What type of turbulence is often encountered in the vicinity of the jet stream, especially where no clouds are present?

Clear Air Turbulence is the correct answer because it refers specifically to turbulence that occurs in clear air, typically at high altitudes and often in the vicinity of the jet stream. This phenomenon can happen without the presence of clouds, which makes it particularly challenging for pilots to detect ahead of time. It is typically associated with wind shear and rapid changes in wind speed or direction, which are prevalent around the jet stream.

Clear Air Turbulence does not have visual indicators like clouds, leading to its unpredictable nature and making it important for pilots to be aware of its potential presence when flying in these conditions. Understanding this specific type of turbulence helps ensure safety and preparedness during flight operations.