What determines the amount of solar radiation. Solar radiation - what is it? Total solar radiation

LECTURE 3

RADIATION BALANCE AND ITS COMPONENTS

Solar radiation reaching earth's surface, partly reflected from it, and partly absorbed by the Earth. However, the Earth not only absorbs radiation, but also emits long-wave radiation itself into the surrounding atmosphere. The atmosphere, absorbing some of the solar radiation and most of the radiation of the earth's surface, itself also emits long-wave radiation. Most of this atmospheric radiation is directed toward the earth's surface. It is calledcounter radiation of the atmosphere .

The difference between the flows of radiant energy coming to the active layer of the Earth and leaving it is calledradiation balance active layer.

The radiation balance consists from shortwave and longwave radiation. It includes the following elements, called components of the radiation balance:direct radiation, scattered radiation, reflected radiation (shortwave), radiation of the earth's surface, counter radiation of the atmosphere .

Let us consider the components of the radiation balance.

direct solar radiation

The energy illumination of direct radiation depends on the height of the Sun and the transparency of the atmosphere and increases with increasing altitude above sea level. The clouds of the lower tier usually completely or almost do not transmit direct radiation.

The wavelengths of solar radiation reaching the earth's surface lie in the range of 0.29-4.0 microns. Approximately half of its energy comes from fluorosynthetically active radiation. In area PAR The attenuation of radiation with a decrease in the height of the Sun occurs faster than in the infrared radiation region. The arrival of direct solar radiation, as already mentioned, depends on the height of the Sun above the horizon, which varies both during the day and during the year. This determines the daily and annual course of direct radiation.

The change in direct radiation during a cloudless day (diurnal variation) is expressed by a unimodal curve with a maximum at true solar noon. In summer, over land, the maximum can occur before noon, since the dustiness of the atmosphere increases by noon.

When moving from the poles to the equator, the arrival of direct radiation at any time of the year increases, since this increases the midday height of the Sun.

The annual course of direct radiation is most pronounced at the poles, since in winter there is no solar radiation at all, and in summer its arrival reaches 900 W / m². In mid-latitudes, the direct radiation maximum is sometimes observed not in summer, but in spring, since in the summer months, due to an increase in the content of water vapor and dust, the transparency of the atmosphere decreases / The minimum falls on the period close to the winter solstice (December). At the equator, there are two maxima equal to approximately 920 W / m² on the days of the spring and autumn equinoxes, and two minimums (about 550 W / m²) on the days of the summer and winter solstices.

scattered radiation

The maximum of scattered radiation is usually much less than the maximum of direct radiation. The greater the height of the Sun and the greater the pollution of the atmosphere, the greater the flux of scattered radiation. Clouds that do not cover the Sun increase the amount of scattered radiation compared to clear skies. The dependence of the arrival of scattered radiation on cloudiness is complex. It is determined by the type and amount of clouds, their vertical power and optical properties. The scattered radiation of a cloudy sky can fluctuate by more than 10 times.

Snow cover, reflecting up to 70-90% of direct radiation, increases diffuse radiation, which then dissipates in the atmosphere. With an increase in the height of the place above sea level, the scattered radiation in clear skies decreases.

Daily and annual course scattered radiation under clear skies generally corresponds to the course of direct radiation. However, in the morning, scattered radiation appears even before sunrise, and in the evening it still enters during the twilight period, that is, after sunset. In the annual course, the maximum of scattered radiation is observed in summer.

Total radiation

The sum of scattered and direct radiation incident on a horizontal surface is calledtotal radiation .

It is the main component of the radiation balance. Its spectral composition, compared with direct and scattered radiation, is more stable and almost does not depend on the height of the Sun when it is more than 15 °.

The ratio between direct and diffuse radiation in the composition total radiation depends on the height of the Sun, cloudiness and pollution of the atmosphere. With an increase in the height of the Sun, the fraction of scattered radiation at cloudless sky decreases. The more transparent the atmosphere, the smaller the proportion of scattered radiation. With continuous dense clouds, the total radiation consists entirely of scattered radiation. In winter, due to the reflection of radiation from the snow cover and its secondary scattering in the atmosphere, the proportion of scattered radiation in the composition of the total increases noticeably.

The arrival of total radiation in the presence of cloudiness varies over a wide range. Its greatest arrival is observed in a clear sky or with a small cloud cover that does not cover the Sun.

In the daily and annual course, the changes in the total radiation are almost directly proportional to the change in the height of the Sun. In the diurnal course, the maximum of total radiation with a cloudless sky usually occurs at noon. In the annual course, the maximum of total radiation is observed in the northern hemisphere, usually in June, in the southern - in December.

reflected radiation. Albedo

Part of the total radiation coming to the active layer of the Earth is reflected from it. The ratio of the reflected part of the radiation to the total incoming radiation is calledreflectivity , oralbedo (A) given underlying surface.

The albedo of a surface depends on its color, roughness, humidity, and other properties.

Albedo of various natural surfaces (according to V. L. Gaevsky and M. I. Budyko)

Surface	Albedo, %	Surface	Albedo, %
Fresh dry snow	80-95	Rye and wheat fields	10-25
polluted snow	40-50	potato fields	15-25
sea ​​ice	30-40	cotton fields	20-25
dark soils	5-15	meadows	15-25
Dry clay soils	20-35	dry steppe	20-30

The albedo of water surfaces at a solar altitude above 60 ° is less than the albedo of land, since the sun's rays, penetrating into the water, are largely absorbed and scattered in it. With a sheer incidence of rays, A \u003d 2-5%, with a height of the Sun less than 10 ° A \u003d 50-70%. The large albedo of ice and snow determines the slow course of spring in the polar regions and the preservation of eternal ice there.

Observations of the albedo of land, sea and cloud cover are carried out with artificial satellites Earth. The albedo of the sea makes it possible to calculate the height of waves, the albedo of clouds characterizes their power, and the albedo of different parts of the land makes it possible to judge the degree of snow coverage of fields and the state of vegetation.

The albedo of all surfaces, and especially water ones, depends on the height of the Sun: the lowest albedo occurs at noon, the highest - in the morning and evening. This is due to the fact that at a low solar altitude, the fraction of scattered radiation in the composition of total radiation increases, which in more than direct radiation is reflected from the rough underlying surface.

Long-wave radiation of the Earth and atmosphere

terrestrial radiationslightly less than the black body radiation at the same temperature.

Radiation from the earth's surface is continuous. The higher the temperature of the radiating surface, the more intense its radiation. There is also a continuous emission of the atmosphere, which, absorbing part of the solar radiation and the radiation of the earth's surface, itself emits long-wave radiation.

In temperate latitudes, with a cloudless sky, atmospheric radiation is 280-350 W / m², and in the case of a cloudy sky, it is 20-30% more. About 62-64% of this radiation is directed towards the earth's surface. Its arrival on the earth's surface is the counter radiation of the atmosphere. The difference between these two fluxes characterizes the loss of radiant energy by the active layer. This difference is calledeffective radiation Eeff .

The effective radiation of the active layer depends on its temperature, on the temperature and humidity of the air, and also on cloudiness. With an increase in the temperature of the earth's surface, Eeff increases, and with an increase in temperature and air humidity, it decreases. Clouds especially affect the effective radiation, since cloud drops radiate almost in the same way as the active layer of the Earth. On average, Eef at night and during the day with a clear sky at different points on the earth's surface varies within 70-140 W / m².

daily course effective radiation is characterized by a maximum at 12-14 h and a minimum before sunrise.annual course effective radiation in regions with a continental climate is characterized by a maximum in the summer months and a minimum in the winter. In areas with a maritime climate, the annual variation of effective radiation is less pronounced than in areas located inland

Radiation from the earth's surface is absorbed by water vapor and carbon dioxide contained in the air. But short-wave radiation from the Sun is largely transmitted by the atmosphere. This property of the atmosphere is called"greenhouse effect" , since the atmosphere in this case acts like glass in greenhouses: the glass transmits the sun's rays well, heating the soil and plants in the greenhouse, but poorly transmits the thermal radiation of the heated soil into the external space. Calculations show that in the absence of an atmosphere, the average temperature of the active layer of the Earth would be 38°C lower than actually observed, and the Earth would be covered with eternal ice.

