bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fishway Entrance Gate Experiments With Adult American Shad
Authors: Mulligan K. B. , Haro A. , Towler B. , Sojkowski B. , Noreika J. 
Published: November 2019

AbstractThe goal of this multiyear study was to examine how changes to an upstream fishway entrance impacted the passage rate of adult American shad (Alosa sapidissima). We evaluated a total of nine treatment conditions that consisted of three fishway entrance gate types and three submergence depths (i.e., the water surface elevation of the tailwater relative to the height of the gate crest). Approximately 2,000 wild, actively migrating shad participated in one of the 64 total trials (6–8 trials per treatment) that were conducted for this experiment. The three fishway entrance gate types were the vertical gate (the most common entrance gate type used in fishways), the overshot gate (less common in fishways), and the reversed overshot gate (novel to fishways). The submergence depths ranged from 30.5 to 91.4 cm above the gate crest. Increases to the submergence depth were shown to be the most influential predictor variable of passage time, followed by gate type and river temperature. The reversed overshot and overshot gates outperformed the vertical gate with the best performance occurring for the newly introduced reversed overshot gate type. The results of this study provide guidance on methods to improve fishway attraction and entry rates to numerous state and federal resource agencies and the hydropower industry.
Geometry of the Deep Calabrian Subduction (Central Mediterranean Sea) From Wide‐Angle Seismic Data and 3‐D Gravity Modeling
Authors: Dellong David , Klingelhoefer Frauke , Dannowski Anke , Kopp Heidrun , Murphy Shane , Graindorge David , Margheriti Lucia , Moretti Milena , Barreca Giovanni , Scarfì Luciano , Polonia Alina , Gutscher Marc‐Andre 
Published: November 2019

AbstractThe Calabrian subduction zone is one of the narrowest arcs on Earth and a key area to understand the geodynamic evolution of the Mediterranean and other marginal seas. Here in the Ionian Sea, the African plate subducts beneath Eurasia. Imaging the boundary between the downgoing slab and the upper plate along the Calabrian subduction zone is important for assessing the potential of the subduction zone to generate megathrust earthquakes and was the main objective of this study. Here we present and analyze the results from a 380‐km‐long, wide‐angle seismic profile spanning the complete subduction zone, from the deep Ionian Basin and the accretionary wedge to NE Sicily, with additional constraints offered by 3‐D gravity modeling and the analysis of earthquake hypocenters. The velocity model for the wide‐angle seismic profile images thin oceanic crust throughout the basin. The Calabrian backstop extends underneath the accretionary wedge to about 100 km SE of the coast. The seismic model was extended in depth using earthquake hypocenters. The combined results indicate that the slab dip increases abruptly from 2–3° to 60–70° over a distance of ≤50 km underneath the Calabrian backstop. This abrupt steepening is likely related to the rollback geodynamic evolution of the narrow Calabrian slab, which shows great similarity to the shallow and deep geometry of the Gibraltar slab.
Direct Observation of Subrelativistic Electron Precipitation Potentially Driven by EMIC Waves
Authors: Capannolo L. , Li W. , Ma Q. , Chen L. , Shen X.‐C. , Spence H. E. , Sample J. , Johnson A. , Shumko M. , Klumpar D. M. , Redmon R. J. 
Published: November 2019

AbstractElectromagnetic ion cyclotron (EMIC) waves are known to typically cause electron losses into Earth's upper atmosphere at >~1 MeV, while the minimum energy of electrons subject to efficient EMIC‐driven precipitation loss is unresolved. This letter reports electron precipitation from subrelativistic energies of ~250 keV up to ~1 MeV observed by the Focused Investigations of Relativistic Electron Burst Intensity, Range and Dynamics (FIREBIRD‐II) CubeSats, while two Polar Operational Environmental Satellites (POES) observed proton precipitation nearby. Van Allen Probe A detected EMIC waves (~0.7–2.0 nT) over the similar L shell extent of electron precipitation observed by FIREBIRD‐II, albeit with a ~1.6 magnetic local time (MLT) difference. Although plasmaspheric hiss and magnetosonic waves were also observed, quasi‐linear calculations indicate that EMIC waves were the most efficient in driving the electron precipitation. Quasi‐linear theory predicts efficient precipitation at >0.8–1 MeV (due to H‐band EMIC waves), suggesting that other mechanisms are required to explain the observed subrelativistic electron precipitation.
Nanogoethite as a Potential Indicator of Remagnetization in Red Beds
Authors: Huang Wentao , Jackson Michael J. , Dekkers Mark J. , Solheid Peat , Zhang Bo , Guo Zhaojie , Ding Lin 
Published: November 2019

