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View Full Version : MODIS: Internal waves in the Banda Sea


tlr online
28-11-04, 01:54
In an area of glinting sun over the Banda Sea, a series of concentric semi-circles emanates north-northwestward from the channel between the Indonesian islands of Alor (west), and Wetar (larger island to northeast). The spreading rings are evidence of a phenomenon known as "internal waves." The waves are called "internal" because they get started within a fluid at the interface between layers that have different densities (such as cold, deep water, and warmer surface waters), rather than at the interface between the water and the air.

Internal waves can have wavelengths that are tens of meters and periods that range from 20-30 minutes up to several hours. Although it can be difficult to imagine, it is possible for these large waves to travel beneath the surface of the ocean without producing observable waves at the surface. This doesn't mean the surface waters aren't affected at all, however. As the waves move through, the surface waters move apart (diverge) over the crest of the waves and come together (converge) over the troughs. Floating plankton and other material in the surface waters become concentrated in the areas of converging waters over the trough, and produce "slicks" in the shape and pattern of the waves.

As part of online materials for a undergraduate course in physical oceanography, a professor at Flinders University of South Australia has made available an easy-to-interpret

http://modis.gsfc.nasa.gov/gallery/images/image11272004_md.jpg

Copyright 2004 NASA