If the input of radiation is greater than the output, then the radiation balance is positive and the active layer of the Earth is heated. With a negative radiation balance, this layer cools. The radiation balance is usually positive during the day and negative at night. Approximately 1-2 hours before sunset, it becomes negative, and in the morning, on average, 1 hour after sunrise, it becomes positive again. The course of the radiation balance in the daytime with a clear sky is close to the course of direct radiation.

The study of the radiation balance of agricultural land makes it possible to calculate the amount of radiation absorbed by crops and soil, depending on the height of the Sun, the structure of crops, and the phase of plant development. To evaluate different methods of regulating temperature and soil moisture, evaporation and other quantities, the radiation balance of agricultural fields is determined for various types of vegetation cover.

Methods for measuring solar radiation and components of the radiation balance

To measure the fluxes of solar radiation are usedabsolute andrelative methods and accordingly developed absolute and relative actinometric instruments. Absolute instruments are usually used only for calibration and verification of relative instruments.

Relative instruments are used for regular observations at a network of weather stations, as well as in expeditions, and in field observations. Of these, thermoelectric devices are most widely used: actinometer, pyranometer and albedometer. The receiver of solar radiation in these devices are thermopiles, composed of two metals (usually manganin and constantan). Depending on the radiation intensity, a temperature difference is created between the junctions of the thermopile and an electric current of various strengths occurs, which is measured by a galvanometer. To convert the divisions of the galvanometer scale into absolute units, conversion factors are used, which are determined for a given pair: actinometric device - galvanometer.

Thermoelectric actinometer (M-3) Savinov - Yanishevsky is used to measure direct radiation coming to the surface perpendicular to the sun's rays.

Pyranometer (M-80M) Yanishevsky is used to measure the total and scattered radiation coming to a horizontal surface.

During observations, the receiving part of the pyranometer is installed horizontally. To determine scattered radiation, the pyranometer is shaded from direct radiation by a shadow screen in the form of a round disk mounted on a rod at a distance of 60 cm from the receiving surface. When measuring total radiation, the shadow screen is moved to the side

Albedometer is a pyranometer fitted as well. For measuring reflected radiation. For this, a device is used that allows you to turn the receiving part of the device up (to measure direct) and down (to measure reflected radiation). Having determined the total and reflected radiation with an albedometer, the albedo of the underlying surface is calculated. For field measurements, the M-69 marching albedometer is used.

Thermoelectric balance meter M-10M. This device is used to measure the radiation balance of the underlying surface.

In addition to the devices considered, luxmeters are also used - photometric devices for measuring illumination, spectrophotometers, various devices for measuring PAR, etc. Many actinometric devices are adapted for continuous recording of the components of the radiation balance.

An important characteristic of the solar radiation regime is the duration of sunshine. It is used to defineheliograph .

In the field, pyranometers, marching albedometers, balance meters and light meters are most often used. For observations among plants, camping albedometers and luxmeters, as well as special micropyranometers, are most convenient.

The energy emitted by the Sun is called solar radiation. When it reaches Earth, most of the solar radiation is converted into heat.

Solar radiation is practically the only source of energy for the Earth and the atmosphere. Compared to solar energy, the importance of other energy sources for the Earth is negligible. For example, the temperature of the Earth, on average, increases with depth (about 1 ° C for every 35 m). Due to this, the surface of the Earth receives some heat from the internal parts. It is estimated that on average 1 cm 2 of the earth's surface receives about 220 J per year from the inner parts of the Earth. This amount is 5000 times less than the heat received from the Sun. The Earth receives a certain amount of heat from stars and planets, but even it is many times (approximately 30 million) less than the heat coming from the Sun.

The amount of energy sent by the Sun to the Earth is enormous. Thus, the power of the solar radiation flux entering an area of ​​10 km 2 is 7-9 kW in a cloudless summer (taking into account the weakening of the atmosphere). This is more than the capacity of the Krasnoyarsk HPP. The amount of radiant energy coming from the Sun in 1 second to an area of ​​15x15 km (this is less area Leningrad) at around noon hours in the summer, exceeds the capacity of all power plants of the collapsed USSR (166 million kW).

Figure 1 - The sun is a source of radiation

Types of solar radiation

In the atmosphere, solar radiation on its way to the earth's surface is partially absorbed, and partially scattered and reflected from clouds and the earth's surface. Three types of solar radiation are observed in the atmosphere: direct, diffuse and total.

direct solar radiation- radiation coming to the earth's surface directly from the solar disk. Solar radiation propagates from the Sun in all directions. But the distance from the Earth to the Sun is so great that direct radiation falls on any surface on the Earth in the form of a beam of parallel rays emanating, as it were, from infinity. Even the entire globe as a whole is so small in comparison with the distance to the Sun that all solar radiation falling on it can be considered a beam of parallel rays without noticeable error.

Only direct radiation reaches the upper boundary of the atmosphere. About 30% of the radiation incident on the Earth is reflected into outer space. Oxygen, nitrogen, ozone, carbon dioxide, water vapor (clouds) and aerosol particles absorb 23% of direct solar radiation in the atmosphere. Ozone absorbs ultraviolet and visible radiation. Despite the fact that its content in the air is very small, it absorbs all the ultraviolet radiation (about 3%). Thus, it is not observed at all near the earth's surface, which is very important for life on Earth.

Direct solar radiation on its way through the atmosphere is also scattered. A particle (drop, crystal or molecule) of air, which is in the path of an electromagnetic wave, continuously “extracts” energy from the incident wave and re-radiates it in all directions, becoming an energy emitter.

About 25% of the energy of the total solar radiation flux passing through the atmosphere is scattered by molecules atmospheric gases and aerosol and turns into diffuse solar radiation in the atmosphere. Thus scattered solar radiation- solar radiation that has undergone scattering in the atmosphere. Scattered radiation comes to the earth's surface not from the solar disk, but from everything vault of heaven. Scattered radiation differs from direct radiation in its spectral composition, since rays of different wavelengths are scattered to different degrees.

Since the primary source of diffuse radiation is direct solar radiation, the flux of diffuse radiation depends on the same factors that affect the flux of direct radiation. In particular, the flux of scattered radiation increases with the increase in the height of the Sun and vice versa. It also increases with an increase in the number of scattering particles in the atmosphere, i.e. with a decrease in the transparency of the atmosphere, and decreases with height above sea level due to a decrease in the number of scattering particles in the overlying layers of the atmosphere. Cloudiness and snow cover have a very great influence on diffuse radiation, which, due to the scattering and reflection of the direct and diffuse radiation incident on them and their re-scattering in the atmosphere, can increase the diffuse solar radiation by several times.

Scattered radiation significantly supplements direct solar radiation and significantly increases the incoming solar energy to the earth's surface. Its role is especially great in winter at high latitudes and in other regions with high cloudiness, where the fraction of scattered radiation may exceed the fraction of direct radiation. For example, in the annual amount of solar energy, scattered radiation accounts for 56% in Arkhangelsk and 51% in St. Petersburg.

Total solar radiation is the sum of the fluxes of direct and diffuse radiation arriving on a horizontal surface. Before sunrise and after sunset, as well as in the daytime with continuous cloudiness, the total radiation is completely, and at low altitudes of the Sun it mainly consists of scattered radiation. In a cloudless or slightly cloudy sky, with an increase in the height of the Sun, the proportion of direct radiation in the composition of the total rapidly increases and in the daytime its flux is many times greater than the flux of scattered radiation. Cloudiness on average weakens the total radiation (by 20-30%), however, with partial cloudiness that does not cover the solar disk, its flux may be greater than with a cloudless sky. The snow cover significantly increases the flux of total radiation by increasing the flux of scattered radiation.

The total radiation falling on the earth's surface, for the most part absorbed by the top layer of soil or a thicker layer of water (absorbed radiation) and converted into heat, and partly reflected (reflected radiation).

The Earth receives from the Sun 1.36 * 10v24 cal of heat per year. Compared to this amount of energy, the remaining amount of radiant energy reaching the Earth's surface is negligible. Thus, the radiant energy of stars is one hundred millionth of the solar energy, cosmic radiation is two billionths, the internal heat of the Earth at its surface is equal to one five thousandth of the solar heat.
Radiation of the Sun - solar radiation- is the main source of energy for almost all processes occurring in the atmosphere, hydrosphere and in the upper layers of the lithosphere.
The unit of measurement of the intensity of solar radiation is the number of calories of heat absorbed by 1 cm2 of an absolutely black surface perpendicular to the direction sun rays, for 1 minute (cal/cm2*min).

