bluuebunny/crossref_metadata_2025_split huggingface dataset:
Historical reconstruction of climatic and elevation preferences and the evolution of cloud forest-adapted tree ferns in Mesoamerica
Authors: Sosa Victoria , Ornelas Juan Francisco , Ramírez-Barahona Santiago , Gándara Etelvina 
Published: November 2016

BackgroundCloud forests, characterized by a persistent, frequent or seasonal low-level cloud cover and fragmented distribution, are one of the most threatened habitats, especially in the Neotropics. Tree ferns are among the most conspicuous elements in these forests, and ferns are restricted to regions in which minimum temperatures rarely drop below freezing and rainfall is high and evenly distributed around the year. Current phylogeographic data suggest that some of the cloud forest-adapted species remainedin situor expanded to the lowlands during glacial cycles and contracted allopatrically during the interglacials. Although the observed genetic signals of population size changes of cloud forest-adapted species including tree ferns correspond to predicted changes by Pleistocene climate change dynamics, the observed patterns of intraspecific lineage divergence showed temporal incongruence.MethodsHere we combined phylogenetic analyses, ancestral area reconstruction, and divergence time estimates with climatic and altitudinal data (environmental space) for phenotypic traits of tree fern species to make inferences about evolutionary processes in deep time. We used phylogenetic Bayesian inference and geographic and altitudinal distribution of tree ferns to investigate ancestral area and elevation and environmental preferences of Mesoamerican tree ferns. The phylogeny was then used to estimate divergence times and ask whether the ancestral area and elevation and environmental shifts were linked to climatic events and historical climatic preferences.ResultsBayesian trees retrievedCyathea, Alsophyla, GymnosphaeraandSphaeropterisin monophyletic clades. Splits for species in these genera found in Mesoamerican cloud forests are recent, from the Neogene to the Quaternary, Australia was identified as the ancestral area for the clades of these genera, except forGymnosphaerathat was Mesoamerica. Climate tolerance was not divergent from hypothesized ancestors for the most significant variables or elevation. For elevational shifts, we found repeated change from low to high elevations.ConclusionsOur data suggest that representatives of Cyatheaceae main lineages migrated from Australia to Mesoamerican cloud forests in different times and have persisted in these environmentally unstable areas but extant species diverged recentrly from their ancestors.
Carbocationic Polymerization
Authors: Puskas Judit E. , Kaszas Gabor 
Published: November 2016

AbstractThis article summarizes fundamental and general aspects of carbocationic polymerizations, with a historical overview and up‐to‐date references. Following general considerations, the basic elements of carbocationic polymerization, such as monomers, initiating systems, solvents, and temperature, are discussed. Special attention is given to carbocation stability, monomer nucleophilicity, and dynamic interactions. The section on the kinetics of carbocationic polymerization presents current understanding of the elementary reactions—initiation, propagation, termination and transfer reactions, and copolymerization. Controlled (living) carbocationic polymerization is discussed in a separate section. Finally, industrial carbocationic polymerizations are also reviewed.
Determining water reservoir characteristics with global elevation data
Authors: van Bemmelen C. W. T. , Mann M. , de Ridder M. P. , Rutten M. M. , van de Giesen N. C. 
Published: November 2016

AbstractQuantification of human impact on water, sediment, and nutrient fluxes at the global scale demands characterization of reservoirs with an accuracy that is presently unavailable. This letter presents a new method, based on virtual dam placement, to make accurate estimations of area‐volume relationships of large reservoirs, using solely readily available elevation data. The new method is based on regional similarity of area‐volume relationships. The essence of the method is that virtual reservoirs are created in the vicinity of an existing reservoir to derive area‐volume relationships for the existing reservoir. The derived area‐volume relationships reproduced in situ bathymetric data well. An intercomparison for twelve reservoirs resulted in an average R2 = 0.93. This is a significant improvement on estimates using the best existing global regression model, which gives R2 = 0.54 for the same set of reservoirs.
Fault‐bound valley associated with the Rembrandt basin on Mercury
Authors: Watters Thomas R. , Montési Laurent G. J. , Oberst Jürgen , Preusker Frank 
Published: November 2016

