Significance of the Time Between Preliminary Breakdown and Return Stoke for Negative Cloud-to-Ground Flashes

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Sunday, 2 February 2014
Hall C3 (The Georgia World Congress Center )
Geoffrey Heidelberger, University of Alabama, Huntsville, AL

Preliminary breakdown (PB) marks the beginning of a negative cloud-to-ground (CG) flash, initiating or leading to the initiation of a stepped leader. PB pulses are short, fast radiation pulses that have a width of 20 -40 microseconds and are bi-polar with an initial polarity that is negative for typical CG flashes. Using the Huntsville Alabama Marx Meter Array (HAMMA), which operates in the very low frequency regime (VLF), all parts of the electric field produced by lightning can be observed. PB pulse trains have a characteristic signature in the HAMMA waveform for negative CG flashes. This study investigates the significance in the variation of time between PB and return stroke (RS), using a PB pulse train locating algorithm. The time when PB occurs is then used to look at leader propagation speeds using source heights from both HAMMA and the North Alabama Lightning Mapping Array (LMA). Further, we examine the relationship in the time between PB to RS and the peak current of the RS based on National Lightning Detection Network (NLDN) measurements.