In what conditions might a pilot encounter "wake turbulence"?

Wake turbulence is a specific type of turbulence that is created by a passing aircraft, particularly large airplanes, as they generate lift. This phenomenon occurs primarily during phases of flight like takeoff and landing when the aircraft is generating a significant amount of lift and is close to the ground.

When a large aircraft is in motion, it leaves a swirling pattern of air behind it, known as wake vortices. These vortices descend and can persist for some time. Therefore, if a smaller aircraft follows closely behind a larger one during takeoff or landing, it can encounter these wake vortices, which can cause erratic flight behavior and pose a risk to the smaller aircraft's stability.

The other conditions provided in the options do not typically lead to encounters with wake turbulence. High-altitude cruising often involves no significant wake effects due to the distance between aircraft. Clear weather with no nearby aircraft eliminates the possibility of any wake turbulence being present. Extended periods of level flight, similarly, do not involve the close proximity to a generating aircraft required for wake turbulence to affect another aircraft.