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ATMOSPHERE 08

Terrestrial Radiation

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 long wave form. This energy heats up the atmosphere from below. This process is known as terrestrial radiation

The long wave radiation is absorbed by the atmospheric gases particularly by carbon dioxide and the other green house gases. 

Thus, the atmosphere is indirectly heated by the earth’s radiation. The atmosphere in turn radiates and transmits heat to the space.

 Finally the amount of heat received from the sun is returned to space, thereby maintaining constant temperature at the earth’s surface and in the atmosphere.

Heat Budget of the Planet Earth

The heat energy reflected, absorbed and radiated back into the space equals the
energy received by the earth. Incoming radiation and the outgoing radiation
pass through the atmosphere. The earth maintains its optimum temperature.

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 surface

Temperature

The interaction of insolation with the atmosphere and the earth’s surface creates  heat which is measured in terms of temperature. While heat represents the molecular movement of particles comprising a substance, the temperature is the measurement in degrees of how hot (or cold) a thing (or a place) .

Distribution of Temperature
Distribution of temperature varies both horizontally and vertically. 

a. Horizontal Distribution of Temperature

b. b. Vertical Distribution of Temperature

Horizontal Distribution of
Temperature

Distribution of temperature across the latitudes over the surface of the earth
is called horizontal distribution of temperature. On maps, the horizontal
distribution of temperature is commonly shown by isotherms. Isotherms are line
connecting points that have an equal temperature at mean sea level.

Factors Affecting the Horizontal Distribution of Temperature

Latitude: 

The angle formed by the solar radiation to the ground iscalled ‘angle of incidence’.

 The solar radiation passes vertically along the equator. The angle of incidence decreases from equator towards the poles. The area heated by the solar
radiation increases towards the poles and therefore, temperature decreases from the equator to the poles.

Distribution of land and water: Land is heated and cooled at a faster rate
due the conduction process whereas water is heated and cooled at slower
rate due to convection process.

Water takes 2.5 times of heat energy to heat a unit area compared to land. Thus, the land will have higher temperature than the water in summer and vice versa during the winter. So more land mass in northern hemisphere (15.28C) leads to higher average temperature than the southern hemisphere.

Ocean currents: Warm ocean currents carry warm water from the tropical region towards the poles and increase the temperature while cold ocean currents carry cold water
from Polar Regions and reduce the temperature along the coasts.

Prevailing winds: Warm winds like trade wind and westerly, that carry
higher heat energy, increase the temperature while cold polar easterlies carry lower heat energy from polar region reduces the temperature.


Cloudiness: The cloudy sky obstructs the solar radiation from the sun to earth and reduces the temperature. But the clear sky during the day allows more solar radiation to reach the earth’s surface and increases the temperature. Meanwhile clear sky at night allows more terrestrial radiation to escape. For example ,the tropical hot deserts experience higher temperature at day and lower temperature at night.

Nature of the surface: The reflection from surface varies based on the nature of land cover. The more reflection from the snow surface leads to low temperature accumulation. But the dense forest, which reflects less heat energy and absorbs more heat energy, leads to higher temperature.

Mountain barriers: If a wind or air mass blows towards the mountain, it influences the distribution of temperature on either side of the mountain.

Factors Affecting the Vertical Distribution of Temperature

We all know that the temperature decreases with increasing altitude from
the surface of the earth. The vertical decrease in temperature of troposphere is
called as ‘Normal Lapse Rate’ or ‘vertical temperature  gradient’ at which the temperature reduces at the rate of 6.5 8C per 1000 meter of ascent. 

This is influenced by the following factors:

a. Amount of terrestrial radiation reaching the altitude 

b. Density of air to absorb the heat energy at higher altitude. 

 

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