The magnetopause deformation due to the upstream magnetosheath pressure perturbations is important to understand the solar wind - magnetosphere coupling process, but how to identify such events from in-situ spacecraft observations is still challenging. In this study, we investigate magnetopause crossing events with fast-moving cold ions in the magnetosphere from Magnetospheric Multiscale (MMS) observations, and find when fast-moving cold ions are present at the magnetopause, they are closely associated with the magnetopause deformation, which is featured by fast magnetopause motion and significant magnetopause normal deflection from model predictions. Therefore, fast-moving cold ions can be a useful indicator to search for magnetopause deformation events. By integrating the cold ion speed, the inferred magnetopause deformation amplitude varies from 0.2 to ∼ 2.5 RE. Further statistics indicate that such magnetopause deformation events prefer to occur under quasi-radial interplanetary magnetic field and fast solar wind conditions, suggesting high-speed magnetosheath jets could be one direct cause of magnetopause deformations.

A 2.5-D PIC kinetic simulation code has been run for excitation of whistler wave and wave-particle interaction process in symmetric magnetic reconnection. The whistler wave is important to the energy release and transfer, which move faster for a perturbation of the magnetic field because of electrons smaller mass during magnetic reconnection. Our simulations suggest that whistler wave can be excited in separatrices line region of magnetic reconnection, and the frequency range of whistler wave is in the lower band (Ωlh< Ω <0.5Ωce). Furthermore, the frequency of whistler wave is oscillation with the change of space position. And the power amplitude of whistler wave also increases with the increasing of reconnection rate. On the other hand, whistler wave can transfer energy to electrons, which increases electrons energy by wave-particle interaction.