What is the primary cause of Wind Shear?

The primary cause of wind shear is steep changes in wind velocity or direction. Wind shear refers to the variation in wind speed and direction over a short distance, either vertically or horizontally. This phenomenon is significant because it can lead to turbulence and affect flight operations, particularly during takeoff and landing.

When there are rapid changes in wind speed or direction, it creates instability in the atmosphere, which can have various impacts, including changes in aircraft performance and the potential for hazardous conditions. For instance, strong surface winds can differ significantly in speed and direction from the winds at higher altitudes, creating a shear layer that pilots must navigate carefully.

In contrast, high altitude temperature variations, pressure systems colliding, and increased humidity levels, while they can influence weather patterns and conditions, do not directly characterize the changes in wind speed or direction necessary to define wind shear. Thus, the identification of steep changes in wind velocity or direction as the correct answer encapsulates the essence of what wind shear entails.