bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reorganization of river networks under changing spatiotemporal precipitation patterns: An optimal channel network approach
Authors: Abed‐Elmdoust Armaghan , Miri Mohammad‐Ali , Singh Arvind 
Published: November 2016

AbstractWe investigate the impact of changing nonuniform spatial and temporal precipitation patterns on the evolution of river networks. To achieve this, we develop a two‐dimensional optimal channel network (OCN) model with a controllable rainfall distribution to simulate the evolution of river networks, governed by the principle of minimum energy expenditure, inside a prescribed boundary. We show that under nonuniform precipitation conditions, river networks reorganize significantly toward new patterns with different geomorphic and hydrologic signatures. This reorganization is mainly observed in the form of migration of channels of different orders, widening or elongation of basins as well as formation and extinction of channels and basins. In particular, when the precipitation gradient is locally increased, the higher‐order channels, including the mainstream river, migrate toward regions with higher precipitation intensity. Through pertinent examples, the reorganization of the drainage network is quantified via stream parameters such as Horton‐Strahler and Tokunaga measures, order‐based channel total length and river long profiles obtained via simulation of three‐dimensional basin topography, while the hydrologic response of the evolved network is investigated using metrics such as hydrograph and power spectral density of simulated streamflows at the outlet of the network. In addition, using OCNs, we investigate the effect of orographic precipitation patterns on multicatchment landscapes composed of several interacting basins. Our results show that network‐inspired methods can be utilized as insightful and versatile models for directly exploring the effects of climate change on the evolution of river drainage systems.
The global warming hiatus: Slowdown or redistribution?
Authors: Yan Xiao‐Hai , Boyer Tim , Trenberth Kevin , Karl Thomas R. , Xie Shang‐Ping , Nieves Veronica , Tung Ka‐Kit , Roemmich Dean 
Published: November 2016

AbstractGlobal mean surface temperatures (GMST) exhibited a smaller rate of warming during 1998–2013, compared to the warming in the latter half of the 20th Century. Although, not a “true” hiatus in the strict definition of the word, this has been termed the “global warming hiatus” by IPCC (2013). There have been other periods that have also been defined as the “hiatus” depending on the analysis. There are a number of uncertainties and knowledge gaps regarding the “hiatus.” This report reviews these issues and also posits insights from a collective set of diverse information that helps us understand what we do and do not know. One salient insight is that the GMST phenomenon is a surface characteristic that does not represent a slowdown in warming of the climate system but rather is an energy redistribution within the oceans. Improved understanding of the ocean distribution and redistribution of heat will help better monitor Earth's energy budget and its consequences. A review of recent scientific publications on the “hiatus” shows the difficulty and complexities in pinpointing the oceanic sink of the “missing heat” from the atmosphere and the upper layer of the oceans, which defines the “hiatus.” Advances in “hiatus” research and outlooks (recommendations) are given in this report.
Crustal structure and deformation across a mature slab tear zone: the case of southern Tyrrhenian subduction (Italy)
Authors: Bianchi Irene , Lucente Francesco Pio , Di Bona Massimo , Govoni Aladino , Piana Agostinetti Nicola 
Published: November 2016

AbstractWe compute S velocity profiles of the crust across the Messina Strait (Italy), the tear zone at the southern end of the Ionian subduction zone. Separating Sicily from Calabria, the Messina Strait hosted some of the strongest earthquakes to ever occur in Italy. Here the motion of the Ionian slab with respect to Sicily creates a complex tectonic setting characterized by lithospheric tearing. We show velocity models of the crust, computed from teleseismic receiver function inversion, outlining the differences between Sicily and Calabria. Strong deformation across the Messina Strait between 10–15 and 30 km depth is expressed by strong anisotropy (up to 10%), developed in a ductile shear zone of the crust. The top of these ductile weaker layers could limit the depth extent of future ruptures.
Semiautomatic mapping of permafrost in the Yukon Flats, Alaska
Authors: Gulbrandsen Mats Lundh , Minsley Burke J. , Ball Lyndsay B. , Hansen Thomas Mejer 
Published: November 2016

