Remote coronal dimmings related to a circular-ribbon flare

Abstract

In this paper, multiwavelength observations of remote coronal dimmings related to an M1.1 circular-ribbon flare (CRF) in active region (AR) 12434 are reported. The confined flare without a CME was observed by AIA and HMI on board SDO on 2015 October 16. Global three-dimensional (3D) magnetic fields before flare were obtained using the potential field source surface modeling. A few minutes before the flare hard X-ray peak time (06:13:48 UT), small-scale, weak dimming appeared $\sim$240$\arcsec$ away from the flare site, which can be observed by AIA only in 131 and 171 {\AA}. Afterwards, long and narrow dimmings became evident in all AIA EUV passbands except 304 {\AA}, 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$\pm0.4$)$\times$10$^4$ Mm$^2$ in 193 {\AA}. The maximal relative intensity decreases in 171 and 193 {\AA} reach 90\% and 80\%, respectively. Subsequently, the dimmings began to replenish and the area decreased slowly, lasting for $\geq$3 hr. The remote dimmings and AR 12434 were connected by large-scale coronal loops. The remote dimmings were associated with the southwest footpoints of coronal loops with weak negative polarities. Possible origins of remote dimmings are discussed.