Temperature inversions
Normal: air cools with height. Temperature inversion: layer where temperature rises with height (warmer air over colder).
Isothermal layer: temperature constant with height (AWH 5.8.2). Boundary between inversion (rising) and normal lapse (falling).
Four formation types:
| Type | How it forms |
|---|---|
| Radiation (nocturnal) | ground cools on clear, calm night, chills air just above it |
| Subsidence | sinking air warms under a high, inversion aloft |
| Frontal | warm air overrides colder air at a front |
| Valley | cold air trapped in valley: drains downslope off high ground, pools on clear, calm night, warmer air above |
Inversion = most stable layer. Effects:
- Traps moisture, smoke, haze below it → poor visibility, fog; worst when relative humidity in layer is high (PHAK ch.12).
- Smooth air.
- Often marked wind shear at top.
Trap: inversion kills mixing; murk stays trapped below, so visibility under it is poor.
References
- FAA Aviation Weather Handbook (FAA-H-8083-28)
- FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25), ch.12