bluuebunny/crossref_metadata_2025_split huggingface dataset:
Upward‐Doming Zones of Gas Hydrate and Free Gas at the Bases of Gas Chimneys, New Zealand's Hikurangi Margin
Authors: Crutchley G. J. , Mountjoy J. J. , Hillman J. I. T. , Turco F. , Watson S. , Flemings P. B. , Davy B. , Woelz S. , Gorman A. R. , Bialas J. 
Published: September 2021

AbstractFocused gas migration through the gas hydrate stability zone in vertical gas conduits is a global phenomenon. The process can lead to concentrated gas hydrate formation and seafloor gas seepage, which influences seafloor biodiversity and ocean biogeochemistry. However, much is unknown about how gas and gas hydrate co‐exist within and around gas conduits. We present seismic imaging of the gas hydrate system beneath a four‐way closure anticlinal ridge at New Zealand's southern Hikurangi subduction margin. Gas has accumulated beneath the base of gas hydrate stability to a thickness of up to ∼240 m, which has ultimately led to hydraulic fracturing and propagation of a vertical gas conduit to the seafloor. Despite the existence of an array of normal faults beneath the ridge, these structures are not exploited as long‐range gas flow conduits. Directly beneath the conduit, and extending upward from the regional base of gas hydrate stability, is a broad zone characterized by both negative‐ and positive‐polarity reflections. We interpret this zone as a volume of sediment hosting both gas hydrate and free gas, that developed due to partial gas trapping beneath a mass transport deposit. Similar highly reflective zones have been identified at the bases of other gas conduits, but they are not intrinsic to all gas conduits through gas hydrate systems. We suggest that pronounced intervening sealing units within the gas hydrate stability zone determine whether or not they form.
Laboratory Measurements of the Impact of Fracture and Fluid Properties on the Propagation of Krauklis Waves
Authors: Cao Haitao , Nakagawa Seiji , Askari Roohollah 
Published: September 2021

AbstractThe Krauklis wave is a slow dispersive wave, generated in fluid‐filled fractures. By analyzing the resonant frequency and quality factor of the Krauklis wave, the fracture dimension and fluid properties can be estimated. However, the accuracy of the estimation of fracture dimension and fluid properties depends on deciphering factors affecting the Krauklis wave such as fluid viscosity, fracture geometry, fracture compliance, and stiffness ratio, some of which have not been experimentally studied yet. We have developed an experimental apparatus to study the Krauklis wave within a trilayer model consisting of a pair of aluminum plates and a mediating viscous fluid layer. We utilize a piezoelectric source and miniature pressure transducers in our measurements. To evaluating the effects of the fracture aperture and fluid viscosity, we examine the impact of complex and realistic fracture geometry by introducing spatially varying aperture, surface roughness, and compliant partial surface contact provided by springs. The phase velocity, resonant frequencies, and quality factors (a) increase with the expansion of fracture aperture and (b) decrease with the increase of the fluid viscosity. Additionally, (c) phase velocity, resonant frequencies, and attenuation decrease with the increase of mechanical compliance. Furthermore, rough and wedge‐shaped fracture surfaces tend to slow down the Krauklis wave. Since the Krauklis wave is used by different disciplines such as volcanology, glaciology, and the petroleum industry to characterize fracture dimensions and properties of the fluids involved, our experimental findings can be used as a benchmark to develop comprehensive theoretical models to better interpret the Krauklis waves.
Numerical Simulation on the Effects of the Horizontal Charge Distribution on Lightning Types and Behaviors
Authors: Xu Dewang , Tan Yongbo , Zheng Tianxue , Lin Hui , Shi Zheng , Lei Yinan , Liu Minzhi , Wang Haichao , Yu Junhao 
Published: September 2021

