Thunderstorm characteristics deduced from fractal analysis and Q-bursts

The meteorological context for mesoscale lightning and the origin of ELF Q-bursts in Africa have been enabled by the MTT Doppler radar installed in Niamey, Niger in summer 2006 for the AMMA (African Monsoon and Multidisciplinary Activity). The radar measurements were supplemented with ground-based electrical and video camera observations. A large number of energetic lightning flashes have been documented in the laterally extensive stratiform regions of squall lines from MCS (Mesoscale Convective System). Some of these special flashes developed after the radar bright band was well developed in the stratiform region and generated large transient electromagnetic signals, or so-called ELF Q-bursts. GPS clocking of these events has enabled their search and identification at remote ELF stations all over the world. These identified flashes have a positive polarity in many cases with a charge moment change (CMC) sometimes ~ 3000 C km, sufficient for generating sprites. This expectation has been confirmed by the first ground-based observation of sprites over Africa. Fractal analysis has been applied to the radar data from African MCS to understand the meteorological conditions behind the local discharges, excitation of energetic Q-burst and sprites in Africa. Fractal dimension D _f varies with the meteorological stages of MCS. D _f of MCS in the bright band reaches about 2.0 indicating the self-organization of thunderstorms when most Q-bursts are generated.