bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigating the source of near‐relativistic and relativistic electrons in Earth's inner radiation belt
Authors: Turner D. L. , O'Brien T. P. , Fennell J. F. , Claudepierre S. G. , Blake J. B. , Jaynes A. N. , Baker D. N. , Kanekal S. , Gkioulidou M. , Henderson M. G. , Reeves G. D. 
Published: December 2016

AbstractUsing observations from NASA's Van Allen Probes, we study the role of sudden particle enhancements at low L shells (SPELLS) as a source of inner radiation belt electrons. SPELLS events are characterized by electron intensity enhancements of approximately an order of magnitude or more in less than 1 day at L < 3. During quiet and average geomagnetic conditions, the phase space density radial distributions for fixed first and second adiabatic invariants are peaked at 2 < L < 3 for electrons ranging in energy from ~50 keV to ~1 MeV, indicating that slow inward radial diffusion is not the dominant source of inner belt electrons under quiet/average conditions. During SPELLS events, the evolution of electron distributions reveals an enhancement of phase space density that can exceed 3 orders of magnitude in the slot region and continues into the inner radiation belt, which is evidence that these events are an important—and potentially dominant—source of inner belt electrons. Electron fluxes from September 2012 through February 2016 reveal that SPELLS occur frequently (~2.5/month at 200 keV), but the number of observed events decreases exponentially with increasing electron energy for ≥100 keV. After SPELLS events, the slot region reforms due to slow energy‐dependent decay over several day time scales, consistent with losses due to interactions with plasmaspheric hiss. Combined, these results indicate that the peaked phase space density distributions in the inner electron radiation belt result from an “on/off,” geomagnetic‐activity‐dependent source from higher radial distances.
Earthquake supercycles on the Mentawai segment of the Sunda megathrust in the seventeenth century and earlier
Authors: Philibosian Belle , Sieh Kerry , Avouac Jean‐Philippe , Natawidjaja Danny H. , Chiang Hong‐Wei , Wu Chung‐Che , Shen Chuan‐Chou , Daryono Mudrik R. , Perfettini Hugo , Suwargadi Bambang W. , Lu Yanbin , Wang Xianfeng 
Published: December 2016

AbstractOver at least the past millennium, the Mentawai segment of the Sunda megathrust has failed in sequences of closely timed events rather than in single end‐to‐end ruptures—each the culmination of an earthquake “supercycle.” Here we synthesize the sixteenth‐ and seventeenth‐century coral microatoll records into a chronology of interseismic and coseismic vertical deformation. We identify at least five discrete uplift events in about 1597, 1613, 1631, 1658, and 1703 that likely correspond to large megathrust ruptures. This sequence contrasts with the following supercycle culmination, which involved only two large ruptures in 1797 and 1833. Fault slip modeling suggests that together the five cascading ruptures involved failure of the entire Mentawai segment. Interseismic deformation rates also changed after the onset of the rupture sequence, as they did after the 1797 earthquake. We model this change as an altered distribution of fault coupling, presumably triggered by the ~1597 rupture. We also analyze the far less continuous microatoll record between A.D. 1 and 1500. While we cannot confidently delineate the extent of any megathrust rupture during that period, all evidence suggests that individual major ruptures involve only part of the Mentawai segment, often overlap below the central Mentawai Islands, often trigger coupling changes, and occur in clusters that cumulatively cover the entire Mentawai segment at the culmination of each supercycle. It is clear that each Mentawai rupture sequence evolves uniquely in terms of the order and grouping of asperities that rupture, suggesting heterogeneities in fault frictional properties at the ~100 km scale.
Submarine groundwater discharge and associated nutrient fluxes into the Southern Yellow Sea: A case study for semi‐enclosed and oligotrophic seas‐implication for green tide bloom
Authors: Liu Jian'an , Su Ni , Wang Xilong , Du Jinzhou 
Published: December 2016

