What is a thermal inversion and when does it typically form?

What is a thermal inversion and when does it typically form?

• A. A condition where temperature increases with height, trapping pollutants; common at night in valleys or under clear skies with high pressure
• B. A condition where temperature decreases with height
• C. A condition where humidity is very low at the surface
• D. A condition where wind speeds exceed 100 mph

Answer: (A)

A thermal inversion is a situation where warmer air sits above cooler air near the ground, so temperature actually increases with height in the lowest part of the atmosphere. This creates a stable layer that prevents vertical mixing, trapping pollutants close to the surface. It typically forms at night in valleys or basins where cold air pools in low-lying areas and the ground undergoes strong radiative cooling. Clear skies and high-pressure conditions amplify radiative cooling, allowing the surface air to become very cool while the air above stays relatively warm. The result is a shallow, stable layer that limits convection and can lead to haze or smog. The inversion usually breaks once the sun heats the ground after sunrise, promoting mixing through rising thermals and wind, which disperses the trapped air.

A thermal inversion is a situation where warmer air sits above cooler air near the ground, so temperature actually increases with height in the lowest part of the atmosphere. This creates a stable layer that prevents vertical mixing, trapping pollutants close to the surface. It typically forms at night in valleys or basins where cold air pools in low-lying areas and the ground undergoes strong radiative cooling. Clear skies and high-pressure conditions amplify radiative cooling, allowing the surface air to become very cool while the air above stays relatively warm. The result is a shallow, stable layer that limits convection and can lead to haze or smog. The inversion usually breaks once the sun heats the ground after sunrise, promoting mixing through rising thermals and wind, which disperses the trapped air.