Inner Magnetospheric ULF Waves: The Occurrence and Distribution of Broadband and Discrete Wave Activity
Inner Magnetospheric ULF Waves: The Occurrence and Distribution of Broadband and Discrete Wave Activity
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DOI：
10.1029/2020ja027887
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发表时间：
2020-08
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影响因子：
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通讯作者：
K. Murphy;A. Inglis;D. Sibeck;C. Watt;I. J. Rae
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文献类型：
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作者：
K. Murphy;A. Inglis;D. Sibeck;C. Watt;I. J. Rae
超低频（ULF）波是在整个磁层中观察到的电磁脉动，由磁层外部和内部的过程驱动。在磁层内，离散和宽带ULF波活动可以通过相干或随机的波粒相互作用耦合到局部等离子体。这些波粒相互作用可以导致局部等离子体的动态变化，包括辐射带电子的快速加速和传输。利用GOES-15的观测结果和自动耀斑振荡推断算法，我们研究了宽带和离散ULF波的分布和发生，以帮助理解相干和随机波粒相互作用的相对重要性。我们发现，离散ULF波的间隔在缓慢和低密度太阳风期间以及Bz接近零时更常见。宽带波在活跃的太阳风期间更常见，包括高太阳风速度和大密度扰动以及大的负Bz期间。我们还发现，在所有的太阳风条件下，宽带超低频波功率的间隔数超过离散波功率，例如，超低频波活动更可能是宽带。这些结果表明，由于非相干宽带波的径向扩散是波粒相互作用的重要驱动力，特别是在活跃的太阳风条件下。然而，在活跃和平静的太阳风条件下都存在离散波，这表明这些波和相应的波粒相互作用不能被忽略，特别是因为离散波粒相互作用往往比径向扩散更有效。
Ultralow frequency (ULF) waves are electromagnetic pulsations observed throughout the magnetosphere driven by processes both external and internal to the magnetosphere. Within the magnetosphere, discrete and broadband ULF wave activity can couple to the local plasma via coherent or stochastic wave‐particle interactions. These wave‐particle interactions can lead to dynamic changes in local plasma including rapid acceleration and transport of radiation belt electrons. Using observations from GOES‐15 and the Automated Flare Inference of Oscillations algorithm we investigate the distribution and occurrence of broadband and discrete ULF waves to help understand the relative importance of coherent and stochastic wave‐particle interactions. We find that intervals of discrete ULF waves are more commonly identified during slow and low‐density solar wind and when Bz is near zero. Broadband waves are more commonly identified during periods of active solar wind, including periods of high solar wind speeds and large density perturbations, and large negative Bz. We also find that under all solar wind conditions the number of intervals of broadband ULF wave power exceeds that of discrete wave power; for example, ULF wave activity is more likely to be broadband. These results suggest that radial diffusion due to incoherent broadband waves is an important driver of wave‐particle interactions, especially during active solar wind conditions. However, the presence of discrete waves during both active and quiet solar wind conditions suggests that these waves and the corresponding wave‐particle interactions cannot be ignored, especially since discrete wave‐particle interactions tend to be more efficient than radial diffusion.