What is Air Turbulence?

You’re sitting comfortably in an airplane seat. Maybe you’re watching a movie or playing a game. The snack and beverage cart is just a few rows in front of you. It’s almost your turn! 

Suddenly, the seatbelt sign comes on. The flight attendant pushes the cart to the back of the plane. The plane starts to bob up and down. A voice comes over the loudspeaker. “Ladies and gentlemen, we are experiencing turbulence…”

Turbulence can be scary. But like many things, it’s a little less scary when you learn the science behind it.

Turbulence refers to unsteady movements in air or water. When you’re in a plane, turbulence results from changes in airflow. Airflow can refer to the movement of air from one area to another. It can also refer to the movement of air relative to the surface of a body travelling through it - like an airplane, for example.  

There are four main causes of turbulence:

1. Thermal turbulence

2. Mechanical turbulence

3. Wind shears

4. Wake turbulence

Let’s look at each of these in more detail.

What is thermal turbulence?

Turbulence caused by rising warm air is called thermal turbulence. Warm air rises because of convection. That is a type of heat transfer that occurs in fluids (liquids and gases). 

Convection happens when there is a temperature difference within a fluid. Molecules in the warmer area have more energy than molecules in the cooler area. Warmer molecules are also less dense. Because warm air rises and cool air sinks, molecules from the cooler area rise toward the warmer, less dense area. This causes molecules to cool, lose energy and drop again. 

The movement of molecules creates a convection current. Convection currents can cause thunderstorms. Thunderstorms are a common cause of thermal turbulence.

Thunderstorms happen when warm, moist air moves up quickly. When this happens, water vapour condenses into droplets. As each droplet condenses, it releases a tiny amount of heat. But when many droplets release heat at the same time, the result is a sudden, warm mass of air. 

These masses of warm air are extremely strong! They can move an airplane up and down. Fortunately, thanks to radar, pilots can find out about thunderstorms along their route and take a different route to their destination instead.

Did you know?

The type of clouds that form thunderstorms are called cumulonimbus clouds. You can easily recognize them by their large, towering size and distinct anvil shape!

What is mechanical turbulence?

Mechanical turbulence happens when natural or human-made objects on the Earth’s surface disrupt airflow. For example, mountains and tall buildings can cause mechanical turbulence.

Mountain range turbulence is a form of mechanical turbulence. It happens when wind blows horizontally over a mountain range. The wind moves like waves over the range’s various mountain peaks. This creates swirls of air called eddies. These waves of air can continue hundreds of kilometres away from a mountain. That’s why they sometimes catch pilots by surprise!

A similar effect happens when wind travels horizontally over the buildings in a city.

What is clear-air turbulence?

Have you ever experienced turbulence in a plane flying through what looked like a perfectly clear blue sky? It’s caused by clear-air turbulence. As the name suggests, it happens in clear, cloudless conditions. 

Clear-air turbulence occurs when two masses of air moving at different speeds meet. A common example is the meeting of jet streams. Jet streams are fast-moving air currents. They circulate the Earth in a region of the atmosphere called the tropopause. That’s the boundary between the troposphere and the stratosphere. The troposphere is the layer of the Earth’s atmosphere closest to the surface.The stratosphere is the layer of atmosphere above the troposphere.

Jet streams travel very fast. When they meet slower-moving air, they form eddies where warm air and cold air meet. For example, this happens when cold Arctic air meets warm air from the south. These rapid changes in wind speed are called wind shears.

Jet streams can cause turbulence that rocks a plane. They are also very unpredictable, so your pilot can’t always avoid them!

What is wake turbulence?

Finally, airplanes themselves can cause turbulence. Think of the pointy tips on airplane wings. When they push through air, they create eddies. And these eddies cause wake turbulence. It’s why pilots can’t take off or land immediately after another plane. It’s also why you never see a plane flying directly behind another one.

Did you know?

If you’ve ever been to an airshow, you may have noticed the planes flying in a V-formation. This was a military tactic developed during WWI to maximize firepower. But the V-formations also mean the planes don’t have to fly through the eddies created by each other’s wings! 

Should you be afraid of turbulence?

Most people agree that turbulence can be uncomfortable. And a lot of us probably find it a little scary. But it’s important to remember that the air travel industry is designed with safety in mind.

For example, air traffic controllers track potential air disturbances. When pilots experience turbulence, they report it to air traffic control. Air traffic control can then advise other pilots planning to fly that route to take a different path.

Modern airplanes are designed to withstand a lot of turbulence. For example, airplanes are designed to handle a load 1.5 times greater than what they experience in a typical flight.

Did you know?

If you’re worried about turbulence, choose a seat near the airplane’s wings. These seats tend to remain the most stable during turbulence.

According to the United States’ Federal Aviation Administration, on average there are only 33 turbulence-related injuries a year. When you think of how many people fly every day, that’s not a lot of injuries! 

People who get injured from turbulence are often not wearing their seatbelts. So the next time you’re on a plane and the seatbelt light comes on, do what it says!