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tlr online
18-10-04, 03:18
Two types of waves ripple through this true-color Terra MODIS scene of the Indian Ocean south of Java, Indonesia. In the thin clouds above the water, atmospheric gravity waves create thin ripples, such as those that occur when a pebble is thrown into still water. These gravity waves sometimes happen when the stable air masses on which these clouds float are disturbed by some sort of terrain, thunderstorm updraft, or vertical wind shear.

Below the gravity waves, internal waves create a pattern of delicate dark and white stripes under the surface of the Indian Ocean. Like all major bodies of water, the Indian Ocean is composed of layers of water with differing densities. The topmost layer is the least dense, with each successively deeper layer being denser. Internal waves move along underwater at the boundary between layers of different densities.

Internal waves are usually caused by the lower layer being forced against a shallow obstacle, like a ridge, by tidal action. The ridge causes a disturbance, which creates a wave in the water layer, similar to the way that the wind can cause waves on the water’s surface. However, unlike normal surface waves, internal waves can stretch tens of kilometers in length and move throughout the ocean for several hours.

Internal waves alter sea surface currents, changing the overall “sea surface roughness.” Where these currents converge, the sea surface is more turbulent, and therefore brighter. Where the currents diverge, the surface is smoother and darker, creating zones called “slicks.”

This image was acquired on October 13, 2004.

http://modis.gsfc.nasa.gov/gallery/images/image10172004_md.jpg

NASA