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1:57pm on Saturday, 30th September, 2006:

Power Shower


It rained so heavily this morning that it woke me up.

One of those questions I've been meaning to research for many years but have never quite got round to is why rain comes down at different speeds. I can see how low clouds would produce raindrops that moved slower (as they wouldn't have reached terminal velocity) but which would be bigger (as they wouldn't have been worn down by friction with the air). High clouds would produce rain that would be going faster, but if it were too high then it would lose volume to air resistance which would become more and more of a factor in slowing it down.

The rain this morning was as if it were being thrown from the sky, though, as if there were some kind of horizontal vortex that was whipping it up then spitting it out at high speed. Downdraughts do exist as weather features, and when monster hailstorms are forming they can be tumbled around for 15 or 20 times before being released to damage your greenhouse and set off your car alarm. Could that happen with rain, though? The stuff this morning was splashing a foot high — it certainly gave the impression of having had extra velocity imparted to it, rather than simply relying on gravity and low air resistance to do its job. I wonder what the fastest impact you can get from raindrops is, in theory? Maybe if it started off as hail but melted on the way down, that could do it.

Yes, I'm British; I talk about the weather, OK?

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Copyright © 2006 Richard Bartle (richard@mud.co.uk).