Atmosphere's real layers: troposphere, tropopause, stratosphere
Four layers: troposphere, stratosphere, mesosphere, thermosphere. Told apart by temperature change, chemical composition, movement, density (PHAK ch.12). Three matter for flying:
| Layer | Vertical extent | Temperature with height |
|---|---|---|
| Troposphere | Surface to about 11 km (36,000 ft) on average | Falls: about 15°C at surface to about -56.5°C at top |
| Tropopause | Top of troposphere, about 11,000 m (36,089 ft) in standard atmosphere | Levels off near -56.5°C, the hand-off point (TC AIM AIR 2.10) |
| Stratosphere | Tropopause to about 50 km (31 mi) | Rises: about -56.5°C to about -3°C at top; ozone absorbs ultraviolet radiation |
Troposphere:
- Almost all weather happens here (AWH 4.3.1).
- Depth varies: shrinks Equator to poles; deeper in summer than winter.
| Location | Depth |
|---|---|
| Equator | About 18-20 km |
| 50°N/S | 9 km |
| Poles | Only 6 km |
(AWH 4.3.1)
Tropopause:
- Lid that traps weather below it.
- Wind speed normally highest at the tropopause, near jet stream core; drops above and below (TC AIM MET 11.2).
Stratosphere:
- Calm, little turbulence.
- Airliners cruise in lower part, above thunderstorm tops and convective turbulence (AWH 4.3.2).
- Very little water vapour.
Mesosphere: above stratosphere; temperature falls again (AWH 4.3.3).
Trap: the standard atmosphere (ISA) treats the troposphere as a fixed 36,000 ft everywhere; the REAL troposphere is thinner at poles, thicker at Equator, deeper in summer.
References
- FAA Aviation Weather Handbook (FAA-H-8083-28) 4.3.1-4.3.2
- TC AIM MET 11.2
- TC AIM AIR 2.10