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Astron. Astrophys. 360, 715-728 (2000)


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Solar flare radio pulsations as a signature of dynamic magnetic reconnection

B. Kliem 1, M. Karlický 2 and A.O. Benz 3

1 Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany (bkliem@aip.de)
2 Academy of Sciences, Astronomical Institute, 251 65 Ondejov, Czech Republic (karlicky@sunkl.asu.cas.cz)
3 ETH, Institute of Astronomy, 8092 Zürich, Switzerland (benz@astro.phys.ethz.ch)

Received 28 September 1999 / Accepted 29 May 2000

Abstract

Decimetric radio observations of the impulsive solar flare on October 5, 1992, 09:25 UT show a long series of quasi-periodic pulsations deeply modulating 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 from a dynamic phase of magnetic reconnection in a large-scale current sheet. The reconnection is dominated by repeated formation and subsequent coalescence of magnetic islands (known as "secondary tearing" or "impulsive bursty" regime of reconnection), while a continuously growing plasmoid is fed by newly coalescing islands. Such a model, involving a current sheet and a growing plasmoid, is consistent with the Yohkoh observations of the same flare (Ohyama & Shibata 1998). We present two-dimensional MHD simulations of dynamic magnetic reconnection that support the model. Within the framework of the proposed interpretation, the radio observations reveal details of plasmoid formation in flares.

Key words: Sun: radio radiation – Sun: flares – Sun: corona – Plasmas – Magnetohydrodynamics (MHD)


© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000

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