The flow of radiant energy from the Sun, reaching the earth's atmosphere, is very constant. Its intensity is called the solar constant (Io) and is taken on average to be 1.88 kcal/cm2 min.
The value of the solar constant fluctuates depending on the distance of the Earth from the Sun and on solar activity. Its fluctuations during the year are 3.4-3.5%.
If the sun's rays everywhere fell vertically on the earth's surface, then in the absence of an atmosphere and with a solar constant of 1.88 cal / cm2 * min, each square centimeter of it would receive 1000 kcal per year. Due to the fact that the Earth is spherical, this amount is reduced by 4 times, and 1 sq. cm receives an average of 250 kcal per year.
The amount of solar radiation received by the surface depends on the angle of incidence of the rays.
The maximum amount of radiation is received by the surface perpendicular to the direction of the sun's rays, because in this case all the energy is distributed to the area with a cross section equal to the cross section of the beam of rays - a. With oblique incidence of the same beam of rays, the energy is distributed over a large area (section c) and a unit surface receives a smaller amount of it. The smaller the angle of incidence of the rays, the lower the intensity of solar radiation.
The dependence of the intensity of solar radiation on the angle of incidence of rays is expressed by the formula:

I1 = I0 * sinh,

where I0 is the intensity of solar radiation at a sheer incidence of rays. Outside the atmosphere, the solar constant;
I1 - the intensity of solar radiation when the sun's rays fall at an angle h.
I1 is as many times less than I0, how many times the section a is less than the section b.
Figure 27 shows that a / b \u003d sin A.
The angle of incidence of the sun's rays (the height of the Sun) is equal to 90 ° only at latitudes from 23 ° 27 "N to 23 ° 27" S. (i.e. between the tropics). At other latitudes, it is always less than 90° (Table 8). According to the decrease in the angle of incidence of the rays, the intensity of solar radiation arriving at the surface at different latitudes. Since the height of the Sun does not remain constant throughout the year and during the day, the amount of solar heat received by the surface changes continuously.

The amount of solar radiation received by the surface is directly related to from the duration of its exposure to sunlight.

In the equatorial zone outside the atmosphere, the amount of solar heat during the year does not experience large fluctuations, while at high latitudes these fluctuations are very large (see Table 9). In winter, the differences in the arrival of solar heat between high and low latitudes are especially significant. AT summer period, in conditions of continuous illumination, the polar regions receive the maximum amount of solar heat per day on Earth. On the day of the summer solstice in the northern hemisphere, it is 36% higher than the daily amount of heat at the equator. But since the duration of the day at the equator is not 24 hours (as at this time at the pole), but 12 hours, the amount of solar radiation per unit of time at the equator remains the largest. The summer maximum of the daily sum of solar heat, observed at about 40-50° latitude, is associated with a relatively long day (greater than at this time by 10-20° latitude) at a significant height of the Sun. Differences in the amount of heat received by the equatorial and polar regions are smaller in summer than in winter.
The southern hemisphere receives more heat in summer than the northern one, and vice versa in winter (it is affected by the change in the distance of the Earth from the Sun). And if the surface of both hemispheres were completely homogeneous, the annual amplitudes of temperature fluctuations in the southern hemisphere would be greater than in the northern.
Solar radiation in the atmosphere undergoes quantitative and qualitative changes.
Even an ideal, dry and clean atmosphere absorbs and scatters rays, reducing the intensity of solar radiation. The weakening effect of the real atmosphere, containing water vapor and solid impurities, on solar radiation is much greater than the ideal one. The atmosphere (oxygen, ozone, carbon dioxide, dust and water vapor) absorbs mainly ultraviolet and infrared rays. The radiant energy of the Sun absorbed by the atmosphere is converted into other types of energy: thermal, chemical, etc. In general, absorption weakens solar radiation by 17-25%.
Molecules of atmospheric gases scatter rays with relatively short waves - violet, blue. This is what explains the blue color of the sky. Impurities equally scatter rays with waves of different wavelengths. Therefore, with a significant content of them, the sky acquires a whitish tint.
Due to the scattering and reflection of the sun's rays by the atmosphere, daylight is observed on cloudy days, objects in the shade are visible, and the phenomenon of twilight occurs.
How longer way beam in the atmosphere, the greater its thickness it must pass and the more significantly the solar radiation is weakened. Therefore, with elevation, the influence of the atmosphere on radiation decreases. The length of the path of sunlight in the atmosphere depends on the height of the Sun. If we take as a unit the length of the path of the solar beam in the atmosphere at the height of the Sun 90 ° (m), the ratio between the height of the Sun and the path length of the beam in the atmosphere will be as shown in Table. ten.

The total attenuation of radiation in the atmosphere at any height of the Sun can be expressed by the Bouguer formula: Im = I0 * pm, where Im is the intensity of solar radiation near the earth's surface changed in the atmosphere; I0 - solar constant; m is the path of the beam in the atmosphere; at a solar altitude of 90 ° it is equal to 1 (the mass of the atmosphere), p is the transparency coefficient ( fractional number, showing what fraction of radiation reaches the surface at m=1).
At a height of the Sun of 90°, at m=1, the intensity of solar radiation near the earth's surface I1 is p times less than Io, i.e. I1=Io*p.
If the height of the Sun is less than 90°, then m is always greater than 1. The path of a solar ray can consist of several segments, each of which is equal to 1. The intensity of solar radiation at the border between the first (aa1) and second (a1a2) segments I1 is obviously equal to Io *p, radiation intensity after passing the second segment I2=I1*p=I0 p*p=I0 p2; I3=I0p3 etc.

The transparency of the atmosphere is not constant and is not the same in various conditions. The ratio of the transparency of the real atmosphere to the transparency of the ideal atmosphere - the turbidity factor - is always greater than one. It depends on the content of water vapor and dust in the air. With the increase geographical latitude turbidity factor decrease: at latitudes from 0 to 20 ° N. sh. it is equal to 4.6 on average, at latitudes from 40 to 50 ° N. sh. - 3.5, at latitudes from 50 to 60 ° N. sh. - 2.8 and at latitudes from 60 to 80 ° N. sh. - 2.0. In temperate latitudes, the turbidity factor is less in winter than in summer, and less in the morning than in the afternoon. It decreases with height. The greater the turbidity factor, the greater the attenuation of solar radiation.
Distinguish direct, diffuse and total solar radiation.
Part of the solar radiation that penetrates through the atmosphere to the earth's surface is direct radiation. Part of the radiation scattered by the atmosphere is converted into diffuse radiation. All solar radiation entering the earth's surface, direct and diffuse, is called total radiation.
The ratio between direct and scattered radiation varies considerably depending on the cloudiness, dustiness of the atmosphere, and also on the height of the Sun. In clear skies, the fraction of scattered radiation does not exceed 0.1%; in cloudy skies, diffuse radiation can be greater than direct radiation.
At a low altitude of the Sun, the total radiation consists almost entirely of scattered radiation. At a solar altitude of 50° and a clear sky, the fraction of scattered radiation does not exceed 10-20%.
Maps of average annual and monthly values ​​of total radiation make it possible to notice the main patterns in its geographical distribution. The annual values ​​of total radiation are distributed mainly zonal. The largest annual amount of total radiation on Earth is received by the surface in tropical inland deserts (Eastern Sahara and the central part of Arabia). A noticeable decrease in total radiation at the equator is caused by high air humidity and high cloudiness. In the Arctic, the total radiation is 60-70 kcal/cm2 per year; in the Antarctic, due to the frequent recurrence of clear days and the greater transparency of the atmosphere, it is somewhat greater.

