Low-cost GNSS receivers have recently been gaining reliability as good candidates for ionospheric studies. In line with these gains are genuine concerns about improving the performance of these receivers. In this work...Low-cost GNSS receivers have recently been gaining reliability as good candidates for ionospheric studies. In line with these gains are genuine concerns about improving the performance of these receivers. In this work, we present a comprehensive investigation of the performances of two antennas(the u-blox ANN-MB and the TOPGNSS TOP-106) used on a low-cost GNSS receiver known as the u-blox ZED-F9P. The two antennas were installed on two identical and co-located u-blox receivers. Data used from both receivers cover the period from January to June 2022. Results from the study indicate that the signal strengths are dominantly greater for the receiver with the TOPGNSS antenna than for the receiver with the ANN-MB antenna, implying that the TOPGNSS antenna is better than the ANN-MB antenna in terms of providing greater signal strengths. Summarily, the TOPGNSS antenna also performed better in minimizing the occurrence of cycle slips on phase TEC measurements. There are no conspicuous differences between the variances(computed as 5-min standard deviations) of phase TEC measurements for the two antennas, except for a period around May-June when the TOPGNSS gave a better performance in terms of minimizing the variances in phase TEC. Remarkably, the ANN-MB antenna gave a better performance than the TOPGNSS antenna in terms of minimizing the variances in pseudorange TEC for some satellite observations. For precise horizontal(North and East) positioning, the receiver with the TOPGNSS antenna gave better results, while the receiver with the ANN-MB antenna gave better vertical(Up) positioning. The errors for the receivers of both antennas are typically within about 5 m(the monthly mean was usually smaller than 1 m) in the horizontal direction and within about 10 m(the monthly mean was usually smaller than 4 m) in the vertical direction.展开更多
The Essential Climate Variables(ECVs),such as the atmospheric thermodynamic state variables and greenhouse gases,play an important role in the atmosphere physical processes and global climate change.Given the need of ...The Essential Climate Variables(ECVs),such as the atmospheric thermodynamic state variables and greenhouse gases,play an important role in the atmosphere physical processes and global climate change.Given the need of improvements in existing ground-based and satellite observations to successfully deliver atmosphere and climate benchmark data and reduce data ambiguity,the Climate and Atmospheric Composition Exploring Satellites mission(CACES)was proposed and selected as a candidate mission of the Strategic Priority Research Program of Chinese Academy Science(SPRPCAS).This paper presents an overview of the key scientific questions and responses of EC Vs in relation to global change;the principles,algorithms,and payloads of microwave occultation using centimeter and millimeter wave signals between low Earth orbit satellites(LEO-LEO microwave occultation,LMO)as well as of the LEO-LEO infrared-laser occultation(LIO);the CACES mission with its scientific objectives,mission concept,spacecraft and instrumentation.展开更多
In this paper we present an approach for forecasting the imminent regional seismic activity by using geomagnetic data and Earth tide data. The time periods of seismic activity are the time periods around the Sun-Moon ...In this paper we present an approach for forecasting the imminent regional seismic activity by using geomagnetic data and Earth tide data. The time periods of seismic activity are the time periods around the Sun-Moon extreme of the diurnal average value of the tide vector module. For analyzing the geomagnetic data behaviour we use diurnal standard deviation of geomagnetic vector components F (North, East, Down) for calculating the time variance GeomagSignal. The Sun storm influence is avoided by using data for daily A-indexes (published by NOAA). The precursor signal for forecasting the incoming regional seismic activity is a simple function of the present and previous day GeomagSignal and A-indexes values. The reliability of the geomagnetic “when, regional” precursor is demonstrated by using statistical analysis of day difference between the times of “predicted” and occurred earthquakes. The base of the analysis is a natural hypothesis that the “predicted” earthquake is the one whose surface energy density in the monitoring point is bigger than the energy densities of all occurred earthquakes in the same period and region. The reliability of the approach was tested using the INTERMAGNET stations data located in Bulgaria, Panagurishte, PAG (Jan 1, 2008-Jan 29, 2014), Romania, Surlari, SUA (Jan 1, 2008-Jan 27, 2014), Italy, L’Aquila, AQU (Jan 1, 2008-May 30, 2013) in the time of EU IRSES BlackSeaHazNet (2011-2014) project. The steps of program for solving the “when, where and how” earthquake prediction problem are shortly described.展开更多
