Rumbling In The Stratosphere

[Yithian]

Mysterious rumblings were recorded in Earth’s stratosphere​

By Ashley Strickland, CNN
Updated 3:33 PM EDT, Thu May 11, 2023

Giant solar balloons were sent 70,000 feet up in the air to record sounds of Earth’s stratosphere — and the microphones picked up some unexpected sounds.

The stratosphere is the second layer of Earth’s atmosphere, and its lower level contains the ozone layer that absorbs and scatters the sun’s ultraviolet radiation, according to NASA. The thin, dry air of the stratosphere is where jet aircraft and weather balloons reach their maximum altitude, and the relatively calm atmospheric layer is rarely disturbed by turbulence.

Daniel Bowman, principal scientist at Sandia National Laboratories in New Mexico, was inspired in graduate school to explore the soundscape of the stratosphere after being introduced to the low-frequency sounds that are generated by volcanoes. Known as infrasound, the phenomenon is inaudible to the human ear.

Bowman and his friends had previously flown cameras on weather balloons “to take pictures of the black sky above and the Earth far below” and successfully built their own solar balloon.

He proposed attaching infrasound recorders to balloons to record the sounds of volcanoes. But then he and his adviser Jonathan Lees of the University of North Carolina, Chapel Hill, “realized that no one had tried to put microphones on stratospheric balloons for half a century, so we pivoted to exploring what this new platform could do,” Bowman said. Lees is a professor of Earth, marine and environmental sciences who researches seismology and volcanology.

“On our solar balloons, we have recorded surface and buried chemical explosions, thunder, ocean waves colliding, propeller aircraft, city sounds, suborbital rocket launches, earthquakes, and maybe even freight trains and jet aircraft,” Bowman said via email. “We’ve also recorded sounds whose origin is unclear.”

The findings were shared Thursday at the 184th Meeting of the Acoustical Society of America in Chicago.

A recording shared by Bowman from a NASA balloon that circled Antarctica contains infrasound of colliding ocean waves, which sounds like continual sighing. But other crackles and rustling have unknown origins.

[...]

“There are many flights with signals whose origin we do not understand,” Bowman said. “They are almost certainly mundane, maybe a patch of turbulence, a distant severe storm, or some sort of human object like a freight train — but it’s hard to tell what is going on sometimes due to the lack of data up there.”

Sarah Albert, a geophysicist at Sandia National Laboratories, has investigated a “sound channel” — a conduit that carries sounds across great distances through the atmosphere — located at the altitudes Bowman studies. Her recordings have captured rocket launches and other unidentified rumblings.

“It may be that sound gets trapped in the channel and echoes around until it’s completely garbled,” Bowman said. “But whether it is near and fairly quiet (like a patch of turbulence) or distant and loud (like a faraway storm) is not clear yet.”

Continued (including sound samples):
https://edition.cnn.com/2023/05/11/world/stratosphere-sounds-scn/index.html