Which nighttime condition is most commonly associated with a ground-based temperature inversion?

• A. Clear, relatively still night
• B. Heavy rain
• C. Strong winds
• D. Dusk with high humidity

Answer: (A)

Radiational cooling at night is the key idea. When the sun has set on a clear night, the ground loses heat rapidly. If the air near the surface becomes cooler than the air above and the winds are light, there’s little mixing to disrupt it, so a cool layer sits near the ground and the temperature actually rises with height in that layer. This is a ground-based temperature inversion.

A clear, relatively still night is the condition that most readily produces this scenario because cloud cover and winds both tend to reduce radiative cooling and mix the air, preventing the formation of a strong near-surface inversion. Heavy rain, strong winds, or dusk with high humidity each introduce factors that either mix the air or prevent the pronounced radiative cooling needed for the inversion, so they’re less associated with the common occurrence of a ground-based inversion.