Impact of ground-level cool condition during monsoon seasons: Occurrences of isolated breakdown pulse trains discharges and their relationship with ground flashes events in tropical thunderstorms

Abstract

These new findings provide detailed understanding into how seasonal monsoon patterns shape the characteristics and behaviour of isolated breakdown pulse (IBP) train discharges and their co-occurrence with ground flashes. Using high-resolution broadband electric radiation field measurements (12.5 to 25 nanoseconds) over a two-second duration, we identified key influences of monsoon variations. Notably, the ground-level cool condition and high humidity during the Northeast monsoon coincided with the IBP train activity. Among 90 samples analysed, most positive IBP train discharges occurred between late evening (6 PM) and midnight (12 AM), while negative IBP train discharges were rare, with only six cases recorded across all monsoon periods. We categorized IBP trains into two types: type-i, consisting of uniform polarity pulses with an average of 19 pulses, and type-ii, featuring a higher average of 95 pulses, followed by sequences of composite bipolar pulses. Interestingly, the occurrence of positive IBP train discharges during storms influenced the production of cloud-to-ground (CG) flashes. Storms with frequent positive IBP train discharges exhibited the highest number of positive CG flashes. Conversely, increased positive IBP train activity corresponded to a reduced percentage of negative CG flashes. These results enhance our understanding of storm electrification dynamics in tropical regions.