Unprecedented Fast Winking of Solar Flares Triggered by Bursty Magnetic Reconnection

Flare ribbons form as a result of energy deposition associated with particles accelerated in low layers of the solar atmosphere. The fine-scale structures of flare ribbons, also called ribbon kernels, offer a potentially powerful diagnostic of the flare reconnection process, however, to date the dynamic evolution of ribbon kernels has not been fully characterized in statistical studies. Here, we checked the state-of-the-art observations (cadence ≤2.5 s) of solar flares in the ultraviolet from space by Interface Region Imaging Spectrograph over the past 12 yr. Our results showed the first statistical study of multiple spatially resolved flare kernel quasiperiodic pulsation events for 31 flares, with the period of 6–24 s. The ribbon kernels have a spatial scale of 480–1200 km and some kernels exhibit an unprecedented fast “winking” process, i.e., quasiperiodic pulsation-like flashing of individual kernels. The shortest heating time reaches about 2–3 s, implying that the energy is deposited only in a small localized region within flare ribbons, persisting for only a few seconds. Meanwhile, some ribbon kernels were observed to slip along the ribbon at speeds of 20–1800 km s⁻¹. These observations strongly imply a joint picture for the dynamics and the bursty nature of ribbon kernels as being due to coupled effects of plasmoid formation and three-dimensional magnetic reconnection in the overlaying coronal current sheet. We suggest that the observed flare behaviors provide strong observational evidences of 3D bursty reconnection.