Let us consider, along with the atmosphere, the thermal regime of the Earth's active layer. The active layer is such a layer of soil or water, the temperature of which experiences daily and annual fluctuations. Observations show that on land, daily fluctuations propagate to a depth of 1 - 2 m, annual fluctuations - to a layer of several tens of meters. In the seas and oceans, the thickness of the active layer is ten times greater than on land. The connection between the thermal regimes of the atmosphere and the active layer of the Earth is carried out using the so-called equation heat balance earth's surface. This equation was first used in 1941 to construct the theory of the daily variation of air temperature by A.A. Dorodnitsyn. In subsequent years, the heat balance equation was widely used by many researchers to study various properties of the surface layer of the atmosphere, up to assessing the changes that will occur under the influence of active influences, for example, on the ice cover of the Arctic. Let us dwell on the derivation of the equation for the heat balance of the earth's surface. Solar radiation that has arrived at the earth's surface is absorbed on land in a thin layer, the thickness of which will be denoted by (Fig. 1). In addition to the flow of solar radiation, the earth's surface receives heat in the form of a flow of infrared radiation from the atmosphere, it loses heat through its own radiation.

Rice. one.

In the soil, each of these streams undergoes a change. If in an elementary layer with a thickness (- the depth counted from the surface into the depth of the soil) the flux Ф has changed by dФ, then we can write

where a is the absorption coefficient, is the density of the soil. Integrating the last relation in the range from to, we obtain

where is the depth at which the flow decreases by a factor of e compared with the flow Ф(0) at. Along with radiation, heat transfer is carried out by turbulent exchange of the soil surface with the atmosphere and molecular exchange with the underlying soil layers. Under the influence of turbulent exchange, the soil loses or receives an amount of heat equal to

In addition, water evaporates from the soil surface (or water vapor condenses), which consumes the amount of heat

The molecular flow through the lower boundary of the layer is written as

where is the coefficient of thermal conductivity of the soil, is its specific heat capacity, is the coefficient of molecular thermal diffusivity.

Under the influence of the influx of heat, the temperature of the soil changes, and at temperatures close to 0, ice melts (or water freezes). Based on the law of conservation of energy in a vertical column of soil, we can write down the thickness.

In equation (19), the first term on the left side is the amount of heat spent on changing the heat content cm 3 of the soil per unit time, the second amount of heat used to melt ice (). On the right side, all heat fluxes that enter the soil layer through the upper and lower boundaries are taken with the “+” sign, and those that leave the layer are taken with the “-” sign. Equation (19) is the heat balance equation for the soil layer thickness. In such general view this equation is nothing more than the heat gain equation written for a layer of finite thickness. It is not possible to extract from it any additional information (compared to the heat influx equation) on the thermal regime of air and soil. However, it is possible to indicate several special cases of the heat balance equation, when it can be used as independent of differential equations boundary condition. In this case, the heat balance equation makes it possible to determine the unknown temperature of the earth's surface. The following are such special cases. On land that is not covered with snow or ice, the value, as already indicated, is quite small. At the same time, the ratio to each of the quantities that are of the order of the molecular range is quite large. As a result, the equation for land in the absence of ice melting processes can be written with a sufficient degree of accuracy in the form:

The sum of the first three terms in equation (20) is nothing but the radiation balance R of the earth's surface. Thus, the equation for the heat balance of the land surface takes the form:

The heat balance equation in the form (21) is used as a boundary condition in the study of the thermal regime of the atmosphere and soil.

The source of heat and light energy for the Earth is solar radiation. Its value depends on the latitude of the place, since the angle of incidence of the sun's rays decreases from the equator to the poles. The smaller the angle of incidence of the sun's rays, the large surface a beam of solar rays of the same cross section is distributed, and therefore there is less energy per unit area.

Due to the fact that during the year the Earth makes 1 revolution around the Sun, moving, maintaining a constant angle of inclination of its axis to the plane of the orbit (ecliptic), seasons of the year appear, characterized by different surface heating conditions.

On March 21 and September 23, the Sun is at its zenith under the equator (equinoxes). On June 22, the Sun is at its zenith over the Northern Tropic, on December 22 - over the Southern. Light zones and thermal zones are distinguished on the earth's surface (according to the average annual isotherm + 20 ° C, the boundary of the warm (hot) zone passes; between the average annual isotherms + 20 ° C and the isotherm + 10 ° C there is a temperate zone; according to the isotherm + 10 ° C - the boundaries cold belt.

