| Surface | Characteristic | Albedo, % |
| Soils | ||
| black soil | dry, level ground freshly plowed, damp | |
| loamy | dry wet | |
| sandy | yellowish whitish river sand | 34 – 40 |
| Vegetation cover | ||
| rye, wheat in the period of full ripeness | 22 – 25 | |
| floodplain meadow with lush green grass | 21 – 25 | |
| dry grass | ||
| Forest | spruce | 9 – 12 |
| pine | 13 – 15 | |
| birch | 14 – 17 | |
| Snow cover | ||
| snow | dry freshly fallen moist clean fine-grained moist soaked in water, gray | 85 – 95 55 – 63 40 – 60 29 – 48 |
| ice | river bluish green | 35 – 40 |
| marine milky blue | ||
| water surface | ||
| at solar altitude 0.1° 0.5° 10° 20° 30° 40° 50° 60-90° | 89,6 58,6 35,0 13,6 6,2 3,5 2,5 2,2 – 2,1 |
The predominant part of the direct radiation reflected by the earth's surface and the upper surface of the clouds goes beyond the atmosphere into the world space. About one third of the scattered radiation also goes into the world space. The ratio of all reflected and scattered solar radiation to the total amount of solar radiation entering the atmosphere is called Earth's planetary albedo. The planetary albedo of the Earth is estimated at 35 - 40%. The main part of it is the reflection of solar radiation by clouds.
Table 2.6
Magnitude dependency To n from the latitude of the place and time of year
| Latitude | Months | |||||||
| III | IV | V | VI | VII | VIII | IX | X | |
| 0.77 | 0.76 | 0.75 | 0.75 | 0.75 | 0.76 | 0.76 | 0.78 | |
| 0.77 | 0.76 | 0.76 | 0.75 | 0.75 | 0.76 | 0.76 | 0.78 | |
| 0.77 | 0.76 | 0.76 | 0.75 | 0.75 | 0.76 | 0.77 | 0.79 | |
| 0.78 | 0.76 | 0.76 | 0.76 | 0.76 | 0.76 | 0.77 | 0.79 | |
| 0.78 | 0.76 | 0.76 | 0.76 | 0.76 | 0.76 | 0.77 | 0.79 | |
| 0.78 | 0.77 | 0.76 | 0.76 | 0.76 | 0.77 | 0.78 | 0.80 | |
| 0.79 | 0.77 | 0.76 | 0.76 | 0.76 | 0.77 | 0.78 | 0.80 | |
| 0.79 | 0.77 | 0.77 | 0.76 | 0.76 | 0.77 | 0.78 | 0.81 | |
| 0.80 | 0.77 | 0.77 | 0.76 | 0.76 | 0.77 | 0.79 | 0.82 | |
| 0.80 | 0.78 | 0.77 | 0.77 | 0.77 | 0.78 | 0.79 | 0.83 | |
| 0.81 | 0.78 | 0.77 | 0.77 | 0.77 | 0.78 | 0.80 | 0.83 | |
| 0.82 | 0.78 | 0.78 | 0.77 | 0.77 | 0.78 | 0.80 | 0.84 | |
| 0.82 | 0.79 | 0.78 | 0.77 | 0.77 | 0.78 | 0.81 | 0.85 | |
| 0.83 | 0.79 | 0.78 | 0.77 | 0.77 | 0.79 | 0.82 | 0.86 |
Table 2.7
Magnitude dependency To in + from the latitude of the place and time of year
(according to A.P. Braslavsky and Z.A. Vikulina)
| Latitude | Months | |||||||
| III | IV | V | VI | VII | VIII | IX | X | |
| 0.46 | 0.42 | 0.38 | 0.37 | 0.38 | 0.40 | 0.44 | 0.49 | |
| 0.47 | 0.42 | 0.39 | 0.38 | 0.39 | 0.41 | 0.45 | 0.50 | |
| 0.48 | 0.43 | 0.40 | 0.39 | 0.40 | 0.42 | 0.46 | 0.51 | |
| 0.49 | 0.44 | 0.41 | 0.39 | 0.40 | 0.43 | 0.47 | 0.52 | |
| 0.50 | 0.45 | 0.41 | 0.40 | 0.41 | 0.43 | 0.48 | 0.53 | |
| 0.51 | 0.46 | 0.42 | 0.41 | 0.42 | 0.44 | 0.49 | 0.54 | |
| 0.52 | 0.47 | 0.43 | 0.42 | 0.43 | 0.45 | 0.50 | 0.54 | |
| 0.52 | 0.47 | 0.44 | 0.43 | 0.43 | 0.46 | 0.51 | 0.55 | |
| 0.53 | 0.48 | 0.45 | 0.44 | 0.44 | 0.47 | 0.51 | 0.56 | |
| 0.54 | 0.49 | 0.46 | 0.45 | 0.45 | 0.48 | 0.52 | 0.57 | |
| 0.55 | 0.50 | 0.47 | 0.46 | 0.46 | 0.48 | 0.53 | 0.58 | |
| 0.56 | 0.51 | 0.48 | 0.46 | 0.47 | 0.49 | 0.54 | 0.59 | |
| 0.57 | 0.52 | 0.48 | 0.47 | 0.47 | 0.50 | 0.55 | 0.60 | |
| 0.58 | 0.53 | 0.49 | 0.48 | 0.48 | 0.51 | 0.56 | 0.60 |
The total radiation that has reached the earth's surface is partially absorbed by soil and water bodies and converted into heat; it is spent on the oceans and seas for evaporation, and is partially reflected into the atmosphere (reflected radiation). The ratio of absorbed and reflected radiant energy depends on the nature of the land, on the angle of incidence of the rays on the water surface. Since it is practically impossible to measure the absorbed energy, the value of the reflected energy is determined.
