Twice the component of the earth's angular velocity about the local vertical, 2Ω sinφ, where Ω is the angular speed of the earth and φ is the latitude. Since the earth is in rigid rotation, the Coriolis parameter is equal to the component of the earth's vorticity about the local vertical. If the Coriolis parameter is denoted by f and the speed of a horizontally moving fluid parcel by V, then fV is the magnitude of the horizontal Coriolis force per unit mass on the parcel. See also Rossby parameter.