Turbulence is one of the main reasons why some passengers absolutely hate flying. While some passengers can handle light jolts in high-speed trains, the same passengers may be more sensitive to minor jolts that will occur as a result of turbulence in the plane. Since not all turbulences are the same, it is necessary to address the various causes. So, what is turbulence? What are the factors that cause turbulence? How many types of Turbulence are there?
What is turbulence?
Irregularities in the airflow that help an airplane fly cause jolts, which is called turbulence. Turbulence, also known as air pockets, can cause a temporary sudden loss of altitude.
Clean air turbulence (CAT)
The Federal Aviation Administration (FAA) defines clean air turbulence (CAT) as “sudden severe turbulence that occurs in cloudless areas and causes aircraft to jolt violently”.
The FAA adds that the CAT definition is most commonly applied to higher altitude turbulence associated with wind shear, which is a change in wind direction or speed over a given distance.
Wind shear (temperature inversions)
Beyond identifying wind shear as a type of turbulence, it is known that temperature inversions can be a cause for wind shear. (Inversion: The formation of a multi-layered air structure by the accumulation of slightly heated air at high air pressure on the heavy and cold air layer.)
Temperature inversions are regions of strong stability that prevent the stable substrate from mixing with the warmer top layer. The greatest shear, and thus the greatest turbulence, is located at the tops of the inversion layer and occurs because the turbulence associated with temperature inversions creates a surface-based inversion, often as the Earth’s surface cools at night.
Jet stream turbulence is another term that can fall under wind shear but can also be categorized as its own turbulence. As the name suggests, turbulence comes from jet streams, which are strong horizontal winds that follow a wave-like pattern as part of the overall wind flow. Jet streams have been observed to occur at altitudes of 8 to 15 kilometers (5 to 9 miles).
Convective (thermal) turbulence
Thermal turbulence is created by columns of localized convective current (a rising column of hot air). These rising air columns come from surface heating or cold air moving over warmer ground.
Eddy turbulence
Wake vortex turbulence is encountered when an aircraft follows or passes behind another aircraft. This is why airplanes set minimum separation distances, caused by wingtip follow eddies created by the first airplane. This is also the reason why larger aircraft add the terms “heavy” or “super” to their call signs as another indication that sufficient space should be given to the 747 or A380.
Mechanical turbulence
Mechanical turbulence occurs when there is friction between the air and the ground. It is often the result of uneven terrain and man-made objects found at low altitudes. This uneven terrain (tall buildings and mountains) causes airflow to be blocked. The density varies depending on the strength of the surface wind and the nature of the surface.
Mountain wave turbulence occurs when strong eddies occur downwind from mountain ridges. Mountain waves are said to produce some of the most violent mechanical turbulence.
Front turbulence
This is accomplished by the removal of warm air by the sloping front surface of the cold air mass. This is where friction occurs between two opposing air masses and creates turbulence in the front zone. When warm air is humid and unstable, there can be a risk of thunderstorms that cause more severe turbulence.
As can be understood from the above definitions, turbulence can be caused by a wide variety of events, both natural and man-made, occurring at various altitudes. In order to avoid turbulence as much as possible, both the pilot and the airline operations personnel need to plan carefully.
