INTERNAL WAVES IN THE OCEAN

The roughness of the sea surface is a phenomenon of common experience. Distortions of a flat surface feel the restoring force of gravity and propagate as traveling surface waves, with periods of up to about 20 seconds, speeds up to tens of ms** minus **1, and amplitudes of up to several meters. An interface between two superposed fluids of different densities can similarly support gravity waves. The restoring forces are weaker, periods and wavelengths are much longer than those of surface waves, and amplitudes can reach many meters. These waves are often observed over the continental shelf in summer, when solar heating produces a warm light surface layer. The review is not comprehensive but attempts to leave the nonspecialist with some idea of how internal waves are measured, how the data are interpreted, what has been learned of the role of internal waves in the ocean, and what problems, both experimental and theoretical, remain. It concentrates on internal waves in the oceans proper, ignoring almost entirely the rather different properties and problems associated with internal waves over continental shelves, and in freshwater lakes.