I always experience winds on our planet and I know it’s caused by different pressure areas. What causes wind to keep perpetually going and not evening out in mostly an equilibrium with the only changes being caused by moving things such as cars.
In: Planetary Science
The sun heats the air causing it to rise. Rising air pulls in more air behind it. This is the main cause of wind. The planet rotates (which also directly affects wind) so there is constant change between day and night, meaning the same location inevitably heats and cools cyclically. Anytime one part of the atmosphere heats more than another part, it will cause wind so the only way to achieve equilibrium is for the sun to die (pretend it doesn’t destroy earth) and the planet freezes.
There’s many things causing the wind but the two biggest ones are the Sun and the Earths rotation.
The Sun is constantly heating one side of the planet so you get a constant heating and cooling effect of the ground and the air which causes air to circulate.
You also have the Earth’s rotation which causes the air to be dragged along for the ride. Because the air is fluid it doesn’t stay in one place over the ground.
There’s other things effecting it was well like Ocean temperature, mountain ranges, and the fact Earth is cooler at the poles vs the equator among other things.
The earth rotates, the sun warms and cools different areas, each with different elevations and amounts of sunlight they absorb into heat. So, the Earth is always going through a cycle of irregular heating and cooling, and since hot air and cold air don’t have the same density, this creates air currents.
Equilibrium in a system very often implies some kind of steady state. In the simplest systems, this is when a system is mostly “closed” ie nothing significant enters or leaves the system. There are, of course, also dynamic steady states but that usually involves a “big picture” view – the dynamic “steady state” usually involves turbulence or chaos in the margins. (Think of a river – at a big picture level, water flows at a steady rate and nearly fixed volume but looked at closely, the river has vortices, eddies and waves that are constantly changing)
This is somewhat similar to the earth, it constantly receives energy from the sun and this cycles between day and night. And that energy heats up stuff differently – water and land don’t heat up at the same rate. This means the air also heats up at different rates. This leads to temperature and therefore pressure differences that cause winds. At a big picture level, these winds are fairly predictable (like an equilibrium state) because of the earth rotation – broadly west to east. But, like a river, looked at closer there will be turbulent behavior. To the earth, as a whole, this is not significant but at a human level, things like tornadoes and hurricanes are a big deal.
Ultimately, the fundamental driver of wind is the uneven heating of Earth’s surface. While Earth’s rotation plays a tremendous role in weather, it pressure differences ultimately come down to uneven heating. There are several causes for this.
First, we have the tropics getting more direct sunlight, and thus more heat, than the poles.
Next we have the day-night cycle: one side of the planet is getting heat and light from the sun while the other half is in darkness.
Third, we have different surface materials. Light-colored materials reflect more sunlight and so, all else being equal, won’t heat up as much in sunlight. Some materials have higher heat capacities than others, meaning it takes more energy to heat them up. In general, bodies of water heat up and cool down more slowly than land.
Mountains act as high-level heat sources, resulting in areas that are warmer than the air otherwise would be at such high elevations.
All this uneven heating means there is never a stable equilibrium.
The sun doesn’t heat the whole Earth equally. These means the atmosphere is heated unevenly. Additionally, we have oceans and deserts, so warm parts of the atmosphere that can take on a lot.of water, depending on where they are, may or may not take on that water.
The air is constantly trying to find equilibrium, we call that process “weather”
Hot air with lots of water is low pressure. High pressure is usually cold air with littler water. These high and low pressure systems are constantly moving around causing wind, and when a low pressure air gets lifted up in the air, it cools down and drops its water, causing rain.
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