Ship-wave-shaped Clouds in the Southern Indian Ocean

Credit: Jeff Schmaltz MODIS Land Rapid Response Team, NASA GSFC, Posted on: Wednesday, 29 October 2008, 07:45 CDT Download full size image

The cloud patterns seen in this image, captured by the MODIS on the Terra satellite on October 16, 2008, are called "ship-wave-shaped clouds". They are called this because they resemble ship waves (or "Kelvin ship waves"), which are the V-shaped wakes left by moving objects, such as ships or even ducks.

In this case, the cloud patterns were caused by the Prince Edward Islands in the South Indian Ocean (not to be confused with the Prince Edward Island in Canada). As the wind flows past the islands, it is swept around and over it leaving a wake similar to that of a ship-- hence the name "ship-wave-shaped" clouds.

The pattern is not accidental or coincidental, there is a physical reason for it. Wind behaves like a fluid; when it encounters an obstacle, it must move around it, leaving behind a wake (like Von Karmann vortices), or a visible wave pattern. Ship-wave-shaped cloud patterns form as the air alternately cools and warms on the wave peaks and troughs, causing clouds to form on the peaks, but not the troughs.

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