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In collaboration with Prof. You-Qiu HU, Mr. Shu-ji Sun

Catastrophic eruption of magnetic flux rope in the corona and solar wind with and without magnetic reconnection 磁场重联对日冕与太阳风中 磁绳灾变式喷发的影响 Yao Chen Univ. of Science & Technology of China yaochen@ustc.edu.cn http://staff.ustc.edu.cn/~yaochen. In collaboration with Prof. You-Qiu HU, Mr. Shu-ji Sun.

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In collaboration with Prof. You-Qiu HU, Mr. Shu-ji Sun

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  1. Catastrophic eruption of magnetic flux rope in the corona and solar wind with and without magnetic reconnection磁场重联对日冕与太阳风中磁绳灾变式喷发的影响Yao ChenUniv. of Science & Technology of Chinayaochen@ustc.edu.cnhttp://staff.ustc.edu.cn/~yaochen In collaboration with Prof. You-Qiu HU, Mr. Shu-ji Sun

  2. Flux rope catastrophe: a trigger mechanism for solar eruptive phenomena (CMEs, Flares, Prominence eruptions) Concept 1: Flux rope a twisted magnetic loop anchored in the photosphere Diagram of a 3d flux rope Chen, J. 1989 Field and current components inside the rope: Poloidal (环向) & toroidal (轴向)

  3. Concept 2: A catastrophe is: An onset of global instability of the magnetic configuration caused by a tiny change of one or a few System parametersa net outward resultant of magnetic forces acting on the flux rope eruption (Meta- stabledynamic- state) Eruptive speed be comparable to the Alfven speed (~ 1000 km/s in the corona)

  4. Chen, J. 1989 All current catastrophe model for CMEs: 2.5-D simplification of a long-3d realistic flux rope

  5. Outline:(1) force balance analysis of a coronal magnetic flux rope日冕磁绳受力分析研究简介(ApJ, 649:1093，2006 by Chen et al.）(2) impact of magnetic reconnection on the rope dynamics磁场重联对磁绳运动学行为的影响

  6. Aims of force balance analysis: (1) to analyze the interplay among the different pieces of magnetic forces (2) to find out the dominant component(s) of magnetic forces in sustaining the rope in equilibrium and causing the eruption

  7. (1) force balance analysis (ApJ, 649:1093，2006) In our flux rope system: Inside the rope: poloidal(环向) and toroidal (轴向或azimuthal方位方向) cur. Along the current sheets: azimuthal current, Self-forces: Azimuthal current: upwards Poloidal current: downwards X photosphere Flux rope

  8. A summary: Magnetic forces acting on the rope currents: • Forces attributed to the rope currents • Force produced by the b.g. potential field • Forces associated with the current in the c.s. • In equilibrium: • Dominant lifting F(force) by the toroidal current inside the rope • Dominant pulling F: by the b.g. potential field • In eruption after catastrophe: • Dominant lifting Fthe toroidal curr. inside the rope • Main pulling Fcurrent in newly-formedc.s. Magnetic reconnectionreduce or eliminate this pulling forcean enhanced outward lifting Lorentz forcelarger acceleration

  9. (2) impact of magnetic reconnection on the rope dynamics • polytropic solar wind (γ=1.05) • ideal MHD V.S. resistive MHD

  10. Ideal MHD: prohibit numerical reconnections along the current sheets (numerical technique: use magnetic flux function to describe the axisymmetric field) current sheets form and develop Resistive MHD: Allow magnetic reconnection to take place along the c.s. currents along the c.s. aredissipated

  11. Results of ideal & resistive MHD calculations: Color contours: velocity B0=6Gauss (magnetic field strength at the base along the equator)

  12. Rapid expansion with fast eruption Resistive Cusp point Rope top Rope axis Rope bottom Ideal Ideal V.S. resistive MHD calculations (t=280 minutes)

  13. B0=4 Gauss Compare with observations: Zhang et al., 2004, ApJ • Velocity profile and value • Acceleration Time ~ 2 hours

  14. Total increase in kinetic energy over the initial meta-stable state: △Ei: ideal MHD △Er: resistive MHD Results: △Er ~ 2 – 3 △Ei 10G 8G 6G 10G 8G4G 6G 4G2G 2G

  15. Summary: I: Magnetic reconnections have significant impacts on CME speed by reducing/eliminating the pulling force by the current sheets. II: Stronger b.g. field enable faster CMEs a smooth transition from fast to slow CMEs (Are there really two types of CMEs?) Increase in kinetic energy: △Ekr ~ 2 – 3 △Eki

  16. Thanks!

  17. Resistive Ideal Ideal B0=6G Cusp point Rope top Rope axis Rope bottom

  18. B0=6G: desity profiles

  19. B0=2G Cusp point Rope top Rope axis Rope bottom B0=10G B0: field atrength at the base of the equator

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