基于淮河流域的地形、岩石地质类型等空间分布特征，对陆面—水文耦合模式CLHMS1.0（Coupled Land Surface？Hydrological Model version 1.0）的河道曼宁糙率系数、水力传导度两个关键参数进行了率定；在此基础上，通过基于CLHMS1.0的...基于淮河流域的地形、岩石地质类型等空间分布特征，对陆面—水文耦合模式CLHMS1.0（Coupled Land Surface？Hydrological Model version 1.0）的河道曼宁糙率系数、水力传导度两个关键参数进行了率定；在此基础上，通过基于CLHMS1.0的多组敏感性试验，分析了河道曼宁糙率系数、水力传导度对CLHMS1.0模拟淮河流域水文过程的影响。研究结果表明，淮河流域上游王家坝子流域曼宁糙率系数的减小，可以显著提高模式对王家坝水文控制站上游模拟的水流流速，减小了模式对王家坝洪峰来临时间模拟偏迟的误差；依据淮河不同子流域的岩石地质类型选定更为合理的水力传导度参数后，模式对淮河流域河道流量等水文过程的模拟更为准确。利用参数率定后的CLHMS1.0对淮河流域1980～1987年逐日水文过程进行了模拟，与观测实况比较结果表明，采用了新的河道曼宁糙率系数和水力传导度参数后，模式对淮河流域逐日水文过程的模拟能力显著提高，且可以更合理地模拟出地表产流和地下水补给对流域河道流量的相对贡献。展开更多
Persistent heavy rainfall events in South China can be divided into pre-and post-monsoon-onset events according to the onset of the South China Sea Summer Monsoon. In this study, daily rainfall data from 174 stations ...Persistent heavy rainfall events in South China can be divided into pre-and post-monsoon-onset events according to the onset of the South China Sea Summer Monsoon. In this study, daily rainfall data from 174 stations in South China and daily NCEP/NCAR reanalysis data are used to investigate pre-monsoon-onset events. The synoptic characteristics of pre-monsoon-onset heavy rainfall events are examined in detail. It is found that 21 heavy rainfall cases happened in the pre-monsoon period between 1961 and 2005. Among them, more than 60% of the events happened under a saddle pattern circulation. Using a case study, the role of the saddle field is investigated and slantwise vorticity development （SVD） theory is applied to diagnose the mechanisms for heavy rainfall development. It is found that a low-level saddle field and low-level jets result in the accumulation of warm moist air in the lower troposphere over South China and provide the necessary unstable conditions for heavy rainfall development. The existence of a saddle field plays an important role in maintaining these unstable conditions. The slantwise movement of the isentropic surface over South China can increase local vorticity and lead to strong vertical motion, which then triggers heavy rainfall.展开更多
Finite-difference methods with high-order accuracy have been utilized to improve the precision of numerical solution for partial differential equations. However, the computation cost generally increases linearly with ...Finite-difference methods with high-order accuracy have been utilized to improve the precision of numerical solution for partial differential equations. However, the computation cost generally increases linearly with increased order of accuracy. Upon examination of the finite-difference formulas for the first-order and second-order derivatives, and the staggered finite-difference formulas for the first-order derivative, we examine the variation of finite-difference coefficients with accuracy order and note that there exist some very small coefficients. With the order increasing, the number of these small coefficients increases, however, the values decrease sharply. An error analysis demonstrates that omitting these small coefficients not only maintain approximately the same level of accuracy of finite difference but also reduce computational cost significantly. Moreover, it is easier to truncate for the high-order finite-difference formulas than for the pseudospectral for- mulas. Thus this study proposes a truncated high-order finite-difference method, and then demonstrates the efficiency and applicability of the method with some numerical examples.展开更多
Passive seismic techniques have revolutionarised seismology, leading for example to increased resolution in surface wave tomography, to the possibility to monitor changes in the propagation medium, and to many new pro...Passive seismic techniques have revolutionarised seismology, leading for example to increased resolution in surface wave tomography, to the possibility to monitor changes in the propagation medium, and to many new processing strategies in seismic exploration. Here we review applications of the new techniques to a very particular dataset, namely data from the Apollo 17 lunar network. The special conditions of the lunar noise environment are investigated, illustrating the interplay between the properties of the noise and the ability to reconstruct Green＇s functions. With a dispersion analysis of reconstructed Rayleigh waves new information about the shallow shear velocity structure of the Moon are obtained. Passive image interferometry is used to study the effect of temperature changes in the subsurface on the seismic velocities providing direct observation of a dynamic process in the lunar environment. These applications highlight the potential of passive techniques for terrestrial and planetary seismology.展开更多
