bluuebunny/crossref_metadata_2025_split huggingface dataset:
A mechanistic model (BCC‐PSSICO) to predict changes in the hydraulic properties for bio‐amended variably saturated soils
Authors: Carles Brangarí Albert , Sanchez‐Vila Xavier , Freixa Anna , M. Romaní Anna , Rubol Simonetta , Fernàndez‐Garcia Daniel 
Published: December 2016

AbstractThe accumulation of biofilms in porous media is likely to influence the overall hydraulic properties and, consequently, a sound understanding of the process is required for the proper design and management of many technological applications. In order to bring some light into this phenomenon we present a mechanistic model to study the variably saturated hydraulic properties of bio‐amended soils. Special emphasis is laid on the distribution of phases at pore‐scale and the mechanisms to retain and let water flow through, providing valuable insights into phenomena behind bioclogging. Our approach consists in modeling the porous media as an ensemble of capillary tubes, obtained from the biofilm‐free water retention curve. This methodology is extended by the incorporation of a biofilm composed of bacterial cells and extracellular polymeric substances (EPS). Moreover, such a microbial consortium displays a channeled geometry that shrinks/swells with suction. Analytical equations for the volumetric water content and the relative permeability can then be derived by assuming that biomass reshapes the pore space following specific geometrical patterns. The model is discussed by using data from laboratory studies and other approaches already existing in the literature. It can reproduce (i) displacements of the retention curve toward higher saturations and (ii) permeability reductions of distinct orders of magnitude. Our findings also illustrate how even very small amounts of biofilm may lead to significant changes in the hydraulic properties. We, therefore, state the importance of accounting for the hydraulic characteristics of biofilms and for a complex/more realistic geometry of colonies at the pore‐scale.
Avoidable impacts of ocean warming on marine primary production: Insights from the CESM ensembles
Authors: Krumhardt Kristen M. , Lovenduski Nicole S. , Long Matthew C. , Lindsay Keith 
Published: December 2016

AbstractAs anthropogenic emissions and warming continue to alter Earth's environment, it is essential to highlight future impacts that can be avoided through mitigation. Here we use two ensembles of the Community Earth System Model (CESM) run under the business‐as‐usual scenario, RCP 8.5, and the mitigation scenario, RCP 4.5, to identify avoidable impacts of anthropogenic warming on marine net primary production (NPP). We emphasize the use of ensembles so as to distinguish long‐term, anthropogenic trends in marine productivity from internal variability. Twentieth century globally integrated marine NPP is 55.7 ± 1 Pg C, with much of the variability attributable to certain regions (e.g., the equatorial Pacific). CESM projections indicate that global marine NPP will drop by ∼4% by 2080 if we follow RCP 8.5, but only by 2% under RCP 4.5. The response to warming on a global scale includes compensating regional effects; NPP increases in polar and eastern equatorial Pacific waters but decreases in the Atlantic, western Pacific, and Indian Oceans. The two main phytoplankton groups simulated in CESM show distinct responses: diatoms decrease their NPP, while small phytoplankton NPP increases over the mid‐21st century. Trends in NPP from mid‐21st century to 2080 are significantly different between the two emission scenarios mainly in the Atlantic Ocean basin and therefore impacts here are “avoidable” if we follow RCP 4.5, rather than RCP 8.5. In contrast, changes in NPP on a global scale and in most areas of the Pacific and Indian basins and the Southern Ocean are not distinguishable between forcing scenarios.
The East Pacific Rise current: Topographic enhancement of the interior flow in the South Pacific Ocean
Authors: Zilberman N. V. , Roemmich D. H. , Gille S. T. 
Published: December 2016

