Excitation of O+ Band EMIC Waves Through H+ Ring Velocity Distributions: Van Allen Probe Observations
Excitation of O+ Band EMIC Waves Through H+ Ring Velocity Distributions: Van Allen Probe Observations
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DOI：
10.1002/2018gl077109
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发表时间：
2018-02
影响因子：
5.2
通讯作者：
Xiongdong Yu;Z. Yuan;Shiyong Huang;Fei Yao;Dedong Wang;H. Funsten;J. Wygant
中科院分区：
文献类型：
--
作者：
Xiongdong Yu;Z. Yuan;Shiyong Huang;Fei Yao;Dedong Wang;H. Funsten;J. Wygant
2014年7月14日，货车艾伦探测器A观测到了具有He+带和O+带波的电磁离子回旋（EMIC）发射的典型情况。这些发射发生在上午部门的赤道内的等离子体，在该地区的O+波段EMIC波更喜欢出现。通过对这些辐射的性质分析，发现He+波段的电磁干扰波是线偏振的，沿背景磁场沿着传播，而O+波段的电磁干扰波是线偏振的，沿左偏方向传播，相对于背景磁场倾斜。利用等离子体环境和粒子数据的现场观测，用线性增长理论研究了O ~+波段EMIC波的激发。线性增长率的计算表明，这些O+带EMIC波可以局部激发的环电流质子的环速度分布。观测到的波谱强度和计算的增长率的比较表明，提供自由能的不稳定性的H+环的密度已减少后，波的增长。因此，本文为O ~+带EMIC波的激发机制提供了直接的观测证据：具有环分布的环电流质子提供了支持等离子体中富O ~+存在时不稳定性的自由能。
A typical case of electromagnetic ion cyclotron (EMIC) emissions with both He+ band and O+ band waves was observed by Van Allen Probe A on 14 July 2014. These emissions occurred in the morning sector on the equator inside the plasmasphere, in which region O+ band EMIC waves prefer to appear. Through property analysis of these emissions, it is found that the He+ band EMIC waves are linearly polarized and propagating quasi‐parallelly along the background magnetic field, while the O+ band ones are of linear and left‐hand polarization and propagating obliquely with respect to the background magnetic field. Using the in situ observations of plasma environment and particle data, excitation of these O+ band EMIC waves has been investigated with the linear growth theory. The calculated linear growth rate shows that these O+ band EMIC waves can be locally excited by ring current protons with ring velocity distributions. The comparison of the observed wave spectral intensity and the calculated growth rate suggests that the density of H+ rings providing the free energy for the instability has decreased after the wave grows. Therefore, this paper provides a direct observational evidence to the excitation mechanism of O+ band EMIC waves: ring current protons with ring distributions provide the free energy supporting the instability in the presence of rich O+ in the plasmasphere.