On Whistler Mode Wave Relation to Electron Field‐Aligned Plateau Populations
On Whistler Mode Wave Relation to Electron Field‐Aligned Plateau Populations
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DOI：
10.1029/2019ja027735
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发表时间：
2020-03
期刊：
影响因子：
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通讯作者：
A. Artemyev;D. Mourenas
中科院分区：
文献类型：
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作者：
A. Artemyev;D. Mourenas
哨声模式波是最强烈的电磁辐射之一，通过波粒共振相互作用在地球内磁层电子群之间的能量重新分配中发挥重要作用。哨声模波通常由横向各向异性等离子体片电子布居（100 -30 keV）通过回旋共振产生，哨声模波可以有效地将一小部分高能电子的种子布居（100 - 100 keV）加速到相对论能量。然而，这些波可以有效地阻尼，通过同时与更多的超热电子（0.1-1千电子伏）通过朗道共振相互作用。最近的观测确实表明，伴随着强烈的哨声模式发射的电子分布通常包含一个平台状的电子种群，其能量接近于与波的朗道共振的能量。然而，同时观察这些波和相关的高原人口并不能证明因果关系。在这里，我们测试的假设，这样一个高原人口可能已经形成的哨声模式波产生较早，或由其他类型的波。结合分析估计和航天器的观测，我们表明，这个高原人口往往是不太可能单独形成的哨声模式波。我们提出了三种可能导致高原种群形成的替代方案，并根据航天器观测结果对这些方案进行了测试。我们发现，高原人口可以形成超低频电场（携带动力阿尔芬波或时域结构）往往伴随着注入等离子体片电子的能源哨声模式波。我们还讨论了电离层二次电子的可能作用。
Whistler mode waves are among the most intense electromagnetic emissions and play an important role in the energy redistribution between electron populations in the Earth inner magnetosphere through wave‐particle resonant interactions. Usually generated by transversely anisotropic plasma sheet electron populations ( ∼ 10–30 keV) through cyclotron resonance, whistler mode waves can effectively accelerate a small fraction of the seed population of energetic electrons ( ∼ 100 keV) up to relativistic energies. However, these waves can be efficiently damped through simultaneous interactions with much more numerous suprathermal electrons ( ∼ 0.1–1 keV) via Landau resonance. Recent observations indeed show that electron distributions accompanied by intense whistler mode emissions often contain a plateau‐like electron population at energies close to the energy of Landau resonance with the waves. However, simultaneous observations of these waves and of the related plateau population does not prove a causal relationship. Here, we test the hypothesis that such a plateau population may have been formed by whistler mode waves generated earlier, or by other types of waves. Combining analytical estimates and spacecraft observations, we show that this plateau population is often unlikely to be formed by whistler mode waves alone. We suggest three alternative scenarios that can lead to the formation of plateau populations and test these scenarios based on spacecraft observations. We show that a plateau population can be formed by ultralow frequency electric fields (carried by kinetic Alfven waves or time domain structures) often accompanying injections of plasma sheet electrons—the energy source for whistler mode waves. We also discuss the possible role of ionospheric secondary electrons.