Wednesday, September 15, 2021

Yes, lightning really does strike upwards

Just recently, a friend was trying to convince a skeptical me that, when lightning strikes, it strikes from the ground UPWARDS, not, as most people usually think, from the heavens down the the ground.

Well, we had a humdinger of a thunderstorm last night, and one of the video shots in particular, may have finally convinced me. The video in question is the one about halfway down that page, by Aleksander Onishchuk, and the point is that it is slowed down. The slow motion lightning strike clearly shows the lightning proceeding from the CN Tower upwards.

Actually, it's not quite as simple as that (of course it's not!) This NASA page explains that cloud-to-ground lightning first traces several paths of negative charge downwards in a series of "spurts", searching for the path of least resistance, although this is largely invisible to us here on the ground, because each one is not that bright. Then, because opposites attract, the generally positively-charged ground sends out a "streamer" up along the best path it found. When these two paths meet, a "return stroke" shoots upwards into the sky, and it is this return stroke, much brighter than the initial spurts, that we actually see. Here is another slowed down video to show the process.

So, yes, technically an upwards flash, but, as the whole thing happens within a few thousandths of a second, it really looks like a stationary flash of light, happening all at once. And, because the whole thing is initially generated up in the clouds, we tend to think of it as a downwards strike from the cloud to the ground

Imcidentally, the other video on that page that is well worth watching is the one by Dilshad Berman, if only for the young lady's unadulterated joy at seeing not one but five (five!) lightning bolts hit (or emit from) the CN Tower.

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