AbstractThawing of permafrost due to global warming can have major impacts on hydrogeological processes, climate feedback, arctic ecology, and local environments. To understand these effects and processes, it is crucial to know the distribution of permafrost. In this study we exploit the fact that airborne electromagnetic (AEM) data are sensitive to the distribution of permafrost and demonstrate how the distribution of permafrost in the Yukon Flats, Alaska, is mapped in an efficient (semiautomatic) way, using a combination of supervised and unsupervised (machine) learning algorithms, i.e., Smart Interpretation and K‐means clustering. Clustering is used to sort unfrozen and frozen regions, and Smart Interpretation is used to predict the depth of permafrost based on expert interpretations. This workflow allows, for the first time, a quantitative and objective approach to efficiently map permafrost based on large amounts of AEM data.
Stratospheric control of planetary waves
Authors: Hitchcock Peter , Haynes Peter H. 
Published: November 2016

AbstractThe effects of imposing at various altitudes in the stratosphere zonally symmetric circulation anomalies associated with a stratospheric sudden warming are investigated in a mechanistic circulation model. A shift of the tropospheric jet is found even when the anomalies are imposed only above 2 hPa. Their influence is communicated downward through the planetary wave field via three distinct mechanisms. First, a significant fraction of the amplification of the upward fluxes of wave activity prior to the central date of the warming is due to the coupled evolution of the stratospheric zonal mean state and the wave field throughout the column. Second, a downward propagating region of localized wave, mean‐flow interaction is active around the central date but does not penetrate the tropopause. Third, there is deep, vertically synchronous suppression of upward fluxes following the central date. The magnitude of this suppression correlates with that of the tropospheric jet shift.
Ion nose spectral structures observed by the Van Allen Probes
Authors: Ferradas C. P. , Zhang J.‐C. , Spence H. E. , Kistler L. M. , Larsen B. A. , Reeves G. , Skoug R. , Funsten H. 
Published: November 2016

AbstractWe present a statistical study of nose‐like structures observed in energetic hydrogen, helium, and oxygen ions near the inner edge of the plasma sheet. Nose structures are spectral features named after the characteristic shapes of energy bands or gaps in the energy‐time spectrograms of in situ measured ion fluxes. Using 22 months of observations from the Helium Oxygen Proton Electron instrument onboard Van Allen Probe A, we determine the number of noses observed, and the minimum L shell reached and energy of each nose on each pass through the inner magnetosphere. We find that multiple noses occur more frequently in heavy ions than in H+ and are most often observed during quiet times. The heavy‐ion noses penetrate to lower L shells than H+ noses, and there is an energy‐magnetic local time (MLT) dependence in the nose locations and energies that is similar for all species. The observations are interpreted by using a steady state model of ion drift in the inner magnetosphere. The model is able to explain the energy and MLT dependence of the different types of nose structures. Different ion charge‐exchange lifetimes are the main cause for the deeper penetration of heavy‐ion noses. The species dependence and preferred geomagnetic conditions of multiple‐nose events indicate that they must be on long drift paths, leading to strong charge‐exchange effects. The results provide important insight into the spatial distribution, species dependence, and geomagnetic conditions under which nose structures occur.
Coronal mass ejections and solar wind mass fluxes over the heliosphere during solar cycles 23 and 24 (1996–2014)
Authors: Lamy P. , Floyd O. , Quémerais E. , Boclet B. , Ferron S. 
Published: November 2016

