Which of the following may contribute to clear air turbulence?

Clear air turbulence is primarily associated with atmospheric conditions that are typically found at high altitudes, especially in the vicinity of jet streams and strong wind currents. The most significant factors that contribute to this phenomenon include high-altitude winds and jet streams, which are fast-moving currents of air that can cause abrupt changes in wind speed and direction, leading to turbulence.

Jet streams, in particular, are known for being a primary source of clear air turbulence, as they can create significant wind shear—the rapid change in wind speed or direction over a short distance. This shear can occur near the edges of the jet stream, creating areas of instability that result in turbulence.

While terrain factors and pressure systems can influence weather patterns and conditions that might lead to turbulence, they do not directly cause clear air turbulence in the way that high-altitude winds and jet streams do. Therefore, the most relevant contributors to clear air turbulence are high-altitude winds and jet streams, making them the correct choices that focus on the dynamics present in the upper atmosphere.