bluuebunny/crossref_metadata_2025_split huggingface dataset:
Using an Arbitrary Moment Predictor to Investigate the Optimal Choice of Prognostic Moments in Bulk Cloud Microphysics Schemes
Authors: Igel Adele L. 
Published: December 2019

AbstractMost bulk cloud microphysics schemes predict up to three standard properties of hydrometeor size distributions, namely, the mass mixing ratio, number concentration, and reflectivity factor in order of increasing scheme complexity. However, it is unclear whether this combination of properties is optimal for obtaining the best simulation of clouds and precipitation in models. In this study, a bin microphysics scheme has been modified to act like a bulk microphysics scheme. The new scheme can predict an arbitrary combination of two or three moments of the hydrometeor size distributions. As a first test of the arbitrary moment predictor (AMP), box model simulations of condensation, evaporation, and collision‐coalescence are conducted for a variety of initial cloud droplet distributions and for a variety of configurations of AMP. The performance of AMP is assessed relative to the bin scheme from which it was built. The results show that no double‐ or triple‐moment configuration of AMP can simultaneously minimize the error of all cloud droplet distribution moments. In general, predicting low‐order moments helps to minimize errors in the cloud droplet number concentration, but predicting high‐order moments tends to minimize errors in the cloud mass mixing ratio. The results have implications for which moments should be predicted by bulk microphysics schemes for the cloud droplet category.
Quantifying Dissolved Organic Carbon Dynamics Using a Three‐Dimensional Terrestrial Ecosystem Model at High Spatial‐Temporal Resolutions
Authors: Liao Chang , Zhuang Qianlai , Leung L. Ruby , Guo Laodong 
Published: December 2019

AbstractArctic terrestrial ecosystems are very sensitive to the global climate change due to the large storage of soil organic carbon and the presence of snow, glacier, and permafrost, which respond directly to near surface air temperature that has warmed in the Arctic by almost twice as much as the global average. These ecosystems play a significant role in affecting regional and global carbon cycling, which have been traditionally quantified using biogeochemical models that have not explicitly considered the loss of carbon due to lateral flow of water from land to aquatic ecosystems. Building upon an extant spatially distributed hydrological model and a process‐based biogeochemical model, we have developed a three‐dimensional terrestrial ecosystem model to elucidate how lateral water flow has impacted the regional dissolved organic carbon (DOC) dynamics in the Tanana Flats Basin in central Alaska. The model explicitly simulates the production, consumption, and transport of DOC. Both in situ observational data and remote sensing‐based products were used to calibrate and validate the model. Our simulations show that (1) plant litter DOC leaching exerts significant controls on soil DOC concentration during precipitation and snowmelt events, (2) lateral transport plays an important role in affecting regional DOC dynamics, and (3) DOC export to the Tanana River is approximately 9.6 × 106 kg C year−1. This study provides a modeling framework to adequately quantify the Arctic land ecosystem carbon budget by considering the lateral transport of carbon affected by permafrost degradation. The quantification of the lateral carbon fluxes will also improve future carbon cycle modeling for Arctic aquatic ecosystems.
A Processes‐Based Dynamic Root Growth Model Integrated Into the Ecosystem Model
Authors: Lu Haibo , Yuan Wenping , Chen Xiuzhi 
Published: December 2019

AbstractPlant roots play a critical role in regulating the uptake of soil water and nutrients. Shifts in root growth and biomass distribution resulting from climate change can impact ecosystem water and carbon cycling. Such interactions between root growth and ecosystem functioning have not been integrated into current terrestrial ecosystem models. Here a three‐dimensional dynamic root model (DyRoot) was developed and implemented into the Integrated Biosphere Simulator (IBIS) ecosystem model for simulating root growth, architecture (i.e., fine and coarse roots), and distribution driven by soil water and nitrogen availabilities. Field root biomass observations were used for model calibration and validation. Results showed that DyRoot was able to simulate the root biomass distribution across five forest ecosystem types with good performance (R2 = 0.79, P < 0.01). The validations of root distribution in three forest chronosequences suggested that DyRoot captured the changes in rooting depth with the increase in stand age. The sensitivity of simulated root distribution to soil water availability was compared against root biomass observations from two precipitation reduction experiments. Results indicated that DyRoot reasonably represented the decrease of root biomass in topsoil layers in response to the deficits of soil moisture simulated by (IBIS). The DyRoot model algorithm in this study has great implications for representing an optimized root distribution in ecosystem models, which can improve model performance by simulating the feedbacks of root evolution in response to climate change. Furthermore, allowing explicit root architecture in the DyRoot model also sheds light on depicting the responses of root traits to environmental changes.
Error Analysis for an Algorithm That Reduces Radiative Transfer Calculations in High‐Resolution Atmospheric Models
Authors: Barker Howard W. , Qu Zhipeng , Cole Jason N. C. 
Published: December 2019