The reflectivity of land and water surfaces is called their albedo. It is calculated as a percentage of the reflected radiation from the incident on a given surface, along with the angle (more precisely, the sine of the angle) of incidence of the rays and the amount of optical masses of the atmosphere they pass through, is one of the most important planetary factors of climate formation.
On land, albedo is determined by the color of natural surfaces. All radiation is able to assimilate a completely black body. The mirror surface reflects 100% of the rays and is not able to heat up. Of real surfaces, pure snow has the highest albedo. Below are the albedo of land surfaces by natural zones.
The climate-forming value of the reflectivity of different surfaces is extremely high. In ice zones at high latitudes, solar radiation, already weakened by the passage of a large number of optical masses of the atmosphere and falling on the surface at an acute angle, is reflected by eternal snow.
The albedo of a water surface for direct radiation depends on the angle at which the sun's rays fall on it. Vertical rays penetrate deep into the water, and it assimilates their heat. Inclined rays from the water are reflected, as from a mirror, and it is not heated: the albedo of the water surface at a Sun height of 90 "is 2%, at a Sun height of 20 ° - 78%.
Surface views and zonal landscapes Albedo
Fresh dry snow…………………………………………… 80-95
Wet snow………………………………………………….. 60-70
Sea ice…………………………………………………….. 30-40
Tundra without snow cover………………………….. 18
Stable snow cover in temperate latitudes 70
The same unstable……………………………………….. 38
Coniferous forest in summer…………………………………………. 10-15
The same, with stable snow cover……….. 45
Deciduous forest in summer……………………………………. 15-20
The same, with yellow leaves in autumn……………….. 30-40
Meadow…………………………………………………………………… 15-25
Steppe in summer…………………………………………………….. 18
Sand of different colors…………………………………….. 25-35
Desert………………………………………………………….. 28
Savannah in dry season……………………………………… 24
The same, in the rainy season………………………………………. eighteen
The entire troposphere………………………………………………… 33
Earth as a whole (planet)…………………………………….. 45
For scattered radiation, the albedo is somewhat less.
Since 2/3 of the earth's area is occupied by the ocean, the assimilation of solar energy by the water surface acts as an important climate-forming factor.
Oceans in subpolar latitudes assimilate only a small fraction of the heat of the Sun that reaches them. Tropical seas, on the contrary, absorb almost all solar energy. The albedo of the water surface, like the snow cover of the polar countries, deepens the zonal differentiation of climates.
In the temperate zone, the reflectivity of surfaces enhances the difference between the seasons of the year. In September and March, the Sun is at the same height above the horizon, but March is colder than September, as the sun's rays are reflected from the snow cover. The appearance of first yellow leaves in autumn, and then hoarfrost and temporary snow increases the albedo and reduces the air temperature. The stable snow cover caused by low temperatures accelerates the cooling and further reduction of winter temperatures.
The total radiation reaching the earth's surface is not completely absorbed by it, but is partially reflected from the earth. Therefore, when calculating the arrival of solar energy for a place, it is necessary to take into account the reflectivity of the earth's surface. Reflection of radiation also occurs from the surface of clouds. The ratio of the entire flux of short-wave radiation Rk reflected by a given surface in all directions to the radiation flux Q incident on this surface is called albedo(A) given surface. This value
shows how much of the radiant energy incident on the surface is reflected from it. Albedo is often expressed as a percentage. Then
(1.3)
In table. No. 1.5 gives the albedo values for various types of the earth's surface. From the data in Table. 1.5 shows that freshly fallen snow has the highest reflectivity. In some cases, a snow albedo of up to 87% was observed, and in the conditions of the Arctic and Antarctic, even up to 95%. Packed, melted and even more polluted snow reflects much less. Albedo of various soils and vegetation, as follows from Table. 4, differ relatively slightly. Numerous studies have shown that the albedo often changes during the day.
