qs092.uchida10 Posted: 17-Jul-95 Updated: 20-Sep-96 Events specified: See title
by Y.Uchida, K.Fujisaki, S.Morita, and T.Yabiku Physics Department, Science University of Tokyo
Abstract: We investigate the detailed development of a polar arcade formation of Feb 24-25, 1993. The event, started as a brightening of a "tooth brush" type structure over the field polarity reversal line in the southern circum-polar region, developed to a fully grown polar arcade formation. The spine which seems to be consisted of the floated up pre-existing longitudinal threads finally balloons up in the westernmost part, to show a structure standing up just like the giant cusp of Jan 25, 1992, if rotated a few tens of degrees to the west. We looked into the faint preflare magnetic loop structures in the region, and found that the preflare structures consist of a double-bipolar arcade, or a quadrupolar connectivity in the region. We compare the Kitt Peak magnetogram rotated to the exact time of the feature to be compared, and found that the central region of the "quadruple" sources are a mixed field region. Further comparative analysis will be made.
A preliminary result was presented by Fujisaki et al. at the Makuhari IAU Colloquium in May, and to be published in the Proceedings of that Meeting. A fuller report will be submitted as Uchida et al. in a Journal in the near future.
Update 20-Sep-96
I am sorry for not responding this notice. You suggested me to submit abstracts of the work going on, and it has taken time to push the work to that level. I could push the works to that level during the last summer vacation, and now I am at 95 percent for submitting two papers in this line. So, I would like you to post the following abstracts of two papers on the TBB by reviving the TBB item qs092.uchida10. Thank you. Yutaka Uchida
Y. UCHIDA, K. FUJISAKI, S. MORITA, S. HIROSE, and S. CABLE (Department of Physics, Science University of Tokyo)
Abstract: Observations by the soft X-ray telescope (SXT) aboard {\it Yohkoh} of arcade flares and arcade formation events outside active regions, with higher sensitivity, wider dynamic range, and higher cadence than those of its predecessors, have revealed clear features contradicting with what are expected in the long-conceived ``reclosing opened-up simple arcade" model for arcade flares and fainter arcade formation events. Those contradictions are basic morphological ones thus far hidden in the faint pre-event coronal structure. In the present paper, we concentrate on the coronal structure related to the polar dark filaments from which polar arcade formation events take place, and show our findings that the faint pre-event structure for those are not what has been considered in the classical model for arcade flaring events, but what is predicted by the quadruple photospheric magnetic source model for the magnetic configuration supporting dark filaments. The widely conceived ``reclosing opened-up simple arcade" model for arcade flares and X-ray arcade formation events seems to be questioned by this finding. (95 percent ready, and welcome any comments.)
POLAR X - RAY ARCADE FORMATION OF FEBRUARY 24-25, 1993 PRODUCING A LARGE CUSP-LIKE FEATURE, AND THE NATURE OF THE ``GIANT CUSP" OF JANUARY 25, 1992
K. FUJISAKI, Y. UCHIDA, S. MORITA, S. HIROSE, and S. CABLE (Department of Physics, Science University of Tokyo)
Abstract: The X-ray polar arcade formation of February 24-25, 1993 is scrutinized from the pre-event structure to the final product, a large cusped arch, in the Yohkoh Soft X-ray Telescope (SXT) data. They are analysed by comparing with the Kitt Peak Magnetograms and the Big Bear H$\alpha$ pictures at the times closest to it, rotated to the exact times of the SXT images. The pre-event coronal structure was found to consist of ``double arcades" whose inside legs seem to land in the region of the other arcade near the ``field polarity-reversal line" in an intermingled way, with the dark filament lying above this region (Uchida et al. 1996). It was found that the Kitt Peak photospheric magnetic field in this region has a mixed polarity belt extending to both sides of the ``field polarity reversal line" (if we have to define it), and the ``field polarity reversal line" turned out to be the ``field polarity reversal line of the averaged (or smeared) field", with certain fraction of the flux transported to the other side in the form of patches. Sometime after the disappearance of the dark filament, a bundle of longitudinal threads (we call it a "spine")rose with a tooth-brush-like connections to the photosphere on the north-western part, and the brightened region extended progressively westward in time. It is obvious that the ``spine" {\it was not} the locus of reconnection points of the once opened-up arcade, because it was consisted of multiple longitudinal threads. Finally, the westmost part of the ``spine" ballooned up, and it eventually developed into a feature just like the ``Giant Cusp" of Jan 25, 1992. Hinted by this, we examined also the Jan 25, 1992 event in detail. The pre-event situation turned out to be exactly similar to the Feb 24-25, 1993 event, and furthermore, we found that the ``Giant Cusp", against the expectation, showed in early phase its southern branch on the visible disk, tens of degrees in longitude behind the main part which occurred near or beyond the limb. This suggests that, contrary to the conventional interpretation that the ``Giant Cusp" is a structure reclosing through magnetic reconnection after once cut open by erupting dark filament. The ``Giant Cusp" of Jan 25, 1992 may well be a ``ballooning-up spine" just like that of the February 24-25, 1993 event, viewed near or behind the limb. All these are difficult to explain by the classical ``reclosing opened-up simple arcade" models, but naturally explicable by the quardruple source model proposed by one of us (YU). (95 percent ready, and welcome any comments.)