Coriolis on Earth

The Coriolis simulator shows the effect in the abstract: a ball on a spinning disk that seems to curve. This one puts it on the planet.

What you’re looking at

The screen is a flat map of Earth. The top is the North Pole, the middle is the equator, the bottom is the South Pole. Drag anywhere to launch a parcel of air, and it curves as it travels.

Watch where it curves:

• North of the equator, every wind bends to its right.
• South of the equator, every wind bends to its left.
• On the equator, it goes perfectly straight.

Try launching two winds in the same direction, one up north and one down south. Same push, opposite curves.

Why it happens here

It’s the exact same physics as the spinning disk. The wind travels in a straight line; the Earth turns underneath it, so from the ground the path looks bent. The strength of that apparent bend depends on latitude: it’s built from sin(latitude), which is zero at the equator and largest at the poles. That’s why the equator is a straight shot and the curves tighten as you head toward either pole.

The real Earth spins slowly enough that this takes hours to show, so the spin rate here is turned way up. Everything else is honest.

Why it matters

This one effect sets the shape of the weather. It’s why hurricanes spin counterclockwise in the Northern Hemisphere and clockwise in the Southern, why the trade winds blow the way they do, and why ocean currents wheel around in great loops. Drag a few winds toward a single point and you can watch them refuse to meet head-on, spiralling instead. That spiral is a storm.