Abstract
Energetic electron (energy higher than 2 MeV) observations by a synchronous satellite chain (which consists of GOES 2, GOES 3, and GMS covering the local time extent of approximately 10 hr) have been used to study the large‐scale characteristics of the dynamic behavior in the near‐earth magnetosphere for substorms, in which low‐latitude positive bay aspects are clearly seen in the ground magnetic data. Simultaneous multi‐satellite observations have clearly demonstrated the local time dependence of electron flux changes during substorms and the longitudinal extent of electron flux variations. Before a ground substorm onset the energetic electron flux decreases in a wide longitudinal region of the nighttime and the flux decrease is seen even on the afternoonside. For the flux behavior associated with the onset of the substorm expansion phase, there exists a demarcation line, the LT position of which can be represented as LT = 24.3 ‐ 1.5 Kp. The flux shows a recovery to a normal level east of the demarcation line, and it shows a decrease west of the demarcation line. The region of the flux decrease during the expansion phase is restricted, and it is observed mainly on the afternoonside. The afternoonside flux decrease has a different characteristic from the nightside flux decrease preceding the expansion phase. The nightside flux decrease‐recovery sequence is observed in a wide region of more than 6 hr in the nighttime and the center of this variation exists in the premidnight region. It should be noted that the afternoonside flux decrease is not observed for every substorm and the nightside signature sometimes becomes a dominent feature even on the afternoonside.
Published Version
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