Heat Budget

• Earth receives solar insolation in the form of short waves and radiates them back into space in the form of long waves.
   
• The long wave radiation is absorbed by atmospheric gases, like carbon dioxide and greenhouse gases. These gases indirectly heat Earth’s atmosphere. 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.
   
• The earth gets energy(heat) from the insolation received this happens through various processes like Conduction, Convection, and advection.

Conduction – Conduction is defined as the flow of energy from a warm body to a cold body when both are in contact. 

Convection – It is the process of transfer of heat usually between fluids such as gases and Liquids. 

Convection is the movement of a mass of material from one location to another in order to transmit heat energy.

• Only in fluids or gases can the convection process work because the internal mass motion of these substances causes the convection of heat energy. After receiving heat energy (insolation) from the sun, the earth’s surface warms up. As a result, the air that comes into touch with the warmer earth’s surface also becomes heated and expands. Vertical air circulation is established as a result of warmer air being lighter and rising upward. On the other hand, as a result of volume contraction, the considerably cooler air in the atmosphere gets heavier and descends to the earth’s surface. Due to the dry adiabatic rate and the warm ground surface, the air that is descending is warmed. Due to an increase in volume and a decrease in density, this heated air ascends once more.

Advection – Transfer of heat especially horizontally in the atmosphere 

• This heat budget keeps the Earth’s temperature in check and ensures life thrives.
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• Earth maintains its temperature as it radiates back heat (radiation) in space which is called Albedo.
   
• Albedo is defined as the fraction of light reflected by any Body.
   
• If we take the entire insolation received as 100 units then this insolation undergoes various activities in space. It may get absorbed, reflected, or scattered. Nearly 35 units are reflected in space even before reaching Earth’s surface.
   
• Of these 35 units, Clouds reflect nearly 27 units of Insolation and 2 units of it by snow and ice-covered areas. 
   
• Snow and Ice have the highest albedo.
   
• 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. 
• 48 units (14 units directly and 34 units from terrestrial radiation) absorbed by the atmosphere 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. 
• Through this process, Earth gets neither too warm nor too cold.
   
• This is termed as heat budget or heat balance of the Earth. 

“Insolation and heat budget” is the topic of Climatology. It deals with, how Earth receives solar Radiation and the mechanism through which it protects Earth from overheating and maintains Earth’s Temperature.  This article is relevant for various examinations including SSC and Banking. Questions about this topic are common these days.