The relation between hot and cool loops |
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| Authors: | Nitta Nariaki |
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| Institution: | (1) Lockheed Martin Solar and Astrophysics Laboratory, , O/L9-41, B/252, 3251 Hanover Street, Palo Alto, CA , 94304, , U.S.A. |
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| Abstract: | In order to study the origin of the hot ( 3 MK) corona above active regions, we compare Yohkoh/SXT X-ray images, which represent a broad temperature range above   2.5 MK, with TRACE EUV coronal images whose primary sensitivities are in the 1–2 MK range. Nearly simultaneous X-ray and EUV snapshots show that there are loops that appear similar in these images of different temperature sensitivities, but they are not exactly cospatial with each other. A significant difference is noted in the active region core, where bright loops are seen in X-ray images but not in EUV images, reflecting their high (5 MK) temperatures. In SXT time-sequence images, these loops are found to undergo repetitive minor brightenings, suggestive of their flare-like origin. This is consistent with the absence of the EUV counterparts of the X-ray loops in TRACE time-sequence images at earlier and later times. We need to revisit the validity of the assumption that coronal loops are steady. |
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