Abstract Details
| Name: Prabir Mitra Affiliation: PRL, Ahmedabad Conference ID: ASI2019_164 Title : Evolution of solar magnetic fields and large-scale reconnection events in extremely complex solar active region NOAA 12673 Authors and Co-Authors : Prabir K. Mitra and Bhuwan Joshi Udaipur Solar Observatory, Physical Research Laboratory, Badi Road, Udaipur-313001, Rajasthan, India Abstract Type : Poster Abstract Category : Sun and the Solar System Abstract : Solar active region NOAA 12673, appeared from 28 August 2017 to 10 September 2017, produced the largest flare of solar cycle 24 of class X9.3 on 6 September. Surprisingly, this enormously complex and dynamic active region emerged during the minimum phase of the solar cycle. In this work, we explore the magnetic field evolution in NOAA 12673 which produced 4 X-class and 27 M-class flares besides several smaller C-class events. The AR first appeared in the eastern limb of the Sun on 28 August, gradually evolved into a complex network of ‘δ-spots’ on September 6 and remained so until its disappearance on the western limb. During the peak flaring phase, this unusually north-south oriented active region contained excessively high non-potential energy which fuelled toward its frequent large-flare producing capability. We particularly focus on the triggering and dynamical evolution of an interesting event in which a small fluxrope structure from the northern region of the AR partially erupted in association with two very impulsive M-class flares on 7 September. The ejecting plasma, at first, was collimated and then, strikingly, changed its motion to almost opposite direction to constitute a coronal mass ejection (CME) with medium speed and angular width. Non-linear-force-free-field (NLFFF) extrapolation clearly indicates the presence of another, larger fluxrope in the active region which remained quiet during the activity whereas the small fluxrope erupted partially. Our analysis suggests that the ejected material from the erupting fluxrope proceeded through a narrow passage of high magnetic decay index which explains its abnormal dynamics. We further present a detailed comparison of the magnetic configuration of AR between 6 and 7 September to explore the circumstances that gave rise to the largest flare (X9.3 flare on 6 September) of the solar cycle 24. |