Subsurface fluid injections can disturb the effective stress regime by elevating pore pressure and potentially reactivate faults and fractures.Laboratory studies indicate that fracture rheology and permeability in suc...Subsurface fluid injections can disturb the effective stress regime by elevating pore pressure and potentially reactivate faults and fractures.Laboratory studies indicate that fracture rheology and permeability in such reactivation events are linked to the roughness of the fracture surfaces.In this study,we construct numerical models using discrete element method(DEM)to explore the influence of fracture surface roughness on the shear strength,slip stability,and permeability evolution during such slip events.For each simulation,a pair of analog rock coupons(three-dimensional bonded quartz particle analogs)representing a mated fracture is sheared under a velocity-stepping scheme.The roughness of the fracture is defined in terms of asperity height and asperity wavelength.Results show that(1)Samples with larger asperity heights(rougher),when sheared,exhibit a higher peak strength which quickly devolves to a residual strength after reaching a threshold shear displacement;(2)These rougher samples also exhibit greater slip stability due to a high degree of asperity wear and resultant production of wear products;(3)Long-term suppression of permeability is observed with rougher fractures,possibly due to the removal of asperities and redistribution of wear products,which locally reduces porosity in the dilating fracture;and(4)Increasing shear-parallel asperity wavelength reduces magnitudes of stress drops after peak strength and enhances fracture permeability,while increasing shear-perpendicular asperity wavelength results in sequential stress drops and a delay in permeability enhancement.This study provides insights into understanding of the mechanisms of frictional and rheological evolution of rough fractures anticipated during reactivation events.展开更多
The Earth is the only body in the solar system for which significant observational constraints are accessible to such a degree that they can be used to discriminate between competing models of Earth's tectonic evo...The Earth is the only body in the solar system for which significant observational constraints are accessible to such a degree that they can be used to discriminate between competing models of Earth's tectonic evolution.It is a natural tendency to use observations of the Earth to inform more general models of planetary evolution.However,our understating of Earth's evolution is far from complete.In recent years,there has been growing geodynamic and geochemical evidence that suggests that plate tectonics may not have operated on the early Earth,with both the timing of its onset and the length of its activity far from certain.Recently,the potential of tectonic bi-stability(multiple stable,energetically allowed solutions)has been shown to be dynamically viable,both from analytical analysis and through numeric experiments in two and three dimensions.This indicates that multiple tectonic modes may operate on a single planetary body at different times within its temporal evolution.It also allows for the potential that feedback mechanisms between the internal dynamics and surface processes(e.g.,surface temperature changes driven by long term climate evolution),acting at different thermal evolution times,can cause terrestrial worlds to alternate between multiple tectonic states over giga-year timescales.The implication within this framework is that terrestrial planets have the potential to migrate through tectonic regimes at similar‘thermal evolution times'(e.g.,points were they have a similar bulk mantle temperature and energies),but at very different'temporal times'(time since planetary formation).It can be further shown that identical planets at similar stages of their evolution may exhibit different tectonic regimes due to random variations.Here,we will discuss constraints on the tectonic evolution of the Earth and present a novel framework of planetary evolution that moves toward probabilistic arguments based on general physical principals,as opposed to particular rheologies,and incorporates the potential of tectonic regime transitions and multiple tectonics states being viable at equivalent physical and chemical conditions.展开更多
In addition to the occurrence of atmospheric blocking, the climatology of the characteristics of blocking events, including duration, intensity, and extension, in four seasons over the Northern Hemisphere was analyzed...In addition to the occurrence of atmospheric blocking, the climatology of the characteristics of blocking events, including duration, intensity, and extension, in four seasons over the Northern Hemisphere was analyzed for the period 1950-2009. The seasonality and spatial variations of these characteristics were studied according to their longitudinal distributions. In general, there were sharp discrepancies in the blocking characteristics between winter and summer, and these differences were more prominent over the Atlantic and Pacific Oceans. The blocking not only occurred more frequently but also underwent stronger amplification in winter; likewise, the blocking occurred less frequently and underwent weaker amplification in summer. There are very strong interrelationships among different blocking characteristics, suggesting