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Global Wind
Patterns

Discover how unequal heating of Earth's surface creates predictable wind belts that shape our weather, climate, and ocean currents.

Earth & Space Science

What Is Wind?

Wind is the horizontal movement of air from areas of high pressure to areas of low pressure. The greater the pressure difference, the stronger the wind.

HIGH Pressure Cool, sinking air WIND LOW Pressure Warm, rising air

Unequal Heating Drives Circulation

Equator Direct rays Angled rays North Pole South Pole Warmest Coldest Coldest

The Three Convection Cells

Earth's atmosphere is divided into three major convection cells in each hemisphere. Together, these six cells redistribute heat from the equator toward the poles.

Hadley Cell
\(0°\) to \(30°\) latitude: warm air rises at the equator, moves poleward, cools, and sinks at \(30°\).
Ferrel Cell
\(30°\) to \(60°\) latitude: air circulates in the opposite direction, driven by the Hadley and Polar cells.
Polar Cell
\(60°\) to \(90°\) latitude: cold air sinks at the poles, flows toward \(60°\), warms, and rises.

Visualizing the Cells

\(90°\)N
\(60°\)N
\(30°\)N
\(0°\)
\(30°\)S
\(60°\)S
\(90°\)S
 Polar Ferrel Hadley Hadley Ferrel Polar Equator (ITCZ)

The Coriolis Effect

Earth rotates on its axis, which deflects moving air. This deflection is called the Coriolis effect. It does not create wind; it curves the direction of wind that is already moving.

Northern Hemisphere
Winds are deflected to the right of their direction of travel.
Southern Hemisphere
Winds are deflected to the left of their direction of travel.

Three Global Wind Belts

The combination of convection cells and the Coriolis effect produces three major wind belts in each hemisphere. Winds are named by the direction from which they blow.

Trade Winds
\(0°\) to \(30°\): blow from east to west (NE trades in N. Hemisphere, SE trades in S. Hemisphere).
Westerlies
\(30°\) to \(60°\): blow from west to east. They carry weather systems across the U.S. and Europe.
Polar Easterlies
\(60°\) to \(90°\): blow from east to west, bringing cold polar air toward the mid-latitudes.

Mapping the Wind Belts

\(90°\)N
\(60°\)N
\(30°\)N
\(0°\)
\(30°\)S
\(60°\)S
\(90°\)S
 Polar Easterlies Westerlies NE Trade Winds SE Trade Winds Westerlies Polar Easterlies

Pressure Belts & Calm Zones

Where convection cells meet, air either rises or sinks, creating pressure belts. These boundaries also produce unique calm zones.

ITCZ (Doldrums)
At \(0°\): rising air creates low pressure, light winds, heavy rainfall, and thick clouds.
Horse Latitudes
At \(30°\)N/S: sinking air creates high pressure, calm winds, and dry conditions (deserts form here).
Subpolar Low
At \(60°\)N/S: rising air creates low pressure, stormy weather, and the polar front.

Direction vs. Name

A common source of confusion: winds are named by where they come from, not where they are going. This is opposite to how we name ocean currents.

Wind Name Blows FROM Blows TOWARD
NE Trade Winds Northeast Northeast Southwest
Westerlies West West East
Polar Easterlies East East West

How Winds Shape Climate

1
Heat redistribution: winds carry warm air from the equator poleward and cool air back, moderating global temperatures.
2
Moisture transport: trade winds carry moisture over oceans, fueling tropical rain. Westerlies bring rain to continents.
3
Desert formation: sinking air at \(30°\) latitude creates dry conditions: the Sahara, Arabian, and Australian deserts sit here.
4
Ocean currents: surface winds push ocean water, creating currents like the Gulf Stream that further affect climate.

How to Model Wind Patterns

1
Draw the latitude lines: mark \(0°\), \(30°\), \(60°\), and \(90°\) in both hemispheres.
2
Label rising/sinking zones: rising at \(0°\) and \(60°\) (low pressure); sinking at \(30°\) and \(90°\) (high pressure).
3
Draw convection loops: connect rising and sinking zones with curved arrows (Hadley, Ferrel, Polar).
4
Apply the Coriolis effect: deflect surface winds right in the N. Hemisphere, left in the S. Hemisphere.
5
Label the wind belts: trade winds (\(0°\)-\(30°\)), westerlies (\(30°\)-\(60°\)), polar easterlies (\(60°\)-\(90°\)).

Example: Identifying a Wind Belt

1
Check the latitude range: \(45°\)N is between \(30°\)N and \(60°\)N.
2
Identify the belt: the \(30°\)-\(60°\) zone contains the westerlies.
3
Verify wind direction: westerlies blow from the west/southwest. Southwest winds confirm it.

Example: Predicting Climate

1
At the equator: warm, moist air rises in the Hadley cell, releasing moisture as heavy rain.
2
Aloft movement: the now-dry air moves poleward toward \(30°\) latitude.
3
Sinking air: at \(30°\), the dry air sinks, creating high pressure. Sinking air warms and absorbs moisture instead of releasing it.
4
Result: very little precipitation, clear skies, and arid conditions: perfect for desert formation.

Example: Coriolis in Action

\(30°\)N
\(15°\)N
\(0°\)
 Without Coriolis With Coriolis (deflected right) = NE Trade Wind

Common Mistakes

✕ Wind Direction Reversal
Saying "westerlies blow toward the west." Westerlies blow from the west, toward the east.
✕ Coriolis Creates Wind
The Coriolis effect only deflects wind that already exists. It does not generate wind: pressure differences do that.
✕ Mixing Up Cells
The Ferrel cell is indirect: it circulates opposite to the Hadley and Polar cells. Students often draw all three the same way.

Summary Table

Feature Trade Winds Westerlies Polar Easterlies
Latitude \(0°\) - \(30°\) \(30°\) - \(60°\) \(60°\) - \(90°\)
Direction (NH) NE to SW SW to NE NE to SW
Cell Hadley Ferrel Polar
Surface Pressure High at \(30°\) Low at \(60°\) High at \(90°\)
Climate Effect Tropical rain & deserts Mid-latitude weather Arctic cold outbreaks

Question 1 of 5

What is the primary cause of global wind patterns?

Question 2 of 5

A "westerly" wind blows from which direction?

Question 3 of 5

The Coriolis effect causes winds in the Northern Hemisphere to be deflected in which direction?

Question 4 of 5

Many of the world's largest deserts are found near \(30°\) latitude. Which convection cell feature best explains this?

Question 5 of 5

Which wind belt is responsible for moving most weather systems across the United States?