Heat Budget of the Earth and Its At­mosphere | Climatology | Geography

In this article we will discuss about the heat budget of the earth and its atmosphere.

(1) Incoming Shortwave Solar Radiation and the Heat Budget of the earth and the Atmosphere:

The earth receives most of its energy from the sun through shortwave solar radiation. The solar en­ergy radiated towards the earth’s surface (1/2 billionth part of the total energy radiated from the outer surface- photosphere-of the sun which is equivalent to 23 tril­lion horse power) is taken as 100 per cent or 100 units.

Out of the total incoming solar radiation entering the earth’s atmosphere 35 per cent is sent back to space through scattering by dust particles (6%), reflection from the clouds (27%) and from the ground surface (2%), 51 per cent is received by the earth’s surface (received as direct radiation), and 14 per cent is ab­sorbed by the atmospheric gases (ozone, oxygen etc.) and water vapour in different vertical zones of the atmosphere.

The 51 per cent solar energy received by the earth comprises 34 per cent as direct solar radiation and 17 per cent as diffuse day light. The heat budget of the atmosphere comprises 48 per cent of solar radiation wherein 14 per cent is received through absorption of the shortwave incoming solar radiation and 34 per cent is received from the outgoing long-wave terrestrial radiation.

(2) Outgoing Long-wave Terrestrial Radiation and Heat Balance:

After receiving energy from the sun (fig. 33.4) the earth also radiates energy out of its surface into the atmosphere through long-waves (fig. 33.4). The terres­trial radiation is also called ‘effective radiation’ be­cause it helps in heating the lower portion of the atmosphere. Twenty three per cent energy (out of 51 % energy which the earth has gained from the sun) is lost through direct long-wave outgoing terrestrial radiation out of which 6 per cent is absorbed by the atmosphere and 17 per cent goes directly to the space.

About 9 per cent of the terrestrial energy is spent in convection and turbulence and 19 per cent is spent through evaporation which is added to the atmosphere as latent heat of condensation. Thus, the total energy received by the atmosphere from the sun (14%) and the earth (34%) becomes 48 per cent which is reradiated to the space in one way or the other.

Energy sent back to space = 35% + 17% (through radiation from the earth) + 48% (through radiation from the atmosphere) = 100%

It may be pointed out that the mechanism of solar and terrestrial radiation is not as simple as men­tioned above, rather it is highly complex. For example, not all the energy received by the atmosphere from the sun and the earth is reradiated directly to the space rather a sizeable amount of energy received by the atmosphere is counter-radiated to the earth’s surface which is again radiated to the space and the atmos­phere. Table 33.4 presents a complex radiation balance of the earth and the atmosphere.