Red sprites

Transcript

Craig Rodger

We used to think we understood lightning, and to some extent, we do understand lightning, but relatively recently, we’ve started to realise that there are a whole lot of things going on in the lightning discharge process that we don’t know about, and one example is anti-matter production in lightning.

But another example is that we think of lightning as being something that happens in the thunderstorm and goes down to the ground or possibly is a flash inside the thunderstorm itself. We’ve started to realise that there’s also upward lightning – lightning that’s occurring at very high altitudes – and there’s a whole lot of different variants of this upward lightning, and they have nice exotic names.

The first one that we discovered was called a red sprite. You could call it upward-going lightning, but when we first discovered red sprites, these pulses – big flashes of pink in the sky high above thunderstorms – they weren’t sure what they were. And rather than calling them upward lightning, which says you understand what they are immediately, the suggestion was made by a researcher from Alaska that we should give it a sort of meaningless name while we went away and tried to work out what they actually were.

And he had just recently watched a Shakespearean play where there were sprites as characters, and he thought this was a lovely name. And the sprites are sort of pinkish-reddish colour, and so we call them red sprites.

And they now have – let’s call them friends – there’s other varieties of upward lightning like jets, elves. Somebody has put forward the idea of a troll, but that name hasn’t taken off yet. Essentially, they’re varieties of high-altitude lightning. They tend to be bigger than the low-altitude lightning that we’re used to, but that’s really just a consequence of the fact that the density of the atmosphere up there is much lower.

There is essentially a one-to-one relationship between lightning and red sprites. A powerful lightning discharge can produce a red sprite.

And as far as we can tell, you always need lightning to produce a red sprite.

Acknowledgements: Associate Professor Craig Rodger, University of Otago, Department of Physics NASA Goddard Space Flight Center Night-time thunderstorm footage courtesy Nathan Boor, Aimed Research, Lightning over rainy streets courtesy of Sterling Coffey A Midsummer Night’s Dreampaintings by Arthur Rackham (1867–1939) Diagram of blue jets and ELVE, courtesy of Abestrobi