The thermal regime of the underlying surface and the atmosphere briefly. Thermal regime of the underlying surface. Change in daily temperature amplitude with height

Heating an n n n surface The heat balance of a surface determines its temperature, magnitude, and change. When heated, this surface transfers heat (in the long-wave range) both to the underlying layers and to the atmosphere. This surface is called the active surface.

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

n Soils in general have a lower heat capacity than water and a higher thermal conductivity. Therefore, soils heat up faster than water, but also cool faster. n Water heats up more slowly and releases heat more slowly. In addition, when the surface layers of water cool, thermal convection occurs, accompanied by mixing.

n n n n Temperature is measured with thermometers in degrees: In the SI system - in degrees Kelvin ºK Non-systemic: In degrees Celsius ºС and degrees Fahrenheit ºF. 0 ºK = - 273 ºC. 0 ºF = -17.8 °C 0 ºC = 32 ºF

ºC=0.56*F-17.8 ºF=1.8*C+32

Daily temperature fluctuations in soils n n n 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. The amplitude of diurnal temperature fluctuations with depth decreases by 2 times for every 15 cm. At an average depth of about 1 m, daily fluctuations in soil temperature "fade out". The layer in which fluctuations in daily temperature values ​​cease is called the layer of constant daily temperature.

n n The amplitude of diurnal temperature fluctuations with depth decreases by 2 times for every 15 cm. At an average depth of about 1 m, daily fluctuations in soil temperature "fade out". The layer in which fluctuations in daily temperature values ​​cease is called the layer of constant daily temperature.

Daily variation of temperature in the soil at different depths from 1 to 80 cm. Pavlovsk, May.

Annual temperature fluctuations in soils n n During the year, the maximum and minimum temperatures are delayed by an average of 20-30 days per meter.

Annual variation of temperature in the soil at different depths from 3 to 753 cm in Kaliningrad

The daily course of land surface temperature n n n In the daily course of surface temperature, dry and devoid of vegetation, on a clear day, the maximum occurs after 13-14 hours, and the minimum - around the time of 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.

n n Daytime maximums of surface temperature can be +80 ºС and more. Daily temperature amplitudes reach 40 ºС. 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).

n Moments of temperature maxima in water bodies are delayed compared to land. The maximum occurs at about 1415 hours, the minimum - 2-3 hours after sunrise.

Daily temperature fluctuations in sea water n n Daily temperature fluctuations on the surface of the Ocean in high latitudes are on average only 0.1 ºС, in temperate 0.4 ºС, in tropical - 0.5 ºС. The penetration depth of these vibrations is 15-20 m.

Annual changes in land temperature n n The warmest month in the northern hemisphere is July, and the coldest month is January. Annual amplitudes vary from 5 ºС at the equator to 60-65 ºС in the sharply continental conditions of the temperate zone.

The annual course of temperature in the ocean n n The annual maximum and minimum temperature on the surface of the Ocean lag about a month in comparison with the land. The maximum in the northern hemisphere occurs in August, the minimum - in February. Annual temperature amplitudes on the surface of the Ocean from 1 ºС in equatorial latitudes to 10.2 ºС in temperate latitudes. Annual temperature fluctuations penetrate to a depth of 200-300 m.

Heat transfer to the atmosphere n n n Atmospheric air is slightly heated by direct sunlight. The atmosphere is heated by the underlying surface. Heat is transferred to the atmosphere by convection, advection, and as a result of heat release during the condensation of water vapor.

Heat transfer during condensation n n By heating the surface, water is converted into water vapour. The water vapor is carried away by the rising air. When the temperature drops, it can turn into water (condensation). This releases heat into the atmosphere.

Adiabatic process n n n In rising air, the temperature changes due to the adiabatic process (by converting the internal energy of the gas into work and work into internal energy). 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 expended on this is released, and the air temperature rises.

n n Dry or containing water vapor, but unsaturated air, rising, adiabatically cools by 1 ºС for every 100 m. Air saturated with water vapor cools by 0.6 ºС when rising by 100 m, since condensation occurs in it accompanied by the release of heat.