AbstractRed beds are well‐known for recording stable natural remanent magnetization (NRM). However, discriminating primary NRM from secondary remanence in red beds is difficult. The Paleogene Nangqian red beds in eastern Tibetan Plateau variably record an overprint related to nearby magmatism and thus provide a great opportunity to characterize remagnetization in red beds. Through comprehensive rock magnetic, Mössbauer spectroscopic, and petrographic analyses, we find that remagnetization was controlled by temperature. Remagnetized red beds contain abundant authigenic hematite and goethite, with some larger grains unblocking at the Néel temperatures and the remainder (nanoparticles) unblocking at lower temperatures. In contrast, red beds retaining primary NRM are characterized by dominance of detrital hematite and magnetite, presence of fine‐grained authigenic hematite, and absence of authigenic goethite and magnetite. High temperature behaviors of NRM/susceptibility are indicative of remagnetization, but the presence of goethite appears to be a more sensitive criterion for diagnosing remagnetization in red beds.
Assessment of ICESat‐2 Ice Sheet Surface Heights, Based on Comparisons Over the Interior of the Antarctic Ice Sheet
Authors: Brunt K. M. , Neumann T. A. , Smith B. E. 
Published: November 2019

AbstractWe collected kinematic Global Navigation Satellite Systems (GNSS) surface height data, on a 750‐km ground‐based traverse of the flat interior of the Antarctic ice sheet, for comparison with Ice, Cloud, and Land Elevation Satellite‐2 (ICESat‐2) surface heights. Vertical errors in the GNSS data are estimated to be 5.6 cm, comparable to results from a previous traverse and with year‐to‐year comparisons. Comparisons of the GNSS heights and 6 months of ICESat‐2 ATL03 photon‐based heights and ATL06 segment‐based heights indicate that the accuracy and precision of ICESat‐2 data are comparable to that of results from the ICESat mission: ATL03 is currently accurate to better than 5 cm with better than 13 cm of surface measurement precision, while ATL06 is currently accurate to better than 3 cm with better than 9 cm of surface measurement precision.
Significant Spatial Variability in Radar‐Derived West Antarctic Accumulation Linked to Surface Winds and Topography
Authors: Dattler Marissa E. , Lenaerts Jan T. M. , Medley Brooke 
Published: November 2019

AbstractAcross the Antarctic Ice Sheet, accumulation heavily influences firn compaction and surface height changes. Therefore, accumulation varies over short distances (<25 km), complicating the derivation of ice sheet mass changes from altimetry and reducing how accurately field measurements can be spatially extrapolated. However, current atmospheric reanalyses have grid spacings (>25 km) that are too coarse to resolve this variability. To address this limitation, we construct a fine‐scale accumulation product from airborne snow radar observations by superimposing along‐track fluctuations in accumulation onto an atmospheric reanalysis product. Our resulting airborne product reflects large‐scale (>25 km) orographic precipitation patterns while providing robust and unprecedented insight into Antarctic accumulation variability on subgrid scales. On these smaller scales, we find significant, regionally dependent accumulation variability (σrelative>40%). This variability in accumulation is correlated with variability in topographic surface slope in the wind direction (p<0.01), confirming that subgrid‐scale accumulation variability is driven by snow redistribution by wind.
HL‐TWiM Empirical Model of High‐Latitude Upper Thermospheric Winds
Authors: Dhadly Manbharat S. , Emmert John T. , Drob Douglas P. , Conde Mark G. , Aruliah Anasuya , Doornbos Eelco , Shepherd Gordon G. , Wu Qian , Makela Jonathan J. , Niciejewski Rick J. , Lee Changsup , Jee Geonhwa , Ridley Aaron J. 
Published: November 2019

