Whether it’s a breeze or a gale, the science behind this invisible force will blow you away

The late Canadian author Marty Rubin wrote that ‘time and the wind never leave anything alone’. Indeed, wherever you are in the world, day or night, at whatever time of year, wind is an invisible, ever-changing force. You can’t see it or hold it, but it’s powerful enough to dry clothes on a washing line, carry sailing ships across the ocean and rip trees from their roots, making it one of the most important factors in determining the weather and climate. Climatologists describe wind as the movement of air caused by the uneven heating of the Earth by the sun and the Earth’s own rotation. This movement creates everything from the merest hint of a gentle breeze to destructive hurricanes and tornadoes. Meteorologists and weather watchers can learn and forecast a lot by measuring the speed, strength and direction of winds and how they interact with rain.

Under pressure

In relatively simple terms, wind occurs because of differences in atmospheric pressure. Air heated by the Earth rises, allowing cooler air to fall in its place. On a global scale, wind generally occurs where high-pressure air masses seek lower-pressure areas. These are called prevailing winds and tend to behave in a predictable pattern over broad areas of the Earth. Winds also occur around moving areas of high and low pressure. In the northern hemisphere the winds rotate counterclockwise around low-pressure fronts and clockwise around high-pressure fronts. In the southern hemisphere that’s reversed. This is why, when you watch a weather forecast on TV, you can see pressure fronts moving in and bringing storms. On a more local scale, winds are affected by the movement of air around seas and lakes, mountains, hills, valleys and even tall buildings.