Using the high-resolution data obtained by the 1-meter New Vacuum Solar Telescope (NVST) at the Fuxian Solar Observatory of Yunnan Observatories of the Chinese Academy of Sciences, Dr. XUE Zhike et al. study statistically six small-scale magnetic reconnections for the first time, and the results have been published recently in The Astrophysical Journal.
Magnetic reconnection plays a crucial role in determining the topology of magnetic fields in cosmic plasma and also provides an efficient way for the conversion of magnetic energy into kinetic energy. Actually, magnetic reconnection is not easy to be observed and confirmed, even though it is generally considered to be directly related to the solar eruptions, such as flares and coronal mass ejections. Previous observational reports on magnetic reconnection are often based on a single event. In addition, magnetic reconnection has not been studied statistically.
Researchers checked the high-resolution data of the NVST from 2012 to 2020 carefully. They found only six cases of magnetic reconnection with obvious inflows and outflows. It is interesting that all of these magnetic reconnections have large separatrix angles. Their morphological characteristics and magnetic field configurations are obtained by the NVST and the Solar Dynamics Observatory (SDO). Meanwhile, several physical parameters of each magnetic reconnection are calculated including the velocities of reconnection inflows, outflows, and separatrix jets, the angles between each pair of separatrices, and the width and length of current sheets and their ratio.
It is found that the outflow velocity, the separatrix jet velocity, and the width and length of the current sheet are positively related to the inflow velocity. However, the separatrix angle does not depend on the inflow velocity, and it is related to the initial magnetic field configuration before magnetic reconnection. Furthermore, besides the inflow velocity, the magnetic diffusivity or the magnetic Reynolds number is also important to determine the width of the current sheet. The magnetic reconnection rates are different among the six reconnection events, and it decreases with the increase of the inflow velocity. The results obtained by the kinetic parameters and by the parameters of the current sheet are consistent. Meanwhile, when the separatrix angle is close to 90°, the jet and the outflow reach their maximum velocities.
These observations are consistent with the results of theoretical model and numerical simulation. However, researchers still do not know how the magnetic reconnection is triggered. They need to observe finer structures and more accurate magnetic fields to improve the observational and theoretical understanding of magnetic reconnection. Fortunately, there are already numerous high-resolution solar telescopes in operation or under development that will help researchers to further study small-scale magnetic reconnections.
Provided by Yunnan Observatories CAS