bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observation of Bottom‐Trapped Topographic Rossby Waves on the Shelf Break of the Chukchi Sea
Authors: Ku Ahyoung , Seung Young Ho , Jeon Chanhyung , Choi Youngseok , Yoshizawa Eri , Shimada Koji , Cho Kyoung‐Ho , Park Jae‐Hun 
Published: June 2020

AbstractThis study investigates topographic Rossby waves (TRWs) with a period of approximately 35 hr using a mooring observation at 194‐m depth on the shelf break of the Chukchi Sea in the Arctic Ocean. We measured velocity, temperature, and salinity for about 1 year from August 2014 to August 2015. The observations reveal that the bottom‐intensified upslope current fluctuations were significantly coherent with near‐bottom temperature fluctuations, with a phase lag of approximately 90°. Near the seafloor, the temperature increased with depth. Therefore, the temperature increases (decreases) with the upslope (downslope) currents. Theoretical estimates of the wavelength, angle of wavenumber vector, and bottom‐trapping depth confirmed that the observed near 35‐hr TRWs are indeed plausible in the study area. Energetic TRWs were observed in September and October, during the sea ice free season, whereas weak TRWs were observed in months with sea ice cover. The TRW events coincided with local wind‐stress events, suggesting that the TRWs were triggered by atmospheric forcing. These findings imply that a longer ice‐free season may allow for a more frequent occurrence of energetic TRWs, which may enhance the water exchange between the shallow continental shelf and the deep ocean.
Morphologic Evidence for Volcanic Craters Near Titan's North Polar Region
Authors: Wood Charles A. , Radebaugh Jani 
Published: June 2020

AbstractCassini Radar observations of Titan have revealed diverse landforms resulting from a variety of geologic processes. Many landforms can be unambiguously interpreted as resulting from atmospheric processes (dunes, rivers, and lakes) or impact cratering. Here we argue from morphological evidence such as nested collapses, elevated ramparts, halos, and islands or floor mountains that some of the abundant small depressions in the north polar region of Titan are volcanic collapse craters. A few similar depressions occur near the south pole; the restriction of this volcanism to polar regions is possibly related to predicted warmer and thinner‐than‐normal ice crust at the low‐elevation poles. The close association of the proposed volcanic craters with polar lakes is consistent with a volcanic origin through explosive eruptions, as either maars or calderas. The apparent freshness of some craters may mean that volcanism has been relatively recently active on Titan or even continues today.
Two Layers of Melting Ice Particles Within a Single Radar Bright Band: Interpretation and Implications
Authors: Li Haoran , Moisseev Dmitri 
Published: June 2020

AbstractDual‐frequency dual‐polarization radar observations of the melting of two ice populations in a stratiform rainfall event are presented. The observed phenomenon occurs as a two‐layer linear depolarization ratio (LDR) signature in a single radar bright band. Doppler spectra observations show that the upper LDR layer is caused by the melting of ice needles, potentially generated by the rime‐splintering process, while the lower one is mainly due to the melting of background ice particles formed at the cloud top. The melting signal of small needles acts as a unique benchmark for detecting the onset of melting and is used to verify the current methods for the identification of melting layer boundaries. The radar‐derived characteristics of the melting layer are found to be dependent on the radar variable and frequency used. The implications of the presented findings for radar‐based studies of precipitation properties in and above the melting layer are also discussed.
Injection of Oxygenated Persian Gulf Water Into the Southern Bay of Bengal
Authors: Sheehan Peter M. F. , Webber Benjamin G. M. , Sanchez‐Franks Alejandra , Matthews Adrian J. , Heywood Karen J. , Vinayachandran P. N. 
Published: June 2020

AbstractPersian Gulf Water (PGW) is an oxygenated, high‐salinity water mass that has recently been detected in the Bay of Bengal (BoB). However, little is known about the transport pathways of PGW into the BoB. Ocean glider observations presented here demonstrate the presence of PGW in the southwestern BoB. Output from an ocean reanalysis product shows that this PGW signal is associated with a northward‐flowing filament of high‐salinity water. Particle tracking experiments reveal two pathways: one in the eastern Arabian Sea that takes a minimum of 2 years and another in the western Arabian Sea that takes a minimum of 3 years. The western pathway connects to the BoB via equatorial currents. The greatest influx of PGW occurs between 82° and 87°E during the southwest monsoon. We propose that injection of PGW to the BoB oxygen minimum zone (OMZ) contributes to keeping oxygen concentrations in the BoB above the level at which denitrification occurs.
Holocene Grassland Fire Dynamics and Forcing Factors in Continental Interior of China
Authors: Li Jianyong , Wang Ninglian 
Published: June 2020

