Heating of the Atmosphere

Heating of the Atmosphere

There are four vertical layers within the atmosphere, each with its own particular characteristics. The outer limit of the atmosphere is set at 1000km, but the vast majority of our weather and climate is found within the lower 12km.

This distance varies between the equator and the poles being 16km and 8km respectively. Beginning at the earth's surface, the four layers of the atmosphere are listed below:

    1. Troposphere - layer characteristics:
      • Decrease of temperature with height (6.4 degrees per 1000m).
      • Increase in wind speeds with height.
      • Fall in pressure with height.
      • An unstable layer due to the presence of cloud, pollution water vapour and dust.
      • The tropopause marks the outer edge of the troposphere and the limit to the earth's weather and climate.
    2. Stratosphere - layer characteristics:
      • Temperatures increase with height in this layer, and it is here that ozone is concentrated, which absorbs UV radiation from the sun.
      • Winds increase with height but pressure falls.
      • The boundary is marked by the stratopause.
    3. Mesosphere - layer characteristics:
      • A rapid fall in temperature with height, caused by a lack of water vapour, cloud and dust).
      • Temperatures are extremely low and winds high.
      • Its boundary is marked by the mesopause.
    4. Thermosphere - layer characteristics:
      • The outer layer of the atmosphere.
      • A rapid increase in temperature with height, exceeding 1000 degrees.

    The diagram below illustrates the changes in temperature and pressure throughout the different layers:

    All energy for the heating of the atmosphere comes from the sun. We do not receive anywhere near the full amount of energy that is emitted, nor does any heating of the atmosphere take place until the light energy from the sun reaches the ground as outlined below:

    Short wave

    Energy that comes from the sun and passes through the atmosphere to earth is in the form of short wave radiation or insolation. It is responsible for the Earth's weather and climate and is converted via photosynthesis to support all forms of life.

    Long wave

    Once insolation has reached the surface of the Earth, it is converted into heat energy. The ground begins to warm and slowly heats the atmosphere above it, meaning that the atmosphere is warmed from ground level upwards. The amount of heating of the atmosphere that occurs depends on the surface (for example, water, ice, grass, sand) that is being heated.

    The diagram below shows the relationship of energy exchange between the Earth and the atmosphere:

    Heating of the Atmosphere

    Not all energy emitted from the Sun reaches the Earth's surface, and there are variations in the amounts received at different locations across the globe. The reasons for this are illustrated in the following statements and diagrams:

    Distance from the Sun

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    As shown in the diagram above, the orbit of the earth around the sun leads to variations in the amount of energy received.

    Position of the Sun in the sky

    Heating of the Atmosphere

    The diagram above shows how energy is far more concentrated at the equator than at the poles. This is because at the equator, there is a smaller surface area to heat and less atmosphere to pass through than at the Poles.

    Length of day and night

    This is strongly linked to the occurrence of seasons in the northern and southern hemispheres. As the sun shifts between the tropics of Cancer and Capricorn the amount of insolation received by different areas changes. For example, in the UK, we receive less insolation between September and March when the Sun is south of the equator, meaning our days are shorter so less insolation is received.

    As energy passes through the atmosphere on its way to Earth, much of it is lost resulting in under 50 %& actually reaching the Earth's surface. Energy is lost via the processes of absorption, by ozone, dust, clouds and carbon dioxide.

    Scattering: This happens if gas molecules divert incoming radiation.

    Reflection: Clouds reflect energy back into space (acts as a barrier). The surface of the earth reflects some energy back into space and this is dependent on its albedo (reflective capacity). Surfaces such as snow and ice can reflect up to 85% of energy compared to 10% over dark soil. The amount of each that occurs is dependent on such factors as cloud amount, pollution, dust and water vapour that are present in the atmosphere.

    The diagram below shows these processes:

    Heating of the Atmosphere

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