The spectrum of electron density fluctuations in the solar wind and its variations with solar wind speed
The spectrum of electron density fluctuations in the solar wind and its variations with solar wind speed
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太阳风中电子密度涨落谱及其随太阳风速的变化
DOI：
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发表时间：
1994
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通讯作者：
H. Misawa
中科院分区：
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作者：
P. K. Manoharan;M. Kojima;H. Misawa
我们描述了在当前太阳周期 22 的前半段使用乌蒂射电望远镜和日地环境实验室三天线系统对太阳距离范围 70-185 R⊙ 进行的同步行星际闪烁 (IPS) 测量。这些测量已用于建立太阳风中电子密度波动的光谱特征，并且我们研究了这些测量与等离子体流速度的关系。在低活动时，对于高速流（Vsw ≈ 600 km s−1），频谱（对 IPS 时间频率范围 1-10 Hz 敏感）很陡，幂律指数 α ≈ 3.8。在高速流的高强度活动期间，频谱不太陡峭，α ≈ 3.4。在低速风（Vsw ≈ 400 km s−1）中，光谱明显更平坦，α ≈ 2.9，并且几乎不随太阳活动而变化。从这项研究中获得的光谱的平均形状与通过其他技术获得的结果一致。通过将当前的估计与早期的航天器数据相结合，可以考虑频率范围 10−5-101 Hz 内的密度涨落谱的形状。结果表明，光谱在不同的光谱域中具有不同的斜率，并且可以通过 Coles 和 Harmon [1989] 提出的三分量模型很好地描述。此外，低速和高速流中频谱的高频分量涉及不同的空间频率范围。
We describe simultaneous interplanetary scintillation (IPS) measurements for the solar distance range 70-185 R⊙ made using the Ooty Radio Telescope and the Solar Terrestrial Environment Laboratory three-antenna system during the first half of the current solar cycle 22. These measurements have been used to establish the spectral characteristics of the electron density fluctuations in the solar wind, and we study the relation of these to the plasma flow speed. At times of low activity, for high-speed streams (Vsw ≈ 600 km s−1) the spectra (sensitive to the IPS temporal frequency range 1-10 Hz) are steep, with a power law exponent α ≈ 3.8. During high levels of activity for high-speed streams, the spectra are less steep with α ≈ 3.4. In the low-speed wind (Vsw ≈ 400 km s−1) the spectra are clearly flatter, α ≈ 2.9, and nearly invariant with solar activity. The average shape of the spectrum obtained from this study is consistent with results obtained via other techniques. By combining the present estimates with earlier spacecraft data, it is possible to consider the shape of the density fluctuation spectrum in the frequency range 10−5-10¹ Hz. It is shown that the spectrum has different slopes in different spectral domains and is well described by a three-component model as proposed by Coles and Harmon [1989]. Moreover, the high-frequency components of the spectra in the low- and high-speed streams involve different spatial frequency ranges.