The sun's rays pass through the transparent atmosphere without heating it, they reach the earth's surface, heat it, and from it, due to long-wave radiation, the air is heated. The degree of heating of the surface, and hence the air, depends primarily on the latitude of the area, as well as on 1) height above sea level (as it rises, the air temperature decreases by an average of 0.6ºС per 100 m; 2) features of the underlying surface which can be different in color and have different albedo - the reflective ability of rocks. Also, different surfaces have different heat capacity and heat transfer. Water, due to its high heat capacity, heats up slowly and slowly, while land is vice versa. 3) from the coasts to the depths of the continents, the amount of water vapor in the air decreases, and the more transparent the atmosphere, the less sunlight is scattered in it by water drops, and more sunlight reaches the Earth's surface.

The totality of solar matter and energy entering the earth is called solar radiation. It is divided into direct and scattered. direct radiation- a set of direct sunlight penetrating the atmosphere with a cloudless sky. scattered radiation- part of the radiation scattered in the atmosphere, while the rays go in all directions. P + P = Total radiation. Part of the total radiation reflected from the Earth's surface is called reflected radiation. Part of the total radiation absorbed by the Earth's surface is absorbed radiation. Thermal energy moving from the heated atmosphere to the surface of the Earth, towards the flow of heat from the Earth is called the counter radiation of the atmosphere.

Annual amount of total solar radiation in kcal/cm 2 year (according to T.V. Vlasova).

Effective Radiation- a value expressing the actual transfer of heat from the Earth's surface to the atmosphere. The difference between the radiation of the Earth and the counter radiation of the atmosphere determines the heating of the surface. Radiation balance directly depends on effective radiation - the result of the interaction of two processes of arrival and consumption of solar radiation. The amount of balance is largely affected by cloudiness. Where it is significant at night, it intercepts the long-wave radiation of the Earth, preventing it from escaping into space.

The temperature of the underlying surface and surface layers of air and the heat balance directly depend on the influx of solar radiation.

The heat balance determines the temperature, its magnitude and change on the surface that is directly heated by the sun's rays. When heated, this surface transfers heat (in the long-wave range) both to the underlying layers and to the atmosphere. The surface itself is called the active surface.

The main components of the heat balance of the atmosphere and the surface of the Earth as a whole

In the diurnal course of surface temperature, dry and devoid of vegetation, on a clear day, the maximum occurs after 14:00, and the minimum occurs around the time of sunrise. Cloudiness, humidity and surface vegetation can disrupt the daily course of temperature.

Daytime maxima of land surface temperature can be +80 o C or more. Daily fluctuations reach 40 o. The values ​​of extreme values ​​and temperature amplitudes depend on the latitude of the place, season, cloudiness, thermal properties of the surface, its color, roughness, nature of the vegetation cover, slope orientation (exposure).

When heated, the surface transfers heat to the soil. Time is spent on the transfer of heat from layer to layer, and the moments of the onset of maximum and minimum temperature values ​​during the day are delayed by every 10 cm by about 3 hours. The deeper the layer, the less heat it receives and the weaker the temperature fluctuations in it. At an average depth of about 1 m, the daily fluctuations in soil temperature "fade out". The layer in which they stop is called the layer of constant daily temperature.

At a depth of 5-10 m in tropical latitudes and 25 m in high latitudes, there is a layer of constant annual temperature, where the temperature is close to the average annual air temperature above the surface.

Water heats up more slowly and releases heat more slowly. In addition, the sun's rays can penetrate great depth directly heating the deeper layers. The transfer of heat to depth is not so much due to molecular thermal conductivity, but to a greater extent due to the mixing of waters in a turbulent way or currents. When cooling down surface layers water, thermal convection occurs, which is also accompanied by mixing.

Unlike land, the diurnal temperature fluctuations on the surface of the ocean are less. In high latitudes, on average, only 0.1ºС, in temperate - 0.4ºС, in tropical - 0.5ºС. The penetration depth of these oscillations is 15-20 m.

Annual temperature amplitudes on the ocean surface from 1ºС in equatorial latitudes to 10.2ºС in temperate latitudes. Annual temperature fluctuations penetrate to a depth of 200-300 m.

