ar045.tsuneta09 Posted: 31-Jul-93 Updated: 11-May-94, 08-Oct-94, 03-Apr-95, 25-Apr-95, 20-Oct-95 Events specified: Active regions late March 1992
S. Tsuneta, J. lemen, G. Slater, A. Title
From the active region tracking SXT movie (March, 1992) produced by Dr. Jim Lemen, everyone had the 'impression' that the active regions located on both norhtern and southern hemisperes are 'interacting'. When we examine the movie carefully, we immediately notice clearer evidence for interaction. There are clear X-type cusp structure just in between the active regions. The X-type structure continues to exist for a few days, and the down-stream side of the reconnection tends to be brighter. This is one of the best example of magnetic reconnection so far discovered in the Yohkoh data.
We will write a letter paper to descibe this extremely interesting phenomena.
Update 20-Oct-95
The following paper was accepted by the Astrophysical Journal(Letters), and would like to succsessfully close the project.
final abstract
INTERACTING ACTIVE REGIONS IN THE SOLAR CORONA Saku Tsuneta
We report an episode from the {\it Yohkoh} soft X-ray observations during which antiparallel coronal magnetic fields from two separate active regions, located in opposite hemispheres, reconnect and form new trans-equatorial coronal loops. Strong evidence for magnetic reconnection consists of (1) trans-equatorial connections not previously observed are newly created; (2) an X-point and separatrix structure are clearly seen in the soft X-ray images; and (3) the plasma temperature of the downstream side of reconnection is about 4--7 MK, whereas that of the upstream side is about 2 MK. The quiet coronal plasma is significantly heated over a few days, and the overall magnetic structure of the region is completely changed as a result of magnetic reconnection. This observation suggests that magnetic reconnection occurs also in the quiet corona in less explosive way than in solar flares, and that it may contribute to the overall heating of the quiet corona.
Update 25-Apr-95
The following paper will be submitted to ApJ soon:
Abstract INTERACTING ACTIVE REGIONS IN THE SOLAR CORONA
S. Tsuneta
We report the episode from the {\it Yohkoh} soft X-ray observation that the trans-equatorial field lines are formed between active regions located on the opposite sides of the solar hemispheres. There are pieces of strong evidence that the formation of the trans-equatorial loops are due to magnetic reconnection: (1) An X-point and the separatrix structure are clearly seen in the soft X-ray images, and (2) The number of trans-equatorial loops increases as a function of time. (3) The plasma temperature of the downstream side of reconnection is about 6-7 MK, whereas that of the upstream side is about 2 MK. The high temperature region borders the low temperature region along the separatrices seen in the X-ray images. This shows that the downstream plasma is heated by magnetic reconnection. We discuss the implication to the coronal heating and to the behavior of the sub-surface toroidal magnetic fields.
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.
Update 08-Oct-94
The event was described in the following publications:
MAGNETIC RECONNECTION IN THE SOLAR CORONA Saku Tsuneta
XIV National SOlar Observatory/SacPeak International summer workshop Solar Active Region Evolution ed. K. S. Balasubramanian, G. Simon Astronomical Society of the Pacific, in press.
Further analysis is made. We obtain the temperature structure of the interacting region. The temperature map clearly shows that the down stream region has much higher temperature, and the upstream and the down stream regions in the T map are well separated by the X_ray separatrix. This is one of the best evidence of the magnetic reconnection in the solar corona.
This result will be presented in the autumn annual meeting of PASJ, and a paper will be prepared.
Update 11-May-94
This is just to report the publication and presentation status of the event regarding this project.
Oral presentation: AAS meeting, June, 1993, Stanford Univeristy SacPeak active region meeting, Sep, 1993, Sacramento peak Observatory
Publication: Tsuneta, Proc. of Sac Peak meeting, 1994, Astronomical Society of the Pacific.
The full letter has not yet been written.