Evolution of fibrils with special reference to flare activity |
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| Authors: | Katsuo Tanaka |
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| Institution: | (1) Big Bear Solar Observatory, Hale Observatories Carnegie Institution of Washington California Institute of Technology, U.S.A. |
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| Abstract: | We show observational results on the pre-flare evolutions of H structures as well as the developments of H flares. It is shown that the chromospheric features are brought to a sheared state before flares due to motions of footpoints which correspond to particular sunspot motions. Generally in evolutions of the chromospheric features it is found that motions and reconnections of the footpoints play essential roles. The following three stages are found for development of the neutral line filament before flares: (1) formation of a filament as a result of reconnection; (2) increase of the shear of the filament due to the shear motion; and (3) reconnection of fine components of the filament to form an elongated component immediately before flares. We further show developments of two particular flares with and without the filament, and point out basic release processes of flares. The flare that occurred at the filament (July 5, 1974) started with the activation of the elongated component of the filament after the process (3). The main phase of a two-ribbon flare is considered as the rises of short components of the filament triggered by the rising motion of the elongated component. The flare of September 10, 1974 occurred at the region where fibrils connect the sunspots in distorted form. Pre-flare distortion was produced by translational rotation of the sunspot. Development of this two-ribbon flare is interpreted as being due to successive rises of the fibrils with a self-trigger mechanism.On leave from Tokyo Astronomical Observatory (present address). |
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