AbstractThe biogenic elements concentrations in a coastal bay/estuary are strongly influenced not only by riverine input but also by submarine groundwater discharge (SGD) which has been identified as a typical process of land/ocean interactions in coastal zones. To assess the role of SGD in nutrient fluxes in the Southern Yellow Sea (SYS), 228Ra activities were measured in seawater collected in May 2014. Analyzing the sources and sinks of 228Ra, the flux of excess 228Ra through SGD was estimated to be (2.2 ± 1.0) ×1015 dpm yr−1. Based on the 228Ra mass balance model, we estimated the average SGD flux to be approximately (1.3 ± 0.87) ×1012 m3 yr−1 over the entire SYS, which is at least 3.3 times the estimated annual delivery from the Changjiang River into the SYS (∼1.3 × 1011 m3 yr−1). The SGD‐derived biogenic elements loads (dissolved inorganic nitrogen (DIN), phosphorus (DIP) and silicon (DSi)) were estimated as (487 ± 384) × 109 mol yr−1, (2.8 ± 2.2) × 109 mol yr−1, and (313 ± 259) × 109 mol yr−1, respectively, which are approximately 18 times, 7 times and 13 times the riverine input from both mainland China and Korea. The accumulation nutrient fluxes derived by SGD may play one of the most important roles in the green tide bloom that originated from the Subei Shoal zone in the SYS. Additionally, DIN and DIP via SGD can provide the necessary amounts of nutrient for recovering nutrient concentrations to normal levels after the green tide bloom is terminated.
Impact of DYNAMO observations on NASA GEOS‐5 reanalyses and the representation of MJO initiation
Authors: Achuthavarier D. , Wang H. , Schubert S. D. , Sienkiewicz M. 
Published: December 2016

AbstractThis study examines the impact of the Dynamics of the Madden‐Julian Oscillation (DYNAMO) campaign in situ observations on NASA Goddard Earth Observing System version 5 (GEOS‐5) reanalyses and the improvements gained thereby in the representation of the Madden‐Julian Oscillation (MJO) initiation processes. To this end, we produced a global, high‐resolution (1/4° spatially) reanalysis that assimilates the level‐4, quality‐controlled DYNAMO upper air soundings from about 87 stations in the equatorial Indian Ocean region along with a companion data‐denied control reanalysis. The DYNAMO reanalysis produces a more realistic vertical structure of the temperature and moisture in the central tropical Indian Ocean by correcting the model biases, namely, the cold and dry biases in the lower troposphere and warm bias in the upper troposphere. The reanalysis horizontal winds are substantially improved, in that, the westerly acceleration and vertical shear of the zonal wind are enhanced. The DYNAMO reanalysis shows enhanced low‐level diabatic heating, moisture anomalies and vertical velocity during the MJO initiation. Due to the warmer lower troposphere, the deep convection is invigorated, which is evident in convective cloud fraction. The GEOS‐5 atmospheric general circulation model (AGCM) employed in the reanalysis is overall successful in assimilating the additional DYNAMO observations, except for an erroneous model response for medium rain rates, between 700 and 600 hPa, reminiscent of a bias in earlier versions of the AGCM. The moist heating profile shows a sharp decrease there due to the excessive convective rain re‐evaporation, which is partly offset by the temperature increment produced by the analysis.
Downward solar global irradiance at the surface in São Paulo city—The climatological effects of aerosol and clouds
Authors: Yamasoe M. A. , do Rosário N. M. E. , Barros K. M. 
Published: December 2016

