At first glance, it may seem that the Earth’s stratosphere is quiet and calm.
But when scientists sent weather balloons 21 kilometers above the Earth’s surface, they detected some mysterious sounds. It is written by many media, among others CNN.
The stratosphere is the second layer of the Earth’s atmosphere, which includes the ozone layer. The air is thin and dry, and the layer is rarely affected by turbulence.
Researchers punch: – I’ve never seen anything like it
Daniel Bowman, a researcher at Sandia National Laboratories in New Mexico, was inspired to explore the acoustic landscape of the stratosphere after being introduced to the low-frequency sounds generated by volcanoes.
Ultrasound is a phenomenon that the human ear cannot hear.
Bowman and other researchers have previously attached cameras to weather balloons. And they and his colleague Jonathan Lees at the University of North Carolina found that no one had attempted to put a microphone on stratospheric balloons in half a century, Bowman says.
Voice from around the world
Balloons can pick up sounds twice as loud as commercial aircraft.
“We’ve recorded on our balloons chemical explosions on Earth’s surface and burials, thunder, ocean crashes, propeller planes, city noise, rocket launches, earthquakes, and maybe even freight trains and jet planes,” Bowman says. CNN He adds:
– We also recorded sounds of unclear origin.
A mysterious sound in the Oslofjord
On Thursday, the researchers shared their findings at the 184th meeting American Vocal Society of Chicago.
In a recording Bowman shared from one of the balloons circling Antarctica, the crashing sound of infrasound can be heard — it sounds like sustained sobs.
But in the audio recording, you can also hear crackling and rustling, and the researchers aren’t sure where the sound came from.
The advantage of balloons being able to fly higher is that the noise level is lower and the balloons can record sounds from all over the world.
But balloons also present challenges for researchers.
In the stratosphere, there is a demanding climate with frequent temperature fluctuations between hot and cold.
Shoot down the spy balloon
Balloons can be a little slow, and we destroyed some of them, says Bowman.
Having gained more experience with the flight itself, the researchers’ biggest challenge now is identifying the mysterious sounds.
They are almost certainly from Earth. Maybe it’s a commotion, a powerful storm in the distance, or some kind of human object like a freight train. The researcher says it is sometimes difficult to know what is being recorded.
Sarah Albert, a geophysicist at Sandia National Laboratories, has done long research on so-called “acoustic channels” — a channel through which sound travels long distances through the atmosphere.
Among other things, it picked up the sounds of rocket launches and other unidentified sounds.
Spotted a “spy balloon” – then realized it
Albert explains that it can be difficult to perceive if the sound is in the immediate vicinity of the balloon, or if the sound is far away.
Bowman and Albert will continue to investigate what sounds are captured in the stratosphere and why only some weather balloons capture sounds.
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