Magnetosonic waves are an important medium for energy transfer in collisionless space plasma.Magnetosonic waves have been widely investigated in the upstream of the bow shock at Mars.These waves are believed to origin...Magnetosonic waves are an important medium for energy transfer in collisionless space plasma.Magnetosonic waves have been widely investigated in the upstream of the bow shock at Mars.These waves are believed to originate from pickup ions or reflected particles.By utilizing MAVEN spacecraft data,we have observed the occurrence of quasi-perpendicularly propagating magnetosonic emissions near the proton gyrofrequency in the Martian magnetotail region.These plasma waves are associated with a significant enhancement of proton and oxygen flux.The excited magnetosonic waves could possibly heat the protons through resonance and facilitate the ionospheric plasma escape.Our results could be helpful to better understand the Mars’magnetospheric dynamics and offer insights into possible energy redistribution between waves and plasma in the Martian nightside magnetosphere.展开更多
Two consecutive magnetic flux ropes, separated by less than 30 s(Dt \ 30 s), are observed within one magnetic reconnection diffusion region without strong guide field in the Earth's magnetotail by Cluster multispa...Two consecutive magnetic flux ropes, separated by less than 30 s(Dt \ 30 s), are observed within one magnetic reconnection diffusion region without strong guide field in the Earth's magnetotail by Cluster multispacecraft. The flux ropes are characterized by bipolar signatures of the south–north magnetic field component Bz accompanied with strong core magnetic field By, intense current J and density depletions inside of them. In spite of the small but non-trivial global scale negative guide field(–By), there exists a directional change of the core fields of two flux ropes, i.e.,-Byfor the first one, and Byfor the second one. The directions of the core fields are the same as the ambient cross-tail magnetic field component(By) just outside of flux ropes. Therefore, we suggest that the core field of flux ropes is formed by compression of the local preexisting Byand that the directional change of core field is due to the change of local preexisting By. Such a change in ambient Bymight be caused by some microscale physics.展开更多
Based on current sheet flapping motion on 27 August 2018 in the dusk flank magnetotail,as recorded by instruments aboard Magnetospheric Multiscale(MMS)spacecraft,we present the first study of guide field reconnection ...Based on current sheet flapping motion on 27 August 2018 in the dusk flank magnetotail,as recorded by instruments aboard Magnetospheric Multiscale(MMS)spacecraft,we present the first study of guide field reconnection observed in the flux rope embedded in kink-like flapping current sheets near the dusk-side flank of the magnetotail.Unlike more common magnetotail reconnections,which are symmetric,these asymmetric small-scale(λ_(i)~650 km)reconnections were found in the highly twisted current sheet when the direction normal to the sheet changes from the Z direction into the Y direction.The unique feature of this unusual reconnection is that the reconnection jets are along the Z direction-different from outflow in the X direction,which is the more usual situation.This vertical reconnection jet is parallel or antiparallel to the up-and-down motion of the tail’s current sheet.The normalized reconnection rate R is estimated to be~0.1.Our results indicate that such asymmetric reconnections can significantly enlarge current sheet flapping,with large oscillation amplitudes.This letter presents direct evidence of guide field reconnection in a highly twisted current sheet,characterized by enlarged current sheet flapping as a consequence of the reconnection outflow.展开更多
已有研究发现金星磁尾的太阳风氢离子(H^(+))和金星电离层氧离子(O^(+))存在大尺度涡流结构,该涡流从磁尾望向星球是逆时针的.为了确定该涡流的存在性,利用金星快车等离子体和高能原子分析仪(Analyzer of Space Plasmas and Energetic A...已有研究发现金星磁尾的太阳风氢离子(H^(+))和金星电离层氧离子(O^(+))存在大尺度涡流结构,该涡流从磁尾望向星球是逆时针的.为了确定该涡流的存在性,利用金星快车等离子体和高能原子分析仪(Analyzer of Space Plasmas and Energetic Atoms on Venus, ASPERA-4)的Fedorov矫正数据,分别在金星公转轨道坐标系(VSO)和太阳风电场坐标系(VSE)下对磁尾等离子体流进行了统计分析.结果显示,在VSO和VSE坐标系中都存在太阳风H^(+)和金星O^(+)的顺时针涡流结构.但是从已有的研究结果看,无论等离子体涡流是逆时针还是顺时针,其产生的磁场都与已知磁尾磁场结构不相符;考虑到金星和火星空间环境的相似性及火星磁尾太阳风H^(+)并不存在完整等离子体涡流的情况,认为金星磁尾可能并不存在大尺度等离子体涡流.金星的等离子体特征需要未来更多卫星观测研究.展开更多
