Daily variation of soil surface temperature. Daily and annual variations in soil temperature
During the day, the soil surface continuously loses or absorbs heat in different ways. Through the earth's surface, heat is transferred upward (to the atmosphere) and downward (to the soil). The soil surface receives total radiation and counter radiation from the atmosphere, and heat also arrives by turbulent thermal conduction. In the same ways, the earth's surface radiates heat into the atmosphere. The incoming heat is distributed in a thin upper layer, which becomes very hot. On the soil surface, the temperature drops quickly when heat is released: the heat accumulated in the thin upper layer quickly leaves it without being replenished from below.
Fig. No. 1 Graph of daily variation of soil surface temperature
The algebraic sum of all heat inflows and outflows on the earth's surface must be equal to zero, but this does not mean that the temperature of the soil surface does not change. If heat transfer is directed downward, then heat from the atmosphere remains in the active soil layer, which leads to an increase in its temperature. When transferred to the atmosphere, heat leaves the active layer, thereby lowering its temperature.
The surface temperature during the day has its maximum, which appears at 13-14 hours, and its minimum, observed half an hour after sunrise. In our case (Fig. No. 1) this is exactly what happens: the lowest surface temperature of 19°C occurs at 6 a.m. - a time approximately after sunrise in the summer. At this time, the transfer of heat from the top layer of soil by effective radiation is balanced by the increased influx of total radiation, as a result of which the radiation balance of the soil surface becomes equal to zero; and the non-radiation balance is insignificant. Then the temperature gradually increases to its highest value at local noon. The radiation balance remains positive until the evening, but you can notice that the soil surface temperature drops. This is due to increased thermal conductivity and evaporation of water.
Maximum temperatures on the soil surface are usually higher than in the air, since during the day solar radiation heats the soil, which then heats the air. This can be seen in the case under study: the maximum soil surface temperature (49°C) is higher than the maximum air temperature (32.8°C) on the same day. Night minima, on the contrary, are lower on the soil surface than in the air, since the soil is first cooled by effective radiation, and the air is cooled from it. On August 19, the minimum soil surface temperature was 19°C, and the minimum air temperature was 21.2°C.
The studies were carried out in August, so the difference between the daily maximum and daily minimum - the daily temperature amplitude - in the case under study is quite high (30°C). Solar radiation at the earth's surface is high during the day, and effective radiation is observed at night. Therefore, judging by the large amplitude, the day was cloudless.
The daily and annual cycle of soil temperature is a measurement of temperature over the course of a day or a year: during the day the soil heats up, at night it cools down, the minimum temperature is in clear weather before sunrise, and the maximum is around 13:00, then the temperature begins to decrease. The amplitude (the difference between the maximum and minimum temperature) is affected by:
time of year (in summer the amplitude is greatest);
geographic latitude (amplitude decreases from the tropics to the poles);
relief (southern slopes heat up more than northern ones);
vegetation and snow cover reduce the amplitude;
loose soils have a larger amplitude than dense ones;
dark soils heat up more than light soils, therefore the temperature amplitude of dark soils is higher than that of light soils;
dry soils heat up more than wet ones;
in cloudy weather the amplitude decreases.
The annual variation of soil surface temperature is determined mainly by the arrival of solar heat during the year. In the temperate latitudes of the northern hemisphere, the maximum average monthly temperature is observed in July, the minimum in January-February. The amplitude of the annual temperature variation is mainly influenced by the same factors as the amplitude of the daily temperature variation, but the amplitude of the annual temperature variation increases with increasing latitude. The soil layer in which the daily and annual temperature variations are observed is called the active layer.
The patterns of heat distribution in the soil obey Fourier's laws.
1. Regardless of the type of soil, the period of oscillations does not change with depth, that is, the interval at all depths between maxima and minima in the daily variation of temperature is 24 hours, in the annual variation - 12 months.
2. An increase in depth in an arithmetic progression leads to a decrease in the temperature amplitude in a geometric progression. Thus, on the surface the daily amplitude is 30 °C, at a depth of 20 cm - 5, at a depth of 40 cm - 1 °C, and from a depth of 70 cm the layer of constant daily temperature begins. The amplitude of annual temperature fluctuations decreases with depth according to the same law. A constant temperature in middle latitudes is observed at a depth of 15...20 cm.