The moments of temperature maxima in water bodies are delayed compared to land. The maximum occurs at about 15-16 hours, the minimum - 2-3 hours after sunrise. The annual maximum temperature on the surface of the ocean in the northern hemisphere occurs in August, the minimum - in February.

The earth's surface, absorbing solar radiation and heating up, itself becomes a source of heat radiation into the atmosphere and through it into the world space. The higher the surface temperature, the higher the radiation. The Earth's own long-wave radiation is mostly retained in the troposphere, which heats up and emits radiation - atmospheric counter-radiation. The difference between the radiation of the earth's surface and the counter-radiation of the atmosphere is called efficient radiation. It shows the actual loss of heat by the Earth's surface and is about 20%.

Rice. 7.2. Scheme of the average annual radiation and heat balance, (according to K.Ya.Kondratiev, 1992)

The atmosphere, unlike the earth's surface, radiates more than it absorbs. The energy deficit is compensated by the arrival of heat from the earth's surface along with water vapor, as well as due to turbulence (during the rise of air heated near the earth's surface). The temperature contrasts that arise between low and high latitudes are smoothed out due to advection - heat transfer by sea and mainly air currents from low to high latitudes (Fig. 7.2, right side). For general geographical conclusions, rhythmic fluctuations in radiation due to the change of seasons are also important, since the thermal regime of a particular area depends on this. The reflective properties of earth covers, the heat capacity and thermal conductivity of media further complicate the transfer of thermal energy and the distribution of thermal energy characteristics.

Heat balance equation. The amount of heat is described by the heat balance equation, which is different for each geographical area. Its most important component is the radiation balance of the earth's surface. Solar radiation is spent on heating the soil and air (and water), evaporation, melting snow and ice, photosynthesis, soil-forming processes and weathering of rocks. Since nature is always characterized by balance, equality is observed between the arrival of energy and its consumption, which is expressed heat balance equation earth surface:

where R- radiation balance; LE is the heat used to evaporate water and melt snow or ice (L- latent heat of evaporation or vaporization; E- the rate of evaporation or condensation); BUT - horizontal heat transfer by air and ocean currents or turbulent flow; R - heat exchange of the earth's surface with air; AT - heat exchange of the earth's surface with soil and rocks; F- energy consumption for photosynthesis; FROM- energy consumption for soil formation and weathering; Q+q- total radiation; a- albedo; I- effective radiation of the atmosphere.

The share of energy spent on photosynthesis and soil formation accounts for less than 1% of the radiation budget, so these components are often omitted from the equation. However, in reality, they can matter, since this energy has the ability to accumulate and transform into other forms (convertible energy). A low-power, but long-term (hundreds of millions of years) process of accumulating convertible energy had a significant impact on the geographic envelope. It accumulated about 11×10 14 J/m 2 of energy in diffuse organic matter in sedimentary rocks, as well as in the form of coal, oil, shale.

The heat balance equation can be derived for any geographic area and time interval, taking into account the specificity of climatic conditions and the contribution of components (for land, ocean, areas with ice formation, non-freezing, etc.).

Transfer and distribution of heat. The transfer of heat from the surface to the atmosphere occurs in three ways: thermal radiation, heating or cooling of air upon contact with land, and evaporation of water. Water vapor, rising into the atmosphere, condenses and forms clouds or falls out as precipitation, and the heat released in this case enters the atmosphere. The radiation absorbed by the atmosphere and the heat of condensation of water vapor delay the loss of heat from the earth's surface. Over arid regions, this influence decreases, and we observe the largest daily and annual temperature amplitudes. The smallest temperature amplitudes are inherent in oceanic regions. As a huge reservoir, the ocean stores more heat, which reduces annual temperature fluctuations due to high temperatures. specific heat water. Thus, on Earth, water plays an important role as a heat accumulator.

The structure of the heat balance depends on geographical latitude and the type of landscape, which, in turn, itself depends on it. It changes significantly not only when moving from the equator to the poles, but also when moving from land to sea. Land and ocean differ both in the amount of absorbed radiation and in the nature of the distribution of heat. In the ocean in summer, heat spreads to a depth of several hundred meters. During the warm season, the ocean accumulates from 1.3×10 9 to 2.5×10 9 J/m 2 . On land, heat spreads to a depth of only a few meters, and during the warm season about 0.1 × 10 9 J/m 2 accumulates here, which is 10-25 times less than in the ocean. Due to the large supply of heat, the ocean cools less in winter than the land. Calculations show that the one-time heat content in the ocean is 21 times greater than its supply to the earth's surface as a whole. Even in a 4-meter layer of ocean water, there is 4 times more heat than in the entire atmosphere.

