Chains of type-I radio bursts and drifting pulsation structures

Aims: Owing to similarities of chains of type-I radio bursts and drifting pulsation structures the question arises as to whether both these radio bursts are generated by similar processes.
Methods: Characteristics and parameters of both these radio bursts are compared.
Results: We present examples of both types of bursts and show their similarities and differences. Then, for chains of type-I bursts, a similar model as for drifting pulsation structures (DPSs) is proposed. We show that, similar to the DPS model, the chains of type-I bursts can be generated by the fragmented magnetic reconnection associated with plasmoid interactions. To support this new model of chains of type-I bursts, we present an effect of merging two plasmoids to form one larger plasmoid on the radio spectrum of DPS. This process can also explain the `wavy' appearance of some chains of type-I bursts. Further, we show that the chains of type-I bursts with the wavy appearance can be used for estimation of the magnetic field strength in their sources. We think that differences of chains of type-I bursts and DPSs are mainly owing to different regimes of the magnetic field reconnection. While in the case of chains of type-I bursts, the magnetic reconnection and plasmoid interactions are in the quasi-separatrix layer of the active region in more or less quasi-saturated regime, in the case of DPSs, observed in the impulsive phase of eruptive flares, the magnetic reconnection and plasmoid interactions are in the current sheet formed under the flare magnetic rope, which moves upwards and forces this magnetic reconnection.