Electromagnetic ion cyclotron waves in the helium branch induced by multiple electromagnetic ion cyclotron triggered emissions
Electromagnetic ion cyclotron waves in the helium branch induced by multiple electromagnetic ion cyclotron triggered emissions
复制标题
多个电磁离子回旋加速器触发发射引起的氦分支中的电磁离子回旋波
DOI：
10.1029/2011gl048427
复制
发表时间：
2011
影响因子：
5.2
通讯作者：
M.Engebretson
中科院分区：
文献类型：
--
作者：
Shoji M.;Y.Omura;B.Grison;J.Pickett;I.Dandouras;M.Engebretson
在最近的星团观测中，发现了内磁层中H+和He+回旋频率之间的电磁离子回旋（EMIC）触发发射。在多次EMIC触发发射之后，偶尔在He+回旋频率以下观察到另一种类型的具有恒定频率的EMIC波。我们用一个一维圆柱形磁通量模型进行了自洽混合模拟，该模型近似于地球内部磁层的偶极磁场。在存在具有足够密度和温度各向异性的高能质子的情况下，由于升调合唱发射的非线性波生长机制，再现了多个EMIC触发发射，并且随后产生了He+EMIC分支中的恒定频率波。通过与多个EMIC上升音发射的相互作用，高能质子的速度分布函数被强烈修改。由于质子的俯仰角散射，使得He+分支波的扩散曲线上速度相空间分布的梯度沿着增大，从而导致He+分支中EMIC波的线性增长。
Electromagnetic ion cyclotron (EMIC) triggered emissions with rising tones between the H+and He+cyclotron frequencies were found in the inner magnetosphere by the recent Cluster observations. Another type of EMIC wave with a constant frequency is occasionally observed below the He+cyclotron frequency after the multiple EMIC triggered emissions. We performed a self‐consistent hybrid simulation with a one‐dimensional cylindrical magnetic flux model approximating the dipole magnetic field of the Earth's inner magnetosphere. In the presence of energetic protons with a sufficient density and temperature anisotropy, multiple EMIC triggered emissions are reproduced due to the nonlinear wave growth mechanism of rising‐tone chorus emissions, and a constant frequency wave in the He+EMIC branch is subsequently generated. Through interaction with the multiple EMIC rising‐tone emissions, the velocity distribution function of the energetic protons is strongly modified. Because of the pitch angle scattering of the protons, the gradient of the distribution in velocity phase space is enhanced along the diffusion curve of the He+branch wave, resulting in the linear growth of the EMIC wave in the He+branch.