bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of Interseismic Coupling Along the North and East Anatolian Faults Inferred From InSAR and GPS Data
Authors: Bletery Quentin , Cavalié Olivier , Nocquet Jean‐Mathieu , Ragon Théa
Published: August 2020

The North Anatolian Fault (NAF) has produced numerous major earthquakes. After decades of quiescence, the Mw 6.8 Elazığ earthquake (24 January 2020) has recently reminded us that the East Anatolian Fault (EAF) is also capable of producing significant earthquakes. To better estimate the seismic hazard associated with these two faults, we jointly invert interferometric synthetic aperture radar (InSAR) and GPS data to image the spatial distribution of interseismic coupling along the eastern part of both the NAF and EAF. We perform the inversion in a Bayesian framework, enabling to estimate uncertainties on both long‐term relative plate motion and coupling. We find that coupling is high and deep (0–20 km) on the NAF and heterogeneous and superficial (0–5 km) on the EAF. Our model predicts that the Elazığ earthquake released between 200 and 250 years of accumulated moment, suggesting a bicentennial recurrence time.
Constraining Projections Using Decadal Predictions
Authors: Befort Daniel J. , O'Reilly Christopher H. , Weisheimer Antje
Published: August 2020

There is increasing demand for robust, reliable, and actionable climate information for the next 1 to 50 years. This is challenging for the scientific community as the longest initialized predictions are limited to 10 years (decadal predictions). Thus, to provide seamless information for the upcoming 50 years, information from decadal predictions and uninitialized projections need to be merged. In this study, the ability to obtain valuable climate information beyond decadal time scales by constraining uninitialized projections using decadal predictions is assessed. The application of this framework to surface temperatures over the North Atlantic Subpolar Gyre region, shows that the constrained uninitialized subensemble has higher skill compared to the overall projection ensemble also beyond 10 years when information from decadal predictions is no longer available. Though showing the potential of such a constraining approach to obtain climate information for the near‐term future, its utility depends on the added value of initialization.
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

The 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

Electron‐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

This 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

An 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

The 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

Tropical 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

Peatlands 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

The 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

Previous 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

Transport 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

The 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

Using 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

Electron 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

Atmospheric 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

Plasma 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

Identification 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

Lightning 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

The 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.
Multisatellite MMS Analysis of Electron Holes in the Earth's Magnetotail: Origin, Properties, Velocity Gap, and Transverse Instability
Authors: Lotekar A. , Vasko I. Y. , Mozer F. S. , Hutchinson I. , Artemyev A. V. , Bale S. D. , Bonnell J. W. , Ergun R. , Giles B. , Khotyaintsev Yu. V. , Lindqvist P.‐A. , Russell C. T. , Strangeway R.
Published: August 2020

We present a statistical analysis of more than 2,400 electrostatic solitary waves interpreted as electron holes (EH) measured aboard at least three Magnetospheric Multiscale (MMS) spacecraft in the Earth's magnetotail. The velocities of EHs are estimated using the multispacecraft interferometry. The EH velocities in the plasma rest frame are in the range from just a few km/s, which is much smaller than ion thermal velocity VTi, up to 20,000 km/s, which is comparable to electron thermal velocity VTe. We argue that fast EHs with velocities larger than about 0.1VTe are produced by bump‐on‐tail instabilities, while slow EHs with velocities below about 0.05VTe can be produced by warm bistream and, probably, Buneman‐type instabilities. We show that typically fast and slow EHs do not coexist, indicating that the instabilities producing EHs of different types operate independently. We have identified a gap in the distribution of EH velocities between VTi and 2VTi, which is considered to be the evidence for self‐acceleration (Zhou & Hutchinson, 2018) or ion Landau damping of EHs. Parallel spatial scales and amplitudes of EHs are typically between λD and 10 λD and between 10−3 Te and 0.1 Te, respectively. We show that electrostatic potential amplitudes of EHs are below the threshold of the transverse instability and highly likely restricted by the nonlinear saturation criterion of electron streaming instabilities seeding electron hole formation:
, where ϖ = min(γ, 1.5 ωce), where γ is the increment of instabilities seeding EH formation, while ωce is electron cyclotron frequency. The implications of the presented results are discussed.
Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ
Authors: Soares G. , Yamazaki Y. , Cnossen I. , Matzka J. , Pinheiro K. J. , Morschhauser A. , Alken P. , Stolle C.
Published: August 2020

