Coriolis Parameter

The Coriolis parameter f measures how strongly Earth’s rotation deflects moving air or water at a given latitude. It depends on the sine of latitude because only the component of Earth’s spin axis perpendicular to the local surface contributes to the apparent sideways deflection; that component is zero at the equator and maximal at the poles. The factor 2 appears because the Coriolis acceleration is twice the rotational contribution in the rotating frame used for weather and ocean dynamics. A larger |f| means stronger turning of motion, with the sign indicating the direction of deflection in each hemisphere.

Use this formula in atmospheric and oceanic dynamics whenever you need to quantify rotational effects from Earth’s spin, such as geostrophic balance, Rossby numbers, or the motion of cyclones, trade winds, and ocean currents. It is especially useful when comparing the Coriolis influence between different latitudes.

• Using cos(latitude) instead of sin(latitude)
• Forgetting that f has units of inverse seconds
• Assuming the formula gives the actual deflection speed rather than the strength parameter used in dynamical equations