Correlation analysis between the channel current and luminosity of initial continuous and continuing current processes in an artificially triggered lightning flash

Using simultaneous high-speed camera records and channel-base current records in an artificially triggered negative lightning event, the correlation between the channel-base current and the integrated luminosity (IL) of the air-ionized part of the lightning channel is analyzed during the periods of the initial continuous current (ICC) process and eight continuing current (CC) processes. Depending on the current's changing trend (ascending or descending) and the luminosity property of the pixels used to calculate the IL from the high-speed camera records (including saturated pixels or not), the ICC and eight CC processes are divided into the saturated ascending stage (Stage-A), the saturated descending stage (Stage-B), the unsaturated ascending stage (Stage-C) and the unsaturated descending stage (Stage-D), including the descending tail stage (Stage-T, in which the channel-base current falls to zero). The analysis shows the following: (1) the IL is linearly correlated with the logarithmic value of the current in both Stage-A and Stage-B of two long CC processes, the ICC process and the CC process after the 7th return stroke, although the regression parameters (intercept and slope) in Stage-B are higher than those in Stage-A. This rule can also be found in most pulses of the long CC processes, where the IL in the descending stage is higher than that in the ascending stage at the same current value, regardless of which threshold index or height range used to calculate the IL are selected and regardless of whether the IL includes saturated pixels or not. (2) In the unsaturated stage of long CC processes, the channel current shows a significant linear correlation with the square root of the IL, and the fit of this relationship is much better than that in the saturated stage. Additionally, in each Stage-T of the eight CC processes following return strokes, the square root of the IL is significantly and linearly correlated with the current, and the regression slope is negatively correlated with the corresponding return stroke peak current. This result means that for the same channel current variation, the lower the return stroke peak current associated with the Stage-T of the CC process, the greater the luminosity variation. (3) For each of the above stages, the statistical model has a better fit when a higher threshold index, a more perpendicular channel or a greater height range is selected in the calculation of the IL.

► Detailed analysis of the correlation between the channel current and luminosity.
► The correlation does not remain unchanged during a flash, even for a pulse.
► Luminosity in ascending stage is lower than that in descending stage for a pulse.
► Current shows linear correlation with SQRT of luminosity for unsaturated stage.