Thermal balance of the earth's surface and the earth-troposphere system. Radiation and heat balances See what the "heat balance of the earth's surface" is in other dictionaries

The atmosphere, like the earth's surface, receives almost all of its heat from the sun. Other sources of heating include heat coming from the bowels of the Earth, but it is only a fraction of a percent of the total amount of heat.

Although solar radiation is the only source of heat for the earth's surface, the thermal regime of the geographic envelope is not only a consequence of the radiation balance. Solar heat is converted and redistributed under the influence of terrestrial factors, and primarily transformed by air and ocean currents. They, in turn, are due to the uneven distribution of solar radiation over latitudes. This is one of the clearest examples of the close global connection and interaction of various components in nature.

For the living nature of the Earth, the redistribution of heat between different latitudes, as well as between oceans and continents, is important. Thanks to this process, a very complex spatial redistribution of heat occurs on the Earth's surface in accordance with the superior directions of movement of air and ocean currents. However, the total heat transfer is directed, as a rule, from low latitudes to high latitudes and from oceans to continents.

The distribution of heat in the atmosphere occurs by convection, heat conduction and radiation. Thermal convection manifests itself everywhere on the planet, winds, ascending and descending air currents are ubiquitous. Convection is especially pronounced in the tropics.

Thermal conductivity, that is, the transfer of heat during direct contact of the atmosphere with a warm or cold surface of the earth, is of relatively little importance, since air is a poor conductor of heat. It is this property that has found wide application in the manufacture of window frames with double glazing.

The inflows and outflows of heat in the lower atmosphere are not the same at different latitudes. North of 38°N sh. more heat is emitted than absorbed. This loss is compensated by warm oceanic and air currents directed to temperate latitudes.

The process of receipt and expenditure of solar energy, heating and cooling of the entire system of the Earth's atmosphere is characterized by a heat balance. If we take the annual supply of solar energy to the upper boundary of the atmosphere as 100%, then the balance of solar energy will look like this: 42% is reflected from the Earth and returns back to outer space (this value characterizes the Earth's albedo), with 38% reflected by the atmosphere and 4% - the surface of the earth. The rest (58%) is absorbed: 14% - by the atmosphere and 44% - by the earth's surface. The heated surface of the Earth gives back all the energy absorbed by it. At the same time, the radiation of energy by the earth's surface is 20%, 24% is spent on heating the air and evaporating moisture (5.6% for heating the air and 18.4% for evaporating moisture).

Such general characteristics of the heat balance of the globe as a whole. In fact, for different latitudinal belts for different surfaces, the heat balance will be far from the same. Thus, the heat balance of any territory is disturbed at sunrise and sunset, when the seasons change, depending on atmospheric conditions (cloudiness, air humidity and dust content in it), the nature of the surface (water or land, forest or onion, snow cover or bare ground). ), altitude above sea level. Most heat is radiated at night, in winter, and through rarefied, clean, dry air at high altitudes. But in the end, the losses due to radiation are compensated by the heat coming from the Sun, and the state of dynamic equilibrium prevails on the Earth as a whole, otherwise it would warm up or, conversely, cool down.

Air temperature

The heating of the atmosphere occurs in a rather complicated way. Short wavelengths of sunlight ranging from visible red to ultraviolet light are converted at the Earth's surface into longer heat waves, which later, when emitted from the Earth's surface, heat the atmosphere. The lower layers of the atmosphere warm up faster than the upper ones, which is explained by the indicated thermal radiation of the earth's surface and the fact that they have a high density and are saturated with water vapor.

A characteristic feature of the vertical distribution of temperature in the troposphere is its decrease with height. The average vertical temperature gradient, that is, the average decrease calculated per 100 m of altitude, is 0.6 ° C. Cooling of moist air is accompanied by moisture condensation. In this case, a certain amount of heat is released, which was spent on the formation of steam. Therefore, when moist air rises, it cools almost twice as slowly as dry air. The geothermal coefficient of dry air in the troposphere is 1 °C on average.

The air that rises from the heated land surface and water bodies enters a zone of low pressure. This allows it to expand, and in connection with this, a certain amount of thermal energy is converted into kinetic energy. As a result of this process, the air is cooled. If at the same time it does not receive heat from anywhere and does not give it anywhere, then the entire described process is called adiabatic, or dynamic cooling. And vice versa, the air descends, enters the zone of high pressure, it is condensed by the air that surrounds it, and the mechanical energy is converted into thermal energy. Because of this, the air experiences adiabatic heating, which averages 1 °C for every 100 m of subsidence.