When lowering, both dry and humid air heat up equally, since moisture condensation does not occur. n For every 100 m of descent, the air heats up by 1ºC. n

Inversion n n n An increase in temperature with height is called an inversion, and a layer in which the temperature increases with height is called an inversion layer. Types of inversion: - Radiation inversion - radiation inversion, formed after sunset, when the sun's rays heat the upper layers; - Advective inversion - is formed as a result of the intrusion (advection) of warm air on a cold surface; - Orographic inversion - cold air flows into depressions and stagnates there.

Types of temperature distribution with height a - surface inversion, b - surface isotherm, c - inversion in the free atmosphere

Advection n n The intrusion (advection) of an air mass formed under other conditions into a given territory. Warm air masses cause an increase in air temperature in a given area, cold air masses cause a decrease.

Daily temperature variation of the free atmosphere n n n The daily and annual temperature variation in the lower troposphere up to a height of 2 km 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. In the 2 m layer, the daily maximum is found at about 14-15 hours and the minimum after sunrise. The amplitude of diurnal temperature amplitude decreases with increasing latitude. The largest in subtropical latitudes, the smallest - in the polar.

n n n Lines of equal temperatures are called isotherms. The isotherm with the highest average annual temperature is called the "Thermal Equator". sh.

Annual variation of air temperature n n n Depends on latitude. From the equator to the poles, the annual amplitude of air temperature fluctuations increases. There are 4 types of annual temperature variation according to the magnitude of the amplitude and the time of the onset of extreme temperatures.

n n Equatorial type - two maxima (after equinoxes) and two minima (after solstices). The amplitude on the Ocean is about 1 ºС, over land - up to 10 ºС. 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 ºС, on land - up to 20 ºС. The temperature is positive throughout the year.

n n Moderate type - one maximum (over land in July, over the Ocean - in August) and one minimum (on land in January, in the ocean - in February), four seasons. The annual temperature amplitude increases with increasing latitude and with increasing distance from the ocean: on the coast 10 ºС, far from the ocean - 60 ºС and more. The temperature during the cold season is negative. Polar type - winter is very long and cold, summer is short and cool. The annual amplitude is 25 ºС and more (over land up to 65 ºС). The temperature is negative most of the year.

n The complicating factors of the annual temperature variation, as well as for the diurnal variation, are the nature of the underlying surface (vegetation, snow or ice cover), the height of the terrain, remoteness from the ocean, the intrusion of air masses different in thermal regime

n n n Average air temperature near the earth's surface in the northern hemisphere in January +8 ºС, in July +22 ºС; in the south - in July +10 ºС, in January +17 ºС. The annual amplitudes of air temperature fluctuations are 14 ºС for the northern hemisphere, and only 7 ºС for the southern one, which indicates the lower continentality of the southern hemisphere. The average annual air temperature near the earth's surface is generally +14 ºС.

World record holders n n n Absolute maximums of air temperature were observed: in the northern hemisphere - in Africa (Libya, +58, 1 ºС) and in the Mexican Highlands (Sao Louis, +58 ºС). in the southern hemisphere - in Australia (+51ºС), absolute minima were noted in Antarctica (-88.3 ºС, Vostok station) and in Siberia (Verkhoyansk, -68 ºС, Oymyakon, -77.8 ºС). The average annual temperature is the highest in North Africa (Lu, Somalia, +31 ºС), the lowest - in Antarctica (Vostok station, -55, 6 ºС).

Thermal belts n n n These are the latitudinal zones of the Earth with certain temperatures. Due to the uneven distribution of land and oceans, air and water currents, thermal zones do not coincide with illumination zones. For the boundaries of the belts, isotherms are taken - lines of equal temperatures.

Thermal zones n n There are 7 thermal zones. - hot zone, located between the annual isotherm +20 ºС of the northern and southern hemispheres; - two temperate zones bounded from the equator by the annual isotherm +20 ºС, and from the poles by the isotherm +10 ºС of the warmest month; - two cold belts located between isotherms +10 ºС and 0 ºС of the warmest month;

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 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, 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. 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.

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 the movement of air and waters of the Ocean, and therefore differ significantly from solar temperatures.

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 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 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.

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 the arrival of the radiant energy of the Sun, evaporation increases, the absolute humidity reaches a maximum at about 09:00. 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 coldest month, the 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 formed 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 in their position in the atmosphere, in their physical structure, and in their 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 (FROM).

