The Crozet Islands in the Southern Ocean. [ ]. A pair of wave clouds formed by island mountains.
An unnamed astronaut on board the International Space Station. Jan. 8, 2023.
This 2023 astronaut photo captures the striking beauty of a pair of perfectly aligned, arrow-shaped wave clouds rippling above the Crozet Islands — an archipelago of uninhabited French islands in the Southern Ocean, located roughly halfway between South Africa and Antarctica. Wave clouds are repeating bands of and non-cloud that look like wispy streaks when viewed from above or below. These bands are created when stable air moves over raised land.
The topography pushes the air upward before pulls it back down, causing the air to oscillate up and down, according to . When the air rises, it cools down, and water vapor condenses into clouds. But when gravity pulls the air downward, it is compressed by increased atmospheric pressure, which heats it up via a process called adiabatic heating and forces any to evaporate, according to the .
Wave clouds are also known as gravity waves. This should not be confused with "gravitational waves," which are ripples in space-time created by extreme cosmic entities such as black holes and colliding galaxies. The wave cloud on the left of the image is formed by air passing over Mount Marion-Dufresne, a 3,576-foot-tall (1,090 meters) peak on East Island; the pattern on the right is caused by Mascarin Peak, a mountain on Possession Island that stands 3,064 feet (933 m) tall.
