Wildland Firefighting Practice Exam

What external factor can initiate vertical air currents in unstable air?

1. Temperature changes

2. Wind shifts

3. Surface heating or orographic lifting

4. Humidity levels

The correct answer is: Surface heating or orographic lifting

Vertical air currents in unstable air are primarily initiated by surface heating or orographic lifting. When the surface of the earth is heated by the sun, it warms the air directly above it. As this air heats up, it becomes less dense and rises. If this process continues, it can create significant vertical air currents, which can be crucial in fire behavior, especially in wildland firefighting scenarios. Orographic lifting occurs when air moves over a mountain or hill, which forces the air to rise. As the air ascends, it cools, and depending on the moisture content, can lead to cloud formation and potentially precipitation. This lifting mechanism also contributes to vertical air currents and is vital in understanding how air behaves in different climates and terrains. Temperature changes can influence air density and contribute to stability or instability in the atmosphere, but they are part of the broader mechanism rather than a direct initiator. Wind shifts can affect the movement and direction of air but do not specifically create vertical currents in the same manner as surface heating and orographic effects. Humidity levels might influence temperature and density as well but do not by themselves initiate the upward movement of air.