OT: seeding the clouds

[Scott]

I know it is possible to encourage precipitation by seeding the clouds with substances like sodium iodide or potassium iodide, from an aircraft.

A friend and I were discussing whether the Australians could have done this at the time of the bush fires. I was saying I didn't think there was much in the way of clouds in the sky at the time and my friend was saying there are always clouds if you go high enough.

I assume you would need fairly dense clouds for this to work and that the Aussies would have tried it if they could. Does anyone know about the feasibility of this?

[Chris Hogg]

Cloud seeding works, but only just, and is unlikely to produce anything like enough rain to extinguish anything as ferocious as an Ozzie forest or bush fire.

[Archibald Tarquin Blenkinsopp Esq]

Smoke seeds clouds.

Manchester used to be the rainiest place in the UK because nothing stopped the clouds coming in from the west as Liverpool just couldn't compete with the level of smoke from factory chimneys in Manchester.

AB

From the well pummelled keyboard of Archibald Tarquin Blenkinsopp Esq

[Martin Brown]

It is actually silver iodide that is the preferred method:

It works very slightly - a few percent more rain at most even if the air is close to saturation. You get clouds but not necessarily rain.

It was on one the R4 Rutherford && Fry science programs this week.

ISTR they reckoned the very best technology would get you 3% more cloud if you were lucky. US military spent a fortune on it in Vietnam.

Well worth a listen - especially if you fancy trying it...

People with more money than sense can hire cloud seeders to try and get better sunny weather for their wedding day (service starts at £100k).

[newshound]

In the dim and distant past there were pictures in, perhaps, my 1930's Childrens' Encyclopedia showing the use of large firework type rockets to disperse silver iodide into looming storm clouds. This was to make them precipitate before they reached vineyards. I think this was in Italy; certainly in a mountainous area.

[Chris Hogg]

I remember a similar picture in the Children's Illustrated Encyclopedia* (probably this,

it certainly had a red cover) although my recollection is of a French village firing an old but mighty cannon straight up into the sky, although not loaded with anything. See also in attempts to prevent hailstorms from damaging the grapes.

• there was a companion volume - Children's' Illustrated Encyclopedia of Scientific Knowledge, which had a blue cover.

[Tim Streater]

They were certainly doing this in Geneva in the late 60s. It was during some thunderstorms and I was told later that the reason was to try to prevent large hailstones forming, which would damage the vines.

[Brian Gaff (Sofa)]

Well you first of allneed the moisture to be there, and if its not how will you form clouds? The warmer the air of course the more moisture it can carry and hence as you say the higher you go with lower air pressure and colder temperatures you might find more clouds forming, but most of those which can produce rain need to be pretty close to the ground to have sufficient moisture to allow the crystals to precipitate moisture adhering to them to start making raindrops heavy enough to fall past the updraught of the thermals. I don't think it is feasible. Brian

[newshound]

Interesting. Mine was the genuine "Arthur Mee's Children's encyclopedia and it was definitely rockets. Come to think of it I am pretty sure it was to avert hail, too.

He was discussed on the radio a couple of years ago, an incredibly prolific writer, IIRC something like 50 million words (i.e. 2500 a day for his whole working life). Can't spot anything about this in Google though.

[newshound]

I was in Geneva in 1970. I certainly remember dramatic thunderstorms coming across the lake and down the valleys, I had a great view from a student tower block.

[Tim Streater]

That would be the Cité Universitaire?

[newshound]

Indeed it would. I couldn't think of the name for the moment. I was there on a three month summer course at CERN, there were also quite a lot of American students there for the summer, with a much more favourable "ratio" than I had experienced at university in the UK.

[Tim Streater]

I was there as a summer student in 1967. From my room at the Cité is also where I saw the thunderstorms and the rockets they sent up. Pretty cracking!

[newshound]

Indeed. The Americans had a pretty good firework display on the lake for the Fourth of July, and I was there for the Fetes de Geneve which, I was told, had a bigger firework display every ten years. Don't recall seeing any "storm" rockets though.

[newshound]

Did you get to meet Weisskopf?

[Tim Streater]

No, but I did meet Rubia though, a few years later (before he was DG, though). And I managed to squeeze into the Main Auditorium when Feynman visited.

[bert]

In article [e-mail]>, Tim Streater [e-mail] writes

No doubt many will remember the Lynmouth floods 1952. Just prior it had been reported the army were experimenting with cloud seeding. Denied of course when the floods happened.

From google search

"The flooding occurred on 15 August 1952, after nine inches of rain fell in the space of 24 hours. The downpour caused a wall of water to surge down from Exmoor onto Lynmouth. ... Among the theories is that the rain was caused by experiments to artificially create rain."

[Tim Streater]

That's a hypothesis, not a theory. And the same has happened a number of times since.