that they are supported by similar physical factors. In addition, the relationship between blocking over different regions and East Asian circulation was examined. Ural-Siberia is a major blocking formation region in all seasons that may exert a downstream impact on East Asia. The impact is generally weak in summer, which is due to its lower intensity and smaller duration. However, the extratropical circulation over East Asia in summer can be disturbed persistently by the frequent occurrence of blocking over the Asian continent or the Western Pacific. In particular, the blocking frequency over the Western Pacific significantly increased during the study period. This climatological information provides a background for studying the impact of blocking on East Asian circulation under both present and future climate conditions.展开更多
The Graz Ionospheric Flux Tube Simulations （GIFTS） has been improved. The improved GIFTS model was used to numerically investigate the energy particle precipitation on the distribution of electron density in the ion...The Graz Ionospheric Flux Tube Simulations （GIFTS） has been improved. The improved GIFTS model was used to numerically investigate the energy particle precipitation on the distribution of electron density in the ionospheric cusp foot-point region under conditions of large plasma convection during magnetic storm. After including the effects of low energy incident particles, the ionospheric electron densities increase remarkably above altitude of -250 km, showing a peak at about 350 km. The percent enhancements of electron densities increase gradually with altitude, exceed- ing 60% near the upper boundary of the calculation. The calculated ionospheric F2-peak was remarkably enhanced and lifted up by the incident low energy electrons.展开更多
New and compiled detrital zircon U-Pb ages from the southern Neoproterozoic-Cambrian Ribeira Belt,SE Brazil,demonstrate Laurentian affinity of the Embu Terrane which is statistically distinct from the adjoining Apia&#...New and compiled detrital zircon U-Pb ages from the southern Neoproterozoic-Cambrian Ribeira Belt,SE Brazil,demonstrate Laurentian affinity of the Embu Terrane which is statistically distinct from the adjoining Apiaíand São Roque terranes with cratonic affinity(e.g.,São Francisco Craton).Zircon provenance results indicate that the type-area of the Embu Terrane is dominated by detrital zircon age modes at ca.1200 Ma,1400 Ma,and 1800 Ma,with maximum depositional age of ca.1000 Ma.In contrast,the Apiaíand São Roque terranes are dominated by Paleoproterozoic detrital zircon ages(ca.2200-2000 Ma age dominant component),with maximum depositional ages of ca.1400 Ma and 1750 Ma,respectively.Multidimensional scaling(MDS)analysis of non-parametric similarity measurements on zircon age populations indicates for the first time that the Embu Terrane encompass two statistically distinct detrital zircon age spectra,which is also reflected in the metamorphic zircon age record.The statistical characterization of the Embu Terrane through populational metrics allow a quantitative comparison with surrounding tectonic domains and rock samples classified such as Embu-type.Our results clearly highlight the distinction between the statistically differentiated Embu Terrane from the Apiaíand São Roque terranes,supporting an allochthonous interpretation.In addition,we demonstrate that rocks samples previously classified as Embu-type are significantly dissimilar to the definition of Embu Terrane,failing to support alternative tectonic models(e.g.,intracontinental evolution).Detrital zircon age spectra reveal that the Apiaíand São Roque terranes have similar zircon provenance to domains sourced from the São Francisco Craton,whereas detrital zircon populations from the Embu Terrane have greater affinity with SW Laurentia basins(and their inferred sediment sources),consistent with previous findings.Therefore,we interpret the Embu Terrane as a Rodinia descendant developed along the active margin of the SW Laurentia that collided with the Ribeira Belt during early Neoproterozoic(810-760 Ma).展开更多
Beijing often suffers under heavy smog.During such events which occur mostly in autumn and winter,people are desperate for fresh air.The formation of heavy smog is due to foremost human induced air pollution,but geogr...Beijing often suffers under heavy smog.During such events which occur mostly in autumn and winter,people are desperate for fresh air.The formation of heavy smog is due to foremost human induced air pollution,but geographic and meteorological conditions,especially below a surface inversion,play an important role.We propose to destroy the inversion by pumping air from above the inversion layer to the surface layer to alleviate the severity of the smog.While long-term air quality improvement depends on the reduction of air pollution emission,air pumping may provide relief in the interim for the Beijing citizens.We estimate that an air pumping at a rate 2×10~7m^3s^(–1)can lead to significantly improved air quality in Beijing,due to(1)direct clean air input;(2)increased instability and vertical mixing and(3)a positive radiation-mixing feedback.The pumping requires an energy input of 10 GW,comparable with the energy consumption in Beijing for air conditioning in summer.We propose to use wind energy from Inner Mongolia for the pumping,which has currently an installed wind energy capacity of 70GW.展开更多
