Magnetic reconnection is one of the most fundamental magnetized plasma processes in solar atmosphere. The leading theories hold that current sheet acts as a necessary prerequisite for the initiation of magnetohydrodynamic (MHD) reconnection process. Thus, studying the formation and evolution process of the current sheet is crucial for understanding the nature of magnetic reconnection in the solar atmosphere.

However, direct and clear observations of small-scale current sheet formation forced by external deformation or perturbations have been rarely reported yet.

In a study published in The Astrophysical Journal on July 8, PhD student CHEN Hechao from Yunnan Observatories of the Chinese Academy of Sciences and the collaborators reported a clear observation on small-scale current sheet formation in two reconnection events, which provides a better understanding of the initiation of small-scale reconnection in the solar atmosphere.

Via the detailed analysis of two small reconnection events occurred near solar active region 12494, scientists found that the current sheet formations within two X-shaped magnetic configurations are both forced by a same physical cause: non-radial rotating motion of mini-filaments.

Based on the multiwavelength imaging observations, they then carefully analyzed the apparent thickness/length, temperature/emission of the current sheet regions and their reconnection rates.

In particular, a chain of high-speed plasmoid ejections was detected along with a set of the reconnected field lines, implying the onset of tearing-mode instability inside its current sheet region.

"These observations not only provide compelling evidence that non-radial rotating motion of filaments can serve as external flows to drive magnetic reconnection, but also give us a basic scenario of current sheet formation within small-scale magnetic reconnection processes,” CHEN said.