How to calculate the moisture coefficient. How is the moisture coefficient determined and why is this indicator so important? In which regions of Russia is the coefficient greater than one
Evaporation
The amount of precipitation does not yet give a complete picture of the moisture supply of the territory, since part of the precipitation evaporates from the surface, and the other part seeps into the soil. At different temperatures, it evaporates from the surface different quantity moisture. The amount of moisture that can evaporate from a water surface at a given temperature is called the volatility. It is measured in millimeters of the evaporated water layer. Evaporation characterizes the possible evaporation. The actual evaporation cannot be more than the annual amount of precipitation. Therefore, in the desert Central Asia it is no more than 150-200 mm per year, although evaporation here is 6-12 times higher. To the north, evaporation increases, reaching 450 mm in the southern part of the taiga Western Siberia and 500-550 mm in mixed and broad-leaved forests of the Russian Plain. Further north of this strip, evaporation again decreases to 100-150 mm in the coastal tundra. In the northern part of the country, evaporation is limited not by the amount of precipitation, as in deserts, but by the amount of evaporation.
Moisture coefficient
To characterize the provision of the territory with moisture, the moisture coefficient is used - the ratio of the annual amount of precipitation to evaporation for the same period.
The lower the humidity coefficient, the drier the climate. Near the northern border of the forest-steppe zone, the amount of precipitation is approximately equal to the annual evaporation. The moisture coefficient here is close to unity. Such moisture is considered sufficient. Humidification of the forest-steppe zone and the southern part of the mixed forest zone fluctuates from year to year in the direction of increasing or decreasing, therefore it is unstable. When the moisture coefficient is less than one, moisture is considered insufficient (steppe zone). In the northern part of the country (taiga, tundra), the amount of precipitation exceeds evaporation. The moisture coefficient here is greater than unity. Such moisture is called excessive.
The moisture coefficient expresses the ratio of heat and moisture in a particular area and is one of the important climatic indicators, as it determines the direction and intensity of most natural processes.
In areas of excessive moisture, there are many rivers, lakes, swamps. Erosion dominates in the transformation of the relief. Meadows and forests are widespread.
High annual values of the moisture coefficient (1.75-2.4) are typical for mountain areas with absolute surface elevations of 800-1200 m. 500 mm per year or more. The minimum values of the moisture coefficient from 0.35 to 0.6 are characteristic of the steppe zone, the vast majority of the surface of which is located at elevations of less than 600 m abs. height. The moisture balance here is negative and is characterized by a deficit of 200 to 450 mm or more, and the territory as a whole is characterized by insufficient moisture, typical of a semi-arid and even arid climate. The main period of moisture evaporation lasts from March to October, and its maximum intensity falls on the hottest months (June - August). Smallest values moisture coefficients are observed in these months. It is easy to see that the amount of excess moisture in mountainous areas is comparable, and in some cases exceeds the total amount of precipitation in the steppe zone.
Moisture coefficient of Vysotsky -- Ivanov
Humidity coefficient -- the ratio between the amount of precipitation for a year or other time and the evaporation rate of a certain area. Humidity coefficient is an indicator of the ratio of heat and moisture. For the first time, a method for characterizing climate as a factor in the water regime of soils was introduced into the practice of soil science by G. N. Vysotsky. He introduced the concept of the moisture coefficient of the territory (K) as a value showing the ratio of the amount of precipitation (Q, mm) to evaporation (V, mm) for the same period (K=Q/V). According to his calculations, this value is 1.38 for the forest zone, 1.0 for the forest-steppe zone, 0.67 for the steppe chernozem zone, and 0.3 for the dry steppe zone.
Subsequently, the concept of the moisture coefficient was developed in detail by B. G. Ivanov (1948) for each soil-geographical zone, and the coefficient became known as Vysotsky coefficient-- Ivanova(KU).
According to the provision of land with water and the characteristics of soil formation on the globe the following areas can be distinguished (Budyko, 1968) (Table 2)
table 2
climatic regions
In accordance with the influx of moisture and its further redistribution, each natural region is characterized by a dryness radiation index
where I am radiation balance, kJ / (cm 2 * year); r -- the amount of precipitation per year, mm; a -- latent heat phase transformations water, J/g.
