Type II–IV radio bursts and compact and diffuse white-light clouds in the outer corona of December 14, 1971

Abstract

The radio observations of type II–IV bursts on December 14, 1971 are analyzed. These radio events were associated with a Hα-spray or eruptive prominence, and later followed by several compact moving clouds observed with the NRL white-light coronagraph aboard OSO-7. There was also observed a diffuse expanding cloud behind the compact moving clouds.

From the comparison of the interferometer observation of the bursts with the optical observation, it is strongly suggested that the compact moving clouds were likely to be the optical counterparts of the sources of moving type IV radio emission. This fact suggests that the magnetic bubbles were really produced in the flare process. The frequency-drift of the first group of type II bursts was so rapid, that we could neither identify the type II shock with the leading edge of the diffuse expanding cloud nor interpret it as the piston-driven shock of the latter. Because of the uncertainty of the velocities of the compact clouds due to the projection effect, the possibility that the type II shock was the piston-driven shock of the compact clouds cannot be excluded. Nevertheless we suggest that the type II shock was a blast type MHD shock and had no direct physical relation to the flare-associated mass-ejection processes. The relation between the type II–IV bursts and the interplanetary shock is also discussed.