bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination Of The Optimal Guide Curve For A Reservoir, Case Study Copa Dam, Boyacá
Authors: Sierra Felipe , Sanabria Jorge , Corzo Gerald , Santos Germán
Published: March 2020

Reservoir operation has been a task that always relate to integrated water resources concepts, the rules of such systems require to adapt to changes in the uses of water or in their prioritization. The storage body of La Copa reservoir, located in the upper Chicamocha river basin in Colombia was originally built with the objective of mitigating the floods over the upper Chicamocha valley. However, an irrigation district was latter established, with the objective of supplying water to farmers. This study presents the analysis and optimization of operational rules to minimize the likelihood of floods and shortages for the irrigation district. This is done by contemplating the uncertainty in the hydrological system.

A methodology is developed to obtain the optimal management and operation of the reservoir, aiming at reducing droughts and flood, which will end up in a regulated basins. A simulation model of the reservoir using the HEC-ResSim tool was used to aim at an optimal guide curve. The guide curve in this study is the base for operational decisions. A continuous simulation hydrological model using the HEC-HMS tool. The model was calibrated using annual series of daily flows as input into the reservoir model.  A two-dimensional hydrodynamic model using (HEC-RAS 2D) was used to test the results of regulation through the comparison of the simulations of the current and optimal regulation conditions.  Several guide curves were developed for the evaluation of the operation. Four of them among are selected and tested using the HEC-ResSim model through the quantification of the minimum and maximum volumes discharge failures. Finally, the guide curve with the least number of failures was selected as the one that provides the best system operation. The benefits of the selected guide curve were verified by the transit of the regulated hydrographs in the 2D hydraulic model. The simulation was carried out in the most period in terms of flows and maximum rainfall, from April 06 to May 15, 2011. The period between April 15 and 21 has the highest flow through the critical sector. On the other hand, unregulated conditions were evaluated using the flows of the hydrological model. It is found that the channel presents a notable improvement, in the simulation of April 15, through the discharges made in a controlled manner from the La Copa reservoir. The methodology presents a simple and practical way to obtain relative optimal operational rules for a multipurpose storage.
Space-based platform asteroid orbit determination and collision warning
Authors: yezhi Song
Published: March 2020

The risk of asteroids impacting the earth is a common space security issue facing human beings. Since the ground-based monitoring network cannot cover the space area comprehensively, there are cases of celestial body out of monitoring. In response to this problem, this report studies the space-based platform's monitoring system, and calculates its performance for orbit determination and monitoring of small celestial bodies. For small celestial bodies that are not in the catalog, the initial orbit determination needs to be performed before the orbit improvement. In addition, this paper proposes a method based on Fibonacci search method to quickly predict the impact location of asteroids.
Spontaneous Formation of Internal Shear Zone in Ice Flowing over a Topographically Variable Bed
Authors: Liu Emma Weijia , Räss Ludovic , Suckale Jenny , Herman Frédéric , Podladchikov Yury
Published: March 2020

The transition from slow flow to rapid sliding is a noticeable feature of both ice sheets and outlet glaciers. Most existing models attempting to understand the complex physical transition processes assume an idealized model geometry with a flat bed. These models have shown that the onset of sliding entails basal refreezing, which in turn suppresses sliding. The theoretical difficulties in understanding sliding commencement in these process-based models contrast with the apparent ubiquity of the transition in the field. Here, we hypothesize that the presence of basal topography could resolve the inconsistency between model predictions and field observations.

We test our hypothesis by investigating the flow-to-sliding transition in a process-based model of ice flowing over bedrock with significant roughness. We assume that the bed is rigid and that the boundary condition at the bed is no-slip. We incorporate variations in basal topography into an iterative nonlinear Stokes solver for thermo-mechanically coupled ice deformation using the Immersed Boundary Method. This approach permits us to address the basal ice to bedrock transition with high accuracy and to study the impact of the shape of this transition zone.

Our results suggest that shear heating in the vicinity of pronounced roughness extends well into the bulk of the ice, leading to a spatially variable viscosity. These spatial variations in topography can therefore significantly impact the overall viscosity distribution in the ice. High shear strain rates localize at the tops of the bedrock topography. Thermo-mechanical feedback lead to the spontaneous formation of internal shear band over time, by connecting the topographic heights. The internal shear zone accommodates the majority of shear deformation, inducing a sliding motion of the upper part of the domain. Our results provide a process-based explanation of recently measured ice deformation data at the West margin of Greenland Ice Sheet (Maier et al. 2019). It is also consistent with the proposed existence of a radio-echo free zone located in the lowest hundreds of meters above bedrock (Drews et al. 2009, Fujita et al. 1999).

 

Maier, Nathan, et al. "Sliding dominates slow-flowing margin regions, Greenland Ice Sheet." Science advances 5.7 (2019): eaaw5406.