Exercise 1.
Calculate the moisture coefficient for the points indicated in the table, determine in which natural zones they are located and what kind of moisture is typical for them.
The moisture coefficient is determined by the formula:
K - moisture coefficient in the form of a fraction or in%; P is the amount of precipitation in mm; Em - volatility in mm. According to N.N. Ivanov, the moisture coefficient for the forest zone is 1.0-1.5; forest-steppe 0.6 - 1.0; steppes 0.3 - 0.6; semi-deserts 0.1 - 0.3; desert less than 0.1.
Moisture characteristics by natural zones
|
Evaporation |
Moisture coefficient |
Moisturizing |
natural area |
||
|
insufficient |
forest-steppe |
||||
|
insufficient | |||||
|
insufficient | |||||
|
insufficient |
semi-desert |
For an approximate assessment of moisture conditions, a scale is used: 2.0 - excessive moisture, 1.0-2.0 - satisfactory moisture, 1.0-0.5 - arid, insufficient moisture, 0.5 - dry
For 1 item:
K = 520/610 K = 0.85
Arid, insufficient moisture, natural zone - forest-steppe.
For 2 items:
K = 110/1340 K = 0.082
Dry, insufficient moisture, natural zone - desert.
For 3 items:
K = 450/820 K = 0.54
Arid, insufficient moisture, natural zone - steppe.
For 4 items:
K = 220/1100 K = 0.2
Dry, insufficient moisture, natural zone - semi-desert.
Task 2.
Calculate the moisture coefficient for the Vologda Oblast, if the average annual precipitation is 700 mm, evaporation is 450 mm. Make a conclusion about the nature of moisture in the area. Consider how moisture will change under different hilly conditions.
Moisture coefficient (according to N. N. Ivanov) is determined by the formula:
where, K - moisture coefficient in the form of a fraction or in%; P is the amount of precipitation in mm; Em - volatility in mm.
K = 700/450 K = 1.55
Conclusion: In the Vologda Oblast, located in natural area- taiga, excessive moisture, because moisture factor is greater than 1.
Humidification in different conditions of a hilly terrain will change, it depends on: the geographical latitude of the area, the area occupied, the proximity of the ocean, the height of the relief, the moisture coefficient, the underlying surface, and the exposure of the slopes.
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Exercise 1. Calculate the moisture coefficient for the points indicated in the table, determine in which natural zones they are located and what kind of moisture is typical for them.
The moisture coefficient is determined by the formula:
K - moisture coefficient in the form of a fraction or in%; P is the amount of precipitation in mm; Em - volatility in mm. According to N.N. Ivanov, the moisture coefficient for the forest zone is 1.0-1.5; forest-steppe 0.6 - 1.0; steppes 0.3 - 0.6; semi-deserts 0.1 - 0.3; desert less than 0.1.
Moisture characteristics by natural zones
For an approximate assessment of moisture conditions, a scale is used: 2.0 - excessive moisture, 1.0-2.0 - satisfactory moisture, 1.0-0.5 - arid, insufficient moisture, 0.5 - dry
For 1 item:
K = 520/610 K = 0.85
Arid, insufficient moisture, natural zone - forest-steppe.
For 2 items:
K = 110/1340 K = 0.082
Dry, insufficient moisture, natural zone - desert.
For 3 items:
K = 450/820 K = 0.54
Arid, insufficient moisture, natural zone - steppe.
For 4 items:
K = 220/1100 K = 0.2
Dry, insufficient moisture, natural zone - semi-desert.
Task 2. Calculate the moisture coefficient for the Vologda Oblast, if the average annual precipitation is 700 mm, evaporation is 450 mm. Make a conclusion about the nature of moisture in the area. Consider how moisture will change under different hilly conditions.
Moisture coefficient (according to N. N. Ivanov) is determined by the formula:
where, K - moisture coefficient in the form of a fraction or in%; P is the amount of precipitation in mm; Em - volatility in mm.
K = 700/450 K = 1.55
Conclusion: In the Vologda region, located in the natural zone - taiga, moisture is excessive, because. moisture factor is greater than 1.
