bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial and Intergeneric Variation in Physiological Indicators of Corals in the South China Sea: Insights Into Their Current State and Their Adaptability to Environmental Stress
Authors: Qin Zhenjun , Yu Kefu , Wang Yinghui , Xu Lijia , Huang Xueyong , Chen Biao , Li Yang , Wang Wenhuan , Pan Ziliang 
Published: May 2019

AbstractIt is well known that coral thermal bleaching is mainly caused by abnormally high temperatures, but the spatial/intergeneric variation in coral‐algal symbiosis and its linkage to coral bleaching susceptibility is not well understood. In this study, 654 coral samples were collected from six coral reef regions (CRRs) in the South China Sea (SCS), between the Nansha Islands (~10°N) and Daya Bay (22°50′N). They were analyzed to explore how geographical/environmental variation affects coral bleaching susceptibility. The results showed significant spatial and intergeneric variation in zooxanthellae density, Chlacontent, and tissue biomass. Massive corals generally showed higher values than branching corals for all three parameters across CRRs. Spatial analysis showed that these parameters were lowest in the Nansha Islands and highest in Daya Bay, indicating increases with latitude. Several factors may have accounted for this trend, with the most important being sea surface temperature and nutrients. Additionally, we observed a relationship between physiological parameters and bleaching susceptibility, which was that branching corals had greater bleaching susceptibility than massive corals. Coral community composition and live coral cover data showing increasing dominance of massive corals in the SCS support the above inference. Relatively high‐latitude areas have been proposed as potential refuges for corals under continued global warming and the physiological parameters in the present study seem to support this. However, in spite of the aforementioned results, the smallest live coral cover was found in the northern CRRs. This suggests that this refuge function is currently compromised, mainly due to increasing destructive anthropogenic actions.
Radiative Convective Equilibrium and Organized Convection: An Observational Perspective
Authors: Jakob C. , Singh M. S. , Jungandreas L. 
Published: May 2019

AbstractRadiative convective equilibrium (RCE) describes a balance between the cooling of the atmosphere by radiation and the heating through latent heat release and surface heat fluxes. While RCE is known to provide an energetic constraint on the atmosphere at the global scale, little is known about the proximity of the atmosphere to RCE at smaller spatial and temporal scales, despite the common use of RCE in idealized modeling studies. Here we provide the first observational evaluation of the scales at which the atmosphere is near RCE. We further use observations of cloud characteristics to investigate the role played by organized convection in the RCE state. While the tropical atmosphere as a whole is near RCE on daily time scales and longer, this is not the case for any given location. Rather, areas in excess of 5,000 × 5,000 km2 must be considered to ensure the atmosphere remains near RCE at least 80% of the time, even for monthly averaged conditions. We confirm that RCE is established through the interplay of regions of active deep convection with high precipitation and weak radiative cooling and regions of subsiding motions leading to shallow cloud states that allow strong radiative cooling with no precipitation. The asymmetry in the maximum amount of radiative cooling and latent heating leads to the well‐known ratio of small areas of precipitation and large regions of subsidence observed in the tropics. Finally, we show that organized deep convection does not occur when regions smaller than 1,000 × 1,000 km2 are near RCE.
Morphological Response of an Alpine Braided Reach to Sediment‐Laden Flow Events
Authors: Bakker Maarten , Antoniazza Gilles , Odermatt Eliott , Lane Stuart N. 
Published: May 2019

