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Explain how environmental factors can result in atmospheric circulation.

Global Wind Patterns

An image showing what winds would look like if Earth did not rotate or tilt. The Earth is divided into two circulation cells - one in the northern hemisphere and one in the southern hemisphere. All of the winds are directed towards the equator. — **If Earth did not rotate and was not tilted on its axis, global winds would move in this simple pattern.**

The atmosphere is a dynamic system that is influenced by a variety of factors including the sun, the oceans, land areas, and gravity. Over years of study, climate scientists have identified a number of global wind patterns that influence life on Earth.

If the Earth did not rotate, warm air would rise at the equator and cool air would sink at the poles – a simple convection current.

This, however, isn’t exactly how global winds move because of the rotation and tilt of the Earth. Instead, the rotation of the Earth causes these winds to curve.

This curving of the winds is due to the Coriolis effect. The Coriolis effect results in the global wind patterns.

A gif of the global wind currents curving around Earth.

These patterns have names like the trade winds, westerlies, or easterlies and create areas such as the doldrums, the bane of many an early sailor, where little to no wind occurs much of the time.

Circulation Cells

In general, rising air forms rain as it cools, which is why rainforests and other areas of high rainfall are found in the areas where the air is rising.

When the falling air warms, it tends to be quite dry and causes deserts, which are located in the areas where cool air is falling. Because of this circulation, the sub-tropics are warm and dry, and the tropics are warm and wet.

An image of Earth, showing how Hadley Cells cause warm, wet areas in the tropics as warm, moist air rises at the equator, the air cools and rain falls on either side of the equator, and dry areas on either side of the tropics form as the cool, dry air descends. — In this satellite image of Earth, you can see the green areas in the tropics, and the dry areas on either side of the tropics, caused by
Hadley cells.

The Coriolis effect combined with the tilt of the earth helps create six main circulation cells in the atmosphere. Each of these cells influences the type of biome that will occur on the land areas beneath them.

Explore the interactive below to learn more about global circulation cells. Which cell is closest to where you live?

The dynamic nature of atmospheric circulation keeps scientists guessing when trying to predict the weather. Many variables play a role in influencing the weather and climate on Earth. A solid knowledge of these variables helps us better understand the influence of weather and climate on the biosphere.

Essential Knowledge

Global wind patterns primarily result from the most intense solar radiation arriving at the equator, resulting in density differences and the Coriolis effect.

AP Exam Tip

You should know that Earth has curved wind patterns due to the rotation of the Earth and how this influences global climate.

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