AbstractWe analyzed the variability of downward solar irradiance reaching the surface at São Paulo city, Brazil, and estimated the climatological aerosol and cloud radiative effects. Eleven years of irradiance were analyzed, from 2005 to 2015. To distinguish the aerosol from the cloud effect, the radiative transfer code LibRadtran was used to calculate downward solar irradiance. Two runs were performed, one considering only ozone and water vapor daily variability, with AOD set to zero and the second allowing the three variables to change, according to mean climatological values. The difference of the 24 h mean irradiance calculated with and without aerosol resulted in the shortwave aerosol direct radiative effect, while the difference between the measured and calculated, including the aerosol, represented the cloud effect. Results showed that, climatologically, clouds can be 4 times more effective than aerosols. The cloud shortwave radiative effect presented a maximum reduction of about −170 W m−2 in January and a minimum in July, of −37 W m−2. The aerosol direct radiative effect was maximum in spring, when the transport of smoke from the Amazon and central parts of South America is frequent toward São Paulo. Around mid‐September, the 24 h radiative effect due to aerosol only was estimated to be −50 W m−2. Throughout the rest of the year, the mean aerosol effect was around −20 W m−2 and was attributed to local urban sources. The effect of the cloud fraction on the cloud modification factor, defined as the ratio of all‐sky irradiation to cloudless sky irradiation, showed dependence on the cloud height. Low clouds presented the highest impact while the presence of high clouds only almost did not affect solar transmittance, even in overcast conditions.
Water isotope diffusion in the WAIS Divide ice core during the Holocene and last glacial
Authors: Jones T. R. , Cuffey K. M. , White J. W. C. , Steig E. J. , Buizert C. , Markle B. R. , McConnell J. R. , Sigl M. 
Published: December 2016

AbstractWe use a high‐resolution water isotope record from the West Antarctic Ice Sheet Divide ice core (WDC) to evaluate the effects of water isotope diffusion for the last 29 ka B.P. Using spectral analysis of the data, we determine diffusion lengths in depth and time domains. The diffusion length quantifies the mean cumulative diffusive displacement of water molecules relative to their original location at time of deposition. We simulate the observed signal with models and find that our understanding of processes and conditions in the ice sheet is incomplete. With the effects of ice‐deformational thinning removed, portions of the Holocene record show total diffusion lengths smaller than predicted for a lower limit case of diffusion through a single ice crystal. Such reduced diffusion is probably due to structural features such as crusts and tortuous porosity that inhibit vapor transport in the firn. In the late glacial portion of the record, diffusion lengths double between ~19.5 and 17 ka B.P. Known dependencies of diffusion on climatic variables do not account for this enhancement in models, and we hypothesize that it could arise from thermal gradients in the firn column, impurity‐driven enhancement of solid ice diffusion, or changes in firn grain properties that alter vapor access to open pores. Despite model uncertainties, the WDC diffusion length chronology will be an essential input to future studies of high‐frequency variability in the water isotope climate record, as it allows for the effects of diffusion to be removed.
Repeated surveys reveal nontectonic exposure of supposedly active normal faults in the central Apennines, Italy
Authors: Kastelic Vanja , Burrato Pierfrancesco , Carafa Michele M. C. , Basili Roberto 
Published: December 2016

AbstractWe investigate the geomorphic processes that expose bedrock fault surfaces from under their slope‐deposit cover in the central Apennines (Italy). These bedrock fault surfaces are generally located at various heights on mountain fronts above the local base level of glacio‐fluvial valleys and intermountain fluvio‐lacustrine basins and are laterally confined to the extent of related mountain fronts. The process that led to the exposure of fault surfaces has often been exclusively attributed to coseismic earthquake slip and used as proxy for tectonic slip rates and earthquake recurrence estimations. We present the results of monitoring the contact between the exposed fault surfaces and slope deposits at 23 measurement points on 12 different faults over 3.4 year long observation period. We detected either downward or upward movements of the slope deposit with respect to the fault surface between consecutive measurements. During the entire observation period all points, except one, registered a net downward movement in the 2.9–25.6 mm/yr range, resulting in the progressive exposure of the fault surface. During the monitoring period no major earthquakes occurred in the region, demonstrating that the measured exposure process is disconnected from seismic activity. Our results indicate that the fault surface exposure rates are rather due to gravitational and landsliding movements aided by weathering and slope degradation processes. The so far neglected slope degradation and other (sub)surface processes should thus be carefully taken into consideration before attempting to recover fault slip rates using surface gathered data.
Quantitative reconstruction of Holocene sea ice and sea surface temperature off West Greenland from the first regional diatom data set
Authors: Krawczyk D. W. , Witkowski A. , Moros M. , Lloyd J. M. , Høyer J. L. , Miettinen A. , Kuijpers A. 
Published: December 2016

