What is the best definition of wind shear?

Wind shear is defined as a variation in wind velocity and/or direction over a short distance. This can occur either vertically, as when winds change with altitude, or horizontally, as when wind speeds differ across shorter distances at the same altitude. The phenomenon of wind shear is significant in aviation because it can lead to sudden changes in aircraft performance, which can be critical during takeoff and landing phases.

Choosing the correct definition emphasizes that wind shear is not limited to one type of variation; it encompasses both wind velocity and direction changes. This broader definition is important because scenarios involving wind shear can involve complex interactions that impact flight safety.

The other options either restrict the definition of wind shear too narrowly by focusing solely on vertical or horizontal variations or inaccurately describe the scale of the phenomenon by suggesting it can occur over a large distance. Wind shear is particularly problematic when it occurs close to the ground, where aircraft are most vulnerable, reinforcing the need for an accurate and comprehensive understanding of the term.