Sometimes the temperature rises with altitude. This phenomenon is called inversion. The causes of u "manifestations are varied: the radiation of the Earth over ice covers, the passage of strong currents of warm air over a cold surface. Inversions are especially characteristic of mountainous regions: heavy cold air flows into mountain hollows and stagnates there, displacing lighter warm air upwards.

Daily and annual changes in air temperature reflect the thermal state of the surface. In the surface layer of air, the daily maximum is set at 2-3 pm, and the minimum is observed after sunrise. The greatest daily amplitude takes place in subtropical latitudes (30 ° C), the smallest - in the polar (5 ° C). The annual course of temperature depends on the latitude, the nature of the underlying surface, the height of the place above the ocean level, the relief, and the distance from the ocean.

Certain geographic regularities have been revealed in the distribution of annual temperatures on the earth's surface.

1. In both hemispheres, average temperatures are decreasing towards the poles. However, the thermal equator - a warm parallel with an average annual temperature of 27°C - is located in the Northern Hemisphere at about 15-20° latitude. This is explained by the fact that land occupies a larger area here than at the geographic equator.

2. From the equator to the north and south, temperatures change unevenly. Between the equator and the 25th parallel, the decrease in temperature is very slow - less than two degrees for every ten degrees of latitude. Between 25° and 80° latitude in both hemispheres, temperatures drop very rapidly. In some places, this decrease exceeds 10 ° C. Further towards the poles, the rate of temperature drop decreases again.

3. Average annual temperatures of all parallels of the Southern Hemisphere are less than the temperature of the corresponding parallels of the Northern Hemisphere. The average air temperature of the predominantly "continental" Northern Hemisphere is +8.6 ° С in January, +22.4 ° С in July; in the Southern "oceanic" hemisphere, the average temperature in July is +11.3 ° С, in January - +17.5 ° С. The annual amplitude of air temperature fluctuations in the Northern Hemisphere is twice as large due to the peculiarities of the distribution of land and sea at the corresponding latitudes and the cooling effect of the grandiose ice dome Antarctica on the climate of the Southern Hemisphere.

Isotherm maps provide important characteristics of the distribution of air temperatures on Earth. Thus, based on the analysis of the distribution of the July isotherms on the earth's surface, the following main conclusions can be formulated.

1. In the extratropical regions of both hemispheres, the isotherms over the continents bend to the north relative to its position on the windows. In the Northern Hemisphere, this is due to the fact that the land is heated more than the sea, and in the South - the opposite ratio: at this time, the land is colder than the sea.

2. Over the oceans, the July isotherms reflect the influence of cold air temperature currents. This is especially noticeable along those western coasts of North America and Africa, which are washed by the cold correspondence of the California and Canary ocean currents. In the Southern Hemisphere, the isotherms are curved in the opposite direction to the north - also under the influence of cold currents.

3. The highest average temperatures in July are observed in the deserts located north of the equator. It is especially hot at this time in California, the Sahara, Arabia, Iran, and the interior of Asia.

The distribution of January isotherms also has its own characteristics.

1. The bends of the isotherms over the oceans to the north and over the land to the south become even more prominent, more contrasting. This is most pronounced in the Northern Hemisphere. The strong bends of the isotherms towards the North Pole reflect an increase in the thermal role of the Gulf Stream ocean currents in the Atlantic Ocean and the Kuro-Sio in the Pacific Ocean.

2. In the extratropical regions of both hemispheres, the isotherms over the continents are noticeably curved to the south. This is due to the fact that in the Northern Hemisphere the land is colder, and in the Southern Hemisphere it is warmer than the sea.

3. The highest average temperatures in January occur in the deserts of the tropical zone of the Southern Hemisphere.

4. The areas of greatest cooling on the planet in January, as in July, are Antarctica and Greenland.

In general, it can be stated that the isotherms of the Southern Hemisphere during all seasons of the year have a more rectilinear (latitudinal) strike pattern. The absence of significant anomalies in the course of isotherms here is explained by the significant predominance of the water surface over land. An analysis of the course of the isotherms indicates a close dependence of temperatures not only on the magnitude of solar radiation, but also on the redistribution of heat by oceanic and air currents.

The concept of the thermobaric field of the Earth

Seasonal fluctuations in the radiation balance

Seasonal fluctuations in the radiation regime of the Earth as a whole correspond to changes in the irradiation of the northern and southern hemispheres during the annual revolution of the Earth around the Sun.

