Global Wind Patterns

Remember…

• When we talked about air pressure we said that cold air sinks and warm air rises. This movement causes air to move.

Key Vocabulary:

• Weather – the condition of Earth’s atmosphere at a specific time and place.

• Wind – the air that moves horizontally or parallel to the ground.

• Meteorologist – a person who studies the weather.

How Wind Forms

1. Sunlight strongly heats an area of the ground. The warm air rises and low pressure forms.

2. Sunlight heats an area of the ground less strongly. The cooler air sinks and high pressure forms.

3. Air moves as wind across the surface from higher to lower pressure.

How far does wind travel?

• The distance wind travels varies. • Some wind die out after traveling only a few

meters. • Global Winds travel thousands of kilometers

in steady patterns and can last for weeks.

Earth’s Rotation Affects Wind Direction

• Because Earth rotates, scientists are able to tell the directions wind will flow.

• The Coriolis Effect is the influence of Earth’s rotation on wind patterns.

• Global winds curve as the Earth turns beneath them. Winds in the northern hemisphere curve right and winds in the southern hemisphere curve left.

Global Wind Patterns

• The Earth’s rotation and the uneven heating of its surface cause a pattern of wind belts separated by calm regions.

Global Wind Patterns – Calm Regions

• The Doldrums – low pressure zone near the equator. Warm air rises and spreads out toward the poles.

• The horse latitudes – high pressure zones located at 30 degrees north and 30 degrees south. Warm air traveling away from the equator cools and sinks in these regions.

Global Wind Patterns – Wind Belts• The trade winds – blow from the east moving from

the horse latitudes toward the equator. These winds die out as they near the equator.

• The Westerlies – blow from the west, moving from the horse latitudes toward the poles.

• The Easterlies – blow from the east, moving from the polar region toward the mid-latitudes. Stormy weather often occurs when the cold air of the easterlies meets the warm air of the westerlies.

Horse Latitude

Doldrums

Jet Streams

• Not all wind occurs near Earth’s surface. • Jet streams flow in the upper troposphere

from west to east for thousands of kilometers. • Air in jet streams often moves at speeds

greater than 200 km per hour. • Just like other global winds jet streams form

because of the uneven heating of Earth’s surface.

• Each hemisphere has two jet streams, a polar jet stream and a subtropical jet stream.

How Does Wind Affect Travel

• Before the invention of steam engines sailors used sails to capture the wind and take them across the ocean.

• Name one area that sailors would have disliked. Why?

• Today jet streams affect air travel. They can make flights shorter or longer.

• Think of one example where a flight might be shortened because of a jet stream.