Gravity Waves

 

Image courtesy MODIS/NASA

The surf's not actually up off the coast of South Island, New Zealand: The large waves that seem to be rolling toward land aren't in the water, but in the air above. This December 21 picture, from NASA's Terra satellite, captured a phenomenon called atmospheric gravity waves.

Such waves form when buoyancy pushes air upward while gravity pulls it downward, giving rise to oscillations in the air. At the low point of a wave, more air touches the surface of the ocean, roughening the otherwise smooth water.

When sunlight hits water at the same angle as a satellite's view, smooth areas reflect light like mirrored surfaces while rough regions scatter light and appear darker. That means if atmospheric gravity waves are present, their pattern becomes visible in the water.

Published December 30, 2010

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