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J. Zhang (George Mason University), K.P. Dere, R.A. Howard (Naval Research Laboratory)
We identify solar coronal mass ejection (CME) sources for 27 (out of 38) major geomagnetic storm events occurred between 1996 and 2000 based on complete solar and interplanetary observations from SOHO, ACE and WIND spacecrafts. Our search begins with selecting all front-side halo CMEs (FSH CMEs) based on a fixed transition window of 30--120 hours before the Dst peak time. Valid transition window is reduced by using solar wind speed of corresponding ICME (Interplanetary CME) for solar CMEs that are ejected at a speed higher than background solar wind. We find that 15 of the 27 (60%) major geomagnetic storms can be uniquely identified with a single FSH CME. However, 6 of the 27 events (20%) have multiple FSH CME sources. The complex solar wind flow of these events indicate interaction of CMEs in their path toward the Earth. The left 6 events (20%) have no FSH CME in the transition window. It appears that 4 out of the 6 events are caused by partial halo gradual CMEs originated from east limb, which are believed to be longitudinal extended gradual CMEs with intrinsic wide-angle. One event is caused by an impulsive CME from west limb, and another event is caused by corotating interaction region (CIR) associated with a low latitude coronal hole.
The average transition time from the Sun to the Earth is 64 hours while it is 78 hours to reach peak of geomagnetic storms. There is a coarse correlation between CME speed (V in km/s) and transition time (to ICME, T in hr.), simply as T=96-V/21. We find that geo-effective CMEs are more likely originated from western hemisphere than from eastern hemisphere. Almost all geo-effective CMEs from western hemisphere are full halo CMEs, while most geo-effective CMEs from eastern hemisphere are partial halo CMEs.
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The author(s) of this abstract have provided an email address for comments about the abstract: jiez@scs.gmu.edu
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.