Dynamics of Threads Wrapping a Filament's Leg Prior to the Eruption on 2021 October 28

Abstract

Although the magnetic field structures of solar filaments have been studied for several decades, the detailed evolution of the structure around a filament prior to its eruption is rarely observed. On 2021 October 28 in AR 12887, a major solar flare (X1.0 class) occurred at 15:35 UT. Based on the Solar Dynamics Observatory high-spatial-resolution observations, we find this flare is associated with the eruption of two filaments, namely F1 and F2. The two filaments are initially independent. The western leg (WLEG) of F1 approaches the northern leg of F2, due to the continuous movement and rotation of the magnetic field in which the WLEG roots in. We find first that there are some threads wrapping the WLEG. Brightening and bidirectionally plasmoid flows that originate from a brightening are detected in these threads, then the threads disappear, and the two filaments connect. NLFFF extrapolation reveals that there is a toroidal magnetic structure enveloping the WLEG and corresponding spatially to the threads. It is expected that a filament is enveloped by toroidal magnetic fields. According to the observations and extrapolation, we suggest that these threads represent the toroidal magnetic fields wrapping the WLEG. This paper provides new details about the dynamics of the toroidal magnetic fields. Magnetic reconnection takes place in the toroidal fields and thus destroys the fields, then F1 and F2 connect, and subsequently, the two filaments erupt and the flare occurs.

Formation of a Long Filament Through the Connection of Two Filament Segments Observed by CHASE

“…This was well supported by observations where a long filament (hot channel) was formed by the reconnection of two filament segments (sheared arcades; Schmieder et al 2004;Joshi et al 2014;Cheng et al 2015;Zhu et al 2015;Chen et al 2016). In addition, erupting filaments were also observed occasionally to interact with a nearby filament, giving rise to a distinct filament with a new footpoint (Jiang et al 2014;Joshi et al 2016;Yang et al 2017;Fang et al 2023).…”