光谱法研究闪电回击放电通道的电阻及电流的热效应

闪电放电通道的电阻及电流产生的热效应对雷电灾害研究以及防护设计都具有重要意义，放电通道的热力学特性与其等离子体辐射光谱密切相关。利用无狭缝摄谱仪获得的两次云对地多回击闪电放电的等离子体辐射光谱，依据谱线波长、强度等信息，结合同步地面电场变化资料，应用空气等离子体传输理论，计算了闪电回击放电通道的电导率、峰值电流、核心通道半径，进而得到了闪电回击等离子体通道单位长度的电阻、峰值电流时的热功率及在回击初始前5 μs内通道储存的热能。并与常规金属导体进行比较，分析了闪电回击放电在峰值电流时等离子体通道的热功率与电阻、电流平方之间的相关性关系。结果表明：利用光谱研究得到的闪电放电通道的电阻为0.04～8.41 Ω·m-1、峰值电流时的热功率为0.88×108～2.20×108 W·m-1、回击初始前5 μs内通道储存的热能为1.47×102～3.66×102 J·m-1，以上结果与文献报道的利用其他方法得到的结果相比，在合理的范围内；与常规金属导体相比，闪电回击放电等离子体通道在峰值电流时的热功率与电阻成正比，但与电流的平方呈指数减小的关系；由于闪电等离子体通道的电阻与温度的3/2次方成反比，通常回击放电通道中峰值电流越大，通道温度越高，而电阻会迅速降低，因此热功率也会急剧减小。此结论进一步验证了采用欧姆加热方法加热等离子体的致命缺点。

Study on the Resistance and Thermal Effects of Current in Lightning Return Stroke Channel by Spectroscopy

The resistance and the thermal effects of current in lightning discharge channel are important to the lightning disaster research and prevention design, and the thermal characteristics of lightning channel are closely related to the spectra of the plasma. In this work, using the spectra of two cloud-to-ground lightning with multiple return strokes obtained by a slit-less spectrograph, and combining with the synchronous electrical information, the electrical conductivity, the peak values of current, the arc channel radius has been calculated, then the resistance per unit length, the thermal power per unit length at the instant of peak current, and the heat energy per unit length during the first 5 μs in the channel are firstly obtained. Meanwhile, compared to the common metal conductors, the relationships between the thermal power and the resistance and the square of the peak current in lightning plasma channel are analyzed. The results shown that the resistances per unit length are estimated by spectra to be 0.04～8.41 Ω·m-1. The thermal peak powers per unit length are in the range of 0.88×108～2.20×108 W·m-1 and the heat energies over the initial 5 μs are in the range of 1.47×102～3.66×102 J·m-1. The values of these parameters are consistent with the values reported in other works; The thermal power at time of peak current increases linearly with the resistance but reduces exponentially with the square of the peak current; Because the resistance in lightning channel is inverse ratio to 2/3 power of the temperature, the stronger peak currents are generally corresponding to the higher temperatures, but the resistance and the thermal power will decrease rapidly with the temperature, which further proves why the plasma cannot be heated by the ohmic heating method.