Up to 80% of the energy absorbed by the ocean is used to evaporate water. This is 12×10 23 J/m 2 per year, which is 7 times more than the same article of the land heat balance. 20% of the energy is spent on turbulent heat exchange with the atmosphere (which is also more than on land). The vertical heat exchange of the ocean with the atmosphere also stimulates the horizontal transfer of heat, due to which it partially ends up on land. A 50-meter layer of water participates in the heat exchange between the ocean and the atmosphere.

Changes in radiation and heat balance. The annual sum of the radiation balance is positive almost everywhere on Earth, with the exception of the glacial regions of Greenland and Antarctica. Its average annual values ​​decrease in the direction from the equator to the poles, following the patterns of distribution of solar radiation over the globe (Fig. 7.3). The radiation balance over the ocean is greater than over land. This is due to the lower albedo of the water surface, increased moisture content in equatorial and tropical latitudes. Seasonal changes in the radiation balance occur at all latitudes, but with varying degrees of severity. At low latitudes, seasonality is determined by the precipitation regime, since thermal conditions change little here. In temperate and high latitudes, seasonality is determined by the thermal regime: the radiation balance changes from positive in summer to negative in winter. The negative balance of the cold period of the year in temperate and polar latitudes is partially compensated by the advection of heat by air and sea currents from low latitudes.

To maintain the energy balance of the Earth, there must be a transfer of heat towards the poles. A little less of this heat is carried by ocean currents, the rest by the atmosphere. Differences in the heating of the Earth determine its action as a geographic heat engine in which heat is transferred from the heater to the refrigerator. In nature, this process is realized in two forms: first, thermodynamic spatial inhomogeneities form planetary systems of winds and sea currents; secondly, these planetary systems themselves participate in the redistribution of heat and moisture on the globe. Thus, heat is transferred from the equator towards the poles by air currents or ocean currents, and cold air or water masses are transferred to the equator. On fig. Figure 7.4 shows the poleward transport of warm surface water in the Atlantic Ocean. The heat transfer towards the poles reaches a maximum near a latitude of 40° and becomes zero at the poles.

The influx of solar radiation depends not only on the geographic latitude, but also on the season (Table 7.4). It is noteworthy that in summer even more heat enters the Arctic than at the equator, however, due to the high albedo of the Arctic seas, ice does not melt here.

Temperature distribution. On the horizontal distribution temperatures affect geographical position, relief, properties and material composition of the underlying surface, systems of ocean currents and the nature of atmospheric circulation in the surface and near-surface layers.

Rice. 7.3. Distribution of the average annual radiation balance on the earth's surface, MJ / (m 2 × year) (according to S.P. Khromov and M.A. Petrosyants, 1994)

Rice. 7.4. Heat transfer in the northern part Atlantic Ocean, °С(according to S. Neshiba, 1991). Shaded areas where surface water warmer than the ocean average. The numbers indicate the volumetric water transfers (million m 3 / s), the arrows indicate the direction of the currents, the thick line indicates the Gulf Stream

Table 7.4. Total radiation entering the earth's surface (N.I. Egorov, 1966)

The radiation balance is called the income-expenditure of radiant energy absorbed and emitted by the underlying surface, the atmosphere or the earth-atmosphere system for various periods of time (6, p. 328).

The incoming part of the radiation balance of the underlying surface R consists of direct solar and diffuse radiation, as well as atmospheric counterradiation absorbed by the underlying surface. The expenditure part is determined by the loss of heat due to its own thermal radiation underlying surface (6, p. 328).

Radiation balance equation:

R=(Q+q) (1-A)+d-

where Q is the flux (or sum) of direct solar radiation, q is the flux (or sum) of scattered solar radiation, A is the albedo of the underlying surface, is the flux (or sum) of atmospheric counter-radiation, and is the flux (or sum) of the intrinsic thermal radiation of the underlying surface, e is the absorptive capacity of the underlying surface (6, p. 328).

