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Session 18 - Flares I.
Oral session, Tuesday, July 01
Ballroom A, Chair: Mona Hagyard

[18.01] X-ray and Microwave Studies of Solar Flares and Magnetic Reconnection: New Results from Yohkoh and Nobeyama

T. Kosugi (Nobeyama Radio Observatory, NAOJ)

Soft and hard X-ray observations from Yohkoh have shown that the solar corona changes its shape much more dynamically than previously expected. Coronal magnetic structures tend to intermittently expand and restructure themselves through magnetic reconnection. Dynamical phenomena, presumably related to this type of magnetic activity, include a wide variety that ranges from tiny transient brightenings (microflares) and jets, through active-region-sized flares, to gigantic large-scale arcade formations. An interesting finding in this context is that both flares (irrespective of whether they are of impulsive or long-duration type) and large-scale arcade formations (believed to be intimately associated with CMEs) show features such as ``loop-with-a-cusp'' structure and ``plasmoid/filament ejection'' in common, which is suggestive that all these phenomena, listed above, can be interpreted by a unified view of magnetic reconnection.

The above-mentioned view needs to be confirmed, however, since X-ray observations do not necessarily reveal cool materials nor magnetic fields that do not contain hot plasmas. The Nobeyama Radioheliograph, operating at 17 GHz (plus at 34 GHz since autumn 1995) with high spatial and temporal resolution, provides supplemental information to the X-ray observations; radio emission is more sensitive than X-rays to magnetic fields, high-energy electrons, and also cool materials. Detailed comparisons of radio and X-ray images have revealed that, more than one systems of magnetic loops are involved in a flaring process. Without doubt their interaction with each other is a key factor that leads to an explosive release of magnetic energy in a form of particle acceleration.

Program listing for Tuesday