In June largest sums Radiation receives the northern hemisphere, and especially inland tropical and subtropical regions. The amounts of solar radiation received by the surface in the temperate and polar latitudes of the northern hemisphere differ little, owing mainly to the long duration of the day in the polar regions. Zoning in the distribution of total radiation above. continents in the northern hemisphere and in the tropical latitudes of the southern hemisphere is almost not expressed. It is better manifested in the northern hemisphere over the Ocean and is clearly expressed in the extratropical latitudes of the southern hemisphere. At the southern polar circle, the value of total solar radiation approaches 0.
In December, the largest amounts of radiation enter the southern hemisphere. The high-lying ice surface of Antarctica, with high air transparency, receives significantly more total radiation than the surface of the Arctic in June. There is a lot of heat in the deserts (Kalahari, Great Australian), but due to the greater oceanicity of the southern hemisphere (the influence of high air humidity and cloudiness), its amounts here are somewhat less than in June at the same latitudes of the northern hemisphere. In the equatorial and tropical latitudes of the northern hemisphere, the total radiation varies relatively little, and the zonation in its distribution is clearly expressed only to the north of the northern tropic. With increasing latitude, the total radiation decreases rather rapidly; its zero isoline passes somewhat north of the Arctic Circle.
The total solar radiation, falling on the Earth's surface, is partially reflected back into the atmosphere. The ratio of the amount of radiation reflected from a surface to the amount of radiation incident on that surface is called albedo. Albedo characterizes the reflectivity of a surface.
The albedo of the earth's surface depends on its condition and properties: color, humidity, roughness, etc. Freshly fallen snow has the highest reflectivity (85-95%). A calm water surface reflects only 2-5% of the sun's rays when it falls vertically, and almost all the rays falling on it (90%) when the sun is low. Albedo of dry chernozem - 14%, wet - 8, forest - 10-20, meadow vegetation - 18-30, sandy desert surfaces - 29-35, surfaces sea ​​ice - 30-40%.
The large albedo of the ice surface, especially covered with fresh snow (up to 95%), is the reason low temperatures in the polar regions in the summer, when the arrival of solar radiation is significant there.
Radiation of the earth's surface and atmosphere. Any body with a temperature above absolute zero(greater than minus 273°), emits radiant energy. The total emissivity of a blackbody is proportional to the fourth power of its absolute temperature (T):
E \u003d σ * T4 kcal / cm2 per minute (Stefan-Boltzmann law), where σ is a constant coefficient.
The higher the temperature of the radiating body, the shorter the wavelength of the emitted nm rays. The incandescent Sun sends into space shortwave radiation. The earth's surface, absorbing short-wave solar radiation, heats up and also becomes a source of radiation (terrestrial radiation). Ho, since the temperature of the earth's surface does not exceed several tens of degrees, its long-wave radiation, invisible.
Earth radiation is largely retained by the atmosphere (water vapor, carbon dioxide, ozone), but rays with a wavelength of 9-12 microns freely go beyond the atmosphere, and therefore the Earth loses some of its heat.
The atmosphere, absorbing part of the solar radiation passing through it and more than half of the earth's, itself radiates energy both into the world space and to the earth's surface. Atmospheric radiation directed towards the earth's surface towards the earth's surface is called opposite radiation. This radiation, like the terrestrial, long-wave, invisible.
Two streams of long-wave radiation meet in the atmosphere - the radiation of the Earth's surface and the radiation of the atmosphere. The difference between them, which determines the actual loss of heat by the earth's surface, is called efficient radiation. Effective radiation is the greater, the higher the temperature of the radiating surface. Air humidity reduces the effective radiation, its clouds greatly reduce it.
The highest value of annual sums of effective radiation is observed in tropical deserts - 80 kcal/cm2 per year - due to high temperature surface, dryness of the air and clarity of the sky. At the equator, with high air humidity, the effective radiation is only about 30 kcal/cm2 per year, and its value for land and for the ocean differs very little. The lowest effective radiation in the polar regions. In temperate latitudes, the earth's surface loses about half of the amount of heat that it receives from the absorption of total radiation.
The ability of the atmosphere to pass the short-wave radiation of the Sun (direct and diffuse radiation) and delay the long-wave radiation of the Earth is called the greenhouse (greenhouse) effect. Thanks to the greenhouse effect average temperature the earth's surface is +16°, in the absence of an atmosphere it would be -22° (38° lower).
Radiation balance (residual radiation). The earth's surface simultaneously receives radiation and gives it away. The arrival of radiation is the total solar radiation and the counter radiation of the atmosphere. Consumption - the reflection of sunlight from the surface (albedo) and the own radiation of the earth's surface. The difference between the incoming and outgoing radiation is radiation balance, or residual radiation. The value of the radiation balance is determined by the equation

R \u003d Q * (1-α) - I,

where Q is the total solar radiation per unit surface; α - albedo (fraction); I - effective radiation.
If the input is greater than the output, the radiation balance is positive; if the input is less than the output, the balance is negative. At night, at all latitudes, the radiation balance is negative; during the day, until noon, it is positive everywhere, except for high latitudes in winter; in the afternoon - again negative. On average per day, the radiation balance can be both positive and negative (Table 11).


On the map of the annual sums of the radiation balance of the earth's surface, one can see abrupt change positions of isolines during their transition from land to the ocean. As a rule, the radiation balance of the Ocean surface exceeds the radiation balance of the land (the effect of albedo and effective radiation). The distribution of the radiation balance is generally zonal. On the Ocean in tropical latitudes, the annual values ​​of the radiation balance reach 140 kcal/cm2 (Arabian Sea) and do not exceed 30 kcal/cm2 at the boundary of floating ice. Deviations from the zonal distribution of the radiation balance in the Ocean are insignificant and are caused by the distribution of clouds.
On land in the equatorial and tropical latitudes, the annual values ​​of the radiation balance vary from 60 to 90 kcal/cm2, depending on the moisture conditions. The largest annual sums of the radiation balance are noted in those areas where the albedo and effective radiation are relatively small (moist tropical forests, savannahs). Their lowest value is in very humid (large cloudiness) and in very dry (large effective radiation) regions. In temperate and high latitudes, the annual value of the radiation balance decreases with increasing latitude (the effect of a decrease in total radiation).
The annual sums of the radiation balance over the central regions of Antarctica are negative (several calories per 1 cm2). In the Arctic, these values ​​are close to zero.
In July, the radiation balance of the earth's surface in a significant part of the southern hemisphere is negative. The zero balance line runs between 40 and 50°S. sh. The highest value of the radiation balance is reached on the surface of the Ocean in the tropical latitudes of the northern hemisphere and on the surface of some inland seas, such as the Black Sea (14-16 kcal/cm2 per month).
In January, the zero balance line is located between 40 and 50°N. sh. (over the oceans it rises somewhat to the north, over the continents it descends to the south). A significant part of the northern hemisphere has a negative radiation balance. Largest values radiation balance are confined to the tropical latitudes of the southern hemisphere.
On average for the year, the radiation balance of the earth's surface is positive. In this case, the surface temperature does not increase, but remains approximately constant, which can only be explained by the continuous consumption of excess heat.
The radiation balance of the atmosphere consists of the solar and terrestrial radiation absorbed by it, on the one hand, and atmospheric radiation, on the other. It is always negative, since the atmosphere absorbs only a small part of solar radiation, and radiates almost as much as the surface.
The radiation balance of the surface and the atmosphere together, as a whole, for the entire Earth for a year is equal to zero on average, but in latitudes it can be both positive and negative.
The consequence of such a distribution of the radiation balance should be the transfer of heat in the direction from the equator to the poles.
Thermal balance. The radiation balance is the most important component of the heat balance. The surface heat balance equation shows how the incoming solar radiation energy is converted on the earth's surface:

where R is the radiation balance; LE - heat consumption for evaporation (L - latent heat of vaporization, E - evaporation);
P - turbulent heat exchange between the surface and the atmosphere;
A - heat exchange between the surface and underlying layers of soil or water.
The radiation balance of a surface is considered positive if the radiation absorbed by the surface exceeds the heat loss, and negative if it does not replenish them. All other terms of the heat balance are considered positive if they cause heat loss by the surface (if they correspond to heat consumption). As. all terms of the equation can change, the heat balance is constantly disturbed and restored again.
The equation of the heat balance of the surface considered above is approximate, since it does not take into account some secondary, but under specific conditions, factors that become important, for example, the release of heat during freezing, its consumption for thawing, etc.
The heat balance of the atmosphere consists of the radiation balance of the atmosphere Ra, the heat coming from the surface, Pa, the heat released in the atmosphere during condensation, LE, and the horizontal heat transfer (advection) Aa. The radiation balance of the atmosphere is always negative. The influx of heat as a result of moisture condensation and the magnitude of turbulent heat transfer are positive. Heat advection leads, on average per year, to its transfer from low latitudes to high latitudes: thus, it means heat consumption at low latitudes and arrival at high latitudes. In a multi-year derivation, the heat balance of the atmosphere can be expressed by the equation Ra=Pa+LE.
The heat balance of the surface and the atmosphere together as a whole is equal to 0 on a long-term average (Fig. 35).