AbstractObservations of absolute velocity based on Argo float profiles and trajectories in the ocean interior show evidence for an equatorward current, the East Pacific Rise current, between 42°S and 30°S, along the western flank of the East Pacific Rise. The East Pacific Rise current carries predominantly intermediate water masses, including Subantarctic Mode Water and Antarctic Intermediate Water, and deeper waters, from the southern edge of the subtropical gyre toward the Equator. The 2004 to 2014 mean East Pacific Rise current transport extrapolated through the 0–2600 m depth range is 8.1 ± 1.6 sverdrup (Sv) (1 Sv = 106 m3 s−1), consistent with a wind‐driven interior transport influenced by the East Pacific Rise topography. While deep ocean mixing and geothermal heating can both create pressure gradients that support geostrophic flows in the deep ocean, this study indicates that about half of the East Pacific Rise current transport is associated with topographic steering of the deep flow over the East Pacific Rise.
Quantifying the time lag between organic matter production and export in the surface ocean: Implications for estimates of export efficiency
Authors: Stange P. , Bach L. T. , Le Moigne F. A. C. , Taucher J. , Boxhammer T. , Riebesell U. 
Published: December 2016

AbstractThe ocean's potential to export carbon to depth partly depends on the fraction of primary production (PP) sinking out of the euphotic zone (i.e., the e‐ratio). Measurements of PP and export flux are often performed simultaneously in the field, although there is a temporal delay between those parameters. Thus, resulting e‐ratio estimates often incorrectly assume an instantaneous downward export of PP to export flux. Evaluating results from four mesocosm studies, we find that peaks in organic matter sedimentation lag chlorophyll a peaks by 2 to 15 days. We discuss the implications of these time lags (TLs) for current e‐ratio estimates and evaluate potential controls of TL. Our analysis reveals a strong correlation between TL and the duration of chlorophyll a buildup, indicating a dependency of TL on plankton food web dynamics. This study is one step further toward time‐corrected e‐ratio estimates.
Statistical distribution of EMIC wave spectra: Observations from Van Allen Probes
Authors: Zhang X.‐J. , Li W. , Thorne R. M. , Angelopoulos V. , Bortnik J. , Kletzing C. A. , Kurth W. S. , Hospodarsky G. B. 
Published: December 2016

AbstractIt has been known that electromagnetic ion cyclotron (EMIC) waves can precipitate ultrarelativistic electrons through cyclotron resonant scattering. However, the overall effectiveness of this mechanism has yet to be quantified, because it is difficult to obtain the global distribution of EMIC waves that usually exhibit limited spatial presence. We construct a statistical distribution of EMIC wave frequency spectra and their intensities based on Van Allen Probes measurements from September 2012 to December 2015. Our results show that as the ratio of plasma frequency over electron gyrofrequency increases, EMIC wave power becomes progressively dominated by the helium band. There is a pronounced dawn‐dusk asymmetry in the wave amplitude and the frequency spectrum. The frequency spectrum does not follow the commonly used single‐peak Gaussian function. Incorporating these realistic EMIC wave frequency spectra into radiation belt models is expected to improve the quantification of EMIC wave scattering effects in ultrarelativistic electron dynamics.
UV photochemistry of carboxylic acids at the air‐sea boundary: A relevant source of glyoxal and other oxygenated VOC in the marine atmosphere
Authors: Chiu R. , Tinel L. , Gonzalez L. , Ciuraru R. , Bernard F. , George C. , Volkamer R. 
Published: December 2016

AbstractPhotochemistry plays an important role in marine dissolved organic carbon (DOC) degradation, but the mechanisms that convert DOC into volatile organic compounds (VOCs) remain poorly understood. We irradiated carboxylic acids (C7–C9) on a simulated ocean surface with UV light (<320 nm) in a photochemical flow reactor and transferred the VOC products into a dark ozone reactor. Glyoxal was detected as a secondary product from heptanoic, octanoic, and nonanoic acid (NA) films, but not from octanol. Primary glyoxal emissions were not observed, nor was glyoxal formed in the absence of ozone. Addition of a photosensitizer had no noticeable effect. The concurrent detection of heptanal in the NA system suggests that the ozonolysis of 2‐nonenal is the primary chemical mechanism that produces glyoxal. This source can potentially sustain tens of parts per trillion by volume (pptv) glyoxal over oceans, and helps to explain why glyoxal fluxes in marine air are directed from the atmosphere into the ocean.
Spectral analysis of Ahuna Mons from Dawn mission's visible‐infrared spectrometer
Authors: Zambon F. , Raponi A. , Tosi F. , De Sanctis M. C. , McFadden L. A. , Carrozzo F. G. , Longobardo A. , Ciarniello M. , Krohn K. , Stephan K. , Palomba E. , Pieters C. M. , Ammannito E. , Russell C. T. , Raymond C. A. 
Published: December 2016