AbstractThe Rembrandt basin is crosscut by the largest fault scarp on Mercury, Enterprise Rupes, and a second scarp complex, Belgica Rupes, extends to the basin's rim. Topographic data derived from MESSENGER orbital stereo images show that these tectonic landforms bound a broad, relatively flat‐floored valley with a mean width of ~400 km. Crosscutting relations suggest that the accumulation of structural relief likely postdates the formation and volcanic infilling of the Rembrandt basin. The valley floor, bound by fault scarps of opposite vergence, is significantly offset below the elevation of the back‐scarp terrains. Along with an offset section of Rembrandt's rim, the elevation differences are evidence that the valley floor was lowered as a result of the formation of bounding fault scarps. The localization of the widely spaced thrust faults of Enterprise and Belgica Rupis and the offset of the valley floor may be the result of long‐wavelength buckling of Mercury's lithosphere.
Fate of the Atlantic Meridional Overturning Circulation: Strong decline under continued warming and Greenland melting
Authors: Bakker P. , Schmittner A. , Lenaerts J. T. M. , Abe‐Ouchi A. , Bi D. , van den Broeke M. R. , Chan W.‐L. , Hu A. , Beadling R. L. , Marsland S. J. , Mernild S. H. , Saenko O. A. , Swingedouw D. , Sullivan A. , Yin J. 
Published: November 2016

AbstractThe most recent Intergovernmental Panel on Climate Change assessment report concludes that the Atlantic Meridional Overturning Circulation (AMOC) could weaken substantially but is very unlikely to collapse in the 21st century. However, the assessment largely neglected Greenland Ice Sheet (GrIS) mass loss, lacked a comprehensive uncertainty analysis, and was limited to the 21st century. Here in a community effort, improved estimates of GrIS mass loss are included in multicentennial projections using eight state‐of‐the‐science climate models, and an AMOC emulator is used to provide a probabilistic uncertainty assessment. We find that GrIS melting affects AMOC projections, even though it is of secondary importance. By years 2090–2100, the AMOC weakens by 18% [−3%, −34%; 90% probability] in an intermediate greenhouse‐gas mitigation scenario and by 37% [−15%, −65%] under continued high emissions. Afterward, it stabilizes in the former but continues to decline in the latter to −74% [+4%, −100%] by 2290–2300, with a 44% likelihood of an AMOC collapse. This result suggests that an AMOC collapse can be avoided by CO2 mitigation.
Lithospheric velocity model of Texas and implications for the Ouachita orogeny and the opening of the Gulf of Mexico
Authors: Yao Yao , Li Aibing 
Published: November 2016

AbstractA 3‐D shear wave velocity model of Texas has been developed from Rayleigh wave phase velocities by using ambient noise data recorded at the USArray stations. In the upper crust, the Ouachita front separates high velocity in the Laurentia to its west from low velocity in the east and south Texas basins. The Ouachita belt is characterized as a high‐velocity zone with local maximums coinciding with known uplifts, which we interpret as accreted island arcs during the Ouachita orogeny. Our model evidences a strong Ouachita lithosphere that helped to buffer crust thinning from the Mesozoic rifting. A significantly low‐velocity anomaly is present in southeast Texas in the lower crust and upper mantle. We associate this anomaly with a past asthenosphere upwelling that likely originated from the edge of the subducted slab during the Ouachita collision and was potentially responsible for the opening of the Gulf of Mexico.
Factors affecting the geoeffectiveness of shocks and sheaths at 1 AU
Authors: Lugaz N. , Farrugia C. J. , Winslow R. M. , Al‐Haddad N. , Kilpua E. K. J. , Riley P. 
Published: November 2016

