasts are small compared with the El Niño forcing. Numerical models have a negative PNA bias at these lead times in La Niña years. Results suggest that the improvement in the midlatitude upper‐level jet rather than in the response to El Niño–Southern Oscillation forcing in the tropics could lead to better S2S predictions.
Southward Shift of Westerlies Intensifies the East Asian Early Summer Rainband Following El Niño
Authors: Kong Wenwen , Chiang John C. H. 
Published: August 2020

AbstractAn intensification of East Asian rainfall usually occurs in summers following El Niño. We propose that this teleconnection is mediated via the westerlies impinging on the Tibetan Plateau, through El Niño's control on tropical tropospheric temperature. This is distinct from previous studies that attribute the El Niño's influence to changes in the western Pacific subtropical anticyclone. The warming in the eastern equatorial Pacific leads to uniform warming of the entire tropical troposphere, which sharpens the temperature gradient between the tropics and the subtropics and shifts the westerlies southward. The westerlies impinge over the Tibetan Plateau for longer and, through interaction with the topography, induce intense and persistent extratropical northerlies downstream of the plateau that in turn intensifies the East Asian rainband. The rainband has previously been shown to intensify in a similar manner in a warming climate, suggesting that the El Niño response provides an analog for future changes.
Using a Deep Neural Network and Transfer Learning to Bridge Scales for Seismic Phase Picking
Authors: Chai Chengping , Maceira Monica , Santos‐Villalobos Hector J. , Venkatakrishnan Singanallur V. , Schoenball Martin , Zhu Weiqiang , Beroza Gregory C. , Thurber Clifford ,   EGS Collab Team
Published: August 2020

AbstractThe important task of tracking seismic activity requires both sensitive detection and accurate earthquake location. Approximate earthquake locations can be estimated promptly and automatically; however, accurate locations depend on precise seismic phase picking, which is a laborious and time‐consuming task. We adapted a deep neural network (DNN) phase picker trained on local seismic data to mesoscale hydraulic fracturing experiments. We designed a novel workflow, transfer learning‐aided double‐difference tomography, to overcome the 3 orders of magnitude difference in both spatial and temporal scales between our data and data used to train the original DNN. Only 3,500 seismograms (0.45% of the original DNN data) were needed to retrain the original DNN model successfully. The phase picks obtained with transfer‐learned model are at least as accurate as the analyst's and lead to improved event locations. Moreover, the effort required for picking once the DNN is trained is a small fraction of the analyst's.
Modulation of Clouds and Rainfall by Tropical Cyclone's Cold Wakes
Authors: Ma Zhanhong , Fei Jianfang , Lin Yanluan , Huang Xiaogang 
Published: August 2020

AbstractTropical cyclones can pump heat into the ocean by producing a long‐lasting subsurface warm anomaly while leaving a relatively short‐term surface cold anomaly via mixing the upper ocean. Although the heat pumping has been found to be crucial in driving oceanic heat transport and thereby regulating climate changes, the contribution of surface cold anomaly to the atmosphere remains unclear. Here we show that local clouds and rainfall are effectively modulated by cold wakes left behind by tropical cyclones using a combination of satellite observations. On average, the negative surface enthalpy flux anomaly associated with the cold wake results in a reduction of rainfall by ~16.6 ± 0.6% (standard error) and a decline of cloud fraction by ~6.7 ± 0.4% over the wake region. Clouds and rainfall tend to be more suppressed for slower moving or stronger TCs. With more intense or slower moving TCs in a warming climate, such a modulation could be amplified accordingly.
Climate Sensitivity of Peatland Methane Emissions Mediated by Seasonal Hydrologic Dynamics
Authors: Feng Xue , Deventer M. Julian , Lonchar Rachel , Ng G. H. Crystal , Sebestyen Stephen D. , Roman D. Tyler , Griffis Timothy J. , Millet Dylan B. , Kolka Randall K. 
Published: August 2020

