A parametric study of the linear growth of magnetospheric EMIC waves in a hot plasma
A parametric study of the linear growth of magnetospheric EMIC waves in a hot plasma
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DOI：
10.1063/1.4953565
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发表时间：
2016-06
影响因子：
2.2
通讯作者：
Qi Wang;Xing Cao;X. Gu;B. Ni;Chen Zhou;R. Shi;Zhengyu Zhao
中科院分区：
文献类型：
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作者：
Qi Wang;Xing Cao;X. Gu;B. Ni;Chen Zhou;R. Shi;Zhengyu Zhao
由于地球磁层中的电磁离子回旋（EMIC）波在相对论电子和高能质子的动态损失以及离子加热中起着至关重要的作用，因此全面了解现实情况下的EMIC波色散关系非常重要，这对于磁层EMIC波的产生、放大和传播具有重要意义。本研究采用全动力学线性色散关系来评估多离子（H+、He+ 和 O+）磁层等离子体（也由热环电流质子组成）中 EMIC 波的线性增长。各向异性热质子的引入强烈改变了EMIC波色散表面，并可能导致H+-、He+-和O+带EMIC发射同时增长。我们的参数分析表明，热质子浓度的增加更有可能产生H+-和He+带EMIC波。虽然H+带发射的激发需要热质子相对较大的温度各向异性，但He+带发射更有可能在背景等离子体较稠密的等离子体层或等离子体层羽流中被触发。此外，He+带波的产生比H+带波对质子温度的变化更敏感。冷重离子（He+和O+）密度的增加增加了H+截止频率，因此拓宽了He+陀螺频率之上的阻带频率覆盖范围，导致H+波段EMIC波的显着阻尼。相比之下，无论所有考虑的变量如何，O+波段EMIC波的特征性表现出比其他两个波段弱得多的时间增长，这表明O+波段发射发生的速率远低于H+和He+波段发射，这与观察结果一致。
Since electromagnetic ion cyclotron (EMIC) waves in the terrestrial magnetosphere play a crucial role in the dynamic losses of relativistic electrons and energetic protons and in the ion heating, it is important to pursue a comprehensive understanding of the EMIC wave dispersion relation under realistic circumstances, which can shed significant light on the generation, amplification, and propagation of magnetospheric EMIC waves. The full kinetic linear dispersion relation is implemented in the present study to evaluate the linear growth of EMIC waves in a multi-ion (H+, He+, and O+) magnetospheric plasma that also consists of hot ring current protons. Introduction of anisotropic hot protons strongly modifies the EMIC wave dispersion surface and can result in the simultaneous growth of H+-, He+-, and O+-band EMIC emissions. Our parametric analysis demonstrates that an increase in the hot proton concentration can produce the generation of H+- and He+-band EMIC waves with higher possibility. While the excitation of H+-band emissions requires relatively larger temperature anisotropy of hot protons, He+-band emissions are more likely to be triggered in the plasmasphere or plasmaspheric plume where the background plasma is denser. In addition, the generation of He+-band waves is more sensitive to the variation of proton temperature than H+-band waves. Increase of cold heavy ion (He+ and O+) density increases the H+ cutoff frequency and therefore widens the frequency coverage of the stop band above the He+ gyrofrequency, leading to a significant damping of H+-band EMIC waves. In contrast, O+-band EMIC waves characteristically exhibit the temporal growth much weaker than the other two bands, regardless of all considered variables, suggesting that O+-band emissions occur at a rate much lower than H+- and He+-band emissions, which is consistent with the observations.