Discussion on the vanishment of solar atmospheric structures during magnetic reconnection

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.

💡 Research Summary

The paper investigates a previously under‑explored aspect of solar magnetic reconnection: the change in the physical length of the reconnecting magnetic structures. The authors define three strict selection criteria for reconnection events: (1) a clear X‑type configuration composed of two independent atmospheric structures, (2) an unambiguous observation of the reconnection process, and (3) the ability to trace the topological connectivity of the structures for at least five minutes before and after the reconnection. By scanning the literature and the archives of the Solar Dynamics Observatory’s Atmospheric Imaging Assembly (SDO/AIA) and the New Vacuum Solar Telescope (NVST), they find 48 AIA‑based and 11 NVST‑based candidate events, but only three satisfy all three criteria.

The three selected events are observed with high spatial (0.163″–0.6″) and temporal (12 s for AIA, 12 s–49 s for NVST) resolution. For each event the authors mark the two end points of each structure (L1, L2 before reconnection; L3, L4 after reconnection) with fixed “X” symbols, ensuring that the points remain stationary throughout the process. Lengths are measured along the central spine of each structure, repeated ten times to estimate the mean square deviation as the measurement error.

Event 1 (AIA 335 Å, 2012‑01‑01) shows a sudden reduction of the combined length of the two pre‑reconnection structures by 47 Mm, corresponding to roughly 14 % of the total length. Event 2 (NVST Hα + AIA 131 Å, 2014‑02‑03) exhibits a 3.7 Mm decrease (≈14 % of the total), while Event 3 (NVST Hα + AIA 171 Å, 2020) shows an 8.2 Mm reduction (≈18 %). In each case, after reconnection the remaining “residue” parts of the original structures reconnect to form two new structures (L3 and L4). The authors note that the lengths of L1–L4 evolve smoothly before and after reconnection, but the abrupt drop occurs precisely during the reconnection interval, indicating a genuine loss of material or magnetic connectivity rather than a gradual contraction.

Three possible explanations are discussed. (i) Magnetic tension could cause a gradual shrinkage of the structures, but this cannot account for the instantaneous, large‑scale shortening observed. (ii) A “bizarre” change in the third dimension (line‑of‑sight) might make part of the structure disappear from the 2‑D image plane; however, no accompanying signatures are detected, making this unlikely to be the dominant cause. (iii) True magnetic annihilation, possibly associated with turbulent diffusion regions, magnetic islands, and rapid energy conversion, could physically eliminate a portion of the magnetic flux. The authors favor this third scenario. Using an estimated magnetic field strength of 75 G and assuming the vanished portion consists of eight cylindrical filaments of radius ~1.6 × 10⁸ cm and length 4.7 × 10⁹ cm, they calculate a magnetic energy loss of ≈6.8 × 10²⁹ erg, comparable to or exceeding the energy released in the observed current sheet (≈2.5 × 10²⁹ erg).

The discussion connects these observations with classic reconnection theory (diffusion region, current sheet, tearing‑mode islands) and recent 3‑D kinetic simulations that show turbulent, chaotic fields and rapid magnetic annihilation in collisionless plasmas. The authors cite MMS spacecraft observations of magnetic field annihilation in Earth’s magnetotail as an analogue, suggesting that similar processes may operate in the solar corona, leading to the observed abrupt loss of length.

Limitations are acknowledged: the sample size is small, the volume and magnetic field strength of the vanished structures are inferred rather than directly measured, and the analysis relies on 2‑D imaging, which cannot fully capture 3‑D topology changes. The paper calls for future high‑resolution, multi‑viewpoint observations (e.g., Solar Orbiter, DKIST) and advanced numerical modeling to verify whether the “vanishment” is indeed magnetic annihilation or an observational artifact.

In summary, this work introduces a novel quantitative metric—sudden reduction of the total length of reconnecting structures—to solar reconnection studies, provides the first observational evidence that a measurable portion of magnetic structures can disappear during reconnection, and proposes magnetic annihilation in turbulent diffusion regions as a plausible physical mechanism. The findings open a new avenue for probing the microphysics of energy release in solar eruptions.