Magnetic fluctuations in the near‐Earth magnetotail are an important signature of substorm onset. In a previous statistical study, we reported their occurrence rates, spatial distributions, and relationship with plasma flows. In the present study, we investigated their spectral properties using 11 years of measurements from the Time History of Events and Macroscale Interactions during Substorms mission for 2008–2018. We found 10,848 severe magnetic fluctuation events with , where σ _B and are the standard deviation and average, respectively, of the magnetic field intensity for the local proton gyroperiod. The occurrence rates of severe magnetic fluctuations show no clear dependence on the F _10.7 index in one solar cycle. We extracted 36 dipolarization events with severe magnetic fluctuations. In the power spectral density (PSD) of the magnetic fluctuations during dipolarizations, the steepness of the spectral slope increased with increasing frequency in almost all the events. The average PSDs are shown sorted by (a) distance to the neutral sheet and (b) ambient magnetic field intensity. In all groups, the slopes of the average PSDs increased abruptly from below ∼10^−1.3 Hz (0.05 Hz) to above ∼10^−1.3 Hz, which is close to the gyrofrequency of O⁺ ions. It is the first time that a change of slope near the proton gyrofrequency (frequency range: 0.05–1 Hz) was found in cases of larger ambient magnetic field intensity, implying that the magnetic fluctuations were relatively strong near the proton gyrofrequency. These results suggest that the magnetic fluctuations contribute to the nonmagnetohydrodynamic effect in the ion motion.

中文翻译：

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近地磁尾中的严重电磁涨落：光谱分析和对太阳活动的依赖性

近地磁尾的磁波动是亚暴爆发的重要标志。在先前的统计研究中，我们报告了它们的发生率，空间分布以及与血浆流量的关系。在本研究中，我们使用2008-2018年亚暴任务期间事件的时间历史和宏观尺度相互作用的11年测量结果，研究了它们的光谱特性。我们发现10848个严重磁性波动事件与，其中σ_乙和是标准偏差和平均值，分别为本地质子gyroperiod的磁场强度的。严重的电磁波动的发生率与F _10.7没有明显的相关性一个太阳周期的指数。我们提取了36个具有严重电磁波动的双极化事件。在双极化过程中，磁起伏的功率谱密度（PSD）中，几乎在所有事件中，频谱斜率的陡度都随频率的增加而增加。所示的平均PSD按（a）到中性片的距离和（b）环境磁场强度分类。在所有组中，平均的PSD的斜率突然从下面〜10增加^-1.3 赫兹（0.05赫兹）以上〜10 ^-1.3  Hz，这是接近0的回转频率⁺离子。这是第一次在环境磁场强度较大的情况下发现质子陀螺频率附近的斜率变化（频率范围：0.05-1 Hz），这表明质子陀螺频率附近的磁起伏相对较大。这些结果表明，磁起伏有助于离子运动中的非磁流体动力学效应。