bluuebunny/crossref_metadata_2025_split huggingface dataset:
Planetary Period Modulation of Reconnection Bursts in Saturn's Magnetotail
Authors: Bradley T. J. , Cowley S. W. H. , Bunce E. J. , Smith A. W. , Jackman C. M. , Provan G. 
Published: November 2018

AbstractWe conduct a statistical analysis of 2,094 reconnection events in Saturn's near‐equatorial magnetotail previously identified in Cassini magnetometer data from intervals during 2006 and 2009/2010. These consist of tailward propagating plasmoids and planetward propagating dipolarizations, with approximately twice as many plasmoids as dipolarizations. We organize these by three related planetary period oscillation (PPO) phase systems, the northern and southern PPO phases relative to noon, the same phases retarded by a radial propagation delay, and the local retarded phases that take account of the azimuth (local time) of the observation. Clear PPO modulation is found for both plasmoid and dipolarization events, with local retarded phases best organizing the event data with the modulation in event frequency propagating across the tail as the PPO systems rotate. This indicates that the events are localized in azimuth, rather than simultaneously affecting much of the tail width. Overall, events occur preferentially by factors of ~3 at northern and southern phases where the tail current sheet is expected locally to be thinnest in the PPO cycle, with field lines contracting back from their maximum radial displacement, compared with the antiphase conditions. Separating the events into those representing the start of independent reconnection episodes, occurring at least 3 hr after the last, and events in subsequent clusters, shows that the above phases are predominantly characteristic of the majority cluster events. The phases at the start of independent reconnection episodes are typically ~60° earlier.
Double Plasma Resonance at Ion Cyclotron Harmonics in the Jovian Magnetosphere
Authors: Shaposhnikov V. E. , Zaitsev V. V. , Litvinenko G. V. 
Published: November 2018

AbstractThe ion cyclotron waves instability near the frequencies of ionic cyclotron harmonics is studied under conditions typical for the Jovian kilometer radio emission source. This instability is caused by the presence of the ions with a nonequilibrium loss cone‐type distribution function in the source. Expressions for the growth rate of the ion cyclotron wave's instability are obtained, and it is shown that the amplification of these waves significantly increases when the frequency of the lower‐hybrid resonance coincides with one of the ion cyclotron harmonics. Possible mechanisms for conversion of the ion cyclotron waves excited in the Jovian kilometer radio emission source into electromagnetic radiation are discussed. It is shown that the conversion of ion cyclotron waves, due to their coalescence with high‐frequency plasma waves, is possible only into ordinary electromagnetic waves, while the process capable of providing conversion of ion cyclotron waves into fast extraordinary electromagnetic waves is scattering by suprathermal electron fluxes. In the latter, despite the thermal spread of electron velocities, the radiation that leaves the source region is concentrated in a narrow frequency range Δω ≪ ω near the local gyrofrequency ω≃ωBe, and the polarization of this radiation corresponds to the extraordinary wave. The estimates of the electron energy, which is necessary for such conversion, have shown the possibility of the process realizing under conditions characteristic for the Jovian kilometer radio emission source.
Improved Interpretation of Deep Seismic Reflection Data in Areas of Complex Geology Through Integration With Passive Seismic Data Sets
Authors: Dentith Michael , Yuan Huaiyu , Murdie Ruth Elaine , Pina‐Varas Perla , Johnson Simon P. , Gessner Klaus , Korhonen Fawna J. 
Published: November 2018