AbstractCoronal mass ejections (CMEs) play a major role in the heliosphere, and their contribution to the solar wind mass flux, already considered in the Skylab and Solwind eras with conflicting results, is reexamined in the light of 19 years (1996–2014) of SOHO observations with the Large Angle and Spectroscopic Coronagraph (LASCO‐C2) for the CMEs and extended for the first time to all latitudes thanks to the whole‐heliosphere data from the Solar Wind ANisotropies (SWAN) instrument supplemented by in situ data aggregated in the OMNI database. First, several mass estimates reported in the ARTEMIS (Automated Recognition of Transient Events and Marseille Inventory from Synoptic maps) catalog of LASCO CMEs are compared with determinations based on the combined observations with the twin STEREO/Sun Earth Connection Coronal and Heliospheric Investigation coronagraphs in order to ascertain their validity. A simple geometric model of the CMEs is introduced to generate Carrington maps of their mass flux and then to produce annualized synoptic maps. The Lyman α SWAN data are inverted to similarly produce synoptic maps to be compared with those of the CME flux. The ratio of the annualized CME to solar wind mass flux is found to closely track the solar cycle over the heliosphere. In the near‐ecliptic region and at latitudes up to ∼55°, this ratio was negligibly small during the solar minima of cycles 22/23 and 23/24 and rose to 6% and 5%, respectively, at the maximum of solar cycles 23 and 24. These maximum ratios increased at higher latitudes, but this result is likely biased by the inherent limitation of determining the true latitude of CMEs.
Effects of ULF wave power on relativistic radiation belt electrons: 8–9 October 2012 geomagnetic storm
Authors: Pokhotelov D. , Rae I. J. , Murphy K. R. , Mann I. R. , Ozeke L. 
Published: November 2016

AbstractElectromagnetic ultralow‐frequency (ULF) waves are known to play a substantial role in radial transport, acceleration, and loss of relativistic particles trapped in the Earth's outer radiation belt. Using in situ observations by multiple spacecraft operating in the vicinity of outer radiation belts, we analyze the temporal and spatial behavior of ULF waves throughout the geomagnetic storm of 8–9 October 2012 and compare with the dynamics of relativistic electron fluxes on board the twin Van Allen Probes spacecraft. The analysis shows that the relativistic electron fluxes reduce from their prestorm levels during the first phase of the storm and rapidly increase during the second phase of the storm. We demonstrate that the behavior of ULF wave power changes throughout the storm, from ULF oscillations being a mixture of compressional and shear magnetic components during the first phase of the storm to ULF oscillations being dominated by transverse (shear) components during the second phase. We analyze the parameters of ULF‐driven radial diffusion throughout the storm and compare the observed diffusion coefficients with their statistical averages. We demonstrate that the observed diffusion coefficients are strong enough to impact the redistribution of relativistic electron fluxes from and to the outer boundary of radiation belts and the diffusion might influence the effects of any local electron acceleration by transporting fluxes inward or outward according to phase space density gradients.
Timescales for the penetration of IMF By into the Earth's magnetotail
Authors: Browett S. D. , Fear R. C. , Grocott A. , Milan S. E. 
Published: November 2016

AbstractPrevious studies have shown that there is a correlation between the By component of the interplanetary magnetic field (IMF) and the By component observed in the magnetotail lobe and in the plasma sheet. However, studies of the effect of IMF By on several magnetospheric processes have indicated that the By component in the tail should depend more strongly on the recent history of the IMF By rather than on the simultaneous measurements of the IMF. Estimates of this timescale vary from ∼25 min to ∼4 h. We present a statistical study of how promptly the IMF By component is transferred into the neutral sheet, based on Cluster observations of the neutral sheet from 2001 to 2008, and solar wind data from the OMNI database. Five thousand nine hundred eighty‐two neutral sheet crossings during this interval were identified, and starting with the correlation between instantaneous measurements of the IMF and the magnetotail (recently reported by Cao et al. (2014)), we vary the time delay applied to the solar wind data. Our results suggest a bimodal distribution with peaks at ∼1.5 and ∼3 h. The relative strength of each peak appears to be well controlled by the sign of the IMF Bz component with peaks being observed at 1 h of lag time for southward IMF and up to 5 h for northward IMF conditions, and the magnitude of the solar wind velocity with peaks at 2 h of lag time for fast solar wind and 4 h for slow solar wind conditions.
Analysis of the global ionospheric disturbances of the March 2015 great storm
Authors: Yao Yibin , Liu Lei , Kong Jian , Zhai Changzhi 
Published: November 2016

