The Mars Orbiter MAGnetometer(MOMAG)is a scientific instrument onboard the orbiter of China’s first mission for Mars—Tianwen-1.Since November 13,2021,it has been recording magnetic field data from the solar wind to ...The Mars Orbiter MAGnetometer(MOMAG)is a scientific instrument onboard the orbiter of China’s first mission for Mars—Tianwen-1.Since November 13,2021,it has been recording magnetic field data from the solar wind to the magnetic pile-up region surrounding Mars.Here we present its in-flight performance and first science results,based on its first one and one-half months’data.Comparing these early MOMAG observations to the magnetic field data in the solar wind from NASA’s Mars Atmosphere and Volatile EvolutioN(MAVEN)mission,we report that the MOMAG magnetic field data are at the same level in magnitude,and describe the same magnetic structures with similar variations in three components.We recognize 158 clear bow shock(BS)crossings in these MOMAG data;their locations match well statistically with the modeled average BS.We also identify and compare five pairs of datasets collected when Tianwen-1’s orbiter and the MAVEN probe made simultaneous BS crossings.These BS crossings confirm the global shape of modeled BS,as well as the south-north asymmetry of the Martian BS.Two cases presented in this paper suggest that the BS is probably more dynamic at flank than near the nose.So far,MOMAG performs well,and provides accurate magnetic field vectors.MOMAG is continuously scanning the magnetic field surrounding Mars.Data from MOMAG’s measurements complement data from MAVEN and will undoubt edly advance our understanding of the plasma environment of Mars.展开更多
Magnetic holes are magnetic depression structures that exist widely in many plasma environments.The magnetic holes with durations of>1 s in the solar wind at Mercury’s orbit have drawn much attention,but the prope...Magnetic holes are magnetic depression structures that exist widely in many plasma environments.The magnetic holes with durations of>1 s in the solar wind at Mercury’s orbit have drawn much attention,but the properties of the magnetic holes with shorter durations are still unclear.Here,we investigate the magnetic holes with durations of 0.1-100 s in the upstream region of Mercury’s bow shock based on observations by the MESSENGER(MErcury Surface,Space ENvironment,GEochemistry,and Ranging)spacecraft.They can be divided into two groups according to the distribution of their duration:small-duration magnetic holes(SDMHs,<0.6 s)and large-duration magnetic holes(LDMHs,>0.6 s).The duration of each group approximately obeys a log-normal distribution with a median of~0.25 s and 3 s,respectively.Approximately 1.7%(32.6%)of the SDMHs(LDMHs)reduce the magnetic field strength by more than 50%.For both groups,some structures have a linear or quasi-linear polarization,whereas others have an elliptical polarization.The magnetic hole events in both groups tend to have a higher rate of occurrence when the interplanetary magnetic field strength is weaker.Their occurrence rates are also affected by Mercury’s foreshock,which can increase(decrease)the occurrence rate of the SDMHs(LDMHs).This finding suggests that Mercury’s foreshock might be one source of the SDMHs and that the foreshock can destroy some LDMHs.These observations suggest that a new group of magnetic holes with durations of<0.6 s exist in the upstream region of Mercury’s bow shock.展开更多
In-flight calibration of the ze ro offset is crucial for ensuring high-precision measure ment of the spaceborne fluxgate magnetomete r.Tianwen-1 is China’s first Mars mission,and its orbiter will re main out of the s...In-flight calibration of the ze ro offset is crucial for ensuring high-precision measure ment of the spaceborne fluxgate magnetomete r.Tianwen-1 is China’s first Mars mission,and its orbiter will re main out of the solar wind for tens of days each year.Previous in-flight calibration methods might not be suitable for this orbiter during such a period.Recently,a new method was proposed by Wang GQ(2022 b),which we refer to as the Wang method Ⅱ for ease of description.Here,we test the performance of this method in the Martian magnetosheath by using magnetic field data measured by the Mars Atmosphere and Volatile EvolutioN(MAVEN) spacecraft.We find that the accuracy of the Wang method Ⅱ is affected by the number of magnetic field subinterval events,the eigenvalues of the minimum variance analysis for each event,and the position of the spacecraft in the magnetosheath.The estimated zero offset varies over a period of~27 days and has a 57.3% probability of accuracy within 2.0 nT.After being smoothed with a temporal window of 27 days,the ze ro offset has a 48.4%(99.3%) probability of accuracy within 1.0(2.0) nT.Our tests suggest that the Wang method Ⅱ provides an option for the Tianwen-1 orbiter to perform in-flight calibration when the orbiter remains out of the solar wind for an extended pe riod of time.展开更多
We report a representative concurrent event of four wave modes at L≈5.0,including electrostatic electron cyclotron harmonic(ECH)waves,exohiss,magnetosonic(MS)waves,and electromagnetic ion cyclotron(EMIC)waves,based o...We report a representative concurrent event of four wave modes at L≈5.0,including electrostatic electron cyclotron harmonic(ECH)waves,exohiss,magnetosonic(MS)waves,and electromagnetic ion cyclotron(EMIC)waves,based on the observations from Van Allen Probe A on October 15,2015.The diffusion coefficients induced by these waves are calculated by using both the Full Diffusion Code and test particle simulations.Moreover,the scattering effects of these waves on energetic electrons are simulated by using a two-dimensional Fokker-Planck diffusion model.The results show that ECH waves mainly scatter low-pitch-angle(<20°)electrons at 0.1-10 keV;exohiss can significantly scatter hundreds of kiloelectron volt electrons to form a reversed energy spectrum;MS waves mainly affect high-pitch-angle electrons(>60°);and EMIC waves scatter only>5 MeV electrons.The combined scattering effects of exohiss and MS waves are stronger than those of exohiss alone.The top-hat pitch angle distributions produced by exohiss are relaxed after adding the effect of MS waves.Because the energies of electrons scattered by ECH waves and EMIC waves are much lower and higher than those scattered by exohiss and MS waves,respectively,the combined scattering effects with the addition of ECH and EMIC waves show little difference from the results for the combination of MS waves and exohiss.These results suggest that distinct wave modes can occur simultaneously and scatter electrons in combination or individually,which requires careful consideration in future global simulations of the complex dynamics of radiation belt energetic electrons.展开更多
Wavelike perturbations in the ionosphere of Titan,the largest satellite of Saturn,are explored based on the Cassini Ion Neutral Mass Spectrometer(INMS)measurements.Strong wavelike perturbations are identified for more...Wavelike perturbations in the ionosphere of Titan,the largest satellite of Saturn,are explored based on the Cassini Ion Neutral Mass Spectrometer(INMS)measurements.Strong wavelike perturbations are identified for more than twenty ion species,from simple ones such as N^(+)and CH_(4)^(+)to complex ones such as C_(2)H_(3)CNH^(+)and C_(4)H_(7)^(+).Simultaneous wavelike perturbations in background N_(2),indicative of atmospheric gravity waves,are also observed,motivating us to speculate that the INMS-derived ion perturbations are wave-driven.The amplitudes of the ion perturbations are found to be larger than that of the N_(2)perturbations.Clear compositional variation is revealed by the data:heavier ion species exhibit greater amplitudes.Such observations might be understood based on considerations either of force balance or chemical loss in Titan’s ionosphere.展开更多