3. The timing of the onset of maximum and minimum temperatures, both in the daily and annual cycles, lags with depth in proportion to its increase; daily - for 2.5...3.5 hours for every 10 cm of depth, annual - for 20...30 days for every meter of depth.
Rice. 4.3. Isopleths of the annual variation of soil temperature in Moscow in a bare area (a) and under grass (b)
Changes in temperature in the soil with depth over the course of a day or year can be represented in the form of an isopleth graph (Fig. 4.3). Having plotted the average temperature values at different depths for a specific observation point in different months (hours), smoothly draw isolines (isopleths) connecting points with equal temperatures.
Test questions and assignments
1. List the processes of heating and cooling of soil. 2. Under what conditions does heat go deep into the soil (insolation type), and under what conditions is the heat flow directed from the depths to the surface (radiation type)? 3. Describe the instruments and methods for measuring soil and soil temperature. 4. What affects the amplitude of the daily variation of soil temperature? 5. What is an isopleth plot?
Daily and annual variations in soil temperature
Observations of soil surface temperature and temperature at various depths have been carried out at some meteorological stations for more than 70-80 years. Processing of these data made it possible to establish patterns of soil temperature changes throughout the day and year.
The change in soil temperature during the day is called the diurnal cycle. The daily variation of temperature usually has one maximum and one minimum. The minimum soil surface temperature in clear weather is observed before sunrise, when the radiation balance is still negative and the heat exchange between air and soil is insignificant. With sunrise, as the sign and magnitude of the radiation balance changes, the soil surface temperature increases, especially in clear weather. The maximum temperature is observed around 13:00, then the temperature begins to decrease, which continues until the morning minimum.
On some days, the indicated daily variation of soil temperature is disrupted under the influence of cloudiness, precipitation and other factors. In this case, the maximum and minimum can shift to a different time. A well-defined and regular diurnal cycle is observed during the warm period in clear weather.
The change in soil temperature throughout the year is called the annual cycle. Typically, the annual cycle graph is based on average monthly soil temperatures. The annual variation of soil surface temperature is determined mainly by the different incoming solar radiation throughout the year. The maximum average monthly soil surface temperatures in temperate latitudes of the northern hemisphere are usually observed in July, when the heat influx to the soil is greatest, and the minimum in January - February.
The difference between the maximum and minimum in a daily or annual cycle is called amplitude temperature progress.
Factors influencing the amplitude of daily and annual variations in soil temperature
The amplitude of the daily variation of soil temperature is influenced by:
1) time of year; in summer the amplitude is greatest, in winter it is smallest;
2) geographic latitude; the amplitude is related to the midday altitude of the Sun, which on the same day increases in the direction from the pole to the equator; therefore, in the polar regions the amplitude is insignificant, and in tropical deserts, where the effective radiation is also high, it reaches 50-60 ° C;
3) terrain; Compared to the plain, the southern slopes heat up more strongly, the northern ones less, and the western ones slightly more strongly than the eastern ones; the amplitude also changes accordingly;
4) vegetation and snow cover; the amplitude of the diurnal cycle under these covers is less than in their absence;
5) heat capacity and thermal conductivity of the soil; the amplitude is inversely related to heat capacity and thermal conductivity;
6) soil color; the amplitude of the daily variation of the surface temperature of dark soils is greater than that of light soils, since the absorption of radiation and its emission on dark surfaces is greater than on light ones; the surfaces of dry and loose soils have a greater amplitude than the surfaces of wet and dense soils;
7) cloudiness: in cloudy weather the amplitude is significantly less than in clear weather.
The amplitude of the annual variation in soil surface temperature is influenced by the same factors as the amplitude of the daily variation, with the exception of the time of year. The amplitude of the annual cycle, in contrast to the daily cycle, increases with increasing latitude. In the equatorial zone it averages 2-3° C, and in the polar regions of the continents it exceeds 70° C (Yakutia).
The amplitude of the annual temperature variation of the bare soil surface is much greater than that of a surface covered with vegetation or snow.
