The sun is the primary control of diurnal march of temperature

The sun is the primary control of diurnal march of temperature. The temperature of land surface represents the balance between incoming solar radiation and outgoing terrestrial radiation.

So long as the angle of the sun rises reaching a peak in the noon, the incoming solar radiation exceeds the outgoing earth radiation. However, the maximum temperature is recorded the late afternoon.

This delay in the occurrence of the maximum is called the lag of the maximum. This is caused because of the fact that although the maximum amount of insolation is received at noon; the earth’s surface and the air lying close to it continue to receive more heat than they lose during the afternoon.

That is why the temperature continues to rise. But from the middle of afternoon to sunrise the loss of heat by earth radiation exceeds the receipts of solar radiation. Therefore the temperature continues to drop until about sunrise the following day.