Atmospheric Circulation

The equator receives a lot of solar energy and is hot, while the poles receive less and stay cold. To balance that temperature difference the atmosphere moves in three cells (Hadley, Ferrel, and Polar), and Earth's rotation bends the winds through the Coriolis effect. So the Northern Hemisphere has trade winds, westerlies, and polar easterlies, and Korea lies in the westerlies belt, so weather moves west to east. Here you can drag the observer-latitude slider and see how the three cells and surface winds change with latitude.

Earth's air conditioning system

🌬️ Why does the atmosphere circulate?

①The equator receives a lot of solar energy (hot), the poles receive less (cold)

②To equalize temperature, the atmosphere circulates

③Like an air conditioner balancing room temperature, the atmosphere transports heat

Three circulation cells

Observer latitude35°N

💡 Key observations

①0~30°: Hadley cell — rises at equator, descends at 30°

②30~60°: Ferrel cell — indirect circulation between Hadley and Polar

③60~90°: Polar cell — descends at pole, rises around 60°

Coriolis effect and surface winds

Coriolis effect

Earth's rotation → moving objects deflect right in the Northern Hemisphere

Southern Hemisphere deflects left. Stronger at higher latitudes

Surface winds (Northern Hemisphere)

0°~30°: NE trade winds / 30°~60°: SW westerlies / 60°~90°: NE polar easterlies

wind directions set by Coriolis deflection

🔄 Understanding the Coriolis effect

①Throw a ball straight on a spinning turntable — looks curved

②Earth rotates, so winds don't go in straight lines — they curve

③Effect = 0 at equator, maximum at poles

Pressure belts and winds

Pressure belts by latitude

equatorial low (0°) → subtropical high (30°) → polar front (60°) → polar high (90°)

rising = low pressure, descending = high pressure — winds blow high→low

📍 Korea's location

①Korea is at ~33~43°N — in the westerlies belt

②Weather thus moves west to east

③Forecasters say "a low approaching from the west" because of the westerlies

Worked Examples and Exam Practice

Example 1

What is the name of the surface wind that blows around latitude 15°N in the Northern Hemisphere?

Latitudes 0~30° are the Hadley cell, rising at the equator and sinking at 30°.

The Coriolis effect deflects this surface wind to the right, making the northeast trade winds.

▸ (Northeast) trade winds

Northern Hemisphere surface winds: 0~30° trades, 30~60° westerlies, 60~90° polar easterlies.

Example 2

Korea (~37°N) lies in which cell and wind belt, and so weather generally moves in which direction?

37°N is between 30~60°, in the Ferrel cell and the westerlies belt.

The westerlies blow west to east, so weather also moves from west to east.

▸ Westerlies belt (Ferrel cell); weather moves W → E

The westerlies are why forecasters watch changes approaching from the west first.

CSAT-style

Which statement about global atmospheric circulation is correct?

①The Coriolis effect is strongest at the equator

②The Hadley cell appears at latitudes 0~30°

③The Northern Hemisphere trade winds are southwesterlies

④The Ferrel cell is a direct circulation

⑤The equator is a high-pressure belt

▸ ② The Hadley cell appears at latitudes 0~30°

The Hadley cell rises at the equator and sinks at 30°, a direct circulation over 0~30°.

The Coriolis effect is strongest at the poles (①), Northern Hemisphere trades are northeasterlies (③), the Ferrel cell is indirect (④), and the equator is a low-pressure belt (⑤).

Summary

Atmospheric circulation core

equator–pole temperature gradient + rotation (Coriolis) → 3 cells + pressure belts/winds

global atmospheric motion that resolves latitudinal energy imbalance

🎯 Exam Points

①3 cells: Hadley (0~30°), Ferrel (30~60°), Polar (60~90°)

②Surface winds: trade (NE), westerlies (SW), polar easterlies (NE) — N. Hemisphere

③Coriolis: deflects right in N. Hem., 0 at equator, max at poles

④Alternating belts: low-high-low-high (equator→pole)

⑤Korea = westerlies belt → weather moves W→E

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