FAA Ground School Practice Test

The difference in wind direction at 5000 feet AGL compared to surface wind is primarily due to what?

1. Thermal updrafts

2. Friction between the wind and the surface

3. Altitude changes

4. Weather front movements

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

The correct answer highlights the role of friction between the wind and the surface in affecting wind direction. At lower altitudes, such as at the surface level, wind is significantly influenced by surface structures, terrain, and vegetation. These can create friction that alters the wind's speed and direction. This friction acts to slow down the wind and can cause it to change direction from the geostrophic wind that would prevail at higher altitudes, such as 5000 feet AGL. As the altitude increases, the influence of this surface friction diminishes, allowing the wind to flow with more consistency and in a more uniform direction aligned with higher atmospheric patterns. Consequently, the wind at higher altitudes tends to be more directly influenced by wider weather systems and less by local terrain or surface conditions. By understanding this mechanism, one can appreciate how variations in wind direction occur with altitude, helping pilots prepare for potential changes they might encounter during flights.