Three-dimensional Numerical Research Of Coronal Mass Ejections

The space weather research includes a number of di?erent physics domains:solar corona, inner heliosphere, magnetosphere, ionosphere electrodynamics, andupper atmosphere and so on. The solar-interplanetary propagation process of thespace disaster weather is one of the most important contents of the space weatherresearch. The magnetohydrodynamic(MHD) modeling plays an very importantrole in studying the process, and can provide appropriate conditions for coupledmodel of magnetosphere, ionosphere electrodynamics, and upper atmosphere.In this paper, we develop solar-interplanetary CESE MHD model(SIP-CESEmodel). Then, we use our newly developed SIP-CESE MHD model to simu-late three-dimensional characters of the propagation and transit process of 12May 1997 CME event and three successive Coronal Mass Ejections (CMEs) ofNovember 4-5, 1998 from sun to earth. In these studies, the three-dimensionalbackground solar wind is derived from a 3D time-dependent numerical MHDmodel by input measured photospheric magnetic fields. The initiation of theseCMEs is partially determined from spacecraft observations.In order to establish 3D model in the spherical shell, a grid system of non-overlapped pentahedron is constructed. Based on the 3-D grid structure, weintegrate numerical models of the Solar Corona, Inner Heliosphere into a coupledmodel (SIP-CESE MHD Model). The model can simulate the three-dimensionalbackground solar wind from Sun to Earth. As validation of the SIP-CESE MHDModel, the model is applied to 3-dimensional MHD equations by time-relaxationapproach, with the purpose of modeling the steady-state solar atmospheric studyby using multipole magnetic fields and measured solar surface magnetic fields,respectively. The model has many advantages. Firstly, space and time are uni-fied and treated on the same footing. Secondly, the gradients of ?ow variablesare solved simultaneously as independent unknowns. Thirdly, It is capable ofhandling both continuous and discontinuous ?ows very well. Finally, no ap-proximation techniques other than Taylor's series expansion are employed in this method, so the computational logic of the present method is considerably simpler.Afterwards, Our newly developed SIP-CESE MHD model is used to simu-late sun-earth connection event with the well-studied 12 May 1997 CME event asan example. The main features and approximations of our numerical model are(1) the background solar wind is derived from a 3D time-dependent numericalMHD model by input measured photospheric magnetic fields and (2) transientdisturbances are derived from solar surface by introducing a mass ?ow of hotplasma. In our simulation, the initial parameters of the CME, such as directionand angular size of the expanding CME, are determined from the observationdata. The numerical simulation provided us with a relatively satisfactory com-parison with the WIND spacecraft observations. This shows that this numericalmodel has capability in modeling realistic 3-dimensional CME.According to Burlaga et al. (2002), only about one-third of Earth directedsolar eruptions leads to the passage of an MC at Earth; the majority of the ejec-tions form either complex ejecta or multiple MCs (when the di?erent MCs in theejecta can still be distinguished at Earth). Homologous eruptions provide a goodexample of potential interactions of CMEs on their way to Earth. We present thesolar-terrestrial transit process of three successive CMEs of November 4-5, 1998originating from active region 8375 by using newly developed SIP-CESE MHDmodel. These CMEs interact with each other while they are propagating in inter-planetary space and finally form a complex ejecta. The quiet solar wind is startedfrom Parker-like 1D solar wind solution and the magnetic field map calculatedfrom the solar photospheric magnetic field data. In our simulation, the ejectionsare initiated using pulse in the real active region 8375. The initial parametersof the CMEs , such as speed, direction and angular size of the expanding CME,are determined from the SOHO/LASCO data with the Cone-model. The resultsshow that our simulation can reproduce and explain some of the general featuresobserved by satellite for the complex ejecta.