Factors affecting insolation

Geography glossary

Also called: Variability of insolation · Topic: Solar Radiation, Heat Balance and Temperature · NCERT: Class 11, Ch 8 "Solar Radiation, Heat Balance and Temperature"

Meaning

Insolation is the incoming solar radiation that reaches the Earth. The amount varies by place and season. NCERT lists five causes:

  • the Earth's rotation on its axis;
  • the angle of the Sun's rays;
  • the length of the day;
  • the transparency of the atmosphere (how clear the air is);
  • the aspect of the land (which way a slope faces).

The last two matter least. Together, these factors explain why some places and seasons are hotter than others.

Example

In June, Chandigarh (about 31°N) has longer days than Thiruvananthapuram (about 8°N), so it receives more hours of sunshine. Across India, monsoon clouds make the air less clear from June onwards. This cuts insolation, which is why May, not June, is India's hottest month.

Don't confuse with

  • Factors controlling temperature: these include altitude, distance from the sea, ocean currents and air masses. They decide how hot a place gets after the sunlight arrives.

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