Insolation: Definition and Impacting Factors

Exploring Insolation: Definition and Factors Impacting Solar Radiation

As we already know, the atmosphere is a mixture of various gases, water vapor and dust particles and it is also very important for the biosphere. We need a suitable temperature to keep ourselves growing and warm. Have we ever thought about where on earth we get this heat and energy? In today's blog, we will try to know the answer to this question.

Sun is the main source of energy on the earth. The sun radiates its energy around space in the form of short waves. This radiated energy is called Solar Radiation. Only 2 billion^th part of the Sun's total solar radiation reaches the Earth. But despite having such a small quantity, it is the only source of energy for all the physical and biological phenomena on the earth.

The solar radiation coming towards the earth in the form of short waves is called Insolation. The amount of insolation that reaches the surface of the Earth is very less than the amount of heat or energy radiated from the Sun, because the Earth is very small from the Sun and secondly it is very far from the Sun. Apart from this, water vapor, dust particles, ozone and other gases present in the atmosphere absorb or reflect some amount of insolation, or refract it.

This energy from the Sun reaches the Earth in the form of short waves at a speed of 3 lakh kilometers per second. At the outer boundary of the atmosphere, 1.94 calories of energy per square centimeter is received from the Sun per minute and this amount of energy does not change but remains constant, due to which it is called the Solar constant.

Factors Impacting Solar Radiation

The amount of insolation is not the same everywhere on the surface of the earth. Its quantity varies according to place and time. Annual insolation is highest in the tropics and gradually decreases as one moves towards the poles. Similarly, insolation is more in summer and less in winter. The following factors affect the amount of insolation received on the surface

The angle of incidence or inclination of the sun's rays:

We all know that the earth being spherical, the sun's rays make different angles at different places along its surface. 

The angle of incidence affects insolation in two ways: 

1. Firstly, when the position of the sun is just above the head, at that time the rays of the sun fall vertically or very straight, due to which the rays of the sun get concentrated on a small area. Hence more heat is received there. If the sun's rays read obliquely, then the sun's rays spread over a larger area and less heat or insolation is received there.
2. Secondly, oblique rays have to travel a greater distance in the atmosphere than direct rays. The longer the sun's rays travel, the more heat is either absorbed or reflected by the atmosphere. For this reason, less heat or insolation is received at a place from oblique rays than from straight rays.

Day Length:

The length of the day varies from place to place and with the seasons. The amount of insolation received at the Earth's surface is directly related to the length of the day. The longer the day, the greater the amount of insolation. On the contrary, the shorter the day, the less amount of insolation or heat will be available.

Transparency of the Atmosphere:

The transparency of the atmosphere also affects the amount of insolation that reaches the surface. The transparency of the atmosphere depends on the presence of clouds, their depth, dust particles and water vapor. Because these are the factors that reflect, absorb or refract the insolation.

Dense clouds block the insolation from reaching the ground, while clear skies do not block the insolation from reaching the ground. This is the reason why insolation is less when the sky is surrounded by clouds as compared to the clear sky. Water vapor also absorbs the insolation and reduces the amount received on the surface.

Effect of water and land:

If there was water or land everywhere on the earth's surface, then the insolation would be almost the same at the same latitude, but there is uneven distribution of water and land on different parts of the earth, due to which there is variation in the receipt of heat. Water heats up more slowly than land and cools down more slowly. As a result, the effect of insolation on water is very less. 

This is because of the following: 

• Water, being liquid, is in constant motion, as a result of which the heat absorbed by the water spreads far and wide and no layer of water becomes very hot. On the contrary, the heat absorbed by the land part gets accumulated in the same part, due to which it becomes hotter than the water.
• Water is transparent due to which the rays of the sun go deep into it. In this way, the sun's rays have to heat the water to a greater depth, due to which the temperature of the water increases less. On the contrary, the sun's rays remain only in the upper part of the land and only its upper part gets heated. This makes the terrestrial part hotter. At sunset, the terrestrial part cools down soon after losing insolation by radiation while the aquatic part cools down late.
• Some part of the heat absorbed by the water is spent in converting the water into vapor, whereas all the insolation received by the land is used to heat it.
• The specific heat of water is much higher than the specific heat of land. For example, if 1 kg of water and 1 kg of rock are heated to raise their temperature by 1 °C, the water will require 5 times as much heat as the rock.

Land Slope:

The rays of the sun fall directly on the slopes of the mountains which face the sun. Due to which more of that heat or insolation is received there and the rays of the sun falling on the shields which are away from the sun, give less heat or insolation.

Number of solar panels:

Black and dark colored spots are formed on the bottom of the Sun and continue to deteriorate. These are called Sunspots. There is a close relationship between solar radiation and the number of sunspots. With the increase and decrease in the number of these stigmas, the amount of insolation on the earth increases and decreases.

Earth's distance from the Sun:

The Earth revolving around the Sun on an elliptical path sometimes comes near and sometimes away from the Sun. 

On July 4, in the position of Aphelion, the Earth is 152 million kilometers from the Sun. Occurs at the maximum distance of 14.70 crore kilometers and is at the minimum distance of 14.70 crore kilometers in the position of Perihelion on 3rd January. Thus, December receives more insolation than June.

Nature of ground:

Some objects on the surface absorb more of the insolation and others less. Where the absorption of insolation is more, the amount of insolation is found to be more, such as areas of black and dark colored soils. Icy and rocky regions reflect most of the amount of insolation. Hence, less insolation is received in such areas.