Heating and cooling of atmosphere
The heating and cooling of the atmosphere happen in the atmosphere in different ways. The earth gets heated due to insolation. Then it transmits the heat using the long waveform to its nearest layer of the atmosphere.
The Air which is in contact with land gets heated slowly. Also, the upper layers of the atmosphere get heated by the lower layers. This process is called Conduction.
The Conduction takes place when two bodies of unequal temperature get in contact with each other. There occurs a flow of energy between them, in the direction from warmer to cooler body.
This transfer of energy takes place until the temperature between two bodies becomes equal or their contact is broken. Conduction is an important process in heating the lower layers of the atmosphere.
Advection vs Convection Upsc
The Air, which is in contact with the earth, rises above vertically due to heating. In heated Air is in the form of current and further transmits the heat of the atmosphere. This process of heating the atmosphere is called convection.
Convection transfer of energy is confined only to the troposphere.
The transfer of heat through the horizontal movement of air is called Advection. The horizontal movement of air is relatively more important than the vertical movement.
In middle latitudes, most diurnal (day and night) variations in daily weather are caused by advection alone.
In tropical regions particularly in northern India during the summer season, local winds called ‘loo’ are the outcome of the advection process.
The insolation received by the earth is in short waves forms and heats up its surface. The earth after being heated itself becomes a radiating body and it radiates energy to the atmosphere in the long waveform.
This energy heats up the atmosphere from below. This process is known as terrestrial radiation.
The longwave radiation is absorbed by atmospheric gases, particularly carbon dioxide and other greenhouse gases. Thus, the atmosphere is indirectly heated by the earth’s radiation.
The atmosphere in turn radiates and transmits heat to space. Finally, the amount of heat received from the sun is returned to space, thereby maintaining a constant temperature at the earth’s surface and in the atmosphere.
Heat Budget of the Planet Earth
The earth as a whole does not accumulate or lose heat. It maintains its temperature.
This can happen only if the amount of heat received in the form of insolation equals the amount lost by the earth through terrestrial radiation. Consider that the insolation received at the top of the atmosphere is 100 per cent.
While passing through the atmosphere some amount of energy is reflected, scattered, and absorbed.
Only the remaining part reaches the earth’s surface. Roughly 35 units are reflected back to space even before reaching the earth’s surface. Of these, 27 units are reflected back from the top of the clouds and 2 units from the snow and ice-covered areas of the earth.
The reflected amount of radiation is called the albedo of the earth. The remaining 65 units are absorbed, 14 units within the atmosphere and 51 units by the earth’s surface.
The earth radiates back 51 units in the form of terrestrial radiation.
Of these, 17 units are radiated to space directly and the remaining 34 units are absorbed by the atmosphere (6 units absorbed directly by the atmosphere, 9 units through convection and turbulence, and 19 units through latent heat of condensation).
48 units absorbed by the atmosphere (14 units from insolation +34 units from terrestrial radiation) are also radiated back into space.
Thus, the total radiation returning from the earth and the atmosphere respectively is 17+48=65 units which balances the total of 65 units received from the sun.
This is termed the heat budget or heat balance of the earth. This explains, why the earth neither warms up nor cools down despite the huge transfer of heat that takes place.
Variation in the Net Heat Budget at the Earth’s Surface
As explained earlier, there are variations in the amount of radiation received at the earth’s surface.
Some part of the earth has a surplus radiation balance while the other part has a deficit.
The figure shows that there is a surplus of net radiation balance between 40 degrees north and south and the regions near the poles have a deficit.
The surplus heat energy from the tropics is redistributed polewards and as a result, the tropics do not get progressively heated up due to the accumulation of excess heat, or the high latitudes get permanently frozen due to excess deficit.
Conduction in geography?
The earth is heated by insolation and then the earth transmits the heat to the atmosphere layers in form of the long waves. The air in contact with land gets heated gradually and the upper layers in contact with the lower layers get heated too. This over process is known as Conduction.