AbstractPrevious studies have generally acknowledged that lightning propagation behaviors and lightning types are closely related to the unbalanced charge amount and vertical stratification of charge structure. In this study, the total charge amount remains nearly balanced (±5%) between the adjacent charge regions where discharges initiate to avoid the interference of a total charge imbalance. Significant influences on the leader propagation tendency and lightning type are revealed by investigating different horizontal charge distribution features emphasizing on the effects of the charge distribution uniformity and the relative position of the high‐density charge center. Sensitivity experiments are performed with a two‐dimensional stochastic discharge model and demonstrate the following. Under a symmetric charge distribution, the more uniform charge distribution is conducive for leaders propagate horizontally; the charge being more compact in the central zone is favorable for vertical extension of leaders. Under an asymmetric charge distribution, a horizontal shift of high‐density charge center is conducive to the extension of leaders in the offset direction. Different charge distributions will change the electrical energy of charge regions resulting in various lightning behaviors. Various charge distributions provide favorable conditions for some lightning flashes (including positive cloud‐to‐ground flashes [PCG], “bolt‐from‐the‐blue” [BFB] flashes and gigantic jets). PCGs are favorably triggered with the more compact upper positive charge (P) and more uniform middle negative charge (N), and BFB discharges can be triggered between the P and N regions when the high‐density charge center in the P region is horizontally shifted. A possible method is provided to explain various lightning behaviors.
Changes in Unevenness of Wet‐Day Precipitation Over China During 1961–2020
Authors: Han Jingya , Miao Chiyuan , Duan Qingyun , Wu Jingwen , Gou Jiaojiao , Zheng Haiyan 
Published: September 2021

AbstractPrecipitation falls unevenly in space and time, which has significant consequences for human society and natural ecosystems. Based on 2,134 gauged observations during 1961–2020 and historical simulations of 14 models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6), we analyze precipitation unevenness over China in terms of the spatiotemporal distribution of wet days (>1 mm) and wet‐day precipitation amount throughout the year. We also explore precipitation extremes related to the unevenness. Spatially, precipitation shows medium unevenness in China. Temporally, the unevenness in distribution of wet days increases from southeast (generally humid) to northwest (generally arid). This temporal unevenness weakened in large parts of western China during 1991–2020 relative to 1961–1990. As for precipitation amount, the distribution of precipitation that falls on wet days is more uneven in water‐limited regions compared with humid regions. Associated with this unevenness, between 1961 and 2020, the top 50% of annual precipitation fell in approximately the 12 wettest days, and the maximum 1‐day precipitation for the year contributed 10% on average to annual precipitation. The period 1991–2020 shows overall greater unevenness in eastern China and less unevenness in western China relative to the first 30 years. Multimodel ensemble means of CMIP6 simulations agree with the basic spatial pattern of observations, while underestimating the magnitude of temporal unevenness of precipitation. If these regional differences in precipitation unevenness were to persist over time, this would likely create some new challenges for water resource management in these areas, e.g., flash drought.
Description of Dust Emission Parameterization in CAS‐ESM2 and Its Simulation of Global Dust Cycle and East Asian Dust Events
Authors: Wu Chenglai , Lin Zhaohui , Liu Xiaohong , Ji Duoying , Zhang He , Li Chao , Lin Guangxing 
Published: September 2021

AbstractThe dust emission parameterization in the Chinese Academy of Sciences Earth System Model version 2 (CAS‐ESM2) is described with emphasis on the implementation process and simulations of global dust cycle and East Asia dust event statistics. The parameterization is based on the scheme of Shao (2004; http://doi.org/10.1029/2003JD004372) which considers two major dust emission mechanisms, namely, saltation bombardment and aggregation disintegration. Shao (2004; http://doi.org/10.1029/2003JD004372) scheme was well tested against field observations and has been widely used in regional dust modeling. Here this scheme is implemented into a global climate model for the first time and thus provides an independent solution for simulating global dust emissions. With this scheme, CAS‐ESM2 reasonably simulates the main dust emission regions in the Earth and reproduces the observations of dust deposition flux and surface dust concentrations at most stations. Compared to the synoptic records of dust events, the model also captures the general patterns and seasonal variations of dust activities in East Asia. However, the model underestimates the frequency of strong dust events (instantaneous surface dust concentrations >1,000 μg m−3) due to the weaker surface winds simulated by the model. The model tends to simulate much weaker and longer‐lasting dust events in Eastern Sources (35–49°N, 94–126.5°E) of northern China, suggesting the weaker and slower‐moving synoptic weather systems associated with dust events in the model. Overall CAS‐ESM2 performs well in simulating the key aspects of global dust distribution and East Asian dust events, yet some biases remain to be improved.
Water Use in the Landscape: A Comparison of Water Quality and Irrigation Technologies on Behavior
Authors: Lee Jonathan M. , Taylor Laura O. , Berglund Emily Z. 
Published: September 2021

