The effects of long upward connecting leader (UCL) channel on electromagnetic fields for lightning striking to tall towers are studied via lightning transmission-line return-stroke model. The current distributions along the lightning channel and the tower are derived, and the resultant lightning electromagnetic fields with various UCL lengths above tower are calculated at close and far distances. It can be found that the contribution of the various components of the electric and magnetic fields depends strongly on the distance to the observation point. Electric field has a shading effect showing that the field amplitude generated by lightning striking to tall towers is smaller than that to ground, and that this shading effect depends on the UCL length and the tower height. However, we cannot find such an effect for the magnetic field. The shading effect of the electric field increases with the increase of the junction height above tower, but disappears when the observation distance exceeds a critical distance. Modeled results are also compared with their measured counterparts associated with lightning striking to the 600 m tall Canton Tower. The proposed model can explain why the ratios of peaks of luminosity to magnetic field of the downward first stroke are considerably larger than those of the subsequent strokes as being due to the fact that the junction height above tower for first stroke is higher than that for subsequent stroke, whereas the downward return stroke speed of first stroke is smaller than that of subsequent stroke.

中文翻译：

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长向上连接先导通道对高塔雷击电磁场的影响

通过雷击传输线回击模型研究了长上行连接先导通道对高塔雷击电磁场的影响。推导出沿雷电通道和塔的电流分布，并计算塔上不同 UCL 长度的近距离和远距离的合成闪电电磁场。可以发现，电场和磁场的各个分量的贡献很大程度上取决于到观察点的距离。电场具有遮蔽效应，表明雷电击中高塔产生的场幅小于对地，这种遮蔽效应取决于UCL长度和塔高。但是，我们找不到磁场的这种效应。电场的遮蔽效应随着塔上结高度的增加而增加，但在观测距离超过临界距离时消失。还将模拟结果与与闪电击中 600 米高的广州塔相关的测量结果进行比较。所提出的模型可以解释为什么向下的第一次冲程的光度与磁场的峰值比显着大于后续冲程的比值，因为第一冲程塔上方的连接高度高于后续冲程。冲程，而第一个冲程的向下回程速度小于后续冲程的向下回程速度。但当观察距离超过临界距离时消失。还将模拟结果与与闪电击中 600 米高的广州塔相关的测量结果进行比较。所提出的模型可以解释为什么向下的第一次冲程的光度与磁场的峰值比显着大于后续冲程的比值，因为第一冲程塔上方的连接高度高于后续冲程。冲程，而第一个冲程的向下回程速度小于后续冲程的向下回程速度。但当观察距离超过临界距离时消失。还将模拟结果与与闪电击中 600 米高的广州塔相关的测量结果进行比较。所提出的模型可以解释为什么向下的第一次冲程的光度与磁场的峰值比显着大于后续冲程的比值，因为第一冲程塔上方的连接高度高于后续冲程。冲程，而第一个冲程的向下回程速度小于后续冲程的向下回程速度。