Latitudinal heat balance means the state of balance which exists between the latitudinal belts.
The insulation on the surface of the earth varies because of its tilted axis.
(i) Insulation decreases pole wards from the equator.
(ii) Between 37° N and 37° S, maximum insulation is received. It is a zone surplus heat.
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(iii) Beyond 37° N and 37° S to the poles, insulation decreases. It is a zone of deficit heat.
If the heat is not transferred from one latitudinal belt to the other, the surplus heat belt will become too hot to live in and the deficit heat belt will become too cold. Hence, transfer of heat takes from surplus heat zone to the deficit heat zone by ocean currents and winds.
There is a state of balance between the incoming solar radiation and the outgoing terrestrial radiation. This equilibrium, in which the temperature of the earth as a whole remains constant, is known as the heat budget or heat balance.
The sun emits 100 units of energy. Out of this incoming solar radiation in the form of short waves, 35 units are reflected back into space, 14 units are absorbed by the atmosphere, and 51 units reach the earth’s surface. The 51 units which the earth receives in the form of short waves is radiated in the form of long waves, 17 units bounce back into space, 34 units are absorbed by the atmosphere. The atmosphere in turn had absorbed 48 units, i.e., 14 unit of the incoming radiation and 34 units of the outgoing terrestrial radiation, net 48 units, which it releases in the night.
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The atmosphere helps in preventing the earth from becoming too hot in the day by absorbing 14 units of the incoming radiation and prevents the earth from becoming too cold in the night by releasing the 48 units absorbed by it.
Thus, there is no net gain or loss between the incoming solar radiation and the outgoing terrestrial radiation, so that there exists a balance between the earth and the atmosphere.