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Smoke from a crop-duster shows wake turbulence

Smoke from a crop-duster shows wake turbulence (NASA Langley Research Center [Public domain], Wikimedia Commons)

STEM in Context

What is Air Turbulence?

Let's Talk Science
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Video Text Images
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Summary

Learn about the science behind the four main causes of 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!

Cumulonimbus clouds as seen from a small aircraft
Cumulonimbus clouds as seen from a small aircraft (Shawn from Airdrie, Canada [CC BY-SA 2.0] via Wikimedia Commons).

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.

Clouds flowing over a mountain range
Clouds flowing over a mountain range (chuyu via iStockphoto).

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.

Animation of jet streams. The strongest winds are coloured red
Jet streams. The strongest winds are coloured red (NASA/Goddard Space Flight Center [Public domain] via Wikimedia Commons animation).

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! 

Wake turbulence created by the wingtips of a C-17 Globemaster. The “smoke angel” is caused by flares released by the aircraft
Wake turbulence created by the wingtips of a C-17 Globemaster. The “smoke angel” is caused by flares released by the aircraft (Tech. Sergeant Russell E. Cooley IV [Public domain] via Wikimedia Commons).

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!

The Ups and Downs of Air Turbulence (2014) by SciShow (3:25 min.).

Starting Points

Connecting and Relating

  • Have you ever experienced turbulence on an airplane? How did it make you feel?

  • Should people planning to fly expect to experience turbulence? Explain.

  • When you fly, is it possible to prepare for air turbulence? Why or why not?

  • Would you want to fly through a thunderstorm? Why or why not?

Connecting and Relating

  • Have you ever experienced turbulence on an airplane? How did it make you feel?

  • Should people planning to fly expect to experience turbulence? Explain.

  • When you fly, is it possible to prepare for air turbulence? Why or why not?

  • Would you want to fly through a thunderstorm? Why or why not?

Relating Science and Technology to Society and the Environment

  •  such things as storms and turbulence.

  • Scientists have a good understanding of turbulence and its impacts on aircraft. But can safety be guaranteed for those travelling by air? Explain.

  • It is currently impossible to have computers model the complexities of turbulence. Do you think we will ever have computers that can do this? Why or why not?

Relating Science and Technology to Society and the Environment

  •  such things as storms and turbulence.

  • Scientists have a good understanding of turbulence and its impacts on aircraft. But can safety be guaranteed for those travelling by air? Explain.

  • It is currently impossible to have computers model the complexities of turbulence. Do you think we will ever have computers that can do this? Why or why not?

Exploring Concepts

  • What causes convection currents in the atmosphere? Describe a weather pattern that results from convection.

  • What is wind? How is wind related to air turbulence?

  • What are jet streams? How do they affect air currents?

  • Using the internet or other sources, research the maximum height a convective air mass, such as that found in a thunderstorm, can reach in the atmosphere. Compare this to the average height that a passenger jet normally flies. What conclusions can you draw?

Exploring Concepts

  • What causes convection currents in the atmosphere? Describe a weather pattern that results from convection.

  • What is wind? How is wind related to air turbulence?

  • What are jet streams? How do they affect air currents?

  • Using the internet or other sources, research the maximum height a convective air mass, such as that found in a thunderstorm, can reach in the atmosphere. Compare this to the average height that a passenger jet normally flies. What conclusions can you draw?

Nature of Science/Nature of Technology

  • How does our understanding of air turbulence provide a good example of the limits of scientific understanding of natural phenomena? Explain.

Nature of Science/Nature of Technology

  • How does our understanding of air turbulence provide a good example of the limits of scientific understanding of natural phenomena? Explain.

Media Literacy

  • What are some examples of turbulence forecasting websites and resources that you can find online?

Media Literacy

  • What are some examples of turbulence forecasting websites and resources that you can find online?

Teaching Suggestions:

  • This video and article can be used to support teaching and learning of Earth Science and Weather related to wind. Concepts introduced include turbulence, air flow, thermal turbulence, convection, heat transfer, fluids, cumulonimbus, mechanical turbulence, mountain range turbulence, eddies, clear-air turbulence, jet streams, tropopause, wind shears and wake turbulence. 

