Successive flarings at distant sites

fl114.hanaoka07
Posted:  11-Mar-93
Updated: 06-Nov-93, 7-Aug-94, 27-May-95, 3-Feb-96, 20-Sep-96
Events specified: Flares on 21-Aug-92 at 00:18, 15-Dec-91 at 01:13 and 16-Dec-91 at 03:25

PI and Collaborators : Y. Hanaoka and Nobeyama Radioheliograph group, Yohkoh team, Magnetograph observers

Motivation : Sometimes a flare triggers another flare at the distant site. From the Radioheliograph and the SXT observation, we found some flares which show such a behavior; an M1.3 flare on August 21 0018UT, 1992 in NOAA7260, a C6.9 flare on December 15 0113UT and a C4.6 flare on December 16 0325UT, 1992 in NOAA7360. There are two bipoles in NOAA7260. About 40 seconds after a flare occurred in the eastern bipole, the other bipole was brightened. After the flare, a loop which connects two bipoles were brightened up. The projected distance between the bipoles is about 80000 km. The region NOAA7360 consisted of distant N and S poralities, but there was another S polarity region close to the N polarity. The projected distance of the N and S polarity of the region NOAA7360 is also 80000 km. In both of the flare on Dec. 15 and the flare on Dec. 16, a small loop which connected the close N and S polarities was brightened first, and several tens of seconds later the distant N polarity region were brightened. Later, the loop, which connected the distant N and S polarities were brightened slowly. In the flare on Dec. 16, the flaring up in the loop brightened later is much more energetic than that of the small loop brightened first. We analyze these flares in detail, and study the mechanism of triggering the successive flaring.

Update 20-Sep-96

The following is the update of my proposal 'fl114.hanaoka07'. I am writing a paper on this subject, and it is almost completed.

Flares : flares and in the region NOAA7360 (Paper I)

M1.3 flare in 7260 on 1992 Aug 21
C5.6 flare in 7420 on 1993 Feb 06
C9.1 flare in 7469 on 1993 Apr 10
C6.2 flare in 7469 on 1993 Apr 11
C4.1 flare in 7518 on 1993 Jun 07
C1.7 flare in 7590 on 1993 Sep 30
C8.9 flare in 7469/7472 on 1993 Apr 11
M4.1 flare in 7315 on 1992 Oct 23
C4.8 flare in 7815 on 1994 Dec 14
M2.5 flare in 7815 on 1994 Dec 14

Abstract. We analyzed several flares, which are presumed to be caused by interactions between an emerging flux and an overlying loop. We call such a basic combination of loops `double-loop configuration', and we reveal its topology on the basis of the microwave and soft X-ray observations of the flares and the magnetograms. In many cases, two of the footpoints of the loops, one from the emerging loop and the other from the overlying loop, are included in a single magnetic polarity patch. Therefore, the footpoints of two loops are distributed in three magnetic patches, and two loops form a `three-legged' structure. In many cases, the emergence of a parasitic polarity near the main preceding-polarity region or the following one in active regions creates this configuration, but in a case two active regions are involved in this configuration. Microflares, jets, and surges also occur in the same magnetic configuration. Hence, the interaction between two loops, which form the three-legged structure, is an important source of the various activities.

Update 3-Feb-96

A paper on this topic is in press, and I am analyzing similar events now. I am going to present a poster about this topic at the workshop 'Solar Flare and Related Disturbances' at Hitachi.

Title : Successive flarings at distant sites

PI and Collaborators : Y. Hanaoka and Nobeyama Radioheliograph group, Yohkoh team, Magnetograph observers

Flares : flares and microflares in the region NOAA7360 (Paper I)

M1.3 flare in 7260 on 1992 Aug 21
C5.6 flare in 7420 on 1993 Feb 06
C9.1 flare in 7469 on 1993 Apr 10
C6.2 flare in 7469 on 1993 Apr 11
C8.9 flare in 7469/7472 on 1993 Apr 11
C4.1 flare in 7518 on 1993 Jun 07
C?   flare in 7590 on 1993 Sep 30
C1.2 flare in 7590 on 1993 Oct 04
C?   flare in 7815 on 1994 Dec 14
M2.5 flare in 7815 on 1994 Dec 14

Abstract. Active region NOAA7360 was observed in 1992 December with various instruments including the {\it Yohkoh} satellite. In this region, a small loop emerged near one of the footpoints of a pre-existing large coronal loop. These loops show evidence that interactions between coronal loops cause flares, microflares, and plasma flow. All of the four flares observed in this region show that brightenings in the small loop occurred first, and then the large loop flared up. The brightenings in the large loop can not occur by themselves, but must be triggered by the brightenings in the small loop. There must be interactions between the loops to cause these flares. As well as the flares, many microflares occurred in the small loop. More than half of them are accompanied by plasma ejection phenomena from the small loop into the large loop. The large loop is filled with ejected plasma with velocities of about 1000 km s$^{-1}$. These ejection phenomena are considered as X-ray jets. The associated occurrences of the microflares and the jets suggest that they are also caused by interactions between the loops. The recurrent occurrences of the homologous flares and microflares mean that the magnetic field structure in this region inevitably causes the activity due to loop-loop interactions; the flares and jets occur under a common magnetic field structure.

