Theory and simulations of broadband electrostatic noise in the geomagnetic tail
Theory and simulations of broadband electrostatic noise in the geomagnetic tail
复制标题
地磁尾宽带静电噪声的理论与模拟
DOI：
10.1029/ja091ia06p06833
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发表时间：
1986
期刊：
影响因子：
--
通讯作者：
H. Okuda
中科院分区：
文献类型：
--
作者：
M. Ashour‐Abdalla;H. Okuda
通过线性理论分析和粒子模拟研究，进一步了解宽频带静电噪声的产生机理和BEN对地磁尾区粒子的影响。等离子体片粒子居群是用逆流离子束以及热离子和电子来模拟的。当束流温度Tb远小于热等离子体片电子Te时，束流-离子声学和离子-离子两流不稳定性都会增加。离子声不稳定性的频率为ω =±(k(nb/ne)1/2 cs−k∥U)≃±k∥U≤ωpe，其中cs = (Te/mi)1/2为离子声速，U为离子束相对于热等离子体片电子的速度。当束流离子温度与热等离子体片粒子的温度相当时，静电离子回旋加速器的不稳定性变得不稳定，在ω > nΩi处产生低频噪声，其中Ωi为离子回旋频率。仿真结果证实了宽带静电噪声的存在，其范围从ω = 0延伸到ω = k·U > ωpe，振幅为E ~ mV/m，与卫星数据吻合较好。观测到的波强度在垂直传播附近也达到峰值，这与空间观测结果也一致。
Linear theory analysis and particle simulation studies were carried out in an attempt to further our understanding of the mechanisms generating broadband electrostatic noise and the effects of BEN on particles in the geomagnetic tail region. The plasma sheet particle population was modeled by counter-streaming ion beams as well as by warm ions and electrons. When the beam temperature, Tb, is much smaller than that of the warm plasma sheet electrons, Te, both beam-ion acoustics and ion-ion two-stream instabilities grow. The frequency of the ion acoustic instability is given by ω = ±(k(nb/ne)1/2 cs − k∥U) ≃ ± k∥U ≤ ωpe where cs = (Te/mi)1/2 is the ion sound speed and U is the ion beam speed relative to the warm plasma sheet electrons. When the beam ion temperature is comparable to the temperature of the warm plasma sheet particles, electrostatic ion cyclotron instabilities become unstable, giving rise to low frequency noise at ω ≲ nΩi where Ωi is the ion gyrofrequency. The simulation results confirm the presence of broadband electrostatic noise extending from ω = 0 to ω = k · U ≲ ωpe, with an amplitude of E ∼ mV/m, which is in good agreement with the satellite data. The observed wave intensity also peaks near perpendicular propagation, which is also in agreement with space observations.