Winds

A Science Class Project

What is Wind?

Wind is the sideways movement of air. Wind moves parallel to the ground. It starts from an area of high pressure to an area of low pressure. Wind is caused by the unequal heating of earth's atmosphere, which causes these differences in air pressure. Wind speed can be measured with an anemometer. We can tell the direction the wind is blowing with a wind vane.

Local Winds and Global Winds

Local winds are winds which blow over short distances. They change speed and direction often and Local winds are caused by the unequal heating of Earth's surface within a small area. There are two types of local winds. Sea breezes and land breezes. Land breezes occur during the day, and sea breezes occur during the night.


Global winds are winds that blow over long distances. They are caused by the unequal heating of Earth's surface within a small area. Global winds in the Northern Hemisphere turn to the right. Global winds in the Southern Hemisphere turn to the left. This is caused by the coriolis effect. The coriolis effect causes winds to turn instead of going straight because of Earth's rotation. There are several types of global winds called global wind belts. Doldrums, horse latitudes, trade winds, jet streams, prevailing westerlies and polar easterlies are all types of global winds. Unlike local winds, global winds rarely change direction or speed. There are large convection currents that occur between the equator and poles. The equator has warm air. The warm air rises, and so does the air over the equator. Cool air from the poles blow in, and this air warms up and the cycle repeats.

Sea and Land Breezes

Sea Breezes are a type of local wind that moves in from the sea and towards the land. Sea breezes occur only during the day. The sun heats both the land and the water. However, the land heats up more faster than the water. The air above the land becomes warmer than the air above the water, which causes wind. The cool air (more dense, more air pressure) over the water moves towards the land. The warm air (less dense, less air pressure) over the land rises up. The air which moves from the sea and moves in to the land is called sea breezes.


Land Breezes are a type of local wind that moves in from the land towards the sea. Land breezes occur only during the night. The land and water cools off. However, the land cools down more faster than the water. The air above the water becomes warmer than the air above the land, which causes wind (unequal heating of the Earth's surface). The cool air over the land moves towards the water. The warm air over the water rises up. The air which moves from the land and moves in to the sea is called land breezes.

The Global Wind Belts

Global Wind Belts are a series of wind belts which circle the Earth. There are sections between the wind belts that are calmer areas.


Prevailing westerlies are that winds blow from west to east between 30° and 60° no matter what hemisphere they are in. These winds always blow FROM west, thus creating their name... prevailing westerlies. Prevailing westerlies are one of the three major global wind belts.



Polar Easterlies blow from the poles and curve to the east. Since they blow towards the east near the poles, they are called polar easterlies. Polar easterlies are one of the three major global wind belts.


Trade Winds are winds that lie between 0° and 30° latitude. These winds are very strong. Sailors usually use these winds so it can help move their cargo to other countries, trading goods. Thus, calling them trade winds. Trade winds are one of the three main global wind belts.


Doldrums are weak winds that are located at the equator, which is 0° latitude. The doldrums are extremely weak and are NOT part of the three main global wind belts.


Horse Latitudes are also very weak, and are located at 30° north and south latitude. Like the doldrums, they are not one of the major global wind belts.


Jet Streams are a band of extremely strong winds that are located in the upper troposphere. Airplanes usually use these streams to travel faster while also saving fuel. Jet streams were discovered during World War II and the wind speeds can be as high as 500 km per hour!