Previous studies suggest that dipolarization fronts (DFs) are 1 to 3RE (RE is the earth radius) wide in the dawn-dusk direction. Recent kinetic simulations have found that DFs may break up into small-scale structures ...Previous studies suggest that dipolarization fronts (DFs) are 1 to 3RE (RE is the earth radius) wide in the dawn-dusk direction. Recent kinetic simulations have found that DFs may break up into small-scale structures after they are produced by reconnection. Motivated by this simulation, we revisited the scale size of DFs in the dawn-dusk direction by using Cluster observations during the years when the inter-distance among Cluster spacecraft was between 1000 and 2000 km. We selected the DFs that were detected by more than one spacecraft and estimated the radii of these DFs by a simple geometrical analysis, which is based on comparison of DF normals observed by different spacecraft. We found a few DFs that were only a few ion inertial lengths in the dawn-dusk direction. These results point out the importance of multi-scale coupling during the evolution of DFs.展开更多
The rotation of the Earth's liquid core creates the Nearly Diurnal Free Wobble (NDFW). It is one of the problems of researching the Earth's liquid core for us to retrieve the parameters of the Earth's Free...The rotation of the Earth's liquid core creates the Nearly Diurnal Free Wobble (NDFW). It is one of the problems of researching the Earth's liquid core for us to retrieve the parameters of the Earth's Free Core Nutation (FCN),from the Earth's liquid core resonance of gravity tide waves on the diurnal frequency band. Since 1987, some scientists in many different countries have come to calculate the parameters of FCN by using the observational data of gravity tide waves on the diumal frequency band. They basically followed the Stacking method, which needed five diurnal waves for the resolution. In this paper, authors introduced the Aky-Btk value method with clearly geometrical meaning as a new method, which only requires three very high signal-noise-ratio waves o1, K1 and P1 for the resolution. Authors chose the observational data of the three superconducting gravimeter stations respectively located in Cantley of Canada, Wuhan of China and Brussels of Belgium, to compute the parameters of FCN. It was the first time that the observational results of the parameters of FCN obtained from gravitational tide were in accord with the parameters of FCN gained from VLBI since 1987.展开更多
This is a concise review of physics of the substorm in the magnetotail.It consists of two parts. The first part summarizes historical developments in the early days of the space age(1960-1975)when the basic concepts s...This is a concise review of physics of the substorm in the magnetotail.It consists of two parts. The first part summarizes historical developments in the early days of the space age(1960-1975)when the basic concepts such as magnetotail and reconnection were established and the leading model of the substorm was introduced.The second part is an overview of the research conducted in recent years(1995-2010)when very significant advances have been achieved in understanding the substorm physics by virtue of several major satellites missions that addressed the magnetotail physics intensively.展开更多
The Substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure curren...The Substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure current for the SCW originally was suggested to be the strong westward auroral electrojet （WEJ）. However, the SCW-WEJ system has no viable generator current. Similarly, the asymmetric or Partial Ring Current （PRC） increases in strength during the growth phase, and is sometimes associated with an enhanced Region 2 field-aligned current （FAC） closing to the ionosphere, but specifics of that closure have been lacking. Here we present a tmifying picture which includes the SCW post- and pre-midnight （AM and PM, respectively） currents and a generator current in the midnight portion of the PRC system, with these currents based upon a model of the nightside magnetotail magnetic geometry. That geometry consists of open north and south lobe regions surrounding a plasmasheet with two types of closed field line regions-stretched lines in the central part of the plasmasheet （SPS） and dipolar lines （DPS） between the low lati- tude boundary layer （LLBL） regions and the SPS. There is also an important plasmasheet transition region （TPS） in which the dipolar field near the plasmapause gradually transforms to stretched lines near the earthward edge of the SPS, and in which the midnight part of the PRC flows. We propose that our proposed near-onset current system consists of a central current which be- comes part of the midnight sector PRC and which is the generator, to which are linked two three-part current systems, one on the dawnside and one on the duskside. The three-part systems consist of up and down FACs closing as Pedersen currents in the iono- sphere. These 3-part systems are not activated until near-onset is reached, because of a lack of ionospheric conductivity in the appropriate locations where the Pedersen current closure occurs. The initial downward FAC of the 3-part dawnside system and the final upward FAC of the 3-part duskside system correspond to the AM and PM current segments, respectively, of the originally proposed SCW.展开更多
