Weather: Wind

Wind is the movement of air across the surface of the Earth. Winds are named after the direction from which they blow. So, Northeasterly winds blow from the northeast. And a land breeze blows from the land towards the ocean.

Air moves because the Sun does not warm the surface of the Earth evenly. If the Earth did not rotate, hot air at the Equator would rise up into the atmosphere. Then it would push cold air from the poles towards the equator. But the Earth’s spin generates a force called the Coriolis force. This force makes things travelling long distances around the Earth appear to curve. This is what causes winds to blow mainly from a certain direction. 

A prevailing wind is a surface wind that blows mostly from a particular direction. 

As you can see in the image below, in the area close to the equator, the winds blow mostly from the northeast. This produces winds called the Prevailing Easterlies. North of the equator these winds are called the Northeasterly Trade Winds. South of the equator these winds are called the Southeasterly Trade Winds. 

Between 30° to 60°N and 30° to 60°S the winds blow mainly from the west. This produces the Prevailing Westerlies. At the poles the Coriolis force produces the Polar Easterlies.

Wind patterns can also be seen on a smaller scale in different regions of the world. In western Canada you could experience a Chinook. Chinooks are winds that become warm and dry as they are pushed down the eastern side of the Rocky Mountains. Chinooks can change the temperature in southern Alberta from -20℃ to over 15℃ in a few hours! On the other side of Canada, some areas are always exposed to very high winds. This is the case for the Wreckhouse area in Newfoundland. And the “Les Suêtes” winds will blow you over in Nova Scotia. 

Measuring Wind

Wind strength is the speed that wind blows. Most of us have experienced short bursts of high-speed wind. These are called gusts. Winds that blow non-stop for around a minute are called squalls. Winds that last longer than a minute have different names, according to their average strength. These include breeze, gale, storm, hurricane and typhoon.

People have created a number of tools to measure the wind. If you see a rooster and the symbols for north, south, east and west on the top of a building, you are looking at a weather vane. This tool pivots in the wind to show what direction the wind is coming from.

At airports, pilots use windsocks to determine wind direction. They can also use them to estimate the speed of the wind. Wind socks are tubes of thin material that move easily. When the wind isn’t blowing, the sock hangs straight down. When the wind is strong, the sock is parallel to the ground.

You can use an anemometer to measure the wind more precisely. Basic anemometers are made of cups mounted on arms. These arms pivot in the wind. The faster the wind blows, the faster the cups spin. Other anemometers look more like propellers with tails. The speed of the propeller indicates wind speed, and the tail shows wind direction.
 

Did you know?
The word anemometer comes from the Greek word anemos meaning ‘wind’ and metron meaning ‘measure.’

The speed of wind can be described using the Beaufort Wind Force Scale. 

The Beaufort Scale

The Beaufort Scale was created by Sir Francis Beaufort in 1805. He did not use wind speeds for each level. Instead he used descriptions of how a sail on a ship moves in different winds. The scale was updated in the 1850s. Meteorologists added the number of turns of an anemometer to each level. The numbers and speeds were made standard in 1923. Today, meteorologists usually describe wind speed in kilometres per hour or miles per hour.

In Canada, maritime winds forecast to be in the range of 6 to 7 are called strong, 8 to 9 are called gale force, 10 to 11 are called storm force, and 12+ is called hurricane force. Wind warnings are issued by Environment Canada.

Did you know?
Wind can be used to generate electricity. Wind turbines are structures placed in windy areas to harness the energy of wind.