In the equatorial zone there are no seasonal fluctuations in solar heat: both in December and July, the radiation balance is 6-8 kcal/cm 2 on land and 10-12 kcal/cm 2 at sea per month.

In tropical zones seasonal fluctuations are already quite clearly expressed. In the Northern Hemisphere - in North Africa, South Asia and Central America - in December, the radiation balance is 2-4 kcal / cm 2, and in June 6-8 kcal / cm 2 per month. The same picture is observed in the Southern Hemisphere: the radiation balance is higher in December (summer), lower in June (winter).

Throughout the temperate zone in December, to the north of the subtropics (the zero balance line passes through France, Central Asia and the island of Hokkaido), the balance is negative. In June, even near the Arctic Circle, the radiation balance is 8 kcal/cm2 per month. The greatest amplitude of the radiation balance is characteristic of the continental Northern Hemisphere.

The thermal regime of the troposphere is determined both by the influx of solar heat and by the dynamics of air masses, which carry out the advection of heat and cold. On the other hand, the air movement itself is caused by a temperature gradient (a drop in temperature per unit distance) between the equatorial and polar latitudes and between oceans and continents. As a result of these complex dynamic processes, the thermobaric field of the Earth was formed. Both of its elements - temperature and pressure - are so interconnected that it is customary in geography to speak of a single thermobaric field of the Earth.

The heat received by the earth's surface is converted and redistributed by the atmosphere and hydrosphere. Heat is spent mainly on evaporation, turbulent heat exchange, and on the redistribution of heat between land and ocean.

The greatest amount of heat is spent on the evaporation of water from the oceans and continents. In the tropical latitudes of the oceans, evaporation consumes approximately 100-120 kcal / cm 2 per year, and in water areas with warm currents up to 140 kcal / cm 2 per year, which corresponds to the evaporation of a 2 m thick water layer. In the equatorial belt, much less energy is spent on evaporation, that is, approximately 60 kcal / cm 2 per year; this is equivalent to the evaporation of a one-meter layer of water.

On the continents, the maximum heat consumption for evaporation occurs in the equatorial zone with its humid climate. In the tropical latitudes of the land there are deserts with negligible evaporation. In temperate latitudes, the cost of heat for evaporation in the oceans is 2.5 times greater than on land. The surface of the ocean absorbs from 55 to 97% of all radiation falling on it. On the entire planet, 80% of solar radiation is spent on evaporation, and about 20% on turbulent heat transfer.

The heat expended on the evaporation of water is transferred to the atmosphere during the condensation of steam in the form of latent heat of vaporization. This process plays a major role in heating the air and the movement of air masses.

The maximum amount of heat for the entire troposphere from the condensation of water vapor is received by equatorial latitudes - approximately 100-140 kcal / cm 2 per year. This is due to the influx of a huge amount of moisture brought here by the trade winds from tropical waters, and the rise of air above the equator. In dry tropical latitudes, the amount of latent heat of vaporization is naturally negligible: less than 10 kcal/cm2 per year in continental deserts and about 20 kcal/cm2 per year over the oceans. Water plays a decisive role in the thermal and dynamic regime of the atmosphere.

Radiative heat also enters the atmosphere through turbulent air heat exchange. Air is a poor conductor of heat, therefore, molecular thermal conductivity can provide heating of only an insignificant (a few meters) lower layer of the atmosphere. The troposphere is heated by turbulent, jet, vortex mixing: the air of the lower layer adjacent to the earth heats up, rises in jets, and the upper cold air descends in its place, which also heats up. In this way, heat is quickly transferred from the soil to the air, from one layer to another.

Turbulent heat flow is greater over continents and less over oceans. It reaches its maximum value in tropical deserts, up to 60 kcal / cm 2 per year, in the equatorial and subtropical zones it decreases to 30-20 kcal / cm 2, and in temperate - 20-10 kcal / cm 2 per year. Over a larger area of ​​the oceans, water gives off about 5 kcal/cm2 per year to the atmosphere, and only in subpolar latitudes the air from the Gulf Stream and Kuroshivo receives heat up to 20-30 kcal/cm2 per year.

In contrast to the latent heat of vaporization, the turbulent flow is weakly retained by the atmosphere. Over deserts, it is transmitted upwards and dissipates, which is why desert zones act as areas of cooling of the atmosphere.

The thermal regime of the continents is different due to their geographical position. The cost of heat for evaporation on the northern continents is determined by their position in the temperate zone; in Africa and Australia - the aridity of their large areas. In all oceans, a huge proportion of heat is spent on evaporation. Then part of this heat is transferred to the continents and insulates the climate of high latitudes.

