Transmission of a Magnetospheric Pc1 Wave Beam Through the Ionosphere to the Ground
Transmission of a Magnetospheric Pc1 Wave Beam Through the Ionosphere to the Ground
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DOI：
10.1029/2018ja025338
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发表时间：
2018-05
期刊：
影响因子：
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通讯作者：
E. Fedorov;V. Pilipenko;M. Engebretson;M. Hartinger
中科院分区：
文献类型：
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作者：
E. Fedorov;V. Pilipenko;M. Engebretson;M. Hartinger
上电离层的一个特征是电离层阿尔文谐振器（IAR）和电离层快模波导（IFW）的出现，它们可以捕获从几赫兹到几赫兹的 Pc1 频率范围内的电磁波能量。这种波捕获确保了电离层传输/反射特性对频率的依赖性。我们基于现实电离层中磁流体动力学全波方程的解，对通过电离层到地面的磁层阿尔文波传输进行数值模拟，其参数是根据国际参考电离层模型重建的。入射波的空间结构被建模为具有有限纬度尺度 λ⊥ 和方位传播波的局域光束。 IAR 和 IFW 模式由于霍尔电导率和地磁场倾角而耦合。南极哈雷天文台已针对夏季白天/夜间条件计算了 Pc1 波（0.1 至 6 Hz 频段）的地面空间和光谱结构，但结果可以定性地应用于任何中纬度地点。考虑了方位角波矢ky=1.7·10−3 km−1、λ⊥=102 km的入射波。该模型预测，在考虑了 π/2 旋转和一些纬度偏移/加宽后，在入射光束下方，地面磁响应“复制”其结构。传输对频率具有振荡依赖性，从而在 IAR 和 IFW 模式的谐振频率处形成“传输窗口”。光谱根据距入射点的距离而变化。 IFW 模式之间的干扰通过波幅纬度变化的非单调和频率相关特征来揭示。
A characteristic feature of the upper ionosphere is the occurrence of the ionospheric Alfvén resonator (IAR) and the ionospheric fast‐mode waveguide (IFW), which can trap electromagnetic wave energy in the Pc1 frequency range from fractions of a hertz to a few hertz. This wave trapping ensures the dependence of ionospheric transmission/reflective properties on frequency. We numerically model magnetospheric Alfvén wave transmission through the ionosphere to the ground based on solution of the magnetohydrodynamic full‐wave equations in a realistic ionosphere, whose parameters are reconstructed from the International Reference Ionosphere model. The spatial structure of an incident wave is modeled as a localized beam with a finite latitudinal scale λ⊥ and an azimuthally propagating wave. The IAR and IFW modes are coupled owing to the Hall conductivity and geomagnetic field inclination. Ground spatial and spectral structures of the Pc1 wave (0.1‐ to 6‐Hz band) have been calculated for summer day/night conditions at the Antarctic Halley observatory, though results may be qualitatively applied to any midlatitude site. An incident wave with azimuthal wave vector ky=1.7·10−3 km−1, and λ⊥=102 km has been considered. The model predicts that beneath the incident beam the ground magnetic response “duplicates” its structure after accounting for a π/2 rotation and some latitudinal shift/widening. The transmission has an oscillatory dependence on frequency, thus forming “transmission windows” at resonant frequencies of IAR and IFW modes. The spectra vary depending on distance from an incidence point. Interference between IFW modes is revealed in the nonmonotonic and frequency‐dependent character of latitudinal variations of wave amplitude.