Source Regions of Coronal Mass Ejections

Abstract

Observations of the solar corona with the Large Angle and Spectrometric Coronagraph Experiment (LASCO) and EUV Imaging Telescope (EIT) instruments on the Solar and Heliospheric Observatory (SOHO) provide an unprecedented opportunity to study coronal mass ejections (CMEs) from their initiation through their evolution out to 30 R☉. The objective of this study is to gain an understanding of the source regions from which the CMEs emanate. To this end, we have developed a list of 32 CMEs whose source regions are located on the solar disk and are well observed in EIT 195 A data during the period from solar minimum in 1996 January through the rising part of the cycle in 1998 May. We compare the EIT source regions with photospheric magnetograms from the Michelson Doppler Imager (MDI) instrument on SOHO and the National Solar Observatory at Kitt Peak and also with Hα data from various sources. The overall results of our study show that 41% of the CME-related transients observed are associated with active regions and have no prominence eruptions, 44% are associated with eruptions of prominences embedded in active regions, and 15% are associated with eruptions of prominences outside active regions. Those CMEs that do not involve prominence eruptions originate in active regions both with and without prominences. We describe six especially well observed events. These case studies suggest that active region CMEs (without eruptive prominences) are associated with active regions with lifetimes between 11 and 80 days. They are also often associated with small-scale emerging or canceling flux over timescales of 6-7 hr. CMEs associated with active region prominence eruptions, on the other hand, are typically associated with old active regions with lifetimes ~6-7 months.