Question

make a mind map on the factors which influence the distribution of insolation.

Answer 1

What are the Factors affecting the distribution of insolation?

 answer - The actual amount of insolation received at a place on the earth varies according to the conditions of the atmosphere as well as the seasons. The following astronomical and geographical factors govern the amount of insolation received at any point on the earth's surface:

(1) Angle of incidence (2) Duration of sunshine

(3) Solar constant (4) Distance between the earth and the sun

(5) Transparency of the atmosphere.

Angle of incidence:

The altitude of the sun, i.e. the angle between its rays and a tangent to the earth's surface at the point of observation, con­trols the amount of insolation received at the earth's surface (Figure 22.3).

As the elevation angle decreases, the area over which the radiation is distributed increases. The vertical rays of the sun heat the minimum possible area, but on the contrary, the oblique rays are spread over a rela­tively larger area, so that the amount of area over which the available solar energy has to be distributed in increased and the energy per unit area on the earth's surface is decreased.

In addi­tion, the oblique rays have to traverse a larger distance through the atmosphere before they strike the surface of the earth. The longer their path, the larger the amount of energy lost by various processes of reflection, absorption, and scattering, etc.

Thus, it is clear that the larger amount of radiant energy is destroyed in case of slanting rays than in vertical rays. Similar effect of the varying angle of sun's rays can be seen in the daily march of the sun across the sky.

At mid-day the intensity of insolation is maximum, but in the morning and evening hours it is reduced because of the slanting rays of the sun. So is the case in winter and at high latitudes, when the-amount of insolation received at the surface of the earth is small.

This is simply the effect of the low angle of incidence. The major factors that determine the sun's altitude or the angle of incidence are the latitude of the place, the time of the day and the season.

Duration of sunshine:

The duration of sunlight hours determines the length of the day, which also affects the amount of solar radiation received at the surface. Undoubtedly, the longer period of sunshine ensures larger supply of radiation which a particular area of the earth will receive.

Obviously, the latitudes exercise the most dominant control over the duration of sunshine and thereby the length of the day. The latitudinal and monthly variations in the length of days have been shown in Table 22.4.

Table 22.4: Maximum length of day in different latitudes.LatitudeLongest dayLatitudeLongest dayor nightor night012 hours63.420 hours1713 hours66.524 hours3114 hours67.41 month4115 hours69.82 months4916 hours78.24 months58.518 hours90.06 months

The inclination of the earth's axis, its parallelism, the earth's rotation and revolution, all these factors combine together to bring about seasonal changes. It is to be remembered that these astronomical factors not only cause differences in the altitude of the sun, but also differences in the length of day from the equator pole-ward.

At the equator the length of days and nights is 12 hours. On the autumnal and vernal equinoxes that occur on September 21 and March 21 respectively, the mid-day sun is overhead at the equator.

Answer 2

• Inclination of the sun's rays
• Length of day
• Distribution of Land and Water
• Thickness of the Atmosphere