bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the  mode interference  of Very Low-Frequency Electromagnetic Waves during Seismic Events
Authors: Borgazzi Andrea Inés , Carrasco Enrique , Lara Alejandro
Published: March 2024

We present the characterization of the  mode interference  of Very Low-Frequency (VLF) electromagnetic waves at dawn/dusk based on amplitude and phase data received by LAVNet (Latin America Very low frequency Network) from signals emitted by Omega-Network stations.
LAVNet is a collaborative project consisting of four receiving stations located at different points in the Americas (Argentina:-65.0W,-30.0S; Chile:-71.99W,-36.64S; Colombia:-76.5W,3.93N and Mexico:-99.15W, 19.47N). Its purpose is to detect and characterize the signatures left by various types of geophysical events when VLF electromagnetic waves, propagating through the Great Circle Path, are captured by these stations.
To identify the signatures of a geophysical events in the VLF signal, where a geophysical event is defined as any event that disturbs the VLF signal from 'above' (outer space) or from 'below' (lithosphere), it is necessary to understand the typical signal's behavior  during all seasons of the year.
In this case, we are interested in the possibility of detecting disturbances in the signal due to activity preceding an earthquake. To achieve this goal first,  it is necessary to characterize the signals over a long period of time (several years) to establish the typical behavior of each path, especially during dawn/dusk when shifts of the mode interference minima  may take place. These shifts would be characteristic of lithospheric activity.
In particular, here we  present the characterization of VLF signals received by the station located in Mexico, specifically the typical minima times during dawn/dusk and its time-shifts along  the year. 
Also, we present a preliminary analysis of the mode shifts related to seismic events observed  in the 2012-2017 time period.
Continuation of the MOPITT record of global carbon monoxide
Authors: Worden Helen , Drummond James
Published: March 2024

Measurements Of Pollution In The Troposphere (MOPITT) on the NASA Terra spacecraft has been measuring the global atmospheric abundance of carbon monoxide (CO) since March 2000. Direct emissions of CO are mainly produced by incomplete combustion from both natural fires and anthropogenic activities, and CO is also produced chemically from methane and volatile organic carbon (VOC) species.  Although CO has a negligible contribution to greenhouse gas radiative absorption, it does play an important role in atmospheric chemistry and climate because it is a dominant sink for the hydroxyl radical (OH) and thus affects the lifetime of methane (CH4) and production of tropospheric ozone (O3). Because of these interactions, the IPCC AR6 estimated that anthropogenic emissions of CO have a significant indirect radiative forcing of 0.23 W/m2.  The MOPITT record is long enough to detect significant trends in atmospheric pollution and assess changes in emissions due to regulations, agricultural burning, technology improvements to combustion efficiency and increasing wildfires due to a warming climate. We will present an overview of the MOPITT data record, the unique combination of thermal and shortwave infrared radiances and discuss the continuation of the MOPITT record with IASI on MetOP, CrIS on SNPP and JPSS satellites and TROPOMI on Sentinel 5P.
Role of catchment morphometrics in addressing the spatial resolution of GRACE-derived total water storage changes
Authors: Bharath Narayana Reddy Komali , Devaraju Balaji
Published: March 2024

The spatial resolution of the total water storage changes from GRACE data is a conundrum, but also the most sought after quantity. The availability of various solutions exacerbates the situation -- unconstrained spherical harmonics, constrained spherical harmonics, mascons and different data processing centers. Some attempts have been made previously to arrive at an answer, and some numbers have been proposed. Notably, in the context of hydrologic applications, the spatial resolution morphs into a question of the catchment sizes and shapes, thereby rendering some of these numbers deficient. This study uses ideas from leakage analysis to arrive at answers for the spatial resolution issue. Care is taken to incorporate the morphometric characteristics of catchments in the answers being arrived at.
Distinct mantle flow patterns in the Sunda subduction zone revealed by a layered anisotropic structure
Authors: Kong Fansheng , Gao Stephen S. , Liu Kelly H. , Li Sijia , Zhang Jie , Li Jiabiao
Published: March 2024

The nearly 6,000 km-long Sunda subduction-collision zone, comprising Sumatra, Java, Banda, and adjacent regions is an ideal locale for investigating interactions between plate (slab) kinematics and plastic flow in the asthenosphere, as well as probing mantle dynamics associated with large-scale anomalous volcanism. These interactions and relationships can be diagnosed by a layered anisotropic structure based on joint analyses of shear wave splitting and receiver functions. The mantle flow field characterized by the layered anisotropic structure exhibits distinct patterns from west to east. In the Sumatra subduction zone, slab advance drives mantle flow from the sub-slab mantle entering the mantle wedge through a slab window and flowing horizontally parallel to the trench, and its vertical component contributes to the significant amount of magma of the Toba supervolcano. By contrast, in the Java subduction zone, slab rollback makes mantle flow traverse a slab window in central Java, where a clockwise rotational pattern in the fast orientations is revealed. The vertical component of the flow field is responsible for the formation of the potassic volcanoes in central Java. To the east, in the Banda arc-continent collision zone which signifies one of the most seismically active and tectonically intricate zones, the mantle flow field is also strongly influenced by plate (slab) kinematics and shows trench-parallel flow pattern in both the sub-slab and wedge mantle. The modulated trench-parallel plastic mantle flows lead to the steepening of the southern portion of the asymmetric spoon-shaped Banda slab, diminishing the vertical viscous flow and the associated dynamic topography, and contributing to the uplift of the Banda basins. 
Forecasting of GICs in Local Power Grid by Comprehensive Analysis Based on Hilbert-Huang Transform and Deep Learning Methods
Authors: Liu Jin , Fang Yihao
Published: March 2024

