Solar flare radio pulsations as a signature of dynamic magnetic reconnection

Decimetric radio observations of the impulsive solar flare on October 5, 19 92, 09:25 UT show a long series of quasi-periodic pulsations deeply modulat ing a continuum in the 0.6-2 GHz range that is slowly drifting toward lower frequencies. We propose a model in which the pulsations of the radio flux are caused by quasi-periodic particle acceleration episodes that result fro m a dynamic phase of magnetic reconnection in a large-scale current sheet. The reconnection is dominated by repeated formation and subsequent coalesce nce of magnetic islands (known as "secondary tearing" or "impulsive bursty" regime of reconnection), while a continuously growing plasmoid is fed by n ewly coalescing islands. Such a model, involving a current sheet and a grow ing plasmoid, is consistent with the Yohkoh observations of the same flare: (Ohyama & Shibata 1998). We present two-dimensional MHD simulations of dyn amic magnetic reconnection that support the model. Within the framework of the proposed interpretation, the radio observations reveal details of plasm oid formation in flares.