AbstractThe global ionospheric storm in March 2015 was investigated by using data from over 3000 GPS stations worldwide. In this study, total electron content (TEC), rate of TEC (ROT), and ROT's standard deviation rate of the TEC index, as well as the second‐order difference operator TECT, were considered as main characteristic methods to distinguish ionosphereic disturbances. The results show that (1) based on the multiple methods above, we all observed that for the first time, there were three equatorward traveling ionospheric disturbances (TIDs) in the main phase of this storm. In North America, the disturbance zone expanded to ~40°N; the disturbance periods and AE peak stages were roughly synchronous. We suggest that these three TIDs were induced by the propagation of atmospheric gravity waves to low latitudes under the action of AE. (2) The most intense positive storm occurred over South America and the South Atlantic (over 300% enhancement; 00:00–05:00 UT on 18 March), whereas a negative storm was observed in the corresponding region of the Northern Hemisphere. Such inverse hemispheric asymmetry in intensity and structure can be explained by the variations of the thermospheric composition, the IMF By component, and the geomagnetic intensity. (3) On 18 March, a negative storm dominated globally (except at certain low latitudes), and tended to propagate equatorward and decay with time, which could be largely attributed to the storm circulation theory. And the evolution of the negative storm was further characterized by the foF2 variations of ionosondes.
Poynting vector and wave vector directions of equatorial chorus
Authors: Taubenschuss Ulrich , Santolík Ondřej , Breuillard Hugo , Li Wen , Le Contel Olivier 
Published: November 2016

AbstractWe present new results on wave vectors and Poynting vectors of chorus rising and falling tones on the basis of 6 years of THEMIS (Time History of Events and Macroscale Interactions during Substorms) observations. The majority of wave vectors is closely aligned with the direction of the ambient magnetic field (B0). Oblique wave vectors are confined to the magnetic meridional plane, pointing away from Earth. Poynting vectors are found to be almost parallel to B0. We show, for the first time, that slightly oblique Poynting vectors are directed away from Earth for rising tones and toward Earth for falling tones. For the majority of lower band chorus elements, the mutual orientation between Poynting vectors and wave vectors can be explained by whistler mode dispersion in a homogeneous collisionless cold plasma. Upper band chorus seems to require inclusion of collisional processes or taking into account azimuthal anisotropies in the propagation medium. The latitudinal extension of the equatorial source region can be limited to ±6∘ around the B0 minimum or approximately ±5000 km along magnetic field lines. We find increasing Poynting flux and focusing of Poynting vectors on the B0 direction with increasing latitude. Also, wave vectors become most often more field aligned. A smaller group of chorus generated with very oblique wave normals tends to stay close to the whistler mode resonance cone. This suggests that close to the equatorial source region (within ∼20∘ latitude), a wave guidance mechanism is relevant, for example, in ducts of depleted or enhanced plasma density.
A two‐dimensional global simulation study of inductive‐dynamic magnetosphere‐ionosphere coupling
Authors: Tu Jiannan , Song Paul 
Published: November 2016