AbstractPeatlands are among the largest natural sources of atmospheric methane (CH4) worldwide. Peatland emissions are projected to increase under climate change, as rising temperatures and shifting precipitation accelerate microbial metabolic pathways favorable for CH4 production. However, how these changing environmental factors will impact peatland emissions over the long term remains unknown. Here, we investigate a novel data set spanning an exceptionally long 11 years to analyze the influence of soil temperature and water table elevation on peatland CH4 emissions. We show that higher water tables dampen the springtime increases in CH4 emissions as well as their subsequent decreases during late summer to fall. These results imply that any hydroclimatological changes in northern peatlands that shift seasonal water availability from winter to summer will increase annual CH4 emissions, even if temperature remains unchanged. Therefore, advancing hydrological understanding in peatland watersheds will be crucial for improving predictions of CH4 emissions.
Platelet Ice Under Arctic Pack Ice in Winter
Authors: Katlein Christian , Mohrholz Volker , Sheikin Igor , Itkin Polona , Divine Dmitry V. , Stroeve Julienne , Jutila Arttu , Krampe Daniela , Shimanchuk Egor , Raphael Ian , Rabe Benjamin , Kuznetsov Ivan , Mallet Maria , Liu Hailong , Hoppmann Mario , Fang Ying‐Chih , Dumitrascu Adela , Arndt Stefanie , Anhaus Philipp , Nicolaus Marcel , Matero Ilkka , Oggier Marc , Eicken Hajo , Haas Christian 
Published: August 2020

AbstractThe formation of platelet ice is well known to occur under Antarctic sea ice, where subice platelet layers form from supercooled ice shelf water. In the Arctic, however, platelet ice formation has not been extensively observed, and its formation and morphology currently remain enigmatic. Here, we present the first comprehensive, long‐term in situ observations of a decimeter thick subice platelet layer under free‐drifting pack ice of the Central Arctic in winter. Observations carried out with a remotely operated underwater vehicle (ROV) during the midwinter leg of the MOSAiC drift expedition provide clear evidence of the growth of platelet ice layers from supercooled water present in the ocean mixed layer. This platelet formation takes place under all ice types present during the surveys. Oceanographic data from autonomous observing platforms lead us to the conclusion that platelet ice formation is a widespread but yet overlooked feature of Arctic winter sea ice growth.
New Constraints on the Young Lava Flow Profile in the Northern Mare Imbrium
Authors: Yuan Yuefeng , Wang Fenghua , Zhu Peimin , Xiao Long , Zhao Na 
Published: August 2020

AbstractPrevious studies showed that the Eratosthenian mare (Em) unit in the northern Mare Imbrium, which is the location of the Chang'e‐3 (CE3) landing site, was simply formed by one period of thick lava flow. However, the CE3 Yutu rover equipped with lunar penetrating radar (LPR) recognized multilayered Em basalts based on the Channel 1 data reprocessed in this paper, indicating that three subdivided thin Eratosthenian lava flows should exist. The spatial variation and thickness distribution of each layer are further estimated based on the location of interfaces recognized from the shallow radar profile. Finally, we build a three‐dimensional stratigraphic model of young mare basalts with filling directions beneath the Chang'e‐3 landing site. The result infers that these young lava flows in the northern Mare Imbrium probably erupted intermittently from the same source.
Continuous Dissolved Gas Tracing of Fracture‐Matrix Exchanges
Authors: Hoffmann R. , Goderniaux P. , Jamin P. , Chatton E. , de la Bernardie J. , Labasque T. , Le Borgne T. , Dassargues A. 
Published: August 2020

AbstractTransport in fractured media plays an important role in a range of processes, from rock weathering and microbial processes to contaminant transport, and energy extraction and storage. Diffusive transfer between the fracture fluid and the rock matrix is often a key element in these applications. But the multiscale heterogeneity of fractures renders the field assessment of these processes extremely challenging. This study explores the use of dissolved gases as tracers of fracture‐matrix interactions, which can be measured continuously and highly accurately using mobile mass spectrometers. Since their diffusion coefficients vary significantly, multiple gases are used to probe different scales of fracture‐matrix exchanges. Tracer tests with helium, xenon, and argon were performed in a fractured chalk aquifer, and resulting tracer breakthrough curves are modeled. Results show that continuous dissolved gas tracing with multiple tracers provides key constrains on fracture‐matrix interactions and reveal unexpected scale effects in fracture‐matrix exchange rates.
Antarctic Elevation Drives Hemispheric Asymmetry in Polar Lapse Rate Climatology and Feedback
Authors: Hahn L. C. , Armour K. C. , Battisti D. S. , Donohoe A. , Pauling A. G. , Bitz C. M. 
Published: August 2020

