A Frontal Thunderstorm With Several Multi-Cell Lines Found to Produce Energetic Preliminary Breakdown
Abstrakt
We combine electromagnetic measurements with meteorological and lightning detection data to explain an observation of unusually strong preliminary breakdown (PB) produced by a thunderstorm system that developed along the Mediterranean Coast of Southern France in the early hours of 19 June 2013. This multi-cellular storm was composed of several parallel convective lines in the NW-SE direction.
Our analysis focuses on 10 sequences of energetic electromagnetic PB pulses recorded by two receivers located at different distances from this thunderstorm. The peak currents, which generated these strong PB pulses, reached -36 kA.
The initial polarity of all observed energetic PB pulses confirmed the movement of the negative charge downward, as in case of PB pulses preceding negative cloud-to-ground discharges. The locations of PB pulses appeared in areas with none or very weak lightning activity.
Most PB pulses were initiated in small, short-living, rapidly moving convective storm cells characterized by low reflectivity values (generally <40 dBZ), weak vertical development, and low flash density. Our findings indicate that the observed thunderstorm might possess temporary strong negatively charged pockets located above a strong positive charge region at low-level.
Such charge arrangement, likely explains our observation of unusually strong PB pulses and the absence of RS pulses in electromagnetic recordings.