Through independent research by the Chinese scientists or their international collaborations,great achievements have been made in interplanetary physics research in China' Mainland during the past two years(2020-2...Through independent research by the Chinese scientists or their international collaborations,great achievements have been made in interplanetary physics research in China' Mainland during the past two years(2020-2022).More than 150 papers have been published in academic journals in this field during this period.These achievements can be grouped into the following areas,at least:(i)solar corona;(ii)solar and interplanetary transient phenomena;(iii)radio bursts;(iv)Magnetohydrodynamic(MHD)numerical modeling;(v)solar energetic particles and cosmic rays.These advances have greatly enriched our understanding of interplanetary physics,i.e.our knowledge of solar activities and solar eruptions,their propagation in the interplanetary space,and the corresponding geoeffects on the Earth.In the sense of application,they have also improved the forecasting of space weather.In this paper we will give a very short review about these advances.展开更多
Muons are the main component of secondary cosmic rays,and the variation in muon intensity indicates the variation in primary cosmic ray intensity.However,before using muons to study the variation in the intensity of c...Muons are the main component of secondary cosmic rays,and the variation in muon intensity indicates the variation in primary cosmic ray intensity.However,before using muons to study the variation in the intensity of cosmic rays,it is necessary to eliminate the atmospheric effects,such as pressure and temperature effects.In this work,the temperature effect of the muons is corrected in terms of empirical method by using ground temperature.The temperature correction is applied to the muon data observed at the Guangzhou station during the period2010–2021 after a barometric correction.It is found that the effect of seasonal variations in temperature on muon counts is greatly eliminated in the corrected data.Furthermore,the muon data are well correlated with the neutron data in comparison,which verifies the reliability of the corrected muon data.Our results show that the correction of muon data by using ground temperature is an effective method.展开更多
The space-borne fluxgate magnetometer(FGM)requires regular in-flight calibration to obtain its zero offset.Recently,Wang GQ and Pan ZH(2021a)developed a new method for the zero offset calibration based on the properti...The space-borne fluxgate magnetometer(FGM)requires regular in-flight calibration to obtain its zero offset.Recently,Wang GQ and Pan ZH(2021a)developed a new method for the zero offset calibration based on the properties of Alfvén waves.They found that an optimal offset line(OOL)exists in the offset cube for a pure Alfvén wave and that the zero offset can be determined by the intersection of at least two nonparallel OOLs.Because no pure Alfvén waves exist in the interplanetary magnetic field,calculation of the zero offset relies on the selection of highly Alfvénic fluctuation events.Here,we propose an automatic procedure to find highly Alfvénic fluctuations in the solar wind and calculate the zero offset.This procedure includes three parts:(1)selecting potential Alfvénic fluctuation events,(2)obtaining the OOL,and(3)determining the zero offset.We tested our automatic procedure by applying it to the magnetic field data measured by the FGM onboard the Venus Express.The tests revealed that our automatic procedure was able to achieve results as good as those determined by the Davis-Smith method.One advantage of our procedure is that the selection criteria and the process for selecting the highly Alfvénic fluctuation events are simpler.Our automatic procedure could also be applied to find fluctuation events for the Davis-Smith method.展开更多
Synthetic Aperture Radar Interferometry(InSAR)has shown its potential on seismic deformation monitoring since it can achieve the accuracy of centimeter level or even the millimeter level.However,the irregular varietie...Synthetic Aperture Radar Interferometry(InSAR)has shown its potential on seismic deformation monitoring since it can achieve the accuracy of centimeter level or even the millimeter level.However,the irregular varieties of ionosphere can induce the additional phase delay on SAR interferometry,restricting its further application in high-precision deformation monitoring.Although several methods have been proposed to correct the ionospheric phase delay on SAR interferometry,the performances of them haven't been evaluated and compared.In this study,three commonly used methods,including polynomial fitting,azimuth offset and split-spectrum are applied to L'Aquila Earthquake to correct the ionospheric phase delay on two Phased Array type L-band Synthetic Aperture Radar(PALSAR)onboard the Advanced Land Observing Satellite-1(ALOS-1)images.The result indicates that these three methods can effectively correct the ionospheric phase delay error for SAR interferometry,where the standard deviations of the ionosphere-corrected results have decreased by almost a factor of 1.8 times for polynomial fitting method,4.2 times for azimuth offset method and 2.5 times for split-spectrum method,compared to those of the original phase.Furthermore,the result of the sliding distribution inversion of the seismic fault shows the best performance for split-spectrum method.展开更多
Investigating the length scales of granules could help understand the dynamics of granules in the photosphere.In this work,we detected and identified granules in an active region near disk center observed at wavelengt...Investigating the length scales of granules could help understand the dynamics of granules in the photosphere.In this work,we detected and identified granules in an active region near disk center observed at wavelength of TiO(7057?)by the 1.6 m Goode Solar Telescope(GST).By a detailed analysis of the size distribution and flatness of granules,we found a critical size that divides the granules in motions into two regimes:convection and turbulence.The length scales of granules with sizes larger than 600 km follow Gauss function and demonstrate“flat”in flatness,which reveal that these granules are dominated by convection.Those with sizes smaller than 600 km follow power-law function and behave power-law tendency in flatness,which indicate that the small granules are dominated by turbulence.Hence,for the granules in active regions,they are originally convective in large length scale,and directly become turbulent once their sizes turn to small,likely below the critical size of 600 km.Comparing with the granules in quiet regions,they evolve with the absence of the mixing motions of convection and turbulence.Such a difference is probably caused by the interaction between fluid motions and strong magnetic fields in active regions.The strong magnetic fields make high magnetic pressure which creates pressure walls and slows down the evolution of convective granules.Such walls cause convective granules extending to smaller sizes on one hand,and cause wide intergranular lanes on the other hand.The small granules isolated in such wide intergranular lanes are continually sheared,rotated by strong downflows in surroundings and hereby become turbulent.展开更多
