The Radius And Characteristic Parameters Evolution Along Radial Direction Of Lightning Plasma Channel

The spectra of six cloud-to-ground lightning are captured by a high-speed spectrograph in Qinghai Province,the temperatures of lightning plasma channel are diagnosed by different radiation components in the spectra.Combining with the synchronized electric field data and optical pictures of lightning channel as well as correlation between spectral radiation intensity and radius of lightning channel,radii of core current channel and the luminous channel are achieved.The some differences have been found in spectral structure and profile of different lightning.The radii of the core current channel and the luminous channel are estimated and their values are0.66-1.01cm and 5.03-7.96cm respectively,which are all in the range of literature reports,and corresponding temperatures are 27300-30300K and 3300-5800K.Based on mentioned above,according to the heat conduction equation and law of energy conservation,temperature distribution along radial direction of the lightning return stroke channel was also achieved and the radii of glowing edge with temperature of around 500K were firstly estimated.The results show that the attenuation of temperature along the channel radial direction is in accord with logarithmic law.Within around 13cm,the channel temperature drops from around30000K to 300K.A high channel temperature of above 20000K exists within radii of about less than 2cm,and the channel temperature gradient is larger and its temperature along the radial direction falls sharply,while channel temperatures gently declines outside this range.The radii of glowing edge are around 6.94-13.0cm.Since electrical conductivity is a function of temperature,electrical conductivity of discharge plasma channel is estimated and its distribution along the radial direction can be firstly obtained.The results show that the attenuation of electrical conductivity along the radial direction also obeys the similar law to the temperature attenuation,and gently slows down as the radius increasing.Within radii of around 4.6cm,the electrical conductivity along the radial direction falls sharply,its attenuation law is consistent with logarithmic law and the electrical conductivity drops from around20000Sm^-11 to 500Sm^-1.Within radii of around 2cm,the electrical conductivity is above 10⁴Sm^-1.When the radius is larger than 4.6cm,the conductivity gently decays,of which attenuation is exponentially along the radial direction.The channel radius is about 9.7cm,the electrical conductivity has been declined around 10^-7Sm^-1,corresponding temperature is around 1500K;The electrical conductivity of glowing edge with temperature of around 500K is 10^-14Sm^-1,which is the same as the order of magnitude of electrical conductivity for the virgin air.