Patterns of heat distribution in soil
Daily and annual fluctuations in soil surface temperature due to thermal conductivity are transferred to its deeper layers. The soil layer in which the daily and annual temperature variations are observed is called the active layer. The propagation of temperature fluctuations deep into the soil (with a homogeneous soil composition) occurs in accordance with the following Fourier laws.
1. Period of oscillation With does not change with depth, i.e., both on the soil surface and at all depths, the interval between two successive minimums or maximums of temperature is 24 hours in a daily cycle, and 12 months in an annual cycle.
2. If the depth increases in an arithmetic progression, then the amplitude decreases in a geometric progression, i.e., with increasing depth, the amplitude quickly decreases.
A layer of soil in which the temperature does not change during the day is called a layer of constant daily temperature.
Soil temperature __67
In middle latitudes, this layer begins at a depth of 70-100 cm. Layer of constant annual temperature in middle latitudes it lies deeper than 15-20 m.
3. Maximum and minimum temperatures at depths occur later than at the soil surface (Table 15). This delay is directly proportional to depth. Daily maximums and minimums lag for every 10 cm of depth by an average of 2.5-3.5 hours, and annual maximums and minimums lag for every meter of depth by 20-30 days.
Table 15
Average time of onset of maximums and minimums in the daily variation of soil temperature (June)
Depth, cm | Minimum, h min | Maximum, h min | Amplitude of temperature fluctuations, °C |
Nukus (near the Aral Sea, desert) |
|||
Leningrad |
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The above Fourier laws are illustrated by graphs of the daily (Fig. 12) and annual (Fig. 13) variations in soil surface temperature and temperature at various depths. These figures clearly show a decrease in amplitude with depth, a delay in the time of onset of maxima and minima with increasing depth, and the independence of the oscillation period from depth.
According to theoretical Fourier calculations, the depth to which the annual variation of soil temperature manifests itself should be approximately 19 times greater than the depth of manifestation of daily fluctuations. In reality, significant deviations from theoretical calculations are observed, and in many cases the penetration depth of annual fluctuations turns out to be greater than calculated. This is due to differences in soil moisture across depths and over time, changes in the thermal diffusivity of the soil with depth, and other reasons. 68
In northern latitudes, the depth of penetration of the annual variation in soil temperature averages 25 m, in middle latitudes - 15-20 m, in southern latitudes - about 10 m.
Soil temperature regime
Rice. 12. Daily variation of soil temperature in June in Tbilisi.
The numbers on the curves indicate the depth in meters.
// /// IV - V VIUGVIIITO-"X XI XII
Rice. 13. Annual variation of average monthly soil temperature with natural surface in Tbilisi. The numbers on the curves indicate the depth in meters.
Thermoisopleths
Materials from long-term observations of soil temperature at various depths can be presented graphically (Fig. 14). This graph relates soil temperature, depth and time. To construct a graph, depths are plotted on the vertical axis, and time (usually months) is plotted on the horizontal axis. The average monthly soil temperature at different depths is plotted on the graph. Then points with the same temperature are connected by smooth lines, which are called thermoisopleths. Thermal isopleths provide a visual representation of the temperature of the active soil layer at any depth in each month. Such graphs are used, for example, to determine the depth of penetration
elimination of critical temperatures that damage the root system of fruit trees.
"/ III V"UNIX XI -1
Rice. 14. Soil temperature isopleths (Tbilisi).
These graphs are also used in public utilities, industrial and road construction, and land reclamation.
The thickness of the frozen layer must be taken into account when laying drains in reclaimed areas.
The change in soil temperature during the day is called the diurnal cycle. Daily variation of temperature usually has one maximum and one minimum. The minimum soil surface temperature in clear weather is observed before sunrise, when the radiation balance is still negative and the heat exchange between air and soil is insignificant. As the sun rises, the temperature of the soil surface increases, especially in clear weather. The maximum temperature is observed around 13:00, then the temperature begins to decrease, which continues until the morning minimum. On some days, the indicated daily variation of soil temperature is disrupted under the influence of cloudiness, precipitation and other factors. In this case, the maximum and minimum can shift to a different time (Fig. 4.2).
