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Nonlinear full-wave analysis of atmospheric luminous emissions above lightning discharges

闪电放电上方大气光发射的非线性全波分析

基本信息

批准号：
13640447
负责人：
NAGANO Isamu
金额：
$ 2.05万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640447/
关键词：
Lightning discharge Electromagnetic pulse Ionosphere Optical emission Elves Electron heating Full wave analysis Parallel computation 雷放雷雷磁波パルス雷離層 full wave計算法衝突周波数

项目摘要

We have investigated the generation mechanism of "elves," the expanding optical rings created 85-95 km above lightning flashes. Elves are believed to be generated through the excitation of the first positive band of nitrogen molecule, which is stimulated by the electron heating due to the lightning-generated intense electromagnetic pulses (EMPs) illuminating the lower ionosphere. By using a full-wave analysis, we have computed rigorously the propagation in a magnetized ionosphere of the EMPs radiated by lightning current strokes. When incident into the lower ionosphere, an intense EMP heats the electrons and then enhances the collision frequency there, causing the absorption of the EMP energy. Though the full wave analysis cannot treat such a nonlinear temporal change of ionospheric parameters, we have approximately incorporated this effect into the calculation by modifying the up-going EMP in the ionosphere. Making use of a newly developed parallel-computation system with 10 PCs, we have computed the temporal and spatial evolution of elves. Computed results have shown that an optical ring is created at the altitudes of 85-100 km above the lightning, quickly expanding horizontally over 200 km within < 1 ms, which is consistent with the actual observations of elves. It has also been found that because of the EMP propagation in the whistler mode along the Earth's magnetic field line above 90 km, there appears appreciable north-south and east-west asymmetry in the elves ring structures.

我们已经研究了“精灵”的产生机制，即在闪电上方85-95公里处产生的膨胀光环。精灵被认为是通过激发氮分子的第一个正带而产生的，这是由于闪电产生的强电磁脉冲（EMP）照射低电离层而产生的电子加热所激发的。利用全波分析方法，对雷电流辐射电磁脉冲在磁化电离层中的传播进行了严格的计算。当入射到低电离层时，强烈的EMP加热电子，然后提高那里的碰撞频率，导致EMP能量的吸收。虽然全波分析不能处理这样的非线性时间变化的电离层参数，我们近似地将这种影响纳入计算通过修改上行电磁脉冲在电离层。利用新开发的10台PC并行计算系统，我们计算了精灵的时空演化。计算结果表明，在闪电上方85-100 km处产生一个光环，并在1 ms内迅速水平扩展到200 km以上，这与精灵的实际观测结果相一致。研究还发现，由于电磁脉冲沿地球磁场线沿着以哨声模式传播，在90 km以上的精灵环结构中出现了明显的南北和东西不对称性。