Even though the rise and fall of diurnal temperature follows the rise and fall of solar radiation, this is not always the case. If we examine the diurnal temperature curve for a number of days, we will find that there are non-periodic variations that are not sun- controlled.

These irregularities are caused by the passage of atmospheric disturbances which occur at irregular periods. These disturbances are accompanied by cloudiness, precipitation and winds which modify temperatures.

In these conditions, the maximum and minimum temperatures may occur at any time of the day or night showing scant regard for the rise and fall of solar radiation.

Generally the tropical regions exhibit the solar control of temperatures, while in the middle and high latitudes the non- periodic control of temperatures is dominant, particularly in winter.