AbstractWe identify all fast‐mode forward shocks, whose sheath regions resulted in a moderate (56 cases) or intense (38 cases) geomagnetic storm during 18.5 years from January 1997 to June 2015. We study their main properties, interplanetary causes, and geoeffects. We find that half (49/94) such shocks are associated with interacting coronal mass ejections (CMEs), as they are either shocks propagating into a preceding CME (35 cases) or a shock propagating into the sheath region of a preceding shock (14 cases). About half (22/45) of the shocks driven by isolated transients and which have geoeffective sheaths compress preexisting southward Bz. Most of the remaining sheaths appear to have planar structures with southward magnetic fields, including some with planar structures consistent with field line draping ahead of the magnetic ejecta. A typical (median) geoeffective shock‐sheath structure drives a geomagnetic storm with peak Dst of −88 nT pushes the subsolar magnetopause location to 6.3 RE, i.e., below geosynchronous orbit and is associated with substorms with a peak AL index of −1350 nT. There are some important differences between sheaths associated with CME‐CME interaction (stronger storms) and those associated with isolated CMEs (stronger compression of the magnetosphere). We detail six case studies of different types of geoeffective shock‐sheaths, as well as two events for which there was no geomagnetic storm but other magnetospheric effects. Finally, we discuss our results in terms of space weather forecasting and potential effects on Earth's radiation belts.
Ionosphere data assimilation modeling of 2015 St. Patrick's Day geomagnetic storm
Authors: Chen C. H. , Lin C. H. , Matsuo T. , Chen W. H. 
Published: November 2016

AbstractThe ionospheric plasma disturbances during a severe storm can affect human activities and systems, such as navigation and HF communication systems. Therefore, the forecast of ionospheric electron density is becoming an important topic recently. This study is conducted with the ionospheric assimilation model by assimilating the total electron content observations into the thermosphere‐ionosphere coupling model with different high‐latitude ionospheric convection models, Heelis and Weimer, and further to forecast the variations of ionospheric electron density during the 2015 St. Patrick's Day geomagnetic storm. The forecast capabilities of these two assimilation models are evaluated by the root‐mean‐square error values in different regions to discuss its latitudinal effects. Results show the better forecast in the electron density at the low‐latitude region during the storm main phase and the recovery phase. The well reproduced eastward electric field at the low‐latitude region by the assimilation model reveals that the electric fields may be an important factor to have the contributions on the accuracy of ionospheric forecast.
A statistical study of magnetospheric electron density using the Cluster spacecraft
Authors: Sandhu J. K. , Yeoman T. K. , Fear R. C. , Dandouras I. 
Published: November 2016

AbstractObservations from the WHISPER (Waves of High frequency and Sounder for Probing of Electron density by Relaxation) instrument on board Cluster, for the interval spanning 2001–2012, are utilized to determine an empirical model describing the total electron density along closed geomagnetic field lines. The model, representing field lines in the region of 4.5≤L< 9.5, includes dependences onLand magnetic local time. Data verification tests ensured that the WHISPER data set provided unbiased measurements for low‐density regions, including comparisons with Plasma Electron and Current Experiment and Electric Field and Waves observations. The model was determined by modeling variations in the electron density along the field lines, which is observed to follow a power law distribution along the geomagnetic field at high latitudes, with power law index values ranging from approximately 0.0 to 1.2. However, a localized peak in electron density close to the magnetic equator is observed, which is described using a Gaussian peak function, with the electron density peak ranging as high as 10 cm−3above the background power law dependence. The resulting model illustrates some key features of the electron density spatial distribution. The role of the number density distribution, represented by the empirical electron density model, in determining the total plasma mass density is also explored. By combining the empirical electron density model with an empirical average ion mass model, the total plasma mass density distribution is inferred, which includes contributions of both the number density and ion composition of the plasma in the region.
Fault geometry inversion and slip distribution of the 2010 Mw 7.2 El Mayor‐Cucapah earthquake from geodetic data
Authors: Huang Mong‐Han , Fielding Eric J. , Dickinson Haylee , Sun Jianbao , Gonzalez‐Ortega J. Alejandro , Freed Andrew M. , Bürgmann Roland 
Published: November 2016

