Private Pilot Private Exam

What is the most frequent cause of ground or surface-based temperature inversions?

1. High winds during the day

2. Terrestrial radiation on a clear, relatively still night

3. Cold fronts passing through

4. Warm air rises rapidly

The correct answer is: Terrestrial radiation on a clear, relatively still night

The most frequent cause of ground or surface-based temperature inversions is indeed terrestrial radiation on a clear, relatively still night. During the night, especially in clear conditions without cloud cover, the ground loses heat rapidly through radiation. This cooling affects the layer of air closest to the surface, which cools down as well. However, with little to no wind, the cooler air gets trapped near the ground while warmer air remains above it, resulting in a temperature inversion. In contrast, high winds during the day tend to mix the air layers, which disrupts the formation of inversions. Cold fronts can cause temperature shifts but typically do not lead to surface inversions during their passage; instead, they often create turbulence and unstable air masses. The rapid rise of warm air is associated with convection and leads to the mixing of air layers, which counters the conditions necessary for a temperature inversion to occur. Thus, terrestrial radiation during calm, clear nights is what primarily leads to these temperature inversions.