ar071.yoshida02 Posted: 28-Aug-94 Updated: 3-Feb-95, 27-May-95, 24-Feb-96, 08-Apr-96 Events specified:
T. Yoshida ( Institute of Astronomy, Univ. of Tokyo )
Master thesis topics Thesis adviser: S. Tsuneta
Date used: May-July, 1992 SXT PFI
The purpose of this analysis is to get the time scales of the loops' time variations and to see the global temperature structures. Here we sum up the images taken in the intervals of one Yohkoh orbit revvolution (100min) and get the good S/N images. Surprisingly, the Yohkoh-SXT structures don't always coincide with the temperature structures, and sometimes these look quite different. For example, very hot (8MK) regions are in some no-structural diffuse corona above the bright magnetic loops. In the events that whole loops are brighten up after the brightenings occure at the footpoints of the loops, not only those bright loop but also the diffusive loops around the bright loops are heated up to very high temperatures (6MK). The temperatures of the compact steady loops (4MK) are generally higher than the temperatures of the diffusive loops (3MK), and there are low temperature layers (5000km 3MK) around the limbs. Then, the temperatures of the footpoints of loops may be lower than those of the tops. Thus, we can get the new information about the coronal heating mechanism from the temperature maps and their time variations.
Preliminary result will be presented in the annual ASJ meeting in the autumn of 1994.
Update 08-Apr-96
We obtain high-quality temperature maps of solar active regions observed by the {\it Yohkoh} Soft X-ray Telescope. The temperatures of active region structures range from 3 MK to 10 MK. The bright X-ray loops do not necessarily have high temperatures, and faint structures sometimes have temperatures as high as 6 MK. The loop structures with shorter lifetime ($<$ a few hours) generally have higher temperatures (5--8 MK) than the loops with longer lifetime (3--4 MK). The plasma with temperature reaching 6--7 MK has cusp structures like solar flares (mini-cusp) or has multiple-loop structures in the temperature maps in most cases. The 6--7 MK plasma is transiently heated either by magnetic reconnection at the neutral sheet above the cusp structures, or by magnetic reconnection of multiple loops. The 3--5 MK plasma is more steadily and uniformly heated. Two different mechanisms are apparently involved in the coronal heating.
Update 24-Feb-96
The conductive loss time scales of the structures with life time shorter than several hours are about 30 minutes ($T=$6MK,$n=$ 10$^{9.5}$cm$^{-3}$,$l=$10$^5$km), and the radiative loss time scales are about 10 hours. The observed time scales are close to these time scales. This indicates that these structures are heated transiently. These are associated with the cusp structures or multiple-loop structures in most cases. The transient heating is, thus, due to magnetic reconnection.
The conductive loss time scales of the structures with life time longer than half a day are about 50 minutes ($T=$4.5MK,$n=$ 10$^{9.5}$cm$^{-3}$,$l=$10$^5$km), and the radiative loss time scales are about 6 hours. The observed time scales are much longer than these time scales. This indicates that the steady plasmas are continuously heated. It is sometimes hard to find the temperature structures corresponding to the steady loop structures seen in X-ray images. Thus, the steady coronal loops may be heated more or less in a loop-independent way.
This indicates that the coronal heating consists of the basal heating and the transient heating. The basal heating mechanism maintains the plasma temperature around 3--5 MK, and the occasional transient heating due to magnetic reconnection produces higher temperature plasma with temperatures up to 10 MK.
Update 27-May-95
The following paper was submitted to the Astrophysical Journal. This is part of Yoshida's master thesis to be submitted to U. Tokyo next spring.
TEMPERATURE STRUCTURE OF SOLAR ACTIVE REGION
Tsuyoshi Yoshida and Saku Tsuneta
We obtain high-quality temperature maps of solar active regions observed by the {\it Yohkoh} Soft X-ray Telescope. The bright X-ray loops do not necessarily have high temperatures, and faint structures soemtimes have temperatures as high as 6 MK. The loop structures with shorter lifetime ($<$ a few hours) have higher temperatures (5--8 MK) than the loops with longer lifetime (4 MK). The plasma with temperature reaching 6--7 MK have cusp structures like solar flares (mini-cusp) or have multiple-loop structure. The 6--7 MK plasma are transiently heated by magnetic reconnection, and the 4--5 MK plasma is more steadily and uniformly heated. Two different mechanisms are apparently involved in the coronal heating.
Update 3-Feb-95
The effect of the mirror scattering on the temperature diagnostics of the active regions was studied by Yoshida. The scattering effect can not be neglected in the analysis, and this places a constraint on the regions where the temperature analysis is possible.
The first draft of the paper was written by Yoshida. Yoshida and Tsuneta are now updating the draft, and the draft for circulation will be completed by mid-February. We plan to submit the paper to ApJ.
This project is a part of T. Yoshida's Master Thesis.