AbstractThis study assesses characteristics of spatial and temporal errors for net (shortwave + longwave) surface irradiances and atmospheric heating rates predicted by the Partitioned‐Gauss‐Legendre Quadrature (PGLQ) algorithm, whose aim is to economize computation of radiative transfer (RT) in high‐resolution cloud system‐resolving models (CSRMs). Most results reported here are for PGLQ having made 200 times fewer calls to the RT models than the Independent Column Approximation, which applies the RT models to each column in CSRM domains. Due to the nature of GLQ, PGLQ yields almost unbiased domain averages. This is shown for data pertaining to two convective cloud systems produced by a CSRM. Relative to the Independent Column Approximation, PGLQ works with much reduced amounts of information, and so it has the potential to produce rare, but sizable, localized errors. Two methods are employed to assess the “randomness” of spatial and temporal series of PGLQ flux and heating rate errors; one of which is developed here. Regarding spatial transects of net surface irradiance errors ΔFNET, ~30–60% of them are considered by both assessment techniques, simultaneously, to be indistinguishable, at the 95% confidence level, from fully uncorrelated sequences. Correspondingly, for time series of ΔFNET (at 8‐s time step), ~15–20% of 128‐step series, and ~10–70% of 30‐step series are considered by both methods, simultaneously, to be random. For time series of errors for net radiative heating rates, ~40% of cloudless series get classed, by both tests simultaneously, as random, compared to ~20% of those that contain some cloud.
Superposed Epoch Analysis of the Energetic Electron Flux Variations During CIRs Measured by BD‐IES
Authors: Yin Zefan , Zou Hong , Ye Yuguang , Zong Qiugang , Wang Yongfu 
Published: December 2019

AbstractThe flux variations of energetic electrons is one of the most important topics to understand dynamic processes in the space environment and the forecast for high‐energy electron burst. BeiDa Image Electron Spectrometer (BD‐IES), an imaging energetic elecstron spectrometer onboard a Chinese navigation satellite at an inclined geosynchronous orbit, can provide 50–600 keV electron flux data, which is used to investigate electron flux variations at GEO orbit during Co‐rotating Interaction Region events (CIRs). The superposed epoch analysis is applied to study the electron flux variations in different energy channels of BD‐IES during CIRs and the results support previous works. It reveals that electron fluxes in different channels all have a dropout before or at CIR interface and then the recovery of electrons with low energy reaches maximum earlier than that of electrons with high energy, with longer time differences for larger energy gap, which is consistent of two major mechanisms for energizing particles: inward radial diffusion and local acceleration. In addition, we investigate the relationship between electron flux enhancement in each energy channel and magnetic locals time and the extent of enhancement for electron flux peak value compared with average value before interface. These results can contribute to our understanding of electron flux variations at GEO during CIRs, and thus lay foundations for forecast research on high‐energy electron enhancement during CIRs.
Threshold of Motion Conditions Under Stokes Flow Regime and Comparison With Turbulent Flow Data
Authors: Shih WuRong , Diplas Panayiotis 
Published: December 2019

