Chapter 1 · Try it yourself

The Wind Turns Right

You would expect the wind to push the sea the same way it blows. It doesn’t. Because the Earth spins, moving water in the Northern Hemisphere veers to the right. Pick a wind and see where the water really goes, and what that does to the coast at Monterey.

Where is the wind coming from?

Map of the central California coast. Monterey CALIFORNIA (land, east) PACIFIC OCEAN (west) N Wind Water

WindNet flow of the top layer of water

The water moves
toward the west

Upwelling

Why 90°?

Ekman spiral seen from above.

Seen from above and to the side (it looks the same whichever way the wind blows). The top layer of water drifts about 45° off the wind. It drags the layer below, which turns a little more and moves a little slower, and so on down. Add up all the layers and the net flow is 90° from the wind. This stack of turning layers is the Ekman spiral.

Simplified model: steady wind over deep water, coast drawn running straight north–south, Ekman transport at exactly 90°. Real coasts, shallow water and changing winds bend the angle.