基金Centre for Atmospheric Research,Nigeria,for providing the research grant required to conduct this study。
文摘Low-cost GNSS receivers have recently been gaining reliability as good candidates for ionospheric studies. In line with these gains are genuine concerns about improving the performance of these receivers. In this work, we present a comprehensive investigation of the performances of two antennas(the u-blox ANN-MB and the TOPGNSS TOP-106) used on a low-cost GNSS receiver known as the u-blox ZED-F9P. The two antennas were installed on two identical and co-located u-blox receivers. Data used from both receivers cover the period from January to June 2022. Results from the study indicate that the signal strengths are dominantly greater for the receiver with the TOPGNSS antenna than for the receiver with the ANN-MB antenna, implying that the TOPGNSS antenna is better than the ANN-MB antenna in terms of providing greater signal strengths. Summarily, the TOPGNSS antenna also performed better in minimizing the occurrence of cycle slips on phase TEC measurements. There are no conspicuous differences between the variances(computed as 5-min standard deviations) of phase TEC measurements for the two antennas, except for a period around May-June when the TOPGNSS gave a better performance in terms of minimizing the variances in phase TEC. Remarkably, the ANN-MB antenna gave a better performance than the TOPGNSS antenna in terms of minimizing the variances in pseudorange TEC for some satellite observations. For precise horizontal(North and East) positioning, the receiver with the TOPGNSS antenna gave better results, while the receiver with the ANN-MB antenna gave better vertical(Up) positioning. The errors for the receivers of both antennas are typically within about 5 m(the monthly mean was usually smaller than 1 m) in the horizontal direction and within about 10 m(the monthly mean was usually smaller than 4 m) in the vertical direction.
基金Supported by the National Natural Science Foundation of China(41775034,41606206)the Strategic Priority Research Program of Chinese Academy of Sciences(XDA15012300)。
文摘The Essential Climate Variables(ECVs),such as the atmospheric thermodynamic state variables and greenhouse gases,play an important role in the atmosphere physical processes and global climate change.Given the need of improvements in existing ground-based and satellite observations to successfully deliver atmosphere and climate benchmark data and reduce data ambiguity,the Climate and Atmospheric Composition Exploring Satellites mission(CACES)was proposed and selected as a candidate mission of the Strategic Priority Research Program of Chinese Academy Science(SPRPCAS).This paper presents an overview of the key scientific questions and responses of EC Vs in relation to global change;the principles,algorithms,and payloads of microwave occultation using centimeter and millimeter wave signals between low Earth orbit satellites(LEO-LEO microwave occultation,LMO)as well as of the LEO-LEO infrared-laser occultation(LIO);the CACES mission with its scientific objectives,mission concept,spacecraft and instrumentation.
文摘In this paper we present an approach for forecasting the imminent regional seismic activity by using geomagnetic data and Earth tide data. The time periods of seismic activity are the time periods around the Sun-Moon extreme of the diurnal average value of the tide vector module. For analyzing the geomagnetic data behaviour we use diurnal standard deviation of geomagnetic vector components F (North, East, Down) for calculating the time variance GeomagSignal. The Sun storm influence is avoided by using data for daily A-indexes (published by NOAA). The precursor signal for forecasting the incoming regional seismic activity is a simple function of the present and previous day GeomagSignal and A-indexes values. The reliability of the geomagnetic “when, regional” precursor is demonstrated by using statistical analysis of day difference between the times of “predicted” and occurred earthquakes. The base of the analysis is a natural hypothesis that the “predicted” earthquake is the one whose surface energy density in the monitoring point is bigger than the energy densities of all occurred earthquakes in the same period and region. The reliability of the approach was tested using the INTERMAGNET stations data located in Bulgaria, Panagurishte, PAG (Jan 1, 2008-Jan 29, 2014), Romania, Surlari, SUA (Jan 1, 2008-Jan 27, 2014), Italy, L’Aquila, AQU (Jan 1, 2008-May 30, 2013) in the time of EU IRSES BlackSeaHazNet (2011-2014) project. The steps of program for solving the “when, where and how” earthquake prediction problem are shortly described.
