Banda Sea, Indonesia

Credit: Jacques Descloitres; MODIS team; NASA, Posted on: Thursday, 2 December 2004, 07:47 CST Download full size image

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.

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