Deadly tornadoes could soon be detected before they hit the ground after scientists discovered a series of mysterious rumblings.

Researchers have worked out that storms emit noises which are undetectable to the human ear.

Microphones pick up the anomaly shortly before the tornado touches the floor until shortly after it leaves.

And while they have been unable to determine exactly what causes the noises, they have narrowed it down to a number of factors which could lead to a dramatic improvement in warnings.

The new system involves three domes arranged in an equilateral triangle, each with a microphone capable of picking up low-frequency sounds sealed inside.


Image: Scientists say the system could significantly improve warnings

This setup allows them to filter out sounds from normal wind and work out which direction the twister is travelling, while the signal itself offers an idea of the tornado's size.

Dr Brian Elbing, of Oklahoma Condition University, part of the research team, said: "Infrasound doesn't need line of sight like radar, so there is hope that this could significantly improve warnings in Dixie Alley where most deaths [from tornadoes] occur."

Dr Elbing and his team recently reported a case in Oklahoma in which they were able to pick up audio clues eight minutes before the twister formed, with a clear signal detected four minutes before it hit the ground.

They say this was vital as the tornado was not picked up by radar.

And while the Oklahoma tornado was only 12 miles from the setup, Dr Elbing said once the sound signal was better understood, the technique could be used to detect one from over 100 miles.

Dr Harold Brooks, a tornado expert at the US National Oceanic and Atmospheric Administration, said: "At this point it is a really intriguing thing, but there is a lot more work that needs to be done in terms of a relatively large scale experiment to actually test it."