AbstractWe present an empirical model of thermospheric winds (High‐latitude Thermospheric Wind Model [HL‐TWiM]) that specifies F region high‐latitude horizontal neutral winds as a function of day of year, latitude, longitude, local time, and geomagnetic activity. HL‐TWiM represents the large‐scale neutral wind circulation, in geomagnetic coordinates, for the given input conditions. The model synthesizes the most extensive collection to date of historical high‐latitude wind measurements; it is based on statistical analyses of several decades of F region thermospheric wind measurements from 21 ground‐based stations (Fabry‐Perot Interferometers and Scanning Doppler Imaging Fabry‐Perot Interferometers) located at various northern and southern high latitudes and two space‐based instruments (UARS WINDII and GOCE). The geomagnetic latitude and local time dependences in HL‐TWiM are represented using vector spherical harmonics, day of year and longitude variations are represented using simple harmonic functions, and the geomagnetic activity dependence is represented using quadratic B splines. In this paper, we describe the HL‐TWiM formulation and fitting procedures, and we verify the model against the neutral wind databases used in its formulation. HL‐TWiM provides a necessary benchmark for validating new wind observations and tuning our physical understanding of complex wind behaviors. Results show stronger Universal Time variation in winds at southern than northern high latitudes. Model‐data intra‐annual comparisons in this study show semiannual oscillation‐like behavior of GOCE winds, rarely observed before in wind data.
Magnetic Reconnection in Three Dimensions: Observations of Electromagnetic Drift Waves in the Adjacent Current Sheet
Authors: Ergun R. E. , Hoilijoki S. , Ahmadi N. , Schwartz S. J. , Wilder F. D. , Burch J. L. , Torbert R. B. , Lindqvist P.‐A. , Graham D. B. , Strangeway R. J. , Le Contel O. , Holmes J. C. , Stawarz J. E. , Goodrich K. A. , Eriksson S. , Giles B. L. , Gershman D. , Chen L. J. 
Published: November 2019

AbstractMagnetic reconnection at the subsolar magnetopause is persistently accompanied by strong fluctuations of the magnetic field (B), plasma density (n), and all components of the electric field (E) and current (J). The strongest fluctuations are at frequencies below the lower hybrid frequency and observed in a thin, intense current sheet adjacent to the electron diffusion region. In this current sheet, the background magnitudes of B and n are changing considerably, creating an inhomogeneous plasma environment. We show that the fluctuations in B and n are consistent with an oscillatory displacement of the current sheet in the surface normal direction. The displacement is propagating parallel to the magnetic reconnection X line. Wavelengths are on the order of or longer than the thickness of the current sheet to which they are confined, so we label these waves electromagnetic drift waves. E and J fluctuations are more complex than a simple displacement. They have significant variations in the component along B, which suggest that the drift waves also may be confined along B. The current sheet is supported by an electron drift driven by normal electric field, which, in turn, is balanced by an ion pressure gradient. We suggest that wave growth comes from an instability related to the drift between the electrons and ions. We discuss the possibility that drift waves can displace or penetrate into the electron diffusion region giving magnetic reconnection three‐dimensional structure. Drift waves may corrugate the X line, possibly breaking the X line and generating turbulence.
Strong Ground Motion Simulation of 2016 ML6.6 Meinong, Taiwan, Earthquake Using the Empirical Green's Function Method
Authors: Chen Ying‐Chi , Huang Huey‐Chu , Iwata Tomotaka , Asano Kimiyuki 
Published: November 2019

AbstractThe Meinong mainshock (ML6.6) occurred in southern Taiwan at 19:57:26.08 (UTC) on 5 February 2016. To study source characteristics of the mainshock, ground motions of the mainshock are simulated using the empirical Green's function method to construct a strong motion generation area (SMGA) source model. Records of the event occurred on 2 May 2010 (ML4.6) are chosen as the empirical Green's functions along with six strong motion stations surrounding the source area. Waveforms of the mainshock at all used stations are simulated utilizing the empirical Green's function method to construct a best‐fit source model by comparing the synthetic waveforms with the observed ones in the frequency range 0.2–10 Hz. The estimated SMGA is located on the NS‐striking fault plane. The size of SMGA is 7.2 km in length along the strike direction by 7.2 km in width along the dip direction. The rupture starts at the bottom left‐hand corner (i.e., southern bottom) of the SMGA and then extends radially toward the upper right‐hand corner with a rupture velocity of 2.6 km/s. The size of the SMGA and the rise time of the mainshock follow the self‐similar empirical relationship by Miyake et al. (2003, https://doi.org/10.1785/0120020183).
A Numerical Study of Convection Initiation Associated With a Gust Front in Bohai Bay Region, North China
Authors: Abulikemu Abuduwaili , Wang Yan , Gao Runxiang , Wang Yuan , Xu Xin 
Published: November 2019

AbstractConvection initiation (CI) associated with a cold pool gust front (GF) of a mesoscale convective system (MCS) occurred in the Bohai Bay region, North China, is investigated using a real‐data, high‐resolution Weather Research and Forecasting model (WRF) simulation. Observations revealed that many CIs occurred successively near the GF, most of which developed significantly in both size and intensity and eventually merged with the MCS. The WRF simulation captured the general features of the CIs, GF, and MCS. Lagrangian vertical momentum budgets were conducted along the backward trajectories of air parcels within a convective cell initiated near the GF. The total vertical acceleration was decomposed into dynamic and buoyant components. The results showed that the dynamic acceleration played a decisive role for the CI, which can be further decomposed into five terms. The horizontal curvature term was rather small, with the height variation of air density almost zero. Although both vertical and horizontal extension terms played a positive role during the CI process, the vertical twisting term had the greatest contribution to the CI. This reflects the vertical tilting (to the forward of the GF) of an elevated updraft which was generated by the convergence of a forward‐tilting updraft at the GF leading edge and another airflow coming from ahead of the GF.
The Regional Hydroclimate Response to Stratospheric Sulfate Geoengineering and the Role of Stratospheric Heating
Authors: Simpson I. R. , Tilmes S. , Richter J. H. , Kravitz B. , MacMartin D. G. , Mills M. J. , Fasullo J. T. , Pendergrass A. G. 
Published: November 2019

AbstractGeoengineering methods could potentially offset aspects of greenhouse gas‐driven climate change. However, before embarking on any such strategy, a comprehensive understanding of its impacts must be obtained. Here, a 20‐member ensemble of simulations with the Community Earth System Model with the Whole Atmosphere Community Climate Model as its atmospheric component is used to investigate the projected hydroclimate changes that occur when greenhouse gas‐driven warming, under a high emissions scenario, is offset with stratospheric aerosol geoengineering. Notable features of the late 21st century hydroclimate response, relative to present day, include a reduction in precipitation in the Indian summer monsoon, over much of Africa, Amazonia and southern Chile and a wintertime precipitation reduction over the Mediterranean. Over most of these regions, the soil desiccation that occurs with global warming is, however, largely offset by the geoengineering. A notable exception is India, where soil desiccation and an approximate doubling of the likelihood of monsoon failures occurs. The role of stratospheric heating in the simulated hydroclimate change is determined through additional experiments where the aerosol‐induced stratospheric heating is imposed as a temperature tendency, within the same model, under present day conditions. Stratospheric heating is found to play a key role in many aspects of projected hydroclimate change, resulting in a general wet‐get‐drier, dry‐get‐wetter pattern in the tropics and extratropical precipitation changes through midlatitude circulation shifts. While a rather extreme geoengineering scenario has been considered, many, but not all, of the precipitation features scale linearly with the offset global warming.
Alluvial Morphodynamics of Bedrock Reaches Transporting Mixed‐Size Sand. Laboratory Experiments
Authors: Jafarinik S. , Hernández Moreira R. , Viparelli E. 
Published: November 2019

AbstractResearch on the morphodynamics of bedrock rivers has primarily focused on bedrock incision, and little is known about the alluvial morphodynamics of rivers with exposed bedrock surfaces. More specifically, there is a lack of information on the morphodynamics of low slope bedrock reaches due to the recent recognition of such systems. Here, we present the results of laboratory experiments specifically designed to gain novel insight into flow resistances, flow hydrodynamics, and sediment transport processes in equilibrium partially exposed bedrock reaches transporting nonuniform sand as bed material in low slope areas. The experiments show that (1) downstream of a stable alluvial‐bedrock transition flow depth decreases in the streamwise direction, (2) bedform amplitude may decrease in the streamwise direction, and (3) stable patterns of downstream fining may form. Given the bedrock geometry, the water surface elevation at downstream boundary and the characteristics of the bedform regime in an alluvial channel subject to the same flow rate and sediment supply at equilibrium control bedform characteristics and sediment sorting patterns in the bedrock reach. When this distance is significantly smaller than the alluvial equilibrium flow depth or when the alluvial equilibrium bedform regime is close to the dune‐antidune transition, bedforms in the bedrock reach are closer to the dune‐antidune transition than at alluvial equilibrium with a consequent reduction in bedform amplitude. If the distance between the water level at the downstream boundary and the bedrock surface is close to the alluvial equilibrium flow depth and the alluvial equilibrium bedforms are well in the dune regime, a stable pattern of downstream fining can be expected. The comparisons between experimental and modeled sediment transport rates and equilibrium grain size distributions of the sediment further show that surface‐based bedload transport models derived for alluvial systems reasonably predict equilibrium sediment transport rates and bed surface size distributions in bedrock reaches if the presence of exposed bedrock is accounted for in terms of alluvial cover fraction.
Road Crossings Increase Methane Emissions From Adjacent Peatland
Authors: Saraswati S. , Strack M. 
Published: November 2019