Figure 4.2. Daily variation of air and soil temperatures on the surface and at various depths (Voronezh, August). (available when downloading the full version of the textbook)
The change in soil temperature throughout the year is called the annual cycle. Typically, the annual cycle graph is based on average monthly soil temperatures. Annual variation of soil surface temperature determined mainly by the different arrivals of solar radiation throughout the year. The maximum average monthly soil surface temperatures in the temperate latitudes of the northern hemisphere are usually observed in July, when the heat influx to the soil is greatest, and the minimum in January - February.
The difference between the maximum and minimum in a daily or annual cycle is called temperature variation amplitude.
The amplitude of the daily variation of soil temperatures is affected by; time of year, geographic latitude, terrain, vegetation and snow cover, heat capacity and thermal conductivity of the soil, soil color, cloudiness (Fig. 4.3).
Figure 4.3. Soil thermoisopleths, annual variation(available when downloading the full version of the textbook)
The amplitude of the annual variation in soil surface temperature is influenced by the same factors as the amplitude of the daily variation, with the exception of the time of year. The amplitude of the annual cycle, in contrast to the daily cycle, increases with increasing latitude.
Daily and annual fluctuations in soil temperature due to thermal conductivity are transferred to its deeper layers. The layer of soil in which the daily and annual temperature variations are observed is called active layer.
The general theory of molecular thermal conductivity proposed by Fourier is applicable to the propagation of heat in soil. Laws of heat propagation in soil are called Fourier's laws.
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1. Processes of heating and cooling of the soil.
2. Thermophysical characteristics of the soil
3. Daily and annual variation of soil temperature. Fourier's laws.
4. Dependence of soil temperature on relief, snow and vegetation cover.
6. The value of soil temperature for plants. Optimization of soil temperature conditions.
1. Processes of heating and cooling of soil
Solar radiation absorbed by land is converted into heat, and part of this heat is used to warm the soil.
The temperature regime of the soil depends on the radiation balance. If it is positive, then the soil surface heats up; and if it is negative, then it cools.
In addition, the soil temperature regime is influenced by processes evaporation And condensation water vapor on the soil surface:
Condensation releases heat, warming the soil.
When evaporation occurs, heat is lost and the soil cools.
There is a continuous exchange of heat between the soil surface and its lower layers.
If the radiation balance is positive, the heat flow is directed from the soil surface inward.
If the radiation balance is negative and the soil surface is colder than the underlying layers, then the heat flow is directed vertically upward.
where d is soil density in kg/m³.
The heat capacity of various soils depends not on their mineral composition, but on the ratio of water and air in their pores. Since the heat capacity of water is approximately 3.5 thousand times greater than that of air, therefore, dry soils have less heat capacity; that is, with the same heat input, they heat up, and when heat is released, they cool more than wet soils.
4. Soil thermal conductivity is the ability of soil to transfer heat from layer to layer.
λ - thermal conductivity coefficient[J·sec/m·ºС].
The highest thermal conductivity is for the mineral part of the soil (i.e. sand, clay), less for soil water and minimal for soil air.
Thermal diffusivity coefficient - characterizes the speed of heat propagation in the soil (the higher it is, the higher the speed).(≈0.1 – 0.2 m²/sec)
Measured in [m²/sec]
The thermophysical characteristics of soil depend on its moisture. As soil moisture increases, the heat capacity constantly increases.
The thermal conductivity of the soil increases until it becomes equal to the thermal conductivity of water [≈ 5.5∙ 10 4 J/sec] and after that it does not change
In this regard, the coefficient of thermal diffusivity with increasing soil moisture first increases sharply and then decreases.
In addition, the temperature regime of the soil depends on:
1. Soil colors (dark ones heat up better).
2. Density of soils (dense soils have greater heat capacity and thermal conductivity than loose soils).
3. Watering and precipitation increase heat loss through evaporation and, thus, cool the soil.
3. Daily and annual variation of soil temperature. Fourier's law
“The change in soil temperature during the day is called daily variation of soil temperature."
The maximum soil temperature during the day is observed at approximately 13:00 local time; minimum – before sunrise. But, under the influence of precipitation, cloudiness and other factors, the maximum and minimum may shift.
“Changes in soil temperature throughout the year - annual variation of soil temperature."
maximum - in July, minimum in January, February.