Drews, Reinhard, et al. "Layer disturbances and the radio-echo free zone in ice sheets." The Cryosphere 3 (2009): 195-203.

Fujita, Shuji, et al. "Nature of radio echo layering in the Antarctic ice sheet detected by a two‐frequency experiment." Journal of Geophysical Research: Solid Earth 104.B6 (1999): 13013-13024.
Crystal fractionation by crystal-driven convection
Authors: Culha Cansu , Suckale Jenny , Keller Tobias , Qin Zhipeng
Published: March 2020

In the last two decades, improved fine scale analysis in crystalline profiles has improved our understanding of igneous processes, while opening our sight to more complexities. As an example, plagioclase crystal profiles in Holyoke flood-basalt flow revealed that the crystals got exposured to different melt environments as the layer underwent fractional crystallization. Fractional crystallization is an essential process for determining the compositional evolution of magmatic systems. The process requires a reactive segregation process, where crystals precipitate from the melt and segregate from their residual melt. In this study, we are motivated by the subtleties in the crystalline record to model the segregation component of fractional crystallization, or crystal fractionation.

 

We build a numerical model with individually resolved, denser-than-melt crystals in a convective flow. We test the low to intermediate crystallinity regime, where the physical processes leading to efficient fractionation are less clear than at high crystallinity. We simulate the physical segregation of crystals from their residual melt at the scale of individual crystals using a direct numerical method. By resolving each of the crystals, we do not require a priori parameterization of crystal-melt interactions. We use tracers in the melt to track the different melts around the crystals.

 

We find that collective sinking of crystal-rich clusters dominate settling at low particle Reynolds numbers. The relatively rapid motion of this cluster strips away the residual melt around the cluster. Compared to individual settling, the resulting crystal fractionation is efficient but heterogeneous at the crystalline scale. Similar to the Holyoke flood-basalt plagioclase profiles, the crystals in our analysis show exposure to different melt environments as they drive crystal fractionation. Our results suggest that cluster driven fractional crystallization will vary in efficiency. At the system scale, this result would suggest a bell curve compositional abundance distribution in volcanic systems.

 
Micro-pulse Lidar Measurements in South China Sea Expedition
Authors: Li Yuan
Published: March 2020

The South China Sea is the third largest inland sea in the world, with unique geographical and climatic conditions, and great economic importance. Observation of aerosols over this region is needed to understand their role in cloud, radiation, and ocean primary production. While the optical properties of marine aerosols over the South China Sea have been studied using solar photometers, there are no lidar studies for this region that the authors know of in publicly accessible scientific literature.

To test the viability of shipborne lidar for aerosol measurement over the South China Sea, a shipborne micro-pulse lidar (Mini-MPL) was used to measure aerosol extinction coefficient in the northern region of the South China Sea over a period of one month from 9th August to 7th September, 2016, along the cruise path of a research vessel. The measurements were inverted to obtain vertical profiles of aerosol extinction coefficient, depolarization ratio, and atmospheric boundary layer height using Mie Theory and the Fernald method. Aerosols were found to be concentrated low in the atmosphere, with more than 73% of total extinction below 2 km and almost no aerosol above 3.5 km. Maximum extinction values in coastal areas were generally about double of values in offshore areas. The aerosol concentration was lower in the northwest side of the South China Sea compared to the northeast side, a pattern that may due to advection by the prevailing summer southwesterly winds. Vertical profiles and back-trajectory calculations indicated vertical and horizontal layering of aerosols from different terrestrial sources. The mean depolarization ratio of the aerosols along the cruise was 0.042. Atmospheric boundary layer height along the cruise was average 653.2 m, with a diurnal cycle reaching its mean maximum of 1041.2 m at 12:00, and its mean minimum of 450.0 m at 20:00.
Hydration of the tropical tropopause layer (TTL) by convective updraft during tropical cyclone ENAWO(2017) and generalization to tropical storms in the southwestern Indian Ocean in summer 2016-2017.
Authors: Héron Damien , Evan Stephanie , Brioude Jerome , Pianezze Joris , Dauhut Thibault , Noel Vincent , Bielli Soline , Barthe Christelle , Cammas Jean-Pierre
Published: March 2020

Stratospheric water vapor variations play an important role on the climate. Predictions of changes in stratospheric humidity are uncertain because of gaps in our understanding of physical processes occurring in the TTL, between 14 and 20 km altitude. In particular, climate models have great difficulties in modelling water vapor variations in the TTL due to a poor representation of tropical convection, which largely controls the vertical transport of water vapor to UTLS, among other things.

