Study On Spectral Characteristics Of Lightning Stepped Leader

Lightning is closely related to human survival activities.It is an instantaneous discharge phenomenon that often occurs in nature.Due to its short time,accompanied by high temperature,high pressure,huge shock wave and strong electromagnetic radiation,it has a great impact on human production and life.Therefore,studying the physical characteristics of lightning plays an important role in the field of forest fire prevention,high pressure transportation,aerospace and other electronic fields.The lightning stepped leader is the initial stage of lightning,which opens the way for lightning and is the subject of most concern to researchers.Through the spectral observation and analysis,the microscopic physical information inside the lightning leader channel can be obtained,which is an effective way to obtain its internal physical parameters.Because of its weak luminescence,it is difficult to be photographed by researchers.So far,the research on lightning mainly focuses on the return discharge.In this paper,we use the high time-resolved spectra recorded in the development of a lightning stepped leader in Qinghai plateau area.The nitrogen and oxygen atomic lines in the near-infrared region are mainly observed in the lightning stepped leader spectra.In the initial stage of the leader,there is a significant secondary ionization nitrogen ion line in the spectrum,with the leader development,the ion line of the secondary ionization gradually disappears,and the nitrogen oxygen atom line is always present.Therefore,it is the best choice to study the physical characteristics of lightning stepped leader by using nitrogen and oxygen atomic lines.In this work,the temperature and electron density of the lightning stepped leader development process are quantitatively calculated by using oxygen atomic spectra.The evolution characteristics of temperature and electron density during the propagation of lightning leader plasma with time and along the channel height are further analyzed.The results show that the electron density of the lightning stepped leader is in the order of 10¹88 cm^-3,and the lightning leader tip temperature is approximately 1.6×10⁴ K.The temperature and electron density of the lightning leader tip decrease with time.With the increasing of the lightning stepped leader channel,the electron density tends to increase.The variation trend of temperature and electron density in lightning channel has good consistency.At the same time,based on the analysis of the leader temperature and electron density,using the plasma conductivity theory,the conductivity of the stepped leader plasma channel decreases with time,with an average value is about 9.5×10³S·m^-1,which confirms that the conductivity of the stepped leader plasma channel is closely related to the channel temperature.In addition,through the analysis of physical parameters such as conductivity,the resistance of the leader channel is simulated by setting radius.The results show that with the development of the stepped leader channel,the resistance increases,and the resistance of the stepped leader channel is inversely proportional to the conductivity,which conforms to Ohm's conductivity law.