The magnetic equator in the Brazilian region has moved over 1,100 km northward since 1957, passing the geomagnetic observatory Tatuoca (TTB), in northern Brazil, around 2013. We recovered and processed TTB hourly mean values of the geomagnetic field horizontal (H) component from 1957 until 2019, allowing the investigation of long‐term changes in the daily variation due to the influence of secular variation, solar activity, season, and lunar phase. The H day‐to‐day variability and the occurrence of the counter electrojet at TTB were also investigated. Until the 1990s, ionospheric solar quiet currents dominated the quiet‐time daily variation at TTB. After 2000, the magnitude of the daily variation became appreciably greater due to the equatorial electrojet (EEJ) contribution. The H seasonal and day‐to‐day variability increased as the magnetic equator approached, but their amplitudes normalized to the average daily variation remained at similar levels. Meanwhile, the amplitude of the lunar variation, normalized in the same way, increased from 5% to 12%. Within the EEJ region, the occurrence rate of the morning counter electrojet (MCEJ) increased with proximity to the magnetic equator, while the afternoon counter electrojet (ACEJ) did not. EEJ currents derived from CHAMP and Swarm satellite data revealed that the MCEJ rate varies with magnetic latitude within the EEJ region while the ACEJ rate is largely constant. Simulations with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model based on different geomagnetic main field configurations suggest that long‐term changes in the geomagnetic daily variation at TTB can be attributed to the main field secular variation.
First Zonal Drift Velocity Measurement of Equatorial Plasma Bubbles (EPBs) From a Geostationary Orbit Using GOLD Data
Authors: Karan Deepak K. , Daniell Robert E. , England Scott L. , Martinis Carlos R. , Eastes Richard W. , Burns Alan G. , McClintock William E.
Published: August 2020

The National Aeronautics and Space Administration (NASA) Global‐scale Observations of the Limb and Disk (GOLD) satellite takes far‐ultraviolet images of the Earth from geostationary orbit. GOLD observes the complete structure of equatorial plasma bubbles (EPBs). Since there are repeated observations of the same regions of the Earth, the zonal drift velocities of EPBs are derived using GOLD data. EPBs observed within 60–25°W longitudes on 27–29 November 2018 are considered in the present analysis. The drift velocities obtained on 27 November 2018 are 116 ± 4, 118 ± 6, and 105 ± 9 m/s at the North and South crests of equatorial ionization anomaly (EIA) and the magnetic equator, respectively. While on 29 November the velocities 107 ± 10, 106 ± 8, and 110 ± 4 m/s are in agreement with the 27th (within the uncertainties), on 28 November the velocities are substantially lower: 80 ± 3, 95 ± 7, and 88 ± 11 m/s. This is the first simultaneous measurement of EPB zonal drift velocities at both crests of EIA and the magnetic equator. On 27–29 November 2018, the average spacing between adjacent EPBs is found to be ~377, 526, and 442 km, respectively.
Nighttime Ionospheric TEC Study Over Latin America During Moderate and High Solar Activity
Authors: Romero‐Hernandez E. , Denardini C. M. , Jonah O. F. , Essien P. , Picanço G. A. S. , Nogueira P. A. B. , Rodriguez‐Martinez M. , Resende L. C. A. , de la Luz V. , Aguilar‐Rodriguez E. , Sergeeva M. , Gonzalez‐Esparza J. A. , Takahashi H. , Perez‐Tijerina E.
Published: August 2020

