9. Radiation and insolation

9.1 Definitions

The measurements are intended to quantify the energy exchanges that take place via electromagnetic radiation; a distinction is made between solar radiation, whose most energetic spectrum on the ground is between 0.2 and 4 µm, and terrestrial radiation emitted by the Earth's surface and atmosphere, whose most intense energy spectrum ranges from 4 to 100 µm.

• The different components of solar radiation relevant to meteorology are:

  • direct solar radiation I, which comes from the solar disk only, excluding any radiation scattered, reflected, or refracted by the atmosphere; it is measured using a pyheliometer, a device whose sensitive surface is always perpendicular to the sun's...