Structural Characteristics of Thunderstorms Associated with Negative Triggered Lightning Flashes

This study utilizes data from a 3-D lightning location system, polarimetric radar, and current measurements from channels of triggered lightning flashes (TLFs) to analyze the structural characteristics of the parent thunderstorms associated with negative TLFs in South China. The triggered-flash region (TFR) displays distinct stratiform cloud characteristics, including lower radar reflectivity heights and a predominance of ice crystals and dry snow above the 0°C layer. In contrast, the thunderstorm convection core region (CCR) tends to have more graupel particles in the mixed-phase layers and exhibit an ice-water content peak approximately 3.4 times that of the TFR. The charge regions involved in discharges in TFRs exhibit a dipolar charge structure, with the −5 °C layer roughly dividing the upper positive and lower negative charge regions. Conversely, the CCRs feature a typical tripolar charge structure. The dominant dipole charge structure in the TFR results in an increase in the negative charge field below the negative charge region with height, providing a necessary condition for successfully triggering negative TLFs. Furthermore, the horizontal extent of TLFs is positively correlated with their duration and charge transfer. Regions where TLF channels with larger charge transfers propagate tend to have greater maximum radar reflectivity but lower average radar reflectivity compared to regions with TLFs with smaller charge transfer.