AbstractThe Capricorn Orogen records the Paleoproterozoic amalgamation of the West Australian Craton. 2‐D deep‐seismic reflection data across the Orogen are difficult to interpret due to the complex geology, and fundamental questions remain about the nature of the basement in the northern part of the Orogen. Passive seismic data have been collected along a 250‐km‐long transect across the central part of the Capricorn Orogen. The passive seismic recordings utilized teleseismic arrivals to construct a velocity section using the receiver function common conversion point method and to estimate crustal thickness and Vp/Vs using the H‐k method. A shear velocity cross section was created using ambient noise‐based methods. An integrated interpretation of all the seismic data sets shows that basement in the central Capricorn Orogen comprises a series of distinct terranes. These are recognized based on changes in crustal reflectivity, velocity and Vp/Vs. We interpret these terranes as originating from an island arc caught in the collision between the Glenburgh Terrane and the Pilbara Craton as part of the 2215–2145 Ma Ophthalmia Orogeny. Although passive seismic data do not have the resolution of reflection data, the information gained from the passive data places important constraints on the reflection interpretation and provides complementary information about changes in crustal composition. We propose that passive seismic data represent a cost‐effective complementary geophysical data set that can greatly assist with the interpretation of deep reflection sections in areas of complex geology.
Roles of Wind‐Driven Currents and Surface Waves in Sediment Resuspension and Transport During a Tropical Storm
Authors: Xie Xiaohui , Li Ming , Ni Wenfei 
Published: November 2018

AbstractSatellite remote sensing shows two hot spots of high suspended sediment concentration during the passage of Hurricane Irene (2011) over Chesapeake Bay: the shallow shoals in the mid Bay and the area around the mouth of the estuary. A coupled ocean wave sediment transport model is used to investigate mechanisms driving sediment resuspension and transport during the storm. The model reproduces the observed spatial variations of suspended sediment concentration and surface wave heights in the estuary and shows that both wave‐ and current‐induced shear stresses are important in stirring bottom sediment. In the mid‐Bay region, large wave‐induced shear stress causes sediment resuspension on the shallow shoals, while wind‐driven currents advect the suspended sediment downstream. Around the mouth of the estuary, the combined action of large waves and strong outflows produces high suspended sediment concentration, resulting in the export of ~0.8 Mt of estuarine sediments to the shelf. The storm‐induced sediment resuspension and export could be an important term in the sedimentary budget of an estuary.
The Aftermath of Petermann Glacier Calving Events (2008–2012): Ice Island Size Distributions and Meltwater Dispersal
Authors: Crawford Anna J. , Mueller Derek , Desjardins Luc , Myers Paul G. 
Published: November 2018

AbstractThree large calving events occurred at Petermann Glacier in northwest Greenland between 2008 and 2012 that generated ice islands (large tabular icebergs) that ranged from ~30 to 300 km2in areal extent. Ice islands are known to deteriorate, via fracture and melt, during their drift through regional water bodies where they pose a potential risk to offshore resource extraction operations and disperse freshwater from the Greenland Ice Sheet. This study presents the first analysis of the deterioration occurring across the flux of ice islands that travel between Nares Strait and the North Atlantic after Petermann Glacier calving events. The evolution of Petermann ice island size distributions was evaluated, and the spatial dispersal of meltwater was quantified, through analyses that utilized the newly developed Canadian Ice Island Drift, Deterioration and Detection Database. Size‐frequency distributions remained relatively consistent, both spatially and temporally, and were well fit by power law models with slopes of approximately −1.7. This suggested that fracture was an important process by which the Petermann ice islands deteriorated, regardless of elapsed time or distance from the glacier. Ice island meltwater fluxes into the Baffin Island and Labrador currents were not large enough to slow down the Atlantic Meridional Overturning Circulation by weakening deep‐water convection in the Labrador Sea. However, augmented meltwater input was calculated within Petermann Fjord (2.0 mSv) and in the vicinity of grounding locations (0.4 mSv). Further research is necessary to better understand how this freshwater alters fjord circulation and influences the composition of local ocean waters.
Ecogeomorphic Feedbacks that Grow Deltas
Authors: Ma Hongxu , Larsen Laurel G. , Wagner R. Wayne 
Published: November 2018

