ABSOLUTE VORTICITY

(or total vorticity) of air particles at any particular point is comprised of two elements: (i) on the rotating earth, air adopts the local vorticity due to the earth's solid-body rotation about its pole-to-pole axis, which is latitude dependent, and is known as the Coriolis parameter. This increases to a maximum over the poles and decreases to zero at the equator. The Coriolis rotation sense is always positive (or zero). (ii) the other element is known as the relative vorticity, the 'spin' tendency of air particles due to their motion relative to the earth - driven by atmospheric forces. Relative vorticity can be either positive (cyclonic sense) or negative (anticyclonic). (See also: Vorticity; Relative vorticity.)