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Title:
Supra-arcade Downflows in Long-Duration Solar Flare Events
Authors:
McKenzie, D. E.
Affiliation:
Montana State University, Bozeman, MT 59717, U.S.A.
Journal:
Solar Physics, v. 195, Issue 2, p. 381-399 (2000). (SoPh Homepage)
Publication Date:
08/2000
Origin:
KLUWER
Abstract Copyright:
(c) 2000 Kluwer Academic Publishers
Bibliographic Code:
2000SoPh..195..381M

Abstract

This report seeks to introduce the reader to a set of observations made during the decay phase of long-duration event (LDE) flares on the Sun. In a number of events, the soft X-ray images from Yohkoh SXT indicate a downward-directed flow field in the region immediately above the flare arcade. The prototypical event is the M5 flare of 20 January 1999, presented by McKenzie and Hudson (1999); since the time that paper was completed, eleven more events, all related to coronal mass ejections, have been found in the interval 1 January 1998 to 8 May 1999. As in the 20 January event, the speeds of downflow are 45-500 km s^-1, lower than both the free fall speed and the typically assumed Alfvén speed. A comparison is drawn between the SXT observations and the EUV and Hα data, where such are available. Important additions to our knowledge since the first paper are: (i) the motion is evidenced by both dark and bright (i.e., X-ray emitting) features, some of which may have a loop-like morphology; (ii) no cool counterparts have been detected in Hα or EUV observations. The data are compared to the expected appearance according to two likely (and opposing) interpretations: an `above-the-arcade coronal rain' interpretation and a `shrinking magnetic flux tube' interpretation. In the current standard explanation of the formation of post-CME arcades, motion of the latter type may be related to outflow from a reconnection site. Movies depicting some of the flare events are on the accompanying CD-ROM.
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