Satellites have detected atmospheric gravity waves off the northern coast of Western Australia this week: https://t.co/CnoFDxfkZr pic.twitter.com/ti1NjFawjsOctober 22, 2019
Rippling gravity (opens in new tab) waves in the sky are usually invisible, but a satellite recently caught a rare glimpse of the phenomenon off the coast of northwestern Australia.
In the images, captured Oct. 21, air moves away from land and over the ocean, and rows of curved white lines emerge, like ripples do in disturbed water. Those thin white bands are clouds forming on the crests of atmospheric gravity waves, according to the Australian meteorology site Weatherzone, which tweeted an animation of the satellite view on Oct. 22.
Gravity waves appear following atmospheric disturbances; in this case, storms in the area produced cold air — which is denser than the warm air over land, Weatherzone says. Interaction between cool and warm air agitated the atmosphere, and the ripples that formed are gravity's way of restoring that lost equilibrium.
Unlike gravitational waves — theoretical ripples in space-time, proposed by Einstein's theory of general relativity — gravity waves are a physical phenomenon. It's easy to picture the physical appearance of gravity waves in liquid: Think of ocean waves, or the ripples that form in a pond after you drop a pebble in the water. While we usually can't see gravity waves in the atmosphere, they behave in the same way that liquids do when they're disturbed, according to the National Oceanic and Atmospheric Administration (NOAA).
Atmospheric gravity waves take shape from the push and pull between gravity and buoyancy; when air is perturbed, gravity pulls the air down and the air's buoyancy pushes it back up. In some cases, when there is enough moisture in the air, water condensation creates white vapor outlines along the crests of the oscillating air waves; the white lines dissipate as the air sinks into troughs.
When that happens, the waves' rippling lines are visible to satellites — such as Japan's geostationary weather satellite Himawari-8, which captured the images featured on Weatherzone.
A large, brownish dust plume carried over the ocean from the Australian coast was also visible in the satellite images, making the ripples even easier to spot, the Australian Broadcasting Corp. (ABC) reported.
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Originally published on Live Science.