AbstractGrasslands cover 41.7% of China's land surface and distribute mainly in NW China. To project future change of grassland fires, it is essential to explore paleofire dynamics. However, comparatively little is known about the patterns and driving forces of grassland fires in NW China due to the scarcity of paleorecords. Here, we present Holocene sedimentary records of grassland fire and vegetation in westerly‐dominated Xinjiang (NW China) to examine fire‐fuel‐climate interactions. We find that grassland fire regime is fuel‐limited, consistent with other grasslands worldwide. We reveal that burning increased throughout the Holocene, due to increasing moisture, grass cover, fuel load, and temperature of spring fire season. The Holocene pattern of burning coincides with several other records nearby and a global‐scale grassland fire record. Our results are different from monsoonal China where fuel load is not a constraining factor and more (less) fires occurred during colder/drier (warmer/moister) periods in the Holocene.
A Mechanism for the Arctic Sea Ice Spring Predictability Barrier
Authors: Bushuk Mitchell , Winton Michael , Bonan David B. , Blanchard‐Wrigglesworth Edward , Delworth Thomas L. 
Published: June 2020

AbstractThe decline of Arctic sea ice extent has created a pressing need for accurate seasonal predictions of regional summer sea ice. Recent work has shown evidence for an Arctic sea ice spring predictability barrier, which may impose a sharp limit on regional forecasts initialized prior to spring. However, the physical mechanism for this barrier has remained elusive. In this work, we perform a daily sea ice mass (SIM) budget analysis in large ensemble experiments from two global climate models to investigate the mechanisms that underpin the spring predictability barrier. We find that predictability is limited in winter months by synoptically driven SIM export and negative feedbacks from sea ice growth. The spring barrier results from a sharp increase in predictability at melt onset, when ice‐albedo feedbacks act to enhance and persist the preexisting export‐generated mass anomaly. These results imply that ice thickness observations collected after melt onset are particularly critical for summer Arctic sea ice predictions.
Fluctuations of the Atlantic North Equatorial Undercurrent and Associated Changes in Oxygen Transports
Authors: Burmeister Kristin , Luebbecke Joke F. , Brandt Peter , Claus Martin , Hahn Johannes 
Published: June 2020

AbstractAlthough the core velocity of the Atlantic North Equatorial Undercurrent (NEUC) is low (0.1−0.3 m s−1), it has been suggested to act as an important oxygen supply route towards the oxygen minimum zone in the eastern tropical North Atlantic. For the first time, the intraseasonal to interannual NEUC variability and its impact on oxygen are investigated based on shipboard and moored velocity observations around 5°N, 23°W. In contrast to previous studies that were mainly based on models or hydrographic data, we find hardly any seasonal cycle of NEUC transports in the central Atlantic. The NEUC transport variability is instead dominated by sporadic intraseasonal events. Only some of these events are associated with high oxygen levels suggesting an occasional eastward oxygen supply by NEUC transport events. Nevertheless, they likely contribute to the local oxygen maximum in the mean shipboard section along 23°W at the NEUC core position.
In Situ Observations of Ionospheric Heating Effects: First Results from a Joint SURA and NorSat‐1 Experiment
Authors: Chernyshov A. A. , Chugunin D. V. , Frolov V. L. , Clausen L. B. N. , Miloch W. J. , Mogilevsky M. M. 
Published: June 2020

AbstractThis work presents the first results of measurements of artificial plasma disturbance characteristics using the low‐orbit NorSat‐1 satellite, which are excited when the ionospheric F2 layer is modified by powerful high‐frequency (HF) waves emitted by the SURA heating facility. NorSat‐1 carries the multineedle Langmuir probe instrument, which is capable of sampling the electron density at a nominal rate up to 1 kHz. The uniqueness of this experiment lies in the fact that the satellite passes very close to the center of the HF‐perturbed magnetic flux tube and in situ observations are first carried out in winter when the absorption is still small in the morning as the Sun is low above the horizon. There are HF‐induced plasma temperature and density variations at satellite altitudes of about 580 km. Plasma irregularities are detected by in situ measurements down to 200 m at the southern border of the SURA heating region.
The Evolution of Long‐Duration Cusp Spot Emission During Lobe Reconnection With Respect to Field‐Aligned Currents
Authors: Carter Jennifer A. , Milan Stephen E. , Fogg Alexandra R. , Sangha Harneet , Lester Mark , Paxton Larry J. , Anderson Brian J. 
Published: June 2020