One of the scientific objectives of the CONCIRTO5 program is to better understand the role of marine deep convective systems, and tropical cyclones in particular, on the hydration of TTL in the Southwestern Indian Ocean.  In March 2017, a rapid deepening of the tropical cyclone Enawo occured north-west of Reunion island before to strike and cross Madagascar from north to south. The progressive intensification of the cyclone to the intense tropical cyclone stage makes it an ideal case study to analyze the transport of water vapor and hydrometeors in the TTL according to the intensity phase of the cyclone. 

We will present modelling results on water vapor transport into the TTL in March 4 during ENAWO’s intensification. On March 4, the mesoscale model Meso-NH simulated a large water vapour transport through the TTL, associated with the injection of ice through the tropopause and the observation of cirrus clouds. The model validation is done by comparison with satellite data (CALIPSO, Meteosat-8). We generalize the intrusion modelling during ENAWO intensification by comparing the brightness temperature observed above the tropical cyclones and the tropical tropopause temperature extracted from ECMWF-Analysis during the 2016-2017 cyclonic season. From these studies, we can estimate the number of intrusions during a cyclonic season and the cyclonic intensity associated with the intrusions.

 

5Effects of convection and cirrus clouds on the Tropical Tropopause Layer over the Indian Ocean
A new model describing Forbush Decreases at Mars: combining the heliospheric modulation and the atmospheric influence
Authors: Guo Jingnan , Wimmer-Schweingruber Robert , Dumbovic Mateja , Heber Bernd , Wang Yuming
Published: March 2020

Forbush decreases are depressions in the galactic cosmic rays (GCRs) which are mostly caused by the modulations of interplanetary coronal mass ejections (ICMEs) and also sometimes by stream/corotating interaction regions (SIRs/CIRs). Forbush decreases have been studied extensively using neutron monitors at Earth and have been recently, for the first time, measured on the surface of another planet - Mars by the Radiation Assessment Detector (RAD), on board Mars Science Laboratory’s (MSL) rover Curiosity. The modulation of the GCR particles by heliospheric transients in space is energy-dependent and afterwards these particles are also interacting with the Martian atmosphere with the interaction process depending on the particle type and energy. In order to study the space weather environment near Mars using the ground-measured Forbush decreases, it is important to understand and quantify the energy-dependent modulation of the GCR particles by not only the pass-by heliospheric disturbances but also the Martian atmosphere. In this study, we develop a model which combines the heliospheric modulation of GCRs and the atmospheric modification of such modulated GCR spectra to quantify the amplitudes of the Forbush decreases at Mars: both on ground and in the interplanetary space near Mars during the pass-by of an ICME/SIR. The modeled results are in good agreement when compared to studies of Forbush decreases caused by ICMEs/SIRs measured by MSL on the surface of Mars and by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft in orbit.  This supports the validity of both the Forbush decrease description and the Martian atmospheric transport models.  Our model can be potentially used to understand the property of ICMEs and SIRs passing Mars.
Using rigid microplate motions to detect the stress buildup preceding large earthquakes: a feasibility test based on synthetic models
Authors: Iaffaldano Giampiero , Martin de Blas Juan
Published: March 2020

Assessing the temporal evolution of stresses along seismogenic faults is typically done by combining geodetic observations collected near the locations of previous large earthquakes with modeling of the interseismic, coseismic, and postseismic deformation. Here we explore whether it is feasible to link the charge phase of large earthquakes to rigid microplate motions, which can be inferred from geodetic observations that are instead collected further away from crustal faults. We use numerical simulations of the dynamics and associated kinematics of an idealized, rigid microplate subject to stress buildups and drop-offs from a series of earthquakes. Simulations span the charging cycle of a single 6.5 < MW < 8 earthquake. Several MW < 6.5 earthquakes distributed according to the Gutenberg-Richter law occur meanwhile. We use large ensembles of simulations featuring randomly-generated earthquake hypocenters and make statistical assessments of the fraction of model time needed for the microplate motions to depart from the initial one to a degree that is larger than typical geodetic uncertainties, and for at least 90% of the remaining time before the large earthquake occurs. We find such a fraction (i) to be only one tenth in simulations that do feature a large earthquake, (ii) to be longer in simulations that do not, and (iii) to remain small for realistic microplate geometries and asthenosphere viscosity/thickness values. Our inferences hold also when we simulate geodetic time series shorter than the large-earthquake cycle, and even when we assume that only half of the stress buildup affects the microplate rigid motion.
Exploring potential of remotely sensed data in parameterization of hydrologic model
Authors: Jadidoleslam Navid , Mantilla Ricardo , Krajewski Witold
Published: March 2020

