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On Coronal Mass Ejections and Configurations of the Ambient Magnetic Field

On Coronal Mass Ejections and Configurations of the Ambient Magnetic Field. Yang Liu Stanford University. Outline. This talk includes two topics: does the background field affect CMEs’ occurrence? does the background field influence CMEs’ propagation?. CMEs’ occurrence: Motivation.

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On Coronal Mass Ejections and Configurations of the Ambient Magnetic Field

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  1. On Coronal Mass Ejections and Configurations of the Ambient Magnetic Field Yang Liu Stanford University COSPAR 2008

  2. Outline COSPAR 2008 • This talk includes two topics: • does the background field affect CMEs’ occurrence? • does the background field influence CMEs’ propagation?

  3. CMEs’ occurrence: Motivation Confined eruption of kink instability. (FE hereafter) Full eruption of kink instability. (KI hereafter) Full eruption of torus instability. (TI hereafter) COSPAR 2008 TRACE 1600 A. Courtesy of L. Green EIT 195 TRACE 171 movie. Courtesy of Schrijver

  4. CMEs’ occurrence: Motivation Full eruption of kink instability (KI) Failed eruption of kink instability (FE) Full eruption of torus instability (TI) Q: what causes these different types of eruptions? COSPAR 2008

  5. CMEs’ occurrence: Motivation COSPAR 2008 MHD simulations (FE vs KI) Courtesy: Kliem & Torok

  6. CMEs’ occurrence: Motivation COSPAR 2008 MHD simulations (FE vs KI) Courtesy: Kliem & Torok

  7. CMEs’ occurrence: Motivation COSPAR 2008 MHD simulation (KI vs TI) Fan & Gibson (2007)

  8. CMEs’ occurrence: Motivation FE versus KI KI versus TI suggest gradient of the overlying field decides eruptions n(FE)<n(KI)<n(TI) COSPAR 2008

  9. CMEs’ occurrence: Methodology COSPAR 2008 Select erupted filaments in active regions; Calculate background field using a potential field source surface model; At each height, compute overlying field by averaging horizontal field along the magnetic neutral line on the photosphere; Derive decay index.

  10. CMEs’ occurrence: Sample COSPAR 2008 • We collect events from literature, and found: • 4 failed eruption (FE) cases (Green et al. 2007); • 4 kink-instability (KI) full eruption cases (Green et al. 2007; Williams, et al. 2005); • 2 torus-instability (TI) full eruption cases (Schrijver et al. 2008).

  11. Result Decay index shows a clearly dividing line between failed eruptions and full eruptions, supportive of MHD simulations. COSPAR 2008

  12. Result COSPAR 2008 • n(FE)<n(KI) & n(FE)<n(TI)  support MHD results; • n(KI)~n(TI)  not support MHD results; • B(FE)>B(KI) & B(FE)>B(TI), probably due to, • F(FE)>F(KI) & F(FE)>F(TI)big active regions? • Big active regions usually produce more events: • Eruptions may be caused by other mechanisms; • Initial heights of filaments are higher.

  13. CMEs’ occurrence: Summary COSPAR 2008 • MHD simulations suggest: n(FE)<n(KI)<n(TI). • This work indicates: • n(FE)<n(KI) & n(FE)<n(TI); but • n(KI)~n(TI); • Field strength at low altitude is much stronger for failed eruption than for full eruptions.

  14. Outline COSPAR 2008 • This talk includes two topics: • does the background field affect CMEs’ occurrence? • does the background field influence CMEs’ propagation?

  15. CMEs’ propagations: Introduction • Purpose: The purpose of this research is to study influence of background field for propagation of halo CMEs. Current-sheet boundary Non-current-sheet boundary The background field was found to have two different configurations: current sheet and non-current sheet (see, e. g. Shultz 1973; Wilcox et al. 1980; Neugebauer et al. 2002, 2004). COSPAR 2008

  16. These two configurations were also successfully reproduced by Zhao & Webb (2003) based on a Potential Field Source Surface model. Current-sheet boundary Non-current-sheet boundary COSPAR 2008

  17. current-sheet boundary Type 1 Type 2 Non-current-sheet boundary Type 3 COSPAR 2008

  18. 3D MHD simulation shows that type 2 and 3 CMEs are faster than type 1 (from Liu & Hayashi 2006). • Can observation support this result? COSPAR 2008

  19. CMEs’ propagation: Methodology • Methodology: we classify the halo CMEs by the magnetic field computed based on the Potential Field Source Surface model, and then compare speed distributions of those three type CMEs. • Assumption: we assume that, statistically, these three types of halo CMEs should have a similar speed distribution in the initial phase. The initial speed of a CME is suggested to be related with characteristic of the associated flare (e. g. Moon et al. 2002, Cheng et al. 2003, Zhang et al. 2004, Qiu et al. 2004). COSPAR 2008

  20. CMEs’ propagation: Data • We select the halo CME events from the CMEs catalog of Gopalswamy’s group. 99 halo CMEs in the period from 2000 to 2004 were chosen. The solar sources were identified by that group, and were confirmed by other groups/works. COSPAR 2008

  21. Examples of the three types of CMEs Type 1 Type 2 Type 3 COSPAR 2008

  22. CMEs’ propagation: Result COSPAR 2008

  23. Open: type 1 Filled: type 2 + type 3 COSPAR 2008

  24. Distribution of CMEs versus flare class. COSPAR 2008

  25. A correlation was found between the speed of type 3 CMEs and the peak X-ray flux of the associated flares. No such correlations are found for types 1 and 2 CMEs. COSPAR 2008

  26. CMEs’ propagation: Summary • Types 2 & 3 CMEs appear to be significantly faster than type 1. This effect is not biased by flare importance. • It is shown that the background magnetic configuration associated with halo CMEs does play a role in deciding the speeds of the CMEs. • A correlation was found between the speed of type 3 CMEs and the peak of X-ray flux of the associated flares. COSPAR 2008

  27. Conclusion COSPAR 2008 • In this talk, I shall try to answer two questions: • does the background field affect CMEs’ occurrence? • does the background field influence CMEs’ propagation? • Yes, configuration of background magnetic field influences occurrence and propagation of CMEs.

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