The amount of solar radiation entering the atmosphere per year (250 kcal/cm2) is taken as 100%. Solar radiation, penetrating into the atmosphere, is partially reflected from the clouds and goes back beyond the atmosphere - 38%, partially absorbed by the atmosphere - 14%, and partially in the form of direct solar radiation reaches the earth's surface - 48%. Of the 48% that reach the surface, 44% are absorbed by it, and 4% are reflected. Thus, the Earth's albedo is 42% (38+4).
The radiation absorbed by the earth's surface is spent as follows: 20% is lost through effective radiation, 18% is spent on evaporation from the surface, 6% is spent on heating the air during turbulent heat transfer (total 24%). The loss of heat by the surface balances its arrival. The heat received by the atmosphere (14% directly from the Sun, 24% from the earth's surface), together with the effective radiation of the Earth, is directed into the world space. The Earth's albedo (42%) and radiation (58%) balance the influx of solar radiation to the atmosphere.

1. General characteristics of solar radiation
2. direct solar radiation
3. Total solar radiation
4. Absorption of solar radiation in the atmosphere

The radiant energy of the Sun, or solar radiation, is the main source of heat for the Earth's surface and for its atmosphere. The radiation coming from the stars and the Moon is negligible compared to solar radiation and does not make a significant contribution to the thermal processes on Earth. The flow of heat directed to the surface from the depths of the planet is also negligibly small. Solar radiation propagates in all directions from the source (the Sun) in the form of electromagnetic waves at a speed close to 300,000 km/sec. In meteorology, mainly thermal radiation is considered, determined by body temperature and its emissivity. Thermal radiation has wavelengths from hundreds of micrometers to thousandths of a micrometer. X-rays and gamma radiation are not considered in meteorology, since they practically do not enter the lower layers of the atmosphere. Thermal radiation is usually divided into short-wave and long-wave radiation. Short-wave radiation is called radiation in the wavelength range from 0.1 to 4 microns, long-wave radiation - from 4 to 100 microns. Solar radiation reaching the Earth's surface is 99% shortwave. Short-wave radiation is subdivided into ultraviolet (UV), with wavelengths from 0.1 to 0.39 microns; visible light (VS) - 0.4 - 0.76 microns; infrared (IR) - 0.76 - 4 microns. Sun and infrared radiation give the greatest energy: sun accounts for 47% of radiant energy, IR - 44%, and UV - only 9% of radiant energy. This distribution of thermal radiation corresponds to the distribution of energy in the spectrum of a completely black body with a temperature of 6000K. This temperature is considered conditionally close to the actual temperature on the surface of the Sun (in the photosphere, which is the source of the radiant energy of the Sun). The maximum radiant energy at such a temperature of the emitter, according to Wien's law l \u003d 0.2898 / T (cm * deg). (1) falls on blue-blue rays with lengths of about 0.475 microns (l. is the wavelength, T is the absolute temperature of the emitter). The total amount of radiated thermal energy is proportional, according to the Stefan-Boltzmann law, to the fourth power of the absolute temperature of the radiator: E \u003d sT 4 (2) where s \u003d 5.7 * 10-8 W / m 2 * K 4 (Stefan-Boltzmann constant). quantitative measure The solar radiation reaching the surface is the energy illumination, or the density of the radiation flux. Energy illumination is the amount of radiant energy per unit area per unit time. It is measured in W / m 2 (or kW / m 2). This means that 1 J (or 1 kJ) of radiant energy is supplied per 1 m 2 per second. The energy illumination of solar radiation incident on an area of ​​a unit area perpendicular to the sun's rays per unit time at the upper boundary of the atmosphere at an average distance from the Earth to the Sun is called the solar constant So. At the same time, the upper boundary of the atmosphere is understood as the condition of the absence of the influence of the atmosphere on solar radiation. Therefore, the value of the solar constant is determined only by the emissivity of the Sun and the distance between the Earth and the Sun. Modern research using satellites and rockets has established the value of So equal to 1367 W / m 2 with an error of ± 0.3%, the average distance between the Earth and the Sun in this case is defined as 149.6 * 106 km. If we take into account changes in the solar constant due to a change in the distance between the Earth and the Sun, then with an average annual value of 1.37 kW / m 2, in January it will be equal to 1.41 kW / m 2, and in June - 1.34 kW / m 2 , therefore, the northern hemisphere receives somewhat less radiation at the boundary of the atmosphere during a summer day than the southern hemisphere during its summer day. Due to the constant change in solar activity, the solar constant may fluctuate from year to year. But these fluctuations, if they exist, are so small that they lie within the limits of measurement accuracy. modern appliances. But during the existence of the Earth, the solar constant most likely changed its value. Knowing the solar constant, it is possible to calculate the amount of solar energy entering the illuminated hemisphere at the upper boundary of the atmosphere. It is equal to the product of the solar constant and the area of ​​the great circle of the Earth. With an average radius of the earth equal to 6371 km, the area of ​​the great circle is p * (6371) 2 = 1.275 * 1014 m 2, and the radiant energy coming to it is 1.743 * 1017 W. For a year it will be 5.49 * 1024 J. The arrival of solar radiation on a horizontal surface at the upper boundary of the atmosphere is called a solar climate. The formation of the solar climate is determined by two factors - the duration of sunshine and the height of the Sun. The amount of radiation falling at the boundary of the atmosphere per unit area of ​​the horizontal surface is proportional to the sine of the height of the Sun, which varies not only during the day, but also depends on the season. As you know, the height of the Sun for the days of the solstice is determined by the formula 900 - (j ± 23.50), for the days of the equinox - 900 -j, where j is the latitude of the place. Thus, the height of the Sun at the equator varies throughout the year from 90° to 66.50°, in the tropics - from 90 to 43°, in the polar circles - from 47 to 0° and at the poles - from 23.5° to 0° . In accordance with such a change in the height of the Sun in winter in each hemisphere, the influx of solar radiation to a horizontal area rapidly decreases from the equator to the poles. In summer, the picture is more complicated: in the middle of summer, the maximum values ​​are not at the equator, but at the poles, where the day length is 24 hours. In the annual course in the extratropical zone, there is one maximum (summer solstice) and one minimum (winter solstice). In the tropical zone, the influx of radiation reaches a maximum twice a year (the days of the equinoxes). Annual amounts of solar radiation vary from 133*102 MJ/m 2 (equator) to 56*102 MJ/m 2 (poles). The amplitude of the annual variation at the equator is small, while in the extratropical zone it is significant.

2 direct solar radiation Direct solar radiation is the radiation coming to the earth's surface directly from the solar disk. Despite the fact that solar radiation propagates from the Sun in all directions, it comes to the Earth in the form of a beam of parallel rays emanating, as it were, from infinity. The influx of direct solar radiation to the earth's surface or to any level in the atmosphere is characterized by energy illumination - the amount of radiant energy received per unit of time per unit area. The maximum influx of direct solar radiation will come to the area perpendicular to the sun's rays. In all other cases, the energy illumination will be determined by the height of the Sun, or the sine of the angle that the sunbeam forms with the surface of the site S’=S sin hc (3) V general case S (energy illumination of a site of a unit area perpendicular to the sun's rays) is equal to So. The flow of direct solar radiation falling on a horizontal area is called insolation.

