Linear and nonlinear properties of ULF waves driven by ring‐beam distribution functions
Linear and nonlinear properties of ULF waves driven by ring‐beam distribution functions
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环束分布函数驱动的 ULF 波的线性和非线性特性
DOI：
10.1029/94ja02899
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发表时间：
1995
影响因子：
--
通讯作者：
H. Karimabadi
中科院分区：
文献类型：
--
作者：
K. Killen;N. Omidi;D. Krauss;H. Karimabadi
考虑了斜传播的可变陡磁声波（也称为激波）的激发问题。在地球弓形激波的上游，以及在贾柯比尼-津纳彗星和格里格-斯凯勒鲁普彗星上，已经观测到了激波。线性理论以及二维（2-D）混合（流体电子，粒子离子）模拟被用来非常详细地确定由环束速度分布产生的波的性质。同时考虑了质子环束和氧环束的影响。质子环束激发的不稳定性研究与地球弓形激波上游区域有关，而氧环束对应于太阳风吸收的彗星离子。线性理论表明，对于环束，存在四个不稳定性，一个在非共振模式上，一个在阿尔芬模式上，两个在磁子/哨子分支上。这些不稳定性的相对增长率是参数的敏感函数。其中一种磁声子不稳定性沿磁场方向增长最大，而另一种磁声子不稳定性沿磁场方向增长最大。作者利用二维模拟研究了这些不稳定性在非线性状态下的竞争。在线性极限下，非线性结果是梁密度和分布函数的函数。通过作为初始值和驱动系统进行模拟，作者发现模拟的结果可能会有所不同，这表明需要后一种类型的模拟来处理观测结果。模拟结果的一般结论是场对准光束不会导致激波的形成，而环束分布则会。参47。， 19个无花果。«少
The problem of the excitation of obliquely propagating magnetosonic waves which can steepen up (also known a shocklets) is considered. Shocklets have been observed upstream of the Earth`s bow shock and at comets Giacobini-Zinner and Grigg-Skjellerup. Linear theory as well as two-dimensional (2-D) hybrid (fluid electrons, particle ions) simulations are used to determine the properties of waves generated by ring-beam velocity distributions in great detail. The effects of both proton and oxygen ring-beams are considered. The study of instabilities excited by a proton ring-beam is relevant to the region upstream of the Earth`s bow shock, whereas the oxygen ring-beam corresponds to cometary ions picked up by the solar wind. Linear theory has shown that for a ring-beam, four instabilities are found, one on the nonresonant mode, one on the Alfven mode, and two along the magnetosonic/whistler branch. The relative growth rate of these instabilities is a sensitive function of parameters. Although one of the magnetosonic instabilities has maximum growth along the magnetic field, the other has maximum growth in oblique directions. The authors have studied the competition of these instabilities in the nonlinear regime using 2-D simulations. As in the linear limit, the nonlinear results are a function of beammore » density and distribution function. By performing the simulations as both initial value and driven systems, the authors have found that the outcome of the simulations can vary, suggesting that the latter type of simulation is needed to address the observations. A general conclusion of the simulation results is that field-aligned beams do not result in the formation of shocklets, whereas ring-beam distributions can. 47 refs., 19 figs.« less