Zijinshan Observatory makes progress in research on solar ring flare and related activities

[ Instrument Network Instrument R & D ] Solar flare is a process of intense energy release in the solar atmosphere in a short period of time. A circular flare (CRF: circular-ribbon flare) is a special flare discovered by the TRACE solar probe in 2009. It usually consists of a circular or elliptical bright band and a dense bright band inside. It has a special magnetic topology. Coronal dimming is a large-scale activity (ranging from tens to hundreds of megameters) associated with solar flare bursts, which manifests as a rapid decrease in coronal extreme ultraviolet and soft X-ray radiation. With the continuous accumulation of high-resolution observational data, the study of ring flares and related activities has gradually become a hot topic in the field of solar physics.

Researchers from the Zijinshan Observatory of the Chinese Academy of Sciences have collaborated with their domestic counterparts to conduct in-depth systematic research on annular flares and related activities. In terms of their chromosphere evaporation, chromosphere compression, quasi-periodic oscillation, energy distribution, and extended motion of flares Made a series of innovative results. Recently, based on data from the Atmospheric Imager (AIA) and Heliospheric Magnetic Imager (HMI) data of the Solar Dynamics Observatory (SDO), they studied in detail a case related to an M-level annular flare on the sun on October 16, 2015. Evolution of the corona darkening event: First, a few minutes before the peak of the hard X-ray flare, a small and weak distal corona darkening is visible only in the AIA 131 Angstrom and 171 Angstrom bands (about 240 arc seconds from the flare ); After that, the long and narrow far-end corona darkening became obvious in all extreme ultraviolet bands except AIA 304 Angstrom, but the flare area itself did not change significantly; the large-scale darkening gradually extended to the southeast, Slowly increase (see Figure 1); finally, the darkening area gradually decreases, and the entire process lasts at least 3 hours. The darkened area reached about 12,000 square meters in AIA 193 Angstroms; the maximum relative brightness reductions in darkened areas at 171 and 193 Angstroms were about 90% and 80%, respectively; the large scale between the remote corona darkening and the active area The crown rings are connected.

Based on the fact that the corona darkening occurred in almost all extreme ultraviolet bands in this event, the author believes that the cause of the corona darkening is likely to be the decrease in local plasma density caused by large-scale coronal ring expansion, rather than temperature changes, as for large areas The problem of where matter in the darkened area is still an unsolved mystery, and more cases need to be analyzed and accumulated and large sample statistical research to gradually unravel the mystery.

The findings were published in the journal Astronomy & Astrophysics 633 (2020) A142. This work was supported by the National Natural Science Foundation of China's major fund, international (regional) cooperation and exchange projects, general projects, the Youth Promotion Committee of the Chinese Academy of Sciences, the ASO-S satellite Chinese Academy of Sciences strategic pilot technology project, and the Macau University of Science and Technology.