AbstractThe present study numerically investigates the effects of bed geometrical properties on particle entrainment driven by Stokes flow. We use different substrate arrangements to alter two important factors: The angle of repose, φ, and degree of exposure, e, of the test particle. The effectiveness of shear flow in mobilizing surface particles will change with e and φ, or collectively, η = e/tanφ, yielding a wide range of critical Shields parameter, θc, values. The use of η is better suited for describing local bed geometry as both e and φ values will change simultaneously during substrate rearranging processes. Furthermore, the range of θc values obtained in this study stems from the limitation of this parameter to relate the applied force variation to local flow and bed conditions. We therefore propose an effective shear ratio, α, to establish such connections between the global and local flow shear intensities. These results provide a unique perspective to examine typical θc data obtained from both Stokes and turbulence regimes. For the case of a single‐particle entrainment under given grain protrusion, Stokes flow‐based θc values are found to be 2 to 3 times larger than the counterpart turbulence data. For the case of channel bed mobility, however, the Shields curve suggests an order of magnitude difference in θc between the two regimes. In part, we attribute this significant θc variation to turbulent flow fluctuations in the first case and varied bed mobility levels in the second, given their distinct theoretical and empirical nature, respectively.
Bias Correction of Airborne Thermal Infrared Observations Over Forests Using Melting Snow
Authors: Pestana Steven , Chickadel C. Chris , Harpold Adrian , Kostadinov Tihomir S. , Pai Henry , Tyler Scott , Webster Clare , Lundquist Jessica D. 
Published: December 2019

AbstractUncooled thermal infrared (TIR) imagers, commonly used on aircraft and small unmanned aircraft systems (UAS, “drones”), can provide high‐resolution surface temperature maps, but their accuracy is dependent on reliable calibration sources. A novel method for correcting surface temperature observations made by uncooled TIR imagers uses observations over melting snow, which provides a constant 0 °C reference temperature. This bias correction method is applied to remotely sensed surface temperature observations of forests and snow over two mountain study sites: Laret, Davos, Switzerland (27 March 2017) in the Alps, and Sagehen Creek, California, USA (21 April 2017) in the Sierra Nevada. Surface temperature retrieval errors that arise from temperature‐induced instrument bias, differences in image resolution, retrieval of mixed pixels, and variable view angles were evaluated for these forest snow scenes. Applying the melting snow‐based bias correction decreased the root‐mean‐square error by about 1 °C for retrieving snow, water, and forest canopy temperatures from airborne TIR observations. The influence of mixed pixels on surface temperature retrievals over forest snow scenes was found to depend on image resolution and the spatial distribution of forest stands. Airborne observations over the forests at Sagehen showed that near the edges of TIR images, at more than 20° from nadir, the snow surface within forest gaps smaller than 10 m was obscured by the surrounding trees. These off‐nadir views, with fewer mixed pixels, could allow more accurate airborne and satellite‐based observations of canopy surface temperatures.
Multiscale Feature‐feature Interactions Control Patterns of Hyporheic Exchange in a Simulated Headwater Mountain Stream
Authors: Herzog Skuyler P. , Ward Adam S. , Wondzell Steven M. 
Published: December 2019

AbstractRecent predictions of hyporheic exchange at the basin‐scale assume individual features control exchange independently of each other, which has been demonstrated in relatively uniform, low‐gradient rivers. However, this assumption may not hold in steep catchments where both the type and size of individual features may vary over short distances, leading to irregular patterns of feature dominance on hyporheic exchange flows. Also, steep longitudinal gradients support substantial downvalley flows in the subsurface, which may create feedbacks between adjacent features. In this study, we test the extent to which features interact with one another and whether they can be aggregated to make reach‐scale predictions in a headwater mountain stream. Using systematic manipulations of a 2‐D stream centerline model and spectral analyses, we test for the presence of both feature‐feature and multiscale interactions. Our results show that changing the height of individual step‐pool features can alter hyporheic flow fields in neighboring, and sometimes distant, features. Spectral analyses revealed two scales of streambed topography—a local scale of single features and an intermediate scale that spanned multiple local‐scale features. All features produced hyporheic exchange, but turnover of deeper hyporheic water only occurred at a few key locations where local‐ and intermediate‐scale features amplified each other. Further, shallow bedrock increases the ratio of local‐ and intermediate‐scale flowpaths to regional‐scale flowpaths. Conceptual models portraying hyporheic exchange as a series of nested flowpaths should include the interactions among streambed topographic features in mountain streams. These results have implications for upscaling, field experiments, and stream restoration in steep catchments.
Multiorder Hydrologic Position in the Conterminous United States: A Set of Metrics in Support of Groundwater Mapping at Regional and National Scales
Authors: Belitz Kenneth , Moore Richard B. , Arnold Terri L. , Sharpe Jennifer B. , Starn J. J. 
Published: December 2019

