Wind is a particular atmospheric phenomenon that is essential for the development of life on our planet as we know it. It is also a resource used by humans to obtain mechanical work and to produce electricity. This is what is called wind energy. But how is wind formed?
When talking about how wind is formed, it is key to understand that its origin is in the interaction between the sun's energy and the properties of the Earth's atmosphere.
Throughout this explanation, we will break down all the factors involved in the formation of wind, starting with the influence of the sun, the variability of temperature and atmospheric pressure, and ending with the types of wind that we can find.
The energy of the sun: The origin of everything
The sun is the main driving force behind wind formation. The Earth constantly receives solar energy, but this energy is not evenly distributed across its surface.
Solar radiation directly affects the equator, where temperatures tend to be much higher than at the poles. This causes the equatorial zones to warm more than the polar zones, generating a gradient or difference in temperature at a global level.
This temperature difference is crucial, because when certain areas heat up, the air above them also heats up and, as it heats up, it expands and becomes less dense.
This warm air, being lighter, tends to rise, and in doing so, it leaves an empty or low-pressure space on the surface. This is where air from other areas comes into play, as air always seeks to fill these empty spaces, moving from high-pressure areas to low-pressure areas to try to balance out the differences.
Atmospheric pressure and air movement
To better understand wind, we need to understand the concept of atmospheric pressure.
Atmospheric pressure is the force exerted by air on the Earth's surface. When an area has warm, less dense air, the pressure in that area will be low. Conversely, where the air is cold and dense, the atmospheric pressure will be higher.
This difference in pressure is what drives air movement: air will always move from areas of high pressure to areas of low pressure.
For example, imagine a beach on a hot day.
During the day, the land surface warms faster than the ocean. This causes the air over the land to warm and rise, creating a low pressure area. Then, cooler sea air, which is under higher pressure, moves toward the land to balance out this difference.
This movement of air, from high to low pressure, is what we call wind.
The rotation of the Earth and the Coriolis effect
In addition to temperature and pressure, another important factor in wind formation is the rotation of the Earth.
Because the Earth spins on its axis, winds do not move in a straight line from high-pressure areas to low-pressure areas. Instead, their path is deflected by the Coriolis effect. This phenomenon causes winds in the Northern Hemisphere to deflect to the right, while in the Southern Hemisphere they deflect to the left.
The Coriolis effect influences wind circulation patterns in the atmosphere. It not only affects surface winds, but also large wind systems in the upper layers of the atmosphere, creating the circulation patterns we know as Hadley, Ferrel and polar cells, which determine the main types of wind globally.
Atmospheric circulation and wind cells
Earth's atmospheric circulation system is made up of several "wind cells," which are currents of air that circulate in specific patterns.
There are three circulation cells in each hemisphere: the Hadley cell, the Ferrel cell, and the polar cell, which I describe below:
- Hadley Cell : Located in the tropics, between the equator and approximately 30 degrees latitude. In this cell, warm air at the equator rises, moves north or south, and then descends in the subtropics, creating a constant circulation pattern.
- Ferrel cell : Located between 30 and 60 degrees latitude, where air moves in the opposite direction to the Hadley cell. This flow is driven by both air coming from the Hadley cells and cold air from the polar cells.
- Polar Cell : Found in regions near the poles, it functions in a similar way to the Hadley Cell, but at higher latitudes, where cold air tends to descend and then move towards the equator.
These circulation cells contribute to the formation of constant winds on our planet, such as the trade winds, westerlies and polar winds.
These winds are large currents of air that move in global patterns, influencing the climate and atmospheric conditions of different regions of the world.
Types of winds: Constant, periodic and local
We can classify wind into different types, depending on its regularity and origin:
- Steady winds : These are winds that maintain a relatively stable direction and speed, such as the trade winds, which blow steadily from high-pressure subtropical areas towards the equator. These winds have been known and used by sailors for centuries due to their stability.
- Periodic winds : These change direction depending on the time of year or day. A clear example is sea and land breezes. During the day, the land heats up faster than the sea, generating breezes that go from the sea to the land. During the night, the process is reversed: the land cools faster and the warmer sea air moves towards the ocean, generating a breeze in the opposite direction.
- Local winds : These are winds that occur due to factors specific to a region. Examples of these are the winds found in valleys and mountains, such as mountain and valley breezes, or the famous mistral wind in France, which flows down from the mountains towards the Mediterranean Sea, cooling the temperatures in the region.
Wind and its importance on Earth
The importance of wind goes far beyond simply moving the leaves of trees. Below I describe some of the effects we experience due to wind and the importance they have.
Winds play a key role in distributing heat and humidity across the planet, regulating temperatures and generating rainfall. This has a direct impact on ecosystems and human life.
At the energy level, wind is also a renewable energy source (wind power) that is widely used today since wind turbines can convert wind energy into electricity.
On the other hand, in agriculture, wind helps in pollination and healthy growth of many plants.
It is also essential in the formation of waves in the ocean, which have a major impact on marine life and coastal climate.
However, it can also have negative effects. When it becomes a hurricane or storm, the wind can cause destruction, eroding the soil, knocking down trees and seriously affecting human constructions.
How is wind measured?
To measure the wind, tools such as the anemometer, which calculates the wind speed, and the weather vane, which indicates its direction, are used.
Wind speed is measured in meters per second (m/s) or kilometers per hour (km/h), although it is also common to measure it in knots, especially in maritime and air navigation.
In meteorology, the Beaufort scale is a widely used reference for classifying wind intensity, from complete calm (0 on the scale) to a hurricane (12 on the Beaufort scale). This classification makes it possible to anticipate the effects of wind on nature and human activities.