Subarcsecond Blobs in Flare-related Coronal Jets

Abstract

Abstract In this paper, we report multiwavelength observations of subarcsecond blobs in coronal jets. In AR 12149, a C5.5 circular-ribbon flare occurred at ∼04:55 UT on 2014 August 24, which consisted of a discrete circular ribbon and a short inner ribbon inside. Two jets (jet1 and jet2) were related to the flare. Jet1 appeared first and experienced untwisting motion during its early propagation along a closed coronal loop. Jet2 appeared 6 minutes later and propagated upward along another closed loop. During its initial phase, a big plasmoid was ejected out of jet2 at a speed of ∼150 km s−1. After the flare peak time (05:02 UT), multiple bright and compact blobs appeared in the lower part of jet2, which were observed by the Slit-Jaw Imager (SJI) on board the Interface Region Imaging Spectrograph. The blobs observed by SJI in 1330 Å have sizes of 0.″45–1.″35, nearly 84% of which are subarcsecond (<1″). The mean value and standard deviation of the sizes are 0.″78 and 0.″19, respectively. The velocities of the blobs range from 10 to more than 220 km s−1, some of which decelerate and disappear during the upward propagation. Three of the blobs had their counterparts in extreme-ultraviolet (EUV) wavelengths observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory spacecraft. The velocities are almost identical in ultraviolet (UV) and EUV wavelengths. We propose that the blobs observed in 1330 Å are the cool component (∼0.025 MK), while the blobs observed in EUV are the hot component of several MK. In jet1, only one blob was present, with a size of ∼1″ and a velocity of ∼40 km s−1. We conclude that the blobs are created by the tearing-mode instability of the current sheet at the base or inside the coronal jets. Our results have important implications for uncovering the fine structures of coronal jets and understanding the relationship between the blobs observed at UV and EUV wavelengths.