An improved ray theory and transfer matrix method‐based model for lightning electromagnetic pulses propagating in Earth‐ionosphere waveguide and its applications
An improved ray theory and transfer matrix method‐based model for lightning electromagnetic pulses propagating in Earth‐ionosphere waveguide and its applications
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DOI：
10.1002/2016jd025599
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发表时间：
2017-01
期刊：
影响因子：
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通讯作者：
Zilong Qin;Ming-li Chen;Baoyou Zhu;Ya-ping Du
中科院分区：
文献类型：
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作者：
Zilong Qin;Ming-li Chen;Baoyou Zhu;Ya-ping Du
提出了一种基于改进射线理论和传输矩阵法的雷电电磁脉冲（LEMP）在地电离层波导（EIWG）中传播的模型，并对模型进行了验证。该模型涉及到一个闪电源的介绍，低电离层的参数化，推导出一个传递函数的所有影响的EIWG的LEMP天波，和LEMP地波的衰减模式的确定。将雷电源简化为一个有限电导的点偶极子。基于射线理论和传递矩阵法，推导了天波的传递函数。地波的衰减模式由福克绕射方程求解。然后将该模型应用于中国中部地区1000 km范围内的几个闪电天线观测。结果表明，该模型能较好地预报所有观测到的闪电天波。模拟和观测结果都表明，夜间的闪电天线波形比白天复杂。特别是当LEMP从东向西传播时（Φ = 270°），在夜间，其天波往往是双峰波形（分散天波），而不是单峰波形。夜间这种分散的天波可能归因于低电离层中的磁离子分裂现象。该模型为我们反演低电离层电子密度剖面，从而利用闪电天电监测其时空变化提供了一种有效的途径。
An improved ray theory and transfer matrix method‐based model for a lightning electromagnetic pulse (LEMP) propagating in Earth‐ionosphere waveguide (EIWG) is proposed and tested. The model involves the presentation of a lightning source, parameterization of the lower ionosphere, derivation of a transfer function representing all effects of EIWG on LEMP sky wave, and determination of attenuation mode of the LEMP ground wave. The lightning source is simplified as an electric point dipole standing on Earth surface with finite conductance. The transfer function for the sky wave is derived based on ray theory and transfer matrix method. The attenuation mode for the ground wave is solved from Fock's diffraction equations. The model is then applied to several lightning sferics observed in central China during day and night times within 1000 km. The results show that the model can precisely predict the time domain sky wave for all these observed lightning sferics. Both simulations and observations show that the lightning sferics in nighttime has a more complicated waveform than in daytime. Particularly, when a LEMP propagates from east to west (Φ = 270°) and in nighttime, its sky wave tends to be a double‐peak waveform (dispersed sky wave) rather than a single peak one. Such a dispersed sky wave in nighttime may be attributed to the magneto‐ionic splitting phenomenon in the lower ionosphere. The model provides us an efficient way for retrieving the electron density profile of the lower ionosphere and hence to monitor its spatial and temporal variations via lightning sferics.