In the measurement of the Newtonian gravitational constant G with the time-of-swing method,the influence of the Earth's rotation has been roughly estimated before,which is far beyond the current experimental preci...In the measurement of the Newtonian gravitational constant G with the time-of-swing method,the influence of the Earth's rotation has been roughly estimated before,which is far beyond the current experimental precision.Here,we present a more complete theoretical modeling and assessment process.To figure out this effect,we use the relativistic Lagrangian expression to derive the motion equations of the torsion pendulum.With the correlation method and typical parameters,we estimate that the influence of the Earth's rotation on G measurement is far less than 1 ppm,which may need to be considered in the future high-accuracy experiments of determining the gravitational constant G.展开更多
Magnetic reconnection is one of the most important,dynamic phenomena in the magnetotail in terms of magnetic field line configuration change and energy release.It is believed to occur in the distant magnetotail mainly...Magnetic reconnection is one of the most important,dynamic phenomena in the magnetotail in terms of magnetic field line configuration change and energy release.It is believed to occur in the distant magnetotail mainly during southward interplanetary magnetic field periods and in the near-Earth magnetotail in association with substorms.In the present paper,we discuss several important issues concerning magnetic reconnection in the magnetotail associated with substorms,such as reconnection signatures,location,timing,spatial scale,and behavior,from the macroscopic,observational point of view.展开更多
Tailward ion outflows in the Martian-induced magnetotail are known to be one of the major channels for Martian atmospheric escape.On the basis of nearly 6.5 years of observations from the Mars Atmosphere and Volatile ...Tailward ion outflows in the Martian-induced magnetotail are known to be one of the major channels for Martian atmospheric escape.On the basis of nearly 6.5 years of observations from the Mars Atmosphere and Volatile EvolutioN(MAVEN)mission,we investigate the statistical distribution of tailward and Marsward fluxes of heavy ions(i.e.,O^(+),and O_(2)^(+))in the near-Mars magnetotail and explore their characteristic responses to the corotating interaction region(CIR),solar wind dynamic pressure,and local magnetic field intensity.Our results show that the tailward fluxes of oxygen ions and molecular oxygen ions in the magnetotail are significantly greater than their Marsward fluxes and that the tailward flux of molecular oxygen ions is generally larger than that of oxygen ions.Furthermore,the tailward ion flux distribution exhibits dependence on the CIR,solar wind dynamic pressure,and local magnetic field strength in a manner stronger than the Marsward ion flux distribution.According to the distribution of tailward ion fluxes,we calculate the corresponding escape rates of heavy ions and show that when the CIR occurs,the total escape rates of oxygen ions and molecular oxygen ions increase by a factor of~2 and~1.2,respectively.We also find that the escape rates of heavy ions increase with the enhancement of solar wind dynamic pressure,whereas the overall effect of the local magnetic field is relatively weak.Our study has important implications for improved understanding of the underlying mechanisms responsible for the Martian atmospheric escape and the evolution of the Martian atmospheric climate.展开更多
