## similarity theory

An empirical method of finding universal relationships between variables that are made dimensionless using appropriate scaling factors.

The dimensionless groups of variables are called Pi groups and are found using a dimensional analysis method known as Buckingham Pi theory. Similarity methods have proved very useful in the atmospheric boundary layer, where the complexity of turbulent processes precludes direct solution of the exact governing equations.

*See*mixed-layer similarity, local free-convection similarity, local similarity.Stull, R. B. 1988. An Introduction to Boundary Layer Meteorology. 666 pp.