Three-and five-minute oscillations are commonly observed in any sunspot.Because they are modulated by the internal thermal and magnetic structures of a sunspot,they could be used as an effective tool for researching s...Three-and five-minute oscillations are commonly observed in any sunspot.Because they are modulated by the internal thermal and magnetic structures of a sunspot,they could be used as an effective tool for researching sunspot seismology.In this paper,we investigate the properties of oscillations in sunspot groups with varying sizes and magnetic fields,and aim to establish the relationships between sunspot oscillations and its internal structure comparatively.We selected three groups of the unipolar sunspot with approximately axial-symmetric magnetic field and calculated their Fourier spectra based on the ultraviolet/extreme ultraviolet emission intensity variations recorded by the Solar Dynamics Observatory/Atmospheric Imaging Assembly.We found that the distribution of three-minute oscillation is defined by the joint effect of diverging magnetic field and the stratification of the sunspot atmosphere.Its distribution could be modified by any invading magnetic structures in the umbra.In contrast,the five-minute oscillations are more prominent in small spots,implying that five-minute oscillation is very closely connected with umbral dynamics.展开更多
Solar Wind(SW)electron precipitation is able to deposit a substantial amount of energy in the nightside Martian upper atmosphere,potentially exerting an influence on its thermal structure.This study serves as the firs...Solar Wind(SW)electron precipitation is able to deposit a substantial amount of energy in the nightside Martian upper atmosphere,potentially exerting an influence on its thermal structure.This study serves as the first investigation of such an issue,with the aid of the simultaneous measurements of both neutral density and energetic electron intensity made on board the recent Mars Atmosphere and Volatile Evolution(MAVEN)spacecraft.We report that,from a statistical point of view,the existing measurements do not support a scenario of noticeable neutral heating via SW electron precipitation.However,during 3%−4%of the MAVEN orbits for which data are available,strong correlation between nightside temperature and electron intensity is observed,manifested as collocated enhancements in both parameters,as compared to the surrounding regions.In addition,our analysis also indicates that neutral heating via SW electron precipitation tends to be more effective at altitudes below 160 km for integrated electron intensities above 0.01 ergs·cm^−2·s^−1 over the energy range of 3−450 eV.The results reported here highlight the necessity of incorporating SW electron precipitation as a heat source in the nightside Martian upper atmosphere under extreme circumstances such as during interplanetary coronal mass ejections.展开更多
On-orbit construction and maintenance technology will play a significant role in future space exploration.The dexterous multifunctional spacecraft equipped with multi-arm,for instance,Spider Fab Bot,has attracted a gr...On-orbit construction and maintenance technology will play a significant role in future space exploration.The dexterous multifunctional spacecraft equipped with multi-arm,for instance,Spider Fab Bot,has attracted a great deal of focus due to its versatility in completing these missions.In such engineering practice,point-to-point moving in a complex environment is the fundamental issue.This paper investigates the three-dimensional point-to-point path planning problem,and a hierarchical path planning architecture is developed to give the trajectory of the multi-arm spacecraft effectively and efficiently.In the proposed 3-level architecture,the high-level planner generates the global constrained centric trajectory of the spacecraft with a rigid envelop assumption;the middle-level planner contributes the action sequence,a combination of the newly developed general translational and rotational locomotion mode,to cope with the relative position and attitude of the arms about the centroid of the spacecraft;the low-level planner maps the position/attitude of the end-effector of each arm from the operational space to the joint space optimally.Finally,the simulation experiment is carried out,and the results verify the effectiveness of the proposed three-layer architecture path planning strategy.展开更多
The particle velocity distribution in space plasma usually exhibits a non-Maxwellian high-energy tail that can be well modeled by kappa distributions.In this study,we focus on the growth rates of the Alfvén-cyclo...The particle velocity distribution in space plasma usually exhibits a non-Maxwellian high-energy tail that can be well modeled by kappa distributions.In this study,we focus on the growth rates of the Alfvén-cyclotron instability driven by ion temperature anisotropy in a kappa plasma.By solving the kinetic linear dispersion equation,we explore the sensitivity of growth rates to the spectral indexκof a bi-kappa distribution under different plasma conditions,including a variety of plasma beta β_(hp) and temperature anisotropy A_(hp) values of hot protons.Furthermore,a concise,analytic scaling formula is derived that relates the dimensionless maximum growth rate to three independent variables:the spectral index and the plasma beta and temperature anisotropy of hot protons.Our results show that as theκ-value increases,the instability bandwidth narrows and the maximum growth rate increases significantly.For higherβ_(hp)and A_(hp)′the maximum instability undergoes a sharp increase as well.When our fits of dimensionless maximum growth rates are compared with solutions to kinetic linear dispersion theory,the results generally exhibit good agreement between them.Especially under the circumstances of largeκ-values and highβ_(hp)and A_(hp)′the scalings of maximum growth rates primarily accurately model the numerical solutions.Our analytic expressions can readily be used in large-scale models of the Earth’s magnetosphere to understand wave generation due to the Alfvén-cyclotron instability.展开更多
We observed an Hα surge that occurred in NOAA Active Region 12401 on 2015 August 17, and we discuss its trigger mechanism, and kinematic and thermal properties. It is suggested that this surge was caused by a chromos...We observed an Hα surge that occurred in NOAA Active Region 12401 on 2015 August 17, and we discuss its trigger mechanism, and kinematic and thermal properties. It is suggested that this surge was caused by a chromospheric reconnection which ejected cool and dense material with transverse velocity of about 21–28 km s-1 and initial Doppler velocity of 12 km s^-1. This surge is similar to the injection of newly formed filament materials from their footpoints, except that the surge here occurred in a relatively weak magnetic environment of 100 G. Thus, we discuss the possibility of filament material replenishment via the erupting mass in such a weak magnetic field, which is often associated with quiescent filaments. It is found that the local plasma can be heated up to about 1.3 times the original temperature, which results in an acceleration of about –0.017 km s^-2. It can lift the dense material up to 10 Mm and higher with an inclination angle smaller than 50°, namely the typical height of active region filaments, but it can hardly inject the material up to those filaments higher than 25 Mm, like some quiescent filaments. Thus, we think that the injection model does not work well in describing the formation of quiescent filaments.展开更多
A sunspot is an ideal waveguide for a variety of magnetohydrodynamic waves,which carry a significant amount of energy to the upper atmosphere and could be used as a tool to probe the magnetic and thermal structure of ...A sunspot is an ideal waveguide for a variety of magnetohydrodynamic waves,which carry a significant amount of energy to the upper atmosphere and could be used as a tool to probe the magnetic and thermal structure of a sunspot.In this study,we used the New Vacuum Solar Telescope and took highresolution image sequences simultaneously in both Ti O(7058±10?A)and Hα(6562±2.5?A)bandpasses.We extracted the area and total emission intensity variations of sunspot umbra and analyzed the signals with synchrosqueezing transform.We found that the area and emission intensity varied with both three and five minute periodicity.Moreover,the area and intensity oscillated in phase with each other,this fact hold in both Ti O and Hαdata.We interpret this oscillatory signal as a propagating slow sausage wave.The propagation speed is estimated at about 8 km s^-1.We infer that this sunspot's umbra could have temperature as low as 2800–3500 K.展开更多