The Geomagnetic Induced Currents (GICs) generated in power grid by large-scale solar events may lead to electrical equipment damage and widespread power outages. Consequently, it is significant to achieve effective GIC prediction and risk assessment for local grids. The Hilbert-Huang Transform (HHT) is used to analyze geomagnetic components and GICs monitoring data. By extracting the responses to storms, the instantaneous amplitudes are synthesized as equivalent GIC disturbance indices. A combined prediction model based on deep learning methods is proposed. Concretely, the observation data of geomagnetic components and GIC are decomposed by Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN), and the Intrinsic Mode Functions (IMFs) are predicted by a combination model constructed by Convolutional Neural Network (CNN) and Long-Short-Term Memory (LSTM) with the attention mechanism. Then, the predicted sequences of IMFs are accumulated to obtain the final forecasting. In addition, the GIC potential risk of local power grid is evaluated comprehensively by considering the solar wind energy injection, geomagnetic disturbances, equivalent GIC indices and the forecasting based on observations. 
Recognizing the shifting ontologies of temporary wetlands through the lens of sociohydrology: Case study of Merjas of the Gharb plain, Morocco
Authors: Choukrani Hajar
Published: March 2024

Temporary wetlands are fluid territories with nonlinear and constantly evolving frontiers between water and land, often at the origin of various ontologies. The present research introduces the multifaceted ways of making sense of temporary wetlands by different stakeholders: as wastelands to be drained and reclaimed, as hotspots of biodiversity to be preserved or restored, as buffer zones, or as hydrosocial territories in which people live and produce. We explore how these ontologies evolved and how they influenced the way these temporary wetlands are perceived and used. The present study was conducted on temporary wetlands (merjas) in the Gharb plain (Morocco). The Gharb plain was mostly drained and reclaimed for agriculture, but about than 30,000 ha of merjas were too costly or too complicated to be drained and developed by the State. Using a socio-hydrological approach to study the interplay between people and these fluid territories, the research delves into the origins of the diverse ontologies and the way these ontologies have shaped the merjas. Ethnographic data were gathered through field surveys, focus groups, and participatory workshops. Hydrological data were obtained by remote sensing computing water and vegetation spectral indices. Two predominant ontologies emerge and clash, giving rise to conflicts among stakeholders. The State’s “buffer zone ontology” views merjas role as floods regulation (especially after the 2009-2010 floods) to safeguard agricultural and urban areas, an option firmly rejected by local communities. In contrast, the “local ontology” embraced by local communities, recognizes the intricate interplay between land and water and seeks to claim the reclaimed merjas for the benefit of the young generation and for the sense of belonging they feel. The perspective of temporary wetlands as ecological systems are neglected and not recognized by all of the stakeholders. These diverse ontologies are intricately linked to different networks of actors, that sometimes coexist, and most times collide. Defining what merjas are remains challenging due to shifting water flows and the existence of multiple stakeholders with divergent ontologies. Facilitating future negotiations regarding the fate of merjas remains challenging because of shifting water patterns and the presence of diverse stakeholders with dichotomous perspectives.
Key words: Temporary wetlands, Ontologies, Stakeholders, sociohydrology, remote sensing, Morocco
Global projections of flood risk under climate change
Authors: Duan Yu
Published: March 2024

Floods are one of the most prevalent natural disasters globally, causing huge annual losses to the population and economies of the world. Identifying the distribution and evolution of global flood risk is essential in context of the growing trend of extreme natural hazards under climate change. This study presents predictions of global flood risk based on Global Climate Models (GCMs) under four Shared Socioeconomic Pathways (SSPs). Here our results demonstrate that a slow increase trend in global flood risk under different scenarios. Currently, about 23% of the global area is at very high risk of floods, which are concentrated in regions with high rainfall, flat terrain, and dense population and economic densities, such as eastern China, Japan and the eastern US. By the end of the 21st century (2081-2100), according to the SSP5-8.5 scenario, the global flood risk increases by up to about 2% overall compared to the baseline period (2001-2020), with an increase in the area at medium, high, and very high flood risk of about 780,316 km2. Over global countries with different income levels, high-income countries typically have a higher risk of floods than low-income countries, with 8 of the 10 most at-risk countries in the world being high-income countries. Singapore, Japan, Luxembourg, and South Korea are among the group of countries with the highest flood risk in the world. This study constructs a framework for global flood risk prediction from disaster-inducing factor, disaster-breeding environment, and disaster-bearing body, rather than just meteorological factors. These results indicate an increasing trend in global flood risk as predicted by a combination of factors, and we need to take mitigation measures to prevent the acceleration of these risks.
Integrating Satellite Observations for Large-Scale Characterization and Monitoring of Flash Droughts in the Contiguous United States
Authors: Farahmand Alireza , Zeraati Masoud , AghaKouchak Amir , Wen Yixin
Published: March 2024

