2023-05-24 17:44:55
published
stratosphere Balloons are recording mysterious sounds – what’s going on up there?
Solar balloons are sent 13 miles into the air to pick up sounds in the stratosphere – and the microphones pick up some unexpected sounds.
That’s what it’s about
Researchers in the USA are investigating background noise in the stratosphere.
The team uses balloons to bring microphones to great heights.
However, the research team cannot explain the origins of some sounds.
The stratosphere is the second layer of the atmosphere that surrounds the earth. At its lower level is the ozone layer, which absorbs and scatters the sun’s ultraviolet radiation. The thin, dry air of the stratosphere is where jet planes and weather balloons reach their maximum altitude, and the relatively calm layer of the atmosphere is rarely disturbed by turbulence, CNN reports.
Fascination of volcanic noise
Daniel Bowman, senior scientist at Sandia National Laboratories in the US state of New Mexico, decided during his undergraduate studies to study the noise of the stratosphere more closely. Bowman was fascinated by the low-frequency sounds that volcanoes make. The phenomenon, known as infrasound, is inaudible to the human ear and immediately fascinated the researcher.
Bowman suggested attaching infrasound recorders to balloons to record the volcanic sounds. But then he and his advisor realized that nobody had tried attaching conventional microphones to stratospheric balloons in half a century – and he and his team wanted to change that.
Balloons can get microphones about twice as high as commercial jets could. In the stratosphere, they record a variety of different sounds.
IMAGO/Panthermedia
The balloons that Bowman and his team use are very simple in construction: they are made of the simplest materials that are available in hardware stores. (icon picture)
IMAGO/Reporters
Explosions, thunder, sea waves
Balloons can get microphones about twice as high as commercial jets could. “With our balloons, we’ve recorded chemical explosions, thunder, ocean waves, propeller planes, city sounds, rocket launches, earthquakes, and maybe even freight trains and jet planes,” Bowman says.
However, the research team could not explain some sounds: “We also recorded noises whose origin is unclear.” The results were presented at the 184th meeting of the Acoustical Society of America in Chicago.
Mysterious crackling
A recording released by Bowman of a Nasa balloon circling over Antarctica contains infrasound from crashing ocean waves that sounds like a constant sigh. However, other noises such as crackling and rustling are of unknown origin.
The balloons that Bowman and his team use are very simple in construction: they are made of the simplest materials that are available in hardware stores. Plastic sheets and adhesive strips are mainly used. Charcoal powder is spread inside the balloons, which heats the inside of the balloon when exposed to the sun. The air in the balloon expands and becomes less dense than the surrounding air. The balloon thus rises into the sky and enters the stratosphere.
Balloons fly hundreds of kilometers
Researchers used GPS to track their balloons because they can travel hundreds of miles and land in awkward places. “There are many flights with signals whose origin we do not understand,” says Bowman. “They are certainly of mundane origin, perhaps a turbulence, a distant severe storm, or a human object like a freight train – but it’s sometimes hard to tell what’s going on because we don’t have additional data.”
“I’ve been doing this for about ten years now, and the fact that there are mysterious sounds that I don’t understand is disturbing,” says the naturalist.
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