Multiwavelength observations of a flux rope formation by series of magnetic reconnection in the chromosphere ^⋆

¹ Korea Astronomy and Space Science Institute (KASI), 305-348 Daejeon, Republic of Korea
e-mail: pankaj@kasi.re.kr
² Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
³ Big Bear Solar Observatory, New Jersey Institute of Technology, Big Bear City, CA 92314, USA
⁴ Space Weather Research Laboratory, New Jersey Institute of Technology, University Heights, Newark, NJ 07102-1982, USA
⁵ University of Science and Technology, 305-348 Daejeon, Republic of Korea

Received: 12 July 2016
Accepted: 28 March 2017

Abstract

Using high-resolution observations from the 1.6 m New Solar Telescope (NST) operating at the Big Bear Solar Observatory (BBSO), we report direct evidence of merging and reconnection of cool Hα loops in the chromosphere during two homologous flares (B and C class) caused by a shear motion at the footpoints of two loops. The reconnection between these loops caused the formation of an unstable flux rope that showed counterclockwise rotation. The flux rope could not reach the height of torus instability and failed to form a coronal mass ejection. The HMI magnetograms revealed rotation of the negative and positive (N1/P2) polarity sunspots in the opposite directions, which increased the right- and left-handed twist in the magnetic structures rooted at N1/P2. Rapid photospheric flux cancellation (duration ~20–30 min, rate ≈3.44 × 10²⁰ Mx h^-1) was observed during and even after the first B6.0 flare and continued until the end of the second C2.3 flare. The RHESSI X-ray sources were located at the site of the loop coalescence. To the best of our knowledge, such a clear interaction of chromospheric loops along with rapid flux cancellation has not been reported before. These high-resolution observations suggest the formation of a small flux rope by a series of magnetic reconnections within chromospheric loops that are associated with very rapid flux cancellation.