AN INTERNAL WAVE is a wave that develops below the surface of a fluid along changes in density. With increased depth, this change may be gradual, or it may occur abruptly at the interface. Similar to the transmission of energy by wind along the surface of the ocean, the density interface beneath the ocean [Page 1079]surface transmits energy to produce internal waves. The greater the difference in density between the two fluids, the faster the wave will move.

Internal waves may have a variety of causes, including the tidal pull of water, wind stress, and energy put into the water by moving vessels. Year-round internal waves caused by tidal forces carry between 30 and 50 percent of their energy away from their source. Seasonal (stormy winter ...