On the Exciters of Type II and Type III Solar Radio Bursts

The exciters of transient solar radio emissions—the type II and type III bursts in the nomenclature by WILD and his collaborators1)—are discussed from the view point of the velocity with which their sources move in the solar atmospheres. Several possible types of motion in the physical condition above the sunspot are considered in order to account for the observed velocity and its variation with height of each type of bursts; Propagations of ordinary and hydromagnetic shocks, with the dissipation of energy flux through irreversible change at the front being taken into account, in a usual model solar atmosphere with a model sunspot field are treated, and it is concluded that the front velocity of hydromagnetic shock, which is assumed to be caused by an initial disturbance like a flare-surge, can be considered as the exciter of the type II burst. On the other hand, the only possible agency, which is responsible for the velocity of the type III bursts at least from the view point of the velocity, seems to be the streaming motion of individual particles along the magnetic lines of force, or in a region free from it. Attribution of the exciter velocities of type II and type III bursts to those of hydromagnetic shock front and free streaming motion of particles respectively, also explains some other features of the observed facts consistently.