Solar Wind Directional Change Triggering Flapping Motions of the Current Sheet: MMS Observations

Abstract

Abstract We report on a flapping motion event near the substorm onset on 17 June 2017 using Magnetospheric Multiscale (MMS) mission data. A strong current density with a maximum value of ~190 nA/m 2 is observed during the flapping. The north‐to‐south (south‐to‐north) crossing of the neutral sheet corresponds to an increase (a decrease) of the Z GSM component of the solar wind V Z, SW . The periods (~8 min) of the flapping and variations of V Z, SW are almost equal. In addition, d V Z, SW /d t and d B X /d t observed by MMS exhibit a strong negative correlation. These observations suggest that the flapping motions are triggered by the solar wind directional change via creating a motion of the current sheet in the north‐south direction. The pressure difference between the northern and southern lobes caused by the solar wind is expected to be a possible contribution to the formation of the flapping.