Discovery Science: Earth – Atmospheric Processes

Earth Science: Atmospheric Processes

The sun is the driving force for processes in the atmosphere, fending off most of the Earth’s damaging ultraviolet radiation, and permitting only the shortwave radiation of visible light to penetrate to the Earth’s surface.

The radiation given off by the sun provides the energy for all meteorological processes and for a multitude of atmospheric phenomena. One-third of the radiation that penetrates to the Earth is reflected by clouds, the Earth’s surface, and the air, re- directing it back into space (albedo). The atmosphere also absorbs some of the shortwave radiation. About half of the radiation reaches the Earth’s surface directly or indirectly through scattering by gases and aerosols.

The Earth not only absorbs radiation, it also gives off radiation in the form of longwave heat. Without the presence of the atmosphere, such terrestrial warming radiation would escape unhindered into outer space and the average global temperature on the Earth’s surface would be about -0.4°F (-18T). However, because of clouds and atmospheric gases, such as carbon dioxide (CO2) and water vapor (H2O), a large part of this radiation is recaptured—only a small part can escape through the so-called atmospheric window.

The predominant part is radiated back to earth as atmospheric back radiation. This process is referred to as a natural green- house effect. This back radiation has an energizing effect on the Earth; the air close to the ground is heated on average to 58°F (14.5°C), leading to water evaporation and the motion of the air and sea.

Radiation balance

There is an overall balance found on Earth, between radiation that is received and given off. However, depending on the latitude there are significant variations. For instance, in the polar regions there is an avarage deficit created due to the polar night, while the tropics have a radiation excess due to solar radiation throughout the entire year.

In order to balance the uneven energy distribution on Earth, global wind systems circulate in the atmosphere while oceanic currents transport energy from the lower latitudes to the higher latitudes.


Some of the received shortwave solar radiation is reflected back into space by clouds and the Earth’s sur face, without utilizing any of the heat. This capability to reflect is strongly dependent on the type and condition of the area that is being irradiated.

While a black body absorbs all radiation and does not reflect anything, a white body produces the opposite effect. The highest albedo values are reached by areas covered with dry snow. The larger the ice cover of the Earth, the less heat is absorbed, causing a temperature drop


SUNLIGHT is composed of the colors of the visible spectrum, with different wavelengths. When sunlight penetrates the atmosphere, air molecules scatter the rays.

The shortwave blue light is scattered about five times as much as the red light, which is why the sky appears blue.