Consecutive observation of electron-only reconnection, magnetotail flapping, and ion reconnection

We report an electron-only reconnection event observed by MMS at ~0748 UT on 17 July 2017, during which only electron outflow becomes prominent. The event was observed simultaneously with an initial flapping motion of the magnetotail current sheet. Multiple perturbations of kink-mode flapping followed with periods of ~11-16s and a propagation velocity ranging from ~200 km/s up to 500 km/s mainly in the duskward direction. During the flapping motion, MMS observed the development of a tailward ion outflow. About 75s later after the initial encounter with the current sheet undergoing the electron-only reconnection, MMS traversed the northern tailward-to-earthward exhaust regions of regular ion reconnection where both ion and electron outflows were detected. The consecutive observation of electron-only reconnection, tail flapping, and ion reconnection might indicate sequential dynamics, e. g., the electron-only reconnection driving the flapping motion, which rapidly involves ions in the reconnection process. We consider two mechanisms, i.e., the current sheet shear instability and the ion drift-kink instability that might explain the MMS observations