Do you love windy days? The answer to that question probably depends upon where you are and what kind of weather you're experiencing. If you're on a tropical beach on a hot, sunny day, then a cool ocean breeze probably feels fantastic.
However, if you're walking several blocks to school on a frigid winter morning, then a bone-chilling breeze probably isn't welcome at all. On those days, the wind just makes you even colder than you already are.
If you spend much time outdoors, you already know that the wind comes and goes. But where does it come from? And where does it go? When it's windy, is there a giant creature in the sky blowing air your way? Is there a huge cosmic fan trying to cool you down?
Fear not! There aren't any massive fans or interstellar monsters creating and sending wind your way. Wind is actually a simple matter of science, and it's caused by something way out in space that you're very familiar with: the Sun!
Does that seem kind of odd to you? After all, wind usually cools you off. How is it that the star that heats our planet is also responsible for those cooling winds? Let's take a closer look at how winds come about.
At its most basic, wind is simply masses of air molecules moving very quickly. The air you breathe is made up of a variety of molecules. Nitrogen (78%) and oxygen (21%) make up most of the air you breathe. In addition to these two elements, there is also water vapor and a mixture of other trace elements.
At every moment of every day, you're surrounded by trillions upon trillions of air molecules that are moving around and colliding with each other, you, and everything else. As these air molecules bounce into and off of you, they exert a force on you that scientists call air pressure.
Scientists define air pressure as the amount of force the air molecules exert on any given area. As a general rule, the more air molecules there are, the greater the air pressure will be. Air pressure is not constant, because it varies as a result of different factors, especially temperature. These differences in air pressure are what give rise to wind.
So how does this relate to the Sun? The Sun heats Earth's surface every single day, but it doesn't do so evenly. Earth's surface is made up of different substances at differing elevations. As a result, the air above it will be unevenly heated by the Sun. For example, the air above land heats up faster than the air above oceans and lakes.
These different air masses will have different air pressures. As air above land heats up, it expands and rises higher into the atmosphere, creating an area of lower pressure in its wake. The air above a nearby ocean, on the other hand, will be cooler and heavier, resulting in higher air pressure.
As the warm air above land rises, the cooler air over the water will move quickly to fill the space left by the rising warm air. These quickly-moving air molecules are what we know as wind! In general, air molecules will tend to move more quickly and create wind as they move from an area of high pressure to an area of lower pressure.
The differences in air pressure that cause most winds are fairly small. For example, gentle winds on a spring day might be the result of a difference in air pressures of about 1% across several states. When air pressure differences are much greater (10%, for example) over a very small area, dangerous winds can form, such as those in a tornado.