A numerical simulation of a negative solar wind impulse: Revisited

Response of the magnetosphere‐ionosphere system to a negative impulse of the solar wind dynamic pressure (the negative SI) is studied again with foci of the following three points; multiple convection oscillations, mirror‐image relationship between the negative and positive SIs, and appearance of the overshielding potential. When the negative impulse impinges on the magnetopause, the Region 1 (R1)‐type field‐aligned current (FAC) and R2‐type FAC appears alternatively in the dayside polar ionosphere (∼70°, ∼10 hLT and 14 hLT). These ionospheric current systems shift nightward and poleward. This alternative appearance of FACs invokes positive and negative ionospheric potential patterns switching alternatively. It is revealed that the negative SI is accompanied with multiple convection oscillations repeating more than the positive SI. We also notice that the magnetospheric current system producing the preliminary impulse (PI) of the intensive negative SI is a mirror‐image of that of the positive SI. The multiple convection oscillations and the mirror‐image relationship were not discussed by Fujita et al. (2004) who studied a moderate‐amplitude negative SI. In addition, the R2‐type FACs induced by the negative and positive SIs tend to yield the overshielding electric potential in the ionosphere. The shielding potential invoked by the SIs has shorter duration than that for the northward turn of the interplanetary magnetic field. The duration is longer for the negative SI than for the positive SI. Key Points Field‐aligned currents of the negative SI change the sign three times The negative SI induces periodic variations of the ionospheric convection