An analysis of heat transfer between the surface of continents and oceans allows us to draw the following conclusions:

1. In the equatorial latitudes of both hemispheres, the atmosphere receives heat from the heated oceans up to 40 kcal / cm 2 per year.

2. Almost no heat enters the atmosphere from continental tropical deserts.

3. The line of zero balance passes through the subtropics, near 40 0 ​​latitude.

4. In temperate latitudes, the heat consumption by radiation is greater than the absorbed radiation; this means that the climatic air temperature of temperate latitudes is determined not by solar, but by advective (brought from low latitudes) heat.

5. The radiation balance of the Earth-Atmosphere is dissymmetric relative to the equatorial plane: in the polar latitudes of the northern hemisphere it reaches 60, and in the corresponding southern latitudes - only 20 kcal/cm 2 per year; heat is transferred to the northern hemisphere more intensively than to the southern, approximately 3 times. The balance of the Earth-atmosphere system determines the air temperature.

8.16. Heating and cooling of the atmosphere in the process of interaction of the "ocean-atmosphere-continent" system

The absorption of solar rays by air gives no more than 0.1 0 C of heat to the lower kilometer layer of the troposphere. The atmosphere receives no more than 1/3 of the heat directly from the Sun, and it absorbs 2/3 from the earth's surface and, above all, from the hydrosphere, which transfers heat to it through water vapor evaporated from the surface of the water shell.

The sun's rays that have passed through the gas envelope of the planet meet water in most places on the earth's surface: on the oceans, in water bodies and land swamps, in moist soil and in the foliage of plants. The thermal energy of solar radiation is spent primarily on evaporation. The amount of heat expended per unit of evaporating water is called the latent heat of vaporization. When steam condenses, the heat of vaporization enters the air and heats it.

The assimilation of solar heat by water bodies differs from the heating of land. The heat capacity of water is about 2 times greater than that of soil. With the same amount of heat, water heats up twice as weakly as soil. On cooling, the ratio is reversed. If a cold air mass penetrates a warm ocean surface, then heat penetrates into a layer up to 5 km. The heating of the troposphere is due to the latent heat of vaporization.

Turbulent air mixing (random, uneven, chaotic) creates convection currents, the intensity and direction of which depend on the nature of the terrain and the planetary circulation of air masses.

The concept of an adiabatic process. An important role in the thermal regime of air belongs to the adiabatic process.

The concept of an adiabatic process. The most important role in the thermal regime of the atmosphere belongs to the adiabatic process. Adiabatic heating and cooling of air occurs in the same mass, without heat exchange with other media.

When air descends from the upper or middle layers of the troposphere or along the slopes of mountains, it enters denser layers from rarefied layers, gas molecules approach each other, their collisions intensify, and the kinetic energy of the movement of air molecules turns into heat. The air is heated without receiving heat either from other air masses or from the earth's surface. Adiabatic heating occurs, for example, in the tropical zone, over deserts and over oceans in the same latitudes. Adiabatic heating of the air is accompanied by its drying (which is the main reason for the formation of deserts in the tropical zone).

In ascending currents, the air cools adiabatically. From the dense lower troposphere, it rises to the rarefied middle and upper troposphere. At the same time, its density decreases, the molecules move away from each other, collide less often, the thermal energy received by air from the heated surface turns into kinetic energy, is spent on mechanical work to expand the gas. This explains the cooling of the air as it rises.

Dry air cools adiabatically by 1 0 C per 100 m of elevation, this is an adiabatic process. However, natural air contains water vapor, which condenses to release heat. Therefore, in fact, the temperature drops by 0.6 0 C per 100 m (or 6 0 C per 1 km of altitude). This is a wet adiabatic process.

When lowering, both dry and humid air heat up equally, since in this case moisture condensation does not occur and the latent heat of vaporization is not released.

The most clearly typical features of the thermal regime of land are manifested in deserts: a large proportion of solar radiation is reflected from their bright surface, heat is not spent on evaporation, and goes to heat dry rocks. From them during the day the air is heated to high temperatures. In dry air, heat does not linger and is freely radiated into the upper atmosphere and interplanetary space. Deserts also serve as cooling windows for the atmosphere on a planetary scale.

In order to correctly assess the degree of heating and cooling of various earth surfaces, calculate evaporation for , determine changes in the moisture content in the soil, develop methods for predicting freezing, and also evaluate the impact of reclamation work on the climatic conditions of the surface air layer, data on the heat balance of the earth's surface are needed.

