Statistical Distributions of Speeds of Coronal Mass Ejections

Abstract

We studied the distribution of plane-of-sky speeds determined for 4315coronal mass ejections (CMEs) detected by the Large Angle andSpectrometric Coronagraph Experiment on board the Solar and HeliosphericObservatory (SOHO LASCO). We found that the speed distributions foraccelerating and decelerating events are nearly identical and to a goodapproximation they can be fitted with a single lognormal distribution.This finding implies that, statistically, there is no physicaldistinction between the accelerating and the decelerating events. Thelognormal distribution of the CME speeds suggests that the same drivingmechanism of a nonlinear nature is acting in both slow and fastdynamical types of CMEs.