Also called gravitational wave.) A wave disturbance in which buoyancy (
or reduced gravity) acts as the restoring force on parcels displaced from hydrostatic equilibrium.
see capillary wave). 2) Heterogeneous fluids, such as the atmosphere, have static stability arising from a stratification in which the environmental lapse rate is less than the process lapse rate. The atmosphere can support short internal gravity waves and long external gravity waves. The short waves (of the order of 10 km) have been associated, for example, with lee waves and billow waves. Such waves have vertical accelerations that cannot be neglected in the vertical equation of perturbation motion. The long gravity waves, moving relative to the atmosphere with speed ±(gH)½, where H is the height of the corresponding homogeneous atmosphere, have small vertical accelerations and are therefore consistent with the quasi-hydrostatic approximation. In neither type of gravity wave, however, is the horizontal divergence negligible. For meteorological purposes in which neither type is desired as a solution, for example, numerical forecasting, they may be eliminated by some restriction on the magnitude of the horizontal divergence. The above discussion is based upon the method of small perturbations. In certain special cases of water waves, for example, the Gerstner wave or the solitary wave, a theory of finite-amplitude disturbances exists.
See shear-gravity wave.
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