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Transition-region explosive events (EEs) are characterized by non-Gaussianline profiles with enhanced wings at Doppler velocities of 50-150 km/s. Theyare believed to be the signature of solar phenomena that are one of the maincontributors to coronal heating. The aim of this study is to investigate thelink of EEs to dynamic phenomena in the transition region and chromosphere inan active region. We analyze observations simultaneously taken by the InterfaceRegion Imaging Spectrograph (IRIS) in the Si IV 1394\AA\ line and the slit-jaw(SJ) 1400\AA\ images, and the Swedish 1-m Solar Telescope (SST) in theH$\alpha$ line. In total 24 events were found. They are associated withsmall-scale loop brightenings in SJ 1400\AA\ images. Only four events show acounterpart in the H$\alpha$-35 km/s and H$\alpha$+35 km/s images. Two of themrepresent brightenings in the conjunction region of several loops that are alsorelated to a bright region (granular lane) in the H$\alpha$-35km/s andH$\alpha$+35 km/s images. Sixteen are general loop brightenings that do notshow any discernible response in the H$\alpha$ images. Six EEs appear aspropagating loop brightenings, from which two are associated with dark jet-likefeatures clearly seen in the H$\alpha$-35 km/s images. We found thatchromospheric events with jet-like appearance seen in the wings of theH$\alpha$ line can trigger EEs in the transition region and in this case theIRIS Si IV 1394\AA\ line profiles are seeded with absorption componentsresulting from Fe II and Ni II. Our study indicates that EEs occurring inactive regions have mostly upper-chromosphere/transition-region origin. Wesuggest that magnetic reconnection resulting from the braidings of small-scaletransition region loops is one of the possible mechanisms of energy releasethat are responsible for the EEs reported in this paper.

Explosive events in active region observed by IRIS and SST/CRISP