A colleague sent me an article that addresses another possible cause of clicks or snaps heard during a close lightning flash prior to thunder arrival. The article proposes that sound can be created through the transduction of electromagnetic energy at audible frequencies to vibrations at those same frequencies in nearby objects. Essentially, the electromagnetic pulse from the current change in the lightning flash would travel at the speed of light to nearby objects. These objects, such as cars, fences and even dry vegetation would act as transducers and convert the electromagnetic energy into acoustic energy (i.e., sound). This acoustic energy would then travel at the speed of sound and be heard by video equipment or the human ear. This may also be the mechanism behind reports of sounds associated with meteors and aurora.
In the clip shown in the previous post, there does seem to be two audible snaps that correspond to two bright light pulses from the close flash. The matching of audio amplitude with the light amplitude would support the emission and conversion of electromagnetic energy to sound energy.
Here is the citation of the article.
Coleman, Timothy A., Kevin R. Knupp, John T. Tarvin, 2009: Review and Case Study of Sounds Associated with the Lightning Electromagnetic Pulse. Mon. Wea. Rev., 137, 3129–3136.
The article does also mention the alternate idea of the sound being created by corona from nearby objects as a result of the rapid electric field change generated by the close flash.
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