# how wind (outdoor/weather) is created.

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how wind (outdoor/weather) is created.

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Air is a gas and gases change volume based in temperature. When temperature changes, gas volume changes, and gas flows in or out to compensate. That is wind. There are other forces also that change pressure and humidity, which again change the characteristics of a gas volume.

warm air rises up, this is because there’s fewer air molecules on top of them.

this in turn is because there’s gravity working on them to pull them down and their own movement and them repelling each other which counteracts that gravity. so there’s more down near the ground where gravity is strongest, and fewer high up where it’s weakest (even though the gravitational difference isnt all that big).

so when air is heated up those molecules move faster, bounce more into the other molecules, since there’s fewer on top of them than to the side, some of them move upwards which reduces the density in that spot.

which in turn means that the surrounding air molecules (which are also always bouncing around just at a slower speed/rate) will less often bounce into a molecule when they fly towards this “empty” space, which means that “the air” moves from the outside towards that spot where the air was heated up.

this is then further impacted by humidity (making the air “heavier” thus less bouncy) and the rotation of the earth (coriolis effect).

Hot air rise. Cold air fall. For scientific reasons, hot stuff try to get less dense and thus tend to rise more easily.

Second part of the process is pressure. When you have something under pressure, it pushes against its boundaries. If there are no boundaries, it moves away to remove the pressure. When something is low pressure, it pull things in. That’s because things try to stay at the same pressure at all time. Example, if you take a bottle and close the cap, if you push on it, you can see the bottle bulge. The gas is trying to escape. If your remove the cap, the air escape by the open cap.

With this, we have both necessary processes understood: Heat make things less dense, which move things higher and vacuum pull things while pressure pushes things.

Imagine you have two columns of air. Nothing stopping them around. One is hot and one is cold. The air in the hot column will try and go up. Because of that, all that hot air going up is pushing at the top (creating high pressure) while making a vacuum (low pressure) at the bottom. If we look at the cold air column, the opposite is happening, the cold air fall, pushing at the bottom (high pressure) and making a vacuum at the top (low pressure). Because these two column are not restricted by a bottle, the area of high pressures try to move away to equalize pressure while the area of low pressure try to pull things for the same reason.

As a result, the hot air column start to expand at the top, filling the low pressure left by the cold air. At the bottom, the cold air goes to fill the vacuum left by the hot air. Wind is just that. That movement of air. The wind we feel on the ground is most often the cold air going to fill area of vacuum left by hot air rising.

One last question remain: Why are there area of cold or hot air? For that, it’s important to understand that “area” is a vague term. It can be a football field, it can be a couple of countries, or it can be a continent. So things can change dramatically from one place to the other. Most commonly it’s because the ground is usually hotter than the sky. Because the ground is mostly opaque, the majority of the ray of light from the sun turn into heat. So the ground gets hot. In the sky, the majority of the heat dissipate in the atmosphere. The full cycle end up being: Cold air fall, get heated by the ground, rise because it’s now hot air, cool because of atmosphere, rinse and repeat.

This is of course only one of the reason why air temperature change, ocean for example don’t heat the same way as the ground, in certain region certain geological land form prevent air from moving properly (mountains, etc…) and finally stuff on the ground can slow the wind down (even if it doesn’t stop it) and make it feel like there is less wind.