基金中国科学院科研装备研制项目(YZ201129)江苏高校优势学科建设工程项目+3 种基金Australian Space Research Program 2(ASRP2)Australian Antarctic Science Grant Program(Project4159)European Space Agency(ESA)project OPSGRAS(4000101628)Austrian National Science Fund(FWF)project BENCHCLIM(P22293-N21)资助
文摘基于淮河流域的地形、岩石地质类型等空间分布特征，对陆面—水文耦合模式CLHMS1.0（Coupled Land Surface？Hydrological Model version 1.0）的河道曼宁糙率系数、水力传导度两个关键参数进行了率定；在此基础上，通过基于CLHMS1.0的多组敏感性试验，分析了河道曼宁糙率系数、水力传导度对CLHMS1.0模拟淮河流域水文过程的影响。研究结果表明，淮河流域上游王家坝子流域曼宁糙率系数的减小，可以显著提高模式对王家坝水文控制站上游模拟的水流流速，减小了模式对王家坝洪峰来临时间模拟偏迟的误差；依据淮河不同子流域的岩石地质类型选定更为合理的水力传导度参数后，模式对淮河流域河道流量等水文过程的模拟更为准确。利用参数率定后的CLHMS1.0对淮河流域1980～1987年逐日水文过程进行了模拟，与观测实况比较结果表明，采用了新的河道曼宁糙率系数和水力传导度参数后，模式对淮河流域逐日水文过程的模拟能力显著提高，且可以更合理地模拟出地表产流和地下水补给对流域河道流量的相对贡献。
基金supported by the National Natural Science Foundation of China under Grant No. 40730951the National Basic Research Program of China (973 Program) under Grant No. 2009CB421404
文摘Persistent heavy rainfall events in South China can be divided into pre-and post-monsoon-onset events according to the onset of the South China Sea Summer Monsoon. In this study, daily rainfall data from 174 stations in South China and daily NCEP/NCAR reanalysis data are used to investigate pre-monsoon-onset events. The synoptic characteristics of pre-monsoon-onset heavy rainfall events are examined in detail. It is found that 21 heavy rainfall cases happened in the pre-monsoon period between 1961 and 2005. Among them, more than 60% of the events happened under a saddle pattern circulation. Using a case study, the role of the saddle field is investigated and slantwise vorticity development （SVD） theory is applied to diagnose the mechanisms for heavy rainfall development. It is found that a low-level saddle field and low-level jets result in the accumulation of warm moist air in the lower troposphere over South China and provide the necessary unstable conditions for heavy rainfall development. The existence of a saddle field plays an important role in maintaining these unstable conditions. The slantwise movement of the isentropic surface over South China can increase local vorticity and lead to strong vertical motion, which then triggers heavy rainfall.
基金supported by China Scholarship Council and partially by the National "863" Program of China under contract No. 2007AA06Z218.
文摘Finite-difference methods with high-order accuracy have been utilized to improve the precision of numerical solution for partial differential equations. However, the computation cost generally increases linearly with increased order of accuracy. Upon examination of the finite-difference formulas for the first-order and second-order derivatives, and the staggered finite-difference formulas for the first-order derivative, we examine the variation of finite-difference coefficients with accuracy order and note that there exist some very small coefficients. With the order increasing, the number of these small coefficients increases, however, the values decrease sharply. An error analysis demonstrates that omitting these small coefficients not only maintain approximately the same level of accuracy of finite difference but also reduce computational cost significantly. Moreover, it is easier to truncate for the high-order finite-difference formulas than for the pseudospectral for- mulas. Thus this study proposes a truncated high-order finite-difference method, and then demonstrates the efficiency and applicability of the method with some numerical examples.
文摘Passive seismic techniques have revolutionarised seismology, leading for example to increased resolution in surface wave tomography, to the possibility to monitor changes in the propagation medium, and to many new processing strategies in seismic exploration. Here we review applications of the new techniques to a very particular dataset, namely data from the Apollo 17 lunar network. The special conditions of the lunar noise environment are investigated, illustrating the interplay between the properties of the noise and the ability to reconstruct Green＇s functions. With a dispersion analysis of reconstructed Rayleigh waves new information about the shallow shear velocity structure of the Moon are obtained. Passive image interferometry is used to study the effect of temperature changes in the subsurface on the seismic velocities providing direct observation of a dynamic process in the lunar environment. These applications highlight the potential of passive techniques for terrestrial and planetary seismology.
