Temperature regime of the underlying surface. Thermal regime of the atmosphere and the earth's surface

Thermal regime earth's surface. Solar radiation coming to the Earth heats mainly its surface. The thermal state of the earth's surface is therefore the main source of heating and cooling of the lower layers of the atmosphere.

The conditions for heating the earth's surface depend on its physical properties. First of all, there are sharp differences in the heating of the surface of land and water. On land, heat propagates in depth mainly by inefficient molecular heat conduction. In this regard, daily temperature fluctuations on the land surface extend only to a depth of 1 m, and annual - up to 10-20 m. In the water surface, the temperature spreads in depth mainly by mixing the water masses; molecular thermal conductivity is negligible. In addition, deeper penetration of radiation into water plays a role here, as well as a higher heat capacity of water compared to land. Therefore, daily and annual temperature fluctuations propagate in water to a greater depth than on land: daily - by tens of meters, annual - by hundreds of meters. As a result, heat entering and leaving the earth's surface is distributed in a thinner layer of land than the water surface. This means that the daily and annual temperature fluctuations on the land surface must be much greater than on the water surface. Since air is heated from the earth's surface, then with the same value of solar radiation in summer and during the day, the air temperature over land will be higher than over the sea, and vice versa in winter and at night.

The heterogeneity of the land surface also affects the conditions of its heating. Vegetation during the day prevents the strong heating of the soil, and at night reduces its cooling. Snow cover protects the soil from excessive heat loss in winter. Diurnal temperature amplitudes under vegetation will thus be reduced. The combined effect of vegetation cover in summer and snowy winter reduces the annual temperature amplitude compared to the bare surface.

The extreme limits of land surface temperature fluctuations are as follows. In the deserts of the subtropics, the temperature can rise to +80°, on the snowy surface of Antarctica it can drop to -90°.

On the water surface, the moments of the onset of the maximum and minimum temperature in the daily and annual course are shifted compared to land. The daily maximum occurs around 15-16 hour, at least 2-3 hour after sunrise. The annual maximum temperature of the ocean surface occurs in the northern hemisphere in August, the annual minimum - in February. The maximum observed temperature of the ocean surface is about 27°, the surface of inland water basins is 45°; the minimum temperature is -2 and -13°, respectively.

Thermal regime of the atmosphere.The change in air temperature is determined by several reasons: solar and terrestrial radiation, molecular thermal conductivity, evaporation and condensation of water vapor, adiabatic changes and heat transfer with air mass.

For the lower layers of the atmosphere, direct absorption of solar radiation has no effect. great importance, their absorption of long-wave terrestrial radiation is much more significant. Molecular thermal conductivity heats the air immediately adjacent to the earth's surface. When water evaporates, heat is expended, and consequently, the air cools; when water vapor condenses, heat is released, and the air heats up.

has a great influence on the distribution of air temperature adiabatic change her, i.e., a change in temperature without heat exchange with the surrounding air. Rising air expands; work is expended on expansion, which leads to a decrease in temperature. When the air is lowered, the reverse process occurs. Dry or non-saturated air cools adiabatically every 100 m lift by 1°. Air saturated with water vapor cools down by a smaller amount (on average by 0.6 per 100 m rise), since in this case condensation of water vapor occurs, which is accompanied by the release of heat.

The transfer of heat together with the mass of air has a particularly great influence on the thermal regime of the atmosphere. As a result general circulation atmosphere, both vertical and horizontal movement of air masses occurs all the time, capturing the entire thickness of the troposphere and penetrating even into the lower stratosphere. The first is called convection second - advection. These are the main processes that determine the actual distribution of air temperature over land and sea surfaces and at different altitudes. Adiabatic processes are only a physical consequence of temperature changes in air moving according to the laws of atmospheric circulation. The role of heat transfer together with the mass of air can be judged by the fact that the amount of heat received by air as a result of convection is 4,000 times greater than the heat received by radiation from the earth's surface, and 500,000 times more

than the heat generated by molecular heat conduction. Based on the equation of state for gases, the temperature should decrease with height. However, when special conditions heating and cooling air temperature may increase with altitude. Such a phenomenon is called temperature inversion. An inversion occurs when the earth's surface is strongly cooled as a result of radiation, when cold air flows into depressions, when air moves downward in a free atmosphere, i.e. above the level of friction. Temperature inversions play an important role in the circulation of the atmosphere and affect the weather and climate. The daily and annual course of air temperature depends on the course of solar radiation. However, the onset of the temperature maximum and minimum is delayed in relation to the maximum and minimum of solar radiation. After noon, the influx of heat from the Sun begins to decrease, but the air temperature continues to rise for some time, because the decrease in solar radiation is replenished by heat radiation from the earth's surface. At night, the decrease in temperature continues until sunrise due to terrestrial heat radiation (Fig. 11). A similar pattern applies to the annual temperature variation. The amplitude of fluctuations in air temperature is less than that of the earth's surface, and with distance from the surface, the amplitude of fluctuations naturally decreases, and the moments of maximum and minimum temperature are more and more late. The magnitude of diurnal temperature fluctuations decreases with increasing latitude and with increasing cloudiness and precipitation. Over the water surface, the amplitude is much less than over land.

If the earth's surface were homogeneous, and the atmosphere and hydrosphere were stationary, then the distribution of heat over the 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. This temperature is called solar.

Actual temperatures depend on the nature of the surface and interlatitudinal heat exchange and differ significantly from solar temperatures. Average annual temperatures at different latitudes in degrees are shown in Table. 1.

A visual representation of the distribution of air temperature on the earth's surface is shown by maps of isotherms - lines connecting points with the same temperatures (Fig. 12, 13).

As can be seen from the maps, the isotherms strongly deviate from parallels, which is explained by a number of reasons: unequal heating of land and sea, the presence of warm and cold sea currents, the influence of general atmospheric circulation (for example, westerly transport in temperate latitudes), the influence of relief (barrier effect on movement air of mountain systems, the accumulation of cold air in intermountain basins, etc.), the magnitude of the albedo (for example, the large albedo of the snow-ice surface of Antarctica and Greenland).

The absolute maximum air temperature on Earth is observed in Africa (Tripoli) - about +58°. The absolute minimum is noted in Antarctica (-88°).

Based on the distribution of isotherms, thermal belts on the earth's surface are distinguished. The tropics and polar circles, limiting the belts with a sharp change in the illumination regime (see Chap. 1), are, in the first approximation, the boundaries of the change in the thermal regime. Since the actual air temperatures differ from solar ones, characteristic isotherms are taken as thermal zones. Such isotherms are: annual 20° (border of pronounced seasons of the year and small temperature amplitude), the warmest month 10° (forest distribution boundary) and the warmest month 0° (border of eternal frost).

Between the annual isotherms of 20 ° of both hemispheres is located hot belt, between the annual isotherm of 20° and the isotherm of the

Post Views: 873

Thermal 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. During preparation, special attention should be paid 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.

A consequence of this equation are the basic laws of propagation temperature fluctuations in 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 in the same number times are related 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 "WITH, 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 (the roughness of the earth's surface and wind speed gradients at different levels, the 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 A and turbulence coefficient TO. They are related by the relation

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 the level of which the air density is equal to 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?

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 noted in summer time, minimum - in winter. IN daily course surface temperature, dry and devoid of vegetation, on a clear day, the maximum occurs after 13:00, and the minimum - around the time of sunrise. Cloudiness disrupts the regular course of surface temperature and causes a shift in the moments of maxima and minima. Humidity and vegetation cover greatly influence the surface temperature. 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 on the surface highest temperature was about 13 hours, at a depth of 10 cm the maximum temperature will come at about 16 hours, and at a depth of 20 cm - about 19 hours, 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, the daily fluctuations in soil temperature "fade out". The layer in which these oscillations practically stop is called the layer constant daily temperature.

The longer the period of 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. Part of the sun's rays falling on the water surface is absorbed by the uppermost layer, and part of them penetrates 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, more quantity heat received by him as a result of radiation, 400 times and as a result of transmission 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.

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 the earth's surface, when it is strongly cooled, as a result of radiation, radiative inversion(radiation inversion) . She appears in the 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.

The thermal state of the 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.

polar type - winter is very long and cold, summer is short and cool. Annual amplitudes are 25° and more (over land up to 65°). The temperature is negative most of the year. The overall picture of the annual course of air temperature is complicated by the influence of factors, among which the underlying surface is of particular importance. Over the water surface, the annual temperature variation is smoothed out; over land, on the contrary, it is more pronounced. Snow and ice cover greatly reduces annual temperatures. The height of the place above the level of the Ocean, relief, distance from the Ocean, and cloudiness also affect. The smooth course of the annual air temperature is disturbed by disturbances caused by the intrusion of cold or, conversely, warm air. An example can be spring returns of cold weather (cold waves), autumn returns of heat, winter thaws in temperate latitudes.

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). Really average annual temperatures air are determined by the thermal balance and depend on the nature of the underlying surface and the continuous interlatitudinal heat exchange carried out by the movement of air and waters of the Ocean, and therefore differ significantly from solar ones.

The actual average annual air temperatures near the earth's surface in low latitudes are lower, and in high latitudes, on the contrary, they are higher than solar ones. In the southern hemisphere, the actual average annual temperatures at all latitudes are lower than in the northern. average temperature air near the earth's surface in the northern hemisphere in January + 8 ° С, in July + 22 ° С; in the south - in July + 10 ° C, in January + 17 ° C. Annual amplitudes of air temperature fluctuations, components for northern hemisphere 14°, and for the southern only 7°, indicate a lesser continentality of the 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 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 belts, limited from the side of the equator by the annual isotherm + 20 °, from the side of 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.

WATER IN THE ATMOSPHERE

The earth's atmosphere contains about 14,000 km 3 of water vapor. Water enters the atmosphere mainly as a result of evaporation from the Earth's surface. Moisture condenses in the atmosphere, is carried by air currents and falls back to the earth's surface. There is a constant cycle of water, possible due to its ability to be in three states (solid, liquid and vapor) and easily move from one state to another.

Characteristics of air humidity.

Absolute humidity - the content of water vapor in the atmosphere in grams per 1 m 3 of air ("; a";).

Relative humidity - the ratio of the actual water vapor pressure to saturation elasticity, expressed as a percentage. Relative humidity characterizes the degree of saturation of air with water vapor.

Humidity deficiency- lack of saturation at a given temperature:

Dew point - the temperature at which water vapor in the air saturates it.

Evaporation and evaporation. Water vapor enters the atmosphere through evaporation from the underlying surface (physical evaporation) and transpiration. The process of physical evaporation consists in overcoming cohesive forces by rapidly moving water molecules, in separating them from the surface and passing into the atmosphere. The higher the temperature of the evaporating surface, the faster the movement of molecules and the more of them enters the atmosphere.

When the air is saturated with water vapor, the evaporation process stops.

The evaporation process requires heat: the evaporation of 1 g of water requires 597 cal, the evaporation of 1 g of ice requires 80 cal more. As a result, the temperature of the evaporating surface decreases.

Evaporation from the ocean at all latitudes is much greater than evaporation from land. Its maximum value for the Ocean reaches 3000 cm per year. In tropical latitudes, the annual amounts of evaporation from the surface of the Ocean are the largest and it changes little during the year. In temperate latitudes, the maximum evaporation from the Ocean is in winter, in polar latitudes - in summer. The maximum evaporation from the land surface is 1000 mm. Its differences in latitudes are determined by the radiation balance and moisture. In general, in the direction from the equator to the poles, in accordance with the decrease in temperature, evaporation decreases.

In the absence of a sufficient amount of moisture on the evaporating surface, evaporation cannot be large even at high temperatures and a huge moisture deficit. Possible evaporation - evaporation- in this case is very large. Above the water surface, evaporation and evaporation coincide. Over land, evaporation can be much less than evaporation. Evaporation characterizes the amount of possible evaporation from land with sufficient moisture. Daily and annual variations in air humidity. Air humidity is constantly changing due to changes in the temperature of the evaporating surface and air, the ratio of evaporation and condensation processes, and moisture transfer.

Daily variation of absolute air humidity may be single or double. The first one coincides with the daily temperature variation, has one maximum and one minimum, and is typical for places with a sufficient amount of moisture. It can be observed over the Ocean, and in winter and autumn over land. The double move has two highs and two lows and is typical for land. The morning minimum before sunrise is explained by very weak evaporation (or even its absence) during the night hours. With an increase in income radiant energy The evaporation of the sun is growing absolute humidity reaches a maximum around 9 o'clock. As a result, the developing convection - the transfer of moisture to the upper layers - occurs faster than its entry into the air from the evaporating surface, therefore, at about 16:00, a second minimum occurs. By evening, convection stops, and evaporation from the surface heated during the day is still quite intense and moisture accumulates in the lower layers of the air, creating a second (evening) maximum around 20-21 hours.

The annual course of absolute humidity also corresponds to the annual course of temperature. In summer the absolute humidity is the highest, in winter it is the lowest. The daily and annual course of relative humidity is almost everywhere opposite to the course of temperature, since the maximum moisture content increases faster than absolute humidity with increasing temperature.

The daily maximum of relative humidity occurs before sunrise, the minimum - at 15-16 hours. During the year, the maximum relative humidity, as a rule, falls on the most cold month, minimum - on the warmest. The exceptions are areas in which moist winds blow from the sea in summer, and dry winds from the mainland in winter.

The distribution of air humidity. The moisture content in the air in the direction from the equator to the poles generally decreases from 18-20 mb to 1-2. The maximum absolute humidity (more than 30 g / m 3) was recorded over the Red Sea and in the delta of the river. Mekong, the largest average annual (more than 67 g / m 3) - over the Bay of Bengal, the smallest average annual (about 1 g / m 3) and the absolute minimum (less than 0.1 g / m 3) - over Antarctica. Relative humidity changes relatively little with latitude: for example, at latitudes 0-10° it is a maximum of 85%, at latitudes 30-40° - 70% and at latitudes 60-70° - 80%. A noticeable decrease in relative humidity is observed only at latitudes of 30-40° in the northern and southern hemispheres. The highest average annual value of relative humidity (90%) was observed at the mouth of the Amazon, the lowest (28%) - in Khartoum (Nile Valley).

condensation and sublimation. In air saturated with water vapor, when its temperature drops to the dew point or the amount of water vapor in it increases, condensation - water changes from a vapor state to a liquid state. At temperatures below 0 ° C, water can, bypassing the liquid state, go into a solid state. This process is called sublimation. Both condensation and sublimation can occur in the air on the nuclei of condensation, on the earth's surface and on the surface of various objects. When the temperature of the air cooling from the underlying surface reaches the dew point, dew, hoarfrost, liquid and solid deposits, and frost settle on the cold surface.

dew - tiny droplets of water, often merging. It usually appears at night on the surface, on the leaves of plants that have cooled as a result of heat radiation. In temperate latitudes, dew gives 0.1-0.3 mm per night, and 10-50 mm per year.

Hoarfrost - hard white precipitate. Formed under the same conditions as dew, but at temperatures below 0° (sublimation). When dew forms, latent heat is released; when frost forms, heat, on the contrary, is absorbed.

Liquid and solid plaque - a thin water or ice film that forms on vertical surfaces (walls, poles, etc.) when cold weather changes to warm weather as a result of contact of moist and warm air with a cooled surface.

Hoarfrost - white loose sediment that settles on trees, wires and the corners of buildings from air saturated with moisture at a temperature well below 0 °. called ice. It usually forms in autumn and spring at a temperature of 0°, -5°.

The accumulation of products of condensation or sublimation (water droplets, ice crystals) in the surface layers of air is called mist or haze. Fog and haze differ in droplet size and cause different degrees of reduced visibility. In fog, visibility is 1 km or less, in haze - more than 1 km. As the droplets get larger, the haze can turn into fog. Evaporation of moisture from the surface of the droplets can cause the fog to turn into haze.

If condensation (or sublimation) of water vapor occurs at a certain height above the surface, clouds. They differ from fog by their position in the atmosphere, physical structure and variety of forms. The formation of clouds is mainly due to the adiabatic cooling of the rising air. Rising and at the same time gradually cooling, the air reaches the boundary at which its temperature is equal to the dew point. This border is called level of condensation. Above, in the presence of condensation nuclei, condensation of water vapor begins and clouds can form. Thus, the lower boundary of the clouds practically coincides with the level of condensation. The upper boundary of the clouds is determined by the level of convection - the boundaries of the distribution of ascending air currents. It often coincides with the delay layers.

At high altitude, where the temperature of the rising air is below 0°, ice crystals appear in the cloud. Crystallization usually occurs at a temperature of -10° C, -15° C. There is no sharp boundary between the location of liquid and solid elements in the cloud, there are powerful transitional layers. The water droplets and ice crystals that make up the cloud are carried upward by the ascending currents and descend again under the action of gravity. Falling below the condensation limit, the droplets can evaporate. Depending on the predominance of certain elements, clouds are divided into water, ice, mixed.

Water Clouds are made up of water droplets. At a negative temperature, the droplets in the cloud are supercooled (down to -30°C). The droplet radius is most often from 2 to 7 microns, rarely up to 100 microns. In 1 cm 3 of a water cloud there are several hundred droplets.

Ice Clouds are made up of ice crystals.

mixed contain water droplets of different sizes and ice crystals at the same time. In the warm season, water clouds appear mainly in the lower layers of the troposphere, mixed - in the middle, ice - in the upper. The modern international classification of clouds is based on their division by height and appearance.

According to their appearance and height, the clouds are divided into 10 genera:

I family (upper tier):

1st kind. Cirrus (C)- separate delicate clouds, fibrous or threadlike, without "shadows", usually white, often shining.

2nd kind. Cirrocumulus (CC) - layers and ridges of transparent flakes and balls without shadows.

3rd kind. Cirrostratus (Cs) - thin, white, translucent shroud.

All clouds of the upper tier are icy.

II family (middle tier):

4th kind. Altocumulus(AC) - layers or ridges of white plates and balls, shafts. They are made up of tiny water droplets.

5th kind. Altostratus(As) - smooth or slightly wavy veil of gray color. They are mixed clouds.

III family (lower tier):

6th kind. Stratocumulus(Sс) - layers and ridges of blocks and shafts of gray color. Made up of water droplets.

7th kind. layered(St) - veil of gray clouds. Usually these are water clouds.

8th kind. Nimbostratus(Ns) - shapeless gray layer. Often "; these clouds are accompanied by underlying ragged rain (fn),

Strato-nimbus clouds mixed.

IV family (clouds of vertical development):

9th kind. Cumulus(Si) - dense cloudy clubs and heaps with an almost horizontal base. Cumulus clouds are water. Cumulus clouds with torn edges are called torn cumulus. (Fc).

10th kind. Cumulonimbus(Sv) - dense clubs developed vertically, watery in the lower part, icy in the upper part.

The nature and shape of clouds are determined by processes that cause air cooling, leading to cloud formation. As a result convection, A heterogeneous surface that develops upon heating produces cumulus clouds (family IV). They differ depending on the intensity of convection and on the position of the level of condensation: the more intense the convection, the higher its level, the greater the vertical power of cumulus clouds.

When warm and cold air masses meet, warm air always tends to rise up cold air. As it rises, clouds form as a result of adiabatic cooling. If warm air slowly rises along a slightly inclined (1-2 km at a distance of 100-200 km) interface between warm and cold masses (ascending slip process), a continuous cloud layer is formed, extending for hundreds of kilometers (700-900 km). A characteristic cloud system emerges: ragged rain clouds are often found below (fn), above them - stratified rain (Ns), above - high-layered (As), cirrostratus (Cs) and cirrus clouds (WITH).

In the case when warm air is vigorously pushed upwards by cold air flowing under it, a different cloud system is formed. Since the surface layers of cold air due to friction move more slowly than the overlying layers, the interface in its lower part bends sharply, warm air rises almost vertically and cumulonimbus clouds form in it. (Cb). If an upward sliding of warm air over cold air is observed above, then (as in the first case) nimbostratus, altostratus and cirrostratus clouds develop (as in the first case). If the upward slide stops, clouds do not form.

Clouds formed when warm air rises over cold air are called frontal. If the rise of air is caused by its flow onto the slopes of mountains and hills, the clouds formed in this case are called orographic. At the lower boundary of the inversion layer, which separates denser and less dense layers of air, waves several hundred meters long and 20-50 m high appear. On the crests of these waves, where the air cools as it rises, clouds form; cloud formation does not occur in the depressions between the crests. So there are long parallel strips or shafts. wavy clouds. Depending on the height of their location, they are altocumulus or stratocumulus.

If there were already clouds in the atmosphere before the onset of wave motion, they become denser on the crests of the waves and the density decreases in depressions. The result is the often observed alternation of darker and lighter cloud bands. With turbulent mixing of air over a large area, for example, as a result of an increase in friction on the surface when it moves from the sea to land, a layer of clouds is formed, which is characterized by unequal power in different parts and even breaks. Heat loss by radiation at night in winter and autumn causes cloud formation in the air with a high content of water vapor. Since this process proceeds calmly and continuously, a continuous layer of clouds appears, melting during the day.

Storm. The process of cloud formation is always accompanied by electrification and accumulation of free charges in clouds. Electrification is observed even in small cumulus clouds, but it is especially intense in powerful cumulonimbus clouds of vertical development with a low temperature in the upper part (t

Between sections of the cloud with different charges or between the cloud and the ground, electrical discharges occur - lightning, accompanied thunder. This is a thunderstorm. The duration of a thunderstorm is a maximum of several hours. About 2,000 thunderstorms occur on Earth every hour. Favorable conditions for the occurrence of thunderstorms are strong convection and high water content of clouds. Therefore, thunderstorms are especially frequent over land in tropical latitudes (up to 150 days a year with thunderstorms), in temperate latitudes over land - with thunderstorms 10-30 days a year, over the sea - 5-10. Thunderstorms are very rare in the polar regions.

Light phenomena in the atmosphere. As a result of reflection, refraction and diffraction of light rays in droplets and ice crystals of clouds, halos, crowns, rainbows appear.

Halo - these are circles, arcs, light spots (false suns), colored and colorless, arising in the ice clouds of the upper tier, more often in cirrostratus. The diversity of the halo depends on the shape of the ice crystals, their orientation and movement; the height of the sun above the horizon matters.

Crowns - light, slightly colored rings surrounding the Sun or the Moon, which are translucent through thin water clouds. There may be one crown adjacent to the luminary (halo), and there may be several "additional rings" separated by gaps. Each crown has an inner side facing the star is blue, the outer side is red. The reason for the appearance of crowns is the diffraction of light as it passes between the droplets and crystals of the cloud. The dimensions of the crown depend on the size of the drops and crystals: the larger the drops (crystals), the smaller the crown, and vice versa. If cloud elements become larger in the cloud, the crown radius gradually decreases, and when the size of cloud elements decreases (evaporation), it increases. Large white crowns around the Sun or Moon "false suns", pillars - signs of good weather.

Rainbow It is visible against the background of a cloud illuminated by the Sun, from which drops of rain fall. It is a light arc, painted in spectral colors: the outer edge of the arc is red, the inner edge is purple. This arc is a part of a circle, the center of which is connected by "; axis"; (one straight line) with the eye of the observer and with the center of the solar disk. If the Sun is low on the horizon, the observer sees half of the circle; if the Sun rises, the arc becomes smaller as the center of the circle falls below the horizon. When the sun is >42°, the rainbow is not visible. From an airplane, you can observe a rainbow in the form of an almost complete circle.

In addition to the main rainbow, there are secondary, slightly colored ones. A rainbow is formed by the refraction and reflection of sunlight in water droplets. The rays falling on the drops come out of the drops as if diverging, colored, and this is how the observer sees them. When the rays are refracted twice in a drop, a secondary rainbow appears. The color of the rainbow, its width, and the type of secondary arcs depend on the size of the droplets. Large drops give a smaller but brighter rainbow; as the drops decrease, the rainbow becomes wider, its colors become blurry; with very small drops, it is almost white. Light phenomena in the atmosphere, caused by changes in the light beam under the influence of droplets and crystals, make it possible to judge the structure and condition of clouds and can be used in weather predictions.

Cloudiness, daily and annual variation, distribution of clouds.

Cloudiness - the degree of cloud coverage of the sky: 0 - clear sky, 10 - overcast, 5 - half of the sky is covered with clouds, 1 - clouds cover 1/10 of the sky, etc. When calculating average cloudiness, tenths of a unit are also used, for example: 0.5 5.0, 8.7 etc. In the daily course of cloudiness over land, two maxima are found - in the early morning and in the afternoon. In the morning, a decrease in temperature and an increase in relative humidity contribute to the formation of stratus clouds; in the afternoon, due to the development of convection, cumulus clouds appear. In summer, the daily maximum is more pronounced than the morning one. In winter, stratus clouds predominate and the maximum cloudiness occurs in the morning and night hours. Over the Ocean, the daily course of cloudiness is the reverse of its course over land: the maximum cloudiness occurs at night, the minimum - during the day.

The annual course of cloudiness is very diverse. At low latitudes, cloud cover does not change significantly throughout the year. Over the continents, the maximum development of convection clouds occurs in summer. The summer cloudiness maximum is noted in the area of ​​monsoon development, as well as over the oceans at high latitudes. In general, in the distribution of cloudiness on Earth, zoning is noticeable, due primarily to the prevailing movement of air - its rise or fall. Two maxima are noted - above the equator due to powerful upward movements of moist air and above 60-70 ° With. and y.sh. in connection with the rise of air in cyclones prevailing in temperate latitudes. Over land, cloudiness is less than over the ocean, and its zonality is less pronounced. Cloud minimums are confined to 20-30°S. and s. sh. and to the poles; they are associated with lowering air.

The average annual cloudiness for the whole Earth is 5.4; over land 4.9; over the Ocean 5.8. The minimum average annual cloudiness is noted in Aswan (Egypt) 0.5. The maximum average annual cloudiness (8.8) was observed in the White Sea; the northern regions of the Atlantic and Pacific oceans and the coast of Antarctica are characterized by large clouds.

Clouds play a very important role in geographical envelope. They carry moisture, rainfall is associated with them. The cloud cover reflects and scatters solar radiation and at the same time delays the thermal radiation of the earth's surface, regulating the temperature of the lower layers of the air: without clouds, fluctuations in air temperature would become very sharp.

Precipitation. Atmospheric precipitation called water that has fallen to the surface from the atmosphere in the form of rain, drizzle, cereals, snow, hail. Precipitation falls mainly from clouds, but not every cloud gives precipitation. The water droplets and ice crystals in the cloud are very small, easily held by the air, and even weak upward currents carry them upward. Precipitation requires cloud elements to grow large enough to overcome rising currents and air resistance. The enlargement of some elements of the cloud occurs at the expense of others, firstly, as a result of the merging of droplets and the adhesion of crystals, and secondly, and this is the main thing, as a result of evaporation of some elements of the cloud, diffuse transfer and condensation of water vapor on others.

The collision of drops or crystals occurs during random (turbulent) movements or when they fall at different speeds. The merging process is hindered by a film of air on the surface of the droplets, which causes colliding droplets to bounce, as well as electric charges. The growth of some cloud elements at the expense of others due to the diffuse transfer of water vapor is especially intense in mixed clouds. Since the maximum moisture content over water is greater than over ice, for ice crystals in a cloud, water vapor can saturate the space, while for water droplets there will be no saturation. As a result, the droplets will begin to evaporate, and the crystals will rapidly grow due to moisture condensation on their surface.

In the presence of droplets of different sizes in a water cloud, the movement of water vapor to larger drops begins and their growth begins. But since this process is very slow, very small drops (0.05-0.5 mm in diameter) fall out of water clouds (stratus, stratocumulus). Clouds that are homogeneous in structure usually do not produce precipitation. Especially favorable conditions for the occurrence of precipitation in clouds of vertical development. In the lower part of such a cloud there are water drops, in the upper part there are ice crystals, in the intermediate zone there are supercooled drops and crystals.

In rare cases, when present in very humid air a large number condensation nuclei, one can observe the precipitation of individual raindrops without clouds. Raindrops have a diameter of 0.05 to 7 mm (average 1.5 mm), larger droplets disintegrate in the air. Drops up to 0.5 mm in diameter form drizzle.

The falling drops of drizzle are imperceptible to the eye. Real rain is the larger, the stronger the ascending air currents overcome by falling drops. At an ascending air speed of 4 m / s, drops with a diameter of at least 1 mm fall on the earth's surface: ascending currents at a speed of 8 m / s cannot overcome even the largest drops. The temperature of the falling raindrops is always slightly lower than the air temperature. If the ice crystals falling from the cloud do not melt in the air, they fall to the surface solid precipitation(snow, grain, hail).

Snowflakes are hexagonal ice crystals with rays formed in the process of sublimation. Wet snowflakes stick together to form snow flakes. Snow pellet is spherocrystals arising from the random growth of ice crystals under conditions of high relative humidity (greater than 100%). If a snow pellet is covered with a thin shell of ice, it turns into ice grits.

hail falls in the warm season from powerful cumulonimbus clouds . Usually hail fall is short-lived. Hailstones are formed as a result of the repeated movement of ice pellets in the cloud up and down. Falling down, the grains fall into the zone of supercooled water droplets and are covered with a transparent ice shell; then they again rise to the zone of ice crystals and an opaque layer of tiny crystals forms on their surface.

The hailstone has a snow core and a series of alternating transparent and opaque ice shells. The number of shells and the size of the hailstone depend on how many times it rose and fell in the cloud. Most often, hailstones with a diameter of 6-20 mm fall out, sometimes there are much larger ones. Usually hail falls in temperate latitudes, but the most intense hail fall occurs in the tropics. In the polar regions, hail does not fall.

Precipitation is measured in terms of the thickness of the water layer in millimeters, which could be formed as a result of precipitation on a horizontal surface in the absence of evaporation and infiltration into the soil. According to the intensity (the number of millimeters of precipitation in 1 minute), precipitation is divided into weak, moderate and heavy. The nature of precipitation depends on the conditions of their formation.

overhead precipitation, characterized by uniformity and duration, usually fall in the form of rain from nimbostratus clouds.

heavy rainfall characterized by a rapid change in intensity and short duration. They fall from cumulus stratus clouds in the form of rain, snow, and occasional rain and hail. Separate showers with an intensity of up to 21.5 mm/min (Hawaiian Islands) were noted.

Drizzling precipitation fall out of stratocumulus and stratocumulus clouds. The droplets that make them up (in cold weather - the smallest crystals) are barely visible and seem to be suspended in the air.

The daily course of precipitation coincides with the daily course of cloudiness. There are two types of daily precipitation patterns - continental and marine (coastal). continental type has two maxima (in the morning and afternoon) and two minima (at night and before noon). marine type- one maximum (night) and one minimum (day). The annual course of precipitation is different in different latitudinal zones and in different parts of the same zone. It depends on the amount of heat, thermal regime, air movement, distribution of water and land, and to a large extent on topography. All the diversity of the annual course of precipitation cannot be reduced to several types, but it can be noted characteristics for different latitudes, allowing us to speak about its zonality. Equatorial latitudes are characterized by two rainy seasons (after the equinoxes) separated by two dry seasons. In the direction of the tropics, changes occur in the annual precipitation regime, expressed in the convergence of wet seasons and their confluence near the tropics into one season with heavy rains, lasting 4 months a year. In subtropical latitudes (35-40°) there is also one rainy season, but it falls in winter. In temperate latitudes, the annual course of precipitation is different over the Ocean, the interior of the continents, and the coasts. Winter precipitation prevails over the Ocean, and summer precipitation over the continents. Summer precipitation is also typical for polar latitudes. The annual course of precipitation in each case can be explained only by taking into account the circulation of the atmosphere.

Precipitation is most abundant in equatorial latitudes, where annual amount they are surpassed by 1000-2000 mm. On the equatorial islands Pacific Ocean falls up to 4000-5000 mm per year, and on the windward slopes of the mountains of tropical islands up to 10000 mm. Heavy rainfall is caused by powerful convective currents of very humid air. To the north and south of the equatorial latitudes, the amount of precipitation decreases, reaching a minimum near the 25-35 ° parallel, where their average annual amount is not more than 500 mm. In the interior of the continents and on the western coasts, rains do not fall in places for several years. In temperate latitudes, the amount of precipitation increases again and averages 800 mm per year; in the inner part of the continents there are fewer of them (500, 400 and even 250 mm per year); on the shores of the Ocean more (up to 1000 mm per year). At high latitudes, at low temperatures and low moisture content in the air, the annual amount of precipitation

The maximum average annual precipitation falls in Cherrapunji (India) - about 12,270 mm. The largest annual precipitation there is about 23,000 mm, the smallest - more than 7,000 mm. The minimum recorded average annual rainfall is in Aswan (0).

The total amount of precipitation falling on the Earth's surface in a year can form a continuous layer up to 1000 mm high on it.

Snow cover. Snow cover is formed by the fall of snow on the earth's surface at a temperature low enough to maintain it. It is characterized by height and density.

The height of the snow cover, measured in centimeters, depends on the amount of precipitation that has fallen on a unit of surface, on the density of snow (the ratio of mass to volume), on the terrain, on the vegetation cover, and also on the wind that moves the snow. In temperate latitudes, the usual height of the snow cover is 30-50 cm. Its highest height in Russia is noted in the basin of the middle reaches of the Yenisei - 110 cm. In the mountains, it can reach several meters.

Having a high albedo and high radiation, the snow cover contributes to lowering the temperature of the surface layers of air, especially in clear weather. Minimum and maximum temperatures air above the snow cover is lower than in the same conditions, but in its absence.

