电离层舒曼共振的空间观测

通过功率谱分析和波阻抗函数计算，本文证实了Aureol 3卫星在电离层高度上(>600km)观测到的极低频(ELF)波场扰动是和舒曼共振相关的电磁振荡.与舒曼共振地面观测相比较，Aureol 3观测到的舒曼共振电场分量具有很好的谐振谱结构，峰值频率和各阶舒曼共振本征频率对应；磁场分量的高阶峰值频率偏离14, 20, 26Hz等舒曼共振本征频率；随着卫星高度的改变，电场与磁场谐振的一阶最大能量峰值并不会发生在同一频率，结合本文分析的数据，分别位于78Hz和10Hz；水平方向的磁场分量更接近南北方向的线极化而不是地球－电离层空腔中的椭圆极化；波阻抗随频率表现出不太规则的准正弦振荡，它会随着频率增加和飞行高度上升呈现减小的趋势.虽然舒曼共振信号和电离层密度梯度间的非线性作用可以解释舒曼共振空间观测的部分特征，但需加入其他机制，如电离层不稳定性，传播模式的耦合，进一步了解电离层高度上舒曼共振各种特征产生的原因.

Spatial observations of Schumann resonance at the ionospheric altitudes

Based on power spectra analysis as well as impedance function calculation, we confirm that the AUREOL-3 satellite in-situ measurements of ELF/VLF electric and magnetic field fluctuations are the results of the fractional transmission into the ionosphere of Schumann resonances from the Earth-ionosphere cavity. Compared with ground-based Schumann resonance observations, the Aureol-3 observed Schumann resonances exhibit some particular features. The horizontal electric component presents distinct resonance spectral structures and peak at eigen-frequencies of Schumann resonances while the three magnetic components usually peak at frequencies departing from the eigen-frequencies. The first-order power maxima of electric and magnetic components also appear at different frequencies, 7.8Hz for the former and 10.0Hz for the latter. The dominant magnetic field components of Schumann resonance in the ionosphere result in a quasi-linear magnetic polarization in horizontal direction other than the elliptical one in the Earth-ionosphere cavity. The experimental wave impedance forms a somewhat indistinct sinusoid with frequency, decreasing with increasing frequency and growing altitude, consistent with theoretical calculation. Although nonlinear interactions between Schumann resonances and ionospheric density fluctuations has been proposed to interpret the characteristics of Schumann resonance observed by the Aureol-3 satellite, some other mechanisms, such as instabilities in the ionosphere, wave coupling between different modes, should be included to better understand the spatial observations of Schumann resonance at the ionospheric altitudes.