Vertical Distribution of Sound Power Within Lightning

Methods for location of infrasonic and low frequency sound sources allow to reconstruct complex lightning geometries, including simultaneously cloud-to-ground return strokes and intracloud discharges. Back-propagating the ground recorded pressure also provides an estimation of the sound source power distribution within a lightning flash, by compensating for propagation effects. Acoustics is therefore a unique observation means for evaluating lightning energy distribution both within and below the thundercloud. Using a thunder database recorded in the (1–100) Hz frequency range during two observation campaigns in Southern France in 2012 and 2018, the vertical repartition of thunder power is investigated statistically over a significant number of flashes, with a majority of negative cloud-to-ground (CG−) events. This repartition is also discussed per sound frequency band. Rare positive cloud-to-ground (CG+) events having lead to sprites (transient luminous events above the cloud in the mesosphere) and a few, entirely intracloud discharges, are also analyzed. Acoustic data are complemented by electromagnetic very high frequency (EM-VHF [60–66] MHz range) detections by Lightning Mapping Arrays for the same events. Vertical localizations of sound and EM-VHF powers within the different thundercloud charged layers are compared. For CG− discharges however, most of the sound power is shown to be emitted along the cloud to ground plasma channels, at an average altitude around 1 km only well below the cloud.