AbstractHolocene oceanographic conditions in Disko Bay, West Greenland, were reconstructed from high‐resolution diatom records derived from two marine sediment cores. A modern data set composed of 35 dated surface sediment samples collected along the West Greenland coast accompanied by remote sensing data was used to develop a diatom transfer function to reconstruct April sea ice concentration (SIC) supported by July sea surface temperature (SST) in the area. Our quantitative reconstruction shows that oceanographic changes recorded throughout the last ~11,000 years reflect seasonal interplay between spring (April SIC) and summer (July SST) conditions. Our records show clear correlation with climate patterns identified from ice core data from GISP2 and Agassiz‐Renland for the early to middle Holocene. The early Holocene deglaciation of western Greenland Ice Sheet was characterized in Disko Bay by initial strong centennial‐scale fluctuations in April SIC with amplitude of over 40%, followed by high April SIC and July SST. These conditions correspond to a general warming of the climate in the Northern Hemisphere. A decrease in April SIC and July SST was recorded during the Holocene Thermal Optimum reflecting more stable spring‐summer conditions in Disko Bay. During the late Holocene, high April SIC characterized the Medieval Climate Anomaly, while high July SST prevailed during the Little Ice Age, supporting previously identified antiphase relationship between surface waters in West Greenland and climate in NW Europe. This antiphase pattern might reflect seasonal variations in regional oceanographic conditions and large‐scale fluctuations within the North Atlantic Oscillation and Atlantic Meridional Overturning Circulation.
Decadal variations in groundwater quality: A legacy from nitrate leaching and denitrification by pyrite in a sandy aquifer
Authors: Jessen Søren , Postma Dieke , Thorling Lærke , Müller Sascha , Leskelä Jari , Engesgaard Peter 
Published: December 2016

AbstractTwenty‐five years of groundwater quality monitoring in a sandy aquifer beneath agricultural fields showed large temporal and spatial variations in major ion groundwater chemistry, which were linked closely to the nitrate (NO3) content of agricultural recharge. Between 1988 and 2013, the NO3 content of water in the oxidized zone of the aquifer nearly halved, following implementation of action plans to reduce N leaching from agriculture. However, due to denitrification by pyrite oxidation in the aquifer, a plume of sulfate‐rich water migrates through the aquifer as a legacy of the historical NO3 loading. Agriculture thus is an important determinant of major ion groundwater chemistry. Temporal and spatial variations in the groundwater quality were simulated using a 2D reactive transport model, which combined effects of the historical NO3 leaching and denitrification, with dispersive mixing into the pristine groundwater residing deeper in the aquifer. Reactant‐to‐product ratios across reaction fronts are altered by dispersive mixing and transience in reactant input functions. Modelling therefore allowed a direct comparison of observed and simulated ratios of concentrations of NO3 (reactant) in the oxidized zone to those of SO4 (product) in the reduced zone, which aided a stoichiometric assessment of the mechanisms of denitrification. Denitrification by pyrite in the Rabis Creek aquifer results in oxidation of S−1 and Fe2+ in pyrite to S6+ in dissolved SO4 and Fe3+ in Fe‐oxide. Neither precipitation of elemental sulfur (S0), nor of jarosite, was supported by observations, and adsorption of sulfate was also dismissed.
Multiple outflows, spatial components, and nonlinearities in age theory
Authors: Calabrese Salvatore , Porporato Amilcare 
Published: December 2016

AbstractWater age has become an important variable for the characterization of hydrologic systems. The goal of this paper is to analyze the role of multiple outflows, spatial components, and nonlinearities in age theory. We first extend the theory to linear systems with multiple outflows, including the relationship between age distribution at death and survival time distribution at birth. We further show that for each outflow there is a survival time distribution at birth, which normalized corresponds to the impulse‐response function for the specific outflow. We also analyze how the impulse‐response function affects both the amplitude gain and time delay of the outflow and the long‐term average partitioning. With regard to linear spatially extended systems, we link the impulse‐response function to the Green's function. This allows us to easily compute the loss function and the age distribution for the system. Finally, we focus on nonlinear systems to analyze the effects of storage‐dependent and age distribution‐dependent loss functions. By considering the Burgers' equation, we show how the relationships between spatial dynamics and the age distribution are complicated by nonlinearities.
An analytical test case for snow models
Authors: Clark Martyn P. , Nijssen Bart , Luce Charles H. 
Published: December 2016