The azimuthal morphology of Earth's ring currents has consistently shown asymmetry during extreme space weather events at low latitudes,particularly during geomagnetic storms.A dawn-dusk pattern has been detected ...The azimuthal morphology of Earth's ring currents has consistently shown asymmetry during extreme space weather events at low latitudes,particularly during geomagnetic storms.A dawn-dusk pattern has been detected during the storm main phase through near-Earth and in-situ magnetic measurements.This asymmetry is believed to arise from asymmetric solar windmagnetosphere coupling and is linked to the closure of the ring current.Recent evidence has confirmed the existence of asymmetric ring currents during quiet times and the storm recovery phase.This phenomenon may be closely related to the evolution of ring currents,including plasma injection and decay processes.In this study,the local time asymmetry of the ring current is estimated using data from low-Earth-orbit Swarm and Macao Science Satellite-1(MSS-1)missions.Spherical harmonics models are developed to quantify the magnetic field of ring currents through external Gauss coefficients during both quiet periods and the storm recovery phase.Several features of dawn-dusk asymmetry are observed in various cases in different months.(1)The maximum difference in magnetic value across local time ranges from 3 to 10 nT,showing relative invariance compared with various Sym-H levels.(2)Stronger magnetic signals are detected at the premidnight sector during quiet times and at the afternoon sector during the storm recovery phase.(3)Magnetic perturbations remain at a lower level during the postmidnight and morning sectors.Although the pattern of local time asymmetry differs between quiet times and the recovery phase,dawn-dusk asymmetry remains the most pronounced feature,affecting the trapping and loss of charged particles in the inner magnetosphere.Combining Swarm and MSS-1 magnetic observations can enable convenient monitoring of the detailed azimuthal local time effects of the ring current at various disturbance levels in the future.展开更多
本文基于自己开发的全球三维磁层模型,模拟研究了IMF(Interplanetary Magnetic Field)北向并且By分量较大(时钟角为60°)时磁层顶三维结构及其重联图像.结果发现,IMF By为正时,在北极隙区附近尾-昏侧存在IMF与地磁场之间稳定持续的...本文基于自己开发的全球三维磁层模型,模拟研究了IMF(Interplanetary Magnetic Field)北向并且By分量较大(时钟角为60°)时磁层顶三维结构及其重联图像.结果发现,IMF By为正时,在北极隙区附近尾-昏侧存在IMF与地磁场之间稳定持续的重联现象;参与重联的地球磁场既有闭合磁力线也有开放磁力线;IMF在北极隙区与地球闭合磁力重联后一端与南磁极相连的磁力线在尾向运动时还可能与北尾瓣的开放磁力线重联而重新闭合,这种重联与磁力线循环过程不同于同一条IMF磁力线分别在南北半球与地磁场重联的模型.南极隙区的重联发生在尾-晨侧,其动力学过程与北极隙区情形类似.我们的模拟结果表明,IMF By较大时不可能发生IMF同一条磁力线分别在南北极隙区重联的情形,也不会因此而减少尾瓣的开放磁力线.展开更多
基金the National Natural Science Foundation of China(42030101,42204158)Shanghai Pujiang Program(No.21PJD078)+1 种基金Shanghai Science and Technology Innovation Action Plan(No.21DZ1206100)the Fundamental Research Funds for the Central Universities.
文摘Magnetosonic waves are an important medium for energy transfer in collisionless space plasma.Magnetosonic waves have been widely investigated in the upstream of the bow shock at Mars.These waves are believed to originate from pickup ions or reflected particles.By utilizing MAVEN spacecraft data,we have observed the occurrence of quasi-perpendicularly propagating magnetosonic emissions near the proton gyrofrequency in the Martian magnetotail region.These plasma waves are associated with a significant enhancement of proton and oxygen flux.The excited magnetosonic waves could possibly heat the protons through resonance and facilitate the ionospheric plasma escape.Our results could be helpful to better understand the Mars’magnetospheric dynamics and offer insights into possible energy redistribution between waves and plasma in the Martian nightside magnetosphere.
基金supported by the National Natural Science Foundation of China(41174140,41374168,and41174147)Research Fund for the Doctoral Program of Higher Education of China(20110141110043)+2 种基金Program for New Century Excellent Talents in University(NCET-13-0446)China Postdoctoral Science Foundation Funded Projectthe Fundamental Research Fund for the Central Universities(2042014kf0017,2012212020206,2012212020204)
文摘Two consecutive magnetic flux ropes, separated by less than 30 s(Dt \ 30 s), are observed within one magnetic reconnection diffusion region without strong guide field in the Earth's magnetotail by Cluster multispacecraft. The flux ropes are characterized by bipolar signatures of the south–north magnetic field component Bz accompanied with strong core magnetic field By, intense current J and density depletions inside of them. In spite of the small but non-trivial global scale negative guide field(–By), there exists a directional change of the core fields of two flux ropes, i.e.,-Byfor the first one, and Byfor the second one. The directions of the core fields are the same as the ambient cross-tail magnetic field component(By) just outside of flux ropes. Therefore, we suggest that the core field of flux ropes is formed by compression of the local preexisting Byand that the directional change of core field is due to the change of local preexisting By. Such a change in ambient Bymight be caused by some microscale physics.