AbstractAhuna Mons is the highest mountain on Ceres. A unique complex in terms of size, shape, and morphology, Ahuna is bordered by flanks of the talus around its summit. Recent work by Ruesch et al. () based on Dawn's Framing Camera images shed light on the possible origin of Ahuna Mons. According to Ruesch et al. (2016), Ahuna Mons is formed by a volcanic process involving the ascent of cryomagma and extrusion onto the surface followed by dome development and subsequent spreading. Here we analyzed in detail the composition of Ahuna Mons, using data acquired by the visible and infrared spectrometer aboard Dawn. The spectral analysis reveals a relatively high abundance of carbonates and a nonhomogeneous variation in carbonate composition and abundance along Ahuna's flanks, associated with a lower amount of the Ceres's ubiquitous NH4‐phyllosilicates over a large portion of the flanks. The grain size is coarser on the flanks than in the surrounding regions, suggesting the presence of fresher material, also compatible with a larger abundance of carbonates. Thermal variations are seen in Ahuna, supporting the evidence of different compactness of the surface regolith in specific locations. Results of the spectral analysis are consistent with a possible cryovolcanic origin which exposed fresher material that slid down on the flanks.
Voluminous eruption from a zoned magma body after an increase in supply rate at Axial Seamount
Authors: Chadwick W. W. , Paduan J. B. , Clague D. A. , Dreyer B. M. , Merle S. G. , Bobbitt A. M. , Caress D. W. , Philip B. T. , Kelley D. S. , Nooner S. L. 
Published: December 2016

AbstractAxial Seamount is the best monitored submarine volcano in the world, providing an exceptional window into the dynamic interactions between magma storage, transport, and eruption processes in a mid‐ocean ridge setting. An eruption in April 2015 produced the largest volume of erupted lava since monitoring and mapping began in the mid‐1980s after the shortest repose time, due to a recent increase in magma supply. The higher rate of magma replenishment since 2011 resulted in the eruption of the most mafic lava in the last 500–600 years. Eruptive fissures at the volcano summit produced pyroclastic ash that was deposited over an area of at least 8 km2. A systematic spatial distribution of compositions is consistent with a single dike tapping different parts of a thermally and chemically zoned magma reservoir that can be directly related to previous multichannel seismic‐imaging results.
Assessing sensitivities in algorithmic detection of tropical cyclones in climate data
Authors: Zarzycki Colin M. , Ullrich Paul A. 
Published: December 2016

AbstractThis study applies a sensitivity analysis (SA) technique (the Morris method, MM) to an automated Lagrangian tropical cyclone (TC) tracking algorithm used on gridded climate data. MM demonstrates the ability to screen for input parameters defining TCs (such as minimum intensity and lifetime) that contribute significantly to sensitivity in output metrics (such as storm count). The SA is performed by tracking TCs in four different reanalyses. Tracked TC trajectories are compared to a pointwise observational record. Results show that using thermally integrated metrics for isolating TC warm cores is superior to single‐temperature levels. Input thresholds defining TC vortex strength during tracking contribute the most variance in all output metrics. Integrated output metrics (such as accumulated cyclone energy) are less variable than “counting” metrics such as TC frequency. MM greatly reduces the computational requirements for tracker optimization, with tracked TCs demonstrating better hit and false alarm rates than previous studies.
Middle atmosphere dynamical sources of the semiannual oscillation in the thermosphere and ionosphere
Authors: Jones M. , Emmert J. T. , Drob D. P. , Siskind D. E. 
Published: December 2016

