On the basis of the plasma, electric and magnetic fields jointly observed by Cluster and the Double Star TC-I spacecraft in the Earth＇s magnetotail, we have investigated the earthward flow bursts by introducing the m...On the basis of the plasma, electric and magnetic fields jointly observed by Cluster and the Double Star TC-I spacecraft in the Earth＇s magnetotail, we have investigated the earthward flow bursts by introducing the momentum equation in the X-direction in the ideal conditions of magneto hydrodynamics （MHD）. One earthward flow burst with a peak in excess of 500 km/s was selected, when the four spacecraft of Cluster were located around -16 RE and TC-1 was located around -10 RE in the X-direction. The inter-spacecraft distances in Y and Z directions were smaller than the statistical spatial scales of the bursty bulk flows. When the Y components of E and -VxB were compared, there was no clear breakdown of the frozen-in condition during the earthward flow burst. With the measured plasma and magnetic parameters from two spacecraft at different positions in the magnetotail, the X component of the pressure gradient was calculated. Magnetic tension was calculated using the mag- netic field measured at four points, which could be compared with the assumed constant in the past research with single satel- lite. When the pressure gradient and the magnetic tension were put into the MHD momentum equation, some samples of the earthward flow bursts were accelerated and some were decelerated. The braking process of the earthward flow burst was more complicated than what the past results had shown. The accelerated samples accounted for about one third of the whole earth- ward flow bursts and discontinuously located among the decelerated elements. The original single earthward flow burst event might be split into several short flow bursts when it was moving to the Earth. Our results may partly illustrate that the duration of fast flows during three phases of substorm becomes short near the Earth. The results are consistent with the past results that fast flows intrude to places earthward the typical braking region.展开更多
The magnetosphere is the outermost layer of the geospace, and the interaction of the solar wind with the magnetosphere is the key element of the space weather cause-and-effect chain process from the Sun to Earth, whic...The magnetosphere is the outermost layer of the geospace, and the interaction of the solar wind with the magnetosphere is the key element of the space weather cause-and-effect chain process from the Sun to Earth, which is one of the most challenging scientific problems in the geospace weather study. The nonlinearity, multiple component, and time-dependent nature of the geospace make it very difficult to describe the physical process in geospace using traditional analytic analysis approach. Numerical simulations, a new research tool developed in recent decades, have a deep impact on the theory and application of the geospace. MHD simulations started at the end of the 1970s, and the initial study was limited to two-dimensional (2D) cases. Due to the intrinsic three-dimensional (3D) characteristics of the geospace, 3D MHD simulations emerged in the 1980s, in an attempt to model the large-scale structures and fundamental physical processes in the magnetosphere. They started to combine with the space exploration missions in the 1990s and make comparisons with observations. Physics-based space weather forecast models started to be developed in the 21st century. Currently only a few space-power countries such as USA and Japan have developed 3D magnetospheric MHD models. With the rapid advance of space science in China, we have developed a new global MHD model, namely PPMLR-MHD, which has high order spatial accuracy and low numerical dissipation. In this review, we will briefly introduce the global 3D MHD modeling, especially the PPMLR-MHD code, and summarize our recent work based on the PPMLR-MHD model, with an emphasis on the interaction of interplanetary shocks with the magnetosphere, large-scale current systems, reconnection voltage and transpolar potential drop, and Kelvin-Helmholtz (K-H) instability at the magnetopause.展开更多
Given a continuous boundary value on the boundary of a ＂simply closed surface＂ as that encloses the whole Earth, a regular harmonic fictitious field V＊（P） in the domain outside an inner sphere Ki that lies inside...Given a continuous boundary value on the boundary of a ＂simply closed surface＂ as that encloses the whole Earth, a regular harmonic fictitious field V＊（P） in the domain outside an inner sphere Ki that lies inside the Earth could be determined, and it is proved that V＊（P） coincides with the Earth＇s real field V（P） in the whole domain outside the Earth. Since in the domain outside the inner sphere Ki and the fictitious regular harmonic function V＊（P） could be expressed as a uniformly convergent spherical harmonic series, it is concluded that the Earth＇s potential field could be expressed as a uniformly convergent spherical harmonic expansion series in the whole domain outside the Earth.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 40931054, 41174141 and 40904042)the National Basic Research Program of China ("973" Project)(Grant No. 2011CB811404)+1 种基金Specialized Research Fund for State Key Laboratories (Grant No. KP201104)supported by Chinese Academy of Sciences (CAS) visiting Professorship for Senior International Scientists (Grant No. 2009S1-54)
