This lesson introduces the Hadley cell, its location, and the unequal heating that drives it. Understanding this circulation helps explain major patterns of tropical rain, subtropical dryness, and global heat distribution.
The Hadley cell, or Hadley circulation, is a large-scale overturning of air in the tropical troposphere. On an annual average, there is one cell in each hemisphere. Each cell extends roughly from the equatorial region toward about 30° latitude and occupies nearly the full depth of the troposphere.
All flashcards
Define the Hadley cell.
It is a tropical, thermally driven circulation in which air rises near the equator, moves poleward near the tropopause, descends in the subtropics, and returns equatorward near the surface.
What does thermally direct mean?
It describes a circulation in which warm air rises and cooler air sinks, as occurs in the Hadley cell.
At what approximate height does the upper branch flow?
Near the tropopause, around 12–15 km above Earth's surface.
How is the annual-mean Hadley circulation arranged?
It is approximately composed of one cell in each hemisphere, with both cells sharing a zone of rising air near the equator.
What does a mass-weighted, zonally averaged stream function diagnose?
It summarizes meridional mass transport at different latitudes and pressure levels.
Quiz questions
Near Earth's surface, which pressure pattern helps drive the Hadley cell's lower branch?Answer: Lower pressure near the equator and higher pressure in the subtropics.
How does Earth's rotation influence winds in the Hadley circulation?Answer: It deflects trade winds westward and poleward upper flow eastward, helping form the subtropical jet.
What does a zonally averaged stream function summarize when diagnosing the Hadley circulation?Answer: Meridional mass transport across latitudes and pressure levels.
What circulation pattern often becomes prominent near a solstice?Answer: A cross-equatorial cell that rises in the warmer hemisphere and descends in the cooler one.
What change in Earth's Hadley circulation has likely occurred since at least the 1980s?Answer: Poleward expansion, with the estimated rate varying by diagnostic.
Based on the Wikipedia article Hadley cell, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.