3. scattered solar radiation Passing through the atmosphere, direct solar radiation is scattered by molecules of atmospheric gases and aerosol impurities. During scattering, a particle in the path of propagation of an electromagnetic wave continuously absorbs energy and re-radiates it in all directions. As a result, a stream of parallel solar rays traveling in a certain direction is re-radiated in all directions. Scattering occurs at all wavelengths electromagnetic radiation, but its intensity is determined by the ratio of the size of the scattering particles and the wavelengths of the incident radiation. In an absolutely pure atmosphere, where scattering is produced only by gas molecules whose dimensions are smaller than the wavelengths of radiation, it obeys Rayleigh's law, which states that spectral density energy illumination of scattered radiation is inversely proportional to the fourth power of the wavelength of scattered rays Dl=a Sl /l 4 (4) where Sl is the spectral density of energy illumination of direct radiation with wavelength l, Dl is the spectral density of energy illumination of scattered radiation with the same wavelength, a is the coefficient of proportionality. According to Rayleigh's law, scattered radiation is dominated by shorter wavelengths, since red rays, being twice as long as violet rays, scatter 14 times less. Infrared radiation is scattered very little. It is believed that about 26% of the total flux of solar radiation is scattered, 2/3 of this radiation comes to the earth's surface. Since scattered radiation does not come from the solar disk, but from the entire sky, its irradiance is measured on a horizontal surface. The unit of measure for the irradiance of scattered radiation is W/m 2 or kW/m 2 . If scattering occurs on particles commensurate with the wavelengths of radiation (aerosol impurities, ice crystals and water droplets), then the scattering does not obey the Rayleigh law and the energy illumination of the scattered radiation becomes inversely proportional not to the fourth, but to smaller powers of wavelengths - i.e. the scattering maximum shifts to the longer wavelength part of the spectrum. With a high content of large particles in the atmosphere, scattering is replaced by diffuse reflection, in which the light flux is reflected by the particles as mirrors, without changing the spectral composition. Since white light is incident, a stream of white light is also reflected. As a result, the color of the sky becomes whitish. Two interesting phenomena are associated with scattering - this is the blue color of the sky and twilight. The blue color of the sky is the color of the air itself, due to the scattering of sunlight in it. Since scattering in a clear sky obeys the Rayleigh law, the maximum energy of scattered radiation coming from the firmament falls on the blue color. The blue color of the air can be seen when looking at distant objects that seem to be shrouded in a bluish haze. With height, as air density decreases, the color of the sky becomes darker and turns into deep blue, and in the stratosphere - into purple. The more impurities are contained in the atmosphere, the greater the proportion of long-wave radiation in the spectrum sunlight, the whiter the sky becomes. Due to the scattering of the shortest waves, direct solar radiation is depleted by waves of this range, so the maximum energy in direct radiation is shifted to the yellow part and the solar disk is colored in yellow. At low angles of the Sun, scattering occurs very intensely, shifting to the long-wavelength part of the electromagnetic spectrum, especially in a polluted atmosphere. The maximum of direct solar radiation shifts to the red part, the solar disk becomes red, and bright yellow-red sunsets occur. After sunset, darkness does not come immediately, similarly in the morning, it becomes light on the earth's surface some time before the appearance of the solar disk. This phenomenon of incomplete darkness in the absence of the solar disk is called evening and morning twilight. The reason for this is the illumination by the Sun, which is under the horizon, of the high layers of the atmosphere and the scattering of sunlight by them. Distinguish astronomical twilight, which continues until the Sun drops below the horizon by 180 and at the same time it becomes so dark that the faintest stars are distinguishable. The first part of the evening astronomical twilight and the last part of the morning astronomical twilight is called civil twilight, during which the Sun falls below the horizon of at least 80 . The duration of astronomical twilight depends on the latitude of the area. Over the equator they are short, up to 1 hour, in temperate latitudes they are 2 hours. At high latitudes in the summer season, evening twilight merges with morning twilight, forming white nights.

4 Absorption of solar radiation in the atmosphere. Solar radiation reaches the upper boundary of the atmosphere in the form of direct radiation. About 30% of this radiation is reflected back into outer space, 70% enters the atmosphere. Passing through the atmosphere, this radiation experiences changes associated with its absorption and scattering. About 20-23% of direct solar radiation is absorbed. Absorption is selective and depends on the wavelengths and material composition of the atmosphere. Nitrogen, the main gas of the atmosphere, absorbs radiation only at very small wavelengths in the ultraviolet part of the spectrum. The energy of solar radiation in this part of the spectrum is very small, and the absorption of radiation by nitrogen has practically no effect on the magnitude of the total energy flux. Oxygen absorbs somewhat more in two narrow regions of the visible part of the spectrum and in the ultraviolet part. Ozone absorbs radiation more vigorously. The total amount of radiation absorbed by ozone reaches 3% of direct solar radiation. The main part of the absorbed radiation falls on the ultraviolet part, at wavelengths shorter than 0.29 microns. In small quantities, ozone also absorbs visible radiation. Carbon dioxide absorbs radiation in the IR range, but due to its small amount, the proportion of this absorbed radiation is generally small. The main absorbers of direct solar radiation are water vapor, clouds and aerosol impurities concentrated in the troposphere. Water vapor and aerosols account for up to 15% of the absorbed radiation, and up to 5% for clouds. Since the main part of the absorbed radiation falls on such variable components of the atmosphere as water vapor and aerosols, the level of absorption of solar radiation varies significantly and depends on the specific conditions of the state of the atmosphere (its humidity and pollution). In addition, the amount of absorbed radiation depends on the height of the Sun above the horizon, i.e. on the thickness of the atmospheric layer that the sun's beam passes through.

5. Visibility, radiation attenuation law, turbidity factor. Scattering of light in the atmosphere leads to the fact that distant objects at a distance become poorly distinguishable not only because of their reduction in size, but also due to the turbidity of the atmosphere. The distance at which the outlines of objects cease to be distinguished in the atmosphere is called the visibility range, or simply visibility. The visibility range is most often determined by eye on certain, pre-selected objects (dark against the sky), the distance to which is known. In very clean air, the visibility range can reach hundreds of kilometers. In air containing a lot of aerosol impurities, the visibility range can be reduced to several kilometers or even meters. So, in light fog, the visibility range is 500-1000 m, and in heavy fog or sandstorm it drops to several meters. Absorption and scattering leads to a significant weakening of the flux of solar radiation passing through the atmosphere. Radiation is attenuated in proportion to the flow itself (with other equal conditions, the greater the flow, the greater the energy loss) and the number of absorbing and scattering particles. The latter depends on the length of the beam path through the atmosphere. For an atmosphere that does not contain aerosol impurities (an ideal atmosphere), the transparency coefficient p is 0.90-0.95. In the real atmosphere, its values ​​range from 0.6 to 0.85 (slightly higher in winter, lower in summer). With an increase in the content of water vapor and impurities, the transparency coefficient decreases. With an increase in the latitude of the area, the transparency coefficient increases due to a decrease in water vapor pressure and less dust in the atmosphere. All attenuation of radiation in the atmosphere can be divided into two parts: attenuation by permanent gases (ideal atmosphere) and attenuation by water vapor and aerosol impurities. The ratio of these processes is taken into account by the turbidity factor 6. Geographic patterns distribution of direct and scattered radiation. The flux of direct solar radiation depends on the height of the Sun above the horizon. Therefore, during the day, the flow of solar radiation at first quickly, then slowly increases from sunrise to noon, and at first slowly, then quickly decreases from noon to sunset. But the transparency of the atmosphere changes during the day, so the curve of the daily course of direct radiation is not smooth, but has deviations. But on average, over a long period of observation, changes in radiation during the day take the form of a smooth curve. During the year, the energy illumination of direct solar radiation for the main part of the Earth's surface changes significantly, which is associated with changes in the height of the Sun. For the northern hemisphere, the minimum values ​​of both direct radiation to the perpendicular surface and insolation occur in December, the maximum values ​​are not in the summer period, but in the spring, when the air is less turbid with condensation products and less dusty. The average midday energy illumination in Moscow in December is 0.54, April 1.05, June-July 0.86-0.99 kW / m 2. The daily values ​​of direct radiation are maximum in summer, at the maximum duration of sunshine. Maximum values direct solar radiation for some points are the following (kW / m 2): Tiksi Bay 0.91, Pavlovsk 1.00, Irkutsk 1.03, Moscow 1.03, Kursk 1.05, Tbilisi 1.05, Vladivostok 1.02, Tashkent 1.06. The maximum values ​​of direct solar radiation increase little with decreasing latitude, despite the increase in the height of the Sun. This is due to the fact that in the southern latitudes the moisture content and dust content of the air increases. Therefore, at the equator, the maximum values ​​are slightly higher than the maxima of temperate latitudes. The largest annual values ​​of direct solar radiation on Earth are observed in the Sahara - up to 1.10 kW / m 2. The seasonal differences in the arrival of direct radiation are as follows. During the summer highest values direct solar radiation are observed at 30-400 latitude of the summer hemisphere, towards the equator and towards polar circles direct solar radiation values ​​decrease. Towards the poles for the summer hemisphere, the decrease in direct solar radiation is small, in the winter it becomes equal to zero. In spring and autumn, the maximum values ​​of direct solar radiation are observed at 10-200 in the spring hemisphere and 20-300 in the autumn. Only the winter part of the equatorial zone receives maximum given period values ​​of direct solar radiation. With height above sea level, the maximum values ​​of radiation increase due to a decrease in the optical thickness of the atmosphere: for every 100 meters of height, the amount of radiation in the troposphere increases by 0.007-0.14 kW / m 2. The maximum radiation values ​​recorded in the mountains are 1.19 kW/m 2 . Scattered radiation arriving at a horizontal surface also changes during the day: it increases before noon and decreases in the afternoon. The magnitude of the scattered radiation flux generally depends on the length of the day and the height of the Sun above the horizon, as well as the transparency of the atmosphere (a decrease in transparency leads to an increase in scattering). In addition, scattered radiation varies over a very wide range depending on the cloudiness. The radiation reflected by the clouds is also scattered. The radiation reflected by the snow is also scattered, which increases its share in winter. Scattered radiation with average cloudiness is more than twice its value on a cloudless day. In Moscow, the average midday value of scattered radiation in summer with a clear sky is 0.15, and in winter with a low Sun - 0.08 kW / m 2. With patchy cloudiness, these values ​​are 0.28 in summer and 0.10 kW/m 2 in winter. In the Arctic, with relatively thin clouds and snow cover, these values ​​can reach 0.70 kW/m 2 in summer. The values ​​of scattered radiation in Antarctica are very high. As the altitude increases, the scattered radiation decreases. Scattered radiation can significantly supplement direct radiation, especially when the sun is low. Due to scattered light, the entire atmosphere during the day serves as a source of illumination: during the day it is light both where the sun's rays do not directly fall, and when the Sun is hidden by clouds. Scattered radiation increases not only the illumination, but also the heating of the earth's surface. The values ​​of scattered radiation are generally less than direct, but the order of magnitude is the same. In tropical and middle latitudes, the amount of scattered radiation is from half to two thirds of the values ​​of direct radiation. At 50-600, their values ​​are close, and closer to the poles, scattered radiation prevails.

