Radiation balance of the atmosphere

The radiation balance takes into account the transformation and behavior of the solar radiant energy when interacting with the atmosphere and the underlying surface, the own radiation of the atmosphere and the underlying surface.

The radiation balance of the underlying surface (at the lower boundary of the atmosphere), the atmosphere and the Earth-atmosphere system (at the upper boundary of the atmosphere) is the final characteristic of all radiation processes. That is, processes associated with the entry, exit and interaction of optical radiation with various components of the atmosphere and the Earth.

For the radiation balance of the underlying surface R n the equation has the form

where and are the fluxes (or sums over a time period) of incoming direct and scattered radiation; E 3 and E a - flows (or amounts) of counter-radiation of the earth's surface and atmosphere; A % albedo of the underlying surface.

The role of various components is visible from the figure, which presents the results of observations in a desert area near Tashkent (42°N, September).

Daily variation of the components of the radiation balance of the underlying surface: 1 – direct radiation; 2 – radiation balance; 3 – scattered radiation; 4 – reflected radiation; 5 – radiation from the underlying surface.

A positive R n balance during the day and a negative balance at night are typical for all parts of the globe in the summer. In winter in the north and partly in temperate latitudes, this radiation balance remains negative around the clock. This zone includes latitudes at which the Sun does not rise above 11° at midday; those. in December the zone boundary lies at 56°, in January - 58°, in February - 66 ○ N. latitude.

The annual cycle is characterized by a distinct latitudinal dependence due to the high altitude of the Sun. In the zone from 40°N. up to 40°S monthly values ​​of the radiation balance on land and sea are always positive with a maximum in July. At higher latitudes and in winter, the radiation balance becomes negative with a minimum in December. According to calculations by M.I. Budyko (1956), medium-

The annual value of the radiation balance of the earth's surface is generally positive and equal to 68 kcal/cm 2 -year (90 W/m 2).

Cloudiness changes not only the input component of the radiation balance (direct and diffuse radiation), but also the output component (radiation of the underlying surface and reflected radiation). As a result, an increase in cloudiness entails a decrease in positive values ​​during the day, and a decrease in negative values ​​at night.

An increase in cloudiness from 3 to 8 points reduces the value by 20%.

An increase in albedo from 10 to 80% (snow) reduces the value by a factor of three.

For the radiation balance of the atmosphere, the equation differs from the previous one (for ) and has the form

Counter-radiation flows of the earth's surface and atmosphere

now constitute the credit side of the balance sheet. Quantity is the part of direct and scattered radiation absorbed by the atmosphere (incoming). The value denotes the radiation of the atmosphere and the underlying surface escaping into outer space. It constitutes the expenditure part of the atmospheric radiation balance. Not all components can be measured directly. Therefore, the value is obtained by calculation.

The radiation balance of the Earth-atmosphere system is determined by the sum

.

The value for individual regions can be positive or negative, but for the globe as a whole it is close to zero. This is explained by the fact that the thermal regime of the globe as a whole maintains a state close to stationary.

Consequently, the positive average annual balance of the underlying surface = 90 W/m 2 is balanced by a negative average annual balance of the same value.

A diagram of the average annual distribution of the flux of incoming solar radiation and the shares of absorbed, scattered, reflected and outgoing fluxes of short-wave radiation is presented in the figure according to calculations by Schneider and Denist (1975)

The average annual flow distribution is taken as 100 conventional units.

From the presented flow distribution it follows:

1. 41 units of direct radiation passed through the atmosphere, and 39 units were scattered (at the stratosphere-troposphere boundary).

2. 17 units of direct solar radiation were scattered by molecules and aerosol, 22 units were absorbed by the hydrosphere and 2 were reflected (went up). Total 41 units;

3. 39 scattered units were divided in this way: 19 units were scattered upward by clouds, 5 units were absorbed by clouds, of the remaining 15 units, 14.5 were absorbed in the hydrosphere, 0.5 were reflected and went upward;

4. out of 17 units scattered by molecules and aerosol, 6 units went up due to backscattering by aerosol, 10.5 units were absorbed by the hydrosphere and 0.5 units were reflected (these 0.5 units and the previous 15 units amounted to 1 unit of reflected radiation) ;

5. a total of 19+6+1+2=28 units left the system;

6. so: 47 units were absorbed in water, 5 units were absorbed by clouds, 3 units were absorbed by ozone in the stratosphere, 17 units were absorbed by water and dust in the troposphere, for a total of 72 units;

7. These 72 units are precisely what is missing in the outgoing radiation, there are 28 units;

If we now include in this diagram the flow of outgoing long-wave radiation (the missing 72 conventional units), we will get a diagram of the global radiation balance of the Earth as a planet.

As can be seen from the diagram, the average annual flux of outgoing short-wave radiation beyond the atmosphere consists largely of that reflected by clouds (19 units). And to a lesser extent, the fluxes backscattered by atmospheric aerosol (6 units) and reflected by the underlying surface (3 units).

The zonal distribution of the Earth's radiation balance is currently measured with satisfactory accuracy using artificial Earth satellites. From these data it follows that with positive average annual values ​​in the equatorial zone over the oceans, they are systematically higher than over land.

Regional features of the radiation balance of the earth's surface, atmosphere and the Earth as a whole consist in their high spatiotemporal variability, caused by significant variations in the components. Therefore, regional monitoring of the latter turns out to be extremely important for interpreting climate changes in individual regions and on the entire planet.