Question

Describe how a Hadley cell works, and explain how Earth's rotation creates the trade winds.

Short answer

A Hadley cell is a large scale atmospheric convection current, where warm air rises at the equator, travels poleward high in the atmosphere, cools, and descends at around 30° north and south. The rotation of Earth affects these movements through the Coriolis Effect, causing the air to deflect to the right in the Northern Hemisphere and to the left in the Southern hemisphere. This deflection, combined with the return flow of air at the surface from high-pressure areas towards the equator, results in the creation of trade winds.

Step-by-step solution

Explaining the Hadley Cell

The Hadley cell is a large-scale atmospheric convection cell in which air rises at the equator and sinks at medium latitudes, typically about 30° north or south. This creates a circular movement of air often referred to as a cell. It begins with solar radiation heating the earth's atmosphere near the equator, causing the warm, moist air to rise (due to its lower density when compared to cooler air). As it rises, it cools, which results in the loss of moisture (precipitation). This air, now free of moisture, starts to descend around 30 degrees latitude in both the northern and southern hemispheres creating a region of high pressure.

Understanding the impact of Earth’s Rotation

As the Earth rotates, it causes an effect on moving objects known as the Coriolis effect. The Coriolis effect causes moving air to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

How Trade Winds are Formed

From step 1, we've established a high-pressure area around 30 degrees latitude. The Coriolis effect (step 2) then comes into play. This high-pressure air flows back towards the equator, but instead of following a straight path, the Coriolis effect causes this air to veer to the west in both hemispheres. This creates a consistent, westward airflow known as the trade winds.