基金support provided by United States Department of Energy Grant DE-FE0023354。
文摘Subsurface fluid injections can disturb the effective stress regime by elevating pore pressure and potentially reactivate faults and fractures.Laboratory studies indicate that fracture rheology and permeability in such reactivation events are linked to the roughness of the fracture surfaces.In this study,we construct numerical models using discrete element method(DEM)to explore the influence of fracture surface roughness on the shear strength,slip stability,and permeability evolution during such slip events.For each simulation,a pair of analog rock coupons(three-dimensional bonded quartz particle analogs)representing a mated fracture is sheared under a velocity-stepping scheme.The roughness of the fracture is defined in terms of asperity height and asperity wavelength.Results show that(1)Samples with larger asperity heights(rougher),when sheared,exhibit a higher peak strength which quickly devolves to a residual strength after reaching a threshold shear displacement;(2)These rougher samples also exhibit greater slip stability due to a high degree of asperity wear and resultant production of wear products;(3)Long-term suppression of permeability is observed with rougher fractures,possibly due to the removal of asperities and redistribution of wear products,which locally reduces porosity in the dilating fracture;and(4)Increasing shear-parallel asperity wavelength reduces magnitudes of stress drops after peak strength and enhances fracture permeability,while increasing shear-perpendicular asperity wavelength results in sequential stress drops and a delay in permeability enhancement.This study provides insights into understanding of the mechanisms of frictional and rheological evolution of rough fractures anticipated during reactivation events.
基金supported in part by the Cyberinfrastructure for Computational Research funded by NSF under Grant CNS-0821727the Data Analysis and Visualization Cyberinfrastructure funded by NSF under grant OCI-0959097Rice University
文摘The Earth is the only body in the solar system for which significant observational constraints are accessible to such a degree that they can be used to discriminate between competing models of Earth's tectonic evolution.It is a natural tendency to use observations of the Earth to inform more general models of planetary evolution.However,our understating of Earth's evolution is far from complete.In recent years,there has been growing geodynamic and geochemical evidence that suggests that plate tectonics may not have operated on the early Earth,with both the timing of its onset and the length of its activity far from certain.Recently,the potential of tectonic bi-stability(multiple stable,energetically allowed solutions)has been shown to be dynamically viable,both from analytical analysis and through numeric experiments in two and three dimensions.This indicates that multiple tectonic modes may operate on a single planetary body at different times within its temporal evolution.It also allows for the potential that feedback mechanisms between the internal dynamics and surface processes(e.g.,surface temperature changes driven by long term climate evolution),acting at different thermal evolution times,can cause terrestrial worlds to alternate between multiple tectonic states over giga-year timescales.The implication within this framework is that terrestrial planets have the potential to migrate through tectonic regimes at similar‘thermal evolution times'(e.g.,points were they have a similar bulk mantle temperature and energies),but at very different'temporal times'(time since planetary formation).It can be further shown that identical planets at similar stages of their evolution may exhibit different tectonic regimes due to random variations.Here,we will discuss constraints on the tectonic evolution of the Earth and present a novel framework of planetary evolution that moves toward probabilistic arguments based on general physical principals,as opposed to particular rheologies,and incorporates the potential of tectonic regime transitions and multiple tectonics states being viable at equivalent physical and chemical conditions.
基金supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region (Grant No. 104410)a grant from Germany/Hong Kong Joint Research Scheme (Grant No.G HK023/09)The figures were prepared by the NCAR Command Language (Version 6.0.0) [Software] (2012),Boulder,Colorado:UCAR/NCAR/CLSL/VETS
文摘In addition to the occurrence of atmospheric blocking, the climatology of the characteristics of blocking events, including duration, intensity, and extension, in four seasons over the Northern Hemisphere was analyzed for the period 1950-2009. The seasonality and spatial variations of these characteristics were studied according to their longitudinal distributions. In general, there were sharp discrepancies in the blocking characteristics between winter and summer, and these differences were more prominent over the Atlantic and Pacific Oceans. The blocking not only occurred more frequently but also underwent stronger amplification in winter; likewise, the blocking occurred less frequently and underwent weaker amplification in summer. There are very strong interrelationships among different blocking characteristics, suggesting that they are supported by similar physical factors. In addition, the relationship between blocking over different regions and East Asian circulation was examined. Ural-Siberia is a major blocking formation region in all seasons that may exert a downstream impact on East Asia. The impact is generally weak in summer, which is due to its lower intensity and smaller duration. However, the extratropical circulation over East Asia in summer can be disturbed persistently by the frequent occurrence of blocking over the Asian continent or the Western Pacific. In particular, the blocking frequency over the Western Pacific significantly increased during the study period. This climatological information provides a background for studying the impact of blocking on East Asian circulation under both present and future climate conditions.