The radiation balance of the earth's surface for the year is positive everywhere on Earth, except for the ice plateaus of Greenland and Antarctica (Fig. 5). This means that the annual influx of absorbed radiation is greater than the effective radiation for the same time. But this does not mean at all that the earth's surface is getting warmer every year. The excess of absorbed radiation over radiation is balanced by the transfer of heat from the earth's surface into the air by thermal conduction and during phase transformations of water (during evaporation from the earth's surface and subsequent condensation in the atmosphere).

Consequently, for the earth's surface there is no radiative equilibrium in the receipt and return of radiation, but there is a thermal equilibrium: the influx of heat to the earth's surface both by radiative and non-radiative ways is equal to its return by the same methods.

Heat balance equation:

where the value of the radiative heat flux is R, the turbulent heat flux between the underlying surface and the atmosphere is P, the heat flux between the underlying surface and the underlying layers is A, and the heat consumption for evaporation (or heat release during condensation) is LE (L - latent heat evaporation, E is the rate of evaporation or condensation) (4, p. 7).

In accordance with the inflow and outflow of heat in relation to the underlying surface, the components of the heat balance can have positive or negative values. In a long-term conclusion, the average annual temperature of the upper layers of soil and water of the World Ocean is considered constant. Therefore, the vertical and horizontal heat transfer in the soil and in the World Ocean as a whole can practically be equated to zero.

Thus, in the long-term derivation, the annual heat balance for the land surface and the World Ocean is made up of the radiation balance, heat losses for evaporation, and turbulent heat exchange between the underlying surface and the atmosphere (Figs. 5, 6). For individual parts of the ocean, in addition to the indicated components of the heat balance, it is necessary to take into account the transfer of heat by sea currents.

Rice. 5. The radiation balance of the Earth and the arrival of solar radiation for the year

The earth receives heat by absorbing short-wave solar radiation in the atmosphere, and especially on the earth's surface. Solar radiation is practically the only source of heat in the "atmosphere-earth" system. Other heat sources (heat released during the decay radioactive elements inside the Earth, gravitational heat, etc.) in total give only one five thousandth of the heat that enters the upper boundary of the atmosphere from solar radiation So and when compiling the heat balance equation, they can be ignored.

Heat is lost with short-wave radiation leaving the world space, reflected from the atmosphere Soa and from the earth's surface SOP, and due to the effective radiation of long-wave radiation Ee by the earth's surface and radiation of the atmosphere Еa.

Thus, at the upper boundary of the atmosphere, the heat balance of the Earth as a planet consists of radiant (radiative) heat transfer:

SO - Soa - Sop - Ee - Ea = ?Se, (1)

where? Se, the change in the heat content of the "atmosphere - Earth" system over a period of time? t.

Consider the terms of this equation for the annual period. The flux of solar radiation at the average distance of the Earth from the Sun is approximately equal to 42.6-10° J/(m2-year). From this flow, the Earth receives an amount of energy equal to the product of the solar constant I0 and the cross-sectional area of ​​the Earth pR2, i.e., I0 pR2, where R is the average radius of the Earth. Under the influence of the Earth's rotation, this energy is distributed over the entire surface of the globe, equal to 4pR2. Consequently, the average value of the solar radiation flux to the horizontal surface of the Earth, without taking into account its attenuation by the atmosphere, is Iо рR2/4рR3 = Iо/4, or 0.338 kW/m2. For a year, about 10.66-109 J, or 10.66 GJ of solar energy, is received on average for each square meter of the surface of the outer boundary of the atmosphere, i.e. Io = 10.66 GJ / (m2 * year).

Consider the expenditure side of equation (1). The solar radiation that has arrived at the outer boundary of the atmosphere partially penetrates the atmosphere, and is partially reflected by the atmosphere and the earth's surface into the world space. According to the latest data, the average albedo of the Earth is estimated at 33%: it is the sum of reflection from clouds (26%) and reflection from the underlying surface (7:%). Then the radiation reflected by the clouds Soa = 10.66 * 0.26 = 2.77 GJ / (m2 * year), the earth's surface - SOP = 10.66 * 0.07 = 0.75 GJ / (m2 * year) and in general, the Earth reflects 3.52 GJ/(m2*year).

