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Amari, T., Luciani, J. F., Aly, J. J., Mikic, Z., and Linker, J. 2003, ApJ, 585, 1073

Coronal Mass Ejection: Initiation, Magnetic Helicity, and Flux Ropes. L. Boundary Motion-Driven Evolution. Amari, T., Luciani, J. F., Aly, J. J., Mikic, Z., and Linker, J. 2003, ApJ, 585, 1073. 2003.6.9 Taiyou Zasshkai Shiota. Abstract.

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Amari, T., Luciani, J. F., Aly, J. J., Mikic, Z., and Linker, J. 2003, ApJ, 585, 1073

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  1. Coronal Mass Ejection: Initiation, Magnetic Helicity, and Flux Ropes. L. Boundary Motion-Driven Evolution Amari, T., Luciani, J. F., Aly, J. J., Mikic, Z., and Linker, J. 2003, ApJ, 585, 1073 2003.6.9 Taiyou Zasshkai Shiota

  2. Abstract • They studied 3D MHD simulation of the triggering of CMEs. • A twisting velocity field to foot points at the bottom of the box • relaxation to numerical force-free state • converging motions of foot points of the force-free field

  3. Introduction What is the nature of the triggering of CMEs ? Observations of preeruptive configuration (reviewed by Priest & Forbes 2002) • shear between Ha fibrils and the inversion line • converging motions toward the inversion line Another important feature of CMEs • the presence of a prominence • the ejection of a plasmoid Important issue Is it necessary to have a twisted flux rope (in equilibrium) prior to disruption? or is the twisted flux rope created as a consequence of reconnection during the disruption ?

  4. 2D Modelizations of the triggering of CMEs the evolutions are driven by slow motions of foot points • purely shearing motion with Cartesian (Aly&Amari 1985; Aly 1990; Amari et al. 1996, 1997; etc.) and spherical geometry (Mikic & Linker 1994; Aly 1995) => the formation and ejection of plasmoid • converging motions analytically (Priest & Forbes 1990; Forbes & Priest 1995) => catastropic non-equilibrium transition with resistive simulations (Forbes 1991; Inhester, Birn, & Hesse 1992) => plasmoid and impulsive phase

  5. 3D Modelizations of the triggering of CMEs the evolutions of bipolar magnetic configurations are also driven by slow motions of foot points • shearing motion; twisting components (Amari et al. 1996; Tokman & Bellan 2002; Hagyard 1990) => the formation and ejection of plasmoid • converging motions have not been considered yet => to investigate the possible effects of the boundary on a bipolar configuration

  6. The important questions The questions answered in this paper. • Do the converging motions contribute to the helicity contents of the magnetic structure? • How long can the field evolve quietly in quasi-static way? • What happens when quiet phase ends, is there production of a twisted magnetic flux rope in equilibrium, or is the system subject immediately to a global disruption?

  7. Definition of magnetic energy and helicity • magnetic energy • magentic helicity where, π: potential field

  8. The tangential Electric field on S • from Ohm’s law • this can be decomposed into irrotational and solenoidal parts • f(x,y,t), g(x,y,t) are

  9. Evolution of magnetic energy and helicity • magnetic energy • magentic helicity

  10. Initial Potential Configuration

  11. MHD equations The equations are solved by semi-implicit scheme.

  12. Twisting motions

  13. The evolution The evolution along this phase is almost quasi-static. Magnetic energy increases monotonically Magnetic helicity increases monotonically

  14. Magnetic Energy and Helicity

  15. Converging motions

  16. Evolution of tS = 200tA t = 450tA t = 480tA

  17. Evolution of tS = 200tA Three part structure t = 498tA t = 530tA

  18. Evolution of tS = 200tA

  19. Transverse magnetic field at z=0

  20. Evolution of tS = 50tA

  21. Evolution of tS = 400tA

  22. Conclusion They reported the results of numerical simulations • A series of initial stable force-free fields B0=B(t0) with |H(t0)|>0 are constructed by deforming a given potential field in two step process (twisting + relaxation) This evolution is almost quasi-static. • Imposing motions converging toward the inversion line, then quiet phase is stopped and configuration experiences a transition to a dynamic and strongly dissipative phase, during which reconnection leads to the formation of a twisted flux rope, however not in equilibrium.

  23. Conclusion(cont.) • Their results may be relevant to the problem of the initiation of CMEs,(global disruption may occur in a magnetic structure with nonzero helicity contents), driven by the converging motions. • Helicity keeps constant value during quasi-static phase, therefore, it neds to have been produced during a prior phase. • Helical structures associated with prominences ejected as part of the CMEs are sometimes observed. However, it is still open problem whether a rope does exist prior to disruption, thus possibly playing a role in its triggering.

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