AbstractBraided gravel‐bed rivers show characteristic temporal and spatial variability in morphological change and bedload transport under steady flow and sediment supply rates. Their morphodynamic behavior and long‐term evolution in response to nonstationary external forcing is less well known. We studied daily morphological changes in a well‐constrained reach of an Alpine braided river that is subject to regulated sediment‐laden flows, associated with hydroelectric power exploitation, as well as occasional floods. We found that net reach erosion and deposition were forced by upstream sediment supply, albeit in a nonlinear fashion. The spatial distribution of morphological change and inferred spatially‐distributed sediment transport rates varied strongly along the braided reach and between successive sequences of flushing. Local morphological change was driven by two factors: (1) local relief, leading to the preferential filling of topographic lows and erosion of highs, particularly during longer duration floods, which allow braided dynamics to be maintained; and (2) system memory, leading to a negative autocorrelation in bed level changes where erosion was followed by deposition of similar magnitude and vice versa. This effect was associated with the temporary storage of high sediment loads from flushing due to the abrupt on‐off nature of these flows and reveals the relatively efficient transport of sediment in a river that is heavily impacted upon by flow abstraction. In general, the internal morphodynamics of the braided river condition their own response to external forcing events and thus sediment transfer.
Reconstructing Coastal Sediment Budgets From Beach‐ and Foredune‐Ridge Morphology: A Coupled Field and Modeling Approach
Authors: Ciarletta Daniel J. , Shawler Justin L. , Tenebruso Christopher , Hein Christopher J. , Lorenzo‐Trueba Jorge 
Published: May 2019

AbstractPreserved beach and foredune ridges may serve as proxies for coastal change, reflecting alterations in sea level, wave energy, or past sediment fluxes. In particular, time‐varying shoreface sediment budgets have been inferred from the relative size of foredune ridges through application of radiocarbon and optically stimulated luminescence dating to these systems over the last decades. However, geochronological control requires extensive field investigation and analysis. Purely field‐based studies might also overlook relationships between the mechanics of sediment delivery to the shoreface and foredune ridges, missing insights about sensitivity to changes in sediment budget. We therefore propose a simple geomorphic model of beach/foredune‐ridge and swale morphology to quantify the magnitude of changes in cross‐shore sediment budget, employing field measurements of ridge volume, ridge spacing, elevation, and shoreline progradation. Model behaviors are constrained by the partitioning of sediment fluxes to the shoreface and foredune ridge and can be used to reproduce several cross‐shore patterns observed in nature. These include regularly spaced ridges (“washboards”), large singular ridges, and wide swales with poorly developed ridges. We evaluate our model against well‐preserved ridge and swale systems at two sites along the Virginia Eastern Shore (USA): Fishing Point, for which historical records provide a detailed history of shoreline progradation and ridge growth, and Parramore Island, for which a relatively more complex morphology developed over a poorly constrained period of prehistoric growth. Our results suggest this new model could be used to infer the sensitivity of field sites across the globe to variations in sediment delivery.
A Statistical Study of Anomalous VHF Propagation Due to the Sporadic‐E Layer in the Air‐Navigation Band
Authors: Sakai J. , Hosokawa K. , Tomizawa I. , Saito S. 
Published: May 2019

AbstractThe sporadic‐E (Es) layer is an ionospheric layer which appears occasionally near 100‐km heights with extremely high electron density. The Es layer may reflect very high‐frequency radio signals when the incident angle is shallow (Es layer anomalous propagation [EsAP]). It is known that radio signals with frequencies above 100 MHz sometimes reach distant locations, more than 600 km apart from the transmitters, due to EsAP. Since air‐navigation radio channels are allocated on frequencies between 108 and 118 MHz, EsAP may interfere with directly propagating wave (ground wave) signals. However, as the occurrence and strength of EsAP on these frequencies have not been studied well, it is difficult to assess the impact of EsAP on the air navigation. In this paper, we report the statistics of the occurrence and strength of EsAP based on a 3‐year continuous monitoring of very high‐frequency air‐navigation radio signal strength on the ground. The statistics show that strong EsAPs occur frequently in summer. The occurrence pattern of EsAP is generally consistent with ionosonde observations of Es layer: Most Es layers appear during summer, primary peak in daytime, with a second peak in the evening. During an extreme EsAP event, in a particular channel, an EsAP signal was superposed on a ground wave signal which resulted in a fluctuation of ground wave signal by more than ±10 dB. Our statistical results suggest that the Es layer has a potential impact on air‐navigation applications.
Stokes‐Brinkman Flow Simulation Based on 3‐D μ‐CT Images of Porous Rock Using Grayscale Pore Voxel Permeability
Authors: Kang Dong Hun , Yang Eomzi , Yun Tae Sup 
Published: May 2019