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 the 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 increased friction on the surface when it moves from the sea to land, a layer of clouds is formed, which differs in 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.

Thunderstorm. 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 are 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 the 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 the geographic 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. Precipitation is water that has fallen to the surface from the atmosphere in the form of rain, drizzle, grains, 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 the 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 fusion process is hindered by a film of air on the surface of the droplets, which causes the colliding droplets to bounce, as well as electric charges of the same name. 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 there are a large number of condensation nuclei in very humid air, 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, solid precipitation (snow, grains, hail) falls to the surface.

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 one can note the characteristic features for different latitudes, which make it possible to speak of 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 the annual amount exceeds 1000-2000 mm. On the equatorial islands of the 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. The minimum and maximum air temperatures above the snow cover are lower than under the same conditions, but in the absence of it.

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 ...

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.

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?

Soil is a component of the climate system, which is the most active accumulator of solar heat entering the earth's surface.

The daily course of the underlying surface temperature has one maximum and one minimum. The minimum occurs around sunrise, the maximum occurs in the afternoon. The phase of the diurnal cycle and its daily amplitude depend on the season, the state of the underlying surface, the amount and precipitation, and also, on the location of the stations, the type of soil and its mechanical composition.

According to the mechanical composition, soils are divided into sandy, sandy loamy and loamy soils, which differ in heat capacity, thermal diffusivity and genetic properties (in particular, in color). Dark soils absorb more solar radiation and therefore warm up more than light soils. Sandy and sandy loamy soils, characterized by a smaller, warmer than loamy.

The annual course of the underlying surface temperature shows a simple periodicity with a minimum in winter and a maximum in summer. In most of Russia, the highest soil temperature is observed in July, in the Far East in the coastal strip of the Sea of ​​Okhotsk, in and - in July - August, in the south of Primorsky Krai - in August.

The maximum temperatures of the underlying surface during most of the year characterize the extreme thermal state of the soil, and only for the coldest months - the surface.

The weather conditions favorable for the underlying surface to reach maximum temperatures are: cloudy weather, when the influx of solar radiation is maximum; low wind speeds or calm, since an increase in wind speed increases the evaporation of moisture from the soil; a small amount of precipitation, since dry soil is characterized by lower heat and thermal diffusivity. In addition, in dry soil there is less heat consumption for evaporation. Thus, absolute temperature maxima are usually observed on the clearest sunny days on dry soil and usually in the afternoon hours.

The geographical distribution of the averages from the absolute annual maximums of the underlying surface temperature is similar to the distribution of the isogeotherms of the average monthly temperatures of the soil surface in the summer months. Isogeotherms are mainly latitudinal. The influence of the seas on the temperature of the soil surface is manifested in the fact that on the western coast of Japan and, on Sakhalin and Kamchatka, the latitudinal direction of the isogeoterms is disturbed and becomes close to the meridional (repeats the outlines of the coastline). In the European part of Russia, the values ​​of the average of the absolute annual maxima of the underlying surface temperature vary from 30–35°C on the coast of the northern seas to 60–62°C in the south of the Rostov Region, in the Krasnodar and Stavropol Territories, in the Republic of Kalmykia and the Republic of Dagestan. In the area, the average of the absolute annual maxima of soil surface temperature is 3–5°C lower than in the nearby flat areas, which is associated with the influence of elevations on the increase in precipitation in the area and soil moisture. Plain territories, closed by hills from the prevailing winds, are characterized by a reduced amount of precipitation and lower wind speeds, and, consequently, increased values ​​of extreme temperatures of the soil surface.

The most rapid increase in extreme temperatures from north to south occurs in the zone of transition from the forest and zones to the zone, which is associated with a decrease in precipitation in the steppe zone and with a change in soil composition. In the south, with a general low level of moisture content in the soil, the same changes in soil moisture correspond to more significant differences in the temperature of soils that differ in mechanical composition.

There is also a sharp decrease in the average of the absolute annual maxima of the temperature of the underlying surface from south to north in the northern regions of the European part of Russia, during the transition from the forest zone to zones and tundra - areas of excessive moisture. The northern regions of the European part of Russia, due to active cyclonic activity, among other things, differ from the southern regions in an increased amount of cloudiness, which sharply reduces the arrival of solar radiation to the earth's surface.