With SDO observations and a data-constrained magnetohydrodynamics(MHD)model,we identify a confined multi-ribbon flare that occurred on 2010 October 25 in solar active region 11117 as a magnetic bald patch(BP)flare wit...With SDO observations and a data-constrained magnetohydrodynamics(MHD)model,we identify a confined multi-ribbon flare that occurred on 2010 October 25 in solar active region 11117 as a magnetic bald patch(BP)flare with strong evidence.From the photospheric magnetic field observed by SDO/HMI,we find there are indeed magnetic BPs on the polarity inversion lines(PILs)which match parts of the flare ribbons.From the 3D coronal magnetic field derived from an MHD relaxation model constrained by the vector magnetograms,we find strikingly good agreement of the BP separatrix surface(BPSS)footpoints with the flare ribbons,and the BPSS itself with the hot flaring loop system.Moreover,the triggering of the BP flare can be attributed to a small flux emergence under the lobe of the BPSS,and the relevant change of coronal magnetic field through the flare is reproduced well by the pre-flare and post-flare MHD solutions,which match the corresponding pre-and post-flare AIA observations,respectively.Our work contributes to the study of non-typical flares that constitute the majority of solar flares but which cannot be explained by the standard flare model.展开更多
Inspired by recent significant agricultural yield losses in the eastern China and a missing operational monitoring system,we developed a comprehensive drought monitoring model to better understand the impact of indivi...Inspired by recent significant agricultural yield losses in the eastern China and a missing operational monitoring system,we developed a comprehensive drought monitoring model to better understand the impact of individual key factors contributing to this issue.The resulting model,the‘Humidity calibrated Drought Condition Index’(HcDCI)was applied for the years 2001 to 2019 in form of a case study to Weihai County,Shandong Province in East China.Design and development are based on a linear combination of the Vegetation Condition Index(VCI),the Temperature Condition Index(TCI),and the Rainfall Condition Index(RCI)using multi-source satellite data to create a basic Drought Condition Index(DCI).VCI and TCI were derived from MODIS(Moderate Resolution Imaging Spectroradiometer)data,while precipitation is taken from CHIRPS(Climate Hazards Group InfraRed Precipitation with Station data)data.For reasons of accuracy,the decisive coefficients were determined by the relative humidity of soils at depth of 10-20 cm of particular areas collected by an agrometeorological ground station.The correlation between DCI and soil humidity was optimized with the factors of 0.53,0.33,and 0.14 for VCI,TCI,and RCI,respectively.The model revealed,light agricultural droughts from 2003 to 2013 and in 2018,while more severe droughts occurred in 2001 and 2002,2014-2017,and 2019.The droughts were most severe in January,March,and December,and our findings coincide with historical records.The average temperature during 2012-2019 is 1℃ higher than that during the period 2001-2011 and the average precipitation during 2014-2019 is 192.77 mm less than that during 2008-2013.The spatio-temporal accuracy of the HcDCI model was positively validated by correlation with agricultural crop yield quantities.The model thus,demonstrates its capability to reveal drought periods in detail,its transferability to other regions and its usefulness to take future measures.展开更多
Magnetic fields play a fundamental role in the structure and dynamics of the solar corona.As they are driven by their footpoint motions on the solar surface,which transport energy from the interior of the Sun into its...Magnetic fields play a fundamental role in the structure and dynamics of the solar corona.As they are driven by their footpoint motions on the solar surface,which transport energy from the interior of the Sun into its atmosphere,the coronal magnetic fields are stressed continuously with buildup of magnetic nonpotentiality in the form of topology complexity(magnetic helicity)and local electric currents(magnetic free energy).The accumulated nonpotentiality is often released explosively by solar eruptions,manifested as solar flares and coronal mass ejections.展开更多
The contact point configuration should be carefully chosen to ensure a stable capture,especially for the non-cooperative target capture mission using multi-armed spacecraft.In this work scenario,the contact points on ...The contact point configuration should be carefully chosen to ensure a stable capture,especially for the non-cooperative target capture mission using multi-armed spacecraft.In this work scenario,the contact points on the base and on the arms are distributed on the opposite side of the target.Otherwise,large forces will be needed.To cope with this problem,an uneven-oriented distribution union criterion is proposed.The union criterion contains a virtual symmetrical criterion and a geometry criterion.The virtual symmetrical contact point criterion is derived from the proof of the force closure principle using computational geometry to ensure a stable grasp,and the geometry criterion is calculated by the volume of the minimum polyhedron formed by the contact points to get a wide-range distribution.To further accelerate the optimization rate and enhance the global search ability,a line array modeling method and a continuous-discrete global search algorithm are proposed.The line array modeling method reduces the workload of calculating the descent direction and the gradient available,while the continuous-discrete global search algorithm reducing the optimization dimension.Then a highly efficient grasping is achieved and the corresponding contact point is calculated.Finally,an exhaustive verification is conducted to numerically analyze the disturbance resistance ability,and simulation results demonstrate the effectiveness of the proposed algorithms.展开更多
基金supported by the NSFC(Grant Nos 42130204 and 42188101)the Strategic Priority Program of the Chinese Academy of Sciences(Grant No.XDB41000000)the support of the Tencent Foundation.
文摘The Mars Orbiter MAGnetometer(MOMAG)is a scientific instrument onboard the orbiter of China’s first mission for Mars—Tianwen-1.Since November 13,2021,it has been recording magnetic field data from the solar wind to the magnetic pile-up region surrounding Mars.Here we present its in-flight performance and first science results,based on its first one and one-half months’data.Comparing these early MOMAG observations to the magnetic field data in the solar wind from NASA’s Mars Atmosphere and Volatile EvolutioN(MAVEN)mission,we report that the MOMAG magnetic field data are at the same level in magnitude,and describe the same magnetic structures with similar variations in three components.We recognize 158 clear bow shock(BS)crossings in these MOMAG data;their locations match well statistically with the modeled average BS.We also identify and compare five pairs of datasets collected when Tianwen-1’s orbiter and the MAVEN probe made simultaneous BS crossings.These BS crossings confirm the global shape of modeled BS,as well as the south-north asymmetry of the Martian BS.Two cases presented in this paper suggest that the BS is probably more dynamic at flank than near the nose.So far,MOMAG performs well,and provides accurate magnetic field vectors.MOMAG is continuously scanning the magnetic field surrounding Mars.Data from MOMAG’s measurements complement data from MAVEN and will undoubt edly advance our understanding of the plasma environment of Mars.
