Got some questions about wind? We explain where it comes from, how it is formed, and how it’s measured in today’s article. Don’t miss the amazing facts at the end!
We’re all familiar with what wind is: that invisible force that dries our clothes, messes our hair up before an important event, or spins those giant wind turbines that are becoming more popular.
But where does wind come from and what causes the wind to blow? I for one have certainly always taken these questions for granted and it took a bit of research to find the answers.
There’s so much about the world that just seems “normal” to us that we sometimes forget to ask the important questions about how and why.
So, what causes wind to blow?
Wind is basically the flow or movement of our air on a massive scale. But it’s not just some spontaneous event that randomly happens. There’s a good reason for it and why some areas get more of it than others.
Our air is made up of tiny molecules. Generally speaking, it is compromised of the following:
- 78% Nitrogen (by volume)
- 21% Oxygen (by volume)
- 1 – 4% Water vapor (by volume, near the Earth’s surface)
- Other trace elements
Air at ground level has these ratios of molecules. These invisible molecules are so densely packed around us that one cubic inch of air around you right now contains approximately 1020 molecules. For those unfamiliar with scientific math notation that’s 100,000,000,000,000,000,000.
As you can imagine, with so many of these molecules moving around freely, it’s not exactly a very orderly arrangement that they have with each other. They collide with each other and their surroundings in a chaotic manner.
In fact, the more air molecules that are found in an area, the higher the air pressure there is in the area. The difference in air pressure between areas is a key factor in understanding how wind is formed.
Air molecules prefer to travel from high-pressure areas to lower pressure areas. Think of it like there not being enough space for them, so they need to “escape” and go somewhere where there is more room and less stress. A bit like escaping the city life for the countryside.
The technical term for this is the pressure gradient force. You can see a great explanation of it in the short video below.
So, why is the air pressure different from one place to the next?
The air pressure is essentially determined by temperature. A low-pressure area is usually warmer and wetter. As the sun heats the air, it rises and leaves behind more space and therefore less pressure. This warmer air, high in the atmosphere may then fall back down to Earth in the form of rain as it condenses.
High-pressure air systems are usually drier and cooler than their low-pressure counterparts.
Since the sun controls our temperature here on Earth (and therefore the air pressure), it essentially controls the flow of wind too.
Take a look at this awesome interactive Earth wind map to see the wind patterns across the planet.
What causes the wind to be stronger in places?
As we learned previously, the flow of wind is caused by differences in air pressure from one place to the next. The air molecules leave an area of high pressure to reach an area of lower pressure, therefore causing the effect we know as wind.
However, winds can vary in speed quite dramatically. So what causes this?
Well, the bigger the difference in air pressure between one area and the next, the stronger the wind will be.
We mentioned the pressure gradient force earlier as the scientific term for explaining how air pressure changes. Well more accurately, it measures how quickly the air pressure changes over distance. If the air pressure changes very quickly over a short distance then the pressure gradient force is said to be large. Large pressure gradients result in strong winds.
Wind is also affected by the surface over which it has to travel. Wind traveling over a heavily forested area will be slowed by friction as the trees provide a resistive force to the movement of the air. Conversely, wind that travels over large flat areas unopposed can travel more freely and pick-up speed. Think of the Great Plains of the American mid-west where the large, flat landscape allows winds to pick up speed unopposed before forming tornados. This isn’t the main reason tornados happen here (these storms form when the wet, warm air from the Gulf of Mexico meets the cold, dry Canadian air) but it certainly contributes.
How do we measure the wind?
Wind speed or strength is measured using a tool called an anemometer. The anemometer “catches” the wind which makes it rotate. The frequency of the rotation is converted into a speed measurement in kph or mph (or more accurately, meters per second)
But wind speed doesn’t have to be measured with a tool like an anemometer. It can also be judged with only your eyes and the surrounding environment. It was originally devised for sailors far out a sea but has since been adapted for wind over land too.
Invented in 1805 by Irishman Francis Beaufort, the Beaufort Scale allows windspeed to be given a numerical value according to its observable impact on the surrounding scenery.
Beaufort number one describes calm wind where smoke still rises vertically and is less than 1 km/h. Beaufort number 12, on the other hand, describes “devastation” caused by hurricane force winds of over 118 km/h.
Check it out in full here.
Fun Facts About Wind Speed
- The fastest wind speed ever recorded on Earth was from inside the eye of a tornado. Joshua Wurman’s tornado research team recorded 301 mph winds in a tornado in Oklahoma on May 3, 1999.
- The fastest wind speed unrelated to tornadoes was recorded during Tropical Cyclone Olivia on Barrow Island, Australia on April 10th, 1996. A weather station clocked wind gusts of 253 mph.
- The fastest recorded wind speed ever recorded in our galaxy was from inside the IGR J17091 black hole. NASA recorded the event using the Chandra X-ray Observatory and measured a wind speed of around 20 million mph! Wow!
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Till next time!