Cloud spirals

Von karman vortices form downwind of the island of tristan da cunha.
Von Karman vortices form downwind of the island of Tristan da Cunha.
NASA Earth Observatory / Joshua Stevens

In 1912, physicist Theodore von Kármán first described a process that makes long, spiraling cloud patterns in the sky. These so-called “von Kármán vortices” arise when winds are diverted around a blunt, high-profile area, often an island rising from the ocean. The alternating direction of rotation in the air forms swirls in the clouds.

Satellites regularly spot these wind and cloud patterns around the world. On June 25, 2017, the image above was captured by the Operational Land Imager (OLI) on the Landsat 8 satellite. It shows vortices on the lee side of Tristan da Cunha, a remote volcanic island in the South Atlantic.

According to Carlos Torres of the Autonomous University of Baja California, the pattern of the swirls depends on the wind intensity. The vortices are driven by the prevailing winds, which can change seasonally and cause differences in the direction and structure of the vortices.

The image is in false-color (OLI bands 6-5-3) to better distinguish areas of land, water, and clouds.

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