8.6 The Atmosphere

8.6.2 Describe the structure of the troposphere and lower stratosphere.

The atmosphere is divided into layers based mainly on temperature change with height.

Two important lower layers are:

• the troposphere, and
• the stratosphere.

Troposphere

The troposphere is the lowest layer of the atmosphere.

It is the layer:

• where we live,
• where most weather occurs, and
• where most clouds and precipitation form.

The troposphere contains about 75% of the total mass of the atmosphere.

In the troposphere, temperature normally decreases with height.

The depth of the troposphere varies with location and temperature. It is generally:

• higher over warm areas, and
• lower over cold areas.

The boundary between the troposphere and the stratosphere is called the tropopause.

Stratosphere

The stratosphere lies above the troposphere.

In the lower stratosphere, temperature generally increases with height.

This is because the stratosphere contains the ozone layer, which absorbs ultraviolet radiation from the sun.

The stratosphere is generally more stable than the troposphere, so there is less vertical mixing and less weather.

8.6.4 Outline the characteristics of the troposphere in terms of:

(a) horizontal and vertical motions;