基金the Fundamental Research Funds for the Central Universities(Grant No.HIT.OCEF.2022041)the National Natural Science Foundation of China(Grant Nos.42241155,41974205,42130204,and 42241133)+4 种基金the Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2022A1515011698,2023A1515030132,and 2022A1515010257)the Shenzhen Science and Technology Research Program(Grant Nos.JCYJ20210324121412034 and JCYJ20210324121403009)the Shenzhen Key Laboratory Launching Project(Grant No.ZDSYS20210702140800001)the Joint Open Fund of Mengcheng National Geophysical Observatory(Grant No.MENGO-202315)the Macao Foundation,the pre-research Project on Civil Aerospace Technologies(Grant No.D020103)funded by the China National Space Administration,and the Chinese Academy of Sciences Center for Excellence in Comparative Planetology。
文摘Magnetic holes are magnetic depression structures that exist widely in many plasma environments.The magnetic holes with durations of>1 s in the solar wind at Mercury’s orbit have drawn much attention,but the properties of the magnetic holes with shorter durations are still unclear.Here,we investigate the magnetic holes with durations of 0.1-100 s in the upstream region of Mercury’s bow shock based on observations by the MESSENGER(MErcury Surface,Space ENvironment,GEochemistry,and Ranging)spacecraft.They can be divided into two groups according to the distribution of their duration:small-duration magnetic holes(SDMHs,<0.6 s)and large-duration magnetic holes(LDMHs,>0.6 s).The duration of each group approximately obeys a log-normal distribution with a median of~0.25 s and 3 s,respectively.Approximately 1.7%(32.6%)of the SDMHs(LDMHs)reduce the magnetic field strength by more than 50%.For both groups,some structures have a linear or quasi-linear polarization,whereas others have an elliptical polarization.The magnetic hole events in both groups tend to have a higher rate of occurrence when the interplanetary magnetic field strength is weaker.Their occurrence rates are also affected by Mercury’s foreshock,which can increase(decrease)the occurrence rate of the SDMHs(LDMHs).This finding suggests that Mercury’s foreshock might be one source of the SDMHs and that the foreshock can destroy some LDMHs.These observations suggest that a new group of magnetic holes with durations of<0.6 s exist in the upstream region of Mercury’s bow shock.
基金supported by the Shenzhen Science and Technology Research Program (JCYJ20210324121412034)the Guangdong Basic and Applied Basic Research Foundation (2022A1515011698)supported by the NASA (National Aeronautics and Space Administration) Mars Exploration Program
文摘In-flight calibration of the ze ro offset is crucial for ensuring high-precision measure ment of the spaceborne fluxgate magnetomete r.Tianwen-1 is China’s first Mars mission,and its orbiter will re main out of the solar wind for tens of days each year.Previous in-flight calibration methods might not be suitable for this orbiter during such a period.Recently,a new method was proposed by Wang GQ(2022 b),which we refer to as the Wang method Ⅱ for ease of description.Here,we test the performance of this method in the Martian magnetosheath by using magnetic field data measured by the Mars Atmosphere and Volatile EvolutioN(MAVEN) spacecraft.We find that the accuracy of the Wang method Ⅱ is affected by the number of magnetic field subinterval events,the eigenvalues of the minimum variance analysis for each event,and the position of the spacecraft in the magnetosheath.The estimated zero offset varies over a period of~27 days and has a 57.3% probability of accuracy within 2.0 nT.After being smoothed with a temporal window of 27 days,the ze ro offset has a 48.4%(99.3%) probability of accuracy within 1.0(2.0) nT.Our tests suggest that the Wang method Ⅱ provides an option for the Tianwen-1 orbiter to perform in-flight calibration when the orbiter remains out of the solar wind for an extended pe riod of time.
基金supported by the National Natural Science Foundation of China (Grant Nos. 42188101, 42174190, 42025404, and 41904143)the Fundamental Research Funds for the Central Universities (Grant No. 2042021kf0016)+2 种基金the B-type Strategic Priority Program of the Chinese Academy of Sciences (Grant No. XDB41000000)the pre-research projects on Civil Aerospace Technologies funded by the China National Space Administration (Grant Nos. D020308 and D020104)the China Postdoctoral Science Foundation Project (Grant No. 2019M662700)
文摘We report a representative concurrent event of four wave modes at L≈5.0,including electrostatic electron cyclotron harmonic(ECH)waves,exohiss,magnetosonic(MS)waves,and electromagnetic ion cyclotron(EMIC)waves,based on the observations from Van Allen Probe A on October 15,2015.The diffusion coefficients induced by these waves are calculated by using both the Full Diffusion Code and test particle simulations.Moreover,the scattering effects of these waves on energetic electrons are simulated by using a two-dimensional Fokker-Planck diffusion model.The results show that ECH waves mainly scatter low-pitch-angle(<20°)electrons at 0.1-10 keV;exohiss can significantly scatter hundreds of kiloelectron volt electrons to form a reversed energy spectrum;MS waves mainly affect high-pitch-angle electrons(>60°);and EMIC waves scatter only>5 MeV electrons.The combined scattering effects of exohiss and MS waves are stronger than those of exohiss alone.The top-hat pitch angle distributions produced by exohiss are relaxed after adding the effect of MS waves.Because the energies of electrons scattered by ECH waves and EMIC waves are much lower and higher than those scattered by exohiss and MS waves,respectively,the combined scattering effects with the addition of ECH and EMIC waves show little difference from the results for the combination of MS waves and exohiss.These results suggest that distinct wave modes can occur simultaneously and scatter electrons in combination or individually,which requires careful consideration in future global simulations of the complex dynamics of radiation belt energetic electrons.
基金supported by the B-type Strategic Priority Program No. XDB41000000funded by the Chinese Academy of Sciences and the pre-research projects on Civil Aerospace Technologies No.s D020105 and D020103+1 种基金funded by China’s National Space Administrationsupport from the National Science Foundation of China through grants 42030201, 41904154 and 42104170
文摘Wavelike perturbations in the ionosphere of Titan,the largest satellite of Saturn,are explored based on the Cassini Ion Neutral Mass Spectrometer(INMS)measurements.Strong wavelike perturbations are identified for more than twenty ion species,from simple ones such as N^(+)and CH_(4)^(+)to complex ones such as C_(2)H_(3)CNH^(+)and C_(4)H_(7)^(+).Simultaneous wavelike perturbations in background N_(2),indicative of atmospheric gravity waves,are also observed,motivating us to speculate that the INMS-derived ion perturbations are wave-driven.The amplitudes of the ion perturbations are found to be larger than that of the N_(2)perturbations.Clear compositional variation is revealed by the data:heavier ion species exhibit greater amplitudes.Such observations might be understood based on considerations either of force balance or chemical loss in Titan’s ionosphere.
