Letter to the Editor

The merging process of chromospheric fibrils into a filament^⋆

¹ School of Physics and Optoelectronics engineering, Anhui University, Hefei 230601, PR China
e-mail: zjun@ahu.edu.cn
² CAS Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
e-mail: yijunhou@nao.cas.cn
³ School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, PR China

Received: 23 November 2021
Accepted: 12 January 2022

Abstract

Context. Although solar filaments have been intensively studied, detailed observations that show an entire process of filament maintenance are rare.

Aims. The aim of this paper is to study the whole process of the material supply and the magnetic flux injection from chromospheric fibrils to a nearby filament.

Methods. Based on multiwavelength observations from the New Vacuum Solar Telescope and the Solar Dynamics Observatory (SDO), we tracked the evolution of the chromospheric fibrils involved in the process of filament maintenance and estimated the relevant kinetic parameters. The possible reconnection process was further analyzed in detail by using the SDO magnetic field and extreme ultraviolet observations.

Results. In the southeast of the filament, two sets of chromospheric fibrils approach and interact with each other, accompanied by weak brightening at the interacting region. Subsequently, a long fibril is formed, keeps moving toward the filament, and finally merges into it. The mergence results in a disturbance in the filament, for example, some of the original filament fibrils move northward. Ten minutes later, a similar process occurs again. By checking the photospheric magnetograms, we find that the two sets of chromospheric fibrils are rooted in a pair of opposite-polarity magnetic patches, and magnetic cancellation takes place between them. We propose that magnetic reconnection could occur between chromospheric fibrils and that it plays an important role in the formation of the new longer fibrils.

Conclusions. Magnetic reconnections between chromospheric fibrils produce new fibrils, which then merge into a nearby filament. Such observations imply that filament material and magnetic flux can be supplied from surrounding chromospheric fibrils.