TheRiceConvectionModel-空间天气学国家重点实验室.ppt

1、很汗呢！,Introduction to Magnetosphere and MHD Modeling to S-M-I system,WangJuanState Key Laboratory for Space Weather, CSSAR,3,Outline,Interaction Between Magnetosphere and Solar Wind Magnetosphere ModelsReconnection Around the subsolar point Polar cusp Magnetic tailKH InstabilityCoupling between Magne

2、tosphere and IonosphereMHD Simulations of SMI SystemWhat has been done,4,Magnetosphere,Under the effect of the solar wind，the intrinsic magnetic field ofthe earth forms a natural protective barrier. In magnetosphere, there are many complex natural phenomena, such as reconnections,magnetic storms, au

3、roras and etc.,Figure 1. Configuration of the magnetosphere in the noon-midnight meridian,5,Transportation of energy and momentumfrom solar wind to Magnetosphere and ionosphere becomes a great hot point in the field of space physics,Magnetosphere,6,Magnetosheath Between bow shock and magnetopause. C

4、ompared with magnetosphere, it has high plasma density and low magnetic intensity Magnetopause boundary (transition region into the magnetosphere) Between magnetosheath and magnetosphere Current piece. ChapmanFerraro current,Basic Structures,Bow shock Solar wind passing through it would be decelerat

5、ed, compressed and heated up.,7,Magnetosphere & Solar Wind,The main body of the solar wind cannot pass through the magnetopausedirectly. The velocity is decelerated to subsonic speed. Then the solar wind pass around the magnetopause. It compresses the dayside of the magneto-pause and stretches the n

6、ight side of the magnetopause to form the magnetic tail.,Its position is mainly controlled by magnetic pressure of magnetosheath and dynamical pressure of the solar wind. Magnetic storms with sudden commencements (ssc) occurs when there are IMF shocks or discontinuities ( kinetic pressure of the sol

7、ar wind increases suddenly), the magnetic field on the ground increases dozens of nTs because of the compression of the magnetopause.,Open field Length: Several hundreds Re . Radius: about 22 Re,Magnetic tail(3 parts: tail lobe, plasma sheet, plasma sheet boundary Estman et al.),8,Magnetosphere Mode

8、ls,Magnetic reconnection model Dungey(1961),Southern IMF Dayside of the magnetosphere. open the closed magnetic lines and magnetic lines transport towards the tail. The convection electric field in the solar wind transport into the magnetosphere, driving convection in the magnetosphere. Geomagnetic

9、tail earthward plasma flow & tailward plasma flow Northern IMF Polar cusp ( dayside is compressed & night side stretches towards the tail ),The magnetic field lines in the magnetosphere are closed. The solar wind send its energy and momentum into the magnetosphere by viscosity. The convection electr

10、ic field in the solar wind transport into the magnetosphere, driving convection in the magnetosphere.,Viscosity model Oxford & Hines(1961),9,The reconnection model proposed by Dungey was validated by observation. It provided a physical mechanism that transform the magnetic energy into kinetic energy

11、 and thermal energy quickly.,Magnetic reconnection plays a great role in the physical process of solar wind heating, connection between solar wind and magnetosphere ,magnetic storms, and etc.,Magnetic reconnection,从1961年至今，对磁层是开放还是闭合，对粘性和重联作用的重要性及具体机制有过很多讨论，也存在不少有待解决的问题。但各种观测都肯定了对流运动的存在，并证实了它是磁层的基本物

12、理过程。而磁层和电离层中的种种现象正是在此对流背景下进行并与之密切相关的。,10,Multi-spacecraft in situ observations were used to infer the global geometry of the magnetic merging line, or X line (Paschmann 2008).,Phan et al.2006 used the Geotail and Wind data during stable dawn ward dominated IMF to infer the presence of a tilted X lin

13、e hinged near the sub-solar point. On the basis of a statistical study of 290 fast flow events measured by Double Star/TC-1 in low latitudes and Cluster in high latitudes, a possible S-shaped X line exists for generic dawn ward IMF cases Pu et al. 2007. The configuration of the merging line inferred

14、 from these observations is consistent with the prediction from the component reconnection hypothesis,11,KH Instability,Figure 1 shows color contours of the physical parameters of an unsteady magnetosphere in the equatorial plane, including the x and y components of the velocity (vx, vy), the total

