An Etymological Dictionary of Astronomy and Astrophysics

A dimensionless number relating the ratio of inertial to Coriolis forces for a given flow of a rotating fluid. It is used in the study of atmospheric motions in planets. In case a small number is involved, cyclones and anticyclones are observed for low and high
pressures. When it is large (Venus) the Coriolis force becomes
negligible and atmospheric motions are barely affected by planetary
rotation.

See also: Named after Carl-Gustav Arvid Rossby (1898-1957), a Swedish-American meteorologist who first explained the large-scale motions of the atmosphere in terms of fluid mechanics; → number.