AbstractWe conducted a multi‐year study in two boreal peatlands to determine the impacts of resource access roads on methane (CH4) emission from adjacent peatland. Data were collected from transects aligned perpendicular to, and on both sides of two roads, one cutting through a bog and one cutting through a fen and from reference areas at each peatland. During the growing seasons of 2016 and 2017, we measured CH4 flux, water table, and peat temperature every second week. At the bog, the road associated impacts (changes to water table, peat temperature, and vegetation cover) were visible up to 20 m on both sides of the road (disturbed areas) with CH4 emission from disturbed areas being significantly higher compared to the reference areas in both years. There were no significant differences in CH4 emissions from disturbed areas compared to reference areas at the fen due to the limited hydrologic impact of the road crossing at this site. Bog plots located upstream of the road on transects located at >20 m from culverts and closer to the road emitted significantly more CH4 (124.6‐mg CH4·m−2·day−1) than other disturbed (10.2 mg CH4·m−2·day‐1) and reference areas (0.7‐mg CH4·m−2·day−1) due to shallower water table and warmer peat temperature. The road induced CH4 emissions (90.8 and 212.2 kg CH4/year for each kilometer of road, in 2016 and 2017, respectively) indicated that road construction across peatlands enhances CH4 emissions from these ecosystems, creating an additional source of anthropogenic greenhouse gas.
The Early to Middle Eocene Transition: An Integrated Calcareous Nannofossil and Stable Isotope Record From the Northwest Atlantic Ocean (Integrated Ocean Drilling Program Site U1410)
Authors: Cappelli C. , Bown P. R. , Westerhold T. , Bohaty S. M. , de Riu M. , Lobba V. , Yamamoto Y. , Agnini C. 
Published: November 2019

AbstractThe early to middle Eocene is marked by prominent changes in calcareous nannofossil assemblages coinciding both with long‐term climate changes and modification of the North Atlantic deep ocean circulation. In order to assess the impact of Eocene climate change on surface water environmental conditions of the Northwest Atlantic, we developed calcareous nannoplankton assemblage data and bulk stable isotope records (δ18O and δ13C) across an early to middle Eocene interval (~52–43 Ma) at Integrated Ocean Drilling Program Site U1410 (Southeast Newfoundland Ridge, ~41°N). At this site, early Eocene sediments are pelagic nannofossil chalk, whereas middle Eocene deposits occur as clay‐rich drift sediments reflecting the progressive influence of northern‐sourced deep currents. Between the end of Early Eocene Climatic Optimum (EECO) and the Ypresian/Lutetian boundary, calcareous nannofossils switched from an assemblage mainly composed of warm‐water and oligotrophic taxa (Zygrhablithus,Discoaster,Sphenolithus,Coccolithus) to one dominated by the more temperate and eutrophic reticulofenestrids. The most prominent period of accelerated assemblage change occurred during a ~2‐Myr phase of relatively high bulk δ18O values possibly related to the post‐EECO cooling. Although the dominance of reticulofenestrids persisted unvaried throughout the middle Eocene interval, early Lutetian (~47.4 to 47 Ma) stable isotope records indicate a reversal in the paleoenvironmetal trends suggesting a potential restoration of warmer conditions. Importantly, our data indicate that the ~2‐Myr interval immediately following the EECO was crucial in establishing the modern calcareous nannofossil assemblage structure and also reveal that the establishment ofReticulofenestra‐dominated assemblage occurred prior to the onset of persistent deep current system in the Northwest Atlantic.