Science

Aiming powerful low-frequency sound waves at clouds could help to increase rainfall

Could we SHAKE rain out of the sky? Aiming powerful low-frequency sound waves at clouds could help to increase rainfall and alleviate droughts, scientists say

  • Researchers use low-frequency sound waves to ‘excite’ water vapour particles
  • The sound causes the particles to vibrate and come together as larger droplets
  • This then allows the larger droplets to fall as rain and increase rainfall levels
  • The team say a test in 2020 saw rainfall increase by as much as 17 per cent

Low-frequency sound waves aimed at a cloud could help to increase rainfall and alleviate drought in otherwise dry areas, according to a team of Chinese scientists.

Researchers from Tsinghua University in Beijing fire sounds at clouds using a frequency of about 50 herts – barely perceptible to human ears – at 160 decibels.

Study author Professor Wang Guangqian said sound waves ‘excite the cloud’ and vibrate it – this leads to a greater probability of water particles colliding and coming together – creating larger droplets and a greater chance of rainfall. 

The team discovered that there were significantly more water droplets in the cloud after they fired their device – which is about as loud as a running jet engine. 

Wang and colleagues believe that this new technology could bring new and greater levels of rainfall to areas of the world that suffer from drought.

Study author Professor Wang Guangqian said sound waves 'excite the cloud' and vibrate it - this leads to a greater probability of water particles colliding and coming together - creating larger droplets and a greater chance of rainfall

Study author Professor Wang Guangqian said sound waves ‘excite the cloud’ and vibrate it – this leads to a greater probability of water particles colliding and coming together – creating larger droplets and a greater chance of rainfall

Tibetan Plateau, also known in China as the Qingha. Low-frequency sound waves aimed at a cloud could help to increase rainfall and alleviate drought in otherwise dry areas, according to a team of Chinese scientists

Tibetan Plateau, also known in China as the Qingha. Low-frequency sound waves aimed at a cloud could help to increase rainfall and alleviate drought in otherwise dry areas, according to a team of Chinese scientists

‘EXCITING CLOUDS’ TO MAKE IT RAIN 

The team used a diesel engine to compress air at sea level that is then fired as sound at a cloud. 

The sound was at frequencies between 50 and 160 hertz and at up to 160 decibels in volume at sea level.

The sound – 30 decibels by the time it reaches the cloud 3,300ft up – acts to vibrate the cloud.

This causes smaller particles of water vapour to oscillate and merge.

As the particles move faster and come together they form larger water droplets that can fall as rain.

In their study – rainfall increased by between 11 and 17 per cent surrounding the experiment. 

During a weather manipulation experiment using the sound wave technology on the Tibetan Plateau in 2020 – they recorded a 17 per cent increase in rainfall.

China has about 20 trillion tonnes of atmospheric water vapour – but only 20 per cent falls as rain naturally to the ground – and at uneven rates across the country.

Wang said the amount that falls as rain in the western regions is even smaller than the national average of 20 per cent, inspiring him to find a way to ‘trigger rain’.

In a paper published in the journal Scientia Sinica Technologica, the team say the sound energy technology is changing cloud physics. 

Wang said that unlike other technologies designed to ‘make it rain’, his produces no chemical pollution, requires no ‘airborne vehicles such as aircraft or rockets’. 

He said future versions could even be developed to be controlled remotely at a very low cost base – making it more viable for more remote and inaccessible areas.

‘There is no chemical pollution or dependence on airborne vehicles, and it can be remotely controlled at low cost,’ Wang wrote in his paper.

According to a report in the South China Morning Post, critics have said the sound method could be damaging to wildlife living in areas where it operates.

It is about the same volume as an operating jet engine, but most humans will never hear it as the frequency of the sound is outside human hearing range – for most. 

While the frequencies it operates – 50 to 160 hertz – is imperceptible to most human ears, it could be picked up by wildlife and disturb their natural rhythms.  

Wang and colleagues believe that this new technology could bring new and greater levels of rainfall to areas of the world that suffer from drought. Stock image

Wang and colleagues believe that this new technology could bring new and greater levels of rainfall to areas of the world that suffer from drought. Stock image

Wang currently uses a diesel engine to produce the sound – it is capable of compressing air at sea level and using it to fire sound at the clouds.

While they are blasting out at 160 decibels at sea level – by the time they reach the clouds 3,300ft up – the volume drops to 30 decibels due to the reduced pressure.

They used radar signals to measure the water droplets inside the clouds before and after firing their device – and while we don’t have figures – they claim there were ‘significantly more water droplets formed’ after the blast of sound.

The increase is thought to be caused by smaller particles oscillating and merging into larger ones which are then large enough to come down as rainfall.

Within a radius of 1,600 feet from the sound generator rainfall increased by between 11 and 17 per cent, according to Wang and his colleagues.

‘The trigger and periodic effect of the acoustic waves on the cloud are proposed to be the key responses of acoustic atmospheric interference,’ Wang wrote.

‘This study is important to further research on atmosphere interference technology based on low frequency strong sound waves.’

However, not everyone believes in the findings.

Speaking anonymously to South China Morning Post, a researcher from the Chinese Academy of Sciences said the experiment would need to be replicated many many times to gather data.

The person said there was no real evidence to support the idea that rainfall was linked to sound, adding that ‘the subject remains more myth than science’.    

The findings have been published in the journal Scientia Sinica Technologica. 

CLOUD SEEDING: MODIFYING THE WEATHER TO MAKE IT RAIN 

The primary goal of cloud seeding technologies is to make it rain – that is increase the amount or type of precipitation that falls from a cloud.

It is a technology that was first proposed in 1891 by Louis Gathmann – who suggested shooting liquid CO2 into rain clouds would cause them to rain.

Over the past century dozens of research teams and individuals have chased the holy grail of rainfall manipulation.

The most common form of cloud seeding involves adding chemicals to the cloud – often silver iodide – in an attempt to trigger a natural reaction.

There are questions over whether this is actually effective, still very much the subject of much academic debate.

Many say any effects seen from cloud seeding are outweighed by the negative impact on the environment surrounding the cloud that has been seeded.  

More recently there have been a number of attempts to use alternative methods beyond chemicals as a way to trigger rainfall.

This included an electronic mechanism in 2010 that fired infrared laser pulses in the air above Berlin – inside a cloud chamber.

The goal was to see if the pulses would encourage atmospheric sulphur dioxide and nitrogen dioxide to forn particles that active seeds naturally.

As part of the experiment the volume of condensed water droplets inside the clouds increased by half – but further work was needed to see any impact on rainfall over time.

The latest seeding experiment, by Chinese researchers, used sound waves.

The goal was to to stimulate the water droplets within the cloud, causing them to vibrate and come together so the larger droplets could fall as rain.

The team claimed a 17 per cent increase in rainfall surrounding the sound generator during an experiment. 




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