HEAT BUDGET

HEAT BUDGET

The insolation is made up of energy transmitted directly through the
atmosphere and scattered energy. Insolation is the amount of solar radiation
that reaches the earth’s surface through shortwaves. The earth also radiates
heat energy like all other hot object. This is known as terrestrial radiation.
The annual mean temperature on the surface of the earth is always constant.
It has been possible because of the balance between insolation and terrestrial
radiation. This balance is termed as a heat budget of the earth.

Let us suppose that the total heat (incoming solar radiation) received at the
top of the atmosphere is 100 units (see fig. 10.2) Roughly 35 units of it are
reflected back into space even before reaching the surface of the earth. Out
of these 35 units, 6 units are reflected back to space from the top of the
atmosphere, 27 units reflected by clouds and 2 units from the snow and ice covered surfaces.
Out of the remaining 65 units (100-35), only 51 units reach the earth’s surface
and 14 units are absorbed by the various gases, dust particles and water vapour of the atmosphere.
The earth in turn radiates back 51 units in the form of terrestrial radiation.
Out of these 51 units of terrestrial radiation, 34 units are absorbed by the
atmosphere and the remaining 17 units directly go to space. The atmosphere
also radiates 48 units (14 units of incoming radiation and 34 units of outgoing
radiation absorbed by it) back to space. Thus 65 units of solar radiation
entering the atmosphere are reflected back into the space. This account of
incoming and outgoing radiation always maintains the balance of heat on the
surface of the earth. Although the earth as a whole, maintains balance between incoming solar
radiation and outgoing terrestrial radiation. But this is not true what we observe
at different latitudes. As previously discussed, the amount of insolation
received is directly related to latitudes. In the tropical region the amount of
insolation is higher than the amount of terrestrial radiation. Hence it is a
region of surplus heat. In the polar regions the heat gain is less than the heat
loss. Hence it is a region of deficit heat. Thus the insolation creates an
imbalance of heat at different latitudes . This is being nullified
to some extent by winds and ocean currents, which transfer heat from surplus
heat regions to deficit heat regions. This is commonly known as latitudinal
heat balance. MORE