  Why and how may some active regions (ARs) frequently produce coronal mass
ejections (CMEs)? It is one of the key questions to deepen our understanding of
the mechanisms and processes of energy accumulation and sudden release in ARs
and to improve our capability of space weather prediction. Although some case
studies have been made, the question is still far from fully answered. This
issue is now being tried to address statistically through an investigation of
waiting times of quasi-homologous CMEs from super ARs in solar cycle 23. It is
found that the waiting times of quasi-homologous CMEs have a two-component
distribution with a separation at about 18 hours. The first component is a
Gaussian-like distribution with a peak at about 7 hours, which indicates a
tight physical connection between these quasi-homologous CMEs. The likelihood
of occurrences of two or more CMEs faster than 1200 km s-1 from the same AR
within 18 hours is about 20%. Furthermore, the correlation analysis among CME
waiting times, CME speeds and CME occurrence rates reveals that these
quantities are independent to each other, suggesting that the perturbation by
preceding CMEs rather than free energy input be the direct cause of
quasi-homologous CMEs. The peak waiting time of 7 hours probably characterize
the time scale of the growth of instabilities triggered by preceding CMEs. This
study uncovers more clues from a statistical perspective for us to understand
quasi-homologous CMEs as well as CME-rich ARs.
