Discussion on the vanishment of solar atmospheric structures during magnetic reconnection

TL;DR

The paper quantifies how solar atmospheric magnetic structures evolve during reconnection by selecting three events with explicit X-type topologies and tracking two independent structures across time. Using SDO/AIA EUV and NVST Hα data, the authors measure the lengths of reconnecting structures (L1–L4) and find that reconnection induces abrupt shortening of the reconnecting segments and formation of residual structures, implying partial vanishment. They discuss several potential mechanisms and propose a fragmentation-driven scenario wherein partial structures truly vanish within the diffusion region, supported by energy estimates showing substantial magnetic energy release (approximately $E \approx 6.8\times10^{29}$ erg) compared to the current-sheet energy. This work provides a quantitative observational window into topological evolution during solar reconnection and links vanishment to magnetic-energy dissipation and volume reduction.

Abstract

In solar atmosphere, magnetic reconnection alters the topological connectivity, and magnetic energy is released. However, the length change of the reconnecting structures has rarely been reported. To identify the evolution of the topological structures, we search for reconnection events which should satisfy 3 criteria. (1) Each event displays an explicit X-type configuration, and the configuration consists of two sets of independent atmospheric structures, (2) the reconnection process is clearly observed, and (3) the topological connectivity of the structures can be tracked from at least 5 minutes prior to the occurrence of magnetic reconnection to 5 minutes after the reconnection. In this work, 3 events are selected and studied. During the reconnection moment, the total length of the two topological structures in each event shortens suddenly, and the decrements for events 1--3 are 47 Mm, 3.7 Mm, and 8.2 Mm, respectively, implying that partial structures vanish observationally during magnetic reconnection process. Several possibilities about the vanishment, e.g. the shrinkage of the reconnecting structures due to magnetic tension, the bizarre change in the third dimension, and magnetic field annihilation, have been discussed.

Figures (4)

• Figure 1: A magnetic reconnection event on 1 January 2012 2016NatPh..12..847L. Panels (a) and (d), the SDO/AIA 335 Å images. Panels (b) and (c), the current sheet in SDO/AIA 171 (211) Å image. The red (L1) and green (L2) dotted lines in panel (a) display two independent atmospheric structures prior to the occurrence of magnetic reconnection, while the pink (L3) and cyan (L4) ones in panel (d) show the newly-formed structures which consist of the residues of L1 and L2 after the reconnection. The blue rectangles in panels (b) and (c) exhibit the current sheet. Panel (e), the lengths of the topological structures L1, L2, L3 and L4, as well as the length sums of L1 plus L2 and L3 plus L4. Panel (f), the length sum variation of L1 plus L2 prior to the reconnection, and L3 plus L4 after the reconnection. The two blue dotted lines in panels (e) and (f) denote the start (00:56:51 UT) and end (00:59:39 UT) time of the reconnection, respectively. To display the exchange of topological connectivity of magnetic field lines during magnetic reconnection process, an animation of the SDO/AIA 335 Å observations from 2012 January 1 00:46:03 UT to 01:03:15 UT, is available. The duration of this animation is 1 s.
• Figure 2: A magnetic reconnection event on 3 February 2014 2015ApJ...798L..11Y. Panels (a) and (d), the NVST H$\alpha$ images. Panels (b) and (c), The SDO/AIA 171 (131) Å image. The red (L1) and green (L2) dotted lines in panel (a) display two independent atmospheric structures prior to the occurrence of magnetic reconnection, while the pink (L3) and cyan (L4) ones in panel (d) show the newly-formed structures which consist of the residues of L1 and L2 after the reconnection. The blue rectangles in panels (b) and (c) exhibit the current sheet. Panel (e), The lengths of the topological structures L1, L2, L3, and L4, as well as the length sums of L1 plus L2 and L3 plus L4. Panel (f), the length sum variation of L1 plus L2 prior to the reconnection, and L3 plus L4 after the reconnection. The two blue dotted lines in panels (e) and (f) denote the start (07:18:16 UT) and end (07:19:41 UT) time of the reconnection, respectively. To display the exchange of topological connectivity of magnetic field lines during magnetic reconnection process, an animation of the NVST H$\alpha$ observations from 2014 February 3 07:06:10 UT to 07:19:05 UT, is available. The duration of this animation is 1 s.
• Figure 3: Similar to Figure \ref{['fig2']}, but for event 3 on 23 October 2015 xue2020. The length sum of L3 and L4 is 8.2 Mm shorter than the length sum of L1 and L2. The reduced length is about 18% of the length sum ($\sim$46 Mm). To display the exchange of topological connectivity of magnetic field lines during magnetic reconnection process, an animation of the NVST H$\alpha$ observations from 2015 October 23 07:37:26 UT to 07:52:07 UT, is available. The duration of this animation is 1 s.
• Figure 4: Schematic drawings illustrating the reconnection process. Panels (a), (b), and (d), the traditional reconnection images. In the diffusion region, magnetic energy converts into heat and kinetic energy by Ohmic dissipation. Panel (c), a new idea about the change of the magnetic structures. While two set of magnetic fields approach together in the 2L region (M2-M3 and N2-N3), the magnetic fields fragment (shown by short arrows). The dissipation of these fragmented fields results in the vanishment of the partial structures. The residues of the magnetic fields form two new structures M1-M2(N2)-N1 and M4-M3(N3)-N4, respectively.