基金the National Natural Science Foundation o China(40404015, 40390150)the Open Foundation of the Key Laboratory o Geospace Environment and Geodesy of Ministry of Education
文摘The Graz Ionospheric Flux Tube Simulations （GIFTS） has been improved. The improved GIFTS model was used to numerically investigate the energy particle precipitation on the distribution of electron density in the ionospheric cusp foot-point region under conditions of large plasma convection during magnetic storm. After including the effects of low energy incident particles, the ionospheric electron densities increase remarkably above altitude of -250 km, showing a peak at about 350 km. The percent enhancements of electron densities increase gradually with altitude, exceed- ing 60% near the upper boundary of the calculation. The calculated ionospheric F2-peak was remarkably enhanced and lifted up by the incident low energy electrons.
基金the Australian Research Council(grant FL160100168 to PAC)the CNPq fellowship(307732/2019-3)+2 种基金FAPESP(grant 2018/10012-0)CNPq(grants 305701/2019-3,443439/2014-1)FAPESP(grants 01/13457-1,06/01327-0).
文摘New and compiled detrital zircon U-Pb ages from the southern Neoproterozoic-Cambrian Ribeira Belt,SE Brazil,demonstrate Laurentian affinity of the Embu Terrane which is statistically distinct from the adjoining Apiaíand São Roque terranes with cratonic affinity(e.g.,São Francisco Craton).Zircon provenance results indicate that the type-area of the Embu Terrane is dominated by detrital zircon age modes at ca.1200 Ma,1400 Ma,and 1800 Ma,with maximum depositional age of ca.1000 Ma.In contrast,the Apiaíand São Roque terranes are dominated by Paleoproterozoic detrital zircon ages(ca.2200-2000 Ma age dominant component),with maximum depositional ages of ca.1400 Ma and 1750 Ma,respectively.Multidimensional scaling(MDS)analysis of non-parametric similarity measurements on zircon age populations indicates for the first time that the Embu Terrane encompass two statistically distinct detrital zircon age spectra,which is also reflected in the metamorphic zircon age record.The statistical characterization of the Embu Terrane through populational metrics allow a quantitative comparison with surrounding tectonic domains and rock samples classified such as Embu-type.Our results clearly highlight the distinction between the statistically differentiated Embu Terrane from the Apiaíand São Roque terranes,supporting an allochthonous interpretation.In addition,we demonstrate that rocks samples previously classified as Embu-type are significantly dissimilar to the definition of Embu Terrane,failing to support alternative tectonic models(e.g.,intracontinental evolution).Detrital zircon age spectra reveal that the Apiaíand São Roque terranes have similar zircon provenance to domains sourced from the São Francisco Craton,whereas detrital zircon populations from the Embu Terrane have greater affinity with SW Laurentia basins(and their inferred sediment sources),consistent with previous findings.Therefore,we interpret the Embu Terrane as a Rodinia descendant developed along the active margin of the SW Laurentia that collided with the Ribeira Belt during early Neoproterozoic(810-760 Ma).
基金supported by the National Natural Science Foundation of China(Grant No.91537211)
文摘Beijing often suffers under heavy smog.During such events which occur mostly in autumn and winter,people are desperate for fresh air.The formation of heavy smog is due to foremost human induced air pollution,but geographic and meteorological conditions,especially below a surface inversion,play an important role.We propose to destroy the inversion by pumping air from above the inversion layer to the surface layer to alleviate the severity of the smog.While long-term air quality improvement depends on the reduction of air pollution emission,air pumping may provide relief in the interim for the Beijing citizens.We estimate that an air pumping at a rate 2×10~7m^3s^(–1)can lead to significantly improved air quality in Beijing,due to(1)direct clean air input;(2)increased instability and vertical mixing and(3)a positive radiation-mixing feedback.The pumping requires an energy input of 10 GW,comparable with the energy consumption in Beijing for air conditioning in summer.We propose to use wind energy from Inner Mongolia for the pumping,which has currently an installed wind energy capacity of 70GW.
基金the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)via the Collaborative Research Center 806(57444011)Patrick Ludwig and Christian Stepanek received funding from the Helmholtz Climate Initiative REKLIM+3 种基金Christian Stepanek acknowledges funding from the Alfred Wegener Institute’s Research Programmesupported by Basic Science Center for Tibetan Plateau Earth System(BSCTPES)the National Natural Science Foundation of China(41988101)All computations were done at the German Climate Computing Center(DKRZ,Project 965)。
