闪电连续电流的光谱分析及通道温度特性研究

Spectral Analysis and Study on the Channel Temperature of Lightning Continuing Current Process

连续电流是闪电放电过程中的一个重要子物理过程,它是指雷暴云局部电荷中心在回击之后沿原通道对地的持续放电过程。在连续电流阶段,原本发光微弱的通道其亮度有时会突然增强,这种现象被称为叠加了M分量,自20世纪连续电流被发现以来,国内外学者进行了许多观测研究。目前主要是利用电磁学和光学的观测手段揭示其放电和发光的宏观特征,利用光谱观测对其通道内部微观的发光信息和物理特性等的研究还很缺乏。如关于连续电流阶段放电通道内的温度特性参数目前鲜有报道,而温度是研究闪电连续电流放电通道物理特性所必需的基本参量,也是预防连续电流引起的雷电灾害事故所关心的参数。依据由无狭缝高速光谱仪观测的一次云对地闪电首次回击后叠加三个M分量的连续电流过程的光谱资料,分析了整个放电过程中光谱的演化特征,计算了连续电流放电过程电流核心通道和外围电晕通道的温度,研究了两者随通道高度的变化特性。结果表明,在初始回击阶段,通道的光辐射主要是激发能较高的一次电离的氮离子辐射,在之后连续电流阶段,通道的光辐射则主要是激发能较低的中性氮、氧原子辐射。离子线辐射在回击初期时最强,氢Hα线和红外波段的中性原子线在M1时最强,连续谱在M2时最强。近红外波段的四条线OⅠ777.4,NⅠ746.8,821.6和868.3 nm在整个放电过程都可以被观测到。在连续电流阶段,电流核心通道温度为42060~43940 K,比相应回击核心通道温度高6020~7900 K;外围电晕通道温度为16170~20500 K;通道核心温度和电晕温度均随时间变化不大;通道核心温度随通道上升呈减小趋势,而外围电晕温度随通道上升呈增大趋势。

Continuing current is an important sub-physical process of lightning discharge.It refers to the process in which the local charge center in the thunder cloud discharges to the ground through the original channel after the return stroke.It is also usually overlapped by the M-component,which is the phenomenon that the brightness of the glowing channel increases suddenly.Since the continuing current was discovered in the 20 th century.Many kinds of research were made by domestic and foreign researchers.The present studies mainly reveal the macroscopic characteristics of the discharge and luminescence using electromagnetic and optical observations.There is a lack of studies on the microcosmic luminescence information and the physical characteristics used by spectral observation.There are few studies about the temperature in the discharge channel of the continuing current.However,the temperature is not only a basic parameter to analyze the physical properties of the continuing current discharge channel but also a concerned parameter to prevent lightning disasters caused by the continuing current.Based on the spectra of a first return stroke and the following continuing current process overlapped with three M-components for cloud-to-ground lightning recorded by a slit-less high-speed spectroscope,the spectral evolution properties during the entire discharge process have been analyzed.The temperatures in the channel core and the corona sheath have been calculated,and the variations of both along the channel height have been studied.The results show that in the stage of the return stroke,the channel optical radiations are mainly the NⅡlines with higher excitation energy.In the continuing current process,the channel optical radiations are mainly the NⅠand OⅠlines with lower excitation energy.The intensity of the ionic lines is strongest at the initial stage of the return stroke,while the intensities of the Hαand the neutral atomic lines are strongest at M1,and the continuum spectrum is strongest at M2.Four lines of OⅠ777.4,NⅠ746.8,821.6 and 868.3 nm in the near-infrared band were observed throughout the discharge process.During the continuing current,the temperatures in the channel core are 42060~43940 K,which are 6020~7900 K higher than the temperature in the channel core of the corresponding return stroke.The temperatures in the outside corona sheath are 16170~20500 K.The temperatures of the channel core,and the corona sheath both remain unchanged with time.The temperature of the channel core decreases with the increase of the channel height,while the temperature of the peripheral corona sheath increases with the increase of the channel height.