The lower positive charge center and its effect on lightning discharges on the Tibetan Plateau

Electrical characteristics of thunderstorms on the central Tibetan Plateau at an altitude of 4508 m have been studied. The evolution of surface electric (E) field and the E field changes produced by lightning flashes under a representative thunderstorm revealed a tripole charge structure with a larger-than-usual lower positive charge center (LPCC). The storms appear to begin with the lower dipole of a normal tripole structure, rather than with the upper dipole followed by the development of a weaker lower positive charge. The flash rate is quite low and the average value is usually 1 fl/min. The IC flashes were usually polarity-inverted and occurred in the lower dipole. The large LPCC did not cause positive CG flashes to occur during the whole storm lifetime, and only negative CG flashes were observed in the late stage of the storm.