Vertical Structure

Earth’s atmosphere can be divided vertically based on its thermal properties. While many layers exists, the only two of significance to a pilot are the troposphere and the stratosphere along with the boundary between these two layers known as the tropopause.

Troposphere

The troposphere is the layer closest to Earth’s surface. The majority of the atmosphere’s mass is contained within the troposphere and so is nearly all of the water vapour. What is typically considered “weather” is, for the most part, found within the troposphere, although severe thunderstorms may penetrate into the stratosphere.

Within the troposphere the temperature generally decreases as altitude increases. This rate of change of temperature with respect to altitude is known as the lapse rate and plays a significant role in atmospheric stability – this will be discussed in a future lesson. The point at which the temperature begins to increase marks the transition from the troposphere to the stratosphere. This transition occurs at very high altitudes.

The vertical extant of the tropopause is:

Greatest around the equator and consistently decreases towards the poles and therefore takes on an elliptical shape
Greater in the summer than during the winter

The location of the tropopause is important because it generally marks the location of the jet stream and clear air turbulence (CAT).

Stratosphere

The stratosphere may be defined as the layer of the earth’s atmosphere above the troposphere, extending to about 50 kilometres above the earth’s surface.