Recent observation-based studies have shown that satellite-based antecedent soil moisture can provide useful information on runoff production. The patterns uncovered can be used to benchmark the degree of coupling between antecedent soil moisture, rainfall totals and runoff production, and to determine if hydrologic models can reproduce these patterns for a particular model parameterization of their rainfall-runoff processes. The goal of our study is twofold; First, it derives the relationships between runoff ratio and its major controls, including rainfall total, antecedent soil moisture, and vegetation using remotely sensed data products. Second, it aims to determine if the model is capable to reproduce these relationships and use them to validate model parameters and streamflow predictions. For this purpose, SMAP (Soil Moisture Active Passive) satellite-based soil moisture, S-band radar rainfall, MODIS (Moderate Resolution Imaging Spectroradiometer) vegetation index, and USGS (United States Geological Survey) daily streamflow observations are used. The study domain consists of thirty-eight basins less than 1000 km2 located in an agricultural region in the United States Midwest. For each basin, daily streamflow predictions, before and after adjustments to the hydrologic model are compared with observations. The comparisons are done for four years (2015-2018) using multiple performance metrics. This study could serve as a data-driven approach for parameterization of rainfall-runoff partitioning in hydrologic models using remotely sensed observations. 
Three-dimensional convection, phase change, and solute transport in mushy sea ice
Authors: Wells Andrew , Parkinson James , Martin Dan , Katz Richard
Published: March 2020

Sea ice is a porous mushy layer composed of ice crystals and interstitial brine. The dense brine tends to sink through the ice, driving convection. Downwelling at the edge of convective cells leads to dissolution of the ice matrix and the development of narrow, entirely liquid brine channels. The channels provide an efficient pathway for drainage of the cold, saline brine into the underlying ocean. This brine rejection provides an important buoyancy forcing for the polar oceans, and causes variation of the internal structure and properties of sea ice on seasonal and shorter timescales. This process is inherently multiscale, with simulations requiring resolution from O(mm) brine-channel scales to O(m) mushy-layer dynamic scales.

 

We present new, fully 3-dimensional numerical simulations of ice formation and convective brine rejection that model flow through a reactive porous ice matrix with evolving porosity. To accurately resolve the wide range of dynamical scales, our simulations exploit Adaptive Mesh Refinement using the Chombo framework. This allows us to integrate over several months of ice growth, providing insights into mushy-layer dynamics throughout the winter season. The convective desalination of sea ice promotes increased internal solidification, and we find that convective brine drainage is restricted to a narrow porous layer at the ice-ocean interface. This layer evolves as the ice grows thicker over time. Away from this interface, stagnant sea ice consists of a network of previously active brine channels that retain higher solute concentrations than the surrounding ice. We investigate the response of ice growth and brine drainage to varying atmospheric cooling conditions, and consider the potential implications for ice-ocean brine fluxes, nutrient transport, and sea ice ecology.
Solifluction patterns arising from competition between gravity and cohesion
Authors: Glade Rachel , Fratkin Mulu , Rowland Joel , Nutt Mara
Published: March 2020

Arctic soil movement, accumulation and stability exert a first order control on the fate of permafrost carbon in the shallow subsurface and landscape response to climate change. A major component of periglacial soil motion is solifluction, in which soil moves as a result of frost heave and flow-like “gelifluction”. Because soliflucting soil is a complex granular-fluid-ice mixture, its rheology and other material properties are largely unknown. However, solifluction commonly produces distinctive spatial patterns of terraces and lobes that have yet to be explained, but may help constrain solifluction processes. Here we take a closer look at these patterns in an effort to better understand material and climatic controls on solifluction. We find that the patterns are analogous to classic instabilities found at the interface between fluids and air—for example, paint dripping down a wall or icing flowing down a cake. Inspired by classic fluid mechanics theory, we hypothesize that solifluction patterns develop due to competition between gravitational and cohesive forces, where grain-scale soil cohesion and vegetation result in a bulk effective surface tension of the soil. We show that, to first order, calculations of lobe wavelengths based on these assumptions accurately predict solifluction wavelengths in the field. We also present high resolution DEM-derived data of solifluction wavelengths and morphology from dozens of highly patterned hillslopes in Norway to explore similarities and differences between solifluction lobes and their simpler fluid counterparts. This work leads us toward quantitative predictions of the presence or absence of solifluction patterns and their response to variation in material properties (e.g., vegetation, rock type, grain size) and climatic conditions (e.g., water content, active layer depth, variability in snow cover).
Rock glacier impact on high-alpine freshwater chemistry
Authors: Nickus Ulrike , Thies Hansjoerg , Krainer Karl , Tessadri Richard
Published: March 2020

