What atmospheric phenomenon can cause reduced visibility during landing?

Fog is a critical atmospheric phenomenon that significantly impacts visibility, especially during landing. It consists of water droplets suspended in the air, which scatter light and create a dense layer that can obscure pilots' sightlines. When visibility is compromised due to fog, pilots might have difficulty judging the distance to the runway and other critical landmarks, increasing the risk associated with landing maneuvers.

While strong headwinds can influence the aircraft's performance and landing speed, they do not directly affect visibility. Clear air turbulence is associated with unstable air masses and can cause in-flight disturbances but does not result in reduced visibility on approach or landing. Similarly, altitude changes themselves don’t inherently affect visibility; rather, it's often the weather conditions related to altitude that can impact sightlines, such as clouds or precipitation, rather than the fundamental process of transitioning between altitudes.