An experimental test of the 'transmission-line model' of electromagnetic radiation from triggered lightning return strokes
An experimental test of the 'transmission-line model' of electromagnetic radiation from triggered lightning return strokes
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DOI：
10.1029/jd093id04p03867
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发表时间：
1988-04
影响因子：
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通讯作者：
J. Willett;V. P. Idone;R. Orville;C. Leteinturier;A. Eybert-Berard;L. Barret;E. Krider
中科院分区：
文献类型：
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作者：
J. Willett;V. P. Idone;R. Orville;C. Leteinturier;A. Eybert-Berard;L. Barret;E. Krider
回击辐射的“传输线”模型是由Uman和McLain(1970)提出的，此后经常被用来从远场推导峰值电流或从测量场和电流估计传播速度，但从未接受过彻底的实验测试。1985年夏天，在佛罗里达州的肯尼迪航天中心，我们能够测量火箭引发的闪电中随后几次回击的峰值电流(具有同轴分流)、二维平均传播速度(使用高速扫描相机)和电场波形(5.15公里范围)。由于条纹相机胶片上的时间模糊性，不可能识别具有特定行程的单个速度测量，对于这些特定行程，电流和场数据是可用的。然而，三次多冲程闪光，每一次都产生了一组紧密的速度测量结果和一组峰值磁场与峰值电流的比率，尽管不一定是针对相同的冲程。另外六次闪光提供了更多没有获得速度信息的电流和磁场测量，而速度测量仅适用于其他闪光。这些数据表明，用条纹相机测得的传播速度与传输线模型所得的传播速度符合得很好。之前观察到的电流场和辐射场波形之间的差异表明，对该模型进行了修改，包括两个波前从离地面较短距离的交界点向上和向下传播，这大大改善了测量和推断的传播速度之间的一致性。
The “transmission-line” model of return-stroke radiation, proposed by Uman and McLain (1970) and invoked frequently thereafter to deduce peak currents from remote fields or to estimate propagation velocities from measured fields and currents, has never received a thorough experimental test. During the summer of 1985 at the Kennedy Space Center in Florida, we were able to measure peak currents (with a coaxial shunt), two-dimensional average propagation speeds (with a high-speed streak camera), and electric field waveforms (at 5.15-km range) for a number of subsequent return strokes in rocket-triggered lightning flashes. Because of the temporal ambiguity on the streak-camera films, it has not been possible to identify individual velocity measurements with particular strokes for which current and field data are available. Three multistroke flashes, however, each yielded a tight cluster of velocity measurements and a group of peak field to peak current ratios, though not necessarily for the same strokes. A further six flashes provided more current and field measurements for which no velocity information was obtained, and velocity measurements only are available for still other flashes. It is shown that these data indicate reasonable agreement between the propagation speeds measured with the streak camera and those deduced from the transmission-line model. The previously observed difference between current and radiation-field waveforms suggests a modification of the model, involving two wave fronts traveling upward and downward away from a junction point a short distance above the ground, which substantially improves the agreement between measured and inferred propagation speeds.