基金supported by NSFC grants(42188101,42174209,42174207)the Specialized Research Fund for State Key Laboratories of Chinathe Strategic Pioneer Program on Space Science II,Chinese Academy of Sciences,grants XDA15350201,XDA15052500.
文摘Based on current sheet flapping motion on 27 August 2018 in the dusk flank magnetotail,as recorded by instruments aboard Magnetospheric Multiscale(MMS)spacecraft,we present the first study of guide field reconnection observed in the flux rope embedded in kink-like flapping current sheets near the dusk-side flank of the magnetotail.Unlike more common magnetotail reconnections,which are symmetric,these asymmetric small-scale(λ_(i)~650 km)reconnections were found in the highly twisted current sheet when the direction normal to the sheet changes from the Z direction into the Y direction.The unique feature of this unusual reconnection is that the reconnection jets are along the Z direction-different from outflow in the X direction,which is the more usual situation.This vertical reconnection jet is parallel or antiparallel to the up-and-down motion of the tail’s current sheet.The normalized reconnection rate R is estimated to be~0.1.Our results indicate that such asymmetric reconnections can significantly enlarge current sheet flapping,with large oscillation amplitudes.This letter presents direct evidence of guide field reconnection in a highly twisted current sheet,characterized by enlarged current sheet flapping as a consequence of the reconnection outflow.
文摘已有研究发现金星磁尾的太阳风氢离子(H^(+))和金星电离层氧离子(O^(+))存在大尺度涡流结构,该涡流从磁尾望向星球是逆时针的.为了确定该涡流的存在性,利用金星快车等离子体和高能原子分析仪(Analyzer of Space Plasmas and Energetic Atoms on Venus, ASPERA-4)的Fedorov矫正数据,分别在金星公转轨道坐标系(VSO)和太阳风电场坐标系(VSE)下对磁尾等离子体流进行了统计分析.结果显示,在VSO和VSE坐标系中都存在太阳风H^(+)和金星O^(+)的顺时针涡流结构.但是从已有的研究结果看,无论等离子体涡流是逆时针还是顺时针,其产生的磁场都与已知磁尾磁场结构不相符;考虑到金星和火星空间环境的相似性及火星磁尾太阳风H^(+)并不存在完整等离子体涡流的情况,认为金星磁尾可能并不存在大尺度等离子体涡流.金星的等离子体特征需要未来更多卫星观测研究.
基金supported by the National Natural Science Foundation of China (NSFC) under grant 41774154 and 41504123the Science Foundation of Jiangxi Province under grant 20122BAB21 2002+1 种基金the Nanchang University graduate innovation special fund project under grant CX2017106the Key Industry Innovation Chain of Shaanxi under grant 2018JQ4032
文摘Previous studies suggest that dipolarization fronts (DFs) are 1 to 3RE (RE is the earth radius) wide in the dawn-dusk direction. Recent kinetic simulations have found that DFs may break up into small-scale structures after they are produced by reconnection. Motivated by this simulation, we revisited the scale size of DFs in the dawn-dusk direction by using Cluster observations during the years when the inter-distance among Cluster spacecraft was between 1000 and 2000 km. We selected the DFs that were detected by more than one spacecraft and estimated the radii of these DFs by a simple geometrical analysis, which is based on comparison of DF normals observed by different spacecraft. We found a few DFs that were only a few ion inertial lengths in the dawn-dusk direction. These results point out the importance of multi-scale coupling during the evolution of DFs.
