Best of the Archives: The Fractal Motion of Clouds

On this date in 1999, we released this Landsat 7 image of a distinctive type of cloud pattern known as a von Karman vortex street. As we wrote then: "This pattern has long been studied in the laboratory, where the vortices are created by oil flowing past a cylindrical obstacle, making a string of vortices only several tens of centimeters long. Study of this classic 'flow past a circular cylinder' has been very important in the understanding of laminar and turbulent fluid flow that controls a wide variety of phenomena, from the lift under an aircraft wing to Earth’s weather. Here, the cylinder is replaced by Alejandro Selkirk Island (named after the true Robinson Crusoe, who was stranded here for many months in the early 1700s). The island is about 1.5 km in diameter, and rises 1.6 km into a layer of marine stratocumulus clouds."