Evolution of the Charge Structure and Lightning Discharge Characteristics of a Qinghai-Tibet Plateau Thunderstorm Dominated by Negative Cloud-to-Ground Flashes

The correlation between the charge structure evolution and lightning type and frequency for a multicell thunderstorm dominated by negative cloud-to-ground (CG) flash on the Qinghai-Tibet Plateau was analyzed using observations from a three-dimensional lightning very high frequency radiation source location system. The analysis results showed the following. (1) In the initial developing stage of the thunderstorm, each cell developed independently and presented an inverted dipole charge structure. As the thunderstorm developed into its mature stage, multiple cells merged, and the charge structure changed to a tripole structure. In the dissipation stage of each thunderstorm region, the charge structure reverted to an inverted dipole or a normal dipole. (2) When the extent of the charge region expanded, the upper and lower charge regions became uneven and asymmetric. (3) In the inverted dipole charge structure, negative CG flashes accounted for 77.2% of the total number of lightning flashes, whereas negative intracloud flashes accounted for only 22.8%. In the tripole charge structure, negative CG flashes, positive intracloud flashes, and negative intracloud flashes accounted for 62%, 21%, and 16%, respectively, of all lightning flashes. These results indicate that the middle negative charge region was the strongest layer of the thunderstorm, while the upper positive charge region was slightly stronger, and the lower positive charge region was the weakest. These findings also indicate that the relative intensity of the charge layers directly determined the lightning quantity and frequency.