Quasiperiodic Super-Alfvénic Slippage along Flare Ribbons Observed by the Interface Region Imaging Spectrograph

The apparent slipping motion of flare loops is regarded as a key feature of the 3D magnetic reconnection in the solar flares. The slippage with a super-Alfvénic speed could be defined as slipping–running reconnection, while the slippage with a sub-Alfvénic speed is called slipping reconnection. Due to the limitation of the observational instrument temporal resolution, the apparent slippage of the flare loop footpoints along the flare ribbons with super-Alfvénic speed is quite rare to our knowledge. In this Letter, we report a unique event that exhibits not only the sub-Alfvénic slippage but also the quasiperiodic super-Alfvénic slippage of ribbon substructures during a C3.4-class flare (SOL2023-01–18-T15:23), using the high-temporal-resolution observations of the Interface Region Imaging Spectrograph (∼2 s). The super-Alfvénic slippage with a speed of up to ∼1688 km s ^−1 is directly observed in this study. The calculated period of the apparent super-Alfvénic slippage in both ribbons is between 8.4 and 11.9 s. This work provides the first observational evidence of the periodicity for the slipping–running magnetic reconnection.