The highest albedo values are observed in the morning and evening. This is explained by the fact that the reflectivity of rough surfaces depends on the angle of incidence of sunlight. With a vertical fall, the sun's rays penetrate deeper into the vegetation cover and are absorbed there. At a low height of the sun, the rays penetrate less into the vegetation and are reflected to a greater extent from its surface. The albedo of water surfaces is, on average, less than the albedo of the land surface. This is explained by the fact that the sun's rays (the short-wave green-blue part of the solar spectrum) penetrate to a large extent into the upper layers of water that are transparent to them, where they are scattered and absorbed. In this regard, the degree of its turbidity affects the reflectivity of water.
Table No. 1.5
For polluted and turbid water, the albedo increases noticeably. For scattered radiation, the albedo of water is on average about 8-10%. For direct solar radiation, the albedo of the water surface depends on the height of the sun: with a decrease in the height of the sun, the albedo value increases. So, with a sheer incidence of rays, only about 2-5% is reflected. When the sun is low above the horizon, 30-70% is reflected. The reflectivity of the clouds is very high. The average cloud albedo is about 80%. Knowing the value of the surface albedo and the value of the total radiation, it is possible to determine the amount of radiation absorbed by a given surface. If A is the albedo, then the value a \u003d (1-A) is the absorption coefficient of a given surface, showing what part of the radiation incident on this surface is absorbed by it.
For example, if a total radiation flux Q = 1.2 cal / cm 2 min falls on the surface of green grass (A \u003d 26%), then the percentage of absorbed radiation will be
Q \u003d 1 - A \u003d 1 - 0.26 \u003d 0.74, or a \u003d 74%,
and the amount of absorbed radiation
B absorb \u003d Q (1 - A) \u003d 1.2 0.74 \u003d 0.89 cal / cm2 min.
The albedo of the surface of water is highly dependent on the angle of incidence of the sun's rays, since pure water reflects light according to Fresnel's law.
At the position of the Sun at the zenith, the albedo of the surface of a calm sea is 0.02. With an increase in the zenith angle of the Sun Z P albedo increases and reaches 0.35 at Z P\u003d 85. The excitement of the sea leads to a change Z P , and significantly reduces the range of albedo values, since it increases at large Z n due to an increase in the probability of rays hitting an inclined wave surface. Excitement affects the reflectivity not only due to the inclination of the wave surface relative to the sun's rays, but also due to the formation of air bubbles in the water. These bubbles scatter light to a large extent, increasing the diffuse radiation coming out of the sea. Therefore, during high sea waves, when foam and lambs appear, the albedo increases under the influence of both factors. Scattered radiation enters the water surface at different angles. cloudless sky. It also depends on the distribution of clouds in the sky. Therefore, the sea surface albedo for diffuse radiation is not constant. But the boundaries of its fluctuations are narrower 1 from 0.05 to 0.11. Consequently, the albedo of the water surface for total radiation varies depending on the height of the Sun, the ratio between direct and scattered radiation, sea surface waves. It should be borne in mind that the northern parts oceans are heavily covered with sea ice. In this case, the albedo of ice must also be taken into account. As you know, significant areas of the earth's surface, especially in middle and high latitudes, are covered with clouds that reflect solar radiation very much. Therefore, knowledge of the cloud albedo is of great interest. Special measurements of cloud albedo were carried out with the help of airplanes and balloons. They showed that the albedo of clouds depends on their shape and thickness. The albedo of altocumulus and stratocumulus clouds has the highest values. clouds Cu - Sc - about 50%.
The most complete data on cloud albedo obtained in Ukraine. The dependence of the albedo and the transmission function p on the thickness of the clouds, which is the result of the systematization of the measurement data, is given in Table. 1.6. As can be seen, an increase in cloud thickness leads to an increase in albedo and a decrease in the transmission function.
Average albedo for clouds St with an average thickness of 430 m is 73%, for clouds Swith at an average thickness of 350 m - 66%, and the transmission functions for these clouds are 21 and 26%, respectively.
The albedo of clouds depends on the albedo of the earth's surface. r 3 over which the cloud is located. From a physical point of view, it is clear that the more r 3 , the greater the flux of reflected radiation passing upward through the upper boundary of the cloud. Since albedo is the ratio of this flow to the incoming one, an increase in the albedo of the earth's surface leads to an increase in the albedo of clouds. The study of the properties of clouds to reflect solar radiation was carried out using artificial Earth satellites by measuring the brightness of clouds. The average cloud albedo values obtained from these data are given in table 1.7.
