POTENTIAL VORTICITY

the ratio of the absolute vorticity (q.v.) of an atmospheric column to the (defined) pressure difference across the column. This quantity is used to label air in much the same way as we use other conservative properties. As a column of air moves along, it 'shrinks' vertically (due to mass divergence) in just the right amount to decrease its absolute vorticity; as it expands vertically (due to mass convergence), its absolute vorticity increases. Therefore, Potential Vorticity tends to remain constant following the motion of the flow, for adiabatic motion.