AbstractReclaimed wastewater for outdoor irrigation purposes is an effective tool for conserving potable water sources and reducing effluent discharge from wastewater treatment facilities. Despite its “green” attributes, we find outdoor watering behavior that is consistent with households treating reclaimed water as a lower quality substitute to potable water for outdoor residential irrigation. Using unique microdata, we estimate the demand for outdoor water and find that after controlling for differences in irrigation water prices, households using reclaim water and households without automatic irrigation systems consume substantially less water in the landscape.
Impacts of Underlying Surface on the Dusty Weather in Central Inner Mongolian Steppe, China
Authors: Bao Chunling , Yong Mei , Bi Lige , Gao Hailin , Li Jun , Bao Yuhai , Gomboludev Purevjav 
Published: September 2021

AbstractDust storms are common in northern China and can adversely affect the environment and human health. The Xilingol grassland is the main source of dust storms in China. However, the impacts of different surface features on dusty weather in the Xilingol League remain unclear. This study analyzed the temporal and spatial variation characteristics of surface features and the corresponding effects on dusty weather using data from 13 meteorological stations, MODIS normalized difference vegetation index (NDVI) data, and soil moisture data collected in Xilingol League from 2005 to 2018. Spatially, the dust outbreak frequency (DOF) of Xilingol League decreased gradually from the western desert steppe to the eastern typical steppe. Temporally, the dust outbreak ratio (DOR) and DOF were highest in spring (March–May), with the highest in April. Dusty weather mostly occur in spring but gradually decreased in this season over the 14‐year period. On the contrary, NDVI and soil moisture increased gradually from the west with less precipitation to the east with more precipitation. And showed fluctuating increasing trends over time. The DOR in Xilingol League was negatively correlated with the NDVI and soil moisture, and with the increase of NDVI and soil moisture from the western desert steppe to the eastern typical steppe and the southern cultivated land, the dust emission threshold also increased. The DOR predicted by Xilingol league in spring was significantly correlated with the actual DOR. Our research can provide specific suggestions for different regions of Xilingol League.
Time Evolution of the Surface Urban Heat Island
Authors: Stewart I. D. , Krayenhoff E. S. , Voogt J. A. , Lachapelle J. A. , Allen M. A. , Broadbent A. M. 
Published: September 2021

AbstractAtmospheric and surface urban heat islands (UHI) originate from common energetic processes, but the status of scientific knowledge on their time evolution is highly disparate. The diurnal cycles of atmospheric UHI are well known based on years of continuous measurements in cities; the cycles of surface UHI, however, cannot be measured continuously or in situ. In this article, we aim to reconcile these differences. We begin with a synthesis of previous work on the diurnal evolution of surface UHI, which leads to a novel but historically minded approach to the research problem. The approach involves a combination of microscale and mesoscale urban climate models, each of which is forced with universally described urban and rural surface parameters and atmospheric profiles. With these models, we produce theoretical time‐temperature curves for the surface UHI that are comparable to the classic curves of atmospheric UHI. This work prompts a critical look at the use of satellite thermal imagery to assess heat islands and heat risks in cities. To that end, we recommend new and more functional definitions of surface temperature. Conceptually, these represent “incomplete” temperatures defined by specific facets of the urban environment.
Modeling Photosynthesis and Exudation in Subtropical Oceans
Authors: Wu Zhen , Dutkiewicz Stephanie , Jahn Oliver , Sher Daniel , White Angelicque , Follows Michael J. 
Published: September 2021

AbstractMarine phytoplankton contributes nearly half of the total primary production on Earth through photosynthesis. Parameterizations of algal photosynthesis commonly employed in global biogeochemical simulations generally fail to capture the observed vertical structure of primary production. Here we examined the consequences of decoupling photosynthesis (carbon fixation) and biosynthesis (biomass building) with accumulation or exudation of excess photosynthate under energy rich conditions in both regional and global models. The results show that the decoupling of these two processes improved the simulated vertical profile of primary production, increased modeled primary production over 30% globally and over 40% in subtropical oceans, improved simulated meridional patterns of particulate C:N:P and increased modeled surface pool of labile/semi‐labile dissolved organic carbon. More generally, these results highlight the importance of exudation, which results from the decoupling of photosynthesis and biosynthesis, as a major physiological process affecting ocean biogeochemistry.
Covariation of Airborne Biogenic Tracers (CO2, COS, and CO) Supports Stronger Than Expected Growing Season Photosynthetic Uptake in the Southeastern US
Authors: Parazoo Nicholas C. , Bowman Kevin W. , Baier Bianca C. , Liu Junjie , Lee Meemong , Kuai Le , Shiga Yoichi , Baker Ian , Whelan Mary E. , Feng Sha , Krol Maarten , Sweeney Colm , Runkle Benjamin R. , Tajfar Elahe , Davis Kenneth J. 
Published: September 2021