AbstractThis paper develops general analytical solutions for examples of water movement through snow and compares the derived analytical solutions to numerical simulations from a coupled energy and mass balance model. The intended use of the test cases is to evaluate the impact of different numerical approximations, especially different vertical discretization strategies and different time stepping schemes. The analytical solutions provide both outflow from the snowpack, as well as vertical profiles of temperature and volumetric liquid water content at different times throughout the analysis period. The derived analytical solutions have close correspondence with model simulations in most cases. The most pronounced differences between the numerical simulations and the analytical solutions are for the fresh snow test case, where the numerical simulations predict earlier arrival of snowpack outflow. The analytical solutions provide a useful test case for physically motivated snow models because the solutions can be used to evaluate the coupling of hydrology and thermodynamics as well as the unsaturated flow of water through porous media.
Measuring household consumption and waste in unmetered, intermittent piped water systems
Authors: Kumpel Emily , Woelfle‐Erskine Cleo , Ray Isha , Nelson Kara L. 
Published: December 2016

AbstractMeasurements of household water consumption are extremely difficult in intermittent water supply (IWS) regimes in low‐ and middle‐income countries, where water is delivered for short durations, taps are shared, metering is limited, and household storage infrastructure varies widely. Nonetheless, consumption estimates are necessary for utilities to improve water delivery. We estimated household water use in Hubli‐Dharwad, India, with a mixed‐methods approach combining (limited) metered data, storage container inventories, and structured observations. We developed a typology of household water access according to infrastructure conditions based on the presence of an overhead storage tank and a shared tap. For households with overhead tanks, container measurements and metered data produced statistically similar consumption volumes; for households without overhead tanks, stored volumes underestimated consumption because of significant water use directly from the tap during delivery periods. Households that shared taps consumed much less water than those that did not. We used our water use calculations to estimate waste at the household level and in the distribution system. Very few households used 135 L/person/d, the Government of India design standard for urban systems. Most wasted little water even when unmetered, however, unaccounted‐for water in the neighborhood distribution systems was around 50%. Thus, conservation efforts should target loss reduction in the network rather than at households.
Unsaturated hydraulic properties of Sphagnum moss and peat reveal trimodal pore‐size distributions
Authors: Weber Tobias K. D. , Iden Sascha C. , Durner Wolfgang 
Published: December 2016

AbstractIn ombrotrophic peatlands, the moisture content of the vadose zone (acrotelm) controls oxygen diffusion rates, redox state, and the turnover of organic matter. Whether peatlands act as sinks or sources of atmospheric carbon thus relies on variably saturated flow processes. The Richards equation is the standard model for water flow in soils, but it is not clear whether it can be applied to simulate water flow in live Sphagnum moss. Transient laboratory evaporation experiments were conducted to observe evaporative water fluxes in the acrotelm, containing living Sphagnum moss, and a deeper layer containing decomposed moss peat. The experimental data were evaluated by inverse modeling using the Richards equation as process model for variably‐saturated flow. It was tested whether water fluxes and time series of measured pressure heads during evaporation could be simulated. The results showed that the measurements could be matched very well providing the hydraulic properties are represented by a suitable model. For this, a trimodal parametrization of the underlying pore‐size distribution was necessary which reflects three distinct pore systems of the Sphagnum constituted by inter‐, intra‐, and inner‐plant water. While the traditional van Genuchten‐Mualem model led to great discrepancies, the physically more comprehensive Peters‐Durner‐Iden model which accounts for capillary and noncapillary flow, led to a more consistent description of the observations. We conclude that the Richards equation is a valid process description for variably saturated moisture fluxes over a wide pressure range in peatlands supporting the conceptualization of the live moss as part of the vadose zone.