Remote coronal dimmings related to a circular-ribbon flare^⋆

¹ Key Laboratory of Dark Matter and Space Science, Purple Mountain Observatory, CAS, Nanjing 210033, PR China
e-mail: zhangqm@pmo.ac.cn
² State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, PR China
³ State Key Laboratory of Space Weather, Chinese Academy of Sciences, Beijing 100190, PR China
⁴ Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Institute of Space Sciences, Shandong University, Weihai, Shandong 264209, PR China
e-mail: ruishengzheng@sdu.edu.cn

Received: 17 November 2019
Accepted: 19 December 2019

Abstract

Aims. In this paper, we report multiwavelength observations of remote coronal dimmings related to an M1.1 circular-ribbon flare in active region (AR) 12434.

Methods. The confined flare without a coronal mass ejection was observed by the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory on 2015 October 16. We obtained global three-dimensional (3D) magnetic fields before the flare using the potential field source surface modeling.

Results. A few minutes before the flare hard X-ray peak time (06:13:48 UT), small-scale, weak dimming appeared ∼240″ away from the flare site, which can be observed by AIA only in 131 and 171 Å. Afterward, long and narrow dimmings became evident in all AIA extreme-ultraviolet passbands except 304 Å, while localized core dimming was not clearly observed near the flare site. The large-area dimmings extended southeastward and the areas increased gradually. The total area of dimmings reaches (1.2 ± 0.4) × 10⁴ Mm² in 193 Å. The maximal relative intensity decreases in 171 and 193 Å reach 90% and 80%, respectively. Subsequently, the dimmings began to replenish and the area decreased slowly, lasting for ≥3 h. The remote dimmings and AR 12434 are connected by large-scale coronal loops. The remote dimmings are associated with the southwest footpoints of coronal loops with weak negative polarities. Possible origins of remote dimmings are discussed.