“The difference between the maximum and minimum values in the daily or annual variation is called the amplitude of the soil temperature variation”
The amplitude of the daily and annual variations in soil temperature depends on:
1. Relief (northern slopes heat up less than southern slopes and, therefore, have a smaller amplitude).
2. Vegetation with snow cover reduces the amplitude, as it reduces the heating and cooling of the soil beneath them.
3. The greater the heat capacity and thermal conductivity of the soil, the smaller its amplitude.
4. Cloudiness – reduces the amplitude of soil temperature.
5. Dark soils have a greater amplitude than light soils, since they absorb and emit radiation better
6. In addition, the amplitude of the daily variation of soil temperature depends on the time of year (it is maximum in summer, minimum in winter).
Fourier's law
The spread of heat deep into the soil occurs in accordance with Fourier's laws:
1).The period of soil temperature fluctuations with depth does not change(that is, the interval between two successive highs and lows, 24 hours, 12 months)
2). The amplitude of the oscillation decreases with depth.
« The layer of soil in which the temperature does not change during the day is called
layer of constant daily soil temperature.”
(in our latitudes it starts from a depth of 70 - 100 cm)
“A layer of the earth’s crust in which the temperature does not change throughout the year - a layer of constant annual temperature.” (for us it starts from a depth of 15 - 20 meters)
“The soil layer in which both daily and annual temperature variations are observed is called the active layer, or
active layer.
3).The maximum and minimum temperatures at depths are delayed compared to the soil surface.
Daily maximums and minimums are delayed by approximately 2.5 - 3.5 hours for every 10 centimeters of depth. Annual highs and lows are approximately
for 20-30 days at 1 meter depth.
4. Dependence of soil temperature on relief, snow and vegetation cover
1. Compared to horizontal areas, the southern slopes heat up more strongly, and the northern slopes heat up less. The western slopes are slightly warmer than the eastern ones (although they are illuminated by the Sun equally, but on the eastern ones part of the heat is spent on the evaporation of dew, since they are illuminated in the first half of the day, and the western ones in the second half, when there is no longer dew).
2. Bare soil heats up more during the day than soil covered with plants, which absorb part of the solar radiation. But at the same time, plants reduce the nighttime cooling of the soil caused by thermal radiation from the Earth. Therefore, at night the soil under vegetation is warmer than bare soil.
3. Snow cover has very low thermal conductivity. This reduces the exchange of heat between the soil and the atmosphere, and protects the soil from deep freezing. (The greater the depth of the snow cover, the shallower the depth of soil freezing. If the snow height is more than 30 centimeters, winter crops do not freeze out in the most severe frosts).
5. Soil freezing and thawing
The soil contains various salts, so it freezes not at 0ºС, but at –0.5; -1.5ºС.
Freezing begins from the upper layers and moves deeper into the soil during the winter.
The depth of freezing depends on:
1. The severity and duration of winter.
2. Snow depths
3. The presence or absence of vegetation cover.
4. Soil moisture (dry ones freeze deeper)
There are areas in the Northern Hemisphere where the soil does not thaw completely even in summer. These are the areas permafrost (permafrost). The thickness of the frozen soil layer ranges from 1 – 2 meters in the south, to 500 meters or more in the north. In summer, the top layer of permafrost thaws to a depth of several tens of centimeters, and some vegetable and grain crops can be cultivated here. But since frozen soil does not allow moisture to pass through, thawed soil is usually excessively wet. Therefore, in the North of our region there are many swamps (hydromorphic soils are formed).
6. The value of soil temperature for plants
Seed germination occurs only at a certain temperature.
Mineral absorption increases with increasing soil temperature.
Cooling the soil below optimal levels retards the growth of underground organs and reduces yield.
But too high a temperature (above optimal) has a negative effect (for example: seed development slows down).
Optimization of soil temperature conditions.
