Fig. 4
From: Two current systems in the preliminary phase of sudden commencements in the magnetosphere
Snapshots of the electric current systems at t = 5.9 min in the same format used in Fig. 3. BH, BC, and BL indicate the projection of the three areas in the ionosphere (Fig. 2) to the lower boundary. The currents from BH and BL are, respectively, the type H current system and the type L current system. The currents from BC belong to the type H current system or the type L current system. The type H current system advances the region of BC from t = 5.5 to 5.9 min. Note that the type L current system goes farther in the longitudinal direction