Humidification in different conditions of a hilly terrain will change, it depends on: the geographical latitude of the area, the area occupied, the proximity of the ocean, the height of the relief, the moisture coefficient, the underlying surface, and the exposure of the slopes.
Literature
1. Brief geographical encyclopedia, Volume 4 / Ch. ed. Grigoriev A.A. M.: Soviet Encyclopedia- 1964, 448 p.
2. Neklyukova N.P. General geography. M.: 1976
3. Pavlova M.D. Workshop on agrometeorology. - L .: Gidrometeoizdat, 1984
4. Pashkang K.V. Workshop on general geography. M.: graduate School. 1982.
As you know, the balance of moisture in nature is maintained by the cycle of water evaporation and precipitation. Areas that receive little rain or snow during the year are considered dry, and areas that experience heavy, frequent rainfall may even suffer from excessive levels of humidity.
But in order for the assessment of moisture to be sufficiently objective, geographers and meteorologists use a special indicator - the coefficient of moisture.
What is the moisture factor?
The degree of moisture in any territory depends on two indicators:
- the number of dropouts per year;
- the amount of moisture evaporated from the soil surface.
Indeed, the humidity of zones with a cool climate, where evaporation is slow due to low temperatures, can be higher than that of a territory located in a hot climate zone, with the same amount of precipitation per year.
How is the moisture content determined?
The formula for calculating the moisture coefficient is quite simple: the annual amount of precipitation must be divided by the annual amount of moisture evaporation. If the division result is less than one, then the area is not sufficiently moistened. 
When the moisture coefficient is equal to or close to unity, the moisture level is considered sufficient. For humid climatic zones, the moisture coefficient significantly exceeds unity.
AT different countries use different methods for determining the coefficient of moisture. The main difficulty lies in the objective determination of the amount of moisture evaporated during the year. In Russia and CIS countries since Soviet Union the technique developed by the outstanding Soviet soil scientist G.N. Vysotsky was adopted.
It is distinguished by high accuracy and objectivity, since it does not take into account the actual level of moisture evaporation, which cannot be more than the amount of rainfall, but the possible amount of evaporation. European and American soil scientists use the Torthwaite method, which is more complex by definition and not always objective.
What is the moisture content for?
Determination of the moisture coefficient is one of the main tools for weather forecasters, soil scientists and scientists in other specialties. Based on this indicator, water supply maps are drawn up, land reclamation plans are developed - draining swampy areas, improving soils for growing crops, etc. 
Meteorologists make their forecasts taking into account many indicators, including the humidity coefficient.
It is important to know that humidity depends not only on air temperature, but also on altitude. As a rule, high values of the coefficient are characteristic of mountainous areas, since it always falls out there than on the plains.
It is not surprising that many small, and sometimes quite major rivers. For areas located at an altitude of 1000-1200 meters above sea level or higher, the humidity coefficient often reaches 1.8 - 2.4. Excess moisture flows downhill in the form of mountain rivers and streams, bringing additional moisture to the drier valleys.
AT natural conditions the value of the moisture coefficient corresponds to the terrain and the presence water resources. Large and small rivers flow in areas of sufficient moisture, there are lakes and streams. With excessive moisture, swamps are often formed that are subject to drainage. 
In areas of insufficient moisture, water bodies are rare, since the soil releases all the moisture that falls on it into the atmosphere.
Calculated according to the formula ,
where is the moisture coefficient,
R is the average annual rainfall, in mm.
E - evaporability value (the amount of moisture that can evaporate from the water surface at a given temperature), in mm.
distinguish the following types of territory:
At >1 - excess moisture ( tundra, forest-tundra, taiga, and with a sufficient amount of heat, forests of temperate and equatorial latitudes) - humid areas
In areas with excessive moisture, the abundance of moisture adversely affects the processes of aeration (ventilation) of the soil, i.e., the gas exchange of soil air with atmospheric air. The lack of oxygen in the soil is formed due to the filling of the pores with water, which is why air does not enter there. This disrupts the biological aerobic processes in the soil, the normal development of many plants is disrupted or even stopped. In such areas, hygrophyte plants grow and hygrophilous animals live, which are adapted to damp and humid habitats. In order to involve territories with excessive moisture in economic, primarily agricultural, circulation, drainage reclamation is necessary, that is, measures aimed at improving the water regime of the territory, removing excess water (drainage).