Table 1.7 - Average albedo values of clouds of different forms
According to these data, cloud albedo ranges from 29 to 86%. Noteworthy is the fact that cirrus clouds have a small albedo compared to other cloud forms (with the exception of cumulus). Only cirrostratus clouds, which are thicker, largely reflect solar radiation (r= 74%).
Page 17 of 81
Total radiation, reflected solar radiation, absorbed radiation, PAR, Earth's albedo
All solar radiation coming to the earth's surface - direct and scattered - is called total radiation. Thus, the total radiation
Q = S? sin h + D,
where S– energy illumination by direct radiation,
D– energy illumination by scattered radiation,
h- the height of the sun.
With a cloudless sky, the total radiation has a daily variation with a maximum around noon and an annual variation with a maximum in summer. Partial cloudiness that does not cover the solar disk increases the total radiation compared to a cloudless sky; full cloudiness, on the contrary, reduces it. On average, cloudiness reduces the total radiation. Therefore, in summer, the arrival of total radiation in the pre-noon hours is on average greater than in the afternoon.
For the same reason, it is larger in the first half of the year than in the second.
S.P. Khromov and A.M. Petrosyants give midday values of total radiation in the summer months near Moscow with a cloudless sky: an average of 0.78 kW / m 2, with the Sun and clouds - 0.80, with continuous clouds - 0.26 kW / m 2.
Falling on the earth's surface, the total radiation is mostly absorbed in the upper thin layer of soil or in a thicker layer of water and turns into heat, and is partially reflected. The amount of reflection of solar radiation by the earth's surface depends on the nature of this surface. The ratio of the amount of reflected radiation to the total amount of radiation incident on a given surface is called the surface albedo. This ratio is expressed as a percentage.
So, from the total flux of total radiation ( S sin h + D) part of it is reflected from the earth's surface ( S sin h + D)And where BUT is the surface albedo. The rest of the total radiation
(S sin h + D) (1 – BUT) is absorbed by the earth's surface and goes to heat the upper layers of soil and water. This part is called absorbed radiation.
The albedo of the soil surface varies within 10–30%; in wet chernozem, it decreases to 5%, and in dry light sand it can rise to 40%. As soil moisture increases, the albedo decreases. The albedo of vegetation cover - forests, meadows, fields - is 10–25%. The albedo of the surface of freshly fallen snow is 80–90%, while that of long-standing snow is about 50% and lower. The albedo of a smooth water surface for direct radiation varies from a few percent (if the Sun is high) to 70% (if low); it also depends on excitement. For scattered radiation, the albedo of water surfaces is 5–10%. On average, the albedo of the surface of the World Ocean is 5–20%. The albedo of the upper surface of the clouds varies from a few percent to 70–80%, depending on the type and thickness of the cloud cover, on average 50–60% (S.P. Khromov, M.A. Petrosyants, 2004).
The above figures refer to the reflection of solar radiation, not only visible, but also in its entire spectrum. Photometric means measure the albedo only for visible radiation, which, of course, may differ somewhat from the albedo for the entire radiation flux.
The predominant part of the radiation reflected by the earth's surface and the upper surface of the clouds goes beyond the atmosphere into the world space. A part (about one-third) of the scattered radiation also goes into the world space.
The ratio of reflected and scattered solar radiation leaving space to the total amount of solar radiation entering the atmosphere is called the planetary albedo of the Earth, or simply Earth's albedo.
In general, the planetary albedo of the Earth is estimated at 31%. The main part of the planetary albedo of the Earth is the reflection of solar radiation by clouds.
Part of the direct and reflected radiation is involved in the process of plant photosynthesis, so it is called photosynthetically active radiation(FAR). FAR - the part of short-wave radiation (from 380 to 710 nm), which is the most active in relation to photosynthesis and the production process of plants, is represented by both direct and diffuse radiation.
Plants are able to consume direct solar radiation and reflected from celestial and terrestrial objects in the wavelength range from 380 to 710 nm. The flux of photosynthetically active radiation is approximately half of the solar flux, i.e. half of the total radiation, and practically regardless of weather conditions and location. Although, if for the conditions of Europe the value of 0.5 is typical, then for the conditions of Israel it is somewhat higher (about 0.52). However, it cannot be said that plants use PAR in the same way throughout their lives and under different conditions. The efficiency of PAR use is different, therefore, the indicators "PAR use coefficient" were proposed, which reflects the efficiency of PAR use and the "Efficiency of phytocenoses". The efficiency of phytocenoses characterizes the photosynthetic activity of the vegetation cover. This parameter has found the widest application among foresters for assessing forest phytocenoses.
