Coriolis Force Calculator
Find the Coriolis acceleration and Coriolis parameter from speed and latitude, with hemisphere deflection direction.
🌀 What is the Coriolis Force?
The Coriolis force is an apparent (fictitious) force that deflects the path of anything moving across Earth's rotating surface, wind, ocean currents, aircraft, artillery shells, even a thrown ball over long enough distances. It exists only because Earth itself is rotating underneath the moving object, an observer standing on the ground sees a sideways curve that an observer floating above the North Pole, watching Earth spin, would not describe as a force at all, just straight-line motion over a turning planet.
Meteorologists rely on the Coriolis force constantly, to explain why wind does not blow directly from high pressure to low pressure but instead curves to flow nearly parallel to isobars (the basis of geostrophic wind), to explain why cyclones rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere, to explain why the trade winds and jet streams take the paths they do, and to build the equations of motion used in every numerical weather prediction model.
A common misconception is that the Coriolis force explains which way water spins down a household drain. It does not, the effect is far too weak at that small scale and short timescale to compete with the basin's shape and any residual swirl in the water. The Coriolis force only becomes dominant over large distances and long durations, such as a storm system spanning hundreds of kilometers over many hours.
This calculator computes both the Coriolis acceleration (the force per unit mass actually felt by a moving parcel) and the Coriolis parameter f (the latitude-only quantity used directly in the geostrophic wind equation), from a speed and a latitude you enter.
📐 Formula
Per the standard atmospheric dynamics formulation (National Weather Service, Wikipedia), this is the horizontal Coriolis acceleration used throughout meteorology and oceanography.
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — Mid-Latitude Wind
Speed = 10 m/s, latitude = 45° (typical mid-latitude storm wind)
Example 2 — High-Latitude Storm
Speed = 25 m/s, latitude = 60° (strong North Atlantic storm wind)
Example 3 — Southern Hemisphere
Speed = 5 m/s, latitude = -30° (light wind off the coast of Australia)
❓ Frequently Asked Questions
🔗 Related Calculators
What is the Coriolis force?
The Coriolis force is an apparent force that deflects moving objects and fluids sideways relative to Earth's rotating surface. It is not a real force in the Newtonian sense, it arises because Earth rotates underneath anything moving across it, and it is what steers wind and ocean currents into curved paths instead of straight lines.
How do you calculate Coriolis acceleration?
Coriolis acceleration per unit mass is a = 2Ωv sinφ, where Ω is Earth's angular velocity (7.2921 x 10^-5 rad/s), v is the object or wind speed in m/s, and φ is latitude in degrees. The result is in m/s².
What is the Coriolis parameter f?
The Coriolis parameter is f = 2Ωsinφ, measured in inverse seconds (s^-1). It depends only on latitude, not speed, and is the quantity meteorologists and oceanographers use directly in the geostrophic wind and current equations.
Why is the Coriolis effect zero at the equator?
At the equator, latitude φ = 0, so sinφ = 0, making both f and the Coriolis acceleration exactly zero. This is why the Coriolis effect cannot organize the rotation needed to spin up a tropical cyclone within roughly 5 degrees of the equator.
Which direction does the Coriolis force deflect moving objects?
In the Northern Hemisphere, moving objects and wind are deflected to the right of their direction of travel. In the Southern Hemisphere, they are deflected to the left. This is why storm systems rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Does the Coriolis effect really determine which way water drains from a sink?
No, this is a common myth. The Coriolis acceleration on a small volume of water moving a short distance over a few seconds is many orders of magnitude smaller than the effects of basin shape, residual swirl, and how the drain was uncovered. The Coriolis effect only becomes dominant over large distances and long timescales, such as storm systems spanning hundreds of kilometers.
What value of Earth's angular velocity does this calculator use?
This calculator uses Ω = 7.2921 x 10^-5 rad/s, Earth's sidereal angular velocity (one full rotation relative to the stars every 23 hours 56 minutes), which is the standard constant used throughout meteorology and oceanography.
How does the Coriolis force relate to geostrophic wind?
Geostrophic wind speed is derived by balancing the horizontal pressure gradient force against the Coriolis force, Vg = (pressure gradient) / (ρf), where f is the same Coriolis parameter computed here. A larger Coriolis parameter (higher latitude) produces a slower geostrophic wind for the same pressure gradient.
Is the Coriolis force stronger at higher latitudes?
Yes. Since f = 2Ωsinφ, the Coriolis parameter increases in magnitude from zero at the equator to its maximum value at the poles (φ = 90°), so for the same speed, the Coriolis acceleration is largest near the poles and smallest near the equator.
Does the Coriolis force affect the speed of a moving object?
No. The Coriolis force always acts perpendicular to the direction of motion, so it changes an object's direction of travel over time but does not do work on it or change its speed.
Can the Coriolis acceleration be negative?
Yes, when latitude is entered as negative (Southern Hemisphere), sinφ is negative, making both the Coriolis parameter f and the Coriolis acceleration negative. The sign indicates the deflection is to the left of motion rather than the right, not that the magnitude of the effect is reduced.
What units does this calculator use for speed?
Speed (v) is entered in meters per second (m/s). To convert from km/h, divide by 3.6, to convert from mph, multiply by 0.44704, before entering the value.