AbstractThe strong global semiannual oscillation (SAO) in thermospheric density has been observed for five decades, but definitive knowledge of its source has been elusive. We use the National Center of Atmospheric Research thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model (TIME‐GCM) to study how middle atmospheric dynamics generate the SAO in the thermosphere‐ionosphere (T‐I). The “standard” TIME‐GCM simulates, from first principles, SAOs in thermospheric mass density and ionospheric total electron content that agree well with observed climatological variations. Diagnosis of the globally averaged continuity equation for atomic oxygen ([O]) shows that the T‐I SAO originates in the upper mesosphere, where an SAO in [O] is forced by nonlinear, resolved‐scale variations in the advective, net tidal, and diffusive transport of O. Contrary to earlier hypotheses, TIME‐GCM simulations demonstrate that intra‐annually varying eddy diffusion by breaking gravity waves may not be the primary driver of the T‐I SAO: A pronounced SAO is produced without parameterized gravity waves.
Opal‐CT in chert beneath the toe of the Tohoku margin and its influence on the seismic aseismic transition in subduction zones
Authors: Kameda Jun , Okamoto Atsushi , Sato Kiminori , Fujimoto Koichiro , Yamaguchi Asuka , Kimura Gaku 
Published: December 2016

AbstractThick accumulation of chert is a ubiquitous feature of old oceanic plates at convergent margins. In this study, we investigate chert fragments recovered by the Integrated Ocean Drilling Program expedition 343 at the Japan Trench where the 2011 Tohoku‐Oki earthquake (Mw 9.0) occurred. This sample provides a unique opportunity to investigate in situ chert diagenesis at an active subduction margin and its influence on the kinematics of megathrust faulting. Our mineralogical analyses revealed that the chert is characterized by hydrous opal‐CT and may therefore be highly deformable via pressure solution creep and readily accommodate shear strain between the converging plates at driving stresses of kilopascal order. As chert diagenesis advances, any further deformation requires stresses of >100 MPa, given the increasing transport distances for solutes as represented in cherts on land. The chert diagenesis is thus related to the mechanical transition from a weakly to strongly coupled plate interface at this margin.
Geologic influence on induced seismicity: Constraints from potential field data in Oklahoma
Authors: Shah Anjana K. , Keller G. Randy 
Published: December 2016

AbstractRecent Oklahoma seismicity shows a regional correlation with increased wastewater injection activity, but local variations suggest that some areas are more likely to exhibit induced seismicity than others. We combine geophysical and drill hole data to map subsurface geologic features in the crystalline basement, where most earthquakes are occurring, and examine probable contributing factors. We find that most earthquakes are located where the crystalline basement is likely composed of fractured intrusive or metamorphic rock. Areas with extrusive rock or thick (>4 km) sedimentary cover exhibit little seismicity, even in high injection rate areas, similar to deep sedimentary basins in Michigan and western North Dakota. These differences in seismicity may be due to variations in permeability structure: within intrusive rocks, fluids can become narrowly focused in fractures and faults, causing an increase in local pore fluid pressure, whereas more distributed pore space in sedimentary and extrusive rocks may relax pore fluid pressure.
Earthquake ground motion amplification for surface waves
Authors: Bowden Daniel C. , Tsai Victor C. 
Published: December 2016

AbstractSurface waves from earthquakes are known to cause strong damage, especially for larger structures such as skyscrapers and bridges. However, common practice in characterizing seismic hazard at a specific site considers the effect of near‐surface geology on only vertically propagating body waves. Here we show that surface waves have a unique and different frequency‐dependent response to known geologic structure and that this amplification can be analytically calculated in a manner similar to current hazard practices. Applying this framework to amplification in the Los Angeles Basin, we find that peak ground accelerations for certain large regional earthquakes are underpredicted if surface waves are not properly accounted for and that the frequency of strongest ground motion amplification can be significantly different. Including surface‐wave amplification in hazards calculations is therefore essential for accurate predictions of strong ground motion for future San Andreas Fault ruptures.
Mapping the conjugate and corotating storm‐enhanced density during 17 March 2013 storm through data assimilation
Authors: Yue Xinan , Wan Weixing , Liu Libo , Liu Jing , Zhang Shunrong , Schreiner William S. , Zhao Biqiang , Hu Lianhuan 
Published: December 2016