Flash droughts are characterized by rapid onset and intensification, capable of significantly impacting agriculture and ecosystems. Flash drought typically starts as a meteorological drought, which can progress into an agricultural drought if conditions worsen. This type of drought is primarily marked by extremely high air temperatures and soil moisture deficits. While the primary cause of drought is a lack of precipitation, other atmospheric and hydrologic anomalies can accelerate the development and severity of flash droughts. For example, low precipitation conditions, combined with high evaporative demand due to elevated air temperatures, low relative humidity, and clear skies, can lead to the rapid emergence of agricultural drought conditions, primarily manifested as increasing soil moisture deficit. As a result, multiple factors can contribute to the occurrence of flash droughts, and it is important to utilize a wide range of reliable data sources to monitor the emergence and expansion of flash droughts.
While prior studies have generally examined flash drought evolution using reanalysis data, there has been no comprehensive exploration of flash drought development at large scales, incorporating a wide range satellite observations. In this study, we characterized flash droughts over the continental US using remote sensing data between 2003 and 2020. Here we employ a unique combination of satellite climatic, agricultural, and ecological variables to investigate large-scale flash drought development. These variables include Atmospheric Infrared Sounder (AIRS) Vapor Pressure Deficit (VPD), Relative Humidity (RH), Temperature (T), GLDAS Soil Moisture, Global Precipitation Measurement (GPM) Precipitation, Moderate Resolution Imaging Spectroradiometer (MODIS) Evapotranspiration, MODIS Leaf Area Index (LAI), and Orbiting Carbon Observatory-2 (OCO-2) Contiguous Solar-Induced Chlorophyll Fluorescence (CSIF). Flash drought events are defined based on soil moisture, with all variables aggregated into 8-day (octad) averages for analyzing their temporal evolution and lead-lag correlations against soil moisture.
Finally, the deteriorating impact of flash droughts associated with background aridity should be considered while monitoring their agricultural, and ecological impacts. Here we also investigate ecosystem responses to flash droughts in 5 different regions characterized utilizing the Aridity Index (AI) across the Contiguous United States (CONUS).
 
The ENSO Modulated Wave Climate Over the Northern South China Sea Under the Collective Impact of Monsoon and Tropical Cyclones
Authors: Niu Qianru , Li Yan , Mu Lin
Published: March 2024

Wave climate in the northern South China Sea (SCS) was accessed during 1990-2020 based on a high-resolution wave model, encompassing the evaluation of the contributions of monsoon and tropical cyclones under the impact of ENSO activities. Using the Gaussian mixture model, the northern SCS was divided into five subareas according to the wave characteristic variations, and pronounced seasonality was observed in both the mean and extreme significant wave heights (Hs) across all subregions. The highest  occurred near the Luzon Strait all year round, with nonnegligible contributions of swells from the western Pacific Ocean superimposed with wind-seas. The significantly enhanced summer  (95th-percentile Hs) indicates its dependence on both the Asian-Australian monsoon and extra-tropical storms. Further analysis revealed increasing trends in mean and extreme Hs during spring and winter, mainly driven by enhanced winter monsoon. The principal component and regression analyses confirm a robust relationship between the mean and extreme wave climate and ENSO over the last few decades. The analysis of covariate on the monthly  and Hs95 revealed that ENSO influence the northern SCS wave climate mainly through its modulation on the gale frequencies instead of the monsoon activities. Driven by the ENSO-related typhoon track variations, the summer Hs95 during La Niña years tends to be weaker than those during normal years at Guangdong Coast and northwest SCS. The shallow-water Hs during fall, on the other hand, was significantly smaller during El Niño years than those during La Niña and normal years.
Drought propagation across meteorological, hydrological and agricultural systems in the Lancang-Mekong River Basin
Authors: Li Yu , Feng Yunfei , Zhang Bingyao , Zhang Chi
Published: March 2024

