Sep 21 Tue 10:00~11:30  太陽系小天体セミナー        zoom

Sep 24 Fri 13:30~15:00  Solar and Space Plasma Seminar    zoom 






Campus: Mitaka
Seminar: Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic: Scheduled
Date and time:24 September (Fri), 13:30-15:00
Place: zoom
Speaker:Daiki Yamasaki
Affiliation: Kyoto University
Title:Numerical modeling of three-dimensional coronal magnetic field in the flare-productive solar active region NOAA 12673

Solar flares are the rapid energy release in the solar outer atmosphere, solar corona. The energy source of the solar flares is widely considered as the magnetic energy accumulated in solar active regions (ARs). Due to the observational limitation, however, it is hard to obtain the coronal vector magnetic field, and thus, we cannot directly detect the formation process of the magnetic flux ropes (MFRs). Hence, it is helpful to understand the formation and the evolution of the flare-productive ARs that the numerical modeling of the three-dimensional coronal magnetic field using an observable photospheric vector magnetic field. In our study, we focus on the AR 12673, which has produced many M-class and several X-class flares, one of which being an X9.3 flare, which is recorded as the largest solar flare in solar cycle 24. We studied the evolution of the three-dimensional flare-productive magnetic field within AR 12673, using a time series of nonlinear force-free field extrapolations of every 12 hr from 2017 September 4 00:00 UT to 6 00:00 UT. Our analysis found that three MFRs formed by September 4, one of which produced the X9.3 flare on September 6. One MFR has positive magnetic twist, which is a different sign from the other two MFRs. Since the temporal evolution of the magnetic flux of the MFR accumulating the positive twist is consistent with the profile of the GOES X-ray flux well observed from September 4 to 6, we suggest that the formation of the MFR having the positive twist is closely related to the occurrence of the M-class flares, including an M5.5 flare. We further found a magnetic null in the magnetic field surrounding the MFRs, in particular above the MFR having positive twist before the M5.5 flare, which is the largest M-flare observed during this period. By comparing with Atmospheric Imaging Assembly 1600 Å images, we found that the footpoints of the overlying field lines are anchored to the area where the brightening was initially observed. Therefore, we suggest that reconnection induced by the torus instability of the positively twisted MFR at the null possibly drove the M5.5 flare. In my presentation, I would also like to discuss the difference of the CME association between two homologous M-class flares observed in the AR 12673.

-Name:Munehito Shoda
Comment:in English,