15、velocity (v), the logarithm of the number density (log10n(cm3), the thermal pressure (log10P(nPa) and the magnetic field (log10B(nT).,The bow shock and the magnetopause intersect with the SunEarth line at about x =14RE and 10 RE, respectively,12,KH Instability,Mechanism -Velocity shear layer across

16、the magnetopause. -Corresponding surface waves. The surface wave increases roughly from 1 RE (at the beginning) to 8 RE (flank region) . - Many vortices are generated along the magnetopause point from the dayside region to the magnetotail, along the direction of the flows near the magnetopause. The

17、magnetopause boundary appears to be wavelike at the flank region. Conclusion: The solar wind momentum and energy is then transported into the magnetosphere directly. frozen-in-flux condition,13,Magnetosphere & Ionosphere,The coupling process between magnetosphere and ionosphere is complex. It can on

18、ly be modeled on the basis of simplification,14,Magnetosphere & Ionosphere,Hypothesis,In the region between inner boundary of magnetosphere and ionosphere, dipole field is dominant. Electrical potential is equi-potential along magnetic field lines. Solve an elliptic equation to obtain the distributi

19、on of the electric potential in the ionosphere.(MUDPACK) Movement in magnetosphere currents closing with the current in ionosphere electric conductivity is the key Pedersen conductivity (uniform distribution), Hall conductivity is ignored.,15,Mapping error of electric field. Potential difference bet

20、ween magnetosphere and corresponding ionosphere point. Presence of parallel electric fields. Deposition of energetic particle from magnetosphere into ionosphere and Solar ultraviolet radiation. increase the electric conductivity in auroral zone, so then affects the distribution of current and electr

21、ic field in the ionosphere, thereby influences electric field and current in the magnetosphere. Electric conductivity in the ionosphere increases. when the high speed electron flow accelerates,Incomplete coupling,Magnetosphere & Ionosphere,16,Magnetosphere & Ionosphere,Coupling process(2 kinds),self

22、-consistent RCM, Wolf and Kanmide,1983 key parameters separated,Intensive study RCM Darren L.De Zeeuw et al.,2004,17,Field-aligned current(Birkeland current),Magnetosphere & Ionosphere,Current flow into and out of the polar ionosphere along the magnetic field lines Birkland,1908.,Horizontal current

23、flow at 100-200km concluded from geomagnetic observation.,Field-aligned current was conformed by satellite observation in the middle of 1960s.,18,Field Aligned Current,The morphology of field aligned current in large scales,Figure . TRIAD observation,Region I Down from dawn side , and up from dusk s

24、ide. Maximum 1.52.5 , dayside. Region II Opposite to region I Maximum 0.51.0 ,nightside.,19,The magnetic field intensity of IMF and the force exerted upon the earth by the solar wind determine some characters of region 1 and 2 field aligned current. Southern density of the currents increases. Northe

25、rn,Field Aligned Current,very strong north Bz effect. Flow direction of NBz is opposite to region 1 current. modulated by By. By0，northern cusp region dominated by current flowing out, southern cusp region dominated by current flowing in; By0, opposite.,20,MHD Simulations of SMI System,Current model

26、s,What has been done,What I will do is using CE/SE + MHD method to model the stable magnetosphere under the steady effects of the solar wind.,a unied treatment of space and time conservation elements (CEs) and solution elements (SEs) solving the physical variables and their spatial derivatives simul

27、taneously a novel shock capturing strategy without using Riemann solvers,CESE has many non-traditional features,3D ideal MHD equations,22,Plans,Curvilinear coordinate system AMR (PARAMESH) Divergence-free condition( powell Source Term in the Divergence Form) Splitting the magnetic field to reduce th

28、e numerical error in the divergence of ( ) Artificial resistance term :,23,Dimensionless elementary unit,Solution domain and grids,内边界以下的区域从解域中剔除，一方面是为了避免Alfven速度过高，另一方面是该区域内地球自转和等离子体动力论效应起重要作用，不适合采用单纯的MHD描述。,initial conditions,24,initial magnetic field,magnetosphere region combined field of the ear

29、ths dipole field and the mirror dipole field( x= 15 Re),magnetic scalar potential,25,solar wind region,the initial value used in the procedure,magnetic field,The first left items of the above expressions is magnetic dipole field , the second items is mirror dipole field .,Figure. Initializing the computation region,26,inner boundary,27,where,28,Results,t =150,t =500,29,References,30,Good luck to you!,