AbstractThe direct flow simulation using high‐resolution micro‐computed tomographic (μ‐CT) images of porous rock can be used to help understand the flow characteristics at the pore‐scale and to estimate fluid properties; however, segmentation of pore space in grayscale 3‐D μ‐CT images, a necessary step in this process, is challenging because of issues related to the image resolution and pore‐filling matrix in the gray‐level images. We present a novel process for determining the voxel porosity and permeability of the gray‐level regime and evaluating the bulk permeability using the Brinkman force lattice Boltzmann method. In this study, μ‐CT images of Berea sandstone are acquired with two spatial resolutions. After the pore size distribution curve is experimentally obtained, the “apparent pore” voxels and “gray pore” voxels are determined based on the designated gray‐level values in the gray‐level (CT number) histogram, the cumulative and fractional pore volumes, and the linear relationship between CT number and individual voxel porosity. The results show that the boundary between apparent and gray pores in terms of size determines the volumetric fraction and specific surface area. Additionally, the permeability computed by considering the gray pore regime based on the proposed method is more similar to the experimentally measured value than the results of other segmentation methods because the gray pore domain is fully incorporated into the flow domain while preserving the pore connectivity. The proposed sequence of pore segmentation presents a method for handling gray‐level pore space without compromising pore connectivity.
Effect of Hydrogeologic and Climatic Variability on Performance of a Groundwater Market
Authors: Khan Hassaan Furqan , Brown Casey M. 
Published: May 2019

AbstractIncentive‐based policies, such as the cap‐and‐trade system, have been shown to be useful in the context of groundwater management. This study compares the performance of a groundwater market with water quotas when assumptions of perfect information are violated due to climate change and hydrogeologic heterogeneity and explores how changes in future climate affect market performance. A subbasin of the Republican River Basin, overlying the Ogallala aquifer in the High Plains of the United States, is used as a case study. Building on a previously developed model, a multiagent system model simulating a groundwater market is developed where self‐interested agents can trade water use permits to maximize individual benefits subject to irrigation and land constraints. This economic model is coupled with a calibrated physically based groundwater model for the study region that allows for an evaluation of streamflow depletion impacts, which has been the focus of management efforts in the basin. Results show that trading of permits between farmers results in increased economic benefits and, in some cases, reduced environmental violations. However, the benefits of a groundwater market are distributed unequally resulting in “winners” and “losers” across the system. Future changes in climate are shown to significantly influence farmers willingness to pay for groundwater and thus increase the variation in groundwater price and pumping. These findings emphasize the importance of addressing hydroclimatologic variability and change in the design of groundwater markets.
Modeling Influence of Sediment Heterogeneity on Nutrient Cycling in Streambeds
Authors: Pescimoro Eugenio , Boano Fulvio , Sawyer Audrey H. , Soltanian Mohamad Reza 
Published: May 2019

AbstractRivers and their hyporheic zones play an important role in nutrient cycling. The fate of dissolved inorganic nitrogen is governed by reactions that occur in the water column and streambed sediments. Sediments are heterogeneous both in term of physical (e.g., hydraulic conductivity) and chemical (e.g., organic carbon content) properties, which influence water residence times and biogeochemical reactions. Yet few modeling studies have explored the effects of both physical and chemical heterogeneity on nutrient transport in the hyporheic zone. In this study, we simulated hyporheic exchange in physically and chemically heterogeneous sediments with binary distributions of sand and silt in a low‐gradient meandering river. We analyzed the impact of different silt/sand patterns on dissolved organic carbon, oxygen, nitrate, and ammonium. Our results show that streambeds with a higher volume proportion of silt exhibit lower hyporheic exchange rates but more efficient nitrate removal along flow paths compared to predominantly sandy streambeds. The implication is that hyporheic zones with a mixture of inorganic sands and organic silts have a high capacity to remove nitrate, despite their moderate permeabilities.
Evaporation Suppression From Water Bodies Using Floating Covers: Laboratory Studies of Cover Type, Wind, and Radiation Effects
Authors: Lehmann Peter , Aminzadeh Milad , Or Dani 
Published: May 2019

