Wind is an important phenomenon that we have all experienced. In this lesson, you’ll learn more about the definition, its causes, and characteristics. Then, test your knowledge with a quiz.
What Is Wind?
We have all experienced the feeling of wind blowing against our bodies.
Winds can range from a light breeze on a hot summer day to tornadoes and hurricanes with speeds of hundreds of kilometers per hour. Have you ever wondered what causes this phenomenon? How is wind formed?Let us start with first defining what wind is. On Earth, we have an atmosphere composed of air molecules. The air is free to move in every which way unless something is blocking it. For the purpose of our discussion, we define wind as the movement of air molecules in the atmosphere. However, it’s important to note that more generally wind can be defined as the flow of any gases, not only air.
Let us now proceed to discuss what causes wind.
Formation of Wind
Air pressure, which you can think of as the amount of force that air molecules exert via their collective weight above a specified area, often differs from one location to another. To draw an analogy, think of a waterfall. The differences in altitudes cause the water to flow downward. Similarly, whenever there is a difference in air pressure over some geographic region, air flows from areas of higher pressure to areas of lower pressure. Let us delve a little deeper.
There are several variables that affect wind formation, including the earth’s rotation and solar energy from the sun. The sun heats up water masses, such as seas and oceans, at a slower rate than their adjacent landmasses. This is because water has a higher specific heat, which is the amount of heat per unit mass necessary to increase its temperature. The warmer land heats up the air above it, causing it to become less dense than the air above the water. What results from this is an air pressure difference between the land and water masses, causing denser air from the sea to flow inland.
You may already have felt this effect as the cool breeze near a lake, sea, or ocean.Something similar happens on the larger scale. Since less solar energy is deposited in polar regions than at the equator, air near the surface of the equator becomes less dense than at the poles, leading to air flow from polar regions to the equator. It’s important to mention that these wind flow patterns are complicated by Earth’s rotation. As the Earth spins around its axis, it produces the Coriolis effect, which for the purpose of our discussion, is the deflection of air to the right in the northern hemisphere and to the left in the southern hemisphere.
In addition, while rotating, the earth drags air molecules at lower latitudes more than those at higher latitudes, which may result in wind near the Earth’s surface.
Characteristics and Properties of Wind
Wind can be characterized by its speed and direction. The direction is often expressed with a reference to where the wind originated; for example, a ‘southerly wind’ refers to wind that starts in the south and blows north. However, the more precise term wind shear or wind gradient is commonly used. It is a quantity that describes the speed and direction of wind flow at a given location.
To recap, we have talked about wind as being air movement through the earth’s atmosphere, or really, the flow of any gas through the air. It results from air molecules traveling from areas of higher air pressure, or the amount of force that air molecules exert via their collective weight above a specified area, to areas of lower air pressure.
The differences in air pressure can be caused by variables such as solar energy, which leads to specific heat (the amount of heat per unit mass necessary to increase its temperature) and the earth’s rotation, which produces the Coriolis effect (the deflection of air to the right in the northern hemisphere and to the left in the southern hemisphere). To characterize wind in terms of its speed and direction, we can use quantities such as wind shear (or wind gradient), which is a quantity that describes the speed and direction of wind flow at a give location.Can you now explain why you might feel a cool breeze in coastal areas?