Mysterious unidentified sound recorded in the stratosphere

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To record sounds in the Earth’s stratosphere, a giant solar balloon was sent 70,000 feet into the sky, and microphones picked up some unexpected sounds.

According to NASA, the stratosphere is the second layer of the Earth’s atmosphere, and its lower layer contains the ozone layer, which absorbs and scatters the sun’s ultraviolet radiation. The thin, dry air of the stratosphere is where jets and weather balloons reach their highest altitudes, and the relatively calm atmosphere is rarely disturbed by turbulence.

Daniel Bowman, principal scientist at Sandia National Laboratories in New Mexico, said his exposure to the low-frequency sounds produced by volcanoes during his graduate studies inspired him to explore the soundscape of the stratosphere. became. This phenomenon, known as infrasound, is inaudible to the human ear.

Bowman and his friends had previously successfully built their own solar balloon, placing a camera on a weather balloon to “take pictures of the black sky above and the earth far below.”

He suggested attaching an infrasound recorder to the balloon to record the sounds of the volcano. But then he and Jonathan Rees, an adviser at the University of North Carolina at Chapel Hill, said, “For half a century, I realized that no one had tried to put a microphone in a balloon in the stratosphere. We turned to exploring what we could do,” says Bowman. He said. Rees is a professor of Earth, Marine and Environmental Sciences, studying seismology and volcanology.

Balloons can carry sensors twice as high as commercial jets can fly.

“Our solar balloon recorded surface and subsurface chemical explosions, lightning, ocean wave crashes, propeller planes, city sounds, suborbital rocket launches, earthquakes, and perhaps even freight trains and jets. ‘” Bowman said in an email. “We also recorded sounds of unknown origin.”

The findings were shared Thursday. 184th Annual Meeting of the Acoustical Society of America (Chicago).

A recording Bowman shared from a NASA balloon that orbited Antarctica contains infrasounds of crashing ocean waves that sound like continuous sighs. However, the cause of other crackling or rustling sounds is unknown.

In the stratosphere, “some flights are emitting a mysterious infrasound signal several times an hour, whose origin is completely unknown,” Bowman said.

Bowman and his collaborators have worked with NASA balloons and other flight providers, but they prefer to build their own balloons, which are about 19.7 to 23 feet (6 to 7 meters) in diameter. I decided to.

Materials are available at hardware and firework stores, and balloons can be assembled on the basketball court.

“Each balloon is made from paint plastic, shipping tape and charcoal dust,” Bowman said in an email. “It costs about $50 to build, but can be built in about 3.5 hours with a team of two. Just take it out into the field on a sunny day, fill it with air, and carry a 1-pound load to about 70,000 feet. I can.”

Charcoal powder is used inside to darken the balloon, and when the sun hits the black balloon, it warms the air inside and makes it more buoyant. A cheap and easy DIY design allows researchers to release multiple balloons to collect as much data as possible.

“It’s really a group of high school students who can use the school gymnasium.” you can make a solar balloonThere’s even a mobile phone app called RedVox that can record infrasound,” Bowman said.

Bowman estimates that between 2016 and April of this year, dozens of solar balloons were launched to collect infrasound records. Originally designed to monitor volcanoes, microbarometers were attached to balloons to record low frequency sounds.

Because balloons can travel hundreds of miles and land in inconvenient locations, the researchers used GPS to track them.

The longest flight to date was 44 days in a NASA helium balloon, recording 19 days of data before the microphone’s battery died. Solar balloon flights, on the other hand, last about 14 hours during the summer and tend to land when the sun goes down.

The benefits of the high altitude that balloons can reach mean lower noise levels, greater detection range, and access to the entire globe. But balloons are also a challenge for researchers. The stratosphere is a harsh environment with extreme temperature fluctuations between hot and cold.

“Solar balloons are a little sluggish, and I’ve had some balloons crash into bushes while trying to launch,” Bowman said. “I had to hike through canyons and over mountains to carry my stuff. and even flew for a full day.”

Lessons learned from multiple balloon flights have eased the process somewhat, but the biggest challenge for researchers now is identifying the signals recorded during the flight.

“There are a lot of flights that send out signals that we don’t know the source of,” Bowman said. “They are arguably mundane and could possibly be a mass of turbulence, a distant violent storm, or some kind of human object like a freight train. But the lack of data suggests that what Sometimes it’s hard to tell what’s going on.”

Geophysicist Sarah Albert of Sandia National Laboratories investigated the high-altitude “sound channels” (conduits that carry sound through the atmosphere over long distances) that Bowman is studying.she The recording shows a rocket launch unidentified rumors such as

“Sound can be trapped in a channel and reverberating around until it’s completely garbled,” says Bowman. “But it’s not yet clear whether it’s fairly quiet up close (like part of the turbulence) or loud in the distance (like a distant storm).”

Bowman and Albert continue to investigate the airborne acoustic channel, trying to figure out where the stratospheric noise is coming from and why some flights record it but others don’t.

Bowman hopes to understand the stratospheric soundscape and reveal important features such as seasonal and spatial variations.

Helium-filled versions of these balloons may one day be used for: Explore other planets like Venuscarrying scientific instruments over or in the planet’s clouds for several days as test flights for larger and more complex missions.