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

• 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

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.

我们研究了“精灵”的产生机制，即在闪电上方 85-95 公里处产生的不断扩大的光学环。精灵被认为是通过氮分子第一正带的激发而产生的，该氮分子是由闪电产生的强电磁脉冲（EMP）照射较低电离层而产生的电子加热所刺激的。通过使用全波分析，我们严格计算了雷电电流冲击辐射的电磁脉冲在磁化电离层中的传播。当入射到较低的电离层时，强烈的电磁脉冲会加热电子，然后提高那里的碰撞频率，导致电磁脉冲能量的吸收。虽然全波分析无法处理电离层参数的这种非线性时间变化，但我们通过修改电离层中的上行电磁脉冲，大致将这种效应纳入计算中。利用新开发的10台PC并行计算系统，我们计算了精灵的时间和空间演化。计算结果表明，在闪电上方85-100公里的高度处形成了一个光学环，并在<1毫秒内迅速水平扩展超过200公里，这与精灵的实际观察结果一致。研究还发现，由于电磁脉冲沿90公里以上地球磁场线以哨声模式传播，精灵环结构出现明显的南北向和东西向不对称性。