Friday, 3 July 2015

Mega Storm

The amazingly warm and humid weather the other day culminated in the biggest thunderstorm I have ever witnessed. Normally one has to wait several minutes between lightning flashes. This one was constant flashes of cloud to cloud lightning and a steady continuous rumble of thunder.

Lightning Clouds. Courtesy of Louise Miller @ Fox Tail Photography

When you consider that a lightning strike is in the order of a billion (1e10+9) Joules and there was approximately one flash per second for the half hour we watched it then that's an amazing amount of power. Even conservatively, 2 seconds per strike at 500e+6J per strike gives 0.9GW of power. Drax power station produces 4GW. That's one storm producing 1.5% of the UK's electricity supply. This is nowhere near as good as one of xkcd's "What If" analyses but it proves the point)

It was incredibly localised too; a friend who lives a couple of miles down the valley reported a bit of horizontal rain but no hail and only very distant thunder.

The most amazing bit were the hailstones that came firing out of the sky, hitting the patio and bouncing a metre into the air from the impact. Louise went out to gather some for a photo, the biggest one measuring around 40mm across. I've never seen hail that big before and I certainly didn't expect it in this country.

Hailstones. Courtesy of Louise Miller @ Fox Tail Photography 

I'm interested how it appears to be comprised of different layers; an opaque inner core with a clear outer layer. This is similar to the different types of ice that form in the mountains with different temperatures and freeze/thaw cycles.

When you consider the processes involved in making a hailstone, that it must have been round and round inside the cumulonimbus several times to build up that much ice it makes it all the more impressive. What sort of vertical wind speed must be required to drive these upwards through the cloud? All of this driven by temperature differences in a fundamentally chaotic climate system caused by an unbridled nuclear reactor millions of miles away.

I'm reminded about the story in The Cloudspotter's Guide about William Rankin, a jet fighter pilot who ejected from his aircraft above a thunderstorm and survived a 40 minute fall through the centre of the thundercloud. He must have felt like he was falling into another dimension.

This and the dents on the roofs of all the cars is a reminder of how amazing and powerful nature is!

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