AP Environmental Science 4.5 - Global Wind Patterns

Main Ideas: Global Wind Patterns

Atmospheric circulation is shaped by three factors:

1. Uneven solar heating: The Sun’s rays strike the equator most directly, warming the air there.
2. Air properties: Warm air is less dense and rises. As it rises, it expands and cools. Cooler air holds less water vapor, so moisture condenses and may fall as precipitation. Cooler, drier air eventually sinks.
3. Earth’s rotation: The Coriolis effect deflects moving air, shaping the direction of prevailing winds.

Hadley Cell and Weather Patterns

• At the equator, strong solar heating causes warm, moist air to rise, creating a low-pressure area.
• As the air rises and cools, water vapor condenses, producing heavy rainfall.
• Higher in the atmosphere, the air spreads toward the poles. Around 30° north and south, it cools, dries, and sinks, creating high-pressure zones.
• The descending dry air helps explain why many of Earth’s major deserts occur around 30° latitude.
• At the surface, air flows from the high-pressure regions near 30° back toward the low-pressure equator, completing the Hadley cell circulation.

Coriolis Effect and Prevailing Winds

Earth’s rotation deflects air moving between pressure zones, so winds do not travel straight north or south.

• From 30° toward the equator: The deflection produces winds that blow from east to west, known as the trade winds.
• From 30° toward 60°: The deflection produces winds that blow from west to east, known as the westerlies.
• The prevailing westerlies help move weather systems across North America from west to east.
• These wind patterns also contribute to ocean-current circulation: clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

Learning Focus

The lesson’s suggested practice is to explain relationships shown in visual models—for example, how solar heating, air density and moisture, pressure differences, and Earth’s rotation combine to create global circulation and weather patterns.

Speakers and Sources Featured

• Presenter: Introduces himself as Mr. Smith.
• Other speakers or external sources: None identified in the subtitles.