The coronal mass ejection waiting-time distribution

The distribution of times $\Delta t$ between coronal mass ejections (CMEs) in the Large Angle and Spectrometric Coronagraph (LASCO) CME catalog for the years 1996-2001 is examined. The distribution exhibits a power-law tail $\propto (\Delta t)^{\gamma}$ with an index $\gamma\approx -2.36\pm 0.11$ for large waiting times ($\Delta t>10 {\rm hours}$). The power-law index of the waiting-time distribution varies with the solar cycle: for the years 1996-1998 (a period of low activity), the power-law index is $\gamma\approx-1.86\pm 0.14$, and for the years 1999-2001 (a period of higher activity), the index is $\gamma\approx-2.98\pm 0.20$. The observed CME waiting-time distribution, and its variation with the cycle, may be understood in terms of CMEs occurring as a time-dependent Poisson process. The CME waiting-time distribution is compared with that for greater than C1 class solar flares in the Geostationary Operational Environmental Satellite (GOES) catalog for the same years. The flare and CME waiting-time distributions exhibit power-law tails with very similar indices and time variation.