Table of Contents:
- What is insulation?
- Components of Insolation
- Solar Constant
- The process that affects the Insolation
- Factors affecting Insolation
- Distribution of Insolation on Earth
What is Insolation?
Solar energy comes in form of a photon in short-wavelength from the sun's upper layer which is the photosphere ( but solar energy is generated in the interior of the Sun via nuclear fissions), it is called incoming solar radiation or simply insolation.
In short, Solar energy received by the earth is called incoming solar radiation or insolation.
Components of photons or solar spectrum components
There are six components based on the wavelength:Note: 1 micron =10(-6) meter.
- X and gamma rays:
- Wavelength 0.0005 to 0.01 micron. This component of a photon gets consumed by the ionosphere of the atmosphere and it does not reach in earth's surface.
- Ultraviolet rays:
- Wavelength varies from 0.2 to 0.4 microns. This component also gets consumed by the ozone layer in the stratosphere and does not reach the ground.
- Visible rays:
- The wavelength varies from 0.4 to 0.7 microns. It is further divided into seven colors. violet color has the shortest wavelength and red color has the longest wave. During sunset and sunrise only red wavelengths of visible.
- Infrared rays:
- The wavelength of 0.7 to 3.0 microns.
- Infrared rays are used in satellites to get clear pictures and ground scenarios from a height.
- Heatwave:
- Wavelength 3.0 to 3000 micron.
- Radio Ray:
- The wavelength is more than 3000 microns.
Solar constant:
At the thermopause or 1000 km height from earth surfaces, the amount of energy received per square meter of areas is called the solar constant. It is generally 1366 Watt or 1.366 kilowatts per square meters areas per hour.- The solar constant is lowest at the aphelion point of the orbit in June month.
- The solar constant is highest at the perihelion point of the orbit in January month.
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| Aphelion and Perihelion point of the earth |
The process that affects the insolation:
Incoming Solar radiation travel from the exosphere to the troposphere in our atmosphere. The following process and factors affect the insolation in the atmosphere:
Incoming Solar radiation travel from the exosphere to the troposphere in our atmosphere. The following process and factors affect the insolation in the atmosphere:
- Absorption of x and gamma-rays in the ionosphere.
- Ultraviolet rays are absorbed in the ozone layer.
- In the troposphere, the following process affect:
- Reflection
- Absorption
- Scattering
- Diffusion
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| Insolation |
Reflection:
- Cloud has some ice crystals with them and as we know ice has high albedos, hence parts of insolation get reflected by clouds.
Absorption:
- Water vapor is also present in the atmosphere. Some parts of insolation get absorbed by water vapor.
Scattering:
- As finer dust particles are present in the atmosphere and parts of insolation get scattered by finer dust particles.
Diffusion:
- As large dust particles are also present in the atmosphere and parts of insolation get diffused by larger dust particles. Diffusion lights can be seen before sunrise and after sunset.
Factors affecting insolation:
- Extraterrestrial factors
- Terrestrial factors
Extraterrestrial factors:
- Sunspot and sun flare activities
- Perihelion and aphelion position of the earth
- Angle of incidence
- Meteorite dust in spaces
Terrestrial factors:
- Atmospheric components such as the ionosphere and ozone layer.
- Clouds and fogs
- Anthropogenic dust and volcanic dust
- Forest and vegetations
Insolation distribution in the earth
Sun comes vertically at the equator and slants at the poles, thus per unit areas, the Equator gets higher insolation as compared to the poles.
Length of day and night varies with latitude, on average, the equator has the longest day throughout the years and day duration decrease towards the poles.
Because of two reasons, the insolation amount is decreased from the equator to the poles.
Length of day and night varies with latitude, on average, the equator has the longest day throughout the years and day duration decrease towards the poles.
Because of two reasons, the insolation amount is decreased from the equator to the poles.
Despite the spatial variation of insolation, also a temporal variation of insolation was found, some time tropic of cancer gets the largest insolation, and sometimes tropic of Capricorn.
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| Insolation distribution |
- Low insolation in higher latitude
- High insolation in the tropical desert
- Medium insolation in the equatorial region due to clouds
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