Experimental Evaluation of The Lightning Flash Multiplicity in a Mountainous Region in Colombia

This paper presents the results of the experimental evaluation of the lightning flash multiplicity of negative cloud-to-ground flashes in a mountainous region of Colombia. This region is known as the Aburrá Valley and is characterized for being located at about 1500 m.a.s.l. with large altitude variations and a significant lightning activity. The analysis is based on the measurement of the electric and magnetic field, and for some events with the simultaneous recording of high speed videos. The field measurements and video recordings were acquired by means of an experimental setup in which the field signals were stored automatically in a local PC and the videos were recorded using a trigger signal sent from the oscilloscope location to the camera location through an internet remote connection. A timestamp was also obtained based on an external trigger pulse generated by the oscilloscope. For a total of 2872 events acquired, 2829 correspond to electromagnetic field waveforms only and 43 to field and simultaneous video recording. The signals and videos were processed by means of standard filtering techniques; based on these data, the peak field time instants and channel luminosity pixels from video frames were extracted and compared. The flash multiplicity was estimated based on a weighted average. From this analysis, it was possible to estimate a lightning flash multiplicity of 4.22 strokes/flash based only on electromagnetic field measurements. From the simultaneous video and field measurements, the flash multiplicity was calculated to be 4.28 strokes/flash. As a conclusion, it was possible to successfully estimate the lightning flash multiplicity on an experimental base. Further work is required in this field in order to obtain a larger number of samples and in different regions of Colombia.