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Heat Balance

Heating and Cooling of the Atmosphere, Terrestrial Radiation, Heat Budget of the Planet Earth, Variation in the Net Heat Budget at the Earth’s Surface etc.

Heating and Cooling of the Atmosphere:

There are different ways of atmospheric heating and cooling. The earth after being heated by short wave insolation transfers the heat to the atmospheric layers near to the earth in the long waveform.

Conduction: 

  1. It is the process when the air in contact with the land heats up at a slow pace and the higher layers in contact with the lower ones also get heated. 
  2. This happens when two objects with unequal temperatures come into contact. and there is a movement of energy from a warm object to a cold object.
  3. The heat transfer continues until both objects reach the same temperature or the contact breaks.
  4. It is important for warming the lower atmospheric layers.                                                                                                            Convection: 
    1. It is the process of vertical heating of the atmosphere when the air in touch with the earth vertically rises on heating developing currents and therefore reflects the atmospheric heat.  
    2. The convective transfer of energy is restricted only to the tropospheric level.                                                                            Advection: 
      1. It is the transmission of heat from the horizontal flow of air. 
      2. The horizontal course of the air is comparatively more considerable than the vertical one. 
      3. Through middle latitudes, a large part of diurnal (day and night) variation in everyday weather occurs just because of advection.
      4. During the summer season, in tropical regions of northern India, local hot winds called ‘loo’ are a result of the advection process. 

Terrestrial Radiation: 

  1. The insolation that the earth receives is in the shape of short waves. It warms up the earth’s outer surface. After being heated, the earth acts like a radiating body that disperses energy to the atmosphere with long waves. This process heats the atmosphere from beneath. This entire activity is the process of terrestrial radiation.
  2. Indirect atmospheric heating due to radiation: the longwave radiation is consumed by the atmospheric gases especially carbon dioxide and various other greenhouse gases.
  3. The atmosphere then disperses and transfers heat into space. 
  4. Lastly, the quantity of heat coming from the sun is reversed to space, thereby sustaining constant temperature at the surface of the earth and the atmosphere. 

Heat Budget of the Planet Earth:

  1. The earth neither accumulates nor loses heat. It just maintains its temperature. This is only possible if the volume of heat obtained in the shape of insolation matches the quantity of heat lost by the earth in the process of terrestrial radiation.
  2. While going through the atmosphere a partial amount of energy is reflected, distributed, and consumed. Only the leftover part enters the surface of the earth. 
  3. Approximately 35 units of energy are reflected into space even before it reaches the earth’s outer cover. Out of this, 27 units go back from the top of the clouds and 2 units go from the ice and snow-covered parts of the earth. The reflected quantity of radiation is called the albedo of the earth. The remaining 65 units are consumed, 51 units into the surface while 14 units within the atmosphere.
  4. The earth returns 51 units in the shape of terrestrial radiation. Out of this, 17 units directly go back into space, and the atmosphere absorbs the leftover 34 units (6 units are taken straight away by the atmosphere, 19 units through latent condensation heat, while 9 units by convection and turbulence). 
  5. 48 units received by the earth’s atmosphere (14 units through insolation and 34 units through terrestrial radiation) are returned into space too. Hence, the cumulative radiation from the earth and the atmosphere is 17+48=65 units that balance of the sum of 65 units that come from the sun. This number is known as the heat balance or heat budget of the earth. 

Net Heat Budget Variation at the Surface: 

  • Some portions of the earth hold a surplus emission balance while the other part has a deficiency
  • There is an extra radiation balance between 40 degrees south and north while the regions near the poles are in deficit
  • The extra heat energy in the tropics gets distributed polewards and because of this, the tropics do not get heated progressively due to the collection of surplus heat, or the high latitudes get enduringly frozen due to extraordinary deficit