文摘The rotation of the Earth's liquid core creates the Nearly Diurnal Free Wobble (NDFW). It is one of the problems of researching the Earth's liquid core for us to retrieve the parameters of the Earth's Free Core Nutation (FCN),from the Earth's liquid core resonance of gravity tide waves on the diurnal frequency band. Since 1987, some scientists in many different countries have come to calculate the parameters of FCN by using the observational data of gravity tide waves on the diumal frequency band. They basically followed the Stacking method, which needed five diurnal waves for the resolution. In this paper, authors introduced the Aky-Btk value method with clearly geometrical meaning as a new method, which only requires three very high signal-noise-ratio waves o1, K1 and P1 for the resolution. Authors chose the observational data of the three superconducting gravimeter stations respectively located in Cantley of Canada, Wuhan of China and Brussels of Belgium, to compute the parameters of FCN. It was the first time that the observational results of the parameters of FCN obtained from gravitational tide were in accord with the parameters of FCN gained from VLBI since 1987.
文摘This is a concise review of physics of the substorm in the magnetotail.It consists of two parts. The first part summarizes historical developments in the early days of the space age(1960-1975)when the basic concepts such as magnetotail and reconnection were established and the leading model of the substorm was introduced.The second part is an overview of the research conducted in recent years(1995-2010)when very significant advances have been achieved in understanding the substorm physics by virtue of several major satellites missions that addressed the magnetotail physics intensively.
文摘The Substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure current for the SCW originally was suggested to be the strong westward auroral electrojet （WEJ）. However, the SCW-WEJ system has no viable generator current. Similarly, the asymmetric or Partial Ring Current （PRC） increases in strength during the growth phase, and is sometimes associated with an enhanced Region 2 field-aligned current （FAC） closing to the ionosphere, but specifics of that closure have been lacking. Here we present a tmifying picture which includes the SCW post- and pre-midnight （AM and PM, respectively） currents and a generator current in the midnight portion of the PRC system, with these currents based upon a model of the nightside magnetotail magnetic geometry. That geometry consists of open north and south lobe regions surrounding a plasmasheet with two types of closed field line regions-stretched lines in the central part of the plasmasheet （SPS） and dipolar lines （DPS） between the low lati- tude boundary layer （LLBL） regions and the SPS. There is also an important plasmasheet transition region （TPS） in which the dipolar field near the plasmapause gradually transforms to stretched lines near the earthward edge of the SPS, and in which the midnight part of the PRC flows. We propose that our proposed near-onset current system consists of a central current which be- comes part of the midnight sector PRC and which is the generator, to which are linked two three-part current systems, one on the dawnside and one on the duskside. The three-part systems consist of up and down FACs closing as Pedersen currents in the iono- sphere. These 3-part systems are not activated until near-onset is reached, because of a lack of ionospheric conductivity in the appropriate locations where the Pedersen current closure occurs. The initial downward FAC of the 3-part dawnside system and the final upward FAC of the 3-part duskside system correspond to the AM and PM current segments, respectively, of the originally proposed SCW.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11575160 and 11805074)the Postdoctoral Science Foundation of China(Grant Nos.2017M620308 and 2018T110750).
文摘In the measurement of the Newtonian gravitational constant G with the time-of-swing method,the influence of the Earth's rotation has been roughly estimated before,which is far beyond the current experimental precision.Here,we present a more complete theoretical modeling and assessment process.To figure out this effect,we use the relativistic Lagrangian expression to derive the motion equations of the torsion pendulum.With the correlation method and typical parameters,we estimate that the influence of the Earth's rotation on G measurement is far less than 1 ppm,which may need to be considered in the future high-accuracy experiments of determining the gravitational constant G.
基金Supported in part by the Global COE Program of Nagoya University "Quest for Fundamental Principles in the Universe(QFPU)" from JSPS and MEXT of Japan
文摘Magnetic reconnection is one of the most important,dynamic phenomena in the magnetotail in terms of magnetic field line configuration change and energy release.It is believed to occur in the distant magnetotail mainly during southward interplanetary magnetic field periods and in the near-Earth magnetotail in association with substorms.In the present paper,we discuss several important issues concerning magnetic reconnection in the magnetotail associated with substorms,such as reconnection signatures,location,timing,spatial scale,and behavior,from the macroscopic,observational point of view.