AbstractCoastal river deltas are complex and dynamic ecosystems where vegetation plays an essential role in influencing, as well as being influenced by, physical processes, creating ecogeomorphic feedbacks between vegetation canopy characteristics and topography. However, this feedback is poorly understood. This knowledge gap is due to difficulties in detecting and quantifying the interactions that define the feedback. Emerging technology and data analysis techniques like transfer entropy have made it possible to overcome former difficulties associated with sampling constraints and delineate bidirectional feedback within many vegetation classes at the delta scale. Here the transfer entropy analysis was consistent with widespread understanding of marsh zonation, yet produced additional insight into which vegetation classes specifically had a dominant impact on topographic change. Ecogeomorphic feedback was resolvable only within native vegetation classes (Nelumbo and Polygonum) that occur over low to moderate elevations within the Wax Lake Delta Louisiana. In contrast, nonnative vegetation classes (Colocasia and Eichhornia) were not as effective at accreting sediment as native classes. The transfer entropy analysis suggests that different vegetation communities play functionally different roles in landscape evolution that should be differentiated in ecogeomorphic models. Within such models, it would be most imperative to resolve detailed flow characteristics at lower to low‐middle island elevations. Furthermore, within elevation zones, it is likely important to differentiate between the roles of multiple vegetation communities rather than treating the entire elevation zone as a single ecogeomorphic entity.
Productivity Evolution in the South Brazilian Bight During the Last 40,000 Years
Authors: Pereira Lígia S. , Arz Helge W. , Pätzold Jürgen , Portilho‐Ramos Rodrigo C. 
Published: November 2018

AbstractMarine productivity largely controls the oceanic uptake of atmospheric carbon dioxide and contributed to the global climate changes that led to the termination of the last glacial cycle. Past changes in marine productivity were presumably associated with disturbances in the Atlantic meridional overturning circulation (AMOC). In the South Atlantic, however, the evolution of marine productivity throughout the last glacial–interglacial cycle is still poorly constrained mainly due to the scarcity of records with high temporal resolution. Here we present high‐resolution records of paleoproductivity and upper‐water‐column properties from the western subtropical South Atlantic covering the last 40,000 years. Our records are based on faunal and stable oxygen isotopic analyses of planktonic foraminifera from a marine sediment core collected from an upwelling region off southeastern South America (27°S). We used the relative abundance of eutrophic planktonic foraminifera (i.e., Globigerinita glutinata and Globigerina bulloides) as proxies of primary productivity. Our findings reveal, for the first time, enhanced primary productivity during Heinrich Stadials along the last glacial, when the AMOC showed reduced strength. Additionally, our results reveal decreased primary productivity over the Last Glacial Maximum, a period of markedly lower sea level; and the Younger Dryas, when the AMOC showed only moderate reductions. The most outstanding productivity decline, however, is depicted at the onset of the Holocene, when the AMOC recovers its strength. We hypothesize that the observed changes were triggered by the dynamics of the Brazil Current primarily driven by disturbances in the AMOC.
Simulating Flood‐Induced Riverbed Transience Using Unmanned Aerial Vehicles, Physically Based Hydrological Modeling, and the Ensemble Kalman Filter
Authors: Tang Qi , Schilling Oliver S. , Kurtz Wolfgang , Brunner Philip , Vereecken Harry , Hendricks Franssen Harrie‐Jan 
Published: November 2018

AbstractFlood events can change the riverbed topography as well as the riverbed texture and structure, which in turn can influence the riverbed hydraulic conductivity (Krb) and river‐aquifer exchange fluxes. A major flood event occurred in the Emme River in Switzerland in 2014, with major implications for the riverbed structure. The event was simulated with the fully integrated hydrological model HydroGeoSphere. The aim was to investigate the effect of the spatial and temporal variability of riverbed topography and Krb on predictions of hydraulic states and fluxes and to test whether data assimilation (DA) based on the ensemble Kalman filter (EnKF) can better reproduce flood‐induced changes to hydraulic states and parameters with the help of riverbed topography changes recorded with an unmanned aerial vehicle (UAV) and through‐water photogrammetry. The performance of DA was assessed by evaluating the reproduction of the hydraulic states for the year 2015. While the prediction of surface water discharge was not affected much by the changes in riverbed topography and in Krb, using the UAV‐derived postflood instead of the preflood riverbed topography reduced the root‐mean‐square error of predicted heads (RMSE [h]) by 24%. If, in addition to using the postflood riverbed topography, also Krb and aquifer hydraulic conductivity (Kaq) were updated through DA after the flood, the RMSE (h) was reduced by 55%. We demonstrate how updating of Krb and Kaq based on EnKF and UAV‐based observations of riverbed topography transience after a major flood event strongly improve predictions of postflood hydraulic states.
Application of the Generalized Clapeyron Equation to Freezing Point Depression and Unfrozen Water Content
Authors: Zhou Jiazuo , Wei Changfu , Lai Yuanming , Wei Houzhen , Tian Huihui 
Published: November 2018

