2018 年 9 月 11 日超强亚暴演化过程研究

This study investigates the energy input and magnetotail evolution of a supersubstorm event (SME_max = 2070 nT) that occurred on September 11, 2018 by using the observations from satellites and ground-based stations. The main observational features are as follows: the onset time of this supersubstorm was 06:41 UT as indicated by the ground-based aurora observations; the Sun erupted multiple coronal mass ejections 2 to 3 days preceding the onset time; a clear tailward high-speed flow was observed by the Geotail in the mid-tail region before the supersubstorm onset; the duration of a southward interplanetary magnetic field reached 280 minutes during the substorm; MMS 1 and Geotail detected multiple high-speed flows in the magnetotail. Through temporal analysis of the observational data, we suggest that the coronal mass ejections probably played an important role for the trigger of this supersubstorm. Magnetic reconnection occurring in the magnetotail before the substorm onset was likely the direct cause of the expansion phase. The sustained southward interplanetary magnetic field and multiple compressions of the magnetosphere by solar wind were significant factors for the evolution of this supersubstorm. We propose that the energy release process in the magnetosphere after the substorm onset occurred simultaneously with the energy storage process. It makes the magnetosphere highly dynamical and is likely a key factor causing the long duration of this supersubstorm. During the expansion phase, multiple magnetic reconnections occurred in the magnetotail. It may indicate that magnetic energy release is dominated by the magnetic reconnection and it is a multiple sporadic release process.