Isolation(Incoming Solar Radiation)

• It is defined as the flux of solar radiation incident upon the earth surface.
• Its value depends upon the geographic location, orientation of the surface, orientation of the surface, time of the day, time of the year and atmospheric condition.

Effect of Atmosphere on Incoming Solar Radiation

• the atmosphere acts as a filter, and absorbs and diffuses a significant proportion of incoming solar radiation.
• Mathematically,

Qs= Cr+Ar +(Q+q)a +Ca+Aa+(Q+q)(1-a)

where, Q and q are direct beam and diffused solar radiation incident on the earth surface and a is albedo.

• The loss of solar energy in the process of passing through the atmospheric layer is called atmospheric depletion. Various processes whereby the heat energy is lost through the atmosphere are scattering, diffusion, absorption and reflection.
• Scattering: Scattering is selective; it is more in short wavelength (blue) than that in longer wavelength (red), especially when the sky is clear.
• If the circumference of scattering particles is less about 1/10th of the wavelength of the incident radiation, the scattering coefficient is inversely proportional to the fourth power of the wavelength of the incident radiation. This is called Rayleigh scattering and its effect is the blue color of sky.
• For larger size of particle with circumference of more than 30 times of wavelength of incident radiation, scattering is independent of the wavelength i.e. white light is scattered. This phenomenon is known as Mie scattering. (Note: particles mean molecules of air, water vapor, dust particles, inert materials etc.)
• Reflection: A part of the solar radiation (5%) above 0.7μ is reflected by water droplets, ice crystals, salt and dust. Thus, a certain amount of energy is lost.
• About 30% of the energy falling on the outer surface of the atmosphere is scattered and reflected.
• Diffusion: When diameter of the particles is larger than the wavelength of incident beam of light, the scattering does not occur and the effect of the particles is of the nature of diffuse reflection or diffusion.
• Absorption: About 17% of the solar radiation is absorbed by the atmosphere. The constituent of atmosphere that absorb the solar radiation significantly are oxygen, ozone, CO2 and water vapor.
• Practically all the radiation in ultraviolet part at wavelengths smaller than 0.33 μ is absorbed by oxygen and ozone in the upper atmosphere.
• Mathematically, disposition of solar radiation is given by the equation;

Qs=Cr+Ar+Ca+Aa+(Q+q)(1-a)+(Q+q)a