Localization and quantification of the acoustical power of lightning flashes

Abstract

Lightning is an ubiquitous source of infrasound, and an essential climate variable. To observe lightning flashes, thunder measurement efficiently complements electromagnetic methods. Using acoustical arrays, time delays between sensors inform on the direction of sound arrival, while the difference between emission time and sound arrival provides the source distance. Combining two allows a geometrical reconstruction of lightning flashes viewed as sets of sound sources. The measured sound amplitude can also be back-propagated, compensating for absorption and density stratification. This allows us to evaluate the acoustical power of each detected source and the total power of an individual flash. This methodology has been carried out to analyse data from two campaigns in Southern continental France in 2012 and in Corsica in 2018. In Corsica, power from reconstructed sources could also be forward-propagated towards several isolated microphones and compared to measurement there, providing an additional validation of the method. A large number of events from the two campaigns has been analysed, including negative and positive cloud to ground discharges and intra-cloud ones. The analysis outlines the method efficiency, and the strong variability of lightning as sound sources, in terms of both power spatial distribution and global values.