Large-scale active coronal phenomena in Yohkoh SXT images |
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| Authors: | Franti?ek Fárník Zdeněk ?vestka Hugh S Hudson Yutaka Uchida |
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| Institution: | (1) Astronomical Institute of Czech Academy of Sciences, 25165 Ond ejov, Czech Republic;(2) Center for Astrophysics and Space Sciences, 92093-0111 UCSD, La Jolla, CA, U.S.A.;(3) Institute for Astronomy, University of Hawaii, 96822 Honolulu, HI, U.S.A.;(4) Physics Department, Science University of Tokyo, 1-3 Kagurazaka, 162 Shinjuku-ku, Tokyo, Japan |
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| Abstract: | We discuss Yohkoh SXT observations of stationary giant post-flare arches which occurred on 3–6 May, 1992 and study in detail the last arch, associated with the flare at 19:02 UT on 5 May, which extended above the west limb. The arch was similar to the first giant arch discovered on board the SMM, on 21–22 May, 1980. We demonstrate that the long lifetimes of these structures necessarily imply additional energy input from the underlying active region: otherwise, conduction would cool these arches in less than one hour and even with the unlikely assumption of conduction inhibited, pure radiative cooling would not produce the temperature decrease observed. All arch tops, although varying in brightness, stayed for several days at a fairly constant altitude of  100 000 km, and the arch studied, on 5–6 May, was just a new brightening of the pre-existing decaying structure. The brightening was apparently due to inflow of hot plasma from the flare region. Yohkoh data confirm that these stationary arches are rare phenomena when compared with the rising arches studied in Paper I and with Uchida et al.'s expanding active regions. |
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