Speeds of rising post-flare structures

Abstract

There are basically two kinds of post-flare coronal structures: those rising with decreasing speed, and others which rise with constant speed for a long period of time. As a rule, those structures with decreasing speed are post-flare loop systems, while those rising with constant speed are postflare giant arches. However, there are exceptions. We demonstrate several cases of post-flare loop systems which rise with constant speed for many hours, three of them observed by Yohkoh. These observations imply that the Kopp and Pneuman interpretation of post-flare loops as sequentially reconnecting open field lines cannot be generally valid. The most likely interpretation is that all post-flare loop systems start with the Kopp and Pneuman process, but in some of them later-formed loops begin to be continuously heated; thus they cease to cool and begin to expand into the corona. This kind of post-flare loops might represent an intermediate stage between the ordinary post-flare loops and post-flare giant arches.