In this work, we present a statistical study of substorms covering a five-year period 2016–2020. Substorm phases were identified from time series of the SuperMAG AL (SML) index using a list of 5,077 previously identified substorm onsets, the SML peak value marking transition from expansion to recovery phase, and the recovery identified as return to activity less than −100 nT in the SML index. Magnetic field observations from THEMIS, RBSP, and MMS missions were used to study the magnetotail characteristics during the substorm evolution. A superposed epoch analysis indicates that the substorm onset occurs almost simultaneously with a few minutes of uncertainty throughout the magnetotail, ranging from geostationary orbit to 20 RE. The onset in the transition region precedes the ground onset by a few minutes. The peak SML time coincides with the peak of the outer transition region ΔB_Z, which suggests that the field-aligned currents driving the SML activity arise from the outer transition region. Analysis of 2D maps of the tail magnetic field shows that the magnetotail current changes are limited to the center of the tail within |Y| < 10R_E. The substorm recovery is fastest in the inner transition region and lasts longer when moving further out. We did not find major asymmetries in the substorm signatures associated with IMF B_Y or B_Z.

中文翻译：

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磁层亚暴期间的磁尾变化

在这项工作中，我们对 2016 年至 2020 年五年期间的亚暴进行了统计研究。亚暴阶段是根据 SuperMAG AL (SML) 指数的时间序列，使用先前确定的 5,077 个亚暴爆发的列表来确定的，SML 峰值标记从扩张到恢复阶段的过渡，并且恢复被确定为恢复活动小于 -100 nT在 SML 索引中。THEMIS、RBSP 和 MMS 任务的磁场观测被用来研究亚暴演化过程中的磁尾特征。叠加历元分析表明，亚暴爆发几乎同时发生，整个磁尾区域存在几分钟的不确定性，范围从地球静止轨道到 20 RE。过渡区的爆发早于地面爆发几分钟。峰值 SML 时间与外部过渡区域 Δ B _Z的峰值一致，这表明驱动 SML 活动的场对准电流源自外部过渡区域。对尾部磁场二维图的分析表明，磁尾电流变化仅限于尾部中心| 是| < ₁₀ RE。亚暴恢复在内部过渡区域最快，并且在向外移动时持续时间更长。我们没有发现与 IMF B _Y或B _Z相关的亚暴特征存在重大不对称性。