Particle entry through reconnection grooves in the magnetopause with a dawnward IMF as simulated by a 3‐D EM Particle Code

We report progress in the long‐term effort to represent the interaction of the solar wind with the Earth's magnetosphere using a three‐dimensional electromagnetic particle code. After a quasi‐steady state is established with an unmagnetized solar wind we gradually switch on a northward interplanetary magnetic field (IMF), which causes a magnetic reconnection on the magnetopause tailward of the dayside cusps and makes the magnetosphere dipolarized. In the case that the northward IMF is switched gradually to dawnward, there is no signature of reconnection in the near‐Earth magnetotail in contrast to the case with the southward turning. On the contrary analysis of magnetic fields in the magnetopause confirms a signature of magnetic reconnection at both the dawnside and duskside. The plasma sheet in the near‐Earth magnetotail clearly thins as in the case of southward turning. Arrival of dawnward IMF to the magnetopause creates a reconnection groove which causes particle entry into the deep region of the magnetosphere via field lines that go near the magnetopause. This deep connection is more fully recognized tailward of Earth. The flank weak‐field region joins onto the plasma sheet and the current sheet to form a geometrical feature called the cross‐tail S that structurally integrates the magnetopause and the tail interior. This structure might contribute to direct entry between the magnetosheath plasma to plasma sheet, in which the entry process heats the magnetosheath plasma to plasma sheet temperatures. In spite of strong plasma entry into the inner magnetosphere, the dawnward IMF prevents the reconnection in the near‐Earth magnetotail due to the penetrated IMF By component. Therefore, the onset of substorms may not take place. However, it is still possible that this particle entry causes pseudo‐substorm onsets.