Drought produces cross-system impacts, and these interactions between multiple systems are also referred to as drought propagation. However, the complex natural processes and anthropogenic disturbances lead to the drought propagation process being non-linear and systems feedback, which is still lack of knowledge in large-scale basins. To address these challenges, we propose a hydro-economic coupled model and investigate drought propagation across meteorological-hydrological-agricultural systems. The results from the Lancang-Mekong River Basin show that drought propagates from the meteorological system to the hydrological system and is weakened by the basin storage capacity. This propagation process shows spatial heterogeneity caused by basin characteristics, highlighting that the upstream (CS location) and downstream (KR and KC location) are more prone to hydrological drought vulnerability. As drought further propagates to the agricultural system, water abstraction behaviours can alleviate the drought situation, leading to crop yield increases ranging from 6.9% to 39.3% through irrigation pathways. Unfortunately, irrigation behaviour also worsens hydrological drought in a feedback loop, where downstream KR (SRI increases by almost 90%) shows more intense variation than upstream PA (SRI increases by around 12%), illustrating the feedback among multi-systems and accumulation in spatial. Moreover, upstream hydropower and downstream agricultural water use show synergistic relationships, revealing that efficient anthropogenic interventions can mitigate the impact of drought on human well-being. This paper provides an in-depth understanding of the complex drought propagation process in nature-human highly coupled Mekong, which may help policymakers and basin managers to better cope with drought.
Impacts of BBOA on the carbon sink of transitional forests in the Cerrado-Amazonian Forest ecotone: results from observational measurements and numerical estimates
Authors: Cirino Glauber , Rodrigues Simone , Moreira Demerval , Palácios Rafael , Lee Sung-Ching , Imbiriba Breno , Vitorino Maria Isabel , Pozzer Andrea , Nogueira José
Published: March 2024

Tropical forests are crucial global climate regulators. They store large amounts of carbon in their living biomass and maintain a delicate biosphere-atmosphere relationship. The carbon cycling in the Amazon Basin has been studied due to the changes promoted in its capacity to absorb and emit large amounts of CO2 concentrations globally in soil, water, and the atmosphere. This research seeks to contribute by identifying human disturbance (biomass burning) and its influence on the Net Exchange of CO2 (NEE) over areas of semideciduous forest located in the Amazon basin. We used micrometeorological measurements (in situ) of 50 km NE of Sinop-MT to calibrate the JULES-CATT-BRAMS numerical system. The model calibration allows estimating the potential for CO2 uptake under smoky conditions, i.e., Aerosol Optical Depth (AOD >> 0.10) and non-polluted (AOD < 0.20). Physiological optimums for AOD, f, PARDF, Tair, VPD, and TdF are determined and used as inputs for approaches concerning Carbon pricing in the Amazon basin. Our preliminary results show statistically significant reductions in %NEE for high aerosol loads (AOD > 1.0), relative irradiance f < 0.60, and Solar Zenith Angle (SZA < 70) values. We found a decrease of about 40 % in f and an increase from 0.10 to 5.0 in the AOD values at 500 nm. Likewise, a 25-110 % increase in NEE flux for AOD levels above approximately 1.25 is significantly linked to the rise of 40-60 % in the Fraction of Diffuse PAR radiation (PARDF) due to the impact of Biomass Burning Organic Aerosols (BBOA). We also noted statistically significant reductions and increases in biophysical variables such as leaf canopy temperature (TdF ~ 3 ºC) and relative humidity (URair ~ 20%), both found under extremely smoky sky conditions. These results can help better represent the physical processes currently implanted in the JULES system and, therefore, the photosynthetic responses of semideciduous forests to regional carbon cycling in the Amazon. Furthermore, we expect this information to guide truly sustainable public policies based on economic development from the preserving forest ecosystems and Brazilian biomes. The noteworthy impact on carbon cycling in semi-deciduous forest environments in the Amazon arises from decreases in the Net Ecosystem Exchange (NEE) flux. This reduction, attributed to the excessive rise in BBOA aerosol concentration, leads to a notable decline in the photosynthetic capacity of plants. Additionally, the substantial decrease in solar radiation fluxes (f < 0.20) caused by regional fires further contributes to this effect. Consequently, these findings significantly enhance our understanding of the carbon cycle in the Amazon region and globally. 
The propagation from meteorological to hydrological drought and its potential influence factors in a typical inland river basin
Authors: Wang Lin
Published: March 2024

