This blog was originally written for Il Trafiletto and accessible here.

Over the past two weeks, two flights have encountered turbulence strong enough to cause several injuries and, in one case, a death suspected to be from a heart attack. But what is turbulence, and how does it form? Here’s a closer look at this fascinating atmospheric phenomenon that anyone who has flown has experienced at least once.

Turbulence refers to the irregular movements of air vortices manifested through chaotic variations in speed and pressure, which can cause oscillations and shaking of the aircraft. A clear example of turbulence is cigarette smoke: initially, its motion is laminar, meaning without vortices, but after a few centimetres, it starts to become turbulent, creating the typical vortices and convolutions.

The most common turbulence phenomena encountered during a flight are convective turbulence (updrafts generated by solar heating, particularly intense over heated surfaces like cities or deserts), orographic turbulence (stationary waves in the atmosphere formed when a uniform airflow meets and overcomes an obstacle, such as mountain ranges, along its path), and wind shear (strong updrafts and downdrafts that can form near stormy areas), typically occurring at relatively low altitudes. However, it is not always possible to associate turbulence with visible atmospheric conditions or detect it with instruments. This is the case with CAT (Clear Air Turbulence), which forms when two layers of air with different temperatures move at different speeds, and the interface between the two layers creates waves in the air that, when breaking, become turbulent. It is precisely this type of turbulence that the Singapore Airlines flight SQ321 on May 21 and Qatar Airways flight QR017 on May 26 encountered.

CAT is usually more intense in the presence of very strong winds like jet streams: “rivers of air” with a cross-section of several tens of kilometers, extending for thousands of kilometers, with winds blowing from west to east at speeds between 150 and 400 km/h. Jet streams are found in the troposphere, the region of the atmosphere closest to the Earth’s surface, at an altitude between 6 and 12 km, the same as commercial flights. When possible, commercial pilots flying from west to east seek these currents to reduce flight times and fuel consumption. Since this type of turbulence has a limited vertical extent, pilots can exit CAT by taking the aircraft to a higher or lower altitude.

According to the latest study by the U.S. Federal Aviation Administration (FAA), between 2009 and 2022, 163 people, including passengers and crew, suffered serious injuries due to turbulence. This is because CAT manifests so suddenly that it is very difficult for crew members to warn passengers to fasten their seatbelts, increasing the risk of being thrown around the cabin.

Although injuries caused by turbulence are not new in aviation, a recent study by the University of Reading suggests that their number is set to increase. The research indicates that the presence of intense turbulence over the North Atlantic has increased by 55% in recent years, rising from 17.7 hours in 1979 to 27.4 hours in 2020. The study attributes the increase in turbulence to climate change: the warmer atmosphere, due to higher carbon dioxide emissions, is increasing wind shear within jet streams, leading to an increase in regions worldwide affected by CAT.

Turbulence is an integral part of flying. Pilots are trained to handle it, and airplanes are designed to withstand it. However, due to its unpredictability, it is always advisable to keep your seatbelt fastened for the entire duration of the flight, regardless of the latest news.