AbstractThe 4 April 2010 Mw 7.2 El Mayor‐Cucapah (EMC) earthquake in Baja, California, and Sonora, Mexico, had primarily right‐lateral strike‐slip motion and a minor normal‐slip component. The surface rupture extended about 120 km in a NW‐SE direction, west of the Cerro Prieto fault. Here we use geodetic measurements including near‐ to far‐field GPS, interferometric synthetic aperture radar (InSAR), and subpixel offset measurements of radar and optical images to characterize the fault slip during the EMC event. We use dislocation inversion methods and determine an optimal nine‐segment fault geometry, as well as a subfault slip distribution from the geodetic measurements. With systematic perturbation of the fault dip angles, randomly removing one geodetic data constraint, or different data combinations, we are able to explore the robustness of the inferred slip distribution along fault strike and depth. The model fitting residuals imply contributions of early postseismic deformation to the InSAR measurements as well as lateral heterogeneity in the crustal elastic structure between the Peninsular Ranges and the Salton Trough. We also find that with incorporation of near‐field geodetic data and finer fault patch size, the shallow slip deficit is reduced in the EMC event by reductions in the level of smoothing. These results show that the outcomes of coseismic inversions can vary greatly depending on model parameterization and methodology.
Transient deformation of karst aquifers due to seasonal and multiyear groundwater variations observed by GPS in southern Apennines (Italy)
Authors: Silverii Francesca , D'Agostino Nicola , Métois Marianne , Fiorillo Francesco , Ventafridda Gerardo 
Published: November 2016

AbstractWe present GPS, hydrological, and GRACE (Gravity Recovery and Climate Experiment) observations in southern Apennines (Italy) pointing to a previously unnoticed response of the solid Earth to hydrological processes. Transient patterns in GPS horizontal time series near to large karst aquifers are controlled by seasonal and interannual phases of groundwater recharge/discharge of karst aquifers, modulating the extensional ∼3 mm/yr strain within the tectonically active Apennines. We suggest that transient signals are produced, below the saturation level of the aquifers and above a poorly constrained depth in the shallow crust, by time‐dependent opening of subvertical, fluid‐filled, conductive fractures. We ascribe this process to the immature karstification and intense tectonic fracturing, favoring slow groundwater circulation, and to multiyear variations of the water table elevation, influenced by variable seasonal recharge. The vertical component displays seasonal and multiyear signals more homogeneously distributed in space and closely correlated with estimates of total water storage from GRACE, reflecting the elastic response of the lithosphere to variations of surface water loads. The different sensitivities of vertical and horizontal components to the hydrologically induced deformation processes allow us to spatially and temporally resolve the different phases of the water cycle, from maximum hydrological loading at the surface to maximum hydrostatic pressure beneath karst aquifers. Finally, we suggest that transient deformation signals in the geodetic series of the Apennines are correlated to large‐scale climatic patterns (Northern Atlantic Oscillation) through their influence on precipitation variability and trends at the regional scale.
Tidal influence on self‐potential measurements
Authors: MacAllister DJ. , Jackson M. D. , Butler A. P. , Vinogradov J. 
Published: November 2016

AbstractLong‐term surface and borehole self‐potential (SP) monitoring was conducted in the UK Chalk aquifer at two sites. The coastal site is ~1.7 km from the coast, and the inland site is ~80 km from the coast. At both sites, power spectral density analysis revealed that SP data contain the main ocean tidal periodic components. However, the principal lunar component (M2), the dominant ocean tidal component, was most significant at the coastal site. The M2 signal in surface‐referenced SP data at the inland site was partly due to telluric currents caused by the geomagnetic ocean dynamo. Earth and/or atmospheric tides also contributed, as the SP power spectrum was not typical of a telluric electric field. The M2 component in borehole‐referenced data at the inland site was below the significance level of the analysis method and was 2 orders of magnitude smaller than the M2 signal in borehole‐referenced SP data at the coastal site. The tidal response of the SP data in the coastal borehole is, therefore, primarily driven by ocean tides. These cause changes in fluid pressure and chemical concentration gradients within the coastal aquifer, leading to time varying electrokinetic and exclusion‐diffusion potentials. Borehole‐referenced SP measurements could be used to characterize and monitor tidal processes in coastal aquifers such as the intrusion of seawater.
Analyzing paleomagnetic data: To anchor or not to anchor?
Authors: Heslop David , Roberts Andrew P. 
Published: November 2016