The thresholds and influencing factors that trigger the transition between meteorological drought and soil drought are poorly understood, which hinders the effective establishment of drought early warning systems and preventive measures. We selected a typical inland river basin with an alpine-oasis-desert ecosystem, the Shiyang River Basin in Northwest China, toidentify the drought events from 1980 to 2020, and then used the Copula function to assess the risk and threshold of the propagation from meteorological drought to soil drought. The Drought Intensity Propagation Index (DIP) and the Drought Duration Propagation Index (DDP) were used to quantify the propagation process of drought characteristics. Furthermore, we identified and quantified the drivers of drought propagation characteristics. The results showed that: (1) the duration of meteorological drought events extended in 85% of the regions and the intensity of drought increased in 26% of the areas from 1980 to 2020, while the duration of soil drought events decreased and the intensity of drought increased in almost all regions; (2) the propagation of drought has spatial heterogeneity, that is, from the upper mountain to the lower oasis, the probability of propagation  from meteorological drought to soil drought decreased, the degree of drought intensity propagation weakened, and the degree of drought duration propagation intensified; (3) the cumulative precipitation deficit thresholds triggering soil drought were -11mm/ month, -7.5mm/ month and -5mm/ month, respectively; (4) precipitation and evapotranspiration were the main driving factors of the drought propagation characteristics, which explained 44% of the drought intensity propagation upstream and explained 60% of the drought duration propagation downstream, respectively. This study further reveals the law and mechanism of drought propagation, which is helpful for the early monitoring and warning of drought events in river basins, and provides new ideas for the construction of drought propagation models.
Lateral middle-lower crustal flow in Southeast Tibetan Plateau: structural analysis from the metamorphic complexes 
Authors: Chen Xiaoyu , Liu Junlai , Zhou Baojun , Shan Hongshuai , Bao Xiaoxi
Published: March 2024

The India-Eurasia collision and subsequent post-collision process since about 55Ma have an important influence on the middle and lower crust activities, formation and evolution of the crust structure in the Tibetan Plateau and its periphery. Several models have been proposed to explain the response of the lateral collision zone in Southeast Tibetan Plateau, such as rigid block extrusion, middle and lower crust channel flow, and crust thickening. There are several metamorphic complexes with Precambrian basement in the margins and interior of the Sundaland block. We have carried out structural analysis, kinematic analysis, shear and exhumation time studies on these complexes, which provide new important clues to explain the flow patterns in Southeast Tibetan Plateau during the India-Eurasia collision.
Structural analysis of the metamorphic complexes reveals that dome structures are widely developed in the southeastern Tibetan Plateau. The cores of the domes are composed of high-grade metamorphic rocks that were deformed at high temperatures and partly superimposed by subsequent low temperature deformation. The mantles of the domes are composed of low-grade metamorphic rocks that were deformed at relatively low temperatures. Shear discontinuity contacts exist in most cases between the core and the mantle. Subhorizontal (bedding-parallel) shearing dominated the deformation of the crustal rocks during doming. Regional-scale A-type domes, local-scale mylonitic foliation, stretching lineation and outcrop-scale A-type folds were formed due to the subhorizontal shearing. Kinematically linked but rheologically decoupled two-layer structures are evidenced by the existence of tectonic discontinuity contacts between the cores and mantles in the domes. New geochronological dating results in combination with dating results in the literature suggest that middle to lower crustal shearing occurred from ca. 30 to 20 Ma. Most of the metamorphic complexes in the southeastern Tibetan Plateau began their exhumation accompanied by ductile shearing since 30 Ma, while the initiation of the exhumation of the complexes was diachronous at different locations, earlier along marginal high-strain zones and later in the interior of the Sundaland block. Exhumation of the complexes is characterized by the two-stage cooling histories of various characteristics, which indicates that the different complexes were sheared and exhumed separately. Formation and exhumation of the domes are related to middle and lower crustal flow, during which shearing, folding and exhumation are simultaneous for particular domes. The middle to lower crustal flow lines constitute a general convergent flow pattern. The counter flow, i.e., southward flow of the rigid upper crust and northward flow of the viscous middle-lower crust, is the most likely explanation for northwestward flow of the dome cores relative to the mantles.
Using Raman Spectroscopy of Carbonaceous Material to Explore the Metamorphic Temperature and its Tectonic Implications in the Southern Hsuehshan Range, Taiwan Orogen
Authors: Hsieh Li-Chen , Lee Yuan-Hsi
Published: March 2024

The mechanisms of regional metamorphism in convergent orogens are still debated, with two perspectives on timing—either linked to convergence processes or pre-convergence rifting. The Hsuehshan Range in Taiwan experienced rifting from the Eocene to the Miocene, followed by a convergence since the late Miocene. In this study, we discuss the metamorphic mechanism of the Hsuehshan Range by combining Raman spectroscopy of carbonaceous material (RSCM) for the peak metamorphic temperatures and zircon fission track for the cooling ages, to constrain the burial temperature before the convergence.In central Hsuehshan Range, RSCM temperatures peaked at 480°C, decreasing northward and southward. In the central-northern region, RSCM temperatures correlated positively with stratigraphic ages. However, in the southern region, east of the Tili Fault, temperatures increased eastward without matching stratigraphic ages.In some areas, RSCM temperatures (260-300°C) indicate total reset during the late Cenozoic orogeny, while zircon fission-track ages show partial reset. Higher RSCM temperatures (>400°C) lack significant new biotite growth.We propose that during the rifting stage, strata experienced peak metamorphism, followed by cooling before the late Cenozoic orogeny, thus explaining inconsistencies between RSCM temperatures and zircon fission track ages. The deposit thickness variations in the rifting basin that are contributed to the RSCM temperatures, show no apparent stratigraphic correlation.
A tracer test for evaluating the heterogeneity of a shallow groundwater aquifer in the Tatun Volcano Group, Taiwan
Authors: Kuo Ching-Huei , Tseng Pei-Yun , Chen Yi-Ling
Published: March 2024