In the Asian part of Russia, the lowest average absolute maxima occur on the islands and in the north (12–19°С). As we move southward, there is an increase in extreme temperatures, and in the north of the European and Asian parts of Russia, this increase occurs more sharply than in the rest of the territory. In areas with a minimum amount of precipitation (for example, the areas between the Lena and Aldan rivers), pockets of increased extreme temperatures are distinguished. Since the regions are very complex, the extreme temperatures of the soil surface for stations located in various forms of relief (mountainous regions, basins, lowlands, valleys of large Siberian rivers) differ greatly. The average values ​​of the absolute annual maximum temperatures of the underlying surface reach the highest values ​​in the south of the Asian part of Russia (except for coastal areas). In the south of Primorsky Krai, the average of absolute annual maxima is lower than in continental regions located at the same latitude. Here their values ​​reach 55–59°С.

The minimum temperatures of the underlying surface are also observed under quite specific conditions: on the coldest nights, at hours close to sunrise, during anticyclonic weather conditions, when low cloudiness favors maximum effective radiation.

The distribution of average isogeotherms from the absolute annual minima of the underlying surface temperature is similar to the distribution of isotherms of minimum air temperatures. In most of the territory of Russia, except for the southern and northern regions, the average isogeotherms of the absolute annual minimum temperatures of the underlying surface take on a meridional orientation (decreasing from west to east). In the European part of Russia, the average of the absolute annual minimum temperatures of the underlying surface varies from -25°C in the western and southern regions to -40 ... -45°C in the eastern and, especially, northeastern regions (Timan Ridge and Bolshezemelskaya tundra). The highest mean values ​​of absolute annual temperature minima (–16…–17°C) occur on the Black Sea coast. In most of the Asian part of Russia, the average of the absolute annual minimums vary within -45 ... -55 ° С. Such an insignificant and fairly uniform distribution of temperature over a vast territory is associated with the uniformity of the conditions for the formation of minimum temperatures in areas subject to the influence of the Siberian.

In areas of Eastern Siberia with complex relief, especially in the Republic of Sakha (Yakutia), along with radiation factors, relief features have a significant effect on the decrease in minimum temperatures. Here, in the difficult conditions of a mountainous country in depressions and basins, especially favorable conditions are created for cooling the underlying surface. The Republic of Sakha (Yakutia) has the lowest average values ​​of the absolute annual minimums of the underlying surface temperature in Russia (up to –57…–60°С).

On the coast of the Arctic seas, due to the development of active winter cyclonic activity, the minimum temperatures are higher than in the interior. The isogeotherms have an almost latitudinal direction, and the decrease in the average of the absolute annual minima from north to south occurs rather quickly.

On the coast, the isogeotherms repeat the outlines of the shores. The influence of the Aleutian minimum is manifested in the increase in the average of the absolute annual minimums in the coastal zone compared to the inland areas, especially on the southern coast of Primorsky Krai and on Sakhalin. The average of the absolute annual minimums here is –25…–30°С.

The freezing of the soil depends on the magnitude of negative air temperatures in the cold season. The most important factor preventing soil freezing is the presence of snow cover. Its characteristics such as formation time, power, duration of occurrence determine the depth of soil freezing. The late establishment of snow cover contributes to greater freezing of the soil, since in the first half of winter the intensity of soil freezing is greatest and, conversely, the early establishment of snow cover prevents significant freezing of the soil. The influence of the thickness of the snow cover is most pronounced in areas with low air temperatures.

At the same depth of freezing depends on the type of soil, its mechanical composition and humidity.

For example, in the northern regions of Western Siberia, with low and thick snow cover, the depth of soil freezing is less than in more southern and warmer regions with small. A peculiar picture takes place in areas with unstable snow cover (southern regions of the European part of Russia), where it can contribute to an increase in the depth of soil freezing. This is due to the fact that with frequent changes of frost and thaw, an ice crust forms on the surface of a thin snow cover, the thermal conductivity coefficient of which is several times greater than the thermal conductivity of snow and water. The soil in the presence of such a crust cools and freezes much faster. The presence of vegetation cover contributes to a decrease in the depth of soil freezing, as it retains and accumulates snow.