What’s the physics behind this lightning strike ?

[TroutMan]

First, you can’t really tell anything about the strike from the video, because the strike moves much faster than the frame rate of the camera. It’s a very incomplete look at what really happened.

I’ll link to an explanation of a lightning strike I made in a recent thread. So you are correct that the discharge you see rises from the ground, but it doesn’t terminate at the umbrella.

@TroutMan

Because it’s a fun fact, not because I’m trying to be pedantic: the lightning actually rose 10-15m away from you, not fell. A typical lightning strike is initiated by a flow of negative charge down from the cloud. As it approaches the ground (50-100 m), a positive streamer reaches up and meets the downward ladder, at which point a return stroke goes from ground to sky. This return stroke is what you see.

This video uses ridiculously fast frame rates so you can actually see how a strike propagates.

@Walken_After_Midnight

Check out the lightning strike when the video starts playing. Pause the video and use the “,” and “.” keys to move backwards and forwards, frame by frame. With this strike, one can visibly see, in one frame, the return stroke starting from the ground. According to Wikipedia, “the rate at which the return stroke current travels has been found to be around 100,000 km/s.”