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An Isaac Newton Institute Workshop

Reconnection in the Sun and Magnetosphere (Hewlett-Packard and Spitalfields Days)

Active-region magnetic structures and their perturbations by flares

Author: Hugh Hudson (UC Berkeley)


The coronal structure of a solar active region consists of magnetic fields originating mostly in subphotospheric current systems. Except for loops with higher density (and therefore higher temperature, except for prominences) this coronal structure is invisible at X-ray wavelengths. In general the plasma beta is low and the Alfven speed is large, especially between the bright loops. Eruptive flares (CMEs) disrupt parts of this magnetic field, forming temporary sources of solar wind. They also launch blast waves that are have recently become detectable in soft X-rays and other wavelengths (in addition to the traditional Moreton wave and meter-wave type II bursts). The blast waves, in the best cases, can be imaged directly in soft X-rays near the flare core at the onset of the eruption. We find that type II bursts commonly occur (in 12/28 cases) in conjunction with the TRACE "kink mode" loop oscillations catalogued by Schrijver, Aschwanden, and Title. The oscillating loops occur in those parts of the active region not participating in the CME (recognized as "dimming" in the low corona). I review the observations of blast waves and kink-mode oscillations and discuss the implications for the eruption process.

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