A recent study published in the Astrophysical Journal Letters by BI Yi from Yunnan Observatories of the Chinese Academy of Sciences (CAS) and WANG Qingmei from Yunnan Normal University reveals new insights into the triggering mechanisms of solar microflares and the self-similarity of solar flares.

Conventional theories of solar flares posit that they are driven by the outbursts of magnetic rope structures, a classical model that explains many features of the Sun's large-scale energy release. However, this study focuses on frequent microflares and reveals that their triggering mechanism may differ from that of large-scale flares. 

The research team, using data from the Solar Orbiter Extreme Ultraviolet Imager (EUI) and multi-platform joint observations by the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), made the first observations of a series of tiny ejections accompanying microflares. These ejections originated from the centers of three homologous microflares in the dipole magnetic field. They first appeared as point-like structures with diameter of only 103 km, then rapidly evolved into a ring-like shape and propagated along the direction perpendicular to the ring structure of the microflares. 

The researchers proposed that these tiny jets may be triggered by reconnection between small-angle misaligned magnetic fields in the braided magnetic field. This mechanism challenges the conventional view and provides a new explanation for the energy release of microflares.

Remarkably, the proposed mechanism shares similarities with the process of nanoflares, long hypothesized as a key source of coronal heating. By demonstrating that small-angle magnetic reconnection triggers both nanoflares and microflares, the study reveals the self-similarity in the physical mechanisms of flares at different energy levels. This implies that the basic physical process of solar flare energy release may be universal in a larger energy scale.

This study not only offers new perspectives on the triggering mechanism of microflares, but also provides important clues for investigating whether similar self-similar properties exist in large-scale flares. Further studies could reveal a unified mechanism for solar flare energy release and advance the understanding of the organization of the coronal magnetic field, the triggering mechanism of magnetic field reconnection, and the contribution to heating. 

This research was supported by the National Science Foundation of China, and the CAS "Light of West China" Program, and the "Yunnan Revitalization Talent Support Program " Innovation Team Project.

Figure 1:(a) Snapshots of 11 tiny ejections (E1-E11, as marked by red arrows) captured in EUI/HRIEUV 174 Å images. Black dashed lines indicate the crossing flaring loops. (b) Time-distance plots taken along the orange dashed lines plotted on panel (a). Image by WANG.

Contact:
BI Yi
Yunnan Observatories, CAS
E-mail: biyi@ynao.ac.cn