Some would explain what causes wind by defining what wind is. The common definition of wind is that it is air that flows from high pressure to low pressure. The direction of the wind is determined by the rotation of the planet. Although this definition may seem enough, there are other questions that arise from it. A truly curious person would want to know what causes differences in pressure and how exactly the Earth’s rotation affects wind direction. Finding the answers to these questions will allow you to know a more exact answer to what causes wind.
First of all, it should be understood that the nearer the air to the ground the more pressure it gets. This is because the air above pushes on the air below. Pressure in different places and times of the day will then vary because of the way energy from the sun is distributed and heated.
As the sun’s rays hit the earth, everything around absorbs the energy and heats the surrounding air. Once the air on land gets heated, it becomes lighter and therefore will tend to move up. The air over the sea which now has higher pressure will replace the displaced land air and will come in as wind. At night, the opposite will happen with warm sea air rising and air over land blowing in to replace it.
Obviously, the Earth’s spherical shape, topography and vegetation all ensure that not every part of the Earth will receive energy in the same manner and amount. Hence there will be differences in air pressure across different locations.
This is half the explanation of what causes wind. The second part is related to the Earth’s rotation. As the world turns, the atmosphere will turn too. Different levels of air however will also experience different effects of the rotation. Air high up in the atmosphere is not as affected as air below. It is this variation in the speed of air turning that causes them to merge resulting in wind near the ground.
A related concept to wind formation and rotation is the Coriolis force. As the Earth rotates, air in the Northern Hemisphere moves to the right while air in the Southern Hemisphere moves to the left. This means that the flow from high pressure to low pressure is not direct. A direct flow is possible though under certain weather conditions.
Wind speed will vary depending on certain conditions. Normal, daily winds however are often regulated or limited in speed by friction with the ground surface.
Some people don’t like windy days. Winds however are a necessary part of life on Earth. It is the movement of the wind that helps move heat away from the Earth. You can just imagine what life would be without windy days.