The present work is a comprehensive study of the ionospheric vertical total electron content (vTEC) variations during the nighttime, based on data collected by ground‐based Global Navigation Satellite System (GNSS) receivers over the Latin American region. We provide a qualitative and quantitative analysis of the ionospheric vTEC trend at 21:00, 00:00, and 03:00 local time (LT), during geomagnetically undisturbed days of 2011 (ascending phase) and 2014 (maximum phase), which encompassed (a) the response to the solar flux variation, (b) the seasonal trend in different latitudes and longitudes, and (c) the interhemispheric asymmetry. One significant result of this study is the development of TEC maps for the Latin American region, which are used for the monitoring and forecasting of the ionosphere for space weather purposes. The nighttime vTEC variations showed a strong latitudinal dependence, especially in the Northern Hemisphere. For 2011, the semiannual anomaly was similar to that observed in daytime; however, in 2014, the receivers at midlatitude presented asymmetric behavior. Similarly, the nighttime winter anomaly (NWA) was very weak in both years. The Equatorial Ionospheric Anomaly (EIA) signature was absent from June to August, a period in which the hemispheric disparity in the vTEC values became more evident, suggesting a feeble interhemispheric circulation. The Midlatitude Summer Nighttime Anomaly (MSNA) was also identified in the Southern Hemisphere, during January and February of 2011 (moderate solar activity). Model approximations suggest that the equatorward winds and the EIA were involved in the formation of the MSNA.
Excitation Mechanism of Ionospheric 6‐Day Oscillation During the 2019 September Sudden Stratospheric Warming Event
Authors: Miyoshi Yasunobu , Yamazaki Yosuke
Published: August 2020

A sudden stratospheric warming (SSW) event in the Antarctic region occurred in September 2019. During the SSW event, the quasi 6‐day wave (Q6DW) was enhanced in the mesosphere, and strong 6‐day oscillations are observed in ionospheric parameters, such as the equatorial electrojet (EEJ) and electron density. The 6‐day variation in the EEJ has a westward moving structure with the zonal wave number 1, indicating the influence of the Q6DW. In this study, we investigate the excitation mechanism of the 6‐day variations in the EEJ and electron density using numerical simulations. The main results are as follows. The 6‐day variations in the ionosphere are not generated by the Q6DW but generated by the waves with periods from 10 to 14 hr. The amplitude of the 10–14 hr waves is modulated with a period of 6 days, due to the nonlinear interaction between the Q6DW and migrating semidiurnal tide. This leads to the 6‐day variations in the EEJ and electron density through the E region dynamo process. At a fixed local time, the secondary waves generated by the Q6DW‐tidal interaction produce westward moving ionospheric 6‐day variations with zonal wave number 1, which cannot be distinguished from the ionospheric variations by the Q6DW itself. The interference of secondary waves leads to a longitudinal asymmetry in the magnitude of the ionospheric 6‐day oscillation.
Ionosphere Feedback to Electron Scattering by Equatorial Whistler Mode Waves
Authors: Artemyev A. V. , Zhang X.‐J. , Angelopoulos V. , Mourenas D. , Vainchtein D. , Shen Y. , Vasko I. , Runov A.
Published: August 2020

Plasma sheet electron precipitation, much of it driven by whistler mode waves, is critical for magnetosphere‐ionosphere coupling. This precipitation leads to a secondary electron population at low altitudes, which moves upward along magnetic field lines to the equatorial plasma sheet. We investigate observational evidence for such electron precipitation and the ionospheric feedback provided by the secondary electron outflows. Using the near‐equatorial Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, we show that whistler mode wave bursts are accompanied by enhanced field‐aligned electrons. The properties of these electrons are not related to the whistler mode waves, as would have been expected from local wave‐particle interactions. Thus, it is unlikely that the field‐aligned electrons are formed by electron Landau resonance with whistler mode waves. This population can be the secondary electron outflows resulting from plasma sheet electron precipitation to the ionosphere. Combining THEMIS, Cluster, and Fast Auroral Snapshot Explorer (FAST) measurements, we show that this field‐aligned electron population is also observed at low altitudes, where it is associated with high‐frequency electrostatic waves. These low‐altitude waves are likely generated by the secondary electron outflows and, in turn, scatter these electrons outside of the loss cone, allowing them to be observed by the wide field‐of‐view particle instrument on the near‐equatorial THEMIS spacecraft. We discuss how this secondary electron population can subsequently alter whistler mode wave generation and propagation in the magnetosphere.
How Does Viscosity Contrast Influence Phase Mixing and Strain Localization?
Authors: Cross Andrew J. , Olree Elizabeth , Couvy Hélène , Skemer Philip
Published: August 2020