AbstractThe storm‐enhanced density (SED) is an electron density enhancement phenomenon extending from the later afternoon at middle latitude to the noontime in high latitude within a narrow band during early stage of geomagnetic storm. Previous investigations were mostly focused on the northern America region due to sparse data coverage in other regions. Recent observational analysis and simulation studies have shown that the SED might be quite complicated both physically and spatial/temporal evolution. In this paper, we obtained the global ionospheric electron density with the spatial/temporal resolution of 5° in latitude, 10° in longitude, ~30 km around F2 peak, and 0.5 h in time, during 17 March 2013 geomagnetic storm through assimilating ground and LEO‐based total electron content (TEC) data into the model. A total of ~450 ground‐based Global Navigation Satellite Systems stations' and ~10 LEO satellites' observations were applied in the assimilation. Of all the data, six satellites with ionospheric radio occultation profiling capability provided the key altitudinal variation information. The SED associated with the tongue of ionization (TOI) and boundary blob can be well identified from the data assimilation results, although their amplitude of enhancement was only up to ~6 TECU (TEC unit, 1 TECU = 1016 el m−2). All structures show very dynamic and complicated time evolution features. During this storm time, we identified two separate SED/TOI/blob structures corotating from Europe to American with conjugate occurrence. This partly supports the mechanism of convection expansion. Given a significant amount of radio occultation will be available in the near future, this method will help up us to resolve global large‐scale ionospheric disturbance down to very small spatial and temporal scale in storm time.
An alternative possibility to equatorial plasma bubble forecasting through mathematical modeling and Digisonde data
Authors: Sousasantos J. , Kherani E. A. , Sobral J. H. A. 
Published: December 2016

AbstractEquatorial plasma bubbles (EPBs), or large‐scale plasma depleted regions, are one of the subjects of great interest in space weather research since such phenomena have been extensively reported to cause strong degrading effects on transionospheric radio propagation at low latitudes, especially over the Brazilian region, where satellite communication interruptions by the EPBs have been, frequently, registered. One of the most difficult tasks for this field of scientific research is the forecasting of such plasma‐depleted structures. This forecasting capability would be of significant help for users of positioning/navigation systems operating in the low‐latitude/equatorial region all over the world. Recently, some efforts have been made trying to assess and improve the capability of predicting the EPB events. The purpose of this paper is to present an alternative approach to EPB prediction by means of the use of mathematical numerical simulation associated with ionospheric vertical drift, obtained through Digisonde data, focusing on telling beforehand whether ionospheric plasma instability processes will evolve or not into EPB structures. Modulations in the ionospheric vertical motion induced by gravity waves prior to the prereversal enhancement occurrence were used as input in the numerical model. A comparison between the numerical results and the observed EPB phenomena through CCD all‐sky image data reveals a considerable coherence and supports the hypothesis of a capability of short‐term forecasting.
The response of the inner magnetosphere to the trailing edges of high‐speed solar‐wind streams
Authors: Denton M. H. , Borovsky J. E. 
Published: December 2016

AbstractThe effects of the leading edge stream interface of high‐speed solar‐wind streams (HSSs) upon the Earth's magnetosphere have been extensively documented. The arrival of HSSs leads to significant changes in the plasmasphere, plasma sheet, ring current, and radiation belts, during the evolution from slow solar wind to persistent fast solar wind. Studies have also documented effects in the lower ionosphere and the neutral atmosphere. However, only cursory attention has been paid to the trailing‐edge stream interface during the transition back from fast solar wind to slow solar wind. Here we report on the statistical changes that occur in the plasmasphere, plasma sheet, ring current, and electron radiation belt during the passage of the trailing‐edge stream interface of HSSs, when the magnetosphere is in most respects in an extremely quiescent state. Counterintuitively, the peak flux of ~1 MeV electrons is observed to occur at this interface. In contrast, other regions of the magnetosphere demonstrate extremely quiet conditions. As with the leading‐edge stream interface, the occurrence of the trailing‐edge stream interface has a periodicity of 27 days, and hence, understanding the changes that occur in the magnetosphere during the passage of trailing edges of HSSs can lead to improved forecasting and predictability of the magnetosphere as a system.