Fig. 1. The original spectra of lightning return stroke channels

Fig. 2. The spectra of lightning return stroke channels at a given height
(a): The spectra of first return stroke R1; (b): The spectra of subsequent return stroke R2; (c): The spectra of subsequent return stroke R3; (d): The spectra of subsequent return stroke R4

Fig. 3. The luminous radius of lightning return stroke channels at a given height by luminous pixels
(a): R1 passagway; (b): R2 passagway; (c): R3 passagway; (d): R4 passagway

Fig. 4. The waveform of fast electric field change caused by lightning
(a): R1 passagway; (b): R2 passagway; (c): R3 passagway; (d): R4 passagway

Fig. 5. Correlation analyses
(a): Correlation analysis between the conductivity and the peak power per unit lenth;(b): Correlation analysis between the return stroke speed and the peak pwoer per unit lenth;(c): Correlation analysis between the initial electric field peak and the peak pwoer per unit lenth;(d): Correlation analysis between the peak current and the peak pwoer per unit lenth