Clear Air Turbulence (CAT)

 

Clear Air Turbulence (CAT) is a weather phenomenon that consists of turbulence produced in a friction-free atmosphere, in other words, turbulence produced at 3000 feet or higher and, is not associated with convective clouds such as cumulus or cumulonimbus. The biggest challenge of CAT is that it is invisible and can be encountered suddenly when there are no clouds. Therefore, it causes many incidents because there is no way to act before the turbulence begins. For example, the flight crew may think of deviating from the route or turning the seat belts on. Flights that encounter severe CAT are usually obligated to divert to the closest airport because passengers may need to receive medical attention. Also, this causes damages and economical penalties to the airlines.  

In theory, CAT forms when adjacent layers of air move at a different speed; a strong shear is formed at the contact point between these two layers, which gives rise to a ripple in the flow. Then whirlwinds are formed, and this is what we call CAT. As I said before, there is no exact way to predict CAT, however, some conditions may provide a clue to the pilots of this danger. For example, when the dew point is way far from the temperature, usually more than 13°, it is likely to encounter Clear Air Turbulence.