Study On The Physical Properties Of Plasma Channel At Different Stages In Lightning Discharge

According to the spectra data of cloud-to-ground (CG) lightning discharge channel have been obtained by using a Slite-less spectrogrograph on Chinese Tibet Plateau, selected the spctra of three lightning processes with multiple return strokes,and combining the spectra of one of the lightning with synchronous electrical information, the correlation among spectral properties, channel temperatures and discharge characteristics, thermal effects of current is discussed for the first time. The results show that the spectral structure varies obviously in different stages of multiple-stroke lightning discharge, and the channel plasma temperature varies significantly from stroke to stroke within a given flash, in other words, the temperatures in initial stage of flash are higher, and then decreases gradually afterwards. The total intensity of spectra is directly proportional to the amplitude of electric field change as well as intensity of discharge current. Moreover, the positive correlation has been confirmed between the channel plasma temperature and the thermal effect which shows the effect of the electric current accumulation. It is confirmed that channel temperature is correlated positively with the energy transmission in one return stroke, but there is no fixed proportionality for them. The main reason may be the discrepancies in channel resistances, heat capacities, and other factors during different strokes, even related to the incomplete synchronization between the electric field and the change of the current in decay stage. The results in this work will give some reference date for futher experiments on high time resolved spectra, study on correlation between spectra and electrical parameters and research on lightning physical mechanism in lightning discharge process.Based on this work, lightning spectra in the near-infrared region of 760 to 970nm were obtained by using Slit-less infrared spectrograph in Shandong region, the temperatures at different positions along the discharge channel are calculated according to neural nitrogen and oxygen radiation, respectively. The evolution characteristic between the channel plasma temperature and the total intensity of spectra along the stroke channel during near-infrared radiation are discussed for the first time. It has been found that the near-infrared spectrum is mainly the contribution of radiation from latter stage of lightning discharge, and there is little difference for spectral structure of different lightning. Moreover, the results show that the channel temperatures are lower than the initial stage and the developing stage of return stroke, and the temperature decreases to 16,000K during this period. In addition, the change tend between the channel temperature and the total intensity of spectra along the stroke channel was consistent with the initial stage of discharge for CG lightning, in other words, for a certain return stroke channel, temperatures and the total intensity of spectra at different positions show signs of falling away with increasing height alone the discharge channel, and it highest in near ground. The result is in accordance with the optical observation of lightning discharge. But there is non-uniformly varied between them in cloud lightning. Also, the channel temperature and the total intensity of spectra are sudden changes in the tortuous positions and the branches and the crunodes of the lightning channel. This work will provide new information on discharge processes with lower amplitude currents and temperatures, and perhaps channel cooling.