| Research Abstract |
Among the new observational findings obtained by the Xray Satellite Yohkoh, the new findings we derived about arcade flarings turn out to be quite different from what the classical "reclosing of once opened-up bipolar arcade model" predicted. In the present work, we concentrate on seeking a new model that can explain these new observational findings. What we have found by the analyses of the Yohkoh data were, (1) faint pre-event structure of arcade formation is not a simple bipolar magnetic arcade as assumed in the classical model, but dual arcades side by side with inner legs crossing is invorved, (2) what we call a "spine" comes up rising sometime after the dark filament flies away, quite unexpected in the classical model. This is consisted of multiple thin threads, and can not be the locus of reconnecting points as may be explained in the classical model, and (3) in arcade flares, we found that there exist large loops connecting the top of the flare cusp back to the photosphere on b
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oth sides, and there is a bright structure near the axis of the dark tunnel below the cusp. These have no model counterpart in the classical model. Those findings, in contrast, are exactly what can be explained in the model proposed by Uchida. We, therefore, revived the "Quadruple Source Model" that was previously proposed by Uchida, but did not become the main stream due to the lack of good enough observation to confirm its coronal characteristic features that time. We have developed the equiliblium solution into a time-dependent simulation scheme, and seek solutions. In 1996, we reached a conclusion that the quadruple source model we have been developing give most of the observed behavior if we start the dynamic simulation from a squeezed state with longitudinal magnetic field in the neutral sheet in the corona above the central polarity-reversal line. The configuration can store magnetic energy in the form of magnetic stress, and can release it when some triggering helicity is injected into the dark filament part and squeeze it out from the neutral sheet. The stress energy stored in the entire region can be released through reconnection then allowed the reconnection to occur at the neutral point. This model explain the above-mentioned observed facts pretty well, and we start reporting about it. Less
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