August 1, 2010 - Cloud vortices off Tristan da Cunha, South Atlantic

Cloud vortices off Tristan da Cunha, South Atlantic

Creating a striking design which looks a bit like a serpent swimming through clouds, curling patterns of eddies are formed as air flows around and over the island of Tristan de Cunha in the South Atlantic. This image was captured by MODIS on the Terra satellite on July 14, 2010.

The island can be seen as a small circle of green at the far left of the image, at the tip of a dark blue triangle of ocean. To the southeast a string of ocean-blue circles are surrounded by rings of bright white cloud, illustrating the symmetric and swirling pattern of airflow on the leeward side of the island. These spiraling cloud patterns, caused when prevailing ocean winds encounter an island, are known as von Karman vortices or “vortex streets”.

Just like the swirls that can be seen in the wake of airplane wings, these vortex streets result from the separation of flow around an immobile body - in this case the island - causing neighboring areas of flow to circulate in alternating clockwise and counter-clockwise directions.

Home to about 275 people, Tristan de Cunha is considered to be the most remote inhabited island in the world, lying 2,816 km (1,750 mi) from South Africa, the nearest land, and 3,360 km (1,510 mi) from South America. The landmass is quite small, measuring 6 m (10 miles) wide, with a total area of 38 sq. m (98 sq. km). However, the terrain is very steep. Queen Mary’s Peak, an active volcano, rises to 2,062 m (6,765 feet) above sea level.

Image Facts
Satellite: Terra
Date Acquired: 07/14/2010
Resolutions: 1km ( B), 500m ( B), 250m ( B)
Bands Used: 1,4,3
Image Credit: Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC