1. Atmospheric circulation features of cyclonic scale. Use of the term is usually reserved for distinguishing between the various dimensions of atmospheric circulation, that is, primary circulation, tertiary circulation. See also general circulation. 2. A circulation induced by the presence of a stronger circulation as a result of dynamical constraints. A frictional secondary flow is an example. 3. Organized flow superimposed on a larger-scale mean circulation. For example, roll vortices are a secondary circulation in the atmospheric boundary layer. They “fill” the boundary layer vertically, but have a width of only two to three times the boundary layer depth, while the mean wind profile extends over a much broader region.