7 Total radiation All solar radiation reaching the earth's surface is called total solar radiation. Under a cloudless sky, total solar radiation has a daily variation with a maximum around noon and an annual variation with a maximum in summer. Partial cloudiness, which does not cover the solar disk, increases the total radiation compared to a cloudless sky, while full cloudiness, on the contrary, reduces it. On average, cloud cover reduces radiation. Therefore, in summer, the arrival of total radiation in the pre-noon hours is greater than in the afternoon, and in the first half of the year more than in the second. The midday values ​​of total radiation in the summer months near Moscow with a cloudless sky average 0.78, with the open Sun and clouds 0.80, with continuous clouds - 0.26 kW / m 2. The distribution of total radiation values ​​over the globe deviates from the zonal , which is explained by the influence of atmospheric transparency and cloudiness. The maximum annual values ​​of total radiation are 84*102 - 92*102 MJ/m 2 and are observed in the deserts of North Africa. Over areas of equatorial forests with high cloudiness, the values ​​of total radiation are reduced to 42*102 - 50*102 MJ/m 2 . To higher latitudes of both hemispheres, the values ​​of total radiation decrease, amounting to 25*102 - 33*102 MJ/m 2 under the 60th parallel. But then they grow again - little over the Arctic and significantly - over Antarctica, where in the central parts of the mainland they are 50 * 102 - 54 * 102 MJ / m 2. In general, the values ​​of total radiation over the Nadoceans are lower than over the corresponding land latitudes. In December, the highest values ​​of total radiation are observed in the deserts of the Southern Hemisphere (8*102 - 9*102 MJ/m2). Above the equator, the total radiation values ​​decrease to 3*102 - 5*102 MJ/m 2 . In the Northern Hemisphere, radiation rapidly decreases towards the polar regions and is zero beyond the Arctic Circle. In the Southern Hemisphere, the total radiation decreases south to 50-600 S. (4 * 102 MJ / m 2), and then increases to 13 * 102 MJ / m 2 in the center of Antarctica. In July, the highest values ​​of total radiation (over 9 * 102 MJ / m 2) are observed over northeast Africa and the Arabian Peninsula. Over the equatorial region, the values ​​of the total radiation are low and equal to those in December. To the north of the tropic, the total radiation decreases slowly to 600 N, and then increases to 8*102 MJ/m 2 in the Arctic. In the southern hemisphere, the total radiation from the equator rapidly decreases to the south, reaching zero values ​​near the polar circle.

8. Reflection of solar radiation. Albedo of the Earth. Upon reaching the surface, the total radiation is partially absorbed in the upper thin layer of soil or water and converted into heat, and partially reflected. The conditions for the reflection of solar radiation from the earth's surface are characterized by an albedo value equal to the ratio of the reflected radiation to the incoming flux (to the total radiation). A = Qref / Q (8) Theoretically, albedo values ​​can vary from 0 (absolutely black surface) to 1 (absolutely white surface). The available observational data show that the albedo values ​​of the underlying surfaces vary over a wide range, and their changes cover almost the entire possible range of reflectivity values ​​of various surfaces. In experimental studies, albedo values ​​were found for almost all common natural underlying surfaces. These studies show, first of all, that the conditions for the absorption of solar radiation on land and in water bodies are markedly different. The highest albedo values ​​are observed for clean and dry snow (90-95%). But since the snow cover is rarely completely clean, the average values ​​of the snow albedo in most cases are 70-80%. For wet and polluted snow, these values ​​are even lower - 40-50%. In the absence of snow, the highest albedo on the land surface is characteristic of some desert regions, where the surface is covered with a layer of crystalline salts (the bottom of dried lakes). Under these conditions, the albedo has a value of 50%. few less value albedo in sandy deserts. The albedo of wet soil is less than the albedo of dry soil. For wet chernozems, the albedo values ​​are extremely small - 5%. The albedo of natural surfaces with a continuous vegetation cover varies within relatively small limits - from 10 to 20-25%. At the same time, the albedo of the forest (especially coniferous) in most cases is less than the albedo of meadow vegetation. The conditions for absorption of radiation in water bodies differ from the conditions for absorption on the land surface. Pure water is relatively transparent to short-wave radiation, as a result of which the sun's rays penetrating into the upper layers are scattered many times and only after that are absorbed to a large extent. Therefore, the process of absorption of solar radiation depends on the height of the Sun. If it stands high, a significant part of the incoming radiation penetrates into the upper layers of the water and is mainly absorbed. Therefore albedo water surface makes up a few percent at a high Sun, and at a low Sun, the albedo increases to several tens of percent. The albedo of the "Earth-atmosphere" system has a more complex nature. Solar radiation entering the atmosphere is partly reflected as a result of backscattering of the atmosphere. In the presence of clouds, a significant part of the radiation is reflected from their surface. The albedo of clouds depends on the thickness of their layer and averages 40-50%. In the complete or partial absence of clouds, the albedo of the system " Earth - atmosphere» significantly depends on the albedo of the earth's surface itself. The nature of the geographical distribution of the planetary albedo according to satellite observations shows significant differences between the albedo of high and middle latitudes of the Northern and Southern hemispheres. In the tropics, the highest albedo values ​​are observed over deserts, in zones of convective cloudiness over Central America and over the oceans. In the Southern Hemisphere, in contrast to the Northern Hemisphere, there is a zonal variation in albedo due to more simple distribution land and sea. Most high values albedo is at polar latitudes. The predominant part of the radiation reflected by the earth's surface and the upper boundary of the clouds goes into the world space. A third of the scattered radiation also goes away. The ratio of the reflected and scattered radiation leaving into space to total solar radiation entering the atmosphere is called the planetary albedo of the Earth or the albedo of the Earth. Its value is estimated at 30%. The main part of the planetary albedo is radiation reflected by clouds. 6.1.8. own radiation. counter radiation. Efficient radiation. Solar radiation, being absorbed by the upper layer of the Earth, heats it, as a result of which the soil and surface water they themselves emit long-wave radiation. This terrestrial radiation is called the intrinsic radiation of the earth's surface. The intensity of this radiation, with some assumption, obeys the Stefan-Boltzmann law for an absolutely black body with a temperature of 150C. But since the earth is not absolutely black body(its radiation corresponds to the radiation of a gray body), in the calculations it is necessary to introduce a correction equal to e=0.95. Thus, the Earth's own radiation can be determined by the formula Ез = esТ 4 (9) It is determined that at the average planetary temperature of the Earth 150С, the Earth's own radiation Ез = 3.73*102 W/m2. Such a large return of radiation from the earth's surface would lead to its very rapid cooling, if this were not prevented by the reverse process - the absorption of solar and atmospheric radiation by the earth's surface. Absolute temperatures on the earth's surface are in the range of 190-350K. At such temperatures, self-radiation has wavelengths in the range of 4-120 µm, and the maximum energy falls on 10-15 µm. The atmosphere, absorbing both solar radiation and the own radiation of the earth's surface, heats up. In addition, the atmosphere is heated in a non-radiative way (by thermal conduction, during the condensation of water vapor). The heated atmosphere becomes a source of long-wave radiation. Most of this atmospheric radiation (70%) is directed towards the earth's surface and is called counterradiation (Ea). Another part of the atmospheric radiation is absorbed by the overlying layers, but as the water vapor content decreases, the amount of radiation absorbed by the atmosphere decreases, and part of it goes into the world space. The earth's surface absorbs the counter radiation almost entirely (95-99%). Thus, the counter radiation is an important source of heat for the earth's surface in addition to the absorbed solar radiation. In the absence of clouds, the long-wave radiation of the atmosphere is determined by the presence of water vapor and carbon dioxide. The influence of atmospheric ozone, in comparison with these factors, is insignificant. Water vapor and carbon dioxide absorb long-wave radiation in the range from 4.5 to 80 microns, but not entirely, but in certain narrow spectral regions. The strongest absorption of radiation by water vapor occurs in the wavelength range of 5-7.5 µm, while in the region of 9.5-12 µm 4.1. Atmospheric transparency windows in the optical range, absorption is practically absent. This range of wavelengths is called the atmospheric transparency window. Carbon dioxide has several absorption bands, of which the most significant band with wavelengths of 13-17 microns, which accounts for the maximum of terrestrial radiation. It should be noted that the content carbon dioxide relatively constant, while the amount of water vapor varies greatly, depending on meteorological conditions. Therefore, a change in air humidity has a significant impact on the amount of atmospheric radiation. For example, the largest counter radiation is 0.35-0.42 kW / m 2 on average annual at the equator, and towards the polar regions it decreases to 0.21 kW / m 2, in the flat areas Ea is 0.21-0.28 kW / m 2 and 0.07-0.14 kW / m 2 - in the mountains. The decrease in counter radiation in the mountains is explained by the decrease in the content of water vapor with height. The counter radiation of the atmosphere usually increases significantly in the presence of clouds. Clouds of the lower and middle tiers, as a rule, are quite dense and radiate as an absolutely black body at the appropriate temperature. High clouds, due to their low density, usually radiate less than a black body, so they have little effect on the ratio of their own and oncoming radiation. Absorption by water vapor and other gases of long-wavelength self-radiation creates " the greenhouse effect”, i.e. saves solar heat in the earth's atmosphere. An increase in the concentration of these gases, primarily carbon dioxide, as a result of human economic activity can lead to an increase in the share of heat remaining on the planet, to an increase in average planetary temperatures and a change in global climate Earth, the consequences of which are still difficult to predict. But it should be noted that the main role in the absorption of terrestrial radiation and the formation of counter radiation is played by water vapor. Through the transparency window, part of the long-wavelength terrestrial radiation escapes through the atmosphere into the world space. Together with atmospheric radiation, this radiation is called outgoing radiation. If we take the influx of solar radiation as 100 units, then the outgoing radiation will be 70 units. Taking into account 30 units of reflected and scattered radiation (Earth's planetary albedo), the Earth gives off as much radiation into outer space as it receives, i.e. is in radiant equilibrium.