AbstractPaleomagnetic directions provide the basis for use of paleomagnetism in chronological and tectonic reconstructions and for constraining past geomagnetic field behavior over a variety of timescales. Crucial to paleomagnetic analysis is the separation and quantification of a characteristic remanent magnetization (ChRM), which relates to a process of interest, from other remanence components. Principal component analysis (PCA) of stepwise demagnetization data is employed routinely in these situations to estimate magnetic remanence directions and their uncertainties. A given ChRM is often assumed to trend toward the origin of a vector demagnetization diagram and prevailing data analysis frameworks allow remanence directions to be estimated based on PCA fits that are forced to pass through the origin of such diagrams, a process referred to as “anchoring.” While this approach is adopted commonly, little attention has been paid to the effects of anchoring and the influence it has on both estimated remanence directions and their associated uncertainties. In almost all cases, anchoring produces an artificially low uncertainty estimation compared to an unanchored fit. Bayesian model selection demonstrates that the effects of anchoring cannot typically be justified from a statistical standpoint. We present an alternative to anchoring that constrains the best fit remanence direction to pass through the origin of a vector demagnetization diagram without unreasonably distorting the representation of the demagnetization data.
A refined methodology for stress inversions of earthquake focal mechanisms
Authors: Martínez‐Garzón Patricia , Ben‐Zion Yehuda , Abolfathian Niloufar , Kwiatek Grzegorz , Bohnhoff Marco 
Published: November 2016

AbstractWe develop an improved methodology for reliable high‐resolution inversions of focal mechanisms to background stress field orientation and stress ratio R in two or three dimensions. The earthquake catalog is declustered to remove events likely affected strongly by local stress interactions rather than reflecting the large‐scale background stress field. The declustered data are discretized with the k‐means algorithm into groups containing a number of focal mechanisms between a minimum number Nmin and 2Nmin. Synthetic tests indicate that Nmin ≈ 30 provides stable inversion results under different stress regimes and noise conditions when R ≈ 0.5, while Nmin ≈ 45 is needed for R near 0 or 1. Additional synthetic tests compare the performance of selecting the fault plane of each focal mechanism using (a) the plane with lowest misfit angle between the slip vector from the focal mechanism and shear traction from the stress tensor and (b) the plane with highest instability coefficient representing proximity to the optimally oriented fault for given stress field and friction coefficient. The instability criterion is found to provide more accurate inversion results under all tested stress regimes, stress ratios, and noise conditions. The refined inversion methodology combines selecting fault planes using the instability criterion iteratively with a damped simultaneous inversion of different focal mechanism groups. Results characterizing neighborhoods of discretized domains merged during the damped inversion provide high‐resolution information independent of the discretization. Some aspects of the methodology are illustrated with focal mechanism data from the San Jacinto Fault Zone in Southern California.
Storm surge along the Pacific coast of North America
Authors: Bromirski Peter D. , Flick Reinhard E. , Miller Arthur J. 
Published: November 2016

AbstractStorm surge is an important factor that contributes to coastal flooding and erosion. Storm surge magnitude along eastern North Pacific coasts results primarily from low sea level pressure (SLP). Thus, coastal regions where high surge occurs identify the dominant locations where intense storms make landfall, controlled by storm track across the North Pacific. Here storm surge variability along the Pacific coast of North America is characterized by positive nontide residuals at a network of tide gauge stations from southern California to Alaska. The magnitudes of mean and extreme storm surge generally increase from south to north, with typically high amplitude surge north of Cape Mendocino and lower surge to the south. Correlation of mode 1 nontide principal component (PC1) during winter months (December–February) with anomalous SLP over the northeast Pacific indicates that the dominant storm landfall region is along the Cascadia/British Columbia coast. Although empirical orthogonal function spatial patterns show substantial interannual variability, similar correlation patterns of nontide PC1 over the 1948–1975 and 1983–2014 epochs with anomalous SLP suggest that, when considering decadal‐scale time periods, storm surge and associated tracks have generally not changed appreciably since 1948. Nontide PC1 is well correlated with PC1 of both anomalous SLP and modeled wave height near the tide gauge stations, reflecting the interrelationship between storms, surge, and waves. Weaker surge south of Cape Mendocino during the 2015–2016 El Niño compared with 1982–1983 may result from changes in Hadley circulation. Importantly from a coastal impacts perspective, extreme storm surge events are often accompanied by high waves.