]> SQUAREWHEELS.org.uk – Lightning & thunder


Lightning & thunder

This page was created on 9 August 2008, and
last modified on 10 February 2011.

During a short but fierce electrical storm over east Berkshire on 27 July 2008, I stood at an open window and took some video-clips with my Canon PowerShot S2 camera. I was fortunate enough to record this exciting sequence—described through the frame-captures below—and the accompanying sound-effect.

Lightning

The six photographs below are consecutive frames from the video-clip. The camera took frames at a rate of one per one-thirtieth of a second.

[PHOTO: sky before lightning: 41kB]

Above: The sky is dark before the lightning.

[PHOTO: electrical activity nearby: 39kB]

Above: A partial upstroke appears to be originating from just a few yards away, but (luckily for me!) the main bolt did not end up striking here in consequence.

[PHOTO: sky white with lightning: 25kB]

Above: The whole sky is now fantastically bright white, possibly as the cloud immediately above reflects numerous upstrokes or inter-cloud strokes; individual raindrops can be seen lit by the flash against the darker backdrops of the nearby buildings and trees.

[PHOTO: forked lightning: 40kB]

Above: This is the classic “forked lightning” as the electrical potential between cloud and ground reaches the critical point and an ionized path through the air is created.

[PHOTO: lightning bolt established: 28kB]

Above: The downstroke now travels between cloud and ground, following the ionized path which had just been “found” by the forked lightning. This is the actual lightning-bolt running to earth, and as can be seen by its brightness and thickness, it is carrying a huge current: it is this part (and not that depicted in the previous three frames) which kills people outright, sets fire to cathedrals, blows trees to pieces, et cetera.

[PHOTO: sky after lightning: 33kB]

Above: Another 130 second later, the sky is dark and all is quiet… until, of course, the thunder-clap!

Thunder

Approximately 2.2 seconds later came the start of the thunder-clap, which was of the type we like to refer to as sheds, because it resembles the noise we like to assume would be made by a load of wooden sheds being demolished! My camera was recording sound at CD-quality (44.1 kHz) but its tiny microphones and automatic recording-level mean that the result isn’t as spectacular as it should be, through a drastic reduction in dynamic range. Still, you should get the idea:

Thunder-clap (mp3, 17″, 271kB).

The rain really was just getting started as this clip progressed.

Discussion

I don’t claim to know a great deal about the electrical phenomena described here, and so particularly welcome any corrections or comments.