Update 27-May-95

The model that a flare is caused by interacting coronal loops is well known, and some observation show the evidence of the loop-loop interaction (Machado et al., 1988; Mandrini et al., 1991). The recent observation with the SXT on board Yohkoh satellite shows flares caused by interacting loops morphologically. We present here a new evidence of the flares and plasma flow caused by interacting loops observed by Yohkoh, the Nobeyama Radioheliograph, and some H-alpha telescopes. The active region NOAA7360 was not very flare-productive, but caused many microflares and several flares during 1992 Dec. 14-16. The activities of this region is mainly caused by two coronal loops. The small one is about 10000 km long. The large loop is about 100000 km long, and is astride the same magnetic neutral line as the small one, but one of the footpoint of the large loop is very close to one of the footpoint of the small loop. Many microflares occurred in the small loop. More than half of them are accompanied by plasma ejection phenomena from the small loop into the large loop. The large loop is filled with the ejected plasma within one or two minutes after the microflare occurrences. Their velocities are about 1000 km/s. These ejection phenomena are considered as coronal jets, which were analyzed by e.g. Shibata et al.(1992). In the above period, Dec. 14-16, there are four flares (all C-class) observed by Yohkoh. In the all of these flares, brightenings in the small loop occurred first, and then the large loop flared up. The released energy due to the brightening in the large loop is comparable to or larger than that of the small loop. The energy release in the small loop only is not so large. In this region, the energy release as large as a C-class flare requires the energy release in the large loop. However, the energy release in the large loop must be leaded by the brightening in the small loop. Therefore in this region the interaction between the small loop and the large one is necessary to cause a flare. Furthermore, the existence of the jets suggests that the microflares in the small loop is not only the phenomena in the small loop itself, but the phenomena related with the large loop. The recurrent occurrences of the homologous flares and microflares mean that the magnetic field structure in this region necessarily causes the brightenings due to loop-loop interactions. Such configuration of the magnetic field is not special; at the colloquium we present some other flares probably due to loop-loop interactions which occurred under the similar magnetic configuration.

Update 7-Aug-94

flares and microflares in the region NOAA7360 on 1992 Dec. 14-16

In the region NOAA7360 there are two loops which are interacting to each other. One of them is large; its length is about 10^5 km. The other loop is much smaller. In the flares at 1992 Dec 15 0113UT and 1992 Dec 16 0605UT, brightenings in the small loop caused electron accelerations in the large loop. Simultaneous brightenings at the both footpoints of the large loop were observed, and the large loop became bright in soft X-rays in the late phase of the flare. Besides these flares, many microflares were observed during Dec 14-16 in the region NOAA7360 with the SXT. All microflares occurred in the small loop, and almost all of them showed plasma flow from the small loop into the large loop. The large loop filled with hot plasma in 1-2 min after the brightenings in the small loop; since the length of the large loop is about 10^5 km, the velocity of the plasma is about 1000 km s^-1. The temperature of the loops during the microflares is about 5-6x10^6 K, the hydrodynamic shock velocity (3 times of the sound velocity) becomes about 1100-1200 km s^-1. Such characteristics of these phenomena are the same as thoes of coronal jets. The region NOAA7360 shows the recurrent jets accompanied by microflares caused by the interacting loops. Such plasma flow was also observed in the region NOAA7260, 7558, and 7590, but now we concentrate on the region NOAA7360.

Update 06-Nov-93

Flares :

NOAA7260 1992 August   21 0018UT
NOAA7360 1992 December 15 0113UT
NOAA7360 1992 December 16 0605UT
NOAA7590 1993 September 30

Two distinct energy transport mechanisms were observed in the above flares. In the primary brightenings of above flares, high speed electrons played an important role; the hard spectra of hard X-rays are observed with the HXT. However, the secondary brightenings in these flares at the distant sites from the primary brightenings show soft spectra of hard X-rays. This fact implies that the secondary brightenings are not caused by high speed electrons, but caused by thermal electrons. The radio observations also give information of the electron energy distributions in such events. The secondary brightenings in the flares on August 21 and September 30 occurred in strong magnetic fields. In these events, thermal electrons of hot plasma observed with the SXT radiate gyroresonance emission, and its intensity is consistent with observed radio flux. This result also suggests that the secondary brightenings are not caused by high-speed electrons. The velocities of the energy transport from the primary flare sites to secondary flare sites are about 2000-4000kms^-1, which are comparable to thermal velocities of flare plasma.