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What causes Air Turbulence when Flying

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Flying through turbulence can prompt even the hardiest of air travelers to reach for their seat belt. With around 65% of weather-related aircraft incidents attributed to turbulence, it can certainly be problematic. But experiencing the odd bumpy flight is completely normal and in the majority of cases, nothing to worry about. Aircraft are built to withstand far more than even ordinary turbulence, plus pilots are trained to understand what causes turbulence and how best they can avoid it.

What causes turbulence?

Air turbulence is caused by many factors. However, four main types of weather conditions are known to cause turbulent flights. These are the jet stream, clear air turbulence, wake turbulence and wind shear.

Weather patterns are formed in the lowest layer of the atmosphere, called the troposphere. Therefore, to try and avoid turbulence, commercial jets typically fly in the next layer up, in the lower stratosphere where skies are calmer at around 39,000 feet.

Jet streams

Jet streams are responsible for our weather patterns and are caused where areas of high and low pressure meet. As the high pressure sinks and the low pressure rises, the stream of air flowing between them creates a vortex called the jet stream. Jet streams are particularly hazardous towards the center where wind speeds can reach up to 250mph. Pilots encountering jet streams flowing in the same direction (tail winds) may choose to follow it or fly higher to avoid it altogether.

Clear air turbulence

If you've ever been on a flight that's experienced a sudden apparent drop in height, the plane has most likely hit a patch of clear air turbulence, sometimes called an ‘air pocket’. Clear air turbulence (CAT) is of great concern for pilots since it occurs in areas without cloud and is therefore invisible to conventional weather radars. Clear air turbulence is the air that has been dissipated around a jet stream so is most often found in the upper troposphere at around 23,000–39,000 ft or near very high mountain ranges.

Wake turbulence

Wake turbulence is caused by the aircraft themselves. They create it when taking-off and landing and also along their flight path. It's much like the trail left behind a speedboat on a lake. Wake disturbance is particularly dangerous for aircraft at lower altitudes which is why it's vital that planes wait a given time before taking off or landing to allow the surrounding air to calm down and dissipate. Planes flying through wake turbulence can experience a great deal of shuddering or jolting and is one of the main reasons why passengers must always wear their seat belts on take-off and landing.

Wind shear

All air turbulence causes wind shear, but that associated with thunderstorms can be excessively dangerous.  Storm clouds produce wide reaching, strong upward and downward currents that can affect planes flying at high altitude, near the ground or even up to twenty miles away where the air seems visibly clear.

During a storm, colder air is forced downwards through the storm cloud. This ‘microburst’ of cold air hits the ground where it can shear up and spread in any direction, much like the gush of water from a tap bouncing up when it hits a basin. This wind shear can be exceptionally damaging to aircraft and has been attributed to several air crashes in the last few decades.

While some weather conditions known to cause turbulence can be largely avoided, air patterns are constantly changing so it's more than likely that some form of turbulence will be encountered during a flight. But with the skill of the pilots combined with the structural safety of the plane, the worst passengers should expect is the odd spilt drink and a bumpy ride.

More about this author: Caroline St Clare

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