Solar radiation from the sun, called solar insolation, undergoes various interactions with the Earth’s atmosphere before reaching the surface. These interactions result in absorption, scattering, and the formation of beam and diffuse radiation, which together form the global radiation received at the surface.
1. Absorption
- Certain atmospheric gases like water vapor, ozone, and carbon dioxide absorb specific wavelengths of solar radiation.
- This reduces the intensity of solar radiation that reaches the surface.
- Energy absorbed is converted to heat, warming the atmosphere.
2. Scattering
- Solar radiation is scattered by air molecules, dust, aerosols, and clouds in the atmosphere.
- Scattering causes the change in direction of solar rays.
- Scattering can be:
- Rayleigh scattering (by molecules, dominant in clear sky – gives the sky its blue color),
- Mie scattering (by dust, haze, smoke – common in polluted or cloudy conditions).
3. Beam (Direct) Radiation
- Portion of solar radiation that reaches the Earth’s surface without any change in direction.
- It travels in a straight line from the sun to the surface.
- Responsible for casting sharp shadows.
4. Diffuse Radiation
- Radiation that is scattered by molecules and particles in the atmosphere before reaching Earth.
- Arrives at the surface from all directions in the sky.
- Present even on clear days and dominant during overcast conditions.
5. Global Radiation
- The sum of beam and diffuse radiation at any location.
- This is the total solar energy available for solar applications like PV panels or solar water heaters.
