Interaction between coronal mass ejections and the solar wind

Observations suggest that the interplanetary extensions of coronal mass ejections (iCMEs) may be accelerated or decelerated in their passage through the solar wind. Interplanetary scintillation measurements (IPS) can detect the passage of iCMEs beyond the field of view of the Large‐Angle and Spectrometric Coronagraph coronagraphs and can provide information on their velocities. The European Incoherent Scatter Radar and the Multi Element Radio Linked Interferometer Network systems, with a field of view covering 10–120 solar radii, can provide information on iCMEs in the inner regions of the solar wind. IPS observations can also provide solar wind velocity measurements ahead of the iCME, and using this information, we consider the velocity profile of a number of clearly defined iCMEs and the relationship between iCME velocities and that of the background solar wind. The results provide additional confirmation that iCMEs converge toward the velocity of the solar wind ahead of the event and that most of the resulting acceleration or deceleration occurs in the innermost regions of the solar wind.