The data they collected showed that the stratosphere sounds quite different than the surface of Earth. On the ground, infrasound sensors pick up signals that have been deflected by winds on their way down, but the balloons floated above those winds – they recorded signatures of turbulence in other parts of the atmosphere, and infrasonic sounds of marine storms.
However, Bowman says that many infrasound signals from the stratosphere didn’t have an obvious origin. He presented the work at a meeting of the Acoustical Society of America in Chicago, Illinois, on 11 May.
These mysterious signals could be related to types of atmospheric turbulence that have never been recorded before, but infrasounds in the stratosphere have only rarely been explored before so it is hard to make educated guesses, says Bowman.
