Decimetric Radio Bursts Observed During the Onset of Solar Eruptive Flares

Abstract In this paper, we present the results of our analysis of solar eruptive flares observed by the Ondřejov radiospectrographs over more than three decades. By combining the eruptive flare model with findings from our magnetohydrodynamic and particle-in-cell simulations, we demonstrate the crucial role of decimetric radio bursts in understanding plasma processes during eruptive flares. We describe unusual drifting continua associated with the rise of a magnetic rope at the onset of these flares. Notably, we report very rare slowly positively drifting bursts (SPDBs) linked to the bright helical structure of the ascending rope. Drifting pulsation structures (DPSs) are identified as signatures of plasmoids, while narrowband decimetric spikes are associated with magnetic reconnection outflows. We also examine pairs of decimetric Type III bursts, which indicate electron beams propagating both upward and downward in the solar atmosphere from the acceleration site, as well as a special Type III burst likely traveling around a plasmoid. We introduce a method for computing period maps and identifying a unique wave/shock feature in the radio spectrum. A movie illustrating the plasma processes responsible for generating the drifting pulsation structure is also shown. The interpretations of all presented bursts are based on the standard model of eruptive flares. However, positional data for sources of these radio bursts are often lacking. To emphasize the importance of spatial information, we present an example of a drifting pulsation structure observed simultaneously with observations from the Expanded Owens Valley Solar Array (EOVSA). Finally, we summarize all discussed bursts in a comprehensive scheme that extends our knowledge about a role of decimetric bursts at the onset of eruptive flares.