AbstractThe lapse rate feedback is the dominant driver of stronger warming in the Arctic than the Antarctic in simulations with increased CO2. While Antarctic surface elevation has been implicated in promoting a weaker Antarctic lapse rate feedback, the mechanisms in which elevation impacts the lapse rate feedback are still unclear. Here we suggest that weaker Antarctic warming under CO2 forcing stems from shallower, less intense climatological inversions due to limited atmospheric heat transport above the ice sheet elevation and elevation‐induced katabatic winds. In slab ocean model experiments with flattened Antarctic topography, stronger climatological inversions support a stronger lapse rate feedback and annual mean Antarctic warming comparable to the Arctic under CO2 doubling. Unlike the Arctic, seasonality in warming over flat Antarctica is mainly driven by a negative shortwave cloud feedback, which exclusively dampens summer warming, with a smaller contribution from the winter‐enhanced lapse rate feedback.
Correlations Between Dispersive Alfvén Wave Activity, Electron Energization, and Ion Outflow in the Inner Magnetosphere
Authors: Hull A. J. , Chaston C. C. , Bonnell J. W. , Damiano P. A. , Wygant J. R. , Reeves G. D. 
Published: August 2020

AbstractUsing measurements from the Van Allen Probes, we show that field‐aligned fluxes of electrons energized by dispersive Alfvén waves (DAWs) are prominent in the inner magnetosphere during active conditions. These electrons have preferentially field‐aligned anisotropies from 1.2 to >2 at energies ranging from tens of electron volts to several kiloelectron volts (keV), with largest values being coincident with magnetic field dipolarizations. Comparisons reveal that DAW energy densities and Poynting fluxes are strongly correlated with precipitating electron energies and energy fluxes and also O+ ion outflow energies. These observations yield empirical inner magnetosphere relations between the DAW and electron inputs and the O+ ion outflow response, providing important constraints for models. They also suggest that DAWs play an important role in enhancing field‐aligned electron input into the ionosphere that facilitates the outflow and subsequent energization of O+ ions in the wave fields into the inner magnetosphere.
Electron Inflow Velocities and Reconnection Rates at Earth's Magnetopause and Magnetosheath
Authors: Burch J. L. , Webster J. M. , Hesse M. , Genestreti K. J. , Denton R. E. , Phan T. D. , Hasegawa H. , Cassak P. A. , Torbert R. B. , Giles B. L. , Gershman D. J. , Ergun R. E. , Russell C. T. , Strangeway R. J. , Le Contel O. , Pritchard K. R. , Marshall A. T. , Hwang K.‐J. , Dokgo K. , Fuselier S. A. , Chen L.‐J. , Wang S. , Swisdak M. , Drake J. F. , Argall M. R. , Trattner K. J. , Yamada M. , Paschmann G. 
Published: August 2020

AbstractElectron inflow and outflow velocities during magnetic reconnection at and near the dayside magnetopause are measured using satellites from NASA's Magnetospheric Multiscale (MMS) mission. A case study is examined in detail, and three other events with similar behavior are shown, with one of them being a recently published electron‐only reconnection event in the magnetosheath. The measured inflow speeds of 200–400 km/s imply dimensionless reconnection rates of 0.05–0.25 when normalized to the relevant electron Alfvén speed, which are within the range of expectations. The outflow speeds are about 1.5–3 times the inflow speeds, which is consistent with theoretical predictions of the aspect ratio of the inner electron diffusion region. A reconnection rate of 0.04 ± 25% was obtained for the case study event using the reconnection electric field as compared to the 0.12 ± 20% rate determined from the inflow velocity.
The Shifting Scales of Western U.S. Landfalling Atmospheric Rivers Under Climate Change
Authors: Rhoades Alan M. , Jones Andrew D. , Srivastava Abhishekh , Huang Huanping , O'Brien Travis A. , Patricola Christina M. , Ullrich Paul A. , Wehner Michael , Zhou Yang 
Published: August 2020

AbstractAtmospheric rivers (ARs) can be a boon and bane to water resource managers as they have the ability to replenish water reserves, but they can also generate million‐to‐billion‐dollar flood damages. To investigate how anthropogenic climate change may influence AR characteristics in the coastal western United States by end century, we employ a suite of novel tools such as variable resolution in the Community Earth System Model (VR‐CESM), the TempestExtremes AR detection algorithm, and the Ralph, Rutz, et al. (2019, https://doi.org/10.1175/BAMS‐D‐18‐0023.1) AR category scale. We show that end‐century ARs primarily shift from being “mostly or primarily beneficial” to “mostly or primarily hazardous” with a concomitant sharpening and intensification of winter season precipitation totals. Changes in precipitation totals are due to a significant increase in AR (+260%) rather than non‐AR (+7%) precipitation, largely through increases in the most intense category of AR events and a decrease in the interval between landfalling ARs.
Potential Evidence of Low‐Energy Electron Scattering and Ionospheric Precipitation by Time Domain Structures
Authors: Shen Yangyang , Artemyev Anton , Zhang Xiao‐Jia , Vasko Ivan Y. , Runov Andrei , Angelopoulos Vassilis , Knudsen David 
Published: August 2020