The earth's surface continuously receives and loses heat as a result of exposure to a variety of flows of short-wave and long-wave radiation. Absorbing to a greater or lesser extent total radiation and counter radiation, the earth's surface heats up and emits long-wave radiation, which means it loses heat. The value characterizing the loss of heat of the earth
surface is the effective radiation. It is equal to the difference between the own radiation of the earth's surface and the counter radiation of the atmosphere. Since the counter radiation of the atmosphere is always somewhat less than that of the earth, this difference is positive. In the daytime, the effective radiation is blocked by the absorbed short-wave radiation. At night, in the absence of short-wave solar radiation, effective radiation lowers the temperature of the earth's surface. In cloudy weather, due to the increase in the counter radiation of the atmosphere, the effective radiation is much less than in clear weather. Less and nightly cooling of the earth's surface. In middle latitudes, the earth's surface loses through effective radiation about half of the amount of heat that they receive from absorbed radiation.

The arrival and consumption of radiant energy is estimated by the value of the radiation balance of the earth's surface. It is equal to the difference between the absorbed and effective radiation, the thermal state of the earth's surface depends on it - its heating or cooling. During the day, it is positive almost all the time, i.e., the heat input exceeds the consumption. At night, the radiation balance is negative and equal to the effective radiation. The annual values ​​of the radiation balance of the earth's surface, with the exception of the highest latitudes, are everywhere positive. This excess heat is spent on heating the atmosphere by turbulent heat conduction, on evaporation, and on heat exchange with deeper layers of soil or water.

If we consider the temperature conditions for a long period (a year or better a number of years), then the earth's surface, the atmosphere separately and the "Earth-atmosphere" system are in a state of thermal equilibrium. Their average temperature varies little from year to year. In accordance with the law of conservation of energy, we can assume that the algebraic sum of heat fluxes coming to the earth's surface and leaving it is equal to zero. This is the equation for the heat balance of the earth's surface. Its meaning is that the radiation balance of the earth's surface is balanced by non-radiative heat transfer. The heat balance equation, as a rule, does not take into account (due to their smallness) such flows as the heat carried by precipitation, energy consumption for photosynthesis, heat gain from biomass oxidation, as well as heat consumption for melting ice or snow, heat gain from freezing water.

The thermal balance of the "Earth-atmosphere" system for a long period is also equal to zero, i.e., the Earth as a planet is in thermal equilibrium: the solar radiation arriving at the upper boundary of the atmosphere is balanced by the radiation leaving the atmosphere from the upper boundary of the atmosphere.

If we take the air coming to the upper boundary as 100%, then 32% of this amount is dissipated in the atmosphere. Of these, 6% goes back into the world space. Consequently, 26% comes to the earth's surface in the form of scattered radiation; 18% of radiation is absorbed by ozone, aerosols and is used to heat the atmosphere; 5% is absorbed by clouds; 21% of radiation escapes into space as a result of reflection from clouds. Thus, the radiation coming to the earth's surface is 50%, of which direct radiation accounts for 24%; 47% is absorbed by the earth's surface, and 3% of the incoming radiation is reflected back into space. As a result, 30% of solar radiation escapes from the upper boundary of the atmosphere into outer space. This value is called the planetary albedo of the Earth. For the Earth-atmosphere system, 30% of reflected and scattered solar radiation, 5% of terrestrial radiation and 65% of atmospheric radiation, i.e., only 100%, go back into space through the upper boundary of the atmosphere.

Let us first consider the thermal conditions of the earth's surface and the uppermost layers of soil and water bodies. This is necessary because the lower layers of the atmosphere are heated and cooled most of all by radiative and non-radiative heat exchange with the upper layers of soil and water. Therefore, temperature changes in the lower layers of the atmosphere are primarily determined by changes in the temperature of the earth's surface and follow these changes.

The earth's surface, i.e., the surface of soil or water (as well as vegetation, snow, ice cover), continuously receives and loses heat in various ways. Through the earth's surface, heat is transferred upward - into the atmosphere and downward - into the soil or water.

First, the total radiation and the counter radiation of the atmosphere enter the earth's surface. They are absorbed to a greater or lesser extent by the surface, i.e., they go to heat the upper layers of soil and water. At the same time, the earth's surface itself radiates and loses heat in the process.

Secondly, heat comes to the earth's surface from above, from the atmosphere, by conduction. In the same way, heat escapes from the earth's surface into the atmosphere. By conduction, heat also leaves the earth's surface down into the soil and water, or comes to the earth's surface from the depths of the soil and water.