AbstractWe track a remarkably bright and persistent auroral cusp spot emission in the high‐latitude Northern Hemisphere polar cap, well inside the main auroral oval, for approximately 11 hr on 16 and 17 June 2012. The auroral emissions are presented in both the Lyman‐α and Lyman‐Birge‐Hopfield bands, as observed by the Special Sensor Ultraviolet Spectrographic Imager on board two of the Defense Meteorological Satellite Programme spacecraft, and supported by detections of precipitating particles by the same spacecraft. The auroral observations are accompanied by patterns of field aligned currents, obtained from the Active Magnetosphere and Planetary Electrodynamics Response Experiment, along with ionospheric convection patterns from the Super Dual Auroral Radar Network. These data provide unprecedented coverage of a cusp spot, unusually seen in both electron and proton aurora. The location and movement of the auroral emissions, current systems, and ionospheric convection patterns are extremely distorted under the northward to Y‐component‐dominated interplanetary magnetic field. The cusp spot emission region is associated with the sunward flow region of the ionosphere. Ion dispersion signatures are detected on traversal of the region of brightest proton auroral emissions. Proton‐excited Lyman‐α emissions are most evident following impulses of high solar wind density. The auroral emissions, field‐aligned current patterns, and ionospheric convection are consistent with a model of a compressed magnetosphere under strongly northward interplanetary magnetic field, following an impact of an Interplanetary Coronal Mass Ejection and associated magnetic cloud at the magnetopause, inducing high‐latitude lobe reconnection that progresses increasingly tailward during the presented interval.
Distinct Raindrop Size Distributions of Convective Inner‐ and Outer‐Rainband Rain in Typhoon Maria (2018)
Authors: Bao Xuwei , Wu Liguang , Zhang Shuai , Li Qingqing , Lin Limin , Zhao Binke , Wu Dan , Xia Weizu , Xu Bin 
Published: June 2020

AbstractUnlike previous studies from a single disdrometer, this study investigates and compares the raindrop size distribution (RSD) characteristics of convective inner‐rainband rain (CIR) and convective outer‐rainband rain (COR) in Typhoon Maria (2018), simultaneously captured for the first time by a newly established observational network including nine disdrometers in the northeastern Fujian Province of China. It is shown that the radar reflectivity for the CIR increases sharply with decreasing height below the melting layer, whereas it remains nearly unchanged for the COR. This suggests the dominance of collision‐coalescence process in the CIR, that is, the collection of small raindrops by larger ones as they fall. Thus, the surface‐level CIR generally has far lower concentration of small raindrops and larger mean raindrop diameter than those previously found in the COR. Close to the tropical cyclone (TC) eyewall, it is found for the first time that although the raindrops are relatively large, the raindrop concentration is too low to yield a high rain rate. In contrast, high rain rates are concentrated at a distance of about 1.5–2.5 times the radius of maximum wind from the TC center, where there are appropriate normalized concentrations (log10Nw) and corresponding raindrop diameters. In addition, this study demonstrates differences between the CIR and COR in terms of the RSD evolution with increasing rain rate and the radar reflectivity–rain rate (Z‐R) and shape‐slope (μ‐Λ) relationships, confirming the existence of different rain microphysics in various rain regions of a TC.
Meter‐Scale Topographic Roughness of the Moon: The Effect of Small Impact Craters
Authors: Cai Yuzhen , Fa Wenzhe 
Published: June 2020