1. Use of thermal insulation and covering materials (polyethylene, glass frames, etc.)
2. Changing the soil albedo by mulching (covered with peat, coal dust, lime)
3. Moistening or drying the soil (this changes the heat consumption for evaporation).
TOPIC: AIR TEMPERATURE REGIME
1. Processes of heating and cooling air.
2. Change in air temperature with altitude.
3. Atmospheric stability.
4. Temperature inversions.
5. Daily and annual air flow.
6. Characteristics of air temperature conditions.
1. Air heating and cooling processes
The lower layers of the atmosphere do not absorb solar radiation well, so the air is heated mainly due to the heat of the earth's surface.
During the day, when the radiation balance is positive, the land has the highest temperature, the air has a lower temperature, and the water is even colder; which has a very high heat capacity.
At night, land cools quickly and has the lowest temperature, air is warmer, and water has the highest temperature, which cools slowly.
Heat transfer in the atmosphere, as well as between the atmosphere and the underlying surface, occurs due to the following processes:
1. Thermal convection - vertical transfer of individual volumes of air. Over warmer areas, the air becomes warmer and therefore lighter than the surrounding air. So he goes up. And its place is taken by colder neighboring air, which also heats up and rises.
Over land, thermal convection occurs during the day during the warm season, and over the seas at night and during the cold season; when the water surface is warmer than the adjacent layers of air.
2. Turbulence – vortex chaotic movements of small volumes of air in the general wind flow. It occurs because individual volumes of air have unequal speeds of movement in the general wind flow. The consequence of turbulence is intense mixing of air.
3. Molecular heat exchange - the exchange of heat between the earth's surface and the adjacent layer of the atmosphere, due to the molecular thermal conductivity of still air. This is a very slow process.
4. Radiative thermal conductivity - the transfer of heat by flows of long-wave radiation from the earth's surface into the atmosphere (E 3) or in the opposite direction (E a).
5. Condensation of water vapor - this releases heat, heating the air. This is especially true for those layers of the atmosphere where clouds form.
2. Change in air temperature with altitude
“The change in air temperature per hundred meters of altitude is called the vertical temperature gradient (VTG)”
|
t n - t in – the difference in air temperature at the lower and upper levels (in degrees Celsius).
Z in - Z n – difference in heights of two levels (in meters).
1. If the temperature at the upper level is less than the temperature at the lower level, then the temperature decreases with height and VGT is positive. This is the normal state of the troposphere. ( troposphere- this is the lowest layer of the atmosphere to a height of 10–12 kilometers from the earth’s surface).
2. If the temperature at the upper level is equal to the temperature at the lower level, then the VGT is 0ºC/100m, that is, the temperature does not change with altitude. This condition is called isothermia.
3. If the temperature at the upper level is greater than the temperature at the lower level, then the temperature increases with height. This condition is called temperature inversion. VGT is negative.
The maximum value of the WHT is achieved over land on clear summer days, when the air temperature at the soil surface can be 10 degrees or more higher than the temperature at a height of 2 meters; that is, in a given two-meter layer of air, in terms of 100 meters, it is more than 500ºС/100m.
Above this layer, the VGT decreases significantly. In addition, in any layer of air, cloudiness, precipitation, and also wind, mixing air masses, contribute to a noticeable decrease in VGT.
3. Atmospheric stability
Atmospheric stability is the ability of the atmosphere to cause air volumes to move in the vertical direction.
If a large volume of air rises, it enters layers with lower atmospheric pressure. As a result, this air expands and its pressure and temperature decrease. When the air descends, the reverse process occurs.
1. If VGT surrounding there will be air less than 1ºС/100m, then the rising air at all altitudes will be colder than the surrounding air and, therefore, heavier. Therefore, it will soon begin to descend. This state is called stable equilibrium of the atmosphere.
2. If the ambient air temperature
equal to 1ºС/100m, then rising
the air will always have the same
temperature, like the surrounding
air. So soon he will stop
rise, but also fall, not
Will. This state of the atmosphere
called indifferent. Stable equilibrium of atmospheres.
3. If the VGT of the surrounding air is more than 1ºС/100m, which often happens in summer, when
strong heating of the earth's surface, then the rising air at all altitudes will be warmer than the surrounding air and it will constantly rise, right up to the upper boundaries of the troposphere; where clouds usually form in it, mainly cumulonimbus, from which showers and hail fall.
This state of the atmosphere is called unstable equilibrium. It is more often observed in hot, sunny weather.
