Which phenomenon is defined as an increase in temperature with altitude?

• A. Inversion
• B. Inversion illusion
• C. Inverter
• D. Isobars

Answer: (A)

A temperature inversion occurs when the air temperature actually increases with height, instead of decreasing as normal. In the lower atmosphere, air typically gets cooler the higher you go, roughly 2°C per 1,000 feet. But when a warmer layer sits above a cooler layer, the temperature profile rises with altitude, creating an inversion. This happens when the surface cools quickly at night (radiational cooling), when air aloft is relatively warm over cooler ground (adiabatic warming or advection), or under subsiding high-pressure conditions.

Inversions act like a lid, making the atmosphere very stable and resisting vertical air movement. That stability often leads to fog or low stratus near the surface and can trap pollutants or smoke, while conditions above the inversion can be quite different. For pilots, this means low-level weather can be poor (fog, reduced visibility) even if higher layers look clear, and there can be a sharp change in air stability at the inversion top.

The other terms don’t describe this vertical temperature behavior: an inversion illusion isn’t a standard weather term, an inverter is electrical equipment, and isobars are lines of equal pressure.