1. September 2007LWS 2007 Halo CMEs and Configuration of the Ambient Magnetic Field Yang Liu – Stanford University yliu@sun.stanford.edu

2. September 2007LWS 2007 Introduction Purpose: The purpose of this research is to study influence of background field for propagation of halo CMEs. 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). Current-sheet boundary Non-current-sheet boundary

3. September 2007LWS 2007 Current-sheet boundary Non-current-sheet boundary These two configurations were also successfully reproduced by Zhao & Webb (2003) based on a Potential Field Source Surface model.

4. September 2007LWS 2007 current-sheet boundary Non-current-sheet boundary

5. September 2007LWS 2007 3D MHD simulation shows that type 2 and 3 CMEs are faster than type 1 (from Liu & Hayashi 2006). Can observation support this result?

6. September 2007LWS 2007 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).

7. September 2007LWS 2007 Data We looked for the halo CMEs 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.

8. September 2007LWS 2007 Examples of the three types of CMEs Type 1 Type 2 Type 3

9. September 2007LWS 2007 Result Type 1Type 2Type 3 number394614 Percentage39%47%14% Median speed (km/s)72812081443 Mean speed (km/s)883±4031345±5961530±736

10. September 2007LWS 2007 Open: type 1 Filled: type 2 + type 3

11. September 2007LWS 2007 Distribution of CMEs versus flare class.

12. September 2007LWS 2007 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.

13. September 2007LWS 2007 Conclusions Types 2 & 3 CMEs appear to be significantly faster than type 1. The average speed of the former is 1388 km/s, while the latter is 883 km/s. 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 determining 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.