Electrical evolution of a rapidly developing MCS during its vigorous vertical growth phase

This study examined the coevolution of storm structure and electrical behavior of a rapidly developing mesoscale convective system (MCS) over Beijing metropolitan region during its vigorous growth phase based on observations and model simulations. When the isolated convection grew upscale and developed into a larger and organized MCS, it is found that the lightning production increased much faster than storm volume growth. Although the overall MCS went through rapid intensification, large differences exist in the radar reflectivity pattern of its convective cell members indicating their differential convective states. Several distribution peaks of lightning radiation pulses are also observed in the vertical direction, suggesting the overall complicated charge distribution inside the MCS. Given the decreased distances among cells during the upscale growth, it is hypothesized that such complicated charge distributions are more conducive to local high electric fields for lightning initiations and hence increased lightning production rates. The electrification-coupled WRF simulations support this proposed hypothesis, which clearly show that the MCS evolves from two layered charge regions to more complicated charge distributions. When some convective cells consisting of the MCS develop toward maturity, the precipitation particles descend to low levels and give rise to a lower positive charge region that is embedded inside a deep-layer negative charge region. In combination with enhanced interactions among the cells, a peak of electric field magnitude is generated at lower levels due to the approaching charge regions with opposite polarities, such that more lightning flashes are produced.