Observations of nonthermal plasmas at different aspect angles
Observations of nonthermal plasmas at different aspect angles
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不同方位角的非热等离子体观测
DOI：
10.1029/ja094ia02p01439
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发表时间：
1989
影响因子：
--
通讯作者：
K. Suvanto
中科院分区：
文献类型：
--
作者：
K. Winser;M. Lockwood;G. Jones;K. Suvanto
欧洲非相干散射设备（EISCAT） CP-3-E实验数据显示，在广泛的纬度范围内，极光区对流速度（bbb20 km s - 1）大幅增加。这些比估计的中性热速度要大，并且允许在一个观测角度范围内研究非热状态下的等离子体。光谱显示了一个明确的中心峰，与明显偏离麦克斯韦形式的离子速度分布函数相一致。随着纵横角的减小，中心峰变得不那么明显。利用基于广义弛豫碰撞模型的O+离子速度分布函数的理论表达式导出的模拟光谱与观测结果进行了比较，结果显示出良好的一阶定性一致性。结果表明，在麦克斯韦分布函数的假设下，由观测得到的离子温度在大向角时高估了真实离子温度，在小向角时低估了真实离子温度。理论分布函数已包含在“标准”非相干散射雷达分析程序中，并尝试从非热等离子体观测中推导出真实的电离层参数。如果将分布函数的表达式扩展到包括混合离子组成，则在拟合某些观测光谱时发现了显着的改进，并且可以对离子组成进行估计。对数据的非麦克斯韦分析显示，在这种情况下，分子离子的光谱形状畸变参数D*明显高于大约40公里厚的薄高度板上的原子离子。如果存在的主要分子离子是NO+，这似乎不太可能。因此，我们认为N2+在这些观察中形成了相当大比例的分子离子。
Data are presented from the EISCAT (European Incoherent Scatter (Facility)) CP-3-E experiment which show large increases in the auroral zone convection velocities (>2 km s−1) over a wide range of latitudes. These are larger than the estimated neutral thermal speed and allow a study of the plasma in a nonthermal state over a range of observing angles. Spectra are presented which show a well-defined central peak, consistent with an ion velocity distribution function which significantly departs from a Maxwellian form. As the aspect angle decreases, the central peak becomes less obvious. Simulated spectra, derived using theoretical expressions for the O+ ion velocity distribution function based on the generalized relaxation collision model, are compared with the observations and show good first-order, qualitative agreement. It is shown that ion temperatures derived from the observations, with the assumption of a Maxwellian distribution function, are an overestimate of the true ion temperature at large aspect angles and an underestimate at low aspect angles. The theoretical distribution functions have been included in the “standard” incoherent scatter radar analysis procedure, and attempts have been made to derive realistic ionospheric parameters from nonthermal plasma observations. If the expressions for the distribution function are extended to include mixed ion composition, a significant improvement is found in fitting some of the observed spectra, and estimates of the ion composition can be made. The non-Maxwellian analysis of the data revealed that the spectral shape distortion parameter, D*, was significantly higher in this case for molecular ions than for atomic ions in a thin height slab roughly 40 km thick. This would seem unlikely if the main molecular ions present were NO+. We therefore suggest that N2+ formed a significant proportion of the molecular ions present during these observations.