Direction finding of ELF hiss emissions in a detached plasma region of the magnetosphere
Direction finding of ELF hiss emissions in a detached plasma region of the magnetosphere
复制标题
磁层分离等离子体区域中 ELF 嘶嘶声发射的方向查找
DOI：
10.1029/ja091ia01p00135
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发表时间：
1986
影响因子：
--
通讯作者：
F. Lefeuvre
中科院分区：
文献类型：
--
作者：
M. Hayakawa;N. Ohmi;M. Parrot;F. Lefeuvre
利用位于赤道平面L = 6.6的地球同步卫星GEOS 2的数据，确定了磁层分离等离子体区极低频辐射的波法向和波分布函数。采用了三种不同的测向方法：(1)基于单一平面波假设的Means法，(2)假设少量平面波的最大似然法，(3)确定波分布函数的最大熵法。这些方法的结果相互比较表明，它们提供了非常可靠和明确的波法线信息。通过对两个赤道极低频嘶嘶事件的分析，发现其波的分布函数由一个单峰组成（即波具有单一的传播方向），并且起源于分离等离子体区域的极低频嘶嘶的波法线与地球磁场的夹角很小；此外，我们还能够对发射的不稳定锥的角宽度进行实验估计。假设这些波是由中能量电子（3 - 30kev）产生的电子回旋不稳定引起的，我们在赤道平面的初始测向结果和先前在较高地磁纬度的相应结果与理论预测进行了比较。所有的特征（形貌和测向结果）都与电子回旋加速器的不稳定性相一致。
Wave normal directions and wave distribution functions of ELF hiss emissions in a detached plasma region of the magnetosphere have been determined, using data from the geostationary satellite GEOS 2 located in the equatorial plane at L = 6.6. Three different methods of direction finding have been utilized: (1) Means's method based on the hypothesis of a single plane wave, (2) the maximum likelihood method, assuming a few plane waves, and (3) the maximum entropy method of determining the wave distribution function. An intercomparison of the results from those methods has proven that they provide very reliable and definite information on the wave normals. From analyses of two equatorial ELF hiss events it is found that the wave distribution function is composed of a single peak (i.e., the waves have a single propagation direction) and that the wave normals of the ELF hiss originating in the detached plasma region make very small angles with the Earth's magnetic field; also, we wore able to make an experimental estimate of the angular width of the unstable cone of the emissions. Both our initial direction finding results in the equatorial plane and the corresponding previous results at higher geomagnetic latitudes are compared with theoretical predictions, assuming that the waves are generated by the electron cyclotron instability due to medium-energy (3–30 keV) electrons. It is concluded that all of the characteristics (morphology and direction-finding results) are consistent with the electron cyclotron instability.