AbstractHigh‐resolution digital terrain models (DTMs) generated from the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Cameras (NACs) provide an opportunity to study surface roughness of the Moon at meter scale. In this study, we mapped and investigated meter‐scale topographic roughness over 462 regions of the Moon using NAC DTMs. Our results show that, at meter to hectometer scales, there are obvious differences in median bidirectional slope, root‐mean‐square (RMS) height, and median absolute slope between maria and highlands. In terms of the median value, ratios of the bidirectional slope, RMS height, and median absolute slope within the maria and highlands are 1: 2.4, 1: 3.0, and 1: 2.7, respectively. However, up to a baseline of ∼0.2 km, no discernible differences in the Hurst exponent and median differential slope exist between the maria and highlands. The Hurst exponent varies from 0.7 to 0.95, with a median value of 0.9 within both the maria and highlands. To identify potential factors affecting meter‐scale roughness of the Moon, we compared the maria with volcanic features on Earth and Mars, as well as the lunar highlands with simulated cratered terrains. We found that the Hurst exponents within the lunar maria are much larger than those of the volcanic features on Earth and Mars, mainly because the lunar maria accumulated more impact craters with diameters smaller than 1 km. The Hurst exponents within the highlands are consistent with those of the simulated cratered terrains, whose surface roughness depends primarily on crater shape, number density, and stratigraphic age. All these results indicate that lunar surface roughness at meter to hectometer scales is mainly controlled by small degraded impact craters.
Photoelectrons as a Tracer of Planetary Atmospheric Composition: Application to CO on Mars
Authors: Wu X.‐S. , Cui J. , Yelle R. V. , Cao Y.‐T. , He Z.‐G. , He F. , Wei Y. 
Published: June 2020

AbstractPhotoelectrons are an extensively studied component of planetary ionospheres which have been frequently used as a diagnostic of ambient magnetic fields. We show in this study that they also provide information on atmospheric composition via the altitude variation of photoelectron intensity at specific energies. Such an idea is applied to Mars for which a large observational sample of photoelectrons is available from the Solar Wind Electron Analyzer measurements made by the Mars Atmosphere and Volatile Evolution (MAVEN). Our analysis reveals a strong decline in photoelectron intensity from 160 to 200 km, but this trend is restricted to a narrow energy range of 10–15 eV. By employing analytical yield spectrum calculations, we derive the model variations based on different choices of the background atmosphere. We find that the presence of CO is crucial for reproducing the observed variations. This allows atmospheric CO densities to be estimated from photoelectron measurements, which are a factor of 3–7 lower than the published densities based on the MAVEN Neutral Gas and Ion Mass Spectrometer measurements and in better agreement with existing model results. In general, the usefulness of photoelectron intensity at a specific energy as a tracer of atmospheric composition relies critically on the species‐dependent inelastic electron impact cross section at this energy.
Magnetic pumping model for energizing superthermal particles applied to observations of the Earth's bow shock
Authors: Lichko E. , Egedal J. 
Published: June 2020

AbstractEnergetic particle generation is an important component of a variety of astrophysical systems, from seed particle generation in shocks to the heating of the solar wind. It has been shown that magnetic pumping is an efficient mechanism for heating thermal particles, using the largest-scale magnetic fluctuations. Here we show that when magnetic pumping is extended to a spatially-varying magnetic flux tube, magnetic trapping of superthermal particles renders pumping an effective energization method for particles moving faster than the speed of the waves and naturally generates power-law distributions. We validated the theory by spacecraft observations of the strong, compressional magnetic fluctuations near the Earth’s bow shock from the Magnetospheric Multiscale mission. Given the ubiquity of magnetic fluctuations in different astrophysical systems, this mechanism has the potential to be transformative to our understanding of how the most energetic particles in the universe are generated.
Spt6 is a maintenance factor for centromeric CENP-A
Authors: Bobkov Georg O. M. , Huang Anming , van den Berg Sebastiaan J. W. , Mitra Sreyoshi , Anselm Eduard , Lazou Vasiliki , Schunter Sarah , Feederle Regina , Imhof Axel , Lusser Alexandra , Jansen Lars E. T. , Heun Patrick 
Published: June 2020

