A non-geostrophic wind that blows parallel to the isobars. It may be expressed by V in the equation: G = 2Dω‎V sin ϕ‎ ± DV²/r + F, where G is the pressure gradient, D the air’s density, ω‎ the angular velocity of the Earth’s rotation about its axis, ϕ‎ the latitude, r the radius of curvature of the air’s path, F the friction, and V the air’s velocity when the forces are in balance. The sign before the second term is + when the motion is around a cyclonic (low-pressure) centre, – when the motion is around an anticyclonic (high-pressure) centre. See also geostrophic wind.