fl203.nitta11 Posted: 03-Apr-95 Updated: 17-Jan-96, 12-Oct-96 Events specified: N/A
N. Nitta, H. S. Hudson, J. R. Lemen and anybody who is willing to do hard work
We empirically know that there are confined as well as eruptive flares. According to Shibata et al. (1995), even an impulsive flare whose brightest part looks like a compact loop invariably has some diffuse outward-moving structure. According to these authors, all eight of the limb events from Masuda (1994) that have SXT coverage have such structures, which they interpret to be "plasmoid" ejections. Such ejections are more difficult to see from disk flares because of typically brighter background emission.
We propose to make a broader survey of limb flares to characterize the tendency towards ejection more quantitatively. The primary purpose is to find out what fraction of flares are eruptive and to analyze data from a few days prior (west) and after (east) in order to see what makes the region produce eruptive flares. It is likely that BCS signals from limb flares are not heavily affected by blueshift components from evaporating plasmas, giving us better estimates of the turbulent velocities than disk flares. We plan to correlate the turbulent velocities from BCS with other parameters of flares such as intensity, hardness, electron temperature, height of hard X-ray sources, etc.
We have tentatively singled out 60-80 limb flare candiates, using the flare catalog the HXT team puts on line and the observing log that is part of Yohkoh software. Some of them may actually not be close to the limb, because somehow ARS did not work properly for them, but the total number of our limb flares will not decrease drastically.
Required Yohkoh data: SXT, HXT, BCS
fl155.shibata09 The role of X-ray filament/loop eruption in flares
We have combined analyses of flares with relatively hard spectra
and limb flares and presented the results in the proceedings of the Bath Conference. An important thing is that limb flares are not the only flares that show eruptive signatures. The abstract follows:We have studied hard and soft X-ray images for some 130 flares observed by Yohkoh. Our sample covers events of wide ranges of intensity, duration and hardness (in terms of hard X-ray spectra). It is found to be difficult to identify a simple soft X-ray loop whose footpoints coincide with hard X-ray emission. Instead, a large fraction of the flares studied show soft X-ray ejecta and a high-temperature area outside the bright flare loop, as predicted by reconnection models.
Because limb flares have an obvious disadvantage of various structures foreshortened although they are resolved in the plane of sky, we need to identify the loops that are involved in a given flare, by comparing SXT images and magnetograms taken earlier (W-limb) or later (E-limb). That is our next rarget.
Update 17-Jan-96
A tentative result was presented at the Hirayama retirement symposium, in which we showed those limb flares without eruption. If there is an eruption, it usually appears later than the hard X-ray peak. It is likely that eruptions explain heating as manifested in gradual low energy hard X-ray variations, but not acceleration. We are still elaborating this conclusion.