Ultramylonites—intensely deformed rocks with fine grain sizes and well‐mixed mineral phases—are thought to be a key component of Earth‐like plate tectonics, because coupled phase mixing and grain boundary pinning enable rocks to deform by grain‐size‐sensitive, self‐softening creep mechanisms over long geologic timescales. In isoviscous two‐phase composites, “geometric” phase mixing occurs via the sequential formation, attenuation (stretching), and disaggregation of compositional layering. However, the effects of viscosity contrast on the mechanisms and timescales for geometric mixing are poorly understood. Here, we describe a series of high‐strain torsion experiments on nonisoviscous calcite‐fluorite composites (viscosity contrast, ηca/ηfl ≈ 200) at 500°C, 0.75 GPa confining pressure, and 10−6–10−4 s−1 shear strain rate. At low to intermediate shear strains (γ ≤ 10), polycrystalline domains of the individual phases become sheared and form compositional layering. As layering develops, strain localizes into the weaker phase, fluorite. Strain partitioning impedes mixing by reducing the rate at which the stronger (calcite) layers deform, attenuate, and disaggregate. Even at very large shear strains (γ ≥ 50), grain‐scale mixing is limited, and thick compositional layers are preserved. Our experiments (1) demonstrate that viscosity contrasts impede mechanical phase mixing and (2) highlight the relative inefficiency of mechanical mixing. Nevertheless, by employing laboratory flow laws, we show that “ideal” conditions for mechanical phase mixing may be found in the wet middle to lower continental crust and in the dry mantle lithosphere, where quartz‐feldspar and olivine‐pyroxene viscosity contrasts are minimized, respectively.
Accelerated Snow Melt in the Russian Caucasus Mountains After the Saharan Dust Outbreak in March 2018
Authors: Dumont M. , Tuzet F. , Gascoin S. , Picard G. , Kutuzov S. , Lafaysse M. , Cluzet B. , Nheili R. , Painter T. H.
Published: August 2020

Light absorbing particles, such as mineral dust, are a potent climate forcing agent. Many snow‐covered areas are subject to dust outbreak events originating from desert regions able to significantly decrease snow albedo. Here, using a combination of Sentinel‐2 imagery, in situ measurements and ensemble detailed snowpack simulations, we study the impact on snow cover duration of a major dust deposition event that occurred in the Caucasus in March 2018. This is, to the best of our knowledge, the first study using ensemble approach and Sentinel‐2 imagery to quantify the impact of a dust event on the snow cover evolution. We demonstrate that the calculation of the impact is strongly affected by the snow model uncertainties but that the March 2018 dust event systematically shortened the snow cover duration in Western Caucasus. The shortening is higher for location with higher accumulation and higher elevation (median values of 23 ± 7 days) than for location at lower elevation (median values of 15 ± 3 days). This is because for sites with higher location and higher accumulation, melt occurs later in the season when more incoming solar energy is available. This highlights the huge impact of a single 1‐day event on snow cover duration, and consequently, on the hydrology of a large region.
Atmospheric Precipitation and Anomalous Upper Mantle in Relation to Intraplate Seismicity in Norway
Authors: Maystrenko Yuriy Petrovich , Brönner Marco , Olesen Odleiv , Saloranta Tuomo Mikael , Slagstad Trond
Published: August 2020