Borehole soundings have revealed a warming of mountain permafrost of up to 1°C during recent decades. There is evidence that the increase in air temperature has favored the solute release from active rock glaciers, and pronounced changes in water quality of headwaters in the Alps have been described. Here, we report on solute concentrations of selected streams and springs in the vicinity of an active rock glacier in the Central European Alps (Lazaun, Italy). Stream water sampling started in 2007, and samples were analysed for major ions and heavy metals. We compare surface freshwaters of different origin and chemical characteristics, i.e. outflows of active and fossil rock glaciers, a spring emerging from a moraine and an ice glacier fed stream. Substance concentrations were highest in springs impacted by active rock glaciers, and dissolved ions increased up to a factor of 3 through the summer season. This pattern reflects a seasonally varying contribution to runoff by the melting winter snow pack, summer precipitation, baseflow and ice melt. Intense geochemical bedrock weathering of freshly exposed mineral surfaces, which are due to the downhill movement of the active rock glacier, is considered as a major reason for the high ion and metal concentrations in late summer runoff. In addition, solutes contained in the ice matrix of the rock glacier are released due to enhanced melting of rock glacier ice. On the contrary, minimum substance concentrations without any seasonal variability were found in the moraine spring.
Changes in biogeochemistry recorded in the Lisan formation and the Dead Sea Basin
Authors: Turchyn Alexandra , Bradbury Harold , Torfstein Adi
Published: March 2020

Terrestrial climate archives provide a rich array of information on regional climate dynamics that often can link to global climate change.  A range of new metal and coupled isotope proxies is helping to unlock the most information from terrestrial archives and this paleoclimate information. The Jordon-Arava valley, tectonically active since the early Neogene, is one of the world’s largest pull-apart basins.  Throughout the Pleistocene to the Holocene, the valley contained a series of lacustrine water bodies.  As the valley is located on the boundary between the African-Arabian deserts and the Mediterranean regional climatic zone, studies of past conditions in these lacustrine bodies allows the reconstruction of changes in the regional hydrological cycle.  Lacustrine sediments, such as those found in the Jordon-Arava valley, record paleoclimatic information similar to that found within marine sedimentary archives and often at much higher resolution, from millennial to even annual timescales. The Lisan Formation is a 40-80m thick Pleistocene marl, which was deposited in Lake Lisan, which existed over the last glacial cycle in the Jordan-Arava Valley. The Lisan Formation contains a significant quantity of annually-precipitated primary aragonite, which has not recrystallised to calcite, allowing for direct U-Th dating, which has led to an exceptional age model for the Lisan Formation.

Here we discuss the measurement of the sulfur and oxygen isotopic composition of gypsum in the Lisan formation, as well as the generation of sulfur nodules within the formation that are not found in the sediment cores of the Dead Sea. We use this data to explore how sediment diagenesis, relating to changes in biogeochemistry, changes as a function of climate change over the last glacial cycle. We then present the calcium isotopic composition of the gypsum and interbedded aragonite, and show how the aragonite calcium isotopic composition covaries with lake level, and thus offers profound insight into the regional hydrological cycle in the Jordon-Arava Valley.
Converging Seismic and Geodetic Data Services
Authors: Carter Jerry A , Meertens Charles , Trabant Chad , Riley James
Published: March 2020

One of the fundamental tenets of the Incorporated Research Institutions for Seismology’s (IRIS’s) mission is to “Promote exchange of seismic and other geophysical data … through pursuing policies of free and unrestricted data access.”  UNAVCO also adheres to a data policy that promotes free and unrestricted use of data.  A major outcome of these policies has been to reduce the time that researchers spend finding, obtaining, and reformatting data.  While rapid, easy access to large archives of data has been successfully achieved in seismology, geodesy and many other distinct disciplines, integrating different data types in a converged data center that promotes interdisciplinary research remains a challenge.  This challenge will be addressed in an integrated seismological and geodetic data services facility that is being mandated by the National Science Foundation (NSF).  NSF’s Seismological Facility for the Advancement of Geoscience (SAGE), which is managed by IRIS, will be integrated with NSF’s Geodetic Facility for the Advancement of Geoscience (GAGE), which is managed by UNAVCO.  The combined data services portion of the facility, for which a prototype will be developed over the next two to three years, will host a number of different data types including seismic, GNSS, magnetotelluric, SAR, infrasonic, hydroacoustic, and many others.  Although IRIS and UNAVCO have worked closely for many years on mutually beneficial projects and have shared their experience with each other, combining the seismic and geodetic data services presents challenges to the well-functioning SAGE and GAGE data facilities that have served their respective scientific communities for more than 30 years. This presentation describes some preliminary thoughts and guiding principles to ensure that we build upon the demonstrated success of both facilities and how an integrated GAGE and SAGE data services facility might address the challenges of fostering interdisciplinary research. 
Accurate Near-Earth-Object Astrometry using Synthetic Tracking and Applications
Authors: Zhai Chengxing , Shao Michael , Saini Navtej , Trahan Russell , Choi Philip , Nazli Kutay , Evans Nez , Owen William
Published: March 2020