At ≈1 - sufficient moisture ( mixed or broadleaf forests)
At 0.3< <1 - увлажнение недостаточное (если <0.6 - steppe, >0.6 - forest-steppe) Allocate different degrees of unstable moisture: territories with To uv \u003d 1-0.6 (100-60%) are characteristic of meadow steppes ( forest-steppe) and savannas, with To uv = 0.6-0.3 (60-30%) - dry steppes, dry savannas. They are characterized by a dry season, which makes agricultural development difficult due to frequent droughts. In the steppes, irrigation is most effective with sufficient river flow. Additional measures are snow accumulation - preserved stubble in the fields and planting shrubs along the edge of the beams so that snow does not blow off into them, and snow retention - rolling snow, creating snow banks, covering snow with straw in order to increase the duration of snowmelt and replenish groundwater reserves. Forest shelterbelts are also effective, which delay the runoff of melted snow water and lengthen the snowmelt period. Windproof (windbreak) forest strips of great length, planted in several rows, weaken the speed of winds, including dry winds, and thereby reduce moisture evaporation.
At<0.3 - скудное увлажнение (если <0.1 - desert, >0.1 - semi-desert) extraarid zones The main reclamation activity in them is irrigation - artificial replenishment of moisture reserves in the soil for the normal development of plants and watering - the creation of sources of moisture (ponds, wells and other water bodies) for domestic and household needs and watering of livestock.
Under natural conditions, in deserts and semi-deserts, plants grow that are adapted to dryness - xerophytes. They usually have a strong root system capable of extracting moisture from the ground, small leaves, sometimes turned into needles and thorns, in order to evaporate less moisture, the stems and leaves are often covered with a wax coating. A special group of plants among them is formed by succulents that accumulate moisture in stems or leaves (cacti, agaves, aloe).
To assess the moisture content in a given landscape, we also use dryness radiation index, which is the reciprocal of the moisture coefficient. And it is calculated according to the formula
5. Air humidity. The main factors affecting the geographical distribution of humidity. Hydrometeors.
The Earth's atmosphere contains about 14 thousand km 3 of water vapor. Water enters the atmosphere as a result of evaporation from the underlying surface.
Evaporation. The process of evaporation from the surface of water is associated with the continuous movement of molecules inside the liquid. Water molecules move in different directions and at different speeds. At the same time, some molecules located near the surface of the water and having a high speed can overcome the forces of surface cohesion and jump out of the water into the adjacent layers of air.
The rate and magnitude of evaporation depend on many factors, primarily on temperature and wind, on the deficit of humidity and pressure. The higher the temperature, the more water can evaporate. The role of wind in evaporation is clear. The wind constantly carries away the air that has managed to absorb a certain amount of water vapor from the evaporating surface, and continuously brings new portions of drier air. According to observations, even a weak wind (0.25 m/s) increases evaporation by almost three times.
During evaporation from the land surface, vegetation plays a huge role, since, in addition to evaporation from the soil, evaporation by vegetation (transpiration) occurs.
AT atmosphere moisture condenses, moves by air currents and again falls in the form of various precipitations on the surface of the Earth, thus making a constant cycle of water
To quantify the content of water vapor in the atmosphere, various characteristics of air humidity are used.
Elasticity (actual) of water vapor (e) - the pressure of water vapor in the atmosphere is expressed in mm Hg. or in millibars (mb). Numerically, it almost coincides with absolute humidity (the content of water vapor in the air in g / m 3), therefore elasticity is often called absolute humidity.
Saturation elasticity (maximum elasticity) (E) - the limit of water vapor content in the air at a given temperature. The value of saturation elasticity depends on the air temperature, the higher the temperature, the more it can contain water vapor.
There are other important characteristics of humidity, such as moisture deficit and dew point.
Moisture deficit (D) - the difference between the saturation elasticity and the actual elasticity:
absolute humidity. The amount of water vapor currently in the air is called absolute humidity. Absolute humidity is expressed in grams per 1 m 3 air or in units of pressure: millimeters and millibars. The most important factor influencing the distribution of absolute humidity is temperature. However, this dependence is somewhat disturbed by the distribution of land and water on the earth's surface, the presence of mountains, plateaus, and other factors. So, in coastal countries, the absolute humidity is usually greater than inside the continents. Nevertheless, temperature still has a dominant value, which can be seen in the following examples.
