Long-wave radiation of the earth's surface and atmosphere

The upper layers of soil, ice, water, and snow cover emit long-wave radiation, which is called the surface's own radiation. It can be calculated using the formula:

,

where: - the Stefan-Boltzmann coefficient.

At the mean annual temperature of the globe of 15 C (288 K), Е = 0.42 kW/m². Such a rapid loss of heat by the Earth's surface would lead to its rapid cooling, if this were not prevented by the reverse process – the absorption of solar and atmospheric radiation by the Earth's surface.

The radiation emitted by the Earth has wavelengths of 4 – 120 µm, is infrared, and is not perceived by the eye.

The atmosphere, absorbing some part of the incoming solar radiation (15%) and most of the radiation from the Earth's surface, itself becomes a source of infrared radiation emission. Most (70%) of atmospheric radiation arrives at the Earth's surface and is called counter-radiation (Е); the remaining part goes into outer space, and this part is called outgoing radiation (Е).

The Earth's surface absorbs counter-radiation almost completely (95 – 99%). This radiation is an important source of heat for the Earth's surface in addition to the absorbed solar radiation.

Counter-radiation increases with increasing cloud cover. For plains stations in temperate latitudes Е = 0.21–0.28 kW/m², for the equatorial region (where the atmosphere is warm and rich in water vapor) - Е = 0.38–0.42 kW/m².

Counter-radiation can be calculated using Brunt's formula:

Е = ⁴(Д + Ge),

where: Д and G are constants; Д = 0.61; G = 0.05;

е – the partial pressure of water vapor, hPa.

In the atmosphere, long-wave radiation is absorbed mainly by two components – СО₂ and Н₂О.

Since counter-radiation is always less than the Earth's own radiation, the Earth loses heat due to the positive difference between its own radiation and counter-radiation. The difference between the Earth's own radiation and the atmosphere's counter-radiation is called effective radiation (Е_е).

Effective radiation on clear days amounts to 0.1 kW/m². With increasing cloud cover, effective radiation decreases.

In temperate latitudes, the Earth's surface loses about half of the amount of heat it receives from absorbed radiation through effective radiation.

By absorbing terrestrial radiation and sending counter-radiation to the Earth's surface, the atmosphere significantly reduces the cooling of the Earth's surface at night. During the day it practically does not hinder the warming of the Earth's surface. This influence of the atmosphere on the thermal regime of the Earth's surface is called the greenhouse effect (greenhouse effect).