AbstractWater reservoirs have been used to mitigate seasonal water shortages since the dawn of civilization. Present day use of water reservoirs continues to expand to meet the increasing demand for irrigation water and to mitigate effects of climate change and droughts. Losses to evaporation are an important challenge to water storage efficiency in arid regions. We study the use and efficiency of self‐assembling floating covers as a simple and scalable solution to evaporation suppression. We report laboratory‐scale studies of evaporation suppression using different cover types under various external conditions that jointly affect surface flux partitioning. Experiments using floating spheres and disks of different colors, sizes, and materials were conducted for a range of external conditions (radiation, wind, and wind + radiation) over a 1.44 m2 water basin placed in a wind tunnel. Considering maximum cover density using spherical and disk‐shaped elements (91% surface cover), the evaporation was suppressed by 80% (for disks) and 70% (for spheres) relative to uncovered water surfaces in agreement with physically based model estimates. Surprisingly, evaporation suppression using black and white floating covers was similar despite significantly different surface energy partitioning pathways. The observed similarity was attributed to thermal decoupling between the top of cover elements and water surfaces. The study shows a high and nearly constant evaporation suppression efficiency of floating covers for a range of external conditions supporting the potential of such simple and scalable solution of evaporation suppression for regions with limited infrastructure or alternative water solutions.
Quantifying Process Connectivity With Transfer Entropy in Hydrologic Models
Authors: Bennett Andrew , Nijssen Bart , Ou Gengxin , Clark Martyn , Nearing Grey 
Published: May 2019

AbstractQuantifying the behavior and performance of hydrologic models is an important aspect of understanding the underlying hydrologic systems. We argue that classical error measures do not offer a complete picture for building this understanding. This study demonstrates how the information theoretic measure known as transfer entropy can be used to quantify the active transfer of information between hydrologic processes at various timescales and facilitate further understanding of the behavior of these systems. To build a better understanding of the differences in dynamics, we compare model instances of the Structure for Unifying Multiple Modeling Alternatives (SUMMA), the Variable Infiltration Capacity (VIC) model, and the Precipitation Runoff Modeling System (PRMS) across a variety of hydrologic regimes in the Columbia River Basin in the Pacific Northwest of North America. Our results show differences in the runoff of the SUMMA instance compared to the other two models in several of our study locations. In the Snake River region, SUMMA runoff was primarily snowmelt driven, while VIC and PRMS runoff was primarily influenced by precipitation and evapotranspiration. In the Olympic mountains, evapotranspiration interacted with the other water balance variables much differently in PRMS than in VIC and SUMMA. In the Willamette River, all three models had similar process networks at the daily time scale but showed differences in information transfer at the monthly timescale. Additionally, we find that all three models have similar connectivity between evapotranspiration and soil moisture. Analyzing information transfers to runoff at daily and monthly time steps shows how processes can operate on different timescales. By comparing information transfer with correlations, we show how transfer entropy provides a complementary picture of model behavior.
Spatial Sequential Modeling and Predication of Global Land Use and Land Cover Changes by Integrating a Global Change Assessment Model and Cellular Automata
Authors: Cao Min , Zhu Yanhui , Quan Jinling , Zhou Sheng , Lü Guonian , Chen Min , Huang Mengxue 
Published: May 2019

