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Global Heat Balance
Greek scholar Aristotle was the first person to classify the heat zones of the Earth. As per his
classification, there are three different heat zones in the Earth, which arise due to difference in
temperature.
1. Although, Aristotles concept was not accurate, his classification according to temperature difference
is generally accepted.
2. The three heat zones of the Earth are Torrid Zone, Frigid Zone and Temperate Zone.
Earths Different Zones
Torrid Zone:
Places near the equator receive more insolation.
The amount of insolation received decreases as
one goes towards the poles.
The region between Tropic of Cancer and the
Tropic of Capricorn receives maximum insolation.
This region always receives heat in a
concentrated manner (over a small area).
This region is hotter than the others because
there is more insolation received during the day,
than the terrestrial radiation lost at night.
Inquiry Question:
If there is more of insolation and less of terrestrial
radiation, wouldnt this zone keep getting hotter and
hotter?
Temperate Zone:
The Northern Temperate zone lies between the Tropic of Cancer and the Arctic Circle. Similarly, the
southern temperate zone lies between the Tropic of Cancer and the Antarctic Circle.
In this zone, the amount of insolation received decreases as we get closer to the poles.
The temperatures generally range from warm to cool. Spring, summer, autumn and winter, the four
seasons occur in these zones.
The North Temperate Zone spans across Europe, Northern Asia, North and Central America.
The South Temperate Zone constitutes southern Australia, southern South America and Southern
Africa.
Frigid Zone:
There is very little insolation received due to the angle of the sun. Also, during a part of the year, the
Suns rays are not received at all. The amount of insolation received is less than the amount of terrestrial radiation given out in space.
Inquiry Question:
How is it possible for this region to give out more energy than it receives?
Changes in the Temperature
Daily:
During the day, the earth receives insolation from the Sun. The earth gets heated gradually after sunrise and
reaches the maximum temperature at about 3 pm.
Morning :
In the morning, the suns rays are slanting.
The incoming insolation is spread over a larger area and so the temperature remains low.
Noon :
The Suns rays cover a small area so the temperature is high.
The increase in temperature is gradual. The highest temperature is usually recorded between 2 pm
3pm.
Evening :
In the evening, the suns rays are slanting again, which indicate a decrease in temperature.
The temperature continues to decrease until sunset and through the night
Night :
There is no incoming insolation during night, hence the temperature continues to decrease.
The coldest part of the night is a little before sunrise since by that time, a great amount of heat has
been radiated out of space.