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Earth’s rotation makes moving air appear to deflect in an Earth-fixed frame. On large weather scales, this Coriolis term interacts with pressure gradients, friction and curvature to shape winds.
By Matan · Updated
Right or left relative to the motion
The Coriolis acceleration is −2Ω × v. For large-scale horizontal motion, f = 2Ωsinφ gives the relevant rotational parameter: deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. It does not create wind from stationary air by itself. [1]
Worked scale at 45° latitude
Using Earth rotation rate 7.292 × 10⁻⁵ s⁻¹ and latitude 45°, f = 1.031 × 10⁻⁴ s⁻¹. For horizontal speed 10 m/s, horizontal Coriolis acceleration magnitude is about 0.00103 m/s². With length scale 1000 km, Rossby number U/(fL) ≈ 0.097, indicating that rotation is important.
Why winds can run along isobars
Away from strong friction and curvature, a nearly steady geostrophic balance pairs the horizontal pressure-gradient acceleration with Coriolis acceleration. Near the surface, friction allows air to cross isobars. Cyclone circulation depends on that force balance and hemisphere, not on rotation acting alone. [1]
Small vortices need separate analysis
For the same speed over a 10 m scale, the Rossby number would be about 9700, so Earth rotation is weak in that comparison. Bath drains and small eddies are usually governed by local geometry and initial motion. Ocean gyres also involve wind stress, boundaries and water-pressure gradients.
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Sources checked; calculations checked where shown. Main claims and model assumptions were checked against the references below. Example arithmetic and units were checked separately. Numerical examples are illustrative calculations, not experimental measurements.
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Sources and further reading
- NOAA: Wind trajectory equations and geostrophic balance
- MIT: Classical Mechanics III, rotating frames
Cite this article
Matan. “Why does the Coriolis effect influence weather patterns.” Your Physicist. Originally published 2023-05-17; updated 2026-09-10. https://your-physicist.com/why-does-the-coriolis-effect-influence-weather-patterns/
Revision history
10 September 2026: Completed the broken passage and added latitude-dependent acceleration and Rossby-number comparisons. Added references and a transparent verification record.
