What makes the wind blow?
Wind is moving air. You can’t see it, but you can see what it does: trees sway, flags flap and kites fly.
Wind happens because the Sun heats Earth unevenly.
- The Sun warms some areas more than others.
- Warm air expands, becomes lighter and rises. This leaves lower air pressure near the ground.
- Cooler air nearby is heavier and has higher pressure.
- Air flows from high pressure to low pressure. That flow is wind.
The bigger the difference in pressure, the stronger the wind.
Measuring wind
| Tool | Measures |
|---|---|
| Wind vane | Direction the wind comes from |
| Wind sock | Direction and rough strength (used at airports) |
| Anemometer | Wind speed, with spinning cups |
Winds are named by where they come from. A north wind blows from the north toward the south.
The Beaufort scale
In 1805, British naval officer Francis Beaufort created a scale to estimate wind speed by observing its effects.
| Force | Name | Speed (km/h) | Signs |
|---|---|---|---|
| 0 | Calm | Under 1 | Smoke rises straight up |
| 2 | Light breeze | 6–11 | Leaves rustle |
| 4 | Moderate breeze | 20–28 | Small branches move; dust blows |
| 6 | Strong breeze | 39–49 | Large branches move; umbrellas hard to use |
| 8 | Gale | 62–74 | Twigs break off trees |
| 10 | Storm | 89–102 | Trees uprooted |
| 12 | Hurricane force | 118 and up | Severe destruction |
Local winds
Sea and land breezes
| Sea breeze (daytime) | Land breeze (night) | |
|---|---|---|
| What heats faster | Land heats faster than water | Land cools faster than water |
| Air rises over | Land | Water |
| Wind blows | From sea to land | From land to sea |
That’s why beaches often feel breezy and cool on sunny afternoons.
Mountain and valley winds
During the day, sunlit mountain slopes warm and air flows uphill (valley breeze). At night, cool air sinks down the slopes (mountain breeze).
Chinooks
A chinook is a warm, dry wind that blows down the eastern slopes of the Rocky Mountains. It can melt snow fast and raise temperatures dramatically. In 1962, a chinook raised Pincher Creek, Alberta’s, temperature by 41 °C in one hour, from −19 °C to 22 °C.
Global winds
The Coriolis effect
Earth spins from west to east. This makes moving air curve: to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is the Coriolis effect.
Wind belts
Uneven heating plus the Coriolis effect create global wind belts called prevailing winds.
| Wind belt | Latitude | Direction | Notes |
|---|---|---|---|
| Trade winds | 0–30° | From the east | Sailing ships used them to cross oceans |
| Westerlies | 30–60° | From the west | Bring most of Canada’s weather from west to east |
| Polar easterlies | 60–90° | From the east | Cold winds from the poles |
Near the equator is a calm zone called the doldrums, where sailors could be stuck for weeks.
The jet stream
The jet stream is a narrow band of very fast wind about 9–12 km up, blowing from west to east, often over 150 km/h and sometimes much faster. Pilots use it: flights from Vancouver to Toronto are often faster than the return trip. The jet stream also steers storms across Canada.
Wind and weather
- Low-pressure systems spin counterclockwise in the Northern Hemisphere and bring storms.
- High-pressure systems spin clockwise and bring calm, clear weather.
- Hurricanes and tornadoes are extreme spinning winds.
Using the wind
People have used wind for thousands of years:
- sailboats
- windmills for grinding grain and pumping water
- kites and gliders
- wind turbines for electricity
Wind power is one of the fastest-growing sources of renewable energy. Canada has many wind farms, especially in Ontario, Quebec and Alberta.
Common mistakes
- Saying a north wind blows toward the north.
- Thinking wind is caused by trees moving. Trees move because of wind.
- Thinking wind always blows from cold to warm places. It blows from high to low pressure.
Try it yourself
- Make a wind vane from a straw, a pin, a pencil eraser and cardboard. Record wind direction each day.
- Use the Beaufort scale to estimate today’s wind speed.
- Light a candle near a cold window (with an adult). Watch which way the smoke drifts and explain.
Quick recap
- Wind is air moving from high pressure to low pressure.
- Uneven heating by the Sun causes pressure differences.
- Sea and land breezes come from differences in heating of land and water.
- The Coriolis effect curves winds into global belts like the westerlies.
- The jet stream steers weather; wind can also generate electricity.