At an altitude of more than 21,300m in the Earth’s stratosphere, scientists discovered “mysterious” sounds that the human ear cannot hear .
According to scientist Daniel Bowman of the Sandia laboratory in New Mexico (USA), in the Earth’s stratosphere exists a type of sound at low frequencies that the human ear cannot hear (also known as infrasound – more than 16 Hz).
About the stratosphere – this is the second layer of the Earth’s atmosphere (at altitudes between 16,000 m and 52,000 m) and directly below it is the ozone layer that absorbs and scatters the sun’s ultraviolet radiation. The thin, dry air of the stratosphere is where jets and weather balloons reach their maximum altitudes, and the relatively calm atmosphere is rarely disturbed by air turbulence.
Balloons were used by Bowman and his colleagues to record sounds in the Earth’s stratosphere. (Photo: CNN)
Bowman and his colleagues had previously used weather balloons with cameras to record atmospheric sounds from Earth to space and back. Now their balloons are integrated with more devices with solar batteries that allow them to operate longer.
Bowman’s experiment is also an experiment to record sound in the stratosphere that scientists have carried out after 50 years. Using a balloon with multiple sensors at the same time will give a more accurate result than using a meteorological aircraft.
Scientist Bowman also shared, he has performed many experiments to record the sound of natural and man-made phenomena such as the sound of a volcanic eruption, thunder, ocean waves, propeller planes, etc. sounds of the city from the air, a rocket launch, an earthquake… Sometimes Bowman also recorded sounds of unknown origin in the air.
The advantage of altitude gained by the balloon means lower noise levels and increased recording range – just like we can hear the voice of the Earth. However, the use of hot air balloons in aerial tests also poses challenges for scientists because the stratosphere is a harsh environment because of constant temperature fluctuations between hot and cold.
“Solar balloons are a bit slow and not every launch is successful,” Bowman said.
This view from one of the Sandia Laboratory’s solar-powered balloons was taken at about 21,000m above the Earth’s surface.
However, Bowman said it is difficult to determine the source of the low-frequency sounds in the stratosphere , which could be man-made, such as when a jet flies over the area, an arrow launch. fire, noise when cargo ships move at sea or the formation of a storm far from the test site. The source of the sound can only be determined if enough data is available.
Scientist Bowman thinks that the above sounds may have reached the stratosphere and their sound waves are bounced back and forth so many times that they are distorted compared to the original sound. According to Bowman, it is not always possible to record sound in the stratosphere even from the same location.
It was this that prompted Bowman and his colleagues to decipher the mystery of Earth’s stratospheric sounds. This will not only help in determining the seasonal changes in Earth’s atmosphere, but will also provide important data to support scientists carrying out atmospheric studies of other planets in their exploration missions. space.