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

摘要

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 190nA/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,V- SW. The periods (8min) of the flapping and variations of V-Z,V- SW are almost equal. In addition, dV(Z, SW)/dt and dB(X)/dt 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.