Table of Contents
What Is the Coriolis Effect?
The Coriolis effect is a fictitious force that deflects moving objects in a rotating reference frame. On Earth, objects moving horizontally are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection is caused by the rotation of the Earth beneath the moving object and is proportional to both the object's velocity and the sine of the latitude.
The Coriolis effect is crucial for understanding large-scale atmospheric and oceanic circulation patterns. It is responsible for the rotation of cyclones (counterclockwise in the Northern Hemisphere, clockwise in the Southern), the deflection of ocean currents, and the formation of trade winds and jet streams. The effect is zero at the equator and maximum at the poles.
Coriolis Formula
Coriolis at Different Latitudes
| Latitude | sin(φ) | Coriolis param. f (s-1) | Deflection (v=10 m/s) |
|---|---|---|---|
| 0° (Equator) | 0 | 0 | 0 m/s² |
| 30° | 0.500 | 7.29×10-5 | 7.29×10-4 m/s² |
| 45° | 0.707 | 1.03×10-4 | 1.03×10-3 m/s² |
| 60° | 0.866 | 1.26×10-4 | 1.26×10-3 m/s² |
| 90° (Pole) | 1.000 | 1.46×10-4 | 1.46×10-3 m/s² |
Observable Effects
- Hurricanes and cyclones rotate due to the Coriolis effect: counterclockwise in the Northern Hemisphere, clockwise in the Southern.
- Trade winds are deflected westward by Coriolis, creating the characteristic northeast and southeast trade wind patterns.
- Ocean gyres (large circular currents) rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern.
- Long-range artillery and missiles must account for Coriolis deflection, which can shift impact points by hundreds of meters.
Frequently Asked Questions
Does the Coriolis effect affect water draining from a sink?
No. The Coriolis force on the small scale of a sink is about 10 million times weaker than other forces like the initial rotation of the water, the shape of the basin, and residual currents. Under extremely controlled laboratory conditions, the Coriolis effect can be detected in draining water, but in everyday life it has absolutely no influence on sink or toilet drainage direction.
Why is the Coriolis effect zero at the equator?
At the equator, the horizontal component of Earth's rotation axis is perpendicular to the surface, and the Coriolis parameter (f = 2ωsinφ) is zero because sin(0°) = 0. Moving objects at the equator feel no horizontal deflection. This is why tropical cyclones cannot form within about 5 degrees of the equator; the Coriolis effect is too weak to initiate rotation.
How does the Coriolis effect influence weather?
The Coriolis effect prevents air from flowing directly from high to low pressure. Instead, air is deflected to create spiral flow patterns. In the Northern Hemisphere, air flows counterclockwise around low-pressure systems (cyclones) and clockwise around high-pressure systems (anticyclones). This creates the characteristic spiral patterns visible in satellite imagery of weather systems.