Synthetic tracking technique uses multiple short exposure images to observe moving objects to prevent the objects from streaking in an individual frame. It integrates frames in post-processing, where the tracking of telescope at any desired rate can be simulated by shifting frames accordingly. Such an approach avoids trailing loss, thus improves detection sensitivity, especially for fast moving objects. It also yields accurate astrometry for moving objects independent of rate of motion with precision comparable to stellar astrometry. Using the Gaia DR2 catalog, we are able to demonstrate 10 mas level near-Earth-object (NEO) astrometry with the synthetic tracking technique. Accurate NEO astrometry allows us to determine NEO orbit more precisely. We discuss applications such as cataloging newly discovered NEOs with less measurements and/or from observation time windows covering shorter orbit arcs, better predicting the chance for a potentially hazardous asteroid to impact the Earth, measuring non-gravitational acceleration to infer physical properties of minor planets, and optical navigation for future spacecraft carrying optical communication lasers.
Long-term runoff forecast using BP neural network based on climatic factors and mutual information method in the Qujiang Catchment of China
Authors: Dai Huihui
Published: March 2020

The formation of runoff is extremely complicated, and it is not good enough to forecast the future runoff only by using the previous runoff or meteorological data. In order to improve the forecast precision of the medium and long-term runoff forecast model, a set of forecast factor group is selected from meteorological factors, such as rainfall, temperature, air pressure and the circulation factors released by the National Meteorological Center  using the method of mutual information and principal component analysis respectively. Results of the forecast in the Qujiang Catchment suggest the climatic factor-based BP neural network hydrological forecasting model has a better forecasting effect using the mutual information method than using the principal component analysis method.
Amazon forest responses to drought: scaling from individuals to ecosystems.
Authors: Saleska Scott R. , Restrepo-Coupe Natalia , Barros Fernanda V. , Bittencourt Paulo R. L. , Prohaska Neill , Penha Deliane V. , Albert Loren P. , Brum Mauro , Pereira Luciano , Leal Leila S. M. , Araujo Alessandro C. , Stark Scott C. , Alves Luciana , Tribuzy Edgard , Camargo Plinio B. , Cosme de Oliveira Raimundo , Ivanov Valeriy , Mauro Jose , Aragao Luiz , Oliveira Rafael S.
Published: March 2020

Scaling from individuals or species to ecosystems is a fundamental challenge of modern ecology and understanding tropical forest response to drought is a key challenge of predicting responses to global climate change.  We here synthesize our developing understanding of these twin challenges by examining individual and ecosystem responses to the 2015 El Niño drought at two sites in the central Amazon of Brazil, near Manaus and Santarem, which span a precipitation gradient from moderate (Manaus) to long (Santarem) dry seasons.  We will focus on how ecosystem water and carbon cycling, measured by eddy flux towers, emerges from individual trait-based responses, including photosynthetic responses of individual leaves, and water cycle responses in terms of stomatal conductance and hydraulic xylem embolism resistance.  We found the Santarem forest (with long dry seasons) responded strongly to drought: sensible heat values significantly increased and evapotranspiration decreased.  Consistent with this, we also observed reductions in photosynthetic activity and ecosystem respiration, showing levels of stress not seen in the nearly two decades since measurements started at this site.  Forests at the Manaus site showed significant, however, less consistent reductions in water and carbon exchange and a more pronounced water deficit.  We report an apparent community level forest composition selecting for assemblies of traits and taxa manifest of higher drought tolerance at Santarem, compared to the Manaus forest (short dry seasons) and other forest sites across Amazonia.  These results suggest that we may be able to use community trait compositions (as selected by past climate conditions) and environmental threshold values (e.g. cumulative rainfall, atmospheric moisture and radiation) as to help forecast ecosystem responses to future climate change.
Improvement of evapotranspiration estimates over arid and semi-arid regions with a physically based water stress constraint scheme
Authors: Zhang Kun , Zheng Donghai , Wang Yunquan , Zhu Gaofeng
Published: March 2020

In the arid and semi-arid regions, the bare soil evaporation dominates the total evapotranspiration (ET). To date, in most of the process-based ET models, the constraint on the actual evaporation from bare soil due to water stress is either related to an empirical function of near-surface humidity or represented by a water stress factor linked with surface soil moisture. However, the relative humidity (RH) shows a hysteretic effect on the ET event, and the relationship between soil water stress and soil moisture is nonlinear, usually leading to the overestimation of ET in arid and semi-arid regions. In this study, we plan to improve the ET estimates on dry land by implementing a physically-based water stress constraint method, which is developed by parameterizing the Buckingham-Darcy’s law and yielded an excellent performance with laboratory data. The physically-based water stress constraint scheme is further incorporated into two different ET models (i.e. PT-JPL, MOD16) to generate the global ET estimates, whereby the latest ERA5-land reanalysis data and MODIS NDVI\LAI is adopted as model inputs. We not only validate the simulated ET with available flux observations but also intercompare the performances of different schemes in estimating ET in the arid and semi-arid regions. This study will provide a new way to characterize the regional soil water stress on the ET estimates especially in the arid and semi-arid conditions.
Fire frequency influenced grazed grasslands' resistance and resilience to extreme drought
Authors: Li Xiran , Hajek Olivia , LaRoe Jillian , Wilkins Kate , Knapp Alan , Smith Melinda D.
Published: March 2020

