Diagnosing The Lightning Plasma Temperature Based On The Collisional-radiative Model

The research on the discharge characteristics and physical mechanism of lightning plasma is one of the most concerned topics at present.Temperature is one of the important parameters which could reflect the discharge characteristics of lightning plasma.So far,lightning plasma has usually been studied on the basis of optical observations.Members of our team obtained lightning spectrum data in the Qinghai plateau by using a slitless spectrogragh with high time resolution.By using these spectra as the research object,the collisional-radiative model was established by combining with the luminescence mechanism of lightning plasma channel for the first time.Nitrogen ion(NII)spectral lines 500.52 and 567.96 nm are one of the stronger spectral lines which can reflect the discharge current intensity in the lightning spectrum.We have calculated the total relative radiation intensity of these two characteristic spectral lines at different temperatures,and then have obtained the relationship between the ratio of the total relative radiation intensity of these two characteristic strong spectral lines and temperature.Finally,the relationship is applied to the experimental spectrum,and the temperature of lightning plasma have been obtained.The main contents are as follows:Firstly,according to the theory of multi-configuration Dirac-Fock method,the atomic parameters such as correlative energy levels,transition probabilities,collision cross sections,collision strengths and electron collision excitation rate coefficients of nitrogen ion(NII)have been calculated based on Flexible Atomic Code program.Secondly,collision radiation model is established according to the theoretical basis,where the intensity of the radiative spectral line of atoms or ions is proportional to the electron collision excitation rate coefficient from the ground state to the excited states and it is also proportional to the transition probability from the high excitation state to the low excitation state.The characteristic spectral lines 567.96 and 500.52 nm of nitrogen ion is stronger in lightning spectra,and the relative radiative intensity of each transition associated with them have been calculated further.The ratio of the relative total radiative intensity of these two strong spectral lines have been obtained at different temperatures.It has laid a foundation for further application in the experimental spectrum.Finally,by analyzing the experimental spectra of six lightnings,the total relative spectral intensities of the characteristic strong spectral lines 567.96 nm and 500.52 nm of them have been obtained,the temperature of these six lightning plasma channels have been also obtained by combining the ratio of the relative total radiation intensity obtained by the collisional-radiative model.In addition,the channel temperature of the six lightning plasmas is estimated by using the multi-spectral method.By comparing with the temperature obtained based on theoretical calculation,it can be found that the differences of the results obtained by two methods were within 2500 K.