AbstractThe location of a point on the landscape within a stream network (hydrologic position) can be an important predictive measure in hydrology. Hydrologic position is defined here by two metrics: lateral position and distance from stream to divide, both measured horizontally. Lateral position (dimensionless) is the relative position of a point between the stream and its watershed divide. Distance from stream to divide (units of length) is an indicator of position within a watershed: generally small near a confluence and generally large in headwater areas. Watersheds and watershed divides are defined here by Thiessen polygons rather than topographic divides. Lateral position and distance from stream to divide are also defined in the context of hydrologic order. Hydrologic order “n” is defined as the network of streams, and associated divides, of ordernand higher. And given that a point can have different positions in different hydrologic orders the term multiorder hydrologic position (MOHP) is used to describe the ensemble of hydrologic positions. MOHP was mapped across the conterminous United States for nine hydrologic orders at a spatial resolution of 30 m (about 8.7 billion pixels). There are 18 metrics for each pixel. Four case studies are presented that use MOHP metrics as explanatory factors in random forest machine learning models. The case studies show that lower order MOHP metrics can serve as indicators of hydrologic process while higher‐order metrics serve as indicators of location. MOHP is shown to have utility as a predictor variable across a large range of scales (50,000 to 8,000,000 km2).
Subtidal Flow Reversal Associated With Sediment Accretion in a Delta Channel
Authors: Zhang Wei , Feng Haochuan , Zhu Yuliang , Zheng Jinhai , Hoitink A. J. F. 
Published: December 2019

AbstractIn branching delta channel networks, tides intrude into parallel river outlets causing complex tidal behavior. The tidal motion can impact the division of river discharge over distributary channels. Under some circumstances, the discharge averaged over a tidal cycle may even reverse, drawing ocean water into the delta, such as observed in the Yangtze Delta, the Fly Delta and the Colorado Delta. Here, we study the flow reversal associated with sediment accumulation of a distributary channel in terms of tidal propagation and subtidal discharge dynamics, by focusing on the Yangtze Delta. The Yangtze Delta channel configuration represents a deep and wide main channel and a smaller side channel that has rapidly accreted over the past decades. A new mechanism is presented, which results in seawater transport across the shallow side channel, posing a risk to freshwater availability. The shallowest section in the side channel nearly acts as a tidal divide. In this section, the tide has the character of a standing wave, which implies that Stokes transport converges from opposite sides of the channel. This leads to significant variation of the total water storage in the side channel and subtidal water levels in the side channel being elevated above that in the main channel. The bulge of water that is stored during spring tide leaves the side channel toward neap tide, explaining reversal of the tide‐averaged discharge and seawater intrusion when the river discharge is low.
Multicomponent Ionic Transport Modeling in Physically and Electrostatically Heterogeneous Porous Media With PhreeqcRM Coupling for Geochemical Reactions
Authors: Muniruzzaman Muhammad , Rolle Massimo 
Published: December 2019