Two enigmatic regions of high intraplate seismicity in Norway (Western Norway and the Nordland area) show a temporal correlation between the number of earthquakes within the upper crystalline crust and intensity of rain and snowmelt at the Earth's surface. This correlation is obvious in the Nordland area where detailed and reliable data on seismicity are available, whereas the correlation is weaker in Western Norway where detailed data on seismicity are missing. Moreover, these discrete zones of high seismic activity coincide spatially with prominent, low‐velocity, and, most likely, thermally anomalous zones in the upper mantle. We propose that in addition to other causes, the high seismicity may be controlled by the anomalous upper mantle, along with topographically induced gravitational potential energy and crustal density variations. Precipitation‐induced, seasonal increases in pore‐fluid pressure within the fractured crystalline bedrock and changes in water loads may modulate the tectonically controlled seismicity.
Microfluidics for interrogating live intact tissues
Authors: Horowitz Lisa F. , Rodriguez Adán D. , Ray Tyler , Folch Albert
Published: August 2020

The intricate microarchitecture of tissues – the “tissue microenvironment” – is a strong determinant of tissue function. Microfluidics offers an invaluable tool to precisely stimulate, manipulate, and analyze the tissue microenvironment in live tissues and engineer mass transport around and into small tissue volumes. Such control is critical in clinical studies, especially where tissue samples are scarce, in analytical sensors, where testing smaller amounts of analytes results in faster, more portable sensors, and in biological experiments, where accurate control of the cellular microenvironment is needed. Microfluidics also provides inexpensive multiplexing strategies to address the pressing need to test large quantities of drugs and reagents on a single biopsy specimen, increasing testing accuracy, relevance, and speed while reducing overall diagnostic cost. Here, we review the use of microfluidics to study the physiology and pathophysiology of intact live tissues at sub-millimeter scales. We categorize uses as either in vitro studies – where a piece of an organism must be excised and introduced into the microfluidic device – or in vivo studies – where whole organisms are small enough to be introduced into microchannels or where a microfluidic device is interfaced with a live tissue surface (e.g. the skin or inside an internal organ or tumor) that forms part of an animal larger than the device. These microfluidic systems promise to deliver functional measurements obtained directly on intact tissue – such as the response of tissue to drugs or the analysis of tissue secretions – that cannot be obtained otherwise.
A wireless, implantable optoelectrochemical probe for optogenetic stimulation and dopamine detection
Authors: Liu Changbo , Zhao Yu , Cai Xue , Xie Yang , Wang Taoyi , Cheng Dali , Li Lizhu , Li Rongfeng , Deng Yuping , Ding He , Lv Guoqing , Zhao Guanlei , Liu Lei , Zou Guisheng , Feng Meixin , Sun Qian , Yin Lan , Sheng Xing
Published: August 2020

Physical and chemical technologies have been continuously progressing advances in neuroscience research. The development of research tools for closed-loop control and monitoring neural activities in behaving animals is highly desirable. In this paper, we introduce a wirelessly operated, miniaturized microprobe system for optical interrogation and neurochemical sensing in the deep brain. Via epitaxial liftoff and transfer printing, microscale light-emitting diodes (micro-LEDs) as light sources and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-coated diamond films as electrochemical sensors are vertically assembled to form implantable optoelectrochemical probes for real-time optogenetic stimulation and dopamine detection capabilities. A customized, lightweight circuit module is employed for untethered, remote signal control, and data acquisition. After the probe is injected into the ventral tegmental area (VTA) of freely behaving mice, in vivo experiments clearly demonstrate the utilities of the multifunctional optoelectrochemical microprobe system for optogenetic interference of place preferences and detection of dopamine release. The presented options for material and device integrations provide a practical route to simultaneous optical control and electrochemical sensing of complex nervous systems.
Immune-based therapies in the management of multiple myeloma
Authors: Zanwar Saurabh , Nandakumar Bharat , Kumar Shaji
Published: August 2020