Indifferent state of the atmosphere. Unstable equilibrium of the atmosphere
4. Temperature inversions
Inversion is an increase in air temperature with height.
Depending on the conditions of education there are:
1. Radiation inversions – occur during radiation cooling of the earth’s surface.
There are two types of radiation inversions:
A). Nocturnal - formed in the warm season in clear, windless weather. They intensify during the night and reach their maximum at dawn. After sunrise, the inversion begins to collapse. The height of the inversion layer is several tens of meters, in closed mountain valleys it is up to 200 meters.
B). Winter - formed both at night and during the day; but only in the cold season, when anticyclonic weather causes long-term (often several weeks in a row) cooling of the earth’s surface. The height of the inversion layer is up to 2-3 kilometers. Particularly strong inversions are observed in closed basins where cold air stagnates. This is typical for Eastern Siberia (for example: Oymyakon and Verkhoyansk - down to -71ºС - the cold pole of the Northern Hemisphere).
2. Advective inversions - are formed during advection, (that is, horizontal movement) of warm air onto a cold surface, which cools the lower layers of this air.
If warm air moves over the snow surface, then such advective inversions are called snow inversions.
5. Daily and annual variation of air temperature
In the daily variation of air temperature (at a height of 2 meters) - maximum at 14 - 15 hours, local time; minimum before sunrise.
The amplitude of the daily variation of air temperature depends on the time of year and cloudiness in the same way as the amplitude of soil temperature.
In addition, the amplitude of the daily variation of air temperature is influenced by the nature of the underlying surface; firstly, this includes the surface topography:
A). In concave relief forms (basins, mountain valleys, ravines) during the day the air stagnates and warms up; and at night, cooled air flows from the slopes to the bottom. As a result, the amplitude increases, the maximum and minimum are more pronounced.
B). Convex relief forms (hills, elevations) are freely blown by the wind, the air above them does not stagnate. During the day, the air warms up less than in the basin, and at night, cooled, it flows down.
The maximum and minimum are less pronounced here, the amplitude is therefore smaller.
In addition, the amplitude of the daily variation in air temperature is affected by snow and vegetation cover - it reduces the amplitude compared to bare soil; because such soil heats up better and cools more, and from it - the lower layer of air.
In the annual course of air temperature in our latitudes, the maximum is observed in July, the minimum in January.
The amplitude of the annual variation in air temperature depends mainly on the geographic latitude of the place (from the equator to the poles it increases), as well as on the distance of the area to the sea (the closer to the sea, the smaller the amplitude even at the same latitude).
The greater the amplitude of the annual variation in air temperature, the more continental the climate.
6. Air temperature characteristics
1.Average temperatures:
A). Average daily temperature is the arithmetic mean of temperatures measured during all observation periods during the day (this is 8 measurements).
b). Average monthly temperature is the arithmetic mean of the average daily temperatures for the entire month.
V). Average annual temperature is the arithmetic mean of the average monthly temperatures for the entire year.
(but the average annual temperature cannot fully characterize the climate; for example: in Ireland and Kalmykia it is +10ºС, but in Ireland the average January temperature is +7ºС, and in Kalmykia -6ºС. The average July temperature is +15ºС, and in Kalmykia +24ºС. Therefore in geography, the average temperatures of January and July are most often used as the coldest and warmest months).
2. Information about average temperatures, maximum and minimum temperatures is significantly supplemented.
A). There are simply maximum and minimum temperatures.
(for example: maximum and minimum daily temperature, ten-day temperature, etc.) that is this is the maximum or minimum temperature for the entire measurement period (day, month, year, etc.
b). And there are absolute maximum and minimum temperatures - this is the lowest or highest temperature observed over a long period on a given day, month, or year as a whole (for example: July 24, or in February, or for the year as a whole).
3. Sums of temperatures – an indicator that conventionally characterizes the amount of heat in a given area for a certain period.
A). Sum of active temperatures - sum of average daily temperatures above +10ºС
b). The sum of effective temperatures is the sum of average daily temperatures measured from the biological minimum of a given crop.
Biological minimum – the minimum average daily temperature at which plants of a given crop are able to develop. (for example: spring wheat +5ºС; corn, cucumbers +10ºС).