Grasslands provide critical ecosystem functions and services globally, including forage production for livestock and other animals. As frequency and intensity of disturbances, including fire and drought, are increasing globally, grasslands and the services they provide are particularly vulnerable. In this changing environment, resistance, the capacity to withstand disturbance, and resilience, the capability to recover from disturbance, are important for the stability of grassland ecosystems during and after extreme climate events. Quantifying how grazed grassland’s resistance and resilience respond to these disturbances provides important information of stability of grassland function under forecast climate change.

In this study, we focus on fire experiments in grasslands located in the Kruger National Park in South Africa (tropical savanna grassland) and the Konza Prairie Biological Station in the US (mesic temperate grassland). Both sites experienced extreme drought (SPEI <-2) this past decade, in 2015 and 2012, respectively. Further, both sites have long-term fire frequency treatments (annually burned, burned every 3-4 years and unburned) that are grazed by large native herbivores (~14 species at Kruger and bison at Konza), which allows us to explore influences of fire frequency on grazed grassland’s resistance and resilience to extreme drought. Using Landsat remote sensing data, we generated 30 m x 30 m NDVI monthly time series for each fire frequency treatment and conducted repeated measures ANOVA to compare the vegetation productivity two years before, during, and two years after the extreme one-year drought events.

Although large reductions in productivity occurred during the extreme drought at both sites and across the grazed fire frequency treatments, full recovery of production was observed the following year, consistent with trends observed in ungrazed grasslands at the study sites. These results suggest that grazed grasslands show high resilience, but low resistance to extreme drought. However, the degree of resistance and resilience was influenced by fire frequency. At Konza, during and after extreme drought in 2012, unburned grassland showed the lowest resistance but higher resilience, while grassland burned every four years and annually had higher resistance but relatively lower resilience. The anomaly of NDVI at Kruger exhibited an opposite pattern. These differences in resistance and resilience of production to extreme drought across the fire frequency treatments are likely due to changes in species composition or ecosystem structure (i.e., increased density of woody species in the absence of fire). Ultimately, these results suggest that fire frequency plays an important role in grazed grassland ecosystems’ vulnerability to extreme drought.
Effect of manure colloid on stability and transport of titanium dioxide
Authors: Shang Jianying , Yan Chaorui
Published: March 2020

This study was to investigate the effect of different manure colloids on the stability and transport of TiO2 NPs. Manure was used in fields as a common organic fertilizer. Different manure colloids were selected to study their effects on the aggregation and transport of nTiO2 at neutral pH conditions. The absorbance and particle size of the nTiO2 suspension at a certain ionic strength and manure colloid concentration were measured to determine the stability and aggregation of the nTiO2 particles at pH 7. Column experiments were performed to examine colloidal transport in quartz sand under water condition similar to those used in stability tests. The interaction energy among the nTiO2 particles and between nTiO2 particle and quartz sand were calculated using the classical DLVO theory to elucidate the underlying mechanisms involved at pH 7. The results showed that manure colloids can promote the dispersion and transport of TiO2 NPs under different conditions. 
Observed variability of Surface Ozone (O3) and its Precursors over the Indian Capital region
Authors: Kunchala Ravi Kumar , Chandel Anshika , Attada Raju , Vellore Ramesh K , Soni Vijay K
Published: March 2020

Ozone (O3) is a greenhouse gas which plays different roles in stratosphere and troposphere. It also has an important role in radiative and chemical balance of the atmosphere, and thus the changes in O3 have greater climatic implications. Although O3 is present in trace amounts in troposphere, it is adequate to govern the oxidation processes in the Earth’s atmosphere by forming OH radicals, as the atmospheric lifetime of many gases is controlled by OH radicals. Rapidly developing countries in tropics and subtropics have realized the importance of tropospheric O3 studies as these regions have very limited measurements of ozone and its precursor gases. Understand the variability of the surface O3 and their association with precursors are extremely important for the policy decisions to mitigate the impacts of ozone on human health and crops and ozone air quality management issues in the region. This study investigates the variability of surface ozone (O3) its association with its precursors (NO, NO2, NOX, CO) at time scales of annual, seasonal and diurnal scales for the duration of three years using ground-based observations from IMD Ayanagar, IMD Lodhi road, CRRI, CV Raman, IGI Palam stations in the Indian Capital region. Further, we will present the back-trajectory analysis to elucidates the transport mechanisms/ pathways on the variability of ozone for the study region.
The integrated stress-strain analysis of calcite twins: Consistent stress and strain determined from natural data
Authors: Wakamori Kei , Yamaji Atsushi
Published: March 2020