Multiple myeloma (MM) is a clonal plasma cell malignancy affecting a predominantly elderly population. The continued development of newer therapies with novel mechanisms of action has reshaped the treatment paradigm of this disorder in the last two decades, leading to a significantly improved prognosis. This has in turn resulted in an increasing number of patients in need of therapy for relapsed/refractory disease. Immune-based therapies, including monoclonal antibodies, immune checkpoint inhibitors, and most promisingly, adoptive cellular therapies represent important therapeutic strategies in these patients due to their non-cross resistant mechanisms of actions with the usual frontline therapies comprising of immunomodulatory drugs (IMiDs) and proteasome inhibitors (PIs). The anti-CD38 antibodies daratumumab and more recently isatuximab, with their excellent efficacy and safety profile along with its synergy in combination with IMiDs and PIs, are being increasingly incorporated in the frontline setting. Chimeric antigen receptor–T cell (CART) therapies and bi-specific T-cell engager (BiTE) represent exciting new options that have demonstrated efficacy in heavily pretreated and refractory MM. In this review, we discuss the rationale for use of immune-based therapies in MM and summarize the currently available literature for common antibodies and CAR-T therapies that are utilized in MM.
Small molecules targeting RORγt inhibit autoimmune disease by suppressing Th17 cell differentiation
Authors: Tan Jun , Liu Huan , Huang Minhao , Li Na , Tang Shibing , Meng Jiayu , Tang Shiyun , Zhou Hongxiu , Kijlstra Aize , Yang Peizeng , Hou Shengping
Published: August 2020

Th17 cells, a lymphocyte subpopulation that is characterized by the expression of the transcription factor “retinoic acid receptor-related orphan receptor gamma-t” (RORγt), plays an important role in the pathogenesis of autoimmune disease. The current study was set up to discover novel and non-steroidal small-molecule inverse agonists of RORγt and to determine their effects on autoimmune disease. Structure-based virtual screening (SBVS) was used to find compounds targeting RORγt. Flow cytometry was used to detect the Th17 cell differentiation. Inverse agonists were intraperitoneally administered to mice undergoing experimental autoimmune uveitis (EAU), experimental autoimmune encephalomyelitis (EAE) or type 1 diabetes. The effects of the inverse agonists were evaluated by clinical or histopathological scoring. Among 1.3 million compounds screened, CQMU151 and CQMU152 were found to inhibit Th17 cell differentiation without affecting the differentiation of Th1 and Treg lineages (both P = 0.001). These compounds also reduced the severity of EAU (P = 0.01 and 0.013) and functional studies showed that they reduced the number of Th17 cell and the expression of IL-17(Th17), but not IFN-γ(Th1) and TGF-β(Treg) in mouse retinas. Further studies showed that these compounds may reduce the expression of p-STAT3 by reducing the positive feedback loop of IL-17/IL-6/STAT3. These compounds also reduced the impaired blood–retinal barrier function by upregulating the expression of tight junction proteins. These compounds were also found to reduce the severity of EAE and type 1 diabetes. Our results showed that RORγt inverse agonists may inhibit the development of autoimmune diseases and may provide new clues for the treatment of Th17-mediated immune diseases.
QM/MM MD simulations reveal an asynchronous PCET mechanism for nitrite reduction by copper nitrite reductase
Authors: Cheng Ronny , Wu Chun , Cao Zexing , Wang Binju
Published: August 2020

The nitrite reduction in copper nitrite reductase is found to proceed through an asynchronous proton-coupled electron transfer (PCET) mechanism, with electron transfer from T1-Cu to T2-Cu preceding the proton transfer from Asp98 to nitrite.
Facile synthesis of Cu-CuFe2O4nanozymes for sensitive assay of H2O2and GSH
Authors: Xia Fan , Shi Qiaofang , Nan Zhaodong
Published: August 2020

Artificial enzymes have drawn substantial research interest from the scientific community due to their advantages over natural enzymes.