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A low velocity layer in the oceans which carries channel waves (q.v.) to long distances. There is no channel north of 55°N. Named for the SOund Fixing And Ranging system used for locating aviators downed at sea. See Figure C-2.


FIG. C-2. Channel waves. (a) The Sofar channel is formed by velocity inversion. The velocity-versus-depth curve changes with latitude and other factors. (b) Energy from a source in the channel is repeatedly refracted or reflected back toward the velocity minimum and so undergoes less divergence than normal. (From Ewing et al., 1948.) (c) Phase and group velocity versus normalized frequency for a liquid layer on an elastic substratum. (From Ewing et al., 1957.) (d) First-mode wavetrain from a source 4 km distant where the ocean constitutes the channel. (e) The high-frequency portion of (d), the water wave; its arrival is used in refraction work to determine the range. (From Clay and Medwin, 1977.)