Two multi-well tracer tests were conducted on two sides of a creek in Tatun Volcano Group, Taiwan to investigate the regional groundwater flow and to examine the heterogeneity of the region with conservative tracers. The sulfonic acids were used due to their reasonably good thermal stability and easily be analyzed by high-performance liquid chromatography (HPLC) using uv-absorbance detection.  Two breakthrough curves with multi-peaks were received and used to understand the existence of a hydraulic connection between injection and production wells but also used to gather crucial information about aquifer properties by using analytical models.  An analytical model, multi-fractures mode, was particularly used in matching tracer return curves.  Results show the existence of a dominated advection through a couple of fast flow paths/fractures between injection and receiving wells for one set while the other pairs have strong dispersion accompanied by the advection flow.
LEO constellation optimization for BDS precise orbit determination in LEO enhanced BDS
Authors: Wu Tianhao , Li Bofeng , Ge Haibo
Published: March 2024

LEO-enhanced GNSS (LeGNSS) has been proposed and quickly gained prominence in recent years. A high-precision orbit is imperative for achieving accuracy in LeGNSS applications. The 'One-step' method has been proven effective in optimizing orbit accuracy in precise orbit determination, especially for BDS. On one hand, the orbital accuracy of BDS GEO is constrained by poor geometry, even with globally distributed stations; on the other hand, in cases with only regional stations available, the accuracy of the entire constellation is significantly compromised. However, constrained by computational costs and the phased development of LEO constellations, the optimization of LEO constellations is crucial for achieving high-precision BDS orbit determination with limited LEO satellites.
Previous research has primarily focused on optimizing LEO constellations to enhance the performance of LeGNSS PPP. In this study, our emphasis shifts towards improving BDS orbit determination accuracy. We analyze the impact of LEO constellation inclination on BDS orbit determination using simulated data.
The walker parameters of the simulated LEO constellations are set at 6/6/1, with the inclination angle ranging from 5° to 90° in 5° increments. We examine the orbit accuracy of BDS GEO, IGSO, and MEO in combination with LEO constellations of varying inclinations for orbit determination at global and regional stations. The key findings are as follows:
For global stations, the orbital accuracy of GEO is significantly influenced by the inclination of LEO satellites, with the worst accuracy at high inclination angles and the best at medium inclination angles. The accuracy improves from 24cm without joint LEO satellites to 0.4cm with the inclusion of joint medium-inclination satellites, while the result of polar orbit is 0.6cm. IGSO and MEO show no clear relationship with the inclination of LEO satellites.
In cases where only regional stations are available, GEO and MEO are more affected by the inclination of LEO satellites. GEO achieves the highest accuracy at medium inclination angles, peaking at 0.9cm when the inclination is 55°. MEO orbit accuracy increases with the inclination angle, with a worst accuracy of 2.3cm when the inclination of LEO is 5°, and reaching the best of 1.2cm when combined with polar orbit LEO satellites. Additionally, implementing a mixed-inclination constellation comprising three 55° satellites and three 90° satellites yields optimal overall orbital accuracy for the BDS, surpassing any single-inclination constellation.
Unbound geodesic orbit in the spacetime of charged black hole under higher derivative gravity
Authors: Cui Yuhao , Lin Kai , Sun Yang-Yi
Published: March 2024

The unbound orbit of photons and particles in the background of a static spherically symmetric charged black hole spacetime under higher derivative gravity is investigated. By solving the geodesic equations, we have derived the effective potential for the motion of photons and particles. We represent the deflection angle of photons and particles using numerical integration, plot and discuss the unbound orbit of photons and particles. Our calculations indicate that the effective potential for particles is influenced by both the horizon radius and electric charge of the black hole. For black holes with a large horizon radius or a large electric charge, there will always be an extremum in the effective potential. In such a scenario, particles with lower energy moving towards the black hole may experience a repulsive force, leading to their rebound instead of being captured, and due to the presence of repulsion, particles beyond the radius corresponding to the extremum of the effective potential cannot exist in bound orbits.
Soil carbon stabilization and potential stabilizing mechanisms along elevational gradients in alpine forest and grassland ecosystems 
Authors: Gubena Adugna Feyissa , Cheng Xiaoli
Published: March 2024

