What are the trade winds, and why do they blow from east to west?
For centuries, sailors crossed oceans by riding a wind that almost never changed direction, and today that same wind decides where the Pacific is warm.
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Which one is it?
The trade winds blow from east to west because of how air circulates between the equator and the sub-tropics. As part of a loop called the , air high up flows toward the poles, and around 30° latitude in both hemispheres it sinks into belts of high pressure. At the surface, that air flows back toward the equator. Because Earth is spinning, the bends this returning air toward the west in both hemispheres. The result is a steady flow that blows mainly from the northeast north of the equator and from the southeast south of it.
For centuries, captains of sailing ships have used this reliable wind to cross the world's oceans. The Portuguese understood its importance in the Atlantic as early as the 15th century. The name has nothing to do with shopping: "trade" originally meant a "path" or "track", so the trade winds are the winds that keep to their track. Only later did people link the word with commerce, because the winds carried merchant ships so well.
Step 1: Air aloft flows toward the poles
Part of the loop in the tropics.
Step 2: It sinks near 30° latitude
High-pressure belts form where the air descends.
Step 3: It flows back toward the equator
At the surface, air runs from the high-pressure belts to the .
Step 4: Earth's spin bends it west
The turns the flow into northeasterly and southeasterly winds.
The trade winds are not only a sailor's story. They carry dust across the Atlantic, and, over the Pacific, push warm surface water westward so that the sea near Indonesia stands about half a metre higher than the sea near Peru. When these winds weaken, warm water surges back east, the sea there warms, and the winds weaken even more: that self-reinforcing swing is El Niño.
Try it
The trade winds through the year
y = 1 · sin(1x + 0)
Challenge · Set the cycle speed to 0.5 so the pattern repeats about once a year, then move the shift until the peak falls in January or February.
Quiz me
0/3
Recap
Air sinking in the subtropics flows back toward the equator, and Earth's spin bends it westward.
💡 A trick to remember it · Think of a conveyor belt of wind that Earth's spin tilts to the west, with sailors riding it and warm water pushed along ahead of it.
Surprising fact · The word "trade" first meant a path or track, not commerce.
Connects to
- 🌐 Why are the world's great deserts in two belts around the globe?
- 🧭 Did the hunt for spices really cause the age of exploration?
- 🌧️ Why does most of India's rain fall in just a few months?
- 🐟 How can a warm patch of the Pacific change the whole world's weather?
- 🌀 Why do hurricanes spin opposite ways in the two hemispheres?
- Jet stream
Sources (2)
No source, no claim. Every fact in this lesson (19 claims) cites at least one of these.