Lightning never strikes twice: True/False?

So if the old tree receives a bolt from above, is it okay to shelter underneath, safe in the knowledge that it won’t be struck again? Absolutely not. This may be a useful metaphor, but it just isn’t true in reality.

The falsehood here isn’t immediately obvious: lightning is a powerful and destructive force of nature quite capable of blowing a tree to bits and shattering rock. After such a dramatic event it seems quite plausible that surrounding air may be somehow sapped of the ability to sustain another bolt from above. But it isn’t so.

A lightning strike is a complicated thing. It begins when a cloud builds up a high electric charge relative to the ground. Eventually the difference is so great that the normal insulation of the air breaks down and a leader darts down from the cloud above, snaking around regions of charged air (this is what produces the forked appearance). When this so-called dart leader comes close enough to the ground another bolt jumps up to meet it, forming a complete path from cloud to ground.

Once the two meet up the charge flows along this conduit. Within a single flash of lightning there will be one or more strikes, sometimes scattered a little, sometimes all on the same spot. And there is nothing to stop strikes in subsequent flashes hitting the same place again.

In nature any high points, including hills, isolated trees, idiots with umbrellas and the like can attract lightning to themselves because they are just that little bit closer to the clouds and so have earlier opportunities to reach out to descending dart leaders. Lightning rods work this way too, being nothing more than artificial high points. Even though the path of lightning through the atmosphere is tortuous and unpredictable, the strike point is less so.

The moral is clear — if you don’t want to be struck by lightning (once, let alone twice), don’t become a high point in a thunderstorm. Lightning can strike twice, but it has at least as much to do with altitude as with luck.

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