Along with annual, monthly and daily fluctuations in temperature, the absolute humidity of the air also fluctuates. The amplitude of annual fluctuations in absolute humidity in the tropical zone is 2-3, in the temperate zone 5-6, and within the continents 9-10 mm.
Absolute humidity decreases with altitude. From observations of 74 ascents of balloons in Europe, it was found that the average annual absolute humidity at the earth's surface is 6.66 mm; at an altitude of 500 m - 6,09 mm; 1 thousand m - 4,77 mm; 2 thousand m - 2.62 mm; 5 thousand m- 0,52 mm; 10 thousand m- 0,02 mm.
If the saturated air is heated, then it again moves away from saturation and again acquires the ability to perceive a new amount of water vapor. Conversely, if saturated air is cooled, it oversaturated and under these conditions begins condensation, i.e., condensation of excess water vapor. If you cool the air that is not saturated with water vapor, then it will gradually approach saturation. The temperature at which unsaturated air becomes saturated is called DEW POINT. If the air cooled to the dew point (τ) cools further, then it also begins to release excess water vapor by condensation. It is clear that the position of the dew point depends on the degree of humidity in the air. The more humid the air, the sooner the dew point will come, and vice versa.
From all that has been said, it is clear that the ability of air to receive and contain various maximum amounts of water vapor is directly dependent on temperature.
If the air contains less water vapor than is needed to saturate it at a given temperature, it can be determined how close the air is to saturation. To do this, calculate the relative humidity.
Relative humidity (r) - the ratio of the actual elasticity of water vapor to saturation elasticity, expressed as a percentage:
When saturated, e \u003d E, r \u003d 100%.
if the relative humidity is close to 100%, then precipitation becomes very likely; at low relative humidity, on the contrary, precipitation will be unlikely.
It is not hard to see that the relationship between relative humidity and air temperature will be largely inverse. The higher the temperature, the further the air is from saturation, and consequently, its relative humidity will be less. In this way, in in polar countries, where low temperatures prevail, relative humidity may be greatest, and in tropical countries it may be less. Low relative humidity is observed in subtropical latitudes, especially on land, the lowest - in deserts, where the average annual relative humidity is less than 30%. Relative humidity is influenced by other factors besides temperature. Therefore, there is no such close relationship that we observed between absolute humidity and temperature.
The annual variation of relative humidity is also the reverse of the annual variation of temperature. Inside the continents in our latitudes, the relative humidity is the highest in winter, and the lowest in summer and spring.
Various hygrometers and psychrometers are used to measure air humidity. Of the hpix, the most widely used are: weight hygrometer, hair hygrometer, hygrograph and Assmann psychrometer.
Geographical distribution of humidity:
The maximum air humidity on land is observed in the area of equatorial forests.
Humidity, like temperature, decreases with latitude. In addition, in winter, it, like temperature, is lower on the continents and higher on the oceans, so in winter the isolines of vapor pressure or absolute humidity, like isotherms, are bent over the continents towards the equator. Over the very cold hinterland of Central and East Asia, even an area of especially low vapor pressure with closed isolines arises.
However, in summer the correspondence between temperature and vapor content is less. Temperatures inside the continents are high in summer, but actual evaporation is limited by moisture reserves, so water vapor can enter the air no more than over the oceans, and in fact it enters less. Consequently, the vapor pressure over the continents is not increased in comparison with the oceans, despite the higher temperature. Therefore, in contrast to the isotherms, the isolines of vapor pressure in summer do not bend over the continents to high latitudes, but pass close to the latitudinal circles. And deserts, such as the Sahara or the deserts of Central and Central Asia, are areas of low vapor pressure with closed isolines.
In continental areas with prevailing year-round air transport from the ocean, for example, in Western Europe, the vapor content is quite large, close to oceanic both in winter and summer. In monsoon regions, such as the south and east of Asia, where air currents are directed from the sea in summer and from land in winter, the vapor content is high in summer and low in winter.
