Study on Physical Characteristics of a Bipolar Cloud-to-Ground Lightning Discharge Plasma

The spectra of a bipolar lightning flash are recorded using a slitless spectrograph in Qinghai, China. The lightning contains two return strokes: the first one is negative stroke, and the subsequent one is weak positive stroke, which occupied the same channel as the first stroke. Both return strokes are followed by long continuing current. The variations of physical characteristic parameters with the rise of height along the channel of bipolar lightning flash are calculated for the first time. The result shows that during two return strokes, the temperature and conductivity are obviously increasing with the rise of height. In contrast, at the initial stage of continuing current after the first return stroke, the temperature and conductivity do not show obvious monotonous variation along the channel, but the total spectral intensity and luminous radius increase clearly with the rise of height along the channel, and all these parameters are larger than that of the first return stroke. The variation of the above parameters along the channel reflects the transmission characteristics of the corresponding discharge current.