AbstractWe present the numerical methods and results of a global two‐dimensional multifluid‐collisional‐Hall magnetohydrodynamic (MHD) simulation model of the ionosphere‐thermosphere system, an extension of our one‐dimensional three‐fluid MHD model. The model solves, self‐consistently, Maxwell's equations, continuity, momentum, and energy equations for multiple ion and neutral species incorporating photochemistry, collisions among the electron, ion and neutral species, and various heating sources in the energy equations. The inductive‐dynamic approach (solving self‐consistently Faraday's law and retaining inertia terms in the plasma momentum equations) used in the model retains all possible MHD waves, thus providing faithful physical explanation (not merely description) of the magnetosphere‐ionosphere/thermosphere (M‐IT) coupling. In the present study, we simulate the dawn‐dusk cross‐polar cap dynamic responses of the ionosphere to imposed magnetospheric convection. It is shown that the convection velocity at the top boundary launches velocity, magnetic, and electric perturbations propagating with the Alfvén speed toward the bottom of the ionosphere. Within the system, the waves experience reflection, penetration, and rereflection because of the inhomogeneity of the plasma conditions. The reflection of the Alfvén waves may cause overshoot (stronger than the imposed magnetospheric convection) of the plasma velocity in some regions. The simulation demonstrates dynamic propagation of the field‐aligned currents and ionospheric electric field carried by the Alfvén waves, as well as formation of closure horizontal currents (Pedersen currents in the E region), indicating that in the dynamic stage the M‐I coupling is via the Alfvén waves instead of field‐aligned currents or electric field mapping as described in convectional M‐I coupling models.
Evidence of a shallow water submarine hydrothermal field off Zannone Island from morphological and geochemical characterization: Implications for Tyrrhenian Sea Quaternary volcanism
Authors: Martorelli E. , Italiano F. , Ingrassia M. , Macelloni L. , Bosman A. , Conte A. M. , Beaubien S. E. , Graziani S. , Sposato A. , Chiocci F. L. 
Published: November 2016

AbstractDiscoveries from multibeam bathymetry and geochemical surveys performed off Zannone Island (western Pontine Archipelago, Tyrrhenian Sea) provide evidence of an undocumented hydrothermal field characterized by ongoing fluid emissions and morphologically complex giant depressions located in shallow water (<150 m water depth). Based on a detailed morpho‐bathymetric study we identify the seabed morphologies produced by hydrothermal fluid emission activity. We recognize five giant depressions (length >250 m) that host pockmarks, mounds, small cones, and active fluid vents, which are interpreted as complex fluid‐escape features developed both through vigorous‐explosive events and steady seepage. Their spatial distribution suggests that the NE‐SW trending faults bounding the Ponza‐Zannone structural high and the shallow fractured basement are favorable conditions for the upward migration of hydrothermal fluids. Moreover, we performed a detailed geochemical study to investigate the source of the hydrothermal fluids. The geochemical signature of the collected fluids provides information of active CO2‐dominated degassing with a significant contribution of mantle volatiles, with measured 3He/4He values > 3.0 Ra that are similar to those recorded at Stromboli and Panarea volcanoes. The hydrothermal system produces volatiles that may originate from residual magma batches, similar to the Pleistocene trachytes cropping out in the SE sector of Ponza Island that were probably intruded in the shallow crustal levels and never erupted. The discovery of the Zannone hydrothermal field updates the record of active hydrothermal areas of the Mediterranean Sea. Moreover, the recognition of several giant hydrothermal depressions characterized by a complex morphology is peculiar for the Mediterranean Sea.
Elastic wave velocity evolution of shales deformed under uppermost crustal conditions
Authors: Bonnelye Audrey , Schubnel Alexandre , David Christian , Henry Pierre , Guglielmi Yves , Gout Claude , Fauchille Anne‐Laure , Dick Pierre 
Published: November 2016

AbstractConventional triaxial tests were performed on a series of samples of Tournemire shale along different orientations relative to bedding (0°, 90°). Experiments were carried out up to failure at increasing confining pressures ranging from 2.5 to 80 MPa, and at strain rates ranging between 3 × 10−7 s−1 and 3 × 10−5 s−1. During each experiment, P and S wave elastic velocities were continuously measured along many raypaths with different orientations with respect to bedding and maximum compressive stress. This extensive velocity measurement setup allowed us to highlight the presence of plastic mechanisms such as mineral reorientation during deformation. The evolution of elastic anisotropy was quantified using Thomsen's parameters which were directly inverted from measurement of elastic wave velocity. Brittle failure was preceded by a change in P wave anisotropy, due to both crack growth and mineral reorientation. Anisotropy variations were largest for samples deformed perpendicular to bedding, at the onset of rupture. Anisotropy reversal was observed at the highest confining pressures. For samples deformed parallel to bedding, the P wave anisotropy change is weaker.