Relative humidity is always high in the equatorial zone, where the content of vapor in the air is very high, and the temperature is not too high due to large clouds. Relative humidity is always high in the Arctic Ocean, in the north of the Atlantic and Pacific Oceans, in Antarctic waters, where it reaches the same or almost the same high values as in the equatorial zone. However, the reason for the high relative humidity is different here. The content of air vapor in high latitudes is insignificant, but the air temperature is also low, especially in winter. Similar conditions are observed in winter over cold continents of middle and high latitudes.
Very low relative humidity (up to 50% and below) is observed all year round in subtropical and tropical deserts, where at high temperatures the air contains little steam.
HYDROMETEORS
precipitation released directly from the air on the earth's surface and on objects (dew, hoarfrost, frost, etc.).
1. Hydrometeors are many small droplets of water or ice falling from the atmosphere, formed on terrestrial objects, lifted by the wind into the air from the surface of the Earth.
Falling out precipitations are overcast, drizzling and torrential.
Precipitation can be characterized as monotonous precipitation. The duration of continuous loss can be from an hour to several days. The reason is nimbostratus and altostratus clouds with continuous cloudiness. By the way, if the temperature is below minus ten degrees, light snow can fall with a cloudy sky (rain, supercooled rain, freezing rain, snow, sleet).
Rain is the condensate of water vapor falling to the surface in the form of water droplets. In diameter, such droplets are from 0.4 to 6 millimeters.
Supercooled rain is ordinary raindrops, but falling when the air temperature is below zero degrees. When in contact with objects, these water droplets instantly freeze and turn into ice.
Freezing rain - drops of water in an ice shell with a diameter of one to three millimeters. Upon impact with objects, the shell is destroyed, water flows out and turns into ice. This is how ice forms.
Snow is frozen drops of water. Fall out in the form of snowflakes (snow crystals) or snow flakes.
Rain with snow - a mixture of raindrops with snowflakes.
Drizzling precipitation has a low intensity, but is characterized by monotony (drizzle, supercooled drizzle, snow grains). They usually begin and end gradually. The duration of such precipitation ranges from several hours to several days. The fallout is caused by stratus clouds or fog in overcast or heavy clouds. Associated phenomena: haze, fog.
Drizzle is very small droplets of water less than 0.5 mm in diameter. When falling on the surface of the water, drizzle does not form divergent circles.
Supercooled drizzle is normal drizzle, but falling when the air temperature is below zero degrees. When in contact with objects, drizzle instantly freezes and turns into ice.
Snow grains are frozen water droplets less than two millimeters in diameter. They look like white grains, grains or sticks.
Rainfall begins and ends abruptly. During the fall, the intensity of precipitation changes. The duration is from several minutes to two hours (rain shower, snow shower, sleet shower, snow pellet, ice pellet, hail). Accompanying phenomena are strong winds and often thunderstorms. The cause of the fallout are cumulonimbus clouds. Cloudiness can be both significant and small.
Heavy rain is a normal downpour.
Showers of snow - a characteristic feature is snow charges lasting from several minutes to half an hour. Visibility varies from 10 kilometers to 100 meters.
Heavy rain with snow is a mixture of raindrops with snowflakes that have a shower character.
Snow groats - rainfall precipitation of white fragile grains with a diameter of up to 5 millimeters.
An ice pellet is a shower of solid ice grains with a diameter of one to three millimeters. Sometimes ice grains are covered with a water film. When the air temperature is below zero degrees, the grains freeze, and ice forms.
Hail is the precipitation of solid precipitation when the air temperature is above ten degrees. Ice cubes come in various shapes and sizes. The average diameter of hailstones is from two to five millimeters, but sometimes much more. Each hailstone consists of several layers of ice. The duration of such precipitation is from one to twenty minutes. Very often, hail is accompanied by a downpour with a thunderstorm, which is typical of the nature of the middle Volga.
