What is Clear Air Turbulence (CAT)?

Clear air turbulence is the most dangerous kind, as it occurs in cloudless skies with perfect visibility and oncoming turbulence cannot be picked up by weather radar. This leaves little to no time for the flight crew to warn passengers to return to their seats and buckle up. Despite, most turbulence-related injuries are due to clear air turbulence.

Clear air turbulence is the term for medium or high level turbulence in regions with significant wind shear. Turbulent areas of this kind are mostly free of clouds. However, sometimes you can find cloud formations (mostly ice clouds) that are typical for turbulent areas, or a higher concentration of water vapor in the vicinity of CAT. Both of these hint strongly at the presence of CAT.

This means that CAT can occur by the flight through a border of different air masses with significantly different densities. For instance where there is a temperature gradient and especially at the tropopause. A strong relationship exists between variations of wind speed from inflowing air and the CAT (wind speed ).

Different type of aircraft have a greater wing spread and mass. The vertical movements are less extreme than in smaller aircraft due to inertia. On the other hand, in wide body aircraft is more loaded. In extreme cases of CAT the structure could be damaged or break up.

*Note
Clear air turbulence (CAT) is turbulence when aircraft encounters when it is not in a cloud. With many types of clouds, especially thunderstorms, pilots can expect turbulence because of the way they are formed. With CAT, there are no clouds around. There are just clear skies as the name implies. It is caused by high altitude winds, mainly the jet stream.

Refer the sources below for more information.

Sources:
https://www.skybrary.aero/index.…/Clear_Air_Turbulence_(CAT)

https://www.sciencedirect.com/…/earth-…/clear-air-turbulence

https://www.faa.gov/docum…/…/advisory_circular/ac_00-30c.pdf

https://www.aviationweather.ws/079_Clear_Air_Turbulence.php