Tropopause - an important indicator of high-altitude flight

Flight attendant professional introduction: The tropopause is located at the top of the troposphere. It is a transition layer with a thickness of several hundred meters to one or two kilometers. Don't underestimate this thin layer, it is an important indicator when the aircraft is flying at high altitude.

The tropopause is like a watershed. Above it is the stratosphere, with clear skies and smooth airflow, and the temperature increases with height; below it is the troposphere, with ever-changing clouds, rain, thunder and lightning, and the temperature decreases with height. Generally speaking, the characteristics of air determine that the air with higher temperature is stable in the upper layer; the air with lower temperature is unstable in the lower layer. Therefore, the stratosphere is stable, while the troposphere is unstable. The tropopause is between the troposphere and stratosphere and indicates weather conditions above and below.

Clouds in the troposphere generally move upward to the tropopause and then stop, so the anvil-shaped cloud top of cumulonimbus clouds is often the same height as the tropopause. Cumulonimbus clouds are very harmful to flying, but we can roughly judge the possible height of cumulonimbus cloud tops based on the height of the tropopause, and try to avoid them when flying. In addition, solid impurities such as dust particles and smoke particles in the troposphere often accumulate below the tropopause, affecting aerial visibility.

The change in the height of the tropopause, the so-called tropopause slope, is also closely related to tropospheric weather. The tropopause is generally higher above warm air masses and lower above cold air masses. Sharp changes or even ruptures in the height of the tropopause often indicate the existence of high-altitude jets and turbulence at a certain height in the lower levels. Aircraft may be greatly affected when passing through these areas.

In addition to indicating the weather, the tropopause height is also an important reference for selecting route altitudes and making aircraft engines more efficient. Aircraft engines are efficient at low temperatures, so where is the lowest temperature among the stratosphere and troposphere? According to the previous introduction, we know that the area near the tropopause is the area with the lowest temperature within tens of kilometers near the surface. Therefore, it is most beneficial to fly in an area slightly higher than the tropopause. From the perspective of economic benefits, the tropopause height should also be considered when planning route altitude.

As an important reference indicator for high-altitude flight, the tropopause is highly valued by the International Civil Aviation Organization. On the high-altitude important weather forecast charts provided to pilots, the tropopause height is an item that must be marked. With the deepening of research, the changing rules of the tropopause will be further revealed.