THERMAL REGIME OF THE UNDERLYING SURFACE AND ATMOSPHERE
The surface directly heated by the sun's rays and giving off heat to the underlying layers and air is called active. The temperature of the active surface, its value and change (daily and annual variation) are determined by the heat balance.
The maximum value of almost all components of the heat balance is observed in the near noon hours. The exception is the maximum heat exchange in the soil, which falls on the morning hours.
The maximum amplitudes of the diurnal variation of the heat balance components are observed in summer, the minimum - in winter. In the diurnal course of surface temperature, dry and devoid of vegetation, on a clear day, the maximum occurs after 13:00, and the minimum occurs around the time of sunrise. Cloudiness disrupts the regular course of surface temperature and causes a shift in the moments of maxima and minima. Big influence surface temperature is influenced by its humidity and vegetation cover. Daytime surface temperature maxima can be + 80°C or more. Daily fluctuations reach 40°. Their value depends on the latitude of the place, time of year, cloudiness, thermal properties of the surface, its color, roughness, vegetation cover, and slope exposure.
The annual course of the temperature of the active layer is different at different latitudes. The maximum temperature in middle and high latitudes is usually observed in June, the minimum - in January. The amplitudes of annual fluctuations in the temperature of the active layer at low latitudes are very small; at middle latitudes on land, they reach 30°. The annual fluctuations in surface temperature in temperate and high latitudes are strongly influenced by snow cover.
It takes time to transfer heat from layer to layer, and the moments of the onset of maximum and minimum temperatures during the day are delayed by every 10 cm by about 3 hours. If the highest temperature on the surface was at about 13:00, at a depth of 10 cm the temperature will reach a maximum at about 16:00, and at a depth of 20 cm - at about 19:00, etc. With successive heating of the underlying layers from the overlying ones, each layer absorbs a certain amount of heat. The deeper the layer, the less heat it receives and the weaker the temperature fluctuations in it. The amplitude of daily temperature fluctuations with depth decreases by 2 times for every 15 cm. This means that if on the surface the amplitude is 16°, then at a depth of 15 cm it is 8°, and at a depth of 30 cm it is 4°.
At an average depth of about 1 m, daily fluctuations in soil temperature "fade out". The layer in which these oscillations practically stop is called the layer constant daily temperature.
How longer period temperature fluctuations, the deeper they spread. In the middle latitudes, the layer of constant annual temperature is located at a depth of 19-20 m, in high latitudes at a depth of 25 m. In tropical latitudes, the annual temperature amplitudes are small and the layer of constant annual amplitude is located at a depth of only 5-10 m. and minimum temperatures are delayed by an average of 20-30 days per meter. Thus, if the lowest temperature on the surface was observed in January, at a depth of 2 m it occurs in early March. Observations show that the temperature in the layer of constant annual temperature is close to the average annual air temperature above the surface.
Water, having a higher heat capacity and lower thermal conductivity than land, heats up more slowly and releases heat more slowly. Some of the sun's rays falling on the water surface are absorbed by the uppermost layer, and some of them penetrate to a considerable depth, directly heating some of its layer.
The mobility of water makes heat transfer possible. Due to turbulent mixing, heat transfer in depth occurs 1000 - 10,000 times faster than through heat conduction. When the surface layers of water cool, thermal convection occurs, accompanied by mixing. Daily temperature fluctuations on the surface of the Ocean in high latitudes are on average only 0.1°, in temperate latitudes - 0.4°, in tropical latitudes - 0.5°. The penetration depth of these vibrations is 15-20m. The annual temperature amplitudes on the surface of the Ocean range from 1° in equatorial latitudes to 10.2° in temperate latitudes. Annual temperature fluctuations penetrate to a depth of 200-300 m. The moments of maximum temperature in water bodies are late compared to land. The maximum occurs at about 15-16 hours, the minimum - 2-3 hours after sunrise.
Thermal regime of the lower layer of the atmosphere.
The air is heated mainly not by the sun's rays directly, but due to the transfer of heat to it by the underlying surface (the processes of radiation and heat conduction). The most important role in the transfer of heat from the surface to the overlying layers of the troposphere is played by heat exchange and transfer of latent heat of vaporization. The random movement of air particles caused by its heating of an unevenly heated underlying surface is called thermal turbulence or thermal convection.
If instead of small chaotic moving vortices, powerful ascending (thermals) and less powerful descending air movements begin to predominate, convection is called orderly. Air warming near the surface rushes upward, transferring heat. Thermal convection can only develop as long as the air has a temperature higher than the temperature of the environment in which it rises (an unstable state of the atmosphere). If the temperature of the rising air is equal to the temperature of its surroundings, the rise will stop (an indifferent state of the atmosphere); if the air becomes colder than the environment, it will begin to sink (the steady state of the atmosphere).
With the turbulent movement of air, more and more of its particles, in contact with the surface, receive heat, and rising and mixing, give it to other particles. The amount of heat received by air from the surface through turbulence is 400 times greater than the amount of heat it receives as a result of radiation, and as a result of transfer by molecular heat conduction - almost 500,000 times. Heat is transferred from the surface to the atmosphere along with the moisture evaporated from it, and then released during the condensation process. Each gram of water vapor contains 600 calories of latent heat of vaporization.
In rising air, the temperature changes due to adiabatic process, i.e. without heat exchange with environment, by converting the internal energy of the gas into work and work into internal energy. Since the internal energy is proportional to the absolute temperature of the gas, the temperature changes. The rising air expands, performs work for which it expends internal energy, and its temperature decreases. The descending air, on the contrary, is compressed, the energy spent on expansion is released, and the air temperature rises.
Dry or containing water vapor, but not saturated with them, air, rising, cools adiabatically by 1 ° for every 100 m. Air saturated with water vapor cools by less than 1 ° when rising to 100 m, since condensation occurs in it, accompanied by release heat, partially compensating for the heat spent on expansion.
The amount of cooling of saturated air when it rises by 100 m depends on the air temperature and on atmospheric pressure and varies widely. Unsaturated air, descending, heats up by 1 ° per 100 m, saturated by a smaller amount, since evaporation takes place in it, for which heat is expended. Rising saturated air usually loses moisture during precipitation and becomes unsaturated. When lowered, such air heats up by 1 ° per 100 m.
As a result, the decrease in temperature during ascent is less than its increase during lowering, and the air that rises and then descends at the same level at the same pressure will have a different temperature - the final temperature will be higher than the initial one. Such a process is called pseudoadiabatic.
Since the air is heated mainly from the active surface, the temperature in the lower atmosphere, as a rule, decreases with height. The vertical gradient for the troposphere averages 0.6° per 100 m. It is considered positive if the temperature decreases with height, and negative if it rises. In the lower surface layer of air (1.5-2 m), vertical gradients can be very large.
The increase in temperature with height is called inversion, and a layer of air in which the temperature increases with height, - inversion layer. In the atmosphere, layers of inversion can almost always be observed. At earth's surface when it is strongly cooled, as a result of radiation, radiative inversion(radiation inversion) . It appears on clear summer nights and can cover a layer of several hundred meters. in winter in clear weather the inversion persists for several days and even weeks. Winter inversions can cover a layer up to 1.5 km.
The inversion is enhanced by the relief conditions: cold air flows into the depression and stagnates there. Such inversions are called orographic. Powerful inversions called adventitious, are formed in those cases when relatively warm air comes to a cold surface, cooling its lower layers. Daytime advective inversions are weakly expressed, at night they are enhanced by radiative cooling. In spring, the formation of such inversions is facilitated by the snow cover that has not yet melted.
Frosts are associated with the phenomenon of temperature inversion in the surface air layer. Freeze - a decrease in air temperature at night to 0 ° and below at a time when the average daily temperatures are above 0 ° (autumn, spring). It may also be that frosts are observed only on the soil when the air temperature above it is above zero.
Thermal state atmosphere affects the propagation of light in it. In cases where the temperature changes sharply with height (increases or decreases), there are mirages.
Mirage - an imaginary image of an object that appears above it (upper mirage) or below it (lower mirage). Less common are lateral mirages (the image appears from the side). The cause of mirages is the curvature of the trajectory of light rays coming from an object to the observer's eye, as a result of their refraction at the boundary of layers with different densities.
The daily and annual temperature variation in the lower troposphere up to a height of 2 km generally reflects the surface temperature variation. With distance from the surface, the amplitudes of temperature fluctuations decrease, and the moments of maximum and minimum are delayed. Daily fluctuations in air temperature in winter are noticeable up to a height of 0.5 km, in summer - up to 2 km.
The amplitude of diurnal temperature fluctuations decreases with increasing latitude. The largest daily amplitude is in subtropical latitudes, the smallest - in polar ones. In temperate latitudes, diurnal amplitudes are different at different times of the year. In high latitudes, the largest daily amplitude is in spring and autumn, in temperate latitudes - in summer.
The annual course of air temperature depends primarily on the latitude of the place. From the equator to the poles, the annual amplitude of air temperature fluctuations increases.
There are four types of annual temperature variation according to the magnitude of the amplitude and the time of the onset of extreme temperatures.
equatorial type characterized by two maxima (after the equinoxes) and two minima (after the solstices). The amplitude over the Ocean is about 1°, over land - up to 10°. The temperature is positive throughout the year.
Tropical type - one maximum (after the summer solstice) and one minimum (after the winter solstice). The amplitude over the Ocean is about 5°, on land - up to 20°. The temperature is positive throughout the year.
Moderate type - one maximum (in the northern hemisphere over land in July, over the Ocean in August) and one minimum (in the northern hemisphere over land in January, over the Ocean in February). Four seasons are clearly distinguished: warm, cold and two transitional. The annual temperature amplitude increases with increasing latitude, as well as with distance from the Ocean: on the coast 10°, away from the Ocean - up to 60° and more (in Yakutsk - -62.5°). The temperature during the cold season is negative.
Distribution of air temperature at the underlying surface.
If the earth's surface were homogeneous, and the atmosphere and hydrosphere were stationary, the distribution of heat over the Earth's surface would be determined only by the influx of solar radiation, and the air temperature would gradually decrease from the equator to the poles, remaining the same at each parallel (solar temperatures). Indeed, the average annual air temperatures are determined by the heat balance and depend on the nature of the underlying surface and the continuous interlatitudinal heat exchange carried out by moving the air and waters of the Ocean, and therefore differ significantly from the solar ones.
The actual average annual air temperatures near the earth's surface are lower in low latitudes, and, on the contrary, higher than solar ones in high latitudes. In the southern hemisphere, the actual average annual temperatures at all latitudes are lower than in the northern. The average air temperature near the earth's surface in the northern hemisphere in January is +8°C, in July +22°C; in the southern - in July + 10 ° С, in January + 17 ° С. southern hemisphere. The average air temperature for the year at the earth's surface is +14 ° C as a whole.
If we mark the highest average annual or monthly temperatures on different meridians and connect them, we get a line thermal maximum, often called the thermal equator. It is probably more correct to consider the parallel (latitudinal circle) with the highest normal average temperatures of the year or any month as the thermal equator. The thermal equator does not coincide with the geographic one and is "shifted" to the north. During the year it moves from 20° N. sh. (in July) to 0° (in January). There are several reasons for the shift of the thermal equator to the north: the predominance of land in the tropical latitudes of the northern hemisphere, the Antarctic cold pole, and, perhaps, the duration of summer matters (summer in the southern hemisphere is shorter).
Thermal belts.
Isotherms are taken beyond the boundaries of thermal (temperature) belts. There are seven thermal zones:
hot belt, located between the annual isotherm + 20 ° of the northern and southern hemispheres; two temperate zones, limited from the side of the equator by the annual isotherm + 20 °, from the poles by the isotherm + 10 ° of the warmest month;
Two cold belts, located between the isotherm + 10 ° and and the warmest month;
Two frost belts located near the poles and bounded by the 0° isotherm of the warmest month. In the northern hemisphere this is Greenland and the space near the north pole, in the southern hemisphere - the area inside the parallel of 60 ° S. sh.
Temperature zones are the basis of climatic zones. Within each belt, large variations in temperature are observed depending on the underlying surface. On land, the influence of relief on temperature is very great. The change in temperature with height for every 100 m is not the same in different temperature zones. The vertical gradient in the lower kilometer layer of the troposphere varies from 0° over the ice surface of Antarctica to 0.8° in summer over tropical deserts. Therefore, the method of bringing temperatures to sea level using an average gradient (6°/100 m) can sometimes lead to gross errors. The change in temperature with height is the cause of vertical climatic zonality.
Thermal regime of the atmosphereThermal energy enters the lower layers of the atmosphere mainly from the underlying surface. The thermal regime of these layers
is closely related to the thermal regime of the earth's surface, so its study is also one of the important tasks of meteorology.
The main physical processes in which the soil receives or gives off heat are: 1) radiant heat transfer; 2) turbulent heat exchange between the underlying surface and the atmosphere; 3) molecular heat exchange between the soil surface and the lower fixed adjacent air layer; 4) heat exchange between soil layers; 5) phase heat transfer: heat consumption for water evaporation, melting of ice and snow on the surface and in the depth of the soil, or its release during reverse processes.
The thermal regime of the surface of the earth and water bodies is determined by their thermophysical characteristics. Special attention in preparation, one should pay attention to the derivation and analysis of the soil thermal conductivity equation (Fourier equation). If the soil is uniform vertically, then its temperature t at a depth z at time t can be determined from the Fourier equation
where a- thermal diffusivity of the soil.
The consequence of this equation are the basic laws of the propagation of temperature fluctuations in the soil:
1. The law of invariance of the oscillation period with depth:
T(z) = const(2)
2. The law of decrease in the amplitude of oscillations with depth:
(3)
where and are amplitudes at depths a- thermal diffusivity of the soil layer lying between the depths ;
3. The law of the phase shift of oscillations with depth (the law of delay):
(4)
where is the delay, i.e. the difference between the moments of the onset of the same phase of oscillations (for example, maximum) at depths and Temperature fluctuations penetrate the soil to a depth znp defined by the ratio:
(5)
In addition, it is necessary to pay attention to a number of consequences from the law of decrease in the amplitude of oscillations with depth:
a) the depths at which in different soils ( ) amplitudes of temperature fluctuations with the same period ( = T 2) decrease by the same number of times relate to each other as square roots of the thermal diffusivity of these soils
b) the depths at which in the same soil ( a= const) amplitudes of temperature fluctuations with different periods ( ) decrease by the same amount =const, are related to each other as the square roots of the periods of oscillations
(7)
It is necessary to clearly understand the physical meaning and features of the formation of heat flow into the soil.
The surface density of the heat flux in the soil is determined by the formula:
where λ is the coefficient of thermal conductivity of the soil vertical temperature gradient.
Instant value R are expressed in kW/m to the nearest hundredth, the sums R - in MJ / m 2 (hourly and daily - up to hundredths, monthly - up to units, annual - up to tens).
The average surface heat flux density through the soil surface over a time interval t is described by the formula
where C is the volumetric heat capacity of the soil; interval; z „ p- depth of penetration of temperature fluctuations; ∆tcp- the difference between the average temperatures of the soil layer to the depth znp at the end and at the beginning of the interval m. Let us give the main examples of tasks on the topic “Thermal regime of the soil”.
Task 1. At what depth does it decrease in e times the amplitude of diurnal fluctuations in soil with a coefficient of thermal diffusivity a\u003d 18.84 cm 2 / h?
Solution. It follows from equation (3) that the amplitude of diurnal fluctuations will decrease by a factor of e at a depth corresponding to the condition
Task 2. Find the depth of penetration of daily temperature fluctuations into granite and dry sand, if the extreme surface temperatures of neighboring areas with granite soil are 34.8 °C and 14.5 °C, and with dry sandy soil 42.3 °C and 7.8 °C . thermal diffusivity of granite a g \u003d 72.0 cm 2 / h, dry sand a n \u003d 23.0 cm 2 / h.
Solution. The temperature amplitude on the surface of granite and sand is equal to:
The penetration depth is considered by the formula (5):
Due to the greater thermal diffusivity of granite, we also obtained a greater penetration depth of daily temperature fluctuations.
Task 3. Assuming that the temperature of the upper soil layer changes linearly with depth, one should calculate the surface heat flux density in dry sand if its surface temperature is 23.6 "FROM, and the temperature at a depth of 5 cm is 19.4 °C.
Solution. The temperature gradient of the soil in this case is equal to:
Thermal conductivity of dry sand λ= 1.0 W/m*K. The heat flux into the soil is determined by the formula:
P = -λ - = 1.0 84.0 10 "3 \u003d 0.08 kW / m 2
The thermal regime of the surface layer of the atmosphere is determined mainly by turbulent mixing, the intensity of which depends on dynamic factors (roughness of the earth's surface and wind speed gradients at different levels, scale of movement) and thermal factors (inhomogeneity of heating of various parts of the surface and vertical temperature distribution).
To characterize the intensity of turbulent mixing, the turbulent exchange coefficient is used BUT and turbulence coefficient TO. They are related by the ratio
K \u003d A / p(10)
where R - air density.
Turbulence coefficient To measured in m 2 / s, accurate to hundredths. Usually, in the surface layer of the atmosphere, the turbulence coefficient is used TO] on high G"= 1 m. Within the surface layer:
where z- height (m).
You need to know the basic methods for determining TO\.
Task 1. Calculate the surface density of the vertical heat flux in the surface layer of the atmosphere through the area at which the air density is normal, the turbulence coefficient is 0.40 m 2 /s, and the vertical temperature gradient is 30.0 °C/100m.
Solution. We calculate the surface density of the vertical heat flux by the formula
L=1.3*1005*0.40*
Study the factors affecting the thermal regime of the surface layer of the atmosphere, as well as periodic and non-periodic changes in the temperature of the free atmosphere. The equations of heat balance of the earth's surface and atmosphere describe the law of conservation of energy received by the active layer of the Earth. Consider the daily and annual course of the heat balance and the reasons for its changes.
Literature
Chapter Sh, ch. 2, § 1 -8.
Questions for self-examination
1. What factors determine the thermal regime of soil and water bodies?
2. What is the physical meaning of thermophysical characteristics and how do they affect the temperature regime of soil, air, water?
3. What do the amplitudes of daily and annual fluctuations in soil surface temperature depend on and how do they depend on?
4. Formulate the basic laws of distribution of temperature fluctuations in the soil?
5. What are the consequences of the basic laws of the distribution of temperature fluctuations in the soil?
6. What are the average depths of penetration of daily and annual temperature fluctuations in the soil and in water bodies?
7. What is the effect of vegetation and snow cover on the thermal regime of the soil?
8. What are the features of the thermal regime of water bodies, in contrast to the thermal regime of the soil?
9. What factors influence the intensity of turbulence in the atmosphere?
10. What quantitative characteristics of turbulence do you know?
11. What are the main methods for determining the turbulence coefficient, their advantages and disadvantages?
12. Draw and analyze the daily course of the turbulence coefficient over land and water surfaces. What are the reasons for their difference?
13. How is the surface density of the vertical turbulent heat flux in the surface layer of the atmosphere determined?
B - glad. Balance, P- heat received at molek. heat exchange with the surface Earth. Len - received from condens. moisture.
Heat balance of the atmosphere:
B - glad. Balance, P- heat costs per molecule. heat exchange with the lower layers of the atmosphere. Gn - heat costs per molecule. heat exchange with the lower soil layers Len is the heat consumption for moisture evaporation.
Rest on the map
10) Thermal regime of the underlying surface:
The surface that is directly heated by the sun's rays and gives off heat to the underlying soil layers and air is called the active surface.
The temperature of the active surface is determined by the thermal balance.
The daily temperature course of the active surface reaches a maximum of 13 hours, the minimum temperature is around the moment of sunrise. Maksim. and min. temperatures during the day can shift due to cloudiness, soil moisture and vegetation cover.
The temperature value depends on:
In the annual course of temperatures, the maximum in medium and high meal in the northern hemisphere is observed in July, and the minimum in January. At low latitudes, the annual amplitudes of temperature fluctuations are small.
The temperature distribution in depth depends on the heat capacity and its thermal conductivity. It takes time to transfer heat from layer to layer, for every 10 meters of successive heating of the layers, each layer absorbs part of the heat, so the deeper the layer, the less heat it receives, and the less temperature fluctuation in it. on average, at a depth of 1 m, daily fluctuations in temperature stop, annual fluctuations in low latitudes end at a depth of 5-10 m. in middle latitudes up to 20 m. in high 25 m. The layer of constant temperatures, the layer of soil which is located between the active surface and the layer of constant temperatures, is called the active layer.
Distribution features. Fourier was involved in the temperature in the earth, he formulated the laws of heat propagation in the soil, or "Fourier's laws":
1))). The greater the density and moisture of the soil, the better it conducts heat, the faster the distribution in depth and the deeper the heat penetrates. Temperature does not depend on soil types. The oscillation period does not change with depth
2))). An increase in depth in an arithmetic progression leads to a decrease in the temperature amplitude in a geometric progression.
3))) The timing of the onset of maximum and minimum temperatures, both in the daily and in the annual course of temperatures, decays with depth in proportion to the increase in depth.
11.Heating of the atmosphere. Advection.. The main source of life and many natural processes on Earth is the radiant energy of the Sun, or the energy of solar radiation. Every minute, 2.4 x 10 18 cal of solar energy enters the Earth, but this is only one two-billionth of it. Distinguish between direct radiation (directly coming from the Sun) and diffuse (radiated by air particles in all directions). Their totality, arriving on a horizontal surface, is called total radiation. The annual value of the total radiation depends primarily on the angle of incidence of the sun's rays on the earth's surface (which is determined by geographic latitude), on the transparency of the atmosphere and the duration of illumination. In general, the total radiation decreases from the equatorial-tropical latitudes towards the poles. It is maximum (about 850 J / cm 2 per year, or 200 kcal / cm 2 per year) - in tropical deserts, where direct solar radiation is most intense due to the high altitude of the Sun and a cloudless sky.
The sun mainly heats the surface of the Earth, it heats the air from it. Heat is transferred to the air by radiation and conduction. The air heated from the earth's surface expands and rises - this is how convective currents are formed. The ability of the earth's surface to reflect the sun's rays is called albedo: snow reflects up to 90% of solar radiation, sand - 35%, and the wet soil surface about 5%. That part of the total radiation that remains after spending it on reflection and on thermal radiation from the earth's surface is called the radiation balance (residual radiation). The radiation balance regularly decreases from the equator (350 J/cm 2 per year, or about 80 kcal/cm 2 per year) to the poles, where it is close to zero. From the equator to the subtropics (forties), the radiation balance throughout the year is positive, in temperate latitudes in winter it is negative. The air temperature also decreases towards the poles, which is well reflected by isotherms - lines connecting points with the same temperature. The isotherms of the warmest month are the boundaries of seven thermal zones. The hot zone is limited by isotherms +20 °c to +10 °c, two moderate poles extend, from +10 °c to 0 °c - cold. Two subpolar frost regions are outlined by a zero isotherm - here ice and snow practically do not melt. The mesosphere extends up to 80 km, in which the air density is 200 times less than at the surface, and the temperature again decreases with height (up to -90 °). This is followed by the ionosphere consisting of charged particles (auroras occur here), its other name is the thermosphere - this shell received due to extremely high temperatures (up to 1500 °). Layers above 450 km, some scientists call the exosphere, from here particles escape into outer space.
The atmosphere protects the Earth from excessive overheating during the day and cooling at night, protects all life on Earth from ultraviolet solar radiation, meteorites, corpuscular streams and cosmic rays.
advection- the movement of air in the horizontal direction and the transfer with it of its properties: temperature, humidity, and others. In this sense one speaks, for example, of the advection of heat and cold. The advection of cold and warm, dry and humid air masses plays an important role in meteorological processes and thus affects the state of the weather.
Convection- the phenomenon of heat transfer in liquids, gases or granular media by flows of the substance itself (it does not matter if it is forced or spontaneous). There is a so-called. natural convection, which occurs spontaneously in a substance when it is heated unevenly in a gravitational field. With such convection, the lower layers of matter heat up, become lighter and float up, while the upper layers, on the contrary, cool down, become heavier and sink down, after which the process repeats again and again. Under certain conditions, the mixing process self-organizes into the structure of individual vortices and a more or less regular lattice of convection cells is obtained.
Distinguish between laminar and turbulent convection.
Natural convection owes many atmospheric phenomena, including the formation of clouds. Thanks to the same phenomenon, tectonic plates move. Convection is responsible for the appearance of granules on the Sun.
adiabatic process- a change in the thermodynamic state of air that proceeds adiabatically (isentropically), that is, without heat exchange between it and the environment (the earth's surface, space, other air masses).
12. Temperature inversions in the atmosphere, an increase in air temperature with height instead of the usual for troposphere her decline. Temperature inversions are also found near the earth's surface (surface Temperature inversions), and in a free atmosphere. Surface Temperature inversions most often formed on calm nights (in winter, sometimes during the day) as a result of intense heat radiation from the earth's surface, which leads to cooling of both itself and the adjacent air layer. Surface thickness Temperature inversions is tens to hundreds of meters. The increase in temperature in the inversion layer ranges from tenths of degrees to 15-20 °C and more. The most powerful winter ground Temperature inversions in Eastern Siberia and Antarctica.
In the troposphere, above the ground layer, Temperature inversions more often they are formed in anticyclones due to air settling, accompanied by its compression, and, consequently, heating (settling inversion). In zones atmospheric fronts Temperature inversions are created as a result of the inflow of warm air onto the underlying cold one. Upper atmosphere (stratosphere, mesosphere, thermosphere) Temperature inversions due to strong absorption of solar radiation. So, at altitudes from 20-30 to 50-60 km located Temperature inversions associated with the absorption of solar ultraviolet radiation by ozone. At the base of this layer, the temperature is from -50 to -70°C, at its upper boundary it rises to -10 - +10°C. Powerful Temperature inversions, starting at an altitude of 80-90 km and extending for hundreds km up, is also due to the absorption of solar radiation.
Temperature inversions are the delaying layers in the atmosphere; they prevent the development of vertical air movements, as a result of which water vapor, dust, and condensation nuclei accumulate under them. This favors the formation of layers of haze, fog, clouds. Due to the anomalous refraction of light in Temperature inversions sometimes arise mirages. AT Temperature inversions are also formed atmospheric waveguides, favorable to the distant propagation of radio waves.
13.Types of annual temperature variation.G The annual course of air temperature in different geographical areas is diverse. According to the magnitude of the amplitude and the time of onset of extreme temperatures, four types of annual variation in air temperature are distinguished.
equatorial type. AT equatorial zone there are two in a year
maximum temperature - after the spring and autumn equinoxes, when
the sun over the equator at noon is at its zenith, and two minima are after
winter and summer solstices, when the sun is at its lowest
height. The amplitudes of the annual variation are small here, which is explained by the small
change in heat gain during the year. Over the oceans, the amplitudes are
about 1 °С, and over the continents 5-10 °С.
Tropical type. In tropical latitudes, there is a simple annual cycle
air temperature with a maximum after summer and a minimum after winter
solstice. Amplitudes of the annual cycle with distance from the equator
increase in winter. The average amplitude of the annual cycle over the continents
is 10 - 20 ° C, over the oceans 5 - 10 ° C.
Temperate type. In temperate latitudes, there is also an annual variation
temperatures with a maximum after the summer and a minimum after the winter
solstice. Over the continents of the northern hemisphere, the maximum
the average monthly temperature is observed in July, over the seas and coasts - in
August. Annual amplitudes increase with latitude. over the oceans and
coasts, they average 10-15 ° C, and at a latitude of 60 ° reach
polar type. polar regions characterized by prolonged cold
in winter and relatively short cool summers. Annual amplitudes over
the ocean and the coasts of the polar seas are 25-40 ° C, and on land
exceed 65 ° C. The maximum temperature is observed in August, the minimum - in
The considered types of annual variation of air temperature are revealed from
long-term data and represent regular periodic fluctuations.
In some years, under the influence of intrusions of warm and cold masses,
deviations from the given types.
14. Characteristics of air humidity.
Air humidity, the content of water vapor in the air; one of the most essential characteristics of weather and climate. V. in. is of great importance in certain technological processes, the treatment of a number of diseases, the storage of works of art, books, etc.
V.'s characteristics in. serve: 1) elasticity (or partial pressure) e water vapor, expressed in n/m 2 (in mmHg Art. or in mb), 2) absolute humidity a - the amount of water vapor in g/m 3; 3) specific humidity q- the amount of water vapor in G on the kg humid air; 4) mixture ratio w, determined by the amount of water vapor in G on the kg dry air; 5) relative humidity r- elasticity ratio e water vapor contained in the air to maximum elasticity E water vapor saturating the space above a flat surface of pure water (saturation elasticity) at a given temperature, expressed in%; 6) moisture deficiency d- the difference between the maximum and actual elasticity of water vapor at a given temperature and pressure; 7) dew point τ - the temperature that air will take if it is cooled isobarically (at constant pressure) to the state of saturation of the water vapor in it.
V. in. the earth's atmosphere varies widely. Thus, near the earth's surface, the content of water vapor in the air averages from 0.2% by volume in high latitudes to 2.5% in the tropics. Accordingly, the vapor pressure e in polar latitudes in winter less than 1 mb(sometimes only hundredths mb) and in summer below 5 mb; in the tropics it rises to 30 mb, and sometimes more. In subtropical deserts e lowered to 5-10 mb (1 mb = 10 2 n/m 2). Relative Humidity r very high in the equatorial zone (average annual up to 85% or more), as well as in polar latitudes and in winter inside the continents of middle latitudes - here due to low air temperature. In summer, monsoon regions are characterized by high relative humidity (India - 75-80%). Low values r are observed in subtropical and tropical deserts and in winter in monsoon regions (up to 50% and below). With height r, a and q are rapidly decreasing. At a height of 1.5-2 km vapor pressure is on average half that of the earth's surface. To the troposphere (lower 10-15 km) accounts for 99% of the water vapor in the atmosphere. On average over each m 2 of the earth's surface in the air contains about 28.5 kg water vapor.
The daily course of vapor pressure over the sea and in coastal areas is parallel to the daily course of air temperature: the moisture content increases during the day with an increase in evaporation. It's the same daily routine. e in the central regions of the continents during the cold season. A more complex diurnal variation with two maxima - in the morning and in the evening - is observed in the depths of the continents in summer. Daily variation of relative humidity r is inverse to the diurnal variation of temperature: in the daytime with an increase in temperature and, consequently, with an increase in saturation elasticity E relative humidity decreases. The annual course of vapor pressure is parallel to the annual course of air temperature; Relative humidity changes with the annual course inversely to temperature. V. in. measured hygrometers and psychrometers.
15. Evaporation- the physical process of the transition of matter from liquid state into gaseous (steam) from the surface of the liquid. The evaporation process is the reverse of the condensation process (transition from vapor to liquid).
The evaporation process depends on the intensity of the thermal motion of the molecules: the faster the molecules move, the faster the evaporation occurs. In addition, important factors affecting the evaporation process are the rate of external (with respect to the substance) diffusion, as well as the properties of the substance itself. Simply put, with wind, evaporation occurs much faster. As for the properties of the substance, then, for example, alcohol evaporates much faster than water. An important factor is also the surface area of the liquid from which evaporation occurs: from a narrow decanter, it will occur more slowly than from a wide plate.
Evaporation- the maximum possible evaporation under given meteorological conditions from a sufficiently moist underlying surface, that is, under conditions of an unlimited supply of moisture. Evaporation is expressed in millimeters of evaporated water and is very different from actual evaporation, especially in the desert, where evaporation is close to zero and evaporation is 2000 mm per year or more.
16.condensation and sublimation. Condensation consists in changing the form of water from its gaseous state (water vapor) to liquid water or ice crystals. Condensation mainly occurs in the atmosphere when warm air rises, cools and loses its ability to contain water vapor (a state of saturation). As a result, excess water vapor condenses in the form of drop clouds. The upward movement that clouds form can be caused by convection in unsustainably stratified air, convergence associated with cyclones, rising air by fronts, and rising over elevated topography such as mountains.
Sublimation- the formation of ice crystals (frost) immediately from water vapor without passing them into water or their rapid cooling below 0 ° C at a time when the air temperature is still above this radiative cooling, which happens on quiet clear nights in the cold part of the year.
Dew- view precipitation formed on the surface of the earth, plants, objects, roofs of buildings, cars and other objects.
Due to the cooling of the air, water vapor condenses on objects near the ground and turns into water droplets. This usually happens at night. In desert regions, dew is an important source of moisture for vegetation. A sufficiently strong cooling of the lower layers of air occurs when, after sunset, the surface of the earth is rapidly cooled by thermal radiation. Favorable conditions for this are a clear sky and a surface covering that easily gives off heat, such as grass. Especially strong dew formation occurs in tropical regions, where the air in the surface layer contains a lot of water vapor and, due to the intense nighttime thermal radiation of the earth, is significantly cooled. Frost forms at low temperatures.
The air temperature below which dew falls is called the dew point.
Frost- a type of precipitation, which is a thin layer of ice crystals formed from atmospheric water vapor. It is often accompanied by fog. Just like dew, it is formed due to cooling of the surface to negative temperatures, lower than the air temperature, and desublimation of water vapor on the surface, which has cooled below 0 ° C. Frost particles resemble snowflakes in shape, but differ from them in less regularity, since they are born in less equilibrium conditions, on the surface of some objects.
frost- type of precipitation.
Hoarfrost is a deposit of ice on thin and long objects (tree branches, wires) in fog.
Directly from the sun's rays, the earth's surface is heated, and already from it - the atmosphere. The surface that receives and gives off heat is called active surface . In the temperature regime of the surface, the daily and annual temperature variations are distinguished. The diurnal variation of surface temperatures – change in surface temperature during the day. The daily course of land surface temperatures (dry and devoid of vegetation) is characterized by one maximum at about 13:00 and one minimum before sunrise. Daytime maxima of land surface temperature can reach 80 0 C in the subtropics and about 60 0 C in temperate latitudes.
Difference between maximum and minimum daily temperature surface is called daily temperature range. The daily temperature amplitude can reach 40 0 С in summer, the smallest amplitude of daily temperatures in winter - up to 10 0 С.
Annual variation of surface temperature- change in the average monthly surface temperature during the year, due to the course of solar radiation and depends on the latitude of the place. In temperate latitudes, the maximum land surface temperatures are observed in July, the minimum - in January; on the ocean, the highs and lows are a month late.
Annual amplitude of surface temperatures equal to the difference between the maximum and minimum average monthly temperatures; increases with increasing latitude of the place, which is explained by the increase in fluctuations in the magnitude of solar radiation. The annual temperature amplitude reaches its greatest values on the continents; much less on the oceans and seashores. The smallest annual temperature amplitude is observed in the equatorial latitudes (2-3 0), the largest - in the subarctic latitudes on the continents (more than 60 0).
Thermal regime of the atmosphere. Atmospheric air is slightly heated by direct sunlight. Because the air shell freely passes the sun's rays. The atmosphere is heated by the underlying surface. Heat is transferred to the atmosphere by convection, advection and condensation of water vapor. The layers of air, being heated by the soil, become lighter and rise upwards, while the colder, hence heavier, air descends. As a result of thermal convection heating of high layers of air. The second heat transfer process is advection– horizontal air transfer. The role of advection is to transfer heat from low to high latitudes; in the winter season, heat is transferred from the oceans to the continents. Water vapor condensation- an important process that transfers heat to high layers of the atmosphere - during evaporation, heat is taken from the evaporating surface, during condensation in the atmosphere, this heat is released.
Temperature decreases with height. The change in air temperature per unit distance is called vertical temperature gradient on average, it is 0.6 0 per 100 m. At the same time, the course of this decrease in different layers of the troposphere is different: 0.3-0.4 0 up to a height of 1.5 km; 0.5-0.6 - between heights of 1.5-6 km; 0.65-0.75 - from 6 to 9 km and 0.5-0.2 - from 9 to 12 km. In the surface layer (2 m thick), the gradients, when converted to 100 m, are hundreds of degrees. In rising air, the temperature changes adiabatically. adiabatic process - the process of changing the air temperature during its vertical movement without heat exchange with the environment (in one mass, without heat exchange with other media).
Exceptions are often observed in the described vertical temperature distribution. It happens that the upper layers of air are warmer than the lower ones adjacent to the ground. This phenomenon is called temperature inversion (increase in temperature with height) . Most often, an inversion is a consequence of a strong cooling of the surface layer of air caused by a strong cooling of the earth's surface on clear, quiet nights, mainly in winter. With a rugged relief, cold air masses slowly flow down along the slopes and stagnate in depressions, depressions, etc. Inversions can also form when air masses move from warm to cold regions, since when heated air flows onto a cold underlying surface, its lower layers noticeably cool (compression inversion).