Earth’s radiation is the energy emitted back into space, largely as a percentage of the total radiation received from the Sun. Albedo, or the amount of light energy reflected by a stellar body, is expressed as a ratio or percentage. The net loss of energy from Earth’s surface is minimal due to atmospheric damping effects. NASA has calculated Earth’s radiation budget, with 51% of the sunlight that reaches the Earth’s surface making up Earth’s radiation. Different surfaces on Earth have different albedo levels, with fresh snow having an albedo of 80-90% and coniferous forests having an albedo of 8%.
Earth’s radiation is the amount of heat or light energy that the Earth emits back into space, largely as a percentage of the total radiation it receives from the Sun. This is also referred to as albedo, which is expressed as a ratio or percentage of the amount of light energy that any stellar body, including planets, asteroids or spacecraft, reflects off their surface with respect to what is received. Another term for terrestrial radiation is Outgoing Longwave Radiation (OLR), which refers generally to the fact that what the Earth radiates into space is mostly infrared light waves invisible to human sight, which are a form of heat energy or body radiation black.
Earth’s surface radiation as a net loss of energy from the surface turns out to be actually quite minimal, due to atmospheric damping effects. The average amount of solar radiation energy received by the Earth above the confines of the atmosphere is estimated at 1,370 watts per square meter. As of 2010, peak space radiation took place in equatorial desert regions at values of about 350 watts per square meter, and dropped to less than 150 watts per square meter as one approached the polar ice caps. The actual amount of radiation escaping into space from any one location depends on short-term conditions in the atmosphere which have a varying effect on the blocking and absorption of long wavelength light. As levels of greenhouse gases in the atmosphere increase due to global industrial activities, so does this heat-trapping effect, overall reducing the overall Earth’s radiation level.
The National Aeronautics and Space Administration (NASA) in the United States has calculated figures for various aspects of Earth’s radiation budget. Of the sunlight received at atmospheric levels, 6% is immediately reflected back into space and another 20% is reflected off the cloud cover. Another 19% of the radiation never reaches the surface, as 16% is absorbed by the atmosphere and 3% by clouds. Of the light that reaches the earth’s surface, 4% of it is instantly reflected back into space. The rest of the light that reaches the surface of the earth and oceans – 51% – is what Earth’s radiation is actually made up of.
Of just over half of the sun’s energy that impacts the Earth’s surface, about 70% of it eventually returns to space, with the rest being absorbed by the atmosphere and water vapour. This means that about one-third of the solar radiation that hits the Earth’s surface is eventually lost into space, as well as one-third of the light that never reaches the surface and is reflected by the atmosphere itself. While the process of energy transfer is continuous, the Earth radiates into space more at night than during the day, as the temperature of the Earth’s surface has a direct impact on the amount of heat that occurs and the planet experiences a gradual cooling effect at night. .
Various surfaces on Earth have different albedo levels, however, or ratios for how much light energy they absorb and reflect. An albedo of 0 would equal total energy absorption and a value of 1 would be total reflection, both of which never actually occur. Surfaces such as concrete have a reflective quality of 55%, grass 25%, and typical terrain 17%. Regions of the Earth that have a very high albedo from the effects of near-total Earth radiation include those covered by fresh snow, where it is between 80% and 90%, and those with a very low albedo and absorption almost total light energy includes coniferous forests at the peak of the growing season, with a reflective quality of 8%.
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