1. The statement that in the horizontal flow of an inviscid barotropic fluid, the vertical component of absolute vorticity of each individual fluid particle remains constant. The principle was first applied to the atmosphere by Rossby and is the dynamical principle underlying the nondivergent barotropic model of the atmosphere. See constant absolute vorticity trajectory. 2. The hypothesis that the vorticity of individual eddies is conserved during the turbulent mixing of a fluid. See vorticity-transport hypothesis.