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.