AbstractLow‐permeability aquitards, such as clay layers and inclusions, are of utmost importance for contaminant transport in groundwater systems. Although most dissolved species, contaminants, and clay surfaces are charged, the role of electrostatic interactions in subsurface flow‐through systems has not been extensively investigated. This study presents a two‐dimensional multicomponent reactive transport investigation of diffusive/dispersive and electrostatic processes in homogeneous and heterogeneous clay systems. The proposed approach is based on multiple continua and is capable to accurately describe charge interactions during ionic transport in the free water, diffuse layer, and interlayer water of charged porous media. The diffuse layer composition is simulated by considering a mean electrostatic potential following Donnan approach, whereas the interlayer composition is calculated by adopting the Gaines‐Thomas convention. Diffusive/dispersive fluxes within each subcontinuum (free water, diffuse layer, and interlayer) are calculated solving the Nernst‐Planck equation while maintaining a net zero‐charge flux. Furthermore, the multidimensional flow and transport model is coupled with the geochemical code PHREEQC, by utilizing the PhreeqcRM module, thus enabling great flexibility to access all PHREEQC's reaction capabilities. The code is benchmarked in 1‐D systems against other software and previously published experimental data. Successively, reactive transport simulations are performed in 2‐D clayey‐sandy flow‐through domains with spatially variable physical and electrostatic properties at both laboratory and field scales. The results reveal that different properties of surface charge, diffuse layer, and Coulombic interactions impact the transport of charged species and lead to distinct spatial distribution of the ions in the different subcontinua and to significantly different breakthrough curves.
Stable and Radioisotope Systematics Reveal Fossil Water as Fundamental Characteristic of Arid Orogenic‐Scale Groundwater Systems
Authors: Moran Brendan J. , Boutt David F. , Munk Lee Ann 
Published: December 2019

AbstractIn arid and semiarid regions, persistent hydrological imbalances illuminate the considerable gaps in our spatiotemporal understanding of fundamental catchment‐scale governing mechanisms. The Salar de Atacama basin is the most extreme example of groundwater‐dominated continental basins and therefore is an ideal place to probe these unresolved questions. Geochemical and hydrophysical observations indicate that groundwaters discharging into the basin reflect a large regional system integrated over 102–104 year timescales. The groundwater here, as in other arid regions, is a critical freshwater resource subject to substantial demand from competing interests, particularly as development of its world‐class lithium brine deposit expands. Utilizing a uniquely large and comprehensive set of H and O isotopes in water, we demonstrate that much of the presumed recharge area on the Altiplano‐Puna plateau exhibits isotopic signatures quite distinct from waters presently discharging within the endorheic Salar de Atacama watershed. δ18O values of predicted inflow source waters are 3.6‰ to 5.6‰ higher than modern plateau waters, and 3H data from 87 discrete samples indicate that nearly all of this inflow is composed of premodern recharge (i.e., fossil water). Under plausible conditions, these distinctions cannot be explained solely by natural variability in modern meteoric inputs or by steady state groundwater flow. We present a conceptual model revealing the extensive influence of transient draining of fossil groundwater storage augmented by regional interbasin flow from the Andes. Our analysis provides robust constraints on fundamental mechanisms governing this arid continental groundwater system and a framework within which to address persistent uncertainties in similar systems worldwide.
Autophagy-activating strategies to promote innate defense against mycobacteria
Authors: Kim Yi Sak , Silwal Prashanta , Kim Soo Yeon , Yoshimori Tamotsu , Jo Eun-Kyeong 
Published: December 2019

AbstractMycobacterium tuberculosis(Mtb) is a major causal pathogen of human tuberculosis (TB), which is a serious health burden worldwide. The demand for the development of an innovative therapeutic strategy to treat TB is high due to drug-resistant forms of TB. Autophagy is a cell-autonomous host defense mechanism by which intracytoplasmic cargos can be delivered and then destroyed in lysosomes. Previous studies have reported that autophagy-activating agents and small molecules may be beneficial in restricting intracellular Mtb infection, even with multidrug-resistant Mtb strains. Recent studies have revealed the essential roles of host nuclear receptors (NRs) in the activation of the host defense through antibacterial autophagy against Mtb infection. In particular, we discuss the function of estrogen-related receptor (ERR) α and peroxisome proliferator-activated receptor (PPAR) α in autophagy regulation to improve host defenses against Mtb infection. Despite promising findings relating to the antitubercular effects of various agents, our understanding of the molecular mechanism by which autophagy-activating agents suppress intracellular Mtb in vitro and in vivo is lacking. An improved understanding of the antibacterial autophagic mechanisms in the innate host defense will eventually lead to the development of new therapeutic strategies for human TB.