AbstractFreezing point and unfrozen water content are key parameters in modeling the heat and mass transfer under the cyclic change of atmosphere temperature. It is theoretically revealed the relation between the measured pore pressure and true pore pressure with physicochemical interactions. A new generalized Clapeyron equation is derived, which addresses the relationship among the measured pore water, ice‐liquid capillary pressure, and pore solution concentration for the frozen soil. The generalized Clapeyron equation is applied to derive the expressions for the freezing point and unfrozen water content in frozen soils at various thermodynamical conditions. The freezing point of soil is calculated and compared with the experimental results, showing that the freezing point depression becomes more pronounced as water content decreases and solution concentration increases. It is also shown that the NaCl solution with relatively high concentration in soil pore approximates the ideal dilute solution while Na2CO3 and some other solutions in soil are significantly different than the ideal dilute solution. Upon assuming the unfrozen water content is only determined by the capillary pressure, the Clapeyron equation links the soil water characteristic curve into the soil freezing characteristic curve. The unfrozen water content in the saline frozen soil and the frozen soil under overburden pressure is also calculated according to the expression derived from the generalized Clapeyron equation.
Time Compression Approximation Relationship for Infiltration in the Presence of a Shallow Water Table: Evaluating the Role of Péclet Number
Authors: Yao Lili , Wang Dingbao , Hooshyar Milad , Singh Arvind , Sivapalan Murugesu 
Published: November 2018

AbstractThe time compression (or time condensation) approximation (TCA) is commonly used in conjunction with an infiltration capacity equation for predicting the postponding infiltration rate, or, more generally, infiltration under time‐varying precipitation. In this paper a power function relationship for TCA between infiltration capacity and its time derivative is proposed for infiltration in the presence of a shallow water table. The results show that the exponent (β) in the power function relationship is not a constant but decreases as infiltration proceeds. The change of β indicates that the TCA relationship changes during infiltration and further suggests the necessity of using different TCA relationships for predicting infiltration rate during different stages after ponding. We argue that the change of β is due to the gradual dynamic change of the relative role of gravity and capillarity during infiltration. A Péclet number (Pe) is proposed for measuring the relative effect of gravity and capillarity. In the early times of infiltration when Pe < 1, with the increase of Pe, β decreases roughly from 3.5 to 2 for clay, silty clay loam, and silty loam, and from 3 to 2 for sandy loam and sand; during the longer times when Pe > 1, β has a linear relationship with Pe. The relationship between Pe and β provides an objective approach to select the suitable TCA function during different infiltration stages after ponding.
Models of Single‐Well Push‐Pull Test With Mixing Effect in the Wellbore
Authors: Wang Quanrong , Shi Wenguang , Zhan Hongbin , Gu Haochen , Chen Kewei 
Published: November 2018

AbstractThe mechanism of solute transport around the wellbore was found to play an important role in the single‐well push‐pull (SWPP) test, but it was grossly overlooked in previous studies. For instance, the mixing effect of injected tracer with water in the wellbore was ignored in analyzing both injection and extraction phases of SWPP. In this study, new models were developed by including such a mixing effect in the wellbore. Two types of boundary conditions at the wellbore were considered: the resident concentration continuity and the flux concentration continuity. To test the assumptions used in the mathematical model, the stochastic modeling, the numerical simulation, and the laboratory‐controlled experiment were executed. Results showed that the SWPP test was sensitive to the mixing effect in both injection and extraction phases. A larger wellbore volume could result in a smaller concentration at the late stage of the extraction phase. Flux concentration continuity was more reasonable in describing solute transport at the wellbore‐aquifer interface than resident concentration continuity, and the difference between them decreased with decreasing radial dispersivity. The MODFLOW/MT3DMS package contained an invalid assumption on the mixing effect for the SWPP test. Stochastic modeling demonstrated that the homogeneous assumption was a good approximation for the reality when the variance of natural logarithm of the autocorrelated hydraulic conductivity field was less than 0.25 (
). The laboratory‐controlled experiment showed that the radial advection‐dispersion equation model of this study worked well for the well‐sorted sand aquifer.
Synergies for Soil Moisture Retrieval Across Scales From Airborne Polarimetric SAR, Cosmic Ray Neutron Roving, and an In Situ Sensor Network
Authors: Fersch B. , Jagdhuber T. , Schrön M. , Völksch I. , Jäger M. 
Published: November 2018