Stress and strain are different physical entities. Do the stress and strain determined from e-twins in a sample of polycrystalline calcite have similar principal orientations and similar shape ratios? Köpping et al. (2019) tackled this question by applying Turner’s (1953) classical method of paleostress analysis to natural data. However, despite the assumption of the method, the orientations of P- and T-axes of an e-twin lamella do not have a one-to-one correspondence with the principal orientations of the stress that formed the lamella. And, the method cannot determine a shape ratio. Another difficulty arises when one tackles the question: Natural calcite has usually been subjected to polyphase tectonics with different stress conditions. One has to separate stresses and to evaluate corresponding strains from a sample. Once lamellae are grouped according to the stresses, the strain achieved by the formation of a group of twin lamellae is easily evaluated by the method of Conel (1962) if the total strain represented by a group is small.

The present authors tackled the question by combining Conel’s strain analysis method with a novel method of paleostress analysis of mechanical twins, which clusters the directional data of e-twins by means of a statistical mixture model and determines stresses for each group of data. And, the appropriate number of stresses is determined by means of Bayesian information criterion. The method also determines the probabilities of each lamella to be formed by the stresses, which are called the memberships of the lamella. The strain achieved under a stress condition can be computed using the memberships. We applied this integrated stress-strain analysis method to Data Sets I and II from two calcite veins in a Miocene forearc basin deposit in central Japan. Since the sampling area was close to a triple-trench junction, the young formation has experienced polyphase tectonics.

As a result, we obtained the consistent stress and strains from both of the data sets. Three stresses were obtained from Data Set I, and the corresponding strains were 0.17, 0.25 and 0.13%. Two stresses were obtained from Data Set II, and the strains were 0.39 and 0.42%. The stress and strain determined from the data sets for each deformation phase were consistent with each other. That is, the principal axes had difference as small as < 20 degrees, and the shape ratios of stress and strain had also similar values. It is not straightforward to generalize this result, but both the stress and strain analyses seem to give appropriate results, providing that polyphase deformations are coped with.
On the earthquake detectability by the Next Generation Gravity Mission (NGGM)
Authors: Cambiotti Gabriele , Douch Karim , Cesare Stefano , Anselmi Alberto , Sneeuw Nico , Marotta Anna Maria , Sabadini Roberto
Published: March 2020

We perform Next Gerataion Gravity Mission (NGGM) simulations over a 12-year operational period by including in the background gravity field the time-dependent gravity anomalies caused by different earthquake scenarios and considering different sources of error on 28-day mean gravity field solutions: the instrumental errors of the interferometer and accelerometers, the time depenendent background model and the atmosphere-ocean dealiasing. In order to assess whether the observational errors mask or not the earthquake-induced gravity signals, we assume known the background gravity field and the spatial and temporal pattern of the earthquake-induced gravity anomalies. Then, for each earthquake, we estimate the amplitude of its gravity anomaly by inverting the NGGM synthetic data time series and we check its consistency with the expected amplitude, as well as with the null hypothesis. In order to investigate case studies representative of the main earthquake characteristics and their compliance with the NGGM specifications, we have considered normal, inverse and strike-slip focal mechanisms striking with different angles with respect to the polar orbit, reaching the Earth surface and in depth, occurring inland, off-shore and close to the coastlines and at the beginning (2-4 years), at the middle (5-7 years) and at the end (8-10 years) of the 12-year operational period. The fault dimensions and slip distribution vary with the seismic moment magnitude and are prescribed according to the circular fault model by Eshelby (1957). Furthermore, we also consider two different rheological stratifications with asthenospheric viscosity of 10¹⁸ and 10¹⁹ Pa s. In order to discuss whether the earthquake signal can be discriminated from other geophysical processes (like atmosphere, ocean, hydrology and glacial isostatic adjustment), we also perform the same inversion but, this time, its amplitude is estimated jointly with the time dependent background gravity field, which we simply model using static values, trends and periodical functions.
Stress analyses of various curvature arched groundsills
Authors: Hou Yu-Jen , Huang Hung-Pin
Published: March 2020

In Taiwan, arched groundsill is frequently used as soil-and-water conservation structures for stabilizing creek bed, guiding flow direction, decreasing the slope of creek bed and reducing the scour effect. Even though much more arched grounsill was built in wild creek recently, its mechanical mechanism is still unclear.

In order to explore the characteristics of arched groundsill, this study intends to find out the scale of stress, moment and displacement distribution on the various curvature arched groundsills by means of the structural analysis software, ABAQUS. Simultaneously, the three-dimensional computational fluid dynamics software, ANSYS-FLUENT, is applied to show the flow condition of different setups. Preliminary result shows that the maximum stress and displacement of arched groundsill increase with curvature. The maximum moment decreases slightly firstly and increases sharply later with curvature.