Island Wakes

One of my favorite aspects of fluid dynamics is watching how patterns repeat at all kinds of scales. The cotton-candy-colored image above is a false-color satellite image of the island Tristan da Cunha (left), a volcanic island group in the South Atlantic. The prevailing winds, oriented roughly left to right in the image, flow over the rocky island and part in a series of swirls that alternate in their direction of rotation: clockwise for the upper set and counter-clockwise for the lower ones. This pattern is called a von Karman vortex street, named for an  aerodynamicist who studied the mechanism. Von Karman vortices are frequently observed in satellite images of remote islands, but they are also common behind spherical and cylindrical objects of all sizes. Sometimes they even show up in sci-fi! (Image credit: NASA Earth Observatory; submitted by Steve G.)

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