is the condition in which a body loses more energy by radiation
than it gains from its surroundings.
The large-scale circulation of the Earth's atmosphere
is driven by the difference in absorbed solar radiation per square meter, as the sun heats the Earth more in the Tropics
, mostly because of geometrical factors. The atmospheric and oceanic circulation redistributes some of this energy as sensible heat
and latent heat
partly via the mean flow and partly via eddies, known as cyclones
in the atmosphere. Thus the tropics radiate less to space than they would if there were no circulation, and the poles radiate more; however in absolute terms the tropics radiate more energy to space.
Personally experiencing radiative cooling
Radiative cooling is commonly experienced on cloudless nights, when heat is radiated into space from the surface of the Earth, or from the skin of a human observer. The effect is well-known among amateur astronomers
, and can personally be felt on the skin of an observer on a cloudless night. To feel the effect, one compares the difference between looking straight up into a cloudless night sky for several seconds, to that of placing a sheet of paper between one's face and the sky. Since outer space radiates at about a temperature of 3 kelvins
(-270 degrees Celsius
or -450 degrees Fahrenheit
), and the sheet of paper radiates at about 300 kelvins (room temperature), the sheet of paper radiates more heat
to one's face than does the darkened cosmos. The effect is blunted somewhat by Earth's surrounding atmosphere which also traps heat. Note that it is not
correct to say that the sheet "blocks the cold" of the night sky; instead, the sheet is literally warming your face, just like a camp fire warms your face; the only difference is that a campfire is several hundred degrees warmer than a sheet of paper, just like a sheet of paper is several hundred degrees warmer than the deep night sky.