AbstractPlasma sheet electron precipitation is critical in magnetosphere‐ionosphere coupling and has long been attributed to electron scattering by whistler‐mode and electron cyclotron harmonic waves. Recent observations have revealed that time domain structures (TDSs) that appear as broadband electrostatic fluctuations may also scatter plasma sheet electrons. However, there has been no observational evidence of TDS scattering electrons into the ionosphere. This study presents potential evidence from conjugate observations between the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission and the low‐altitude Enhanced Polar Outflow Probe (e‐POP) spacecraft. During the five events presented, THEMIS observed intense electron injections accompanied by TDSs, while e‐POP captured precipitation of plasma sheet electrons with energies ∼100–325 eV over a broad pitch angle range. The observed TDSs can efficiently scatter these electrons exceeding the strong diffusion limit. Our results suggest that TDSs may contribute to plasma sheet electron scattering around times of injections.
Mechanical Imaging of a Volcano Plumbing System From GNSS Unsupervised Modeling
Authors: Beauducel François , Peltier Aline , Villié Antoine , Suryanto Wiwit 
Published: August 2020

AbstractIdentification of internal structures in an active volcano is mandatory to quantify the physical processes preceding eruptions. We propose a fully unsupervised Bayesian inversion method that uses the point compound dislocation model as a complex source of deformation, to dynamically identify the substructures activated during magma migration. We applied this method at Piton de la Fournaise. Using 7‐day moving trends of Global Navigation Satellite System (GNSS) data preceding the June 2014 eruption, we compute a total of 15 inversion models of 2.5 million forward problems each, without a priori information. Obtained source shapes (dikes, prolate ellipsoids, or pipes) show magma migration from 7–8 km depth to the surface, drawing a mechanical “tomography” of the magma pathway. Our results also suggest source geometries compatible with observed eruptive fissures and seismicity distribution. In case of finite magma volume involved in final dike injection, source volume estimates from this method allow forecasting volumes of erupted lava.
Properties of Lightning Generated Whistlers Based on Van Allen Probes Observations and Their Global Effects on Radiation Belt Electron Loss
Authors: Green A. , Li W. , Ma Q. , Shen X.‐C. , Bortnik J. , Hospodarsky G. B. 
Published: August 2020

AbstractLightning generated whistlers (LGWs) play an important role in precipitating energetic electrons in the Earth's inner radiation belt and beyond. Wave burst data from the Van Allen Probes are used to unambiguously identify LGWs and analyze their properties at L < 4 by extending their frequencies down to ~100 Hz for the first time. The statistical results show that LGWs typically occur at frequencies from 100 Hz to 10 kHz with the major wave power below the equatorial lower hybrid resonance frequency, and their wave amplitudes are typically strong at L < 3 with an occurrence rate up to ~30% on the nightside. The lifetime calculation indicates that LGWs play an important role in scattering electrons from tens of keV to several MeV at L < ~2.5. Our newly constructed LGW models are critical for evaluating the global effects of LGWs on energetic electron loss at L < 4.
Predicting the Time of Arrival of Coronal Mass Ejections at Earth From Heliospheric Imaging Observations
Authors: Braga Carlos Roberto , Vourlidas Angelos , Stenborg Guillermo , Dal Lago Alisson , Mendonça Rafael Rodrigues Souza de , Echer Ezequiel 
Published: August 2020

AbstractThe time of arrival (ToA) of coronal mass ejections (CMEs) at Earth is a key parameter due to the space weather phenomena associated with the CME arrival, such as intense geomagnetic storms. Despite the incremental use of new instrumentation and the development of novel methodologies, ToA estimated errors remain above 10 h on average. Here, we investigate the prediction of the ToA of CMEs using observations from heliospheric imagers, i.e., from heliocentric distances higher than those covered by the existent coronagraphs. In order to perform this work, we analyze 14 CMEs observed by the heliospheric imagers HI‐1 onboard the twin STEREO spacecraft to determine their front location and speed. The kinematic parameters are derived with a new technique based on the Elliptical Conversion (ElCon) method, which uses simultaneous observations from the two viewpoints from STEREO. Outside the field of view of the instruments, we assume that the dynamics of the CME evolution is controlled by aerodynamic drag, i.e., a force resulting from the interaction with particles from the background solar wind. To model the drag force, we use a physical model that allows us to derive its parameters without the need to rely on drag coefficients derived empirically. We found a CME ToA mean error of 1.6 ± 8.0 h ToA and a mean absolute error of 6.9 ± 3.9 h for a set of 14 events. The results suggest that observations from HI‐1 lead to estimates with similar errors to observations from coronagraphs.