Global Wind Patterns
Explain that unequal solar heating drives large-scale atmospheric circulation: Hadley cells (0-30°), Ferrel cells (30-60°), and polar cells (60-90°) produce the trade winds, westerlies, and polar easterlies; describe how the Coriolis effect from Earth's rotation deflects winds rightward in the Northern Hemisphere; explain the jet stream as a fast high-altitude wind that steers weather systems; connect jet stream waviness and Arctic amplification to prolonged extreme weather
The lesson
The sun does not heat every part of Earth by the same amount. Near the equator, sunlight lands almost straight down, so the ground and air warm up a lot. Near the poles, sunlight arrives at a low angle and spreads out, so the air stays cold. That difference in heat is what gets the whole atmosphere moving.
As warm air rises at the equator and cold air sinks at the poles, the moving air breaks into three bands in each hemisphere: the Hadley cell from 0° to 30°, the Ferrel cell from 30° to 60°, and the polar cell from 60° to 90°. Where each cell meets the ground, it drives a different surface wind: the trade winds, the westerlies, and the polar easterlies.
Earth is also spinning, and that spin bends the path of any air moving across it. This is called the Coriolis effect. If you are standing in the Northern Hemisphere, it pushes moving air to the right of the direction it is heading, curling the trade winds, westerlies, and polar easterlies into the diagonal paths you see on wind maps.
Kofi checks a weather map before a school trip to Manchester and spots the jet stream, a fast river of wind high above the westerlies, curving over the Atlantic toward Britain. That is one reason rain so often reaches the UK from the west: the westerlies and the jet stream are both carrying weather systems eastward. Some weeks the jet stream stops flowing in a fairly straight line and loops into big waves instead, something scientists link to Arctic amplification, the Arctic warming faster than the rest of the planet. When the jet stream turns wavy and slows down, a loop can get stuck in place, and the storm or heat wave sitting inside it lingers for days or weeks longer than usual.
Uneven heating drives three wind cells in each hemisphere, Earth's spin curves those winds to the right in the Northern Hemisphere, and the jet stream steers weather systems, so a wavier jet stream can leave the same weather stuck in place for much longer.
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8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.