Turbulent plasma model of the narrowband dm-spikes

Starting from radio spectrum features of the narrowband dm-spikes, it is suggested that they are generated at positions in the solar are atmosphere where the upper hybrid frequency is equal to the low harmonics of the electron cyclotron frequency. It is assumed that a radio source plasma is in a turbulent state. The upper hybrid waves are generated by an anisotropic electron beam which propagates along magnetic loop lines. Collisional damping and turbulent changes of plasma parameters in the radio source cause strong intensity-frequency variations of the upper hybrid waves. These waves are then transformed into observed narrowband dm-spikes. Using this model, the artificial radio spectra are computed. It is shown that a chain of narrowband spikes is generated at a one cyclotron harmonic, in one turbulent magnetic flux tube. On the other hand, a cloud of spikes (or their harmonic clouds) results from a superposition of many chains of spikes generated in many turbulent magnetic flux tubes (in several cyclotron harmonics). Finally, further features of the narrowband dm-spikes are discussed in the framework of the proposed model.