  • To engage prior knowledge and introduce new terminology before reading this article, teachers could have students complete a Vocabulary Preview learning strategy. Ready-to-use Vocabulary Preview reproducibles for this video and article are available in [Google doc] and [PDF] formats. 

  • Before students read this article, they could also watch: What Is Wind? This video may provide a review of concepts already learned or an introduction of new content. If this is new content, teachers could use the Video Review learning strategy to have students analyze and reflect on the concepts contained in the video. Ready-to-use reproducibles for this strategy can be downloaded in [Google doc] and [PDF] formats.

  • After students have reviewed how wind is formed, teachers could lead a discussion about the flow of air molecules and how this affects atmospheric conditions. The video The Ups and Downs of Air Turbulence provides concrete examples of how moving air and convection help create turbulence. Teachers could use a Question Creation Chart (QC2) to encourage students to think deeper about this topic. Ready-to-use reproducibles for this strategy can be downloaded in [Google doc] and [PDF] formats.

  • After reading the article and engaging in discussion, teachers could use the Concept Definition Web learning strategy to provide students with an opportunity to consolidate recently learned information. This can be done individually or in small groups. Ready-to-use reproducibles for this Concept Definition Web is available in [Google doc] and [PDF] formats.

Teaching Suggestions:

  • This video and article can be used to support teaching and learning of Earth Science and Weather related to wind. Concepts introduced include turbulence, air flow, thermal turbulence, convection, heat transfer, fluids, cumulonimbus, mechanical turbulence, mountain range turbulence, eddies, clear-air turbulence, jet streams, tropopause, wind shears and wake turbulence. 

  • To engage prior knowledge and introduce new terminology before reading this article, teachers could have students complete a Vocabulary Preview learning strategy. Ready-to-use Vocabulary Preview reproducibles for this video and article are available in [Google doc] and [PDF] formats. 

  • Before students read this article, they could also watch: What Is Wind? This video may provide a review of concepts already learned or an introduction of new content. If this is new content, teachers could use the Video Review learning strategy to have students analyze and reflect on the concepts contained in the video. Ready-to-use reproducibles for this strategy can be downloaded in [Google doc] and [PDF] formats.

  • After students have reviewed how wind is formed, teachers could lead a discussion about the flow of air molecules and how this affects atmospheric conditions. The video The Ups and Downs of Air Turbulence provides concrete examples of how moving air and convection help create turbulence. Teachers could use a Question Creation Chart (QC2) to encourage students to think deeper about this topic. Ready-to-use reproducibles for this strategy can be downloaded in [Google doc] and [PDF] formats.

  • After reading the article and engaging in discussion, teachers could use the Concept Definition Web learning strategy to provide students with an opportunity to consolidate recently learned information. This can be done individually or in small groups. Ready-to-use reproducibles for this Concept Definition Web is available in [Google doc] and [PDF] formats.

Learn more

What Airplane Turbulence Is And Why It's No Big Deal (2018) 

This video (3:08 min.) from Tech Insider explaining the types of turbulence, what causes them and how they are not really as dangerous as they may seem. Note that this resource was also used as a reference.

Violent turbulence: A look at what causes shakes mid-flight (2016) 

Article from CBC News with infographics discussing the different degrees of severity of turbulence, the dangers associated with turbulence and the safety measures put in place to prevent injuries from turbulence.

References

Coffey, H. (2019, February 14). What is turbulence and can it cause your plane to crash? Independent.

Helmenstine, A. M. (2019, February 2). Convection currents in science, what they are and how they work. ThoughtCo.

National Severe Storms Laboratory. (n.d.). Severe weather 101 - Thunderstorms.

National Weather Service. (n.d.). Turbulence.

Pattenden, R., & Gonzalez, J. P. (2009, October 10). Turbulence. AviationKnowledge.

SciShow. (2014, December 15). The ups and downs of air turbulence.