Quantitative spectral analysis of natural lightning return stroke followed by continuing current with M-components

Using time-resolved spectra from three cloud-to-ground (CG) and one tall-object lightning return stroke with continuing current (CC) process and M-components, the temperatures and electron densities calculated from the different sets of ionic and neutral line emissions for long-duration (nearly one millisecond) visible channels with lengths of several hundred meters were quantitatively analyzed. Our analysis showed the following results: (1) The temperature and electron density calculated from the singly ionized lines were noticeably higher than those calculated from the neutral atomic lines. (2) The temperature calculated using the singly ionized lines during the CC process was lower than that of the corresponding return stroke for three lightning. The remaining one lightning return stroke was closely followed by two consecutive M-components. The temperature calculated using the singly ionized lines for the second M-component was higher than that of the corresponding return stroke. The electron density calculated using the singly ionized lines during the CC process was higher than that of the corresponding return stroke. (3) The temperatures and electron densities calculated using the singly ionized lines decreased as the height of the channel increased, while those calculated using the neutral atomic lines increased with increasing channel height. (4) The maximum gradient values of the temperatures calculated from ionic and neutral lines along the channel were 22,200 K/km and 9000 K/km, respectively, which were observed in the first M-component of lightning B. These results verified that the lateral corona discharge was predominantly responsible for the continuing current process.