Solar radiation refers to the energy transmitted from the sun to the earth through the atmosphere.
It passes in the atmosphere in form of a beam of short wave rays (solar shortwave radiation)
Solar radiation is received in a place during the day in a form of light and it is converted into heat at the earth’s surface
The amount of solar radiation received in a place also varies from time to time. The air, clouds, and the ozone in the atmosphere absorb some of this energy while dust particles and clouds reflect and scatter the energy into the space.
The earth, therefore, absorbs only a fraction of the energy emitted by the sun. The nature of the earth’s surface (Albedo) is used to express the ability of a surface to reflect insolation
Conditions Influencing the In-coming Solar Radiation In an area:
Latitude
The angular distance of a place from the equator partly determines the distance from the sun to the earth’s surface.
This further determines the angle of incidence at which the sun’s rays fall upon the earth’s surface
Hence, there’s always maximum insolation in the low latitudes because the sun’s rays strike the earth’s surface at right angles and have a short distance to travel through the atmosphere.
There’s intensive heating since there’s a smaller surface area per ray.
The sun’s rays are however less intensive towards the mid-latitudes and polar regions (high latitudes) because of the long distance, they travel through the atmosphere and the oblique angle at which they strike the earth’s surface
Rotation of the earth
The rotation of the earth on its axis causes changes in solar radiation received in a place.
Within the tropics when the sun is overhead, high amounts of solar radiation are received.
The absence of the overhead sun at the poles, arctic and sub-arctic regions reduces the insolation rates
Revolution of the earth
This causes seasonal variation in the amount of insolation received in the different places of the earth.
More solar radiation is experienced during the summer season compared to the winter season
Cloud cover
Clouds in the atmosphere absorb, reflect and refract insolation.
This reduces the amount of solar radiation reaching the earth’s surface hence implying that areas with thick cloud cover experience less solar radiation as compared to areas with clear skies
Aspect
Areas in the direct path of the sun’s rays especially in the mid and high latitudes receive more solar radiation as compared to those areas sheltered from the sun’s rays.
For instance, in the mid-latitudes of the Northern hemisphere, the south-facing slopes receive more solar radiation than the north-facing slopes.
This is because the south-facing slopes are in the direct path of the sun’s rays. The reverse is also true
Humidity
The amount of water vapor in the atmosphere may absorb or reflect solar radiation. It prevents some percentage of the solar radiation from reaching the earth’s surface.
Areas with a low humid content such as arid and semi-arid regions on the other hand experience more insolation on their surfaces because direct heat from the sun is received
Impurities in the atmosphere
Impurities such as smoke and dust particles tend to absorb part of the solar radiation reaching the earth’s surface.
This means that areas with a lot of atmospheric impurities receive less solar radiation as compared to areas with clear atmospheric conditions
The sun’s hot spots
The surface of the sun has certain sections which are hotter and emit more radiation.
Therefore, sections on the earth’s surface that receive heat directly from these hot spots experience greater solar radiation. The reverse is also true.
Green house effect
The increase in the number of greenhouse gases like carbon dioxide, methane, nitrous oxide, and carbon monoxide in the atmosphere affects the ozone layer hence triggering off the occurrence of global warming which ultimately increases the amount of solar radiation.
On the other hand, areas with limited atmospheric greenhouse gases have an intact ozone layer hence they experience less solar radiation reaching the earth’s surface
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