Fine Structures of Type-IV Solar Radio Bursts Associated with Stationary and Moving Sources

Various types of fine structure in the continuum emission of type-IV radio bursts are considered as applied to different types of radiation sources, both stationary and moving. In the case of stationary sources, the origin of the fine structure is associated both with processes in individual magnetic loops (quasi-periodic acceleration and magnetohydrodynamic waves), and with large-scale processes associated with the propagation of magnetohydrodynamic disturbances, the formation of loop arcades, and processes of discrete acceleration of particles synchronous with them, causing the pulsating nature of radio emissions. For the case of a moving source, the generation mechanism largely depends on the magnetic structure of the source (an expanding magnetic arc or an isolated plasma cloud). In this case, the connection with coronal mass ejections and shock waves is also important. Secondary pulsations are explained by a magnetohydrodynamic fluctuation source in the form of a magnetic loop or cloud. The absence of other fine structures in the continuum of moving type-IV bursts may be due to the critical angle of the loss cone for the excitation of whistlers.