Characterization of Electric Fields Produced by Preliminary Breakdown Pulses Observed in Bogota, Colombia

In this paper, the characteristics of electric fields due to preliminary breakdown pulses (PBP) that precede the first return strokes (FRS) are presented. These pulses exist due to the electrical activity formed inside the clouds prior to the occurrence of the stepped leader. The electric field signatures were recorded in Bogota, Colombia with an altitude of 2550 m. For the measurement campaign, a broadband parallel-plate antenna system with a 500 ms full observation window and a pre-trigger of 250 ms were used. The measurements were carried out during two rainy seasons recording 180 waveforms. From recorded data, it was found that 37.5% of negative cloud-to-ground (CG) flashes exhibited PBP. With respect to the PBP trains a duration between 0.4 ms and 22.3 ms was observed. For the same temporal parameter, the arithmetic mean (AM) and the geometric mean (GM) were 4.7 ms and 3.1 ms, respectively. On the other hand, the GM of the time interval between the largest peak of the PBP train and the peak value of the FRS was 10.1 ms, while its AM was 27.9 ms. In addition, the GM of the ratio between the maximum value of the PBP train and its respective FRS was 0.51, with changes between 0.12 (minimum) and 2.1 (maximum). Finally, the number of individual pulses per train between 4 and 39.