Velocities of type II solar radio events

Radial velocities for 144 simple but representative type II bursts were determined from measured frequency time histories. The velocity distribution is peaked in the region between 500 and 700 km s ^–1 (with the exact value dependent upon the coronal density model assumed) and skewed towards the larger velocities. In 85 % of the cases it was found that the velocities were constant with height. In the remaining 15 % the drift rate decreased drastically at low frequencies. This tended to occur for events having high initial velocities. The measured velocity is dependent upon the properties of the flare event but does not appear to be related to other characteristics of the radio burst. Comparisons show that the group of type II events studied had a velocity distribution which was comparable with that for coronal mass ejection events seen in association with type II bursts. The measured velocities were however statistically smaller than those of interplanetary type II bursts.