Dynamics of reconnection nanojets in eruptive and confined solar flares

Abstract

Recent observations reveal small-scale reconnection-driven plasma ejections, often termed nanojets, triggered by magnetic field interactions at slight misalignment angles. These fast, collimated plasma ejections are ∼1.5 Mm long and ∼0.5 Mm wide. In this study, we analyze two high-resolution extreme ultraviolet imaging data sets from the Extreme Ultraviolet Imager on board the Solar Orbiter mission, corresponding to an eruptive (M7.6) and a confined (C1.2) flare, to investigate the dynamics of nanoflare ejections and, for the first time, compare their properties in distinct magnetic environments. We identified 59 nanoflare ejections: 44 in the eruptive flare and 15 in the confined flare event. Our analysis reveals that these events form two distinct classes: confined events exhibit lower speeds (41–174 km s −1) and lower kinetic energies (1020–1022 erg), placing them closely in or near the picoflare energy regime, while eruptive events show higher speeds (131–775 km s−1) and higher kinetic energies (1022–1024 erg), falling within the nanoflare regime. Furthermore, magnetic field extrapolations reveal a highly sheared arcade with greater twist and higher magnetic energy density in the eruptive event, compared to the less twisted configuration in the confined event. We infer that this sheared arcade configuration in the eruptive event creates favorable conditions for higher speeds and kinetic energies, unlike the less braided structure in the confined event. Our findings highlight the crucial role of the surrounding magnetic environment in regulating the energetics of nanoflare ejections in the solar atmosphere.