1.2 Regions of Atmosphere
The atmosphere is divided into following layers:

• Troposphere

• Stratosphere

• Mesosphere

• Thermosphere

The Troposphere – is the lowest layer of the atmosphere. In this region the temperature decreases with height, and nearly all significant weather occurs.

The Tropopause - the upper limit of the troposphere where temperature stops decreasing with an increase of height. The tropopause is therefore the upper limit of significant weather, the first point of lowest temperature, and additionally it is the region for maximum wind strengths.

The height of the tropopause varies with Altitude, season of the year, and prevailing weather conditions with the result that it is usually higher in low Altitudes, in summer and in fine weather.

Typical heights for the tropopause are:

              Altitude Tropopause Height
              Equator 16-17 km 53,000-57,000 ft
              45°N/S 10-12 km 33,000-39,000 ft

The Stratosphere, extends from the tropopause to approximately 50 km amsl, and is characterised by the temperature being steady or increasing with height.

The Mesosphere, extends from 50 km to 80 km. The temperature generally decreases with height.

The Thermosphere or Ionosphere: This is the region where the temperature increases with the altitude.