Question

Define the term insolation and explain various factors affecting insolation.

Answer 1

Approach:

• Define Insolation.
• Then while explaining the factors again try to break the answer and write in point form.
• Give sub-head to each and every point.
• Divide the words equally.

The earth’s surface receives most of its energy in short wavelengths. The energy received by the earth is known as incoming solar radiation which in short is termed as insolation. The solar output received at the top of the atmosphere varies slightly in a year due to the variations in the distance between the earth and the sun. However, the effect of this variation in the solar output is masked by other factors like the distribution of land and sea and the atmospheric circulation. Hence, this variation in the solar output does not have a great effect on daily weather changes on the surface of the earth.

Variability of Insolation at the Surface of the Earth

The amount and the intensity of insolation vary during a day, in a season and in a year. The factors that cause these variations in insolation are : (i) the rotation of the earth on its axis; (ii) the angle of inclination of the sun’s rays; (iii) the length of the day; (iv) the transparency of the atmosphere

The rotation of the earth on its axis
The fact that the earth’s axis makes an angle of 66½ with the plane of its orbit around the sun has a greater influence on the amount of insolation received at different latitudes.

The angle of inclination of the sun’s rays
The second factor determines the amount of insolation received is the angle of inclination of the rays. This depends on the latitude of a place. The higher the latitude the less is the angle they make with the surface of the earth resulting in slant sun rays. The area covered by vertical rays is always less than the slant rays. If more area is covered, the energy gets distributed and the net energy received per unit area decreases. Moreover, the slant rays are required to pass through a greater depth of the atmosphere resulting in more absorption, scattering and diffusion.

The length of the day
Duration of the day varies from place to place and season to season. It decides the amount of insolation received on the earth’s surface. The longer the duration of the day, the greater is the amount of insolation received. Conversely shorter the duration of the day leads to receipt of less insolation.

The transparency of the atmosphere
The transparency of the atmosphere depends upon the cloud cover and its thickness, dust particles, water vapour, etc. They reflect, absorb or transmit insolation. Thick cloud hinders the solar radiation to reach the earth’s surface. Similarly, water vapour absorbs solar radiation resulting in less amount of insolation reaching the surface.

Solar radiation provides more than 99.9 per cent of the energy that heats the earth. Undoubtedly, the radiant energy from the sun is the most important control of our weather and climate. Actually, it is this amount of energy received from the sun that acts as the driving force for all the atmospheric as well as biologic processes on the earth. Besides, all other sources of energy found on earth such as coal, oil, and wood etc. are nothing but converted a form of solar energy.