基金supported by the National Natural Science Foundation of China (grants 42025404, 42188101, 41904144, and 41674163)the preresearch projects on Civil Aerospace Technologies (grants D020303, D020104, and D020308)+2 种基金funded by the China National Space Administrationthe B-type Strategic Priority Program of the Chinese Academy of Sciences (grant XDB41000000)the Fundamental Research Funds for the Central Universities (grants 2042021kf1045 and 2042021kf1056)
文摘Tailward ion outflows in the Martian-induced magnetotail are known to be one of the major channels for Martian atmospheric escape.On the basis of nearly 6.5 years of observations from the Mars Atmosphere and Volatile EvolutioN(MAVEN)mission,we investigate the statistical distribution of tailward and Marsward fluxes of heavy ions(i.e.,O^(+),and O_(2)^(+))in the near-Mars magnetotail and explore their characteristic responses to the corotating interaction region(CIR),solar wind dynamic pressure,and local magnetic field intensity.Our results show that the tailward fluxes of oxygen ions and molecular oxygen ions in the magnetotail are significantly greater than their Marsward fluxes and that the tailward flux of molecular oxygen ions is generally larger than that of oxygen ions.Furthermore,the tailward ion flux distribution exhibits dependence on the CIR,solar wind dynamic pressure,and local magnetic field strength in a manner stronger than the Marsward ion flux distribution.According to the distribution of tailward ion fluxes,we calculate the corresponding escape rates of heavy ions and show that when the CIR occurs,the total escape rates of oxygen ions and molecular oxygen ions increase by a factor of~2 and~1.2,respectively.We also find that the escape rates of heavy ions increase with the enhancement of solar wind dynamic pressure,whereas the overall effect of the local magnetic field is relatively weak.Our study has important implications for improved understanding of the underlying mechanisms responsible for the Martian atmospheric escape and the evolution of the Martian atmospheric climate.
基金supported by the National Natural Science Foundation of China(Grant Nos.12250014,and 12250012)the Macao Foundation。
文摘The azimuthal morphology of Earth's ring currents has consistently shown asymmetry during extreme space weather events at low latitudes,particularly during geomagnetic storms.A dawn-dusk pattern has been detected during the storm main phase through near-Earth and in-situ magnetic measurements.This asymmetry is believed to arise from asymmetric solar windmagnetosphere coupling and is linked to the closure of the ring current.Recent evidence has confirmed the existence of asymmetric ring currents during quiet times and the storm recovery phase.This phenomenon may be closely related to the evolution of ring currents,including plasma injection and decay processes.In this study,the local time asymmetry of the ring current is estimated using data from low-Earth-orbit Swarm and Macao Science Satellite-1(MSS-1)missions.Spherical harmonics models are developed to quantify the magnetic field of ring currents through external Gauss coefficients during both quiet periods and the storm recovery phase.Several features of dawn-dusk asymmetry are observed in various cases in different months.(1)The maximum difference in magnetic value across local time ranges from 3 to 10 nT,showing relative invariance compared with various Sym-H levels.(2)Stronger magnetic signals are detected at the premidnight sector during quiet times and at the afternoon sector during the storm recovery phase.(3)Magnetic perturbations remain at a lower level during the postmidnight and morning sectors.Although the pattern of local time asymmetry differs between quiet times and the recovery phase,dawn-dusk asymmetry remains the most pronounced feature,affecting the trapping and loss of charged particles in the inner magnetosphere.Combining Swarm and MSS-1 magnetic observations can enable convenient monitoring of the detailed azimuthal local time effects of the ring current at various disturbance levels in the future.
文摘本文基于自己开发的全球三维磁层模型,模拟研究了IMF(Interplanetary Magnetic Field)北向并且By分量较大(时钟角为60°)时磁层顶三维结构及其重联图像.结果发现,IMF By为正时,在北极隙区附近尾-昏侧存在IMF与地磁场之间稳定持续的重联现象;参与重联的地球磁场既有闭合磁力线也有开放磁力线;IMF在北极隙区与地球闭合磁力重联后一端与南磁极相连的磁力线在尾向运动时还可能与北尾瓣的开放磁力线重联而重新闭合,这种重联与磁力线循环过程不同于同一条IMF磁力线分别在南北半球与地磁场重联的模型.南极隙区的重联发生在尾-晨侧,其动力学过程与北极隙区情形类似.我们的模拟结果表明,IMF By较大时不可能发生IMF同一条磁力线分别在南北极隙区重联的情形,也不会因此而减少尾瓣的开放磁力线.
