fl187.tsuneta12 Posted: 28-Aug-94 Updated: 03-Apr-95, 17-Jul-95 Events specified: N/A
S. Tsuneta (Institute of Astronomy, U. Tokyo)
The purpose of this study is to investigate the temperature structure of the X-point reconnection region. A preliminary study is going on:
Case No.1: Temperature structture around the X-point of the interacting active region (see my separate TeamBB proposal)
We found the clear temperature structure: the upstream temperature is 2 MK, whereas the downstream temperature is 6MK. These two temperature structures are separated by the separatrix identifiable in X_ray images.
Case No.2: LDE flare (1992 Feb 21, 1991 Dec 2, 1993 March 11) The shell-like temperature within the flare loops was already reported by Tsuneta (1992, PASJ special issue). Further analysis on the X-ray dim structure indicates that the shell structture extends outside the flare loops, implying that the reconnection point is located far above the top of the cusp (see also Masuda, 1994, Shibata et al., 1994).
One common feature of these two reconnection is that the angle of the separatrices is almost 90 degree, suggesting very efficient magnetic reconnection.
This result will be presented in the ASJ meeting in the autumn, 1994.
Update 17-Jul-95
The sequel paper on 1992 February 21 event was accepted by ApJ, and I will successfully close the analyss of this event as well as this project.
The final abstract follows:
STRUCTURE AND DYNAMICS OF MAGNETIC RECONNECTION IN A SOLAR FLARE
Saku Tsuneta Institute of Astronomy, The University of Tokyo, Mitaka, Tokyo 181
We report a detailed analysis of the temperature structure of a prototypical flare that occurred on 1992 February 21. In the decay phase of this flare, the outer loops systematically have higher temperatures, reaching the peak (12 MK) far outside the apparent bright X-ray loop where the X-ray intensity is only 2 $\sim$ 5 \% of the peak. In between the high temperature ridges, a distinct vertical channel with temperature as low as 8$\sim$10 MK is seen at the loop top. In the model presented here, these high temperature ridges are heated by standing isothermal slow shocks attached to a reconnection point higher in the corona. The cool channel would be formed by conduction cooling as the hot reconnection outflow (12$\sim$13 MK) traverses with Mach speed $\sim$ 1 (800 km sec$^{-1}$) from the slow shock region to the loop top. The reconnection point is located 8 $\sim$ 18 $\times$ 10$^4$ km above the apparent top of the flare loop (6 $\times$ 10$^4$ km), and the inflow speed is estimated to be about 56 km sec$^{-1}$ (Alfven Mach number $\sim$ 0.07). The bright soft X-ray loops are the reconnected flux tubes subsequently filled with evaporated plasma.
Update 03-Apr-95
The following paper is in press:
Proc. China-Japan Solar Physics Seminar eds. G. Ai, T. Sakurai, 1995, in press.
STRUCTURE AND DYNAMICS OF MAGNETIC RECONNECTION IN THE SOLAR CORONA
Saku Tsuneta Institute of Astronomy, The University of Tokyo Mitaka, Tokyo 181, Japan
Yohkoh observations of an LDE flare show that the outer soft X-ray loops systematically have higher temperatures, reaching the peak (13 MK) far outside the bright X-ray loop. The reconnection point is estimated to be located twice as high as the apparent top of the flare loop. The high temperature ridges are heated by the standing isothermal slow shocks with length of a few 10$^4$ km. The bright soft X-ray loops are the reconnected loops subsequently filled with evaporated plasmas. We also present the observation that the trans-equatorial field lines in the quiet Sun are formed between the active regions located on the opposite hemispheres. There are pieces of evidence that these field lines are formed by magnetic reconnection.
The full paper to a refereed jounal is being written based on the proceedings paper.