However, because the planet is rotating, the air flow from center to periphery is not direct, but is twisted due to the Coriolis effect. This is an apparent, but fictitious, force that arises when an observer is in a rotating reference frame, due to the conservation of angular momentum of the air as it moves towards or away from the Earth's axis of rotation. Viewed from above this twist in wind direction is in the opposite direction as the rotation of the planet.