The earth's surface, heated as a result of the absorption of solar radiation, becomes a source of long-wave radiation that heats the atmosphere. The surface of any body that has a temperature above absolute zero continuously radiates thermal energy. The earth's surface and atmosphere are no exception. According to the Stefan-Boltzmann law, the intensity of radiation depends on the temperature of the body and its emissivity:

E = wT4, (2)

where E is the radiation intensity, or self-radiation, W / m2; c is the emissivity of the body relative to a completely black body, for which c = 1; y - Stefan's constant - Boltzmann, equal to 5.67 * 10-8 W / (m2 * K4); T -- absolute temperature body.

Values ​​for various surfaces range from 0.89 (smooth water surface) to 0.99 (dense green grass). On average, for the earth's surface, v is taken equal to 0.95.

The absolute temperatures of the earth's surface are between 190 and 350 K. At such temperatures, the emitted radiation has wavelengths of 4-120 microns and, therefore, all of it is infrared and is not perceived by the eye.

The intrinsic radiation of the earth's surface - E3, calculated by formula (2), is equal to 12.05 GJ / (m2 * year), which is 1.39 GJ / (m2 * year), or 13% higher than the solar radiation that arrived at the upper boundary of the atmosphere S0. Such a large return of radiation by the earth's surface would lead to its rapid cooling, if this were not prevented by the process of absorption of solar and atmospheric radiation by the earth's surface. Infra-red terrestrial radiation, or own radiation of the earth's surface, in the wavelength range from 4.5 to 80 microns is intensively absorbed by atmospheric water vapor and only in the range of 8.5 - 11 microns passes through the atmosphere and goes into world space. In turn, atmospheric water vapor also emits invisible infrared radiation, most of which is directed down to the earth's surface, and the rest goes into world space. Atmospheric radiation coming to the earth's surface is called the counter radiation of the atmosphere.

From the counter radiation of the atmosphere, the earth's surface absorbs 95% of its magnitude, since, according to Kirchhoff's law, the radiance of a body is equal to its radiant absorption. Thus, the counterradiation of the atmosphere is an important source of heat for the earth's surface in addition to the absorbed solar radiation. The counter radiation of the atmosphere cannot be directly determined and is calculated by indirect methods. The counter radiation of the atmosphere absorbed by the earth's surface Eza = 10.45 GJ / (m2 * year). With respect to S0, it is 98%.

The counter radiation is always less than that of the earth. Therefore, the earth's surface loses heat due to the positive difference between its own and counter radiation. The difference between the self-radiation of the earth's surface and the counter-radiation of the atmosphere is called the effective radiation (Ee):

Ee \u003d Ez - Eza (3)

solar heat exchange on earth

Effective radiation is the net loss of radiant energy, and hence heat, from the earth's surface. This heat escaping into space is 1.60 GJ / (m2 * year), or 15% of the solar radiation that arrived at the upper boundary of the atmosphere (arrow E3 in Fig. 9.1). In temperate latitudes, the earth's surface loses through effective radiation about half of the amount of heat that it receives from absorbed radiation.

The radiation of the atmosphere is more complex than the radiation of the earth's surface. First, according to Kirchhoff's law, energy is emitted only by those gases that absorb it, i.e. water vapor, carbon dioxide and ozone. Secondly, the radiation of each of these gases has a complex selective character. Since the content of water vapor decreases with height, the most strongly radiating layers of the atmosphere lie at altitudes of 6-10 km. Long-wave radiation of the atmosphere into the world space Еa=5.54 GJ/(m2*year), which is 52% of the influx of solar radiation to the upper boundary of the atmosphere. The long-wave radiation of the earth's surface and the atmosphere entering space is called the outgoing radiation EU. In total, it is equal to 7.14 GJ/(m2*year), or 67% of the influx of solar radiation.

Substituting the found values ​​of So, Soa, Sop, Ee and Ea into equation (1), we get - ?Sz = 0, i.e., the outgoing radiation, together with the reflected and scattered short-wave radiation Soz, compensate for the influx of solar radiation to the Earth. In other words, the Earth, together with the atmosphere, loses as much radiation as it receives, and, therefore, is in a state of radiative equilibrium.

The thermal equilibrium of the Earth is confirmed by long-term observations of temperature: average temperature Earth changes little from year to year, and from one long-term period to another remains almost unchanged.