There are mysterious rumblings in the stratosphere. A recent study detected infrasound signals, too low-pitched for humans to hear and which only happen a few times each hour at about 13 miles in altitude.
But these sounds were different from anything known at the Earth’s surface and what created them is a mystery.
The troposphere, where our weather happens, is awash with infrasounds that can travel great distances. These include sounds created by thunder, tornados, ocean waves, volcanoes, earthquakes, rocket launches, wind turbines, planes and traffic.
In contrast, the stratosphere is far calmer, rarely disturbed by turbulence, storms or aircraft. But it can pick up infrasounds from the troposphere and researchers have long thought that there must be an acoustic duct, a sound channel between
