Flare‐Associated Coronal Mass Ejections with Large Accelerations

Abstract

It is well known that while flare-associated coronal mass ejections (CMEs) show higher speeds and little acceleration in the corona, filament-associated CMEs have lower speeds and large accelerations. In this paper, we examine three flare-associated CMEs with relatively large accelerations as counterexamples of the former tendency. The estimated accelerations are all larger than 45 m s(-2) below 15 R-circle dot. By analyzing SOHO EIT, SOHO LASCO, and GOES data, we attempt to find out what kind of physical characteristics control such strong accelerations. The first event is the 1999 July 9 event associated with a C1.1 flare. Considering the fact that its CME appearance, seen in the LASCO running difference imagery, is quite similar to the shape of a helmet streamer, we speculate that its eruption is related to the destabilization of a helmet streamer, which may induce the weak X-ray flare. The second event is the 1999 August 17 event associated with a C2.6 flare. The CME speed abruptly increased from 232 to 909 km s(-1) for 1 hr, and the strong acceleration is coincident with the occurrence of a subsequent flare/CME. The third event is the 2000 November 24 event associated with a C4.1 flare. The CME speed first decreased and then constantly accelerated for 3 hr. The start of such an acceleration is also coincident with a subsequent CME/flare event. For the last two CME events, the Lorentz forces acting on the subsequent events may play an important role in accelerating CMEs. Our results show that large accelerations of flare-associated CMEs, as counterexamples of the two classes of CMEs, seem to be caused by other solar activities, such as helmet streamer disruptions or subsequent CMEs/flares.