AbstractThe Atmospheric Carbon Transport (ACT)‐America Earth Venture mission conducted five airborne campaigns across four seasons from 2016 to 2019, to study the transport and fluxes of Greenhouse gases across the eastern United States. Unprecedented spatial sampling of atmospheric tracers (CO2, carbon monoxide [CO], carbonyl sulfide [COS]) related to biospheric processes offers opportunities to improve our qualitative and quantitative understanding of seasonal and spatial patterns of biospheric carbon uptake. Here, we examine co‐variation of boundary layer enhancements of CO2, CO, and COS across three diverse regions: the crop‐dominated Midwest, evergreen‐dominated South, and deciduous broadleaf‐dominated Northeast. To understand the biogeochemical processes controlling these tracers, we compare the observed co‐variation to simulated co‐variation resulting from model‐ and satellite‐ constrained surface carbon fluxes. We found indication of a common terrestrial biogenic sink of CO2 and COS and secondary production of CO from biogenic sources in summer throughout the eastern US, driven by stomatal conductance. Upper Midwest crops drive CO2 and COS depletion from early to late summer. Northeastern temperate forests drive CO2 and COS depletion in late summer. The unprecedented ACT‐America flask samples uncovered evidence that southern humid temperate forests photosynthesize and absorb CO2 and COS, and emit CO precursors, deep into the growing season. Satellite‐ constrained carbon fluxes capture much of the observed seasonal and spatial variability, but underestimate the magnitude of net CO2 and COS depletion in the South, indicating a stronger than expected net sink of CO2 in late summer. Additional sampling of the South will more accurately constrain underlying biological processes and climate sensitivities governing southern carbon dynamics.
Isolating Detrital and Diagenetic Signals in Magnetic Susceptibility Records From Methane‐Bearing Marine Sediments
Authors: Johnson Joel E. , Phillips Stephen C. , Clyde William C. , Giosan Liviu , Torres Marta E. 
Published: September 2021

AbstractVolume‐dependent magnetic susceptibility (κ) is commonly used for paleoenvironmental reconstructions in both terrestrial and marine sedimentary environments where it reflects a mixed signal between primary deposition and secondary diagenesis. In the marine environment, κ is strongly influenced by the abundance of ferrimagnetic minerals regulated by sediment transport processes. Post‐depositional alteration by H2S, however, can dissolve titanomagnetite, releasing reactive Fe that promotes pyritization and subsequently decreases κ. Here, we provide a new approach for isolating the detrital signal in κ and identifying intervals of diagenetic alteration of κ driven by organoclastic sulfate reduction (OSR) and the anaerobic oxidation of methane (AOM) in methane‐bearing marine sediments offshore India. Using the correlation of a heavy mineral proxy from X‐ray fluorescence data (Zr/Rb) and κ in unaltered sediments, we predict the primary detrital κ signal and identify intervals of decreased κ, which correspond to increased total sulfur content. Our approach is a rapid, high‐resolution method that can identify overprinted κ resulting from pyritization of titanomagnetite due to H2S production in marine sediments. In addition, total organic carbon, total sulfur, and authigenic carbonate δ13C measurements indicate that both OSR and AOM can drive the observed κ loss, but AOM drives the greatest decreases in κ. Overall, our approach can enhance paleoenvironmental reconstructions and provide insight into paleo‐positions of the sulfate‐methane transition zone, past enhancements of OSR or paleo‐methane seepage, and the role of detrital iron oxide minerals on the marine sediment sulfur sink, with consequences influencing the development of chemosynthetic biological communities at methane seeps.
Effect of Semidiurnal Lunar Tides Modulated by Quasi‐2‐Day Wave on Equatorial Electrojet During Three Sudden Stratospheric Warming Events
Authors: Li Yaxian , Chen Gang , Zhang Shaodong , Gong Wanlin , Ma Zheng , Huang Kaiming , Gong Yun 
Published: September 2021