Thirdly, the earth's surface receives heat when water vapor condenses on it from the air or, on the contrary, loses heat when water evaporates from it. In the first case, latent heat is released, in the second case, heat passes into a latent state.

In any period of time, the same amount of heat goes up and down from the earth's surface as it receives from above and below during this time. If it were otherwise, the law of conservation of energy would not be fulfilled: it would be necessary to assume that energy arises or disappears on the earth's surface. However, it is possible that, for example, more heat may go up than came from above; in this case, the excess heat transfer should be covered by the arrival of heat to the surface from the depths of the soil or water.

So, the algebraic sum of all incomes and expenses of heat on the earth's surface should be equal to zero. This is expressed by the equation of the heat balance of the earth's surface.

To write this equation, first, we combine the absorbed radiation and the effective radiation into a radiation balance.

The arrival of heat from the air or its return to the air by thermal conduction will be denoted by P. The same income or consumption by heat exchange with deeper layers of soil or water will be called A. The loss of heat during evaporation or its arrival during condensation on the earth's surface will be denoted by LE, where L is the specific the heat of evaporation and E is the mass of evaporated or condensed water.

It can also be said that the meaning of the equation is that the radiative balance on the earth's surface is balanced by non-radiative heat transfer (Fig. 5.1).

Equation (1) is valid for any period of time, including for many years.

The fact that the heat balance of the earth's surface is zero does not mean that the surface temperature does not change. When the heat transfer is directed downward, the heat that comes to the surface from above and leaves it deep into it remains to a large extent in the uppermost layer of soil or water (in the so-called active layer). The temperature of this layer, and therefore the temperature of the earth's surface, increases as well. On the contrary, when heat is transferred through the earth's surface from the bottom up, into the atmosphere, the heat escapes primarily from the active layer, as a result of which the surface temperature drops.

From day to day and from year to year, the average temperature of the active layer and the earth's surface in any place varies little. This means that during the day, almost as much heat enters the depths of the soil or water during the day as it leaves it at night. But still, during the summer days, the heat goes down a little more than it comes from below. Therefore, the layers of soil and water, and therefore their surface, are heated day by day. In winter, the reverse process occurs. These seasonal changes in heat input - heat consumption in soil and water almost balance out over the year, and the average annual temperature of the earth's surface and the active layer varies little from year to year.

Heat balance of the Earth- the ratio of the income and consumption of energy (radiant and thermal) on the earth's surface, in the atmosphere and in the Earth-atmosphere system. The main source of energy for the overwhelming majority of physical, chemical and biological processes in the atmosphere, hydrosphere and in the upper layers of the lithosphere is solar radiation, so the distribution and ratio of the components of the heat balance characterize its transformations in these shells.

The heat balance is a particular formulation of the law of conservation of energy and is compiled for a section of the Earth's surface (the heat balance of the earth's surface); for a vertical column passing through the atmosphere (heat balance of the atmosphere); for the same column passing through the atmosphere and the upper layers of the lithosphere or the hydrosphere (thermal balance of the Earth-atmosphere system).

The equation for the heat balance of the earth's surface:

R + P + F0 + LE = 0. (15)

represents the algebraic sum of energy flows between an element of the earth's surface and the surrounding space. In this formula:

R - radiation balance, the difference between the absorbed short-wave solar radiation and long-wave effective radiation from the earth's surface.

P is the heat flux that occurs between the underlying surface and the atmosphere;

F0 - heat flow is observed between the earth's surface and deeper layers of the lithosphere or hydrosphere;

LE - heat consumption for evaporation, which is defined as the product of the mass of evaporated water E and the heat of evaporation L heat balance

These streams include the Radiation balance (or residual radiation) R - the difference between the absorbed short-wave solar radiation and the long-wave effective radiation from the earth's surface. The positive or negative value of the radiation balance is compensated by several heat fluxes. Since the temperature of the earth's surface is usually not equal to the air temperature, a heat flux P arises between the underlying surface and the atmosphere. A similar heat flux F0 is observed between the earth's surface and deeper layers of the lithosphere or hydrosphere. In this case, the heat flux in the soil is determined by molecular thermal conductivity, while in water bodies, heat transfer, as a rule, has a turbulent character to a greater or lesser extent. The heat flux F0 between the surface of the reservoir and its deeper layers is numerically equal to the change in the heat content of the reservoir over a given time interval and the heat transfer by currents in the reservoir. In the heat balance of the earth's surface, the heat consumption for evaporation LE is usually of significant importance, which is defined as the product of the mass of evaporated water E and the heat of evaporation L. The value of LE depends on the moistening of the earth's surface, its temperature, air humidity and the intensity of turbulent heat transfer in the surface air layer, which determines the rate of transfer of water vapor from the earth's surface to the atmosphere.

The atmosphere heat balance equation has the form:

Ra + Lr + P + Fa = ΔW, (16)

where ΔW is the change in heat content inside the vertical wall of the atmospheric column.

The heat balance of the atmosphere is composed of its radiation balance Ra; heat input or output Lr during phase transformations of water in the atmosphere (r is the sum of precipitation); the arrival or consumption of heat P, due to the turbulent heat exchange of the atmosphere with the earth's surface; heat gain or loss Fa caused by heat exchange through the vertical walls of the column, which is associated with ordered atmospheric motions and macroturbulence. In addition, the equation for the heat balance of the atmosphere includes the term ΔW, which is equal to the change in heat content inside the column.

The heat balance equation for the Earth-atmosphere system corresponds to the algebraic sum of the terms of the equations for the heat balance of the earth's surface and atmosphere. The components of the heat balance of the earth's surface and atmosphere for various regions of the globe are determined by meteorological observations (at actinometric stations, at special heat balance stations, on meteorological satellites of the Earth) or by climatological calculations.

The average latitudinal values ​​of the components of the heat balance of the earth's surface for the oceans, land and Earth and the heat balance of the atmosphere are given in tables, where the values ​​of the terms of the heat balance are considered positive if they correspond to the arrival of heat. Since these tables refer to average annual conditions, they do not include terms characterizing changes in the heat content of the atmosphere and the upper layers of the lithosphere, since for these conditions they are close to zero.

For the Earth as a planet, together with the atmosphere, the heat balance scheme is shown in Fig. A unit surface of the outer boundary of the atmosphere receives a solar radiation flux equal to an average of about 250 kcal / cm 2 per year, of which about 1/3 is reflected into the world space, and 167 kcal / cm 2 per year is absorbed by the Earth

Heat exchange spontaneous irreversible process of heat transfer in space, due to a non-uniform temperature field. In the general case, heat transfer can also be caused by the inhomogeneity of the fields of other physical quantities, for example, the difference in concentrations (diffusion thermal effect). There are three types of heat transfer: thermal conductivity, convection and radiant heat transfer (in practice, heat transfer is usually carried out by all 3 types at once). Heat transfer determines or accompanies many processes in nature (for example, the evolution of stars and planets, meteorological processes on the surface of the Earth, etc.). in technology and everyday life. In many cases, for example, when studying the processes of drying, evaporative cooling, diffusion, heat transfer is considered together with mass transfer. Heat transfer between two coolants through a solid wall separating them or through the interface between them is called heat transfer.

Thermal conductivity one of the types of heat transfer (energy of thermal motion of microparticles) from more heated parts of the body to less heated ones, leading to temperature equalization. With thermal conductivity, the transfer of energy in the body is carried out as a result of the direct transfer of energy from particles (molecules, atoms, electrons) that have more energy to particles with less energy. If the relative change in the thermal conductivity temperature at a distance of the mean free path of particles l is small, then the basic law of thermal conductivity (Fourier law) is satisfied: the heat flux density q is proportional to the temperature gradient grad T, i.e. (17)

where λ is the thermal conductivity, or simply thermal conductivity, does not depend on grad T [λ depends on the aggregate state of the substance (see table), its atomic and molecular structure, temperature and pressure, composition (in the case of a mixture or solution).

The minus sign on the right side of the equation indicates that the direction of the heat flow and the temperature gradient are mutually opposite.

The ratio of the Q value to the cross-sectional area F is called the specific heat flux or heat load and is denoted by the letter q.

(18)

The values ​​of the thermal conductivity coefficient λ for some gases, liquids and solids at an atmospheric pressure of 760 mm Hg is selected from the tables.

Heat transfer. Heat transfer between two coolants through a solid wall separating them or through the interface between them. Heat transfer includes heat transfer from a hotter fluid to the wall, thermal conductivity in the wall, heat transfer from the wall to a colder moving medium. The intensity of heat transfer during heat transfer is characterized by a heat transfer coefficient k, numerically equal to the amount of heat that is transferred through a unit of wall surface per unit time at a temperature difference between liquids of 1 K; dimension k - W/(m2․K) [kcal/m2․°С)]. The value R, the reciprocal of the heat transfer coefficient, is called the total thermal resistance heat transfer. For example, R of a single-layer wall

,

where α1 and α2 are the heat transfer coefficients from the hot liquid to the wall surface and from the wall surface to the cold liquid; δ - wall thickness; λ is the coefficient of thermal conductivity. In most cases encountered in practice, the heat transfer coefficient is determined empirically. In this case, the results obtained are processed by the similarity theory methods

Radiant heat transfer - radiative heat transfer is carried out as a result of the processes of transformation of the internal energy of matter into radiation energy, the transfer of radiation energy and its absorption by matter. The course of processes of radiant heat transfer is determined by the mutual arrangement in space of the bodies exchanging heat, the properties of the medium separating these bodies. The essential difference between radiant heat transfer and other types of heat transfer (thermal conduction, convective heat transfer) is that it can also occur in the absence of a material medium separating the heat transfer surfaces, since it is carried out as a result of the propagation of electromagnetic radiation.

The radiant energy incident in the process of radiant heat transfer onto the surface of an opaque body and characterized by the value of the incident radiation flux Qinc is partially absorbed by the body and partially reflected from its surface (see Fig.).

The flux of absorbed radiation Qabs is determined by the relation:

Qabs \u003d A Qpad, (20)

where A is the absorptive capacity of the body. Due to the fact that for an opaque body

Qfall \u003d Qab + Qotr, (21)

where Qotr is the flux of radiation reflected from the surface of the body, this last value is equal to:

Qotr \u003d (1 - A) Qpad, (22)

where 1 - A \u003d R is the reflectivity of the body. If the absorptivity of a body is 1, and therefore its reflectivity is 0, that is, the body absorbs all the energy incident on it, then it is called an absolutely black body. Any body whose temperature is different from absolute zero emits energy due to the heating of the body. This radiation is called the body's own radiation and is characterized by the flux of its own radiation Qe. Self-radiation, related to the unit surface of the body, is called the flux density of its own radiation, or the emissivity of the body. The latter, in accordance with the Stefan-Boltzmann law of radiation, is proportional to the temperature of the body to the fourth power. The ratio of the emissivity of a body to the emissivity of a completely black body at the same temperature is called the degree of blackness. For all bodies, the degree of blackness is less than 1. If for some body it does not depend on the wavelength of radiation, then such a body is called gray. The nature of the distribution of radiation energy of a gray body over wavelengths is the same as that of an absolutely black body, that is, it is described by Planck's law of radiation. The degree of blackness of a gray body is equal to its absorption capacity.

The surface of any body entering the system emits fluxes of reflected radiation Qotr and its own radiation Qcob; the total amount of energy leaving the surface of the body is called the effective radiation flux Qeff and is determined by the relation:

Qeff \u003d Qotr + Qcob. (23)

Part of the energy absorbed by the body returns to the system in the form of its own radiation, so the result of radiant heat transfer can be represented as the difference between the fluxes of its own and absorbed radiation. Value

Qpez \u003d Qcob - Qabs (24)

is called the resulting radiation flux and shows how much energy the body receives or loses per unit time as a result of radiant heat transfer. The resulting radiation flux can also be expressed as

Qpez \u003d Qeff - Qpad, (25)

that is, as the difference between the total consumption and the total arrival of radiant energy on the surface of the body. Hence, given that

Qpad = (Qcob - Qpez) / A, (26)

we obtain an expression that is widely used in calculations of radiant heat transfer:

The task of calculating radiant heat transfer is, as a rule, to find the resulting radiation fluxes on all surfaces included in a given system, if the temperatures and optical characteristics of all these surfaces are known. To solve this problem, in addition to the last relation, it is necessary to find out the relationship between the flux Qinc on a given surface and the fluxes Qeff on all surfaces included in the radiant heat exchange system. To find this relationship, the concept of the average angular coefficient of radiation is used, which shows what proportion of the hemispherical (that is, emitted in all directions within the hemisphere) radiation of a certain surface included in the radiant heat exchange system falls on this surface. Thus, the flux Qfall on any surfaces included in the radiant heat exchange system is defined as the sum of the products Qeff of all surfaces (including the given one, if it is concave) and the corresponding angular coefficients of radiation.

Radiant heat transfer plays a significant role in heat transfer processes occurring at temperatures of about 1000 °C and above. It is widely used in various fields of technology: in metallurgy, thermal power engineering, nuclear power engineering, rocket technology, chemical technology, drying technology, and solar technology.

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 of 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 is the absolute body temperature.

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, it is all 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 absorption of solar and atmospheric radiation by the earth's surface. Infrared 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: the average temperature of the Earth varies little from year to year, and remains almost unchanged from one long-term period to another.