6. Clouds and overcast. Types of precipitation and types of annual precipitation.
The main reason for the formation of clouds is the upward movement of air, with this movement of air, water vapor is adiabatically cooled and condensed. All clouds, according to the nature of the structure and the height at which they form, are divided into 4 families, 10 main genera of clouds. 1st family: clouds of the upper tier, the lower limit is 6000m. This family includes cirrus, cirrocumulus, cirrostratus clouds; 2 family: clouds of the middle tier, lower limit 2 km; Clouds of the lower tier from 2000 - near the earth's surface (stratocumulus, stratus, nimbostratus); Clouds of vertical development , the upper limit is the limit of the level of cirrus clouds, the lower one is 500m (cumulus, cumulonimbus). Upper clouds are usually icy. They are thin, transparent, light, without shadows, white, the sun shines through. Clouds of the middle and lower tiers, usually water, mixed, denser than cirrus, they can cause colored crowns around the sun and moon due to the diffraction of light and water droplets. The clouds of the lower tier are composed of tiny drops of water and snowflakes. Clouds of vertical development are formed during ascending air currents. Convection clouds have a diurnal course. Clouds of vertical development are formed more often on the plains. Cloudiness - the degree of cloud coverage of the sky or the total amount of clouds in the sky. Cloudiness is determined by eye points, expressed as how many tens of shares of the sky are covered with clouds. Mark 1, 2, 3, points, which is 0.1, 0.2, 0.3 of the sky covered with clouds. On the surface of the globe, cloudiness is unevenly distributed, in the equatorial zone it is large throughout the year. It decreases towards the tropics, reaching its lowest value from 20-30°C, where deserts have a large distribution. Further to high latitudes, it increases, reaching the highest values of 70-80 ° C, and towards the poles it decreases again due to a decrease in the amount of water vapor. and in Antarctica up to 86%.
Atmospheric precipitation is moisture that has fallen to the surface from the atmosphere in the form of rain, drizzle, grains, snow, hail. Precipitation falls from clouds, but not every cloud gives precipitation. The formation of precipitation from the cloud is due to the coarsening of droplets to a size that can overcome ascending currents and air resistance. The coarsening of drops occurs due to the merging of drops, the evaporation of moisture from the surface of drops (crystals) and condensation water vapor on others.
Precipitation forms:
1. rain - has drops ranging in size from 0.5 to 7 mm (average 1.5 mm);
2. drizzle - consists of small drops up to 0.5 mm in size;
3.sneg - consists of hexagonal ice crystals formed in the process of sublimation;
4.snow groats - rounded nucleoli with a diameter of 1 mm or more, observed at temperatures close to zero. Grains are easily compressed by fingers;
5. ice groats - the nucleoli of the groats have an icy surface, it is difficult to crush them with your fingers, when they fall to the ground they jump;
6.grad - large rounded pieces of ice ranging in size from a pea to 5-8 cm in diameter. The weight of hailstones in some cases exceeds 300 g, sometimes it can reach several kilograms. Hail falls from cumulonimbus clouds.
Precipitation types:
1. Heavy precipitation - uniform, long in duration, falls from nimbostratus clouds;
2. Heavy rainfall - characterized by a rapid change in intensity and short duration. They fall from cumulonimbus clouds as rain, often with hail.
3. Drizzling precipitation - in the form of drizzle falls from stratus and stratocumulus clouds.
The daily course of precipitation coincides with the daily course of cloudiness. There are two types of daily precipitation patterns - continental and marine (coastal). The 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 at different latitudes and even within the same zone. It depends on the amount of heat, thermal regime, air circulation, distance from the coast, the nature of the relief.
Precipitation is most abundant in equatorial latitudes, where their annual amount (GKO) exceeds 1000-2000 mm. On the equatorial islands of the Pacific Ocean, precipitation is 4000-5000 mm, and on the lee slopes of tropical islands up to 10,000 mm. Heavy rainfall is caused by powerful upward currents of very humid air. To the north and south of the equatorial latitudes, the amount of precipitation decreases, reaching a minimum of 25-35º, where the average annual value does not exceed 500 mm and decreases in inland regions to 100 mm or less. In temperate latitudes, the amount of precipitation slightly increases (800 mm). At high latitudes, the GKO is insignificant.
The maximum annual amount of precipitation was recorded in Cherrapunji (India) - 26461 mm. The minimum recorded annual precipitation is in Aswan (Egypt), Iquique - (Chile), where in some years there is no precipitation at all.
