Disturbed region and a shock wave driven by a coronal mass ejection

The existence of a disturbed region in front of a coronal mass ejection (CME) has been proved; its variation with increasing CME velocity has been investigated. It has been shown that a plasma density discontinuity, which can be interpreted as a shock wave, is formed in front of the disturbed region at CME velocities that are about or above the local Alfvén velocity. Within the experimental error, the observed shock-front width is estimated to be about the mean free path for proton-proton collisions at distances R < 15−20 R⊙ from the center of the Sun; i.e., the energy dissipation mechanism in the front is conceivably collisional at these distances.