fl132.uchida08 Posted: 31-Jul-93 Updated: 10-Mar-94, 8-Nov-94, 17-Jul-95, 20-Sep-96 Events specified: flare on 17-Feb-92 at 15:38 UT
Y.Uchida, J.Khan, G.Doschek, U.Feldman, Masuda, A.McAllister and any other team member who is willing to collaborate
Feb 17, 1992 flare was a canonical loop flare which showed various interesting features. First of all, it started to brighten from both footpoints and the bright region in the loop moved about along the loop before it finally came to the top of the loop and stayed there until it faded. The shape of the loop was initially a simple half-circle type, but very much distorted into a question mark shape (probably the loop was twisted), and restored to the the original smooth shape as it faded. It is remarked that the footpoints stayed bright until much later than the BATSE hard X-ray spikes. Another point of interest is that the so-called Neupert effect (the time profile of the soft X-ray flux increase is steeper when the hard X-ray spikes take place. This has been interpreted as indicating that the mass injected into the loop increases due to the electron bombardment) does not seem to have its original significance; It turned out by measuring the contribution of the soft X-ray emission from each part that the hump in the rising part of the soft X-ray profile in the total (non spatially-resolved) profile is just the sum of the smoothly increasing curve of the loop part contribution, plus the increase and decrease of the brightness of the footpoints without affecting the amount of the hot mass in the loop, differing (delicately) from the original interpretation. This flare was a near-the-limb flare, and not suited for the investigation of the blueshifts, but it is seen clearly that the rise in the SXV line intensity came before the impulsive bursts by tens of seconds.
(This proposal was not submitted by some accident while we thought it was. In the meantime the work progressed, and we expect to be able to finish in two three months.)
Update 20-Sep-96
Sorry for not responding your notice for a long time. I would now like you to revive the item fl132.uchida08, and post the following abstract. The paper is about 98 percent ready. Upon your request for an abstract, we tried to bring this to that
level in the last summer, and it is now in that level. I would like you to
post the abstract on the TBB, so that it will be open to the team.
Yutaka Uchida
DYNAMICAL DEVELOPMENT IN THE INITIAL PHASE OF A LOOP FLARE
OBSERVED BY YOHKOH
Y. Uchida, J. I. Khan, G. A. Doschek, S. Masuda, A. H. McAllister, S. Hirose, U. Feldman, and C-C. Cheng
(Science University of Tokyo, Mullard Space Science Laboratory, E.~O.~Hulburt Center for Space Research, NRL, Solar-terrestrial Environment Laboratory, Nagoya, University, High Altitude Observatory/NCAR)
Abstract: The initial development of a simple loop flare observed by the {\it Yohkoh\/} satellite on 1992 February 17 is described in this paper. {\it Yohkoh\/} soft X-ray images of the flare revealed noticeably dynamic behavior during the faint initial stages before the flare maximm although the source in the later main phase of the flare was quite stationary staying at the top part of the loop. Following the initial brightening of the footpoints, the loop top started to increase in brightness, and a bright ``blob'' emerged from that region moved down with a velocity of a few hundred km/s along the loop toward the northern footpoint and then bounced back up the loop. A similar but less pronounced effect was seen for the southern leg. The shape of the flare loop appeared to distort into a sort of ``question mark'' shape in projection as the bright blob appeared, and relaxed to a smooth semi-circular form as the loop top brightness increased to its maximum. The source at the loop top stayed there as the brightest part of the flare in the remaining life of the flare. The dynamical behavior of this flare, such as the motion of the blob (possibly a magnetohydrodynamic shock containing high energy particles) and the deformation of the loop shape, is highly suggestive of a magnetohydrodynamic character of the flaring process. The results of analyses comparing the hard X-ray time profile and images and the line-of-sight velocity in high temperature lines seem to support this dynamical picture. (98 percent prepared during the time in which the item has been dropped from the TBB. Any comments are heartily welcome.)
Update 17-Jul-95
I am very close in finishing up the paper. The write-up delayed by my involvement to the organization of the Makuhari Meeting, and unexpectedly later than I thought, but all the material, discussion and conclusions, and the draft are here, and it is 95% done. I will let you know when done.
Update 8-Nov-94
We examined the dynamical phenomena occurring in the initial stage of the simple loop flare on Feb 17, 1992, and found the following: (i) Footpoints brightened, and as it faded the top part of the loop got brighter, and a blob-like feature moved doun toward the northern foot, with a less bright effect going down to the southern footpoint, too. The blob touched down the foot and then it seemed to bounce back towards the top of the loop, and the bright region seemed to stay there after some oscillation, and the source increased after that its intensity by a factor of ten or more. The first brightening of the footpoints coincided the first major spike in HXT, and the second sharper major spike was emitted at the moment when the blob touched down at the northern foot. (ii) The shape of the loop was distorted into a question mark shape when the blob appeared at the loop top, and restored a simple loop shape by the time the loop top gained its brightness. The question mark shape seen was consistent with a twisted loop in a right-handed sense. (iii) The brightening in the BCS lines started more than 1 min earlier than any trace of the hard X-ray spikes, and the footpoint area maintained its soft X-ray brightness until much later than the end of the hard X-ray bursts. From these results, we argued about the merits and demerits of the models proposed thus far, and it was remarked that an MHD model proposed by Uchida and Shibata (1988) ought to be paid more attention in the light of these observations.
Update 10-Mar-94
We have worked in the last months on this topic as follows, and obtained the following results: (i) Finding of the correlated behavior of the blue- and redshifts of the Ca line with the appearance of the bright knot at high part of the loop. Together with the detailed analysis of the SXT images, we concluded that we found that the shape of the loop changed between the appearance of the bright knot and the maximum brightness of the loop top, and the redshift and the following peak of the blueshift are corresponding to the expanding motion of the sput gas to the north footpoint, and the blueshift following it corresponds to the expanding motion of the sput gas from the top to the south footpoint. The shifts are consistent with the observed motion if we take the distortion of the loop into a question mark shape in projection as due to its distortion into right-handedly twisted loop. We are now seeking after the shifts in S XV lines by using "subtraction of the average of the pre-flare S XV emission" method. (ii) Have done detailed comparison of the HXT sources with the SXT sources. It is found that the HXT image at the first spike coincides with the SXT footpoints of the loop, but the image of the HXT source at the second spike is a single source which coincides with the appearance of the loop top source of SXT.