Spectrum carries important information reflecting atomic and molecular processes inside a light source. Accurate spectral diagnosis is vital in revealing the microscopic physical mechanism of the lightning discharge process. Spectral correction was applied considering the influence of atmospheric attenuation, grating efficiency, and camera response on the observed spectrum, thereby solving the problems of atmospheric attenuation in long‐distance lightning spectrum observations. Based on the restored spectrum, the temperature of the lightning return stroke channel was calculated by the ionic and atomic lines respectively. The result showed that corrected temperature at the initial stage of the return stroke, calculated by the ionic line, could reach up to 40,000 K, which was about 10,000 K higher than the values directly obtained from the observed spectrum. Atmospheric attenuation of the atomic spectral line in the near‐infrared band is relatively weak; therefore, atmospheric attenuation was inferred to have a relatively less effect on the channel temperature that was calculated by the atomic spectral lines. This work provided the attenuation ratio of the characteristic lines in lightning spectra with distance, and can used for more precisely quantitative investigation on the physical characteristics of the lightning process. It also has application value for improving the spectral diagnostic techniques on celestial body and other natural luminous process.
Two positive cloud‐to‐ground lightning spectra have been captured by a slit‐less spectrograph. In combination with the synchronous electric field change waveshape, the discharge characteristics along the channel have been investigated. The results show that the total intensity of ionic lines in spectra and the electrical conductivity increase with the increase of channel height. According to the positive correlation between the total intensity of ionic lines and the discharge current, it is found that the current intensity of downward positive cloud‐to‐ground lightning increases with the increase of channel height. Comparing it with the reported current attenuation along the channel of downward negative lightning, it is deduced that the increasing or decreasing of the current along the discharge channel is likely to be related to the current direction.
Based on the spectra of an apparent natural ball lightning (BL) taken by a slit-less spectrograph with a high-speed camera as a recording system in the Qinghai Plateau of China, the temperature and time-evolution characteristics of this object were investigated. We found that for most of its life, the BL maintains a generally stable luminosity with an obvious periodic oscillation that is only discernible on the spectra captured by the high-speed camera. Soil constituents (Si I, Fe I, and Ca I lines) contribute the majority of bright light, while air compositions (N I and O I lines) dominate the periodic feature of the BL. There are some differences between the temperature values calculated by the spectral lines of different elements in the spectrum. The temperature estimated by the O I lines was the highest, ranging from 7170 to 11 410 K. The mean temperatures gained by O I, Si I, and Fe I lines and continuous spectra were 8750, 4330, 4600, and 2700 K, respectively. This means that the BL has an energy source core, where the spectral lines with higher upper excitation energy should be more intense than that in its periphery. In addition, during the luminously stable stage, the temperature showed an obvious periodic oscillation with time, and its variation tendency was synchronous with the evolution of the light intensity and spectral characteristics.
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