文摘On the basis of the plasma, electric and magnetic fields jointly observed by Cluster and the Double Star TC-I spacecraft in the Earth＇s magnetotail, we have investigated the earthward flow bursts by introducing the momentum equation in the X-direction in the ideal conditions of magneto hydrodynamics （MHD）. One earthward flow burst with a peak in excess of 500 km/s was selected, when the four spacecraft of Cluster were located around -16 RE and TC-1 was located around -10 RE in the X-direction. The inter-spacecraft distances in Y and Z directions were smaller than the statistical spatial scales of the bursty bulk flows. When the Y components of E and -VxB were compared, there was no clear breakdown of the frozen-in condition during the earthward flow burst. With the measured plasma and magnetic parameters from two spacecraft at different positions in the magnetotail, the X component of the pressure gradient was calculated. Magnetic tension was calculated using the mag- netic field measured at four points, which could be compared with the assumed constant in the past research with single satel- lite. When the pressure gradient and the magnetic tension were put into the MHD momentum equation, some samples of the earthward flow bursts were accelerated and some were decelerated. The braking process of the earthward flow burst was more complicated than what the past results had shown. The accelerated samples accounted for about one third of the whole earth- ward flow bursts and discontinuously located among the decelerated elements. The original single earthward flow burst event might be split into several short flow bursts when it was moving to the Earth. Our results may partly illustrate that the duration of fast flows during three phases of substorm becomes short near the Earth. The results are consistent with the past results that fast flows intrude to places earthward the typical braking region.
基金supported by the National Basic Research Program of China (Grant No.2012CB825602)National Natural Science Foundation of China (Grant Nos.41204118 & 41231067)in part by the Specialized Research Fund for State Key Laboratories of China
文摘The magnetosphere is the outermost layer of the geospace, and the interaction of the solar wind with the magnetosphere is the key element of the space weather cause-and-effect chain process from the Sun to Earth, which is one of the most challenging scientific problems in the geospace weather study. The nonlinearity, multiple component, and time-dependent nature of the geospace make it very difficult to describe the physical process in geospace using traditional analytic analysis approach. Numerical simulations, a new research tool developed in recent decades, have a deep impact on the theory and application of the geospace. MHD simulations started at the end of the 1970s, and the initial study was limited to two-dimensional (2D) cases. Due to the intrinsic three-dimensional (3D) characteristics of the geospace, 3D MHD simulations emerged in the 1980s, in an attempt to model the large-scale structures and fundamental physical processes in the magnetosphere. They started to combine with the space exploration missions in the 1990s and make comparisons with observations. Physics-based space weather forecast models started to be developed in the 21st century. Currently only a few space-power countries such as USA and Japan have developed 3D magnetospheric MHD models. With the rapid advance of space science in China, we have developed a new global MHD model, namely PPMLR-MHD, which has high order spatial accuracy and low numerical dissipation. In this review, we will briefly introduce the global 3D MHD modeling, especially the PPMLR-MHD code, and summarize our recent work based on the PPMLR-MHD model, with an emphasis on the interaction of interplanetary shocks with the magnetosphere, large-scale current systems, reconnection voltage and transpolar potential drop, and Kelvin-Helmholtz (K-H) instability at the magnetopause.
基金Supported by the National Natural Science Foundation of China （No.40637034, No. 40574004）, the National 863 Program of China （No. 2006AA12Z211）. The author thanks Prof. Dr. Sjoberg for his valuable comments on the original manuscript.
文摘Given a continuous boundary value on the boundary of a ＂simply closed surface＂ as that encloses the whole Earth, a regular harmonic fictitious field V＊（P） in the domain outside an inner sphere Ki that lies inside the Earth could be determined, and it is proved that V＊（P） coincides with the Earth＇s real field V（P） in the whole domain outside the Earth. Since in the domain outside the inner sphere Ki and the fictitious regular harmonic function V＊（P） could be expressed as a uniformly convergent spherical harmonic series, it is concluded that the Earth＇s potential field could be expressed as a uniformly convergent spherical harmonic expansion series in the whole domain outside the Earth.
