The radiation flux from the Sun received by the Earth at its average distance. The irradiance over all wavelengths is referred to as the total solar irradiance (TSI). At visible and near-infrared wavelengths the solar irradiance shows very little variation (a fraction of a percent) with time and is the main component of the TSI. The ultraviolet and X-ray irradiances show much larger variations due to active regions and solar flares. Although much smaller than the visible and near-infrared irradiance, this high-energy radiation is absorbed by the Earth's atmosphere and is very important for atmospheric chemistry.
Subjects: Astronomy and Astrophysics.