Alpine ecosystems potentially store a large amount of soil organic carbon (SOC) but are highly sensitive to climate change. Therefore, assessing SOC stabilization mechanisms in these ecosystems is vital to understanding the C dynamics in terrestrial ecosystems. Here, we investigated the soil aggregate distribution, aggregate stability, and associated SOC contents and enzymatic activities within alpine forest and grassland soils along an elevation gradient in the Yulong Mountains of Southwest China. Our results showed that the SOC contents and its cycling enzymes in bulk soils and aggregates were higher within grassland soils than in forestland soils, with higher levels and activities in the topsoil (0–10 cm) than in the subsurface soil (10–20 cm) at each elevation. The large macroaggregates (>2000 µm) accounted for the largest proportions of aggregate fractions (50.54% and 49.11%) and contributed the greatest proportions of C (55.44% and 52.12%) to the whole soil C within forest and grassland soils, respectively. Generally, the proportions of large macroaggregates, microaggregates (53–250 µm), mean weight diameter, geometric mean diameter, and SOC contents in bulk soils and aggregates increased significantly with increasing elevation across different soil depths and land types, suggesting that soil C stability was improved with increasing elevation. The δ13C values of the aggregates showed an increasing trend of 13C enrichment with decreasing aggregate size classes and were correlated with the corresponding enzyme activities. Potential C flow between the aggregates was detected from macro- to microaggregates in the order: large macroaggregate → small macroaggregate (250–2000 µm) → microaggergate → silt + clay (<53 µm) fractions, suggesting the predominant formation and stabilization of recent C inputs in the macroaggregate fractions. Climate factors, soil factors, Al/Fe oxides, and aggregate stability indices interactively explained 86% and 52% of the variation in soil C within forest and grassland soils, respectively. Among them, incorporating the Al/Fe oxides increased the total explained variations in SOC by approximately 10%, exceeding the variations explained by climate or soil factors. Overall, our results provide useful insights into the patterns and mechanisms of soil C stabilization along elevation gradients in alpine ecosystems.
Enhancing Dispersion Imaging with the Frequency-Bessel Method Using the Kolmogorov-Smirnov Subarry Partition Test: A Case Study of SGB Dense Array
Authors: Song Shuhao , Chen Xiaofei
Published: March 2024

Recent studies on the frequency-Bessel transform (F-J) method demonstrate the ability of the array-based method to extract higher-mode surface wave dispersion curves from ambient noise. Presently, the subarray selection of F-J method for three-dimensional imaging predominantly relies on regular partition shapes. However, a crucial tradeoff arises concerning partition size: a larger size improves dispersion curve quality at lower frequencies but deviates from the assumption of a flattened velocity structure required by F-J method. Conversely, a smaller size ensures compliance with the flattened structure assumption but limits usability to higher frequencies. This tradeoff becomes particularly challenging in scenarios with relatively shallow depth scales, such as fault imaging, where subsurface velocity structures exhibit significant variations.
To address this dilemma, we propose a novel strategy employing dispersion curves from small partitions as probes. We use the Kolmogorov-Smirnov (K-S) test to assess the flattened velocity structure within a larger partition by utilizing these probes. This process streamlines the elimination of arrays within the larger partition that diverge from the assumption of a flattened structure. Consequently, when utilizing the larger partition, we can maximize the compliance of the flattened structure assumption.
       In this study, we leverage noise cross-correlation functions from a dense array at the Sage Brush Flat (SGB) site, located in the intricate trifurcation area south of Anza in Southern California. The array comprises geophones arranged in a 600m×600m configuration. We hope that the implementation of this partition strategy will enhance the feasibility of array-based surface wave tomography methods, especially in dense arrays within regions characterized by complex shallow velocity structures.
Recognizing misinformation using geolocation: Spatial examination of Information Inferred from Tweets meta-fields
Authors: Zohar Motti
Published: March 2024

In recent years, Twitter has surged as a formidable communication platform, hosting over 500 million users worldwide. Despite a mere fraction of tweets (1–3%) containing direct geolocation, the abundance of metadata fields, including user-generated content, holds promise for inferring crucial spatial information. This study, aligning with principles of recognizing fake news and bolstering science credibility and public awareness, utilized GeoNames and OpenStreetMap datasets alongside a curated dataset of Tweets. Leveraging these resources, it aimed to infer tweet locations from text-based meta-fields and the user’s profile of location and description, emphasizing the verification of inferred locations' reliability amidst the prevalence of misinformation. Analysis revealed a strong correlation between distances derived from textual content and user-provided location meta-fields, indicative of potential links to actual device locations and phenomena described within tweets. Emphasizing the critical principles of recognizing misinformation and verifying geolocated data in tweets, this study emphasizes the importance of fostering science credibility and public awareness. It highlights the potential for accurately inferring device locations and validating information shared in tweets thus fostering the ability to detect fake news and promoting accurate scientific information dissemination for broader public awareness.
Evaluating the effects of rock check dams on soil and vegetation ten years after a wildfire in a Mediterranean forest ecosystem
Authors: Zema Demetrio Antonio , Plaza-Àlvarez Pedro Antonio , Carmona Yanez Maria Dolores , Lucas-Borja Manuel Esteban , Zupanc Vesna , Martinez-Hontecillas Adrian
Published: March 2024

