The footpoints of giant arches |
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| Authors: | Sara F Martin Zdeněk F ?vestka Arvind Bhatnagar |
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| Institution: | (1) Big Bear Solar Observatory, Solar Astronomy 264-33, California Institute of Technology, 91125 Pasadena, CA, U.S.A.;(2) SRON Laboratory for Space Research, Utrecht, The Netherlands;(3) Udaipur Solar Observatory, 313001 Udaipur, India |
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| Abstract: | We have detected chromospheric footpoints of the giant post-flare coronal arches discovered by HXIS a few years ago. H photographs obtained at Big Bear and Udaipur Solar Observatories show chromospheric signatures associated with 5 sequential giant arch events observed in the interval from 6 to 10 November, 1980. The set of footpoints at one end of the arches consists of enhancements within a plage at the northeast periphery of the active region and the set of footpoints at the other end of the arch consists of brightenings of the chromosphere south of the active region. Both sets of footpoints show very slow brightness variations correlated in time with the brightness variations of the X-ray arches. Current-free modelling of the coronal magnetic field by Kopp and Poletto (1989), based on a Kitt Peak magnetogram, confirms the identification of the two sets of footpoints by showing magnetic field lines connecting them.The brightenings appear as a succession of point-like enhancements whose individual lifetimes are of the time-scale of minutes but which continue to occur for periods of several hours. This behaviour allows us to infer a fine structure in the coronal arches, undetectable in the X-ray images. The discovery of these brightenings and their location at the periphery of the active region also alters our conception of the relationship of the giant arches to the flares that begin concurrently with them. The giant arch phenomenon appears now to be either: (1) a long-lived, semi-permanent, coronal structure which is revived and fed with plasma and energy by underlying dynamic flares, or alternatively (2) a system of high-altitude loops which open at the onset of every such flare and subsequently reconnect over intervals of many hours. |
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