9. Radiation balance of the earth's surface The radiation balance of the earth's surface is the difference between the arrival of radiation on the earth's surface (in the form of absorbed radiation) and its consumption as a result of thermal radiation (effective radiation). The radiation balance changes from nightly negative values ​​to daytime positive values ​​in the summer at a Sun height of 10-15 degrees and vice versa, from positive to negative - before sunset at the same Sun heights. In winter, the transition of the values ​​of the radiation balance through zero occurs at large angles of the Sun (20-25 degrees). At night, in the absence of total radiation, the radiation balance is negative and equal to the effective radiation. The distribution of the radiation balance over the globe is fairly even. The annual values ​​of the radiation balance are positive everywhere, except for Antarctica and Greenland. Positive annual values ​​of the radiation balance mean that the excess of absorbed radiation is balanced by non-radiative heat transfer from the earth's surface to the atmosphere. This means that there is no radiation equilibrium for the earth's surface (the incoming radiation is greater than its return), but there is a thermal equilibrium that ensures the stability of the thermal characteristics of the atmosphere. The largest annual values ​​of the radiation balance are observed in the equatorial zone between 200 north and south latitudes. Here it is more than 40 * 102 MJ / m 2. To higher latitudes, the values ​​of the radiation balance decrease and, near the 60th parallel, range from 8*102 to 13*102 MJ/m 2 . Further to the poles, the radiation balance decreases even more and amounts to 2*102 - 4*102 MJ/m 2 in Antarctica. Over the oceans, the radiation balance is greater than over land at the same latitudes. Significant deviations from zonal values ​​are also found in deserts, where the balance is lower than the latitudinal value due to high effective radiation. In December, the radiation balance is negative in a significant part of the Northern Hemisphere north of the 40th parallel. In the Arctic, it reaches values ​​of 2*102 MJ/m 2 and below. To the south of the 40th parallel, it increases to the Southern Tropic (4 * 102 - 6 * 102 MJ / m 2), and then decreases to South Pole, amounting to 2*102 MJ/m 2 on the coast of Antarctica In June, the radiation balance is maximum over the Northern Tropic (5*102 - 6*102 MJ/m 2). To the north, it decreases, remaining positive until North Pole, and to the south it decreases, becoming negative off the coast of Antarctica (-0.4 -0.8 * 102 MJ / m 2).

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If the atmosphere passed all the sun's rays to the surface of the earth, then the climate of any point on the Earth would depend only on geographical latitude. So it was believed in ancient times. However, when sunlight passes through earth's atmosphere there is, as we have already seen, their weakening due to the simultaneous processes of absorption and scattering. Water droplets and ice crystals, which make up clouds, absorb and scatter a lot.

That part of the solar radiation that reaches the earth's surface after being scattered by its atmosphere and clouds is called scattered radiation. The portion of solar radiation that passes through the atmosphere without being scattered is calleddirect radiation.

Radiation is scattered not only by clouds, but also in a clear sky by molecules, gases and dust particles. The ratio between direct and scattered radiation varies over a wide range. If, with a clear sky and vertical incidence of sunlight, the fraction of scattered radiation is 0.1% of direct radiation, then

in overcast skies, diffuse radiation may be greater than direct radiation.

In those parts of the earth where clear weather prevails, for example in Central Asia, the main source of heating of the earth's surface is direct solar radiation. In the same place where cloudy weather prevails, such as in the north and northwest European territory USSR, scattered solar radiation acquires significant significance. Tikhaya Bay, located in the north, receives scattered radiation almost one and a half times more than direct radiation (Table 5). In Tashkent, on the contrary, diffuse radiation is less than 1/3 of direct radiation. Direct solar radiation in Yakutsk is greater than in Leningrad. This is explained by the fact that in Leningrad there are more cloudy days and less transparency of the air.

Albedo of the earth's surface. The earth's surface has the ability to reflect rays falling on it. The amount of absorbed and reflected radiation depends on the properties of the earth's surface. The ratio of the amount of radiant energy reflected from the surface of the body to the amount of incident radiant energy is called albedo. Albedo characterizes the reflectivity of the body surface. When, for example, they say that the albedo of freshly fallen snow is 80-85%, this means that 80-85% of all radiation falling on the snow surface is reflected from it.

The albedo of snow and ice depends on their purity. AT industrial cities in connection with the deposition of various impurities on the snow, mainly soot, the albedo is less. On the contrary, in the Arctic regions, the snow albedo sometimes reaches 94%. Since the albedo of snow is the highest in comparison with the albedo of other types of the earth's surface, the warming of the earth's surface occurs weakly under snow cover. The albedo of herbaceous vegetation and sand is much less. The albedo of herbaceous vegetation is 26% and that of sand is 30%. This means that grass absorbs 74% of the sun's energy, while sand absorbs 70%. The absorbed radiation is used for evaporation, plant growth and heating.

Water has the highest absorption capacity. Seas and oceans absorb about 95% of the solar energy entering their surface, i.e., the water albedo is 5% (Fig. 9). True, the albedo of water depends on the angle of incidence of the sun's rays (VV Shuleikin). When rays fall vertically from the surface clean water only 2% of the radiation is reflected, and at low standing of the sun - almost all.