基金Supported by the Strategic Priority Research Program of Chinese Academy of Sciences(XDB 41000000)National Natural Science Foundation of China(41531073,41731067,41861164026,41874202,41474153,42074183 and U1738128)+2 种基金the Youth Innovation Promotion Association of Chinese Academy of Sciences(2016133)Pandeng Program of National Space Science CenterChinese Academy of Sciences。
文摘Through independent research by the Chinese scientists or their international collaborations,great achievements have been made in interplanetary physics research in China' Mainland during the past two years(2020-2022).More than 150 papers have been published in academic journals in this field during this period.These achievements can be grouped into the following areas,at least:(i)solar corona;(ii)solar and interplanetary transient phenomena;(iii)radio bursts;(iv)Magnetohydrodynamic(MHD)numerical modeling;(v)solar energetic particles and cosmic rays.These advances have greatly enriched our understanding of interplanetary physics,i.e.our knowledge of solar activities and solar eruptions,their propagation in the interplanetary space,and the corresponding geoeffects on the Earth.In the sense of application,they have also improved the forecasting of space weather.In this paper we will give a very short review about these advances.
基金supported by grants NSFC 41774182,NSFC 42074206,and NSFC 41874206。
文摘Muons are the main component of secondary cosmic rays,and the variation in muon intensity indicates the variation in primary cosmic ray intensity.However,before using muons to study the variation in the intensity of cosmic rays,it is necessary to eliminate the atmospheric effects,such as pressure and temperature effects.In this work,the temperature effect of the muons is corrected in terms of empirical method by using ground temperature.The temperature correction is applied to the muon data observed at the Guangzhou station during the period2010–2021 after a barometric correction.It is found that the effect of seasonal variations in temperature on muon counts is greatly eliminated in the corrected data.Furthermore,the muon data are well correlated with the neutron data in comparison,which verifies the reliability of the corrected muon data.Our results show that the correction of muon data by using ground temperature is an effective method.
基金financially supported by the Shenzhen Science and Technology Research Program(grant no.JCYJ2021032412141-2034)the National Natural Science Foundation of China(grant nos.41804157,41774171,41774167,41974205,41804157,and 41904156)+3 种基金financial support from the pre-research Project on Civil Aerospace Technologies(grant no.D020103)funded by the China National Space Administrationthe 111 Project(grant no.B18017)the Chinese Academy of Sciences Center for Excellence in Comparative Planetologythe Macao Foundation.
文摘The space-borne fluxgate magnetometer(FGM)requires regular in-flight calibration to obtain its zero offset.Recently,Wang GQ and Pan ZH(2021a)developed a new method for the zero offset calibration based on the properties of Alfvén waves.They found that an optimal offset line(OOL)exists in the offset cube for a pure Alfvén wave and that the zero offset can be determined by the intersection of at least two nonparallel OOLs.Because no pure Alfvén waves exist in the interplanetary magnetic field,calculation of the zero offset relies on the selection of highly Alfvénic fluctuation events.Here,we propose an automatic procedure to find highly Alfvénic fluctuations in the solar wind and calculate the zero offset.This procedure includes three parts:(1)selecting potential Alfvénic fluctuation events,(2)obtaining the OOL,and(3)determining the zero offset.We tested our automatic procedure by applying it to the magnetic field data measured by the FGM onboard the Venus Express.The tests revealed that our automatic procedure was able to achieve results as good as those determined by the Davis-Smith method.One advantage of our procedure is that the selection criteria and the process for selecting the highly Alfvénic fluctuation events are simpler.Our automatic procedure could also be applied to find fluctuation events for the Davis-Smith method.
基金National Science Foundation of China(Nos.42074040,41941019,41790445)National Key R&D Program of China(Nos.2020YFC1512001,2019YFC1509800)Shenzhen Science and Technology Program(No.KQTD20180410161218820)。
文摘Synthetic Aperture Radar Interferometry(InSAR)has shown its potential on seismic deformation monitoring since it can achieve the accuracy of centimeter level or even the millimeter level.However,the irregular varieties of ionosphere can induce the additional phase delay on SAR interferometry,restricting its further application in high-precision deformation monitoring.Although several methods have been proposed to correct the ionospheric phase delay on SAR interferometry,the performances of them haven't been evaluated and compared.In this study,three commonly used methods,including polynomial fitting,azimuth offset and split-spectrum are applied to L'Aquila Earthquake to correct the ionospheric phase delay on two Phased Array type L-band Synthetic Aperture Radar(PALSAR)onboard the Advanced Land Observing Satellite-1(ALOS-1)images.The result indicates that these three methods can effectively correct the ionospheric phase delay error for SAR interferometry,where the standard deviations of the ionosphere-corrected results have decreased by almost a factor of 1.8 times for polynomial fitting method,4.2 times for azimuth offset method and 2.5 times for split-spectrum method,compared to those of the original phase.Furthermore,the result of the sliding distribution inversion of the seismic fault shows the best performance for split-spectrum method.
基金the National Natural Science Foundation of China(Nos.41822404,11973083,42074205,11763004,11729301,11803005,12111530078 and 12173012)Shenzhen Technology Project(JCYJ20190806142609035 and GXWD 20201230155427003-20200804151658001)。
文摘Investigating the length scales of granules could help understand the dynamics of granules in the photosphere.In this work,we detected and identified granules in an active region near disk center observed at wavelength of TiO(7057?)by the 1.6 m Goode Solar Telescope(GST).By a detailed analysis of the size distribution and flatness of granules,we found a critical size that divides the granules in motions into two regimes:convection and turbulence.The length scales of granules with sizes larger than 600 km follow Gauss function and demonstrate“flat”in flatness,which reveal that these granules are dominated by convection.Those with sizes smaller than 600 km follow power-law function and behave power-law tendency in flatness,which indicate that the small granules are dominated by turbulence.Hence,for the granules in active regions,they are originally convective in large length scale,and directly become turbulent once their sizes turn to small,likely below the critical size of 600 km.Comparing with the granules in quiet regions,they evolve with the absence of the mixing motions of convection and turbulence.Such a difference is probably caused by the interaction between fluid motions and strong magnetic fields in active regions.The strong magnetic fields make high magnetic pressure which creates pressure walls and slows down the evolution of convective granules.Such walls cause convective granules extending to smaller sizes on one hand,and cause wide intergranular lanes on the other hand.The small granules isolated in such wide intergranular lanes are continually sheared,rotated by strong downflows in surroundings and hereby become turbulent.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.12173012 and 12111530078)the Shenzhen Technology project(GXWD20201230155427003-20200804151658001)supported by the Joint Funds of the NSFC(U1931107)。
文摘Three-and five-minute oscillations are commonly observed in any sunspot.Because they are modulated by the internal thermal and magnetic structures of a sunspot,they could be used as an effective tool for researching sunspot seismology.In this paper,we investigate the properties of oscillations in sunspot groups with varying sizes and magnetic fields,and aim to establish the relationships between sunspot oscillations and its internal structure comparatively.We selected three groups of the unipolar sunspot with approximately axial-symmetric magnetic field and calculated their Fourier spectra based on the ultraviolet/extreme ultraviolet emission intensity variations recorded by the Solar Dynamics Observatory/Atmospheric Imaging Assembly.We found that the distribution of three-minute oscillation is defined by the joint effect of diverging magnetic field and the stratification of the sunspot atmosphere.Its distribution could be modified by any invading magnetic structures in the umbra.In contrast,the five-minute oscillations are more prominent in small spots,implying that five-minute oscillation is very closely connected with umbral dynamics.