Rock check dams are transverse structures built across small gullies for controlling water flow and soil erosion. Typically, rock check dams are made of stones without masonry, concrete, or wood logs. These structures can effectively be used after wildfires in Mediterranean forest as anti-erosive measures at the basin scale. However, although the number of rock check dams continues to increase on the global scale as a response to the needs for erosion control and sediment transport regulation, their expected morphological impacts – e.g., reduction in the upstream slope of reaches and/or stabilization of gully beds - are often not achieved due to factors as poor construction quality, inadequate location and unsuitable design criteria. More specifically, observations carried out in several studies about the morphology of sections and bed material in channels with rock check dams indicate possible increases in erosion downstream of structures as well as negative impacts on plant diversity, soil properties and overall torrent systems. This research aims to achieve a comprehensive synthesis of effects of rock check dam on channel morphology, bed sediments, plant diversity, soil properties by observations made ten years after a wildfire in a Mediterranean forest ecosystem. The role of complex interactions between ecological elements, geomorphic processes and engineering activities is highlighted with the ultimate aim to improve the use of rock check dams for soil conservation and water resources management after wildfires in semi-arid conditions.
A high-resolution map of soil organic carbon in cropland of Southern Chinas
Authors: Hu Bifeng , Xie Modian , Zhou Yin , Ni Hanjie , He Xiangyu , Zhu Qian , Geng Yibo , Chen Songchao , Li Hongyi , Shi Zhou
Published: March 2024

An accurate and fine map of soil organic carbon (SOC) plays a vital role in understanding the global carbon cycle and achieving soil carbon sequestration potential. Although global and national maps of SOC are already available with various spatial resolutions, limited sample size, and relative coarse resolution hinder its accuracy and application in local regions. Here, we collected 13,424 soil samples and information of 45 environmental covariates from cropland in Jiangxi Province, Southern China during 2012 and 2013. Then, the optimal covariates were selected by a recursive feature elimination algorithm for mapping SOC. After that, we deployed the random forest (RF) to produce a fine map (30 m) of SOC in the cropland of Jiangxi Province and 100 times bootstrapping was performed to calculate the prediction uncertainty. Finally, we determined the impacts of various covariates on SOC variability using RF and partial least squares structural equation modeling. Our results showed that compared with the predictive model without soil management information, introducing soil management information improved the predictability of SOC with an increase in R2 by 7.35% (0.73 vs 0.68) and decrease in RMSE by 7.03% (2.91 vs 3.13 g kg-1). Our results well estimated the uncertainty of the predicted result with a PICP of 0.91 for a 90% prediction interval. Soil properties and soil management activities make the largest contribution for modelling SOC. Specifically, the total nitrogen content, straw return amount, total potassium content, and multi-resolution valley bottom flatness were found as the most important factors for mapping SOC in the cropland of our study area. Overall, this study deepened our knowledge of the variation of SOC and also emphasizes that incorporating soil management information could help us to achieve more accurate predictions of SOC.
Impact of inconsistency of multiple land use/land cover products on permafrost modeling on the Tibetan Plateau
Authors: Pan Yongjie , Xu Xiaoming
Published: March 2024

The Tibetan Plateau (TP), with an average elevation of over 4000m, has the largest area of permafrost in the mid-latitudes. With global warming, the degradation of permafrost is expected to intensify, which in turn will have significant impacts on regional ecology, hydrology and infrastructure engineering. Accurately modeling the extent of permafrost and permafrost change is now a crucial challenge for climate change research and climate modeling in this region. The simulation of permafrost extent in climate models and land surface models is influence by various factors, including atmospheric forcing, land surface conditions, soil conditions and deficiencies in the model schemes. Land use and land cover (LULC), is a crucial component of surface characteristics in land surface models, is directly affecting the surface energy balance and permafrost simulation results. To investigate the effect of LULC uncertainty on permafrost simulation, we conducted simulation experiments on the TP using the Community Land Model, version 5 (CLM5) with five high-resolution LULC products in this study. Firstly, we evaluated the simulation results using shallow soil temperature data and deep borehole data at several sites. The results show that the model performs well in simulating shallow soil temperatures and deep soil temperature profiles. The effect of different land use products on the shallow soil temperature and deep soil temperature contours is not obvious due to the small differences in land use products at these sites. Although there is little difference in the simulating results of different land use products when compared to the permafrost distribution map, the differences are noticeable for the simulation of the active layer. Land cover had a greater impact on soil temperature simulations in regions with larger land use inconsistency, such as at the junction of bare soil and grassland in the northwestern part of the TP, as well as in the southeast region with complex topography. The main way in which this effect occurs is that land cover affects the net surface radiation, which in turn causes differences in soil temperature simulations. In addition, we discuss other factors affecting permafrost simulation results and point out that increasing the model plant function types as well as carefully selecting LULC products is one of the most important ways to improve the simulation performance of land-surface models in permafrost regions.