Tom Choularton: Can we really control the weather?
Friday 06 November 2009
Recently both Russia and China have claimed to be able to use cloud seeding to increase rainfall and snowfall, or change the location of where it falls. In the past, snow-making experiments have been carried out in North American ski resorts in the past with little evidence of success. So how have the Russian and Chinese scientists achieved this feat and what evidence is there that it is in fact due to cloud seeding?
The seeding method used is to add tiny particles of silver iodide to the clouds and there is solid science behind this method. At temperatures a few degrees below zero degrees centigrade, clouds consist mainly of supercooled water droplets. These clouds can be quite stable, but silver iodide has an ice-like structure and it will cause a few of these water droplets to freeze. Once you have ice particles mixed in with the supercooled droplets, these crystals grow rapidly to form snowflakes, causing the cloud to precipitate. The effect is that the water is released from the cloud.
This form of cloud seeding is not new - It has been used since the 1960s in the western USA to try to make rain, as well as being used in Israel in the past. The difficulty is it has always been hard to prove whether the cloud would have rained naturally if it hadn’t been seeded. Even tests where seeding lots of clouds takes place and un-seeded clouds are used as controls haven’t produce statistically significant results. Therefore, if it works at all it can’t be hugely effective.
So although the underlying science behind the technique seems to be sound, what is presently wrong with the technique?
We at Manchester University have been flying the UK atmospheric research aircraft in clouds that may or may not produce rain or snow, to investigate effective conditions for cloud seeding in different environments. Last winter, we were flying in low clouds with temperatures just below freezing and we did not manage to seed any of the clouds and they were left entirely natural. We found that on many occasions these clouds already contained a mixture of supercooled water droplets and ice crystals, and the ice crystals were growing and falling out as snow. However this wasn’t on account of our seeding efforts.
Interestingly, the origin of these ice particles seemed to be due to freezing caused by particles of dust, ash and organic material carried up into the cloud (some of which can be attributed to pollution). We found that once some ice is formed there is a powerful secondary ice particle production process which occurs at about minus six degrees Celsius. This produces lots of ice crystals, meaning that even if the clouds had been seeded with silver iodide, it would have had little effect. Snow was being produced very effectively and quite naturally anyway.
Interestingly, when we flew higher into clouds, well above the ground and away from a lot of the particulate material, we did find clouds at colder temperatures, as cold as -30C that were made up entirely of supercooled water droplets so maybe seeding these would have had an impact.
So does cloud seeding work? Well our studies indicate that in many clouds that produce lots of snow it does not seem to, because there is plently of natural ice already. However, I don’t completely dismiss it as a method – I do believe it’s possible it can be effective in some clouds in the right conditions and at the right temperature. Nevertheless, I feel some of the stronger claims made recently need further verification, before we herald this as a breakthrough in scientists’ ability to manipulate natural weather cycles.
Professor Tom Choularton is Head of the School of Earth, Atmospheric & Environmental Sciences is supporting the Science: [So what? So everything] campaign, which aims to highlight the leading UK science research that will shape the future of Britain.
- 2 Disney heiress Abigail disowns her share of family profits in West Bank company
- 3 The secret report that helps Israel hide facts
- 4 Israel's propaganda machine is finally starting to misfire
- 5 'Hello mum, this is going to be hard for you to read ...'
Sally Farmiloe dead: Howards' Way actress, and former mistress of Jeffrey Archer, dies aged 60
Russell Brand accuses FOX News anchor Sean Hannity of terrorism after aggressive Israel-Gaza debate
Pope Francis issues top 10 tips for happiness – including don’t try to convert other people
Sabina Altynbekova, the girl branded 'too good looking' for volleyball, says social media obsession with her is a 'bit much'
Justin Bieber posts Instagram photo of Orlando Bloom crying after Ibiza fight 'over Miranda Kerr'
The secret report that helps Israel hide facts
Land for gas: Merkel and Putin discussed secret deal could end Ukraine crisis
Woman and two children killed by mob in riots over 'blasphemous' Facebook post in Pakistan
A day in the life of Vladimir Putin: The dictator in his labyrinth
Putin is 'thuggish, dishonest and reckless', says British ambassador to US
Richard Dawkins tweets: 'Date rape is bad, stranger rape is worse'
- < Previous
- Next >
£35000 - £40000 per annum + competitive: Progressive Recruitment: .Mid Level V...
£40000 - £45000 per annum + Competitive Benefits: Progressive Recruitment: Dig...
£40000 - £50000 per annum + Car, Medical, Fuel + More!: Progressive Recruitmen...
£50000 - £60000 per annum + benefits: Progressive Recruitment: An absolutely o...