基金the B-type Strategic Priority Program No.XDB41000000 funded by the Chinese Academy of Sciencesthe pre-research project on Civil Aerospace Technologies No.D020105 funded by China’s National Space Administrationthe National Natural Science Foundation of China through grants 41525015,41774186,41904154,and 42030201.
文摘Solar Wind(SW)electron precipitation is able to deposit a substantial amount of energy in the nightside Martian upper atmosphere,potentially exerting an influence on its thermal structure.This study serves as the first investigation of such an issue,with the aid of the simultaneous measurements of both neutral density and energetic electron intensity made on board the recent Mars Atmosphere and Volatile Evolution(MAVEN)spacecraft.We report that,from a statistical point of view,the existing measurements do not support a scenario of noticeable neutral heating via SW electron precipitation.However,during 3%−4%of the MAVEN orbits for which data are available,strong correlation between nightside temperature and electron intensity is observed,manifested as collocated enhancements in both parameters,as compared to the surrounding regions.In addition,our analysis also indicates that neutral heating via SW electron precipitation tends to be more effective at altitudes below 160 km for integrated electron intensities above 0.01 ergs·cm^−2·s^−1 over the energy range of 3−450 eV.The results reported here highlight the necessity of incorporating SW electron precipitation as a heat source in the nightside Martian upper atmosphere under extreme circumstances such as during interplanetary coronal mass ejections.
基金supported by the National Natural Science Foundation of China(Grant Nos.62003115 and 11972130)the Shenzhen Natural Science Fund(the Stable Support Plan Program GXWD2020123015542700320200821170719001)。
文摘On-orbit construction and maintenance technology will play a significant role in future space exploration.The dexterous multifunctional spacecraft equipped with multi-arm,for instance,Spider Fab Bot,has attracted a great deal of focus due to its versatility in completing these missions.In such engineering practice,point-to-point moving in a complex environment is the fundamental issue.This paper investigates the three-dimensional point-to-point path planning problem,and a hierarchical path planning architecture is developed to give the trajectory of the multi-arm spacecraft effectively and efficiently.In the proposed 3-level architecture,the high-level planner generates the global constrained centric trajectory of the spacecraft with a rigid envelop assumption;the middle-level planner contributes the action sequence,a combination of the newly developed general translational and rotational locomotion mode,to cope with the relative position and attitude of the arms about the centroid of the spacecraft;the low-level planner maps the position/attitude of the end-effector of each arm from the operational space to the joint space optimally.Finally,the simulation experiment is carried out,and the results verify the effectiveness of the proposed three-layer architecture path planning strategy.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.42204163,42188101,42025404,42241143,41774167,41774171,41974205,41804157,41904156,42130204,and 42241133)the B-type Strategic Priority Program of the Chinese Academy of Sciences(Grant No.XDB41000000)+3 种基金the National Key R&D Program of China(Grant Nos.2022YFF0503700 and 2022YFF0503900)the pre-research projects on Civil Aerospace Technologies(Grant No.D020103)funded by the China National Space Administrationthe Macao Foundation,the Fundamental Research Funds for the Central Universities(Grant No.2042022kf1012the Shenzhen Key Laboratory Launching Project(Grant No.ZDSYS20210702140800001).TieLong Zhang was supported by the Chinese Academy of Sciences Center for Excellence in Comparative Planetology.
文摘The particle velocity distribution in space plasma usually exhibits a non-Maxwellian high-energy tail that can be well modeled by kappa distributions.In this study,we focus on the growth rates of the Alfvén-cyclotron instability driven by ion temperature anisotropy in a kappa plasma.By solving the kinetic linear dispersion equation,we explore the sensitivity of growth rates to the spectral indexκof a bi-kappa distribution under different plasma conditions,including a variety of plasma beta β_(hp) and temperature anisotropy A_(hp) values of hot protons.Furthermore,a concise,analytic scaling formula is derived that relates the dimensionless maximum growth rate to three independent variables:the spectral index and the plasma beta and temperature anisotropy of hot protons.Our results show that as theκ-value increases,the instability bandwidth narrows and the maximum growth rate increases significantly.For higherβ_(hp)and A_(hp)′the maximum instability undergoes a sharp increase as well.When our fits of dimensionless maximum growth rates are compared with solutions to kinetic linear dispersion theory,the results generally exhibit good agreement between them.Especially under the circumstances of largeκ-values and highβ_(hp)and A_(hp)′the scalings of maximum growth rates primarily accurately model the numerical solutions.Our analytic expressions can readily be used in large-scale models of the Earth’s magnetosphere to understand wave generation due to the Alfvén-cyclotron instability.
基金supported by the National Natural Science Foundation of China (41731067 and 41822404)Shenzhen Technology Project (JCYJ20170307150645407)+6 种基金the Fundamental Research Funds for the Central Universities (Grant No. HIT.BRETV.201901)the support by China Postdoctoral Science Foundation (2018M641812)support of the US NSF (AGS-1821294)the National Natural Science Foundation of China (11729301)supported by NJIT and US NSF AGS 1821294 grantpartly supported by the Korea Astronomy and Space Science Institute and Seoul National Universitythe strategic priority research program of Chinese Academy of Science (CAS) (Grant No. XDB09000000)
文摘We observed an Hα surge that occurred in NOAA Active Region 12401 on 2015 August 17, and we discuss its trigger mechanism, and kinematic and thermal properties. It is suggested that this surge was caused by a chromospheric reconnection which ejected cool and dense material with transverse velocity of about 21–28 km s-1 and initial Doppler velocity of 12 km s^-1. This surge is similar to the injection of newly formed filament materials from their footpoints, except that the surge here occurred in a relatively weak magnetic environment of 100 G. Thus, we discuss the possibility of filament material replenishment via the erupting mass in such a weak magnetic field, which is often associated with quiescent filaments. It is found that the local plasma can be heated up to about 1.3 times the original temperature, which results in an acceleration of about –0.017 km s^-2. It can lift the dense material up to 10 Mm and higher with an inclination angle smaller than 50°, namely the typical height of active region filaments, but it can hardly inject the material up to those filaments higher than 25 Mm, like some quiescent filaments. Thus, we think that the injection model does not work well in describing the formation of quiescent filaments.
