Longwave (LW) radiation, in the context of climate science, is electromagnetic thermal radiation emitted by Earth's surface, atmosphere, and clouds. Longwave radiation may also be referred to as terrestrial radiation, thermal infrared radiation, or thermal radiation. This radiation is in the infrared portion of the spectrum, but is distinct from (i.e., has a longer wavelength than) the shortwave (SW) near-infrared radiation found in sunlight.
Outgoing longwave radiation (OLR) is the longwave radiation emitted to space from the top of Earth's atmosphere. It may also be referred to as emitted terrestrial radiation. Outgoing longwave radiation plays an important role in planetary cooling.
Longwave radiation generally spans wavelengths ranging from 3–100 microns (μm). A cutoff of 4 μm is sometimes used to differentiate sunlight from longwave radiation. Less than 1% of sunlight has wavelengths greater than 4 μm. Over 99% of outgoing longwave radiation has wavelengths between 4 μm and 100 μm.
The flux of energy transported by outgoing longwave radiation is typically measured in units of watts per meter squared (W m−2). In the case of global energy flux, the W/m2 value is obtained by dividing the total energy flow over the surface of the globe (measured in watts) by the surface area of the Earth, .
Emitting outgoing longwave radiation is the only way Earth loses energy to space, i.e., the only way the planet cools itself. Radiative heating from absorbed sunlight, and radiative cooling to space via OLR power the heat engine that drives atmospheric dynamics.
The balance between OLR (energy lost) and incoming solar shortwave radiation (energy gained) determines whether the Earth is experiencing global heating or cooling (see Earth's energy budget).
Outgoing longwave radiation (OLR) constitutes a critical component of Earth's energy budget.
The principle of conservation of energy says that energy cannot appear or disappear. Thus, any energy that enters a system but does not leave must be retained within the system.
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Greenhouse gases are those gases in the atmosphere that raise the surface temperature of planets such as the Earth. What distinguishes them from other gases is that they absorb the wavelengths of radiation that a planet emits, resulting in the greenhouse effect. The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by water vapor (), carbon dioxide (), methane (), nitrous oxide (), and ozone (). Without greenhouse gases, the average temperature of Earth's surface would be about , rather than the present average of .
In meteorology, cloud forcing, cloud radiative forcing (CRF) or cloud radiative effect (CRE) is the difference between the radiation budget components for average cloud conditions and cloud-free conditions. Much of the interest in cloud forcing relates to its role as a feedback process in the present period of global warming. The following equation calculates this change in the radiation budget at the top of the atmosphere The net cloud radiative effect can be decomposed into its longwave and shortwave components.
Longwave (LW) radiation, in the context of climate science, is electromagnetic thermal radiation emitted by Earth's surface, atmosphere, and clouds. Longwave radiation may also be referred to as terrestrial radiation, thermal infrared radiation, or thermal radiation. This radiation is in the infrared portion of the spectrum, but is distinct from (i.e., has a longer wavelength than) the shortwave (SW) near-infrared radiation found in sunlight. Outgoing longwave radiation (OLR) is the longwave radiation emitted to space from the top of Earth's atmosphere.
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