“Discovering Mysterious Sounds in the Earth’s Stratosphere”

The stratosphere is the second layer of the Earth’s atmosphere, located between the troposphere and the mesosphere and starting more than 10 km above the surface of the planet. There is a process called temperature inversion, which means it warms with altitude. The lower level contains the ozone layer, which absorbs and scatters ultraviolet radiation generated by the sun.

The thin, dry air found in this layer of the atmosphere allows the movement of jet aircraft and weather balloons. Passenger planes, on the other hand, fly in the lower stratosphere, which allows them to avoid turbulence.

From the volcano to the stratosphere

Daniel Bowman, a scientist at Sandia National Laboratories in New Mexico, was inspired in college to study sounds from the stratosphere. The scientist and his colleagues had previously been taking pictures of the sky, using cameras placed on weather balloons. Then they came up with the idea of ​​using a solar balloon to study volcanoes.

They created their own model and attached infrasound recorders to it, so that they could record the low-frequency sounds coming from the volcano. Infrasound is inaudible to the human ear, but can be detected by special devices.

After some time, the scientist, along with his advisor Jonathan Lees, a professor of Earth, Marine and Environmental Sciences at the University of North Carolina at Chapel Hill, noticed that no one had used a similar solution for stratospheric balloons. They built their own objects from painting plastic, conveyor belt and coal dust with a diameter of 6 to 7 meters.

Mysterious sounds in the atmosphere

Giant solar balloons were sent into the air to an altitude of 21 km, to analyze sounds from the Earth’s stratosphere. Microbarometers, originally used by them to monitor volcanic activity, have been used to record low-frequency sounds. The scientists tracked the objects using GPS because they would travel hundreds of miles and could sometimes land in hard-to-explore locations.

As a result of the action of the microphones, sounds such as surface and underground explosions, thunder, earthquakes, sounds generated by ocean waves, planes, freight trains, rockets and sounds from the city were recorded. However, scientists have also discovered sounds whose origin is unclear.

The amazing discovery was announced this week at the 184th meeting of the Acoustical Society of America in Chicago. Footage from a NASA balloon that circled Antarctica shows infrasound created by the movement of ocean waves, but there are also strange cracklings and rustling sounds. Mysterious infrasound signals appear on the tapes several times an hour and occur only on selected flights. The source of these sounds is completely unknown.

Bowman and Albert continue to plan study unidentified sounds to determine where stratospheric rumbles come from and why some flights pick them up and others don’t. They also indicate that perhaps the helium balloons they designed could one day be used to explore other planets, such as Venus or Mars.