Spectral Correction Impacts of Lightning from Tall Buildings on Channel Temperature Inversion

Abstract

During the lightning spectral observation, the spectral intensity is significantly reduced due to instrumental factors and other factors. The spectral intensity attenuation significantly affects the accuracy of temperature calculations. Temperature, as a fundamental parameter, is inextricably linked to other parameters within the lightning discharge channel, and accurate determination of the plasma temperature is crucial for gaining insights into the dynamic and physical processes of the discharge. Up to now, there have been no detailed and definitive reports on the influence of instrumental response on tall building lightning spectroscopy and temperature diagnostics.Based on the spectral analysis of a lightning return stroke channel spectrum, the spectral is corrected by accounting for the instrumental response. Then, the spectral structure and line intensities before and after correction are compared and analyzed. Nitrogen ionized (NII) lines in the visible region and neutral oxygen (OI) lines in the near-infrared region are selected for temperature calculations using the multi-line method. The influence of spectral correction on the temperature analysis of the tall building lightning return stroke channel is investigated. Results show that after correction, the intensity of spectral lines is significantly enhanced. In particular, the spectral line structure in the visible region changes significantly, while the spectral line structure in the near-infrared region changes little. The continuum radiation in the visible region of the corrected tall building lightning spectrum is significantly enhanced, which is different from the results of natural cloud-to-ground lightning spectra after considering the instrumental response correction. Due to the significant enhancement of the continuum radiation intensity in the visible region resulting from the spectral correction, the continuum radiation intensity should be subtracted when using NII lines in the visible region to calculate the tall building lightning temperature. In this case, the coefficient of fitted line and the calculation accuracy increases, while the average temperature decreases by 4660 K compared to that before correction. Conversely, since the original continuum radiation intensity of tall building lightning spectra in the near-infrared region is relatively low, the spectral correction has little effect on the continuum spectrum intensity. Therefore, after spectral correction, when using OI lines in the near-infrared region to calculate the temperature, the determination coefficient of the linear fitting increases, resulting in improved fitting performance and an increase of 1540 K in the average temperature.

Keywords

• tall building lightning
• spectral correction
• multiple line method
• temperature