基金the Joint Funds of the National Natural Science Foundation of China(NSFC,U1931107)the Key Applied Basic Research Program of Yunnan Province(2018FA035)+3 种基金the NSFC(Nos.11803005 and 11911530690)Shenzhen Technology Project(JCYJ20180306172239618)the NSFC(Grant Nos.11427901,11673038,11773038,11873062 and 11973056)the Open Research Program(KLSA202007)of Key Laboratory of Solar Activity of National Astronomical Observatory of China。
文摘A sunspot is an ideal waveguide for a variety of magnetohydrodynamic waves,which carry a significant amount of energy to the upper atmosphere and could be used as a tool to probe the magnetic and thermal structure of a sunspot.In this study,we used the New Vacuum Solar Telescope and took highresolution image sequences simultaneously in both Ti O(7058±10?A)and Hα(6562±2.5?A)bandpasses.We extracted the area and total emission intensity variations of sunspot umbra and analyzed the signals with synchrosqueezing transform.We found that the area and emission intensity varied with both three and five minute periodicity.Moreover,the area and intensity oscillated in phase with each other,this fact hold in both Ti O and Hαdata.We interpret this oscillatory signal as a propagating slow sausage wave.The propagation speed is estimated at about 8 km s^-1.We infer that this sunspot's umbra could have temperature as low as 2800–3500 K.
基金supported by the National Natural Science Foundation of China (41531073, 41374176, 41574170, 41231068 and 41574171)the Specialized Research Fund for State Key Laboratories
文摘With SDO observations and a data-constrained magnetohydrodynamics(MHD)model,we identify a confined multi-ribbon flare that occurred on 2010 October 25 in solar active region 11117 as a magnetic bald patch(BP)flare with strong evidence.From the photospheric magnetic field observed by SDO/HMI,we find there are indeed magnetic BPs on the polarity inversion lines(PILs)which match parts of the flare ribbons.From the 3D coronal magnetic field derived from an MHD relaxation model constrained by the vector magnetograms,we find strikingly good agreement of the BP separatrix surface(BPSS)footpoints with the flare ribbons,and the BPSS itself with the hot flaring loop system.Moreover,the triggering of the BP flare can be attributed to a small flux emergence under the lobe of the BPSS,and the relevant change of coronal magnetic field through the flare is reproduced well by the pre-flare and post-flare MHD solutions,which match the corresponding pre-and post-flare AIA observations,respectively.Our work contributes to the study of non-typical flares that constitute the majority of solar flares but which cannot be explained by the standard flare model.
基金Under the auspices of Shenzhen Science and Technology Program(No.KQTD20180410161218820)Guangdong Basic and Applied Basic Research Foundation(No.2021A1515012600)。
文摘Inspired by recent significant agricultural yield losses in the eastern China and a missing operational monitoring system,we developed a comprehensive drought monitoring model to better understand the impact of individual key factors contributing to this issue.The resulting model,the‘Humidity calibrated Drought Condition Index’(HcDCI)was applied for the years 2001 to 2019 in form of a case study to Weihai County,Shandong Province in East China.Design and development are based on a linear combination of the Vegetation Condition Index(VCI),the Temperature Condition Index(TCI),and the Rainfall Condition Index(RCI)using multi-source satellite data to create a basic Drought Condition Index(DCI).VCI and TCI were derived from MODIS(Moderate Resolution Imaging Spectroradiometer)data,while precipitation is taken from CHIRPS(Climate Hazards Group InfraRed Precipitation with Station data)data.For reasons of accuracy,the decisive coefficients were determined by the relative humidity of soils at depth of 10-20 cm of particular areas collected by an agrometeorological ground station.The correlation between DCI and soil humidity was optimized with the factors of 0.53,0.33,and 0.14 for VCI,TCI,and RCI,respectively.The model revealed,light agricultural droughts from 2003 to 2013 and in 2018,while more severe droughts occurred in 2001 and 2002,2014-2017,and 2019.The droughts were most severe in January,March,and December,and our findings coincide with historical records.The average temperature during 2012-2019 is 1℃ higher than that during the period 2001-2011 and the average precipitation during 2014-2019 is 192.77 mm less than that during 2008-2013.The spatio-temporal accuracy of the HcDCI model was positively validated by correlation with agricultural crop yield quantities.The model thus,demonstrates its capability to reveal drought periods in detail,its transferability to other regions and its usefulness to take future measures.
基金Thiswork is jointly supported by the National Natural Science Foundation of China(NSFC 42174200,41822404,and 41731067)the Fundamental Research Funds for the Central Universities(HIT.OCEF.2021033)+1 种基金the Shenzhen Science and Technology Program(RCJC20210609104422048 and JCYJ20190806142609035)Y.G.is supported by NSFC(11773016 and 11961131002)and 2020YFC2201201.We thank Dr.Aiying Duan for a careful reading of themanuscript.We are very grateful to the six reviewers for helpful comments and suggestions,which improved our manuscript.
文摘Magnetic fields play a fundamental role in the structure and dynamics of the solar corona.As they are driven by their footpoint motions on the solar surface,which transport energy from the interior of the Sun into its atmosphere,the coronal magnetic fields are stressed continuously with buildup of magnetic nonpotentiality in the form of topology complexity(magnetic helicity)and local electric currents(magnetic free energy).The accumulated nonpotentiality is often released explosively by solar eruptions,manifested as solar flares and coronal mass ejections.
基金supported by the National Natural Science Foundation of China(Nos.62003115,11972130)Shenzhen Natural Science Fund(the Stable Support Plan Program GXWD20201230155427003-20200821170719001).
文摘The contact point configuration should be carefully chosen to ensure a stable capture,especially for the non-cooperative target capture mission using multi-armed spacecraft.In this work scenario,the contact points on the base and on the arms are distributed on the opposite side of the target.Otherwise,large forces will be needed.To cope with this problem,an uneven-oriented distribution union criterion is proposed.The union criterion contains a virtual symmetrical criterion and a geometry criterion.The virtual symmetrical contact point criterion is derived from the proof of the force closure principle using computational geometry to ensure a stable grasp,and the geometry criterion is calculated by the volume of the minimum polyhedron formed by the contact points to get a wide-range distribution.To further accelerate the optimization rate and enhance the global search ability,a line array modeling method and a continuous-discrete global search algorithm are proposed.The line array modeling method reduces the workload of calculating the descent direction and the gradient available,while the continuous-discrete global search algorithm reducing the optimization dimension.Then a highly efficient grasping is achieved and the corresponding contact point is calculated.Finally,an exhaustive verification is conducted to numerically analyze the disturbance resistance ability,and simulation results demonstrate the effectiveness of the proposed algorithms.
