Lower Charge Region Research Articles

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

AbstractThe 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.

Lightning activity and electrical structure in a thunderstorm that continued for more than 24 h

Based on the 2A12 product of the TRMM satellite, lightning data observed by SAFIR3000, and a cloud-to-ground (CG) lightning location network, lightning activity and electrical structure were analyzed in a thunderstorm that occurred in Hubei province of China on 30–31 May 2007. This thunderstorm considered to be unusual because it continued for more than 24 h and produced a heavy rainfall in a wide area had some analogous electric characteristics to normal thunderstorms. In convective areas of the thunderstorm, CG flashes tended to be of negative polarity and were spatially clustered. In stratiform areas of the storm, CG flashes tended to be of positive polarity and had a scattered spatial distribution. Based on the spatial distribution of lightning radiation sources observed by SAFIR3000, a typical tripolar electrical structure was inferred to dominate the convective areas, whereas a dipolar structure with anomalously low charge heights was inferred in the stratiform areas. The polarity of the CG flashes appeared to be same as that of the second charge region, as counted from the lower charge region. The mean ratios of positive cloud-to-ground (PCG) flashes were small with 3.52% during active stage and big with 21.25% during decaying stage. It was found that during the decaying stage, the concentration of ice particles in the convective areas decreased much more rapidly than did the concentration in stratiform areas due to the rapidly weakening updraft in convective areas, being related to that negative cloud-to-ground (NCG) flashes activity mainly occurring in the convective areas weakened more rapidly than the PCG flashes activity mainly occurring in the stratiform areas. The main negative charge involved in lightning discharges was located in the region with the highest concentration of graupel particles, and the main upper positive charge involved in lightning discharges was located in the lower part of the region with the highest concentration of ice crystal particles.