Atmospheric Gravity Waves: Satellite Captures Rare Images of Normally Invisible Phenomenon

Images captured by satellites have revealed an unusual atmospheric phenomenon that's usually invisible off the northwestern coast of Australia.

The phenomenon—known as atmospheric gravity waves—are essentially ripples in the sky, which, in this case, were triggered by thunderstorms taking place in Australasia region over the past few days.

"Gravity waves are everywhere, all the time, in all sorts of fluids," Adam Morgan, a meteorologist from the Australian Bureau of Meteorology, told Newsweek. "Just like water, Earth's atmosphere is a fluid, so waves are everywhere in the atmosphere too."

"When we talk about waves being generated, we're essentially talking about oscillations—those localized up and down, or back and forth motions that kind of look like the sine or cosine waves you might have learned about in maths at school," he said. "In the atmosphere, oscillations like this within the air create waves that can travel in any direction."

According to Morgan, the waves were created by cold air flowing out of thunderstorms during hot days.

"There was a big thunderstorm over the northwest of Western Australia and the disturbance in this case was the cold air falling out of the thunderstorm and into the warmer air near the surface," Morgan told ABC News.

"The difference in density there causes the disturbance and then the gravity wave can travel out as the cold air spreads out," he said.

Morgan noted that the gravity waves can travel significant distances before they begin to dissipate.

A gusty south easterly surge over NW WA - perhaps enhanced by outflow from last night's thunderstorms over the Northern Interior - carries a plume of dust out over the Indian Ocean.

— Andrew Miskelly (@andrewmiskelly) October 21, 2019

"The disturbance will exist until everything rebalances itself, that's why they can travel a long way," he said. "If you've ever been to the swimming pool and someone jumps in and does a dive bomb at one end of the pool, you might get the wave right at the other end of the pool after a bit of time."

Morgan added that while the atmospheric gravity waves are very common, we cannot usually see them unless they produce clouds—which can happen in some cases—or other visible phenomena.

"Most of the time, gravity waves are invisible," Morgan told Newsweek. "When we do see them it's often at the boundary between two different fluids—like waves on the sea surface at the boundary between the air and the ocean. In the atmosphere, we don't usually see gravity waves by eye in satellite imagery unless they show up in clouds."

"In the case earlier this week off northern Western Australia, there was just enough moisture in the air above the surface of the ocean to create lines of cloud along the crests of the gravity wave as it spread out," he said. "This particular gravity wave case was quite extensive and created a long line of cloud, which meant it was easy to pick up on satellite imagery."

Earth, Australia
A satellite and 3D rendered world globe Earth image of Australia. Photo Maps4media via Getty Images.

Also visible in the satellite image is a large plume of dust being blown off the Australian coast, which was generated by a dust storm in the Pilbara region.

"The brown, orange tinge is dust being pushed off the coast because of the windy conditions," Morgan said. "The cold outflow that falls out of that thunderstorm is quite gusty and those gusts have picked up a lot of dust and pushed it offshore. So when you look at the satellite image, it actually looked quite impressive."

Atmospheric gravity waves go unnoticed by people on the ground, although they can potentially cause turbulence for aircraft, although this is usually not too severe.

This article was updated to include additional comments from Adam Morgan.