AUSTIN (KXAN) — Aviation is possible for humans through an understanding of physics and engineering, allowing us to overcome gravity and cross long distances in a way that would have been just a dream for most of our history.

However, natural occurrences can impede aviation; one of these is turbulence, an atmospheric phenomenon that induces chaotic changes to pitch, roll and yaw. It recently impacted a Lufthansa flight from Austin to Frankfurt, Germany and caused injuries to seven people.

The Federal Aviation Administration recommends passengers remain seated with safety belts buckled during flights in order to protect against unexpected turbulence. According to the agency, turbulence caused at least 146 injuries between 2009-2021.

How does turbulence form?

According to the National Weather Service, there are four causes of turbulence: mechanical, thermal, pressure fronts and wind shear. The impact of turbulence is rated from light (slight strain against safety restraints) to extreme (may cause structural damage).

Mechanical turbulence is created by the friction between wind and obstacles on the ground. Obstacles (trees, mountains, buildings, etc.) impede the wind, creating eddies of fast-moving air downstream. Faster windspeed creates bigger eddies and more severe turbulence.

Courtesy NWS

Thermal turbulence, caused by convection, happens below clouds and typically only impacts planes during takeoff and landing. Hot ground causes air to rise, cooling as it moves away from the heat, which leads to increased density and a resulting fall back down. An everyday example is a boiling pot of water.

Courtesy NWS

Frontal turbulence arises when low and high-pressure fronts collide — the warm air of a high-pressure front is lifted over the cold front. This collision can also form thunderstorms; if so, the turbulence will be more severe.

Courtesy NWS

Wind shear, or the change in wind direction and/or speed, can also create turbulence. This can occur at much higher altitudes than the other three causes and can reach well above the flight ceiling of commercial aircraft.

That high-altitude wind shear occurs in “patches” around the jet streams, which are narrow bands of fast-moving air. It is called clear air turbulence.

Clear air turbulence forecast for March 3 at 41,000 feet. (Courtesy NOAA)

Thunderstorms, according to the NWS, create strong vertical currents of air that can “displace an aircraft up or down vertically as much as 2000 to 6000 feet.” Usually, this kind of turbulence occurs at altitudes between 12,000 and 20,000 feet, and up to 20 miles away from the storm cell.