Evaporation on the continent is usually greater than evaporation. Air humidity

Water in the atmosphere. Water properties

Water is everywhere on earth. Oceans, seas, rivers, lakes and other bodies of water occupy 71% of the earth's surface. The water contained in the atmosphere is the only substance that can be there in all three phase states (solid, liquid and gaseous) at the same time.

The most important physical properties of water for meteorology are presented in Table 6.

Table 6 - Physical characteristics of water (Rusin, 2008)

Water properties important for climate formation:

water is an absorber of radiant energy;

It has one of the highest values of specific heat capacity among other substances on earth (this affects the difference in the heating of land and sea, the penetration of radiation and heat deep into the soil and water bodies);

ideal (almost) solvent;

The dipole (bipolar) structure of water molecules provides a high boiling point (without hydrogen bonds, the boiling point would be -80°C).

Expansion upon freezing unlike other substances that shrink. (the maximum density of water is observed at a temperature of +4°C; the density of ice is less than the density of water: distilled by 1/9, sea by 1/7; lighter ice floats on the surface of the water).

Thanks to the processes of evaporation and condensation in the atmosphere, the water cycle continuously occurs, in which a significant amount of it participates. On average, the long-term water cycle is characterized by the following data (Table 1):

Table 1 - Characteristics of the water cycle on Earth (Matveev, 1976)

	Precipitation, mm/year	Evaporation, mm/year	Drain, mm/year
Continents
World Ocean
Earth

From the surface of the oceans (361 million km 2) a layer of water 1127 mm thick (or 4.07 10 17 kg of water) evaporates during the year, from the surface of the continents - 446 mm (or 0.66 10 17 kg of water). The thickness of the annual precipitation layer on the oceans is 1024 mm (or 3.69 10 17 kg of water), on the continents - 700 mm (or 1.04 10 17 kg of water). The amount of precipitation on the continents significantly exceeds evaporation (by 254 mm, or by 0.38 10 17 kg of water). This means that a significant amount of water vapor comes to the continents from the oceans. On the other hand, water (254 mm) that has not evaporated on the continents flows into rivers and further into the ocean. On the oceans, evaporation exceeds (by 103 mm) the amount of precipitation. The difference is replenished by water runoff from the oceans.

Evaporation and evaporation

Water enters the atmosphere as a result of evaporation from the Earth's surface (reservoirs, soil); it is released by living organisms in the process of life (respiration, metabolism, transpiration in plants); it is a by-product of volcanic activity, industrial production and the oxidation of various substances.

Evaporation(usually water) - the entry of water vapor into the atmosphere due to the detachment of the fastest moving molecules from the surface of water, snow, ice, wet soil, droplets and crystals in the atmosphere.

Evaporation from the earth's surface is called physical evaporation. Physical evaporation and transpiration together - total evaporation.

The essence of the evaporation process is the separation of individual water molecules from the water surface or from moist soil and the transition of air as water vapor molecules. The vapor in the atmosphere condenses when the air cools. The condensation of water vapor can also go through sublimation (the process of direct transition of a substance from gaseous to solid, bypassing liquid). Water is removed from the atmosphere by precipitation.

The molecules of a liquid are always in motion, and some of them can break through the surface of the liquid and escape into the air. Those molecules are torn off, the speed of which is higher than the speed of movement of molecules at a given temperature and is sufficient to overcome the forces of cohesion (molecular attraction). As the temperature rises, the number of detached molecules increases. Vapor molecules can return from air to liquid. When the temperature of a liquid rises, the number of molecules leaving it becomes greater than the number of returning ones, i.e. liquid evaporates. A decrease in temperature slows down the transition of liquid molecules into air and causes vapor condensation. If water vapor enters the air, then it, like all other gases, creates a certain pressure. As water molecules pass into the air, the vapor pressure in the air increases. When a state of mobile equilibrium is reached (the number of molecules leaving the liquid is equal to the number of returning molecules), then evaporation stops. Such a state is called saturation , water vapor in this state - saturating , and the air rich . The pressure of water vapor at saturation is called saturated steam pressure (E), or saturation elasticity, or maximum elasticity.

Until the saturation state is reached, then the process of water evaporation takes place, while the elasticity of water vapor (e) above the liquid is less than the maximum elasticity: e<Е.

If the number of returning water molecules is greater than the number of departing ones, then the process of condensation or sublimation (above ice) takes place: e>E.

Saturated water vapor pressure depends on

air temperature,

on the nature of the surface (liquid, ice),

from the shape of this surface,

salinity of water.

Most of the water vapor enters the atmosphere from the surface of the seas and oceans. This is especially true for humid, tropical regions of the Earth. In the tropics, evaporation exceeds precipitation. At high latitudes, the reverse is true. In general, over the entire globe, the amount of precipitation is approximately equal to evaporation.

Evaporation is regulated by some physical properties of the area, in particular, the temperature of the surface of the water and large reservoirs, and the wind speeds prevailing here. When the wind blows over the surface of the water, it carries the humidified air aside and replaces it with fresh, drier air (i.e., advection and turbulent diffusion are added to molecular diffusion). The stronger the wind, the faster the air changes and the more intense the evaporation.

Evaporation can be characterized by the speed of the process. Evaporation rate (V) is expressed in millimeters of a layer of water evaporated per unit of time from a unit of surface. It depends on saturation deficit, atmospheric pressure and wind speed.

Evaporation in real conditions is difficult to measure. To measure evaporation, evaporators of various designs or evaporation basins (with a cross-sectional area of 20 m 2 or 100 m 2 and a depth of 2 m) are used. But the values obtained from evaporators cannot be equated with evaporation from a real physical surface. Therefore, calculation methods are resorted to: evaporation from the land surface is calculated from data on precipitation, runoff and soil moisture content, which are easier to obtain by measurements. Evaporation from the sea surface can be calculated using formulas close to the total equation.

Distinguish between actual evaporation and evaporation.

Evaporation- potential evaporation in a given area under the existing atmospheric conditions in it.

This implies either evaporation from the water surface in the evaporator; evaporation from the open water surface of a large reservoir (natural freshwater); evaporation from the surface of excessively moistened soil. Evaporation is expressed in millimeters of evaporated water per unit time.

Evaporation is low in the polar regions: about 80mm/year. This is due to the fact that low temperatures of the evaporating surface are observed here, and the pressure of saturated water vapor E S and the actual pressure of water vapor are small and close to each other, therefore the difference (E S – e) is small.

In temperate latitudes, evaporation changes within a wide range and tends to increase when moving from the northwest to the southeast of the mainland, which is explained by an increase in the saturation deficit in the same direction. The lowest values in this belt of Eurasia are observed in the northwest of the mainland: 400–450 mm, the highest (up to 1300–1800 mm) in Central Asia.

in the tropics evaporation is low on the coasts and sharply increases in the inland parts to 2500–3000 mm.

near the equator evaporation is relatively low: does not exceed 100 mm due to the small saturation deficit.

Actual evaporation on the oceans coincides with evaporation. On land, it is significantly less, mainly depending on the moisture regime. Difference between evaporation and precipitation can be used to calculate the air humidity deficit.

The most important component of the water balance is evaporation. The problem of obtaining climate-reliable information on evaporation is much more acute than on precipitation. The vast majority of known data is based on calculation methods. Calculations are more or less reliable above the water surface, where one can take evaporation for evapotranspiration and calculate this value. