Vishal Joshi1 and Nandita Srivastava2
1Astronomy and Astrophysics Division, Physical Research
Laboratory, Ahmedabad 380 009, India
2Udaipur Solar Observatory, Physical Research Laboratory,
Udaipur 313 004, India
Abstract. The observations taken in He 304 oby the EIT telescope aboard SoHO reveals that these images are extremely useful in tracing prominences because of the relatively sharper spine which is better visible in 304o than in Halpha . We have developed a geometric technique of measuring the height of prominences. The technique was applied to six eruptive quiescent prominence images recorded by EIT in He 304 Aoduring January 2000- July 2003 in an attempt to identify the precursors of geo-effective caronal mass ejections (CMEs) that are associated with eruptive prominences. Our analyses show that prominence eruptions evolve through a pre-eruptive phase and an eruptive phase, which are characterized by lower velocities of several km s-1 and eruptive velocities of several tens to hundreds of km s-1 , respectively. The analyses also show that during the pre-eruptive phase, a prominence rises at a constant acceleration of several cm s-2 and not at constant velocity as reported by previous workers. We suggest that this phase is indicative of the precursor of prominence erup- tion. This might be useful in predicting the occurrence of an associated coronal mass ejection.
Keywords: Sun : prominences - Sun : coronal mass ejections (CMEs) - Sun : corona