Researchers at the University of Reading, UK, have assembled compelling evidence confirming what scientists have long predicted: air travel has become more rugged due to changes in the upper atmosphere's jet stream. Mark Prosser and his team analyzed climate data from 1979 to 2020 and revealed a significant increase in turbulence around the world over the past four decades.
Clear air turbulence, which occurs when different bodies of air collide at different speeds, has been influenced by atmospheric conditions. In the North Atlantic, a key region for major flight paths, severe turbulence increased 55%, from 17.7 hours in 1979 to 27.4 hours in 2020. Moderate turbulence also increased 37%, recording 96, 1 hours compared to 70 hours during the same period.
These changes can be attributed to changes in the jet stream caused by warmer air temperatures as a result of higher carbon dioxide concentrations. Intensifying wind shear (changes in wind speed and direction) leads to increased turbulence, according to Prosser.
Interestingly, turbulence has been increasing at a higher rate than climate models anticipated given the current level of global warming. The impact is being felt not only in the North Atlantic and the continental US, but also on flight paths over Europe, the Middle East and the South Atlantic.
Prosser predicts that the turbulence will continue to worsen as the weather continues to change. This poses challenges for airlines as they face increased wear and tear on aircraft and higher fuel costs due to flight diversions out of turbulence-prone areas. Ultimately, this translates into significant financial losses for the industry.
Passengers and crew may also experience longer periods of being tethered during flights to minimize the risk of injury. However, Prosser says there is little cause for undue concern, as fatalities resulting from turbulence on commercial airliners are extremely rare.
What is Air Turbulence?
The word turbulence derives from the Latin turbulentĭa and refers to the condition of that which is turbulent (disordered or agitated). An airplane, it can be said, suffers turbulence when it moves violently due to changes in the speed and direction of air currents. When air particles become disordered, disturbances appear, usually in the form of windmills.
Air turbulence is when the air starts to flow in a chaotic or random way. At high altitudes, the wind generally moves in a smooth horizontal current called "sheet flow." This provides the ideal conditions for a stable flight.
In an ideal combustion, all the fuel introduced into the chamber would be burned. In reality, combustion is all the more efficient the closer it approaches that ideal, and turbulence plays an important role in that efficiency. When the engine runs at low revs and it is more difficult to achieve a good burn, turbulence becomes more relevant.
The flows that do not present turbulence, but a smooth and stable movement, without any disturbance, are called laminar. If the moving fluid undergoes a variation or disorder of a certain importance, its flow becomes turbulent.
What causes air turbulence?
The type of turbulence that affects commercial passenger flights has three main causes.
The first is thunderstorms. Within a thunderstorm, there is a strong up-and-down movement of air, creating a lot of turbulence that can spread to the surrounding region. Thunderstorms can also create "atmospheric waves," which travel through the surrounding air and eventually break up, causing turbulence.
Fortunately, pilots can usually see thunderstorms ahead (either with the naked eye or on radar) and will do their best to avoid them.
The other common causes of turbulence create what is commonly called "clear air turbulence." It comes from air that looks perfectly clear, with no clouds, making it harder to dodge.
Prosser warns that the turbulence will continue to worsen as the weather continues to change. This could result in increased wear and tear on aircraft, leading to higher maintenance costs and increased fuel consumption as pilots reroute flights to avoid turbulence-prone areas. Consequently, the aviation industry stands to lose substantial amounts of money.
Why is turbulence necessary for good combustion?
Combustion is a chemical reaction between an oxidizer (usual oxygen in the air) and a fuel. Activation energy, such as the spark produced by the spark plug, triggers the process by igniting the mixture. But it is necessary that this mixture be as homogeneous as possible so that all the fuel is burned and the greatest power is generated in each explosion.
Turbulence helps the elements mix better and therefore the engine runs more efficiently. Its presence in the mixture significantly affects the speed of propagation of the flame and other essential aspects for correct combustion.
To achieve this, the intake ducts or the combustion chamber itself can be designed in such a way that the generation of turbulence is favoured, either at the entrance of the mixture to the cylinder or during the compression phase.
Will climate change make turbulence worse?
Climate change is having a bigger impact on the jet stream than previously thought, evidence of an increased risk of turbulence affecting aircraft.
The turbulence associated with cumulus clouds – particularly cumulonimbus (thunderstorm clouds) – comes as no surprise to pilots. As an aircraft approaches these cloud formations or penetrates into them, the degree of agitation in the air increases, which is manifested in the aircraft in the form of rattling, more or less intense.
The new study shows for the first time that while the temperature difference between Earth's poles and the equator is narrowing at ground level due to climate change, the opposite is true at around 34,000 feet, the cruising altitude of a typical aeroplane.
These researchers suggest that the probability of suffering the unpleasant and dangerous experience of a severe CAT on a flight could double or even triple in the coming decades.
In a more recent study, also led by Professor Williams, thanks to atmospheric simulations carried out with a supercomputer, it has been possible to quantify how turbulence will increase on transatlantic flights in winter at a cruising altitude of 12 kilometres, in the period 2050-2018.
While the weak to moderate CAT will increase by 75%, the moderate will increase by 94% and the moderate to severe by 149%.
How dangerous is air turbulence?
Around the world, air turbulence causes hundreds of injuries each year to passengers and flight attendants on commercial aircraft. But, given the hundreds of millions of people who fly each year, those are pretty good odds.
Turbulence is usually short-lived. Furthermore, modern airplanes are designed to comfortably withstand all but the most extreme air turbulence.
And among the people who are injured, the vast majority are those who are not buckled up. So if you're worried, the easiest way to protect yourself is to wear a seat belt.
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