AbstractReplication and transcription of genomic DNA requires partial disassembly of nucleosomes to allow progression of polymerases. This presents both an opportunity to remodel the underlying chromatin and a danger of losing epigenetic information. Centromeric transcription is required for stable incorporation of the centromere-specific histone dCENP-A in M/G1 phase, which depends on the eviction of previously deposited H3/H3.3-placeholder nucleosomes. Here we demonstrate that the histone chaperone and transcription elongation factor Spt6 spatially and temporarily coincides with centromeric transcription and prevents the loss of old CENP-A nucleosomes in both Drosophila and human cells. Spt6 binds directly to dCENP-A and dCENP-A mutants carrying phosphomimetic residues alleviate this association. Retention of phosphomimetic dCENP-A mutants is reduced relative to wildtype, while non-phosphorylatable dCENP-A retention is increased and accumulates at the centromere. We conclude that Spt6 acts as a conserved CENP-A maintenance factor that ensures long-term stability of epigenetic centromere identity during transcription-mediated chromatin remodeling.
A multi-omics analysis reveals the unfolded protein response regulon and stress-induced resistance to folate-based antimetabolites
Authors: Reich Stefan , Nguyen Chi D. L. , Has Canan , Steltgens Sascha , Soni Himanshu , Coman Cristina , Freyberg Moritz , Bichler Anna , Seifert Nicole , Conrad Dominik , Knobbe-Thomsen Christiane B. , Tews Björn , Toedt Grischa , Ahrends Robert , Medenbach Jan 
Published: June 2020

AbstractStress response pathways are critical for cellular homeostasis, promoting survival through adaptive changes in gene expression and metabolism. They play key roles in numerous diseases and are implicated in cancer progression and chemoresistance. However, the underlying mechanisms are only poorly understood. We have employed a multi-omics approach to monitor changes to gene expression after induction of a stress response pathway, the unfolded protein response (UPR), probing in parallel the transcriptome, the proteome, and changes to translation. Stringent filtering reveals the induction of 267 genes, many of which have not previously been implicated in stress response pathways. We experimentally demonstrate that UPR‐mediated translational control induces the expression of enzymes involved in a pathway that diverts intermediate metabolites from glycolysis to fuel mitochondrial one‐carbon metabolism. Concomitantly, the cells become resistant to the folate-based antimetabolites Methotrexate and Pemetrexed, establishing a direct link between UPR‐driven changes to gene expression and resistance to pharmacological treatment.
A synthetic ion channel with anisotropic ligand response
Authors: Muraoka Takahiro , Noguchi Daiki , Kasai Rinshi S. , Sato Kohei , Sasaki Ryo , Tabata Kazuhito V. , Ekimoto Toru , Ikeguchi Mitsunori , Kamagata Kiyoto , Hoshino Norihisa , Noji Hiroyuki , Akutagawa Tomoyuki , Ichimura Kazuaki , Kinbara Kazushi 
Published: June 2020

AbstractBiological membranes play pivotal roles in the cellular activities. Transmembrane proteins are the central molecules that conduct membrane-mediated biochemical functions such as signal transduction and substance transportation. Not only the molecular functions but also the supramolecular properties of the transmembrane proteins such as self-assembly, delocalization, orientation and signal response are essential for controlling cellular activities. Here we report anisotropic ligand responses of a synthetic multipass transmembrane ion channel. An unsymmetrical molecular structure allows for oriented insertion of the synthetic amphiphile to a bilayer by addition to a pre-formed membrane. Complexation with a ligand prompts ion transportation by forming a supramolecular channel, and removal of the ligand deactivates the transportation function. Biomimetic regulation of the synthetic channel by agonistic and antagonistic ligands is also demonstrated not only in an artificial membrane but also in a biological membrane of a living cell.
Rational design of aptamer switches with programmable pH response
Authors: Thompson Ian A. P. , Zheng Liwei , Eisenstein Michael , Soh H. Tom 
Published: June 2020

AbstractAptamer switches that respond sensitively to pH could enhance control over molecular devices, improving their diagnostic and therapeutic efficacy. Previous designs have inserted pH-sensitive DNA motifs into aptamer sequences. Unfortunately, their performance was limited by the motifs’ intrinsic pH-responses and could not be tuned to operate across arbitrary pH ranges. Here, we present a methodology for converting virtually any aptamer into a molecular switch with pH-selective binding properties — in acidic, neutral, or alkaline conditions. Our design inserts two orthogonal motifs that can be manipulated in parallel to tune pH-sensitivity without altering the aptamer sequence itself. From a single ATP aptamer, we engineer pH-controlled target binding under diverse conditions, achieving pH-induced selectivity in affinity of up to 1,000-fold. Importantly, we demonstrate the design of tightly regulated aptamers with strong target affinity over only a narrow pH range. Our approach offers a highly generalizable strategy for integrating pH-responsiveness into molecular devices.