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Grade 10-11 (age 15-17)

high school Atmospheric Circulation

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. Change the observer latitude and watch the three cells and surface winds.

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

35°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?
1
Latitudes 0~30° are the Hadley cell, rising at the equator and sinking at 30°.
2
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?
1
37°N is between 30~60°, in the Ferrel cell and the westerlies belt.
2
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.
exam-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°
1
The Hadley cell rises at the equator and sinks at 30°, a direct circulation over 0~30°.
2
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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