AbstractCharacterizing land use and land cover change (LUCC) is critical for understanding the interaction between human activities and global environmental changes, such as in biological diversity and the carbon cycle. Both natural cycles and human activities can be better examined with more accurate sources of land use data with higher spatial resolution. More importantly, it is crucial to consider spatial heterogeneity to simulate future changes in LUCC. In this paper, a modeling strategy (hereinafter referred to as GCAM‐CA) that combines a global change assessment model (GCAM) with cellular automata (CA) is proposed. This modeling strategy is designed to sequentially spatialize global LUCCs with 1‐km spatial resolution and 5‐year temporal resolution from 2010 to 2100. The GCAM model is employed to predict the land use and land cover area demands for 283 world regions, which are divided by intersecting 32 geopolitical and socioeconomic regions and 18 agroecological zones. The spatialization rules of CA is trained separately for each world region to distinguish global land use and land cover types. The different spatialization rules and trends in land use and land cover demand for each of the 283 regions reflect the spatial heterogeneity in the GCAM‐CA model. We implement and validate the model for the simulation from 2000 to 2010. Next, the model is used to simulate three future scenarios, REF, G26, and G45, demonstrating that the GCAM‐CA model is effective for future global‐scale simulation of LUCCs. GCAM‐CA is freely available at the open geographic modeling and simulation platform (OpenGMS, http://geomodeling.njnu.edu.cn/GCAM‐CA.jsp).
Toward a Resilient Global Society: Air, Sea Level, Earthquakes, and Weather
Authors: Anenberg Susan C. , Dutton Andrea , Goulet Christine A. , Swain Daniel L. , van der Pluijm Ben 
Published: May 2019

AbstractSociety's progress along the four corners of prepare, absorb, respond and adapt resilience square is uneven, in spite of our understanding of the foundational science and a growing sense that urgent action is needed. The resilience vignettes describe the meaning and impact of current and near‐term change in four major domains: human health impacts from air pollution, coastal inundation from sea‐level rise, damaging earthquakes in populated areas, and impacts from extreme precipitation. Given our understanding of the scientific principles, societal action, from preparation to adaption, will be critical in minimizing the negative impacts of change. The unprecedented rates of change in today's Earth system argue for urgent action in support of a resilient global society.
Ural Blocking as a Driver of Early‐Winter Stratospheric Warmings
Authors: Peings Y. 
Published: May 2019

AbstractThis study explores the early‐winter atmospheric response to Ural blocking anomalies in November, using a nudging technique to constrain the temperature and dynamics in a high‐top atmospheric model. Persistent Ural blocking anomalies in November are associated with a warm Arctic/cold Siberia pattern and increased upward planetary waves entering the stratosphere, leading to a warming of the polar vortex. This stratospheric response then propagates in the troposphere, leading to increased occurrence of the negative North Atlantic Oscillation in December and January. In contrast, simulations with perturbed Barents‐Kara sea ice and Siberian snow in November do not reproduce a significant atmospheric response. In simulations including a slab ocean, the Ural blocking induces Barents‐Kara sea ice and Siberia snow anomalies that resemble composite analyses from observations. These results highlight Ural blocking variability in November as a robust driver of early‐winter stratospheric warming while questioning causality between sea ice/snow and Ural blocking anomalies.
Lake Water Depth Controlling Archaeal Tetraether Distributions in Midlatitude Asia: Implications for Paleo Lake‐Level Reconstruction
Authors: Wang H. , He Y. , Liu W. , Zhou A. , Kolpakova M. , Krivonogov S. , Liu Z. 
Published: May 2019

AbstractLake‐level reconstructions, related to terrestrial hydrological changes, are important for our understanding of past and future climates. Currently, however, reliable lake‐level proxies are still limited. Here we report distributions of archaeal tetraether lipids in 70 surface sediment samples collected from 55 lakes in midlatitude Asia. We have found that among various lake physico‐chemical characteristics, the relative abundances of crenarchaeol and Hydroxylated isoprenoid glycerol dialkyl glycerol tetraethers (%cren and %OH‐GDGTs) are best correlated with lake water depth, due to a preference of Thaumarchaeota, the producer of these biomarkers, for a niche in subsurface lake water. This supports the recent hypothesis based on single‐lake investigations that %cren and %OH‐GDGTs are potentially novel lake‐level proxies. Our results also suggest that %OH‐GDGTs is less affected by soil input than %cren. Nevertheless, other confounding factors should be well constrained and local/site‐specific calibrations are needed before the two molecular proxies are used quantitatively in down‐core applications.