WWW LWC web site


Scheme of work

The structure of the atmosphere

The atmospheric heat budget

Factors affecting insolation

Planetary surface winds

The general atmospheric circulation

Equatorial climates

Tropical wet and dry climates

Tropical monsoon climates

Tropical storms

Air masses affecting the UK



Urban climates

Climate change in the last 20.000 years

Evidence of climate change

Global warming?

Effects of global warming


The atmospheric heat budget

The Earth and the atmosphere are heated by energy from the sun. The atmospheric heat budget of the Earth depends on the balance between insolation and out going terrestrial radiation. This budget has remained constant over the last few thousand years.

Now try this exercise

The amount of energy received from the sun is determined by;

  • The solar constant - varies slightly and affects longer term climate rather than short term weather variations.
  • The distance from the sun - the eccentric orbit of the Earth can cause a variation of up to 6% in the solar constant.
  • The altitude of the sun in the sky - the equator receives more energy as solar radiation strikes the Earth head on, whereas at 60 N or 60 S the angle creates twice the area to cover and increases the amount of atmosphere to go through.
  • The length of day and night -

The Earth receives energy from the sun as insolation. Some is lost as it passes through the atmosphere but overall the surface has a net gain of energy, the exception being the polar regions. Only about 24% of this insolation reaches the surface as it is either absorb, reflected or scattered

The atmosphere in contrast has a net deficit of energy. Because of this difference, heat is transferred from the surface to the atmosphere by radiation, conduction and by the release of latent heat

Heat budget by latitude

There are variations in energy and heat between latitudes. Low latitudes have a net surplus of energy, mainly because of their relative proximity to the sun. The high latitudes (pole wards of 40 N and 40 S) have a net deficit. As the tropics are not heating up and the poles are not cooling down, a transfer of heat must occur.

This occurs by:

  • Horizontal heat transfers: air movement (winds, 80%, including the jet streams, hurricanes and depressions) and water movement (ocean currents).
  • Vertical heat transfers: energy is transferred from the warm surface vertically by radiation, conduction and convection. Latent heat also helps to transfer energy, e,g, when water is evaporated. This energy is released when condensation occurs in the upper atmosphere