It should be emphasized that plants themselves are able to form PAR in the vegetation cover. This is achieved due to the location of the leaves towards the sun's rays, the rotation of the leaves, the distribution of leaves of different sizes and angles at different levels of phytocenoses, i.e. through the so-called canopy architecture. In the vegetation cover, the sun's rays are repeatedly refracted, reflected from the leaf surface, thereby forming their own internal radiation regime.
The radiation scattered within the vegetation cover has the same photosynthetic value as the direct and diffuse radiation entering the surface of the vegetation cover.
| Table of contents |
|---|
| Climatology and meteorology |
| DIDACTIC PLAN |
| Meteorology and climatology |
| Atmosphere, weather, climate |
| Meteorological observations |
| Application of cards |
| Meteorological Service and World Meteorological Organization (WMO) |
| Climate-forming processes |
| Astronomical factors |
| Geophysical factors |
| Meteorological factors |
| About solar radiation |
| Thermal and radiative equilibrium of the Earth |
| direct solar radiation |
| Changes in solar radiation in the atmosphere and on the earth's surface |
| Radiation Scattering Phenomena |
| Total radiation, reflected solar radiation, absorbed radiation, PAR, Earth's albedo |
| Radiation of the earth's surface |
| Counter-radiation or counter-radiation |
| Radiation balance of the earth's surface |
| Geographic distribution of the radiation balance |
| Atmospheric pressure and baric field |
| pressure systems |
| pressure fluctuations |
| Air acceleration due to baric gradient |
| The deflecting force of the Earth's rotation |
| Geostrophic and gradient wind |
| baric wind law |
| Fronts in the atmosphere |
| Thermal regime of the atmosphere |
| Thermal balance of the earth's surface |
| Daily and annual variation of temperature on the soil surface |
| Air mass temperatures |
| Annual amplitude of air temperature |
| Continental climate |
| Cloud cover and precipitation |
| Evaporation and saturation |
| Humidity |
| Geographic distribution of air humidity |
| atmospheric condensation |
| Clouds |
| International cloud classification |
| Cloudiness, its daily and annual variation |
| Precipitation from clouds (precipitation classification) |
| Characteristics of the precipitation regime |
| The annual course of precipitation |
| Climatic significance of snow cover |
| Atmospheric chemistry |
| The chemical composition of the Earth's atmosphere |
| Chemical composition of clouds |
| Chemical composition of precipitation |
| Precipitation acidity |
| General circulation of the atmosphere |
Total radiation
All solar radiation reaching the earth's surface is called total solar radiation.
Q = S sin h c + D (34)
where S is the irradiance of direct radiation, h c is the height of the Sun, D is the irradiance of scattered radiation.
With a cloudless sky, the 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 the 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 one, which is explained by the influence of atmospheric transparency and cloudiness. The maximum annual values of total radiation are 84*10 2 - 92*10 2 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*10 2 - 50*10 2 MJ/m 2 . To higher latitudes of both hemispheres, the values of total radiation decrease, amounting to 25*10 2 - 33*10 2 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 * 10 2 - 54 * 10 2 MJ / m 2. Over the oceans, in general, the values of total radiation 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*10 2 - 9*10 2 MJ/m 2). Above the equator, the total radiation values decrease to 3*10 2 - 5*10 2 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 50-60 0 S. (4 * 10 2 MJ / m 2), and then increases to 13 * 10 2 MJ / m 2 in the center of Antarctica.
In July, the highest values of total radiation (over 9 * 10 2 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 60 0 N, and then increases to 8*10 2 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.
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 the value albedo, equal to the ratio of the reflected radiation to the incoming flux (to the total radiation).
A \u003d Q neg / Q (35)
Theoretically, albedo values can vary from 0 (perfectly black surface) to 1 (perfectly 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 snow albedo in most cases is 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%. Slightly less than the albedo value 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, the albedo of the water surface is a few percent when the Sun is high, and when the Sun is low, 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 Earth-atmosphere system depends significantly 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 the zones of convective cloudiness over Central America and over the waters of the oceans. In the Southern Hemisphere, in contrast to the Northern Hemisphere, a zonal albedo variation is observed due to a simpler distribution of land and sea. The highest albedo values are found in 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 the total amount of solar radiation entering the atmosphere is called Earth's planetary albedo or Earth's albedo. Its value is estimated at 30%. The main part of the planetary albedo is radiation reflected by clouds.
