Ocean waves and muffled whispers, mysterious sounds detected in Earth’s second layer of atmosphere

Scientists have detected infrasound noises - sound waves inaudible to the human ear - in the stratosphere, the second layer of Earth's atmosphere. It is surprising because the region was till now believed to be calm and quiet.

The mysterious noise has no known origin and experts recorded it using a solar-powered balloon in the zone between about 10-50 kms above the surface of the earth. Siddharth Krishnamoorthy, a research technologist at NASA's Jet Propulsion Laboratory in California's Pasadena said the experts have been arguing about what these sounds are.

According to a report in Washington Post, scientists sped up the noise a few thousand times and it sounded like muffled whispers. When these mysterious noises were separated from other sounds captured from the zone, they sounded like distant ocean waves slamming into each other.

"I've been doing it for about 10 years now, and, you know, the fact that there's mysterious sounds that I don't understand is troubling, but it's not like a revelation," said researcher Daniel Bowman, principal scientist at Sandia National Laboratories in New Mexico.

The team had sent the balloons up to take pictures of the black sky and Earth below. Once Bowman realised that no one has sent microphones to the stratosphere in the past 50 years, they decided to do it which led to the discovery of the mystery sound waves. They were trying to pick up the low-frequency sounds generated by volcanoes.

Some sounds like continual sighing, crackles, and rustling were also recorded. Their origin is currently unclear. "There are mysterious infrasound signals that occur a few times per hour on some flights, but the source of these is completely unknown."