1. With regard to atmospheric circulation, a wave in the major belt of westerlies that is characterized by large length and significant amplitude. The wave length is typically longer than that of the rapidly moving individual cyclonic and anticyclonic disturbances of the lower troposphere. The angular wavenumber of long waves is generally taken to be from 1 to 5. Compare short wave; see Rossby wave. 2. (Also called shallow water wave. ) A wave with a relatively long wave length and period. For ocean waves, this is typically a wave of period greater than about 10 s and wave length greater than about 150 m.