AbstractThe consistent determination of soil moisture across scales is a persistent challenge in hydrology. Several measurement methods exist at distinct scales, each of which is challenging in terms of data processing, removal of vegetation and surface effects, and calibration. While in situ measurements are trusted at the point scale, distributed sensor networks extend the areal representation to the field scale. At this scale, also cosmic ray neutron sensing (CRNS) has become an established method to derive volume‐averaged, root zone soil moisture over several tens of hectometers, but the signal is often biased due to biomass water. With airborne synthetic aperture radar (SAR) remote sensing, it is possible to cover regional scales, but the method is limited to the topmost soil layer and sensitive to vegetation parameters. In this study, the performance and synergistic potential of these complementary methods is investigated for the determination of soil moisture within a 55 km2 Alpine foothill river catchment in Southern Germany. The individual approaches are evaluated and brought into synergy for a 9 ha grassland and several other locations within the catchment. The results indicate that the sensor network data provide valuable information to calibrate the mobile CRNS rover, and to optimize the vegetation removal within the polarimetric SAR retrieval algorithm. The root‐mean‐square errors for polarimetric SAR soil permittivity are 9.32 with the standard agriculture approach, 4.29 with the semi‐stand‐alone approach, and 0.31 with the sensor network optimized approach. Furthermore, the CRNS soil moisture product was improved by considering the remotely sensed cross‐polarized backscatter product as a biomass water proxy.
A High‐Resolution Global Map of Soil Hydraulic Properties Produced by a Hierarchical Parameterization of a Physically Based Water Retention Model
Authors: Zhang Yonggen , Schaap Marcel G. , Zha Yuanyuan 
Published: November 2018

AbstractA correct quantification of mass and energy exchange processes among Earth's land surface, groundwater, and atmosphere requires an accurate parameterization of soil hydraulic properties. Pedotransfer functions (PTFs) are useful in this regard because they estimate these otherwise difficult to obtain characteristics using texture and other ubiquitous soil data. Most PTFs estimate parameters of empirical hydraulic functions with modest accuracy. In a continued pursuit of improving global‐scale PTF estimates, we evaluated whether improvements can be obtained when estimating parameters of hydraulic functions that make physically based assumptions. To this end, we developed a PTF that estimates the parameters of the Kosugi retention and hydraulic conductivity functions (Kosugi, 1994, https://doi.org/10.1029/93WR02931, 1996, https://doi.org/10.1029/96WR01776), which explicitly assume a lognormal pore size distribution and apply the Young‐Laplace equation to derive a corresponding pressure head distribution. Using a previously developed combination of machine learning and bootstrapping, the developed five hierarchical PTFs allow for estimates under practical data‐poor to data‐rich conditions. Using an independent global data set containing nearly 50,000 samples (118,000 retention points), we demonstrated that the new Kosugi‐based PTFs outperformed two van Genuchten‐based PTFs calibrated on the same data. The new PTFs were applied to a 1 × 1 km2 global map of texture and bulk density, thus producing maps of the parameters, field capacity, wilting point, plant available water, and associated uncertainties. Soil hydraulic parameters exhibit a much larger variability in the Northern Hemisphere than in the Southern Hemisphere, which is likely due to the geographical distribution of climate zones that affect weathering and sedimentation processes.