Two‐dimensional hybrid code simulation of electromagnetic ion cyclotron waves of multi‐ion plasmas in a dipole magnetic field
Two‐dimensional hybrid code simulation of electromagnetic ion cyclotron waves of multi‐ion plasmas in a dipole magnetic field
复制标题
DOI：
10.1029/2009ja015158
复制
发表时间：
2010-09
影响因子：
--
通讯作者：
Y. Hu;R. Denton;J. Johnson
中科院分区：
文献类型：
--
作者：
Y. Hu;R. Denton;J. Johnson
用二维杂化码（粒子离子和流体电子）模拟了偶极磁场中H+-He+-O+等离子体中的位波。这些波是由具有各向异性温度的高能环电流质子驱动的。等离子体的初始状态由各向异性MHD编码导出，使得系统处于MHD平衡状态，J × B−∇·P = 0。假设冷物质（温度为~ eV）是各向同性的，并且具有空间均匀的密度分布。我们选择的参数使得在磁赤道附近产生频率< ω的主位波。每个重离子的存在引入了一个新的色散面。当波在赤道附近生长时，它们以左偏振光为主，具有较小的波法向角。在向高纬度传播的过程中，波变成线性或右手极化，法线角度更大，它们遇到O+回旋加速器频率的二次谐波，He+-O+双离子频率，可能还有O+回旋加速器频率的一次谐波。在这个过程中，一些波被波粒相互作用吸收，一些波被He+-O+双离子频率反射，一些波在同一色散表面上传输，还有一些波可能穿过所谓的停止带。这些影响的相对重要性随离子组成，特别是O+浓度的不同而不同。例如，当≪0.5%时，基本上所有的波能都通过共振到达电离层边界。当ηO+ = 0.5%时（对这种情况进行了最详细的研究），高纬度地区的时间平均坡印廷矢量几乎总是朝极地方向，尽管在He+-O+双离子共振中可以看到一些反射的明显证据。
[1] A two-dimensional hybrid code (particle ions and fluid electrons) is used to simulate EMIC waves in a H+-He+-O+ plasma in a dipole magnetic field. The waves are driven by energetic ring current protons with anisotropic temperature ( >1). The initial state of the plasma is derived from an anisotropic MHD code so that the system is in MHD equilibrium, J × B−∇·P = 0. The cold species (with temperature of ∼eV) are assumed to be isotropic and have a spatially uniform density distribution. We choose our parameters so that the EMIC waves are generated near the magnetic equator with frequencies < ω < The presence of each heavy-ion species introduces a new dispersion surface. When the waves grow near the equator, they are dominantly left-handed polarized and have small wave normal angle. While propagating toward high latitudes, the waves become linearly or right-handed polarized with a larger normal angle, and they encounter the second harmonic of the O+ cyclotron frequency, the He+-O+ bi-ion frequency, and possibly the first harmonic of the O+ cyclotron frequency. In this process, some waves are absorbed by the wave-particle interaction, some waves are reflected by the He+-O+ bi-ion frequency, some are transmitted on the same dispersion surface, and some may tunnel through the so-called stop band. The relative importance of these effects varies with the ion composition and especially with the concentration of O+, = For instance, for ≪0.5%, essentially all the wave energy passes through the resonances to reach the ionospheric boundary. For ηO+ = 0.5% (the case examined in most detail), the time-averaged Poynting vector at high latitudes is almost always in the poleward direction, even though clear evidence of some reflection at the He+-O+ bi-ion resonance is seen.