Whether it's a gentle gust that rattles a window or a hurricane force that can rip off roofs, all wind is essentially the same thing: movement of air across the earth's surface. A quick glance out the window can tell you about how fast the wind is blowing, and in which direction. But what makes the air move? What forces are behind it? To answer these questions, it's important to know a thing or two about the earth's atmosphere.
You've probably heard weather forecasters talk about high and low-pressure systems. Although "light as air" is a common expression, the kilometers and kilometers of air in the atmosphere above are actually pushing down on us — this is called air pressure. (Water exerts the same type of force, only it's heavier. That's why you might notice your eardrums popping at the bottom of a swimming pool.)
Differences in air pressure are caused by changes in temperature on the earth's surface. Picture an air mass as being like a giant Fast Fact: A barometer is an instrument used to measure air pressure.bubble. When it warms up, it becomes less dense and it begins to rise, leaving a gap below. This means there is less air pressure, or an area of low pressure, at the surface. Cooler air from the surrounding area rushes in — remember that wind is simply moving air - and though we can't always sense the change in pressure, we can see, hear and feel the wind that this pressure change creates.
If warm air rises, then cool air must fall, which is exactly what causes a high-pressure air system. A "bubble" of cool air is dense, with tightly packed molecules that push downwards. But as the bubble falls, its air molecules get warmer and move faster. The air diverges, or spreads out, across the earth's surface.
Changing Winds, Changing WeatherFast Fact: Wind can be used for electrical energy production. Wind turbines are structures that are placed in windy areas to harness the power of wind.
All of this is happening all the time, all over the world. Air is dynamic; it's constantly moving in between high and low-pressure systems. Meteorologists use computer programs to figure out where these systems are, and where they are going.
High-pressure systems usually mean calmer conditions and sunnier skies. But a low-pressure system generally makes for unstable conditions and stronger winds, because the warm air masses of these systems can rise so rapidly. As the warm air shoots up in to the atmosphere, cool air swooshes in. Pay attention next time you notice the weather quickly change for the worse — you might be seeing a low-pressure system moving in.
Air pressure isn't the only factor that affects winds around the world. Geographic features — the lay of the land, so to speak — also play a role. The Rockies in western Canada are responsible for Chinooks, winds that become warm and dry as they are pushed down the eastern side of the mountain range. Chinook means "snow-eater," an apt description for this weird weather phenomenon that can send temperatures in Alberta soaring, from as low as -20 to over ten or 15 degrees Celsius in a matter of hours.
Global PatternsFast Fact: Prevailing winds, such as jet streams, are winds that are created from global circulation patterns.
Chinooks, and most other winds that we see on a day-to-day basis affect fairly small regions. But way up in the atmosphere, wind patterns exist on a much larger, global scale. Scientists have recently been able to map some these patterns using satellite photos.
The jet stream, for example, is like a wind superhighway in the sky. It's made of a band of fast moving winds that travel west to east almost 9,000 metres above North America. It's the reason why airlines must allow extra time for flights heading west — the plane has to move against the jet stream, which slows it down.
Although we might not feel the direct affects of winds high in the atmosphere, they do affect seasonal weather patterns and play a role in large-scale storms, like hurricanes.
Wind — What is it Good for?
Throughout history, people have learned to harness wind for recreation, transportation and energy. Wind power has been in the news more and more lately as Canadians look for alternative energy sources. The large blades on modern wind turbines, when propelled by wind, create energy that is converted to electricity.
Since 2000, over 30 new wind energy projects have been created in Canada. Although we often see images of the destructive power of wind, after a hurricane or tornado hits, wind farms across the country are making a positive difference in our growing cities.
Environment Canada Weather Office: http://www.weatheroffice.ec.gc.ca/
Meteorological Service of Canada: http://www.msc-smc.ec.gc.ca/
Canada Wind Farms and Turbines: http://www.canwea.ca/en/CanadianWindFarms.html
Thanks to Colleen Kimmett for her expertise and help on answering this question.