Kinematics of coronal mass ejections between 2 and 30 solar radii

Kinematics of more than 5000 coronal mass ejections (CMEs) measured in the distance range 2–30 solar radii is investigated. A distinct anticorrelation between the acceleration, a, and the velocity, v, is found. In the linear form, it can be represented as , where km s-1, i.e., most of CMEs faster than 400 km s-1 decelerate, whereas slower ones generally accelerate. After grouping CMEs into the width and mean-distance bins, it was found that the slope k1 depends on these two parameters: k1 is smaller for CMEs of larger width and mean-distance. Furthermore, the obtained CME subsets show distinct quadratic-form correlations, of the form . The value of k2 decreases with increasing distance and width, whereas v0 increases with the distance and is systematically larger than the slow solar wind speed by 100–200 km s-1. The acceleration-velocity relationship is interpreted as a consequence of the aerodynamic drag. The excess of v0 over the solar wind speed is explained assuming that in a certain fraction of events the propelling force is still acting in the considered distance range. In most events the inferred propelling force acceleration at 10 solar radii ranges between and 10 m s-2, being on average smaller at larger distances. However, there are also events that show m s-2, as well as events indicating . Implications for the interplanetary motion of CMEs are discussed, emphasizing the prediction of the 1 a.u. arrival time.