Private Pilot Private Exam

Why might wind direction differ between 5,000 feet AGL and the surface level?

1. Altitude adjustments made by pilots.

2. Friction between the wind and the surface.

3. Temperature differences at varying altitudes.

4. Changes in humidity levels.

The correct answer is: Friction between the wind and the surface.

Wind direction can differ between 5,000 feet AGL and the surface level primarily due to the friction between the wind and the surface. At lower altitudes, the wind encounters obstacles, such as buildings, trees, and uneven terrain, which create drag. This friction slows down the wind and alters its direction as it makes contact with the surface. At higher altitudes, like 5,000 feet, the wind is less influenced by these surface features. The airflow is more uniform and can follow the general wind patterns that are typically seen in the upper atmosphere, which are less affected by surface friction. Hence, the difference in wind direction between these two altitudes is a direct result of the varying impact of friction at lower levels, leading to the phenomenon where surface winds often blow at different angles compared to the winds aloft. While temperature differences and humidity levels can affect wind patterns and stability, the primary factor causing discrepancies in wind direction specifically between surface level and higher altitudes is the influence of surface friction.