Atmospheric circulation is the large-scale movement of air that redistributes heat around Earth. In this lesson, we begin with the forces behind global circulation and examine the Hadley cell, the largest and most powerful of the three major circulation cells in each hemisphere.
The tropics receive more direct solar energy per unit area than the poles. This uneven heating creates temperature and pressure differences that set air in motion. Warm air tends to rise; cooler, denser air tends to sink. The resulting movement transfers heat from tropical regions toward higher latitudes, while Earth and its atmosphere also radiate energy to space.
All flashcards
What is atmospheric circulation?
The large-scale movement of air that redistributes heat around Earth.
What maintains the Ferrel cell?
It is maintained largely by interactions with the Hadley and polar cells, rather than by direct surface heating.
What is longitudinal overturning circulation?
Air circulation along east–west pathways driven by temperature contrasts, including those between land and water.
How does the Walker circulation operate under ordinary tropical Pacific conditions?
Air rises over the warmer western Pacific, returns eastward aloft, descends over the cooler east, and flows westward at the surface.
How do El Niño and La Niña differ in the tropical Pacific?
They are opposite sea-surface temperature anomalies: El Niño is unusually warm, while La Niña is unusually cool.
Quiz questions
What primarily maintains the Ferrel cell between about 30° and 60° latitude?Answer: Interactions with the neighboring Hadley and polar circulation cells.
Why are surface winds in the polar cell called polar easterlies?Answer: They flow away from the poles and are deflected westward by Earth's rotation.
What creates a daytime sea breeze?Answer: Cooler air moves from sea toward land as air rises over the warmer land.
Under ordinary tropical Pacific conditions, what do surface easterly winds do?Answer: They push warm surface water toward the western Pacific.
How can El Niño affect marine ecosystems off South America?Answer: It can suppress the upwelling of cold, nutrient-rich deep water.