Spectrum Of Solar Radiation On Earth

Solar irradiance is the power per unit area received from the sun in the form of electromagnetic radiation as reported in the wavelength range of the measuring instrument.

Spectrum of solar radiation on earth.

The sun emits radiation from x rays to radio waves but the irradiance of solar radiation peaks in the visible wavelengths see figure below. The three relevant bands or ranges along the solar radiation spectrum are ultraviolet visible par and infrared. Solar radiation is the earth primary natural source of energy and by a long way. But this is because the solar radiation in that example is the value close to the surface of the sun.

The spectrum of the sun s solar radiation is close to that of a black body with a temperature of about 5 800 k. Common units of irradiance are joules per second per m 2 of surface that is illuminated per nm of wavelength e g between 300 nm and 301 nm or w m 2 nm 1 for the plot below. Solar radiation is radiant electromagnetic energy from the sun. As a consequence the solar radiation influences many aspects of the earth.

The earth reradiates nearly as a blackbody at a mean temperature of 290 k. The current most accurate tsi values from the total irradiance monitor tim on nasa s solar radiation and climate experiment sorce is 1360 8 0 5 w m2 during the 2008 solar minimum as compared to previous estimates of 1365 4 1 3 w m2 established in the 1990s. This radiant energy is necessary for the metabolism of the environment and its inhabitants 1. The solar irradiance is measured in watt per square metre w m 2 in si units solar irradiance is often integrated over a given time period in order to report the radiant energy emitted into the surrounding environment.

The sun emits em radiation across most of the electromagnetic spectrum although the sun produces gamma rays as a result of the nuclear fusion process internal absorption and thermalization convert these super high energy photons to lower energy photons before they reach the sun s. It provides light and heat for the earth and energy for photosynthesis. The geothermal heat flux generated by the earth interior natural terrestrial radioactivity and cosmic radiation which are all negligible relative to solar radiation. But the earth only receives about one two billionth of the solar radiation due to its distance from the sun.

The solar constant i sc is the average radiation intensity falling on an imaginary surface perpendicular to the sun s rays and at the edge of the earth s atmosphere figure 2 1 the word constant is a little misleading since because of the earth s elliptical orbit the intensity of the solar radiation falling on the earth changes by about 7 between january 1 st when the earth. Overall and on average the solar energy into the atmosphere is of a similar magnitude to the terrestrial radiation out of the atmosphere. However 99 per cent of the energy of solar radiation is contained in the wavelength band from 0 15 to 4 μm comprising the near ultraviolet visible and near infrared regions of the solar spectrum with a maximum at about 0 5 μm.