In the polar and high-mountain regions, snow cover is permanent. In temperate latitudes, the duration of its occurrence varies depending on climatic conditions. Snow cover that persists for a month is called stable. Such snow cover is formed annually in most of the territory of Russia. In the Far North, it lasts 8-9 months, in the central regions - 4-6, on the shores of the Azov and Black Seas, the snow cover is unstable. Snow melting is mainly caused by exposure to warm air coming from other areas. Under the action of sunlight, about 36% of the snow cover melts. Warm rain helps melt. Contaminated snow melts faster.

Snow not only melts, but also evaporates in dry air. But the evaporation of snow cover is less important than melting.

Hydration. To estimate the surface moistening conditions, it is not enough to know only the amount of precipitation. With the same amount of precipitation, but different evapotranspiration, the moistening conditions can be very different. To characterize the conditions of moisture, use moisture coefficient (K), representing the ratio of the amount of precipitation (r) to evaporation (Eat) for the same period.

Moisture is usually expressed as a percentage, but it can be expressed as a fraction. If the amount of precipitation is less than evaporation, i.e. TO less than 100% (or TO less than 1), moisture is insufficient. At TO more than 100% moisture may be excessive, at K=100% it is normal. If K=10% (0.1) or less than 10%, we speak of negligible moisture.

In semi-deserts, K is 30%, but 100% (100-150%).

During the year, an average of 511 thousand km 3 of precipitation falls on the earth's surface, of which 108 thousand km 3 (21%) fall on land, the rest in the Ocean. Almost half of all precipitation falls between 20°N. sh. and 20°S sh. The polar regions account for only 4% of precipitation.

On average, as much water evaporates from the Earth's surface in a year as falls on it. The main ";source"; moisture in the atmosphere is Ocean in subtropical latitudes, where surface heating creates conditions for maximum evaporation at a given temperature. In the same latitudes on land, where evaporation is high, and there is nothing to evaporate, drainless regions and deserts arise. For the Ocean as a whole, the balance of water is negative (evaporation is more precipitation), on land it is positive (evaporation is less precipitation). The overall balance is equalized by means of a drain "surplus"; water from land to ocean.

mode atmosphere The Earth has been investigated as ... influence on radiation and thermalmodeatmosphere determining the weather and... surfaces. Most of thermal the energy it receives atmosphere, comes from underlyingsurfaces ...

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

The maximum value of all elements 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, and the minimum ones in winter.

In the diurnal course of surface temperature, dry and devoid of vegetation, on a clear day, the maximum occurs after 14 hours, and the minimum is around sunrise. Cloudiness can disturb the diurnal variation of temperature, causing a shift in the maximum and minimum. Humidity and surface vegetation have a great influence on the course of temperature.

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

The spread of heat from the active surface depends on the composition of the underlying substrate, and will be determined by its heat capacity and thermal conductivity. On the surface of the continents, the underlying substrate is soil, in the oceans (seas) - water.

Soils in general have a lower heat capacity than water and a higher thermal conductivity. Therefore, they heat up and cool down faster than water.

Time is spent on the transfer of heat from layer to layer, and the moments of the onset of maximum and minimum temperature values ​​during the day are delayed by every 10 cm by about 3 hours. The deeper the layer, the less heat it receives and the weaker the temperature fluctuations in it. The amplitude of diurnal temperature fluctuations with depth decreases by 2 times for every 15 cm. At an average depth of about 1 m, the daily fluctuations in soil temperature "fade out". The layer where they stop is called layer of constant daily temperature.

The longer the period of temperature fluctuations, the deeper they spread. Thus, in the middle latitudes, the layer of constant annual temperature is at a depth of 19–20 m, in high latitudes, at a depth of 25 m, and in tropical latitudes, where annual temperature amplitudes are small, at a depth of 5–10 m. years are delayed by an average of 20-30 days per meter.

The temperature in the layer of constant annual temperature is close to the average annual air temperature above the surface.

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. Humidity and vegetation cover greatly influence the surface temperature. 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 maximum temperature will come 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.

The longer the period of 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 the environment, due to the conversion of 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 atmospheric pressure and varies within wide limits. 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 the 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.

The thermal state of the 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.

polar type - winter is very long and cold, summer is short and cool. Annual amplitudes are 25° and more (over land up to 65°). The temperature is negative most of the year. The overall picture of the annual course of air temperature is complicated by the influence of factors, among which the underlying surface is of particular importance. Over the water surface, the annual temperature variation is smoothed out; over land, on the contrary, it is more pronounced. Snow and ice cover greatly reduces annual temperatures. The height of the place above the level of the Ocean, relief, distance from the Ocean, and cloudiness also affect. The smooth course of the annual air temperature is disturbed by disturbances caused by the intrusion of cold or, conversely, warm air. An example can be spring returns of cold weather (cold waves), autumn returns of heat, winter thaws in temperate latitudes.

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 in low latitudes are lower, and in high latitudes, on the contrary, they are higher than solar ones. 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 south - +10° C in July, +17° C in January. 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, bounded 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.