Clouds usually come in chaotic, shifting forms that look like cotton balls, dragons, or even your favorite cartoon character if you squint just right. But in 2014, NASA’s Terra satellite captured a near-perfect circle of clouds hovering above the Pacific Ocean.
Spotted a few thousand kilometers southwest of Hawaii, this unusual ring floated above open water on a clear day. It wasn’t the result of Photoshop or some rare cosmic coincidence, either, NASA says. Instead, it was a subtle but powerful reminder of the complex physics playing out in Earth’s atmosphere every day—something often invisible unless you’re looking down on things from above.
Meteorologists refer to this type of formation as an open-cell convection. At its heart, it’s a product of a natural process called Rayleigh-Bénard convection. These types of patterns form when fluid (or in this case, air) is heated from below.
Depending on how the air flows, the result can be a “closed cell,” where clouds form at the center, or an “open cell,” where clouds form at the edges and leave a clear middle—like this image of a circle of clouds.
Scientists believe this particular event began when a patch of the ocean—possibly warmed more than its surroundings—triggered rising air currents. As the moist air rose and cooled, it formed cumulus clouds and a light drizzle of rain. That rain then cooled the air beneath it, creating a downdraft.
When that cool air spread outward and hit warmer air at the edges, it forced the warmer air to rise, thus producing the bright circle of clouds visible from orbit in this photograph.
Though they’re not particularly rare, circular formations like this one weren’t well understood until weather satellites began offering a top-down view of Earth’s skies. Before then, meteorologists relying on ground-based observations simply couldn’t see the full pattern.
The launch of NASA’s TIROS-1 satellite in 1960 changed the way we view clouds and gave rise to a deeper understanding of atmospheric dynamics on a global scale. There’s still a lot we’re figuring out, though, like why clouds vanish during eclipses.
