Stratospheric conditions

050-09-07Pablo Asensio Martínez2026-04-011 min

The stratosphere is the layer of the atmosphere situated immediately above the troposphere. The boundary between the two is the tropopause, which in the International Standard Atmosphere (ISA) is found at 36,090 feet (11 km).

Atmosphere Layers

Characteristics of the Lower Stratosphere

  1. Temperature:
    • It is an isothermal layer in its lower part (up to approx. 60,000 feet), meaning the temperature remains constant with height (at -56.5°C in ISA).
    • Above that level, the temperature begins to increase gradually due to the absorption of ultraviolet radiation by ozone.
  2. Stability:
    • Because the temperature does not decrease with height, the stratosphere is extremely stable.
    • There is very little vertical air movement.
  3. Humidity and Clouds:
    • The air is very dry.
    • There are practically no clouds, except for the tops of violent Cumulonimbus clouds penetrating the tropopause or very rare polar stratospheric clouds.
  4. Density:
    • Air density decreases rapidly with height.

Advantages of Stratospheric Flight

Most modern commercial aircraft fly in the lower stratosphere (or near the tropopause) for several reasons:

  1. Fuel Efficiency: Jet engines operate more efficiently at high altitudes due to the low temperature and low air density.
  2. Speed:
    • Low air density reduces parasite drag.
    • A higher True Airspeed (TAS) is obtained for the same Indicated Airspeed (IAS).
  3. Comfort (Less Turbulence): Being above most weather phenomena and in a stable layer, the flight is much smoother.
  4. Weather Avoidance: The vast majority of clouds and storms, which are confined to the troposphere, are avoided.

Considerations

  • Wind: Although there is less vertical movement, horizontal winds can be very strong (Jet Streams).
  • Ozone and Radiation: At these altitudes, exposure to cosmic radiation and ozone is higher than at lower levels.