The apparent deflection of moving objects, including winds and ocean currents, caused by the rotation of the Earth: to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
- Named after the French scientist Gaspard-Gustave de Coriolis; it is an apparent (inertial) force that arises because the observer is on a rotating Earth.
- It is zero at the equator and increases toward the poles, which is why tropical cyclones cannot form right on the equator (too little deflection to start the rotation).
- It explains the direction of the planetary winds (north-east and south-east trades rather than due-north and due-south) and the curving of ocean currents into gyres.
- Combined with the pressure-gradient force, it produces the geostrophic balance that makes winds blow roughly parallel to the isobars.
- Buys Ballot's law follows from it: in the Northern Hemisphere, if you stand with your back to the wind, low pressure lies to your left.
The right-in-north, left-in-south rule, the zero-at-equator point (and why cyclones avoid the equator), and Buys Ballot's law are frequently tested climatology facts.
Deflection is to the right in the Northern Hemisphere and to the left in the Southern, not the reverse; the force is maximum at the poles and zero at the equator; it is an apparent force, not a real push.
Earth's rotation deflects winds and currents right in the north and left in the south, zero at the equator and greatest at the poles.