AbstractWe present an analysis of perturbations and wave characteristics in equatorial electrojet (EEJ) and equatorial zonal winds in the mesosphere and lower thermosphere region during three sudden stratospheric warming (SSW) events, based on the wind observations by two meteor radars in Indonesia and geomagnetic field observations in India. During three SSWs, remarkable semidiurnal perturbations occurred in the EEJ, accompanied by the strong 2‐day periodic perturbations simultaneously. The semidiurnal lunar (L2) tidal amplitudes in the EEJ and zonal winds showed the prominent enhancements during the episodes of EEJ perturbations. The time‐period power spectra of L2 tidal amplitudes in both the EEJ and zonal winds presented the obvious and coincident quasi‐2‐day wave (QTDW) enhancements during these periods. Our results first reveal the important contribution of QTDW to the distinctive EEJ perturbations during SSWs, and the semidiurnal lunar tides modulated by QTDW serve as the main forcing agent therein.
Reanalysis of the Ionospheric Total Electron Content Anomalies Around the 2011 Tohoku‐Oki and 2016 Kumamoto Earthquakes: Lack of a Clear Precursor of Large Earthquakes
Authors: Ikuta Ryoya , Oba Ryoto , Kiguchi Daiki , Hisada Tomoya 
Published: September 2021

AbstractWe investigate the veracity of the reports by Iwata and Umeno (2016, https://doi.org/10.1002/2016ja023036) and Iwata and Umeno (2017, https://doi.org/10.1002/2017ja023921), both of which claimed that the observed perturbations in Global Navigation Satellite System (GNSS)‐based ionospheric total electron content (TEC) could serve as a "precursor" of large earthquakes based on correlation analysis. Iwata and Umeno (2016, https://doi.org/10.1002/2016ja023036) defined a spatial correlation of residuals between the observed and predicted TEC time series. They reported that the correlation value is significantly larger before large earthquakes than those observed during non‐earthquake periods. Iwata and Umeno (2017, https://doi.org/10.1002/2017ja023921), who applied the same method to other large earthquake, claimed that the preseismic ionospheric disturbances can be distinguished from other non‐earthquake phenomena based on the small percentage of area where the correlation value exceeds the criterion. They also claimed that the low propagation velocity of the correlation peaks is also a preseismic characteristic. Here we tested their claims using a larger data set. As a result, these three characteristics they claimed to have captured as evidence of earthquake precursors are not significant being frequently observed during normal (nonearthquake) days. In addition to that, the criteria of Iwata and Umeno (2017, https://doi.org/10.1002/2017ja023921) cannot be applied to the large earthquake discussed by Iwata and Umeno (2016, https://doi.org/10.1002/2016ja023036), and vice versa. Therefore, we can find no basis for claiming that they detected precursors to the earthquakes. The calculation procedure of the correlation function shows that the value is more of an indicator that amplifies small variations synchronized between nearby stations, like medium‐scale traveling ionospheric disturbances rather than earthquake precursors.
Latitudinal Beaming of Jupiter's Radio Emissions From Juno/Waves Flux Density Measurements
Authors: Louis C. K. , Zarka P. , Dabidin K. , Lampson P.‐A. , Magalhães F. P. , Boudouma A. , Marques M. S. , Cecconi B. 
Published: September 2021

AbstractThe observations from the Juno spacecraft in polar orbit of Jupiter provide for the first time a complete view of Jupiter's radio emissions from all latitudes. Characterizing the latitudinal distribution of radio emissions' occurrence and intensity is a useful step for elucidating their origin. Here, we analyze for that purpose the first 3 years of observations from the Waves experiment on the Juno spacecraft (mid‐2016 to mid‐2019). Two prerequisites for the construction of the latitudinal distribution of intensities for each Jovian radio component are (a) to work with absolute flux densities and (b) to be able to associate each radio measurement with a specific radio component. Accordingly, we develop a method to convert the Juno/Waves data in flux densities and then we build a catalog of all Jovian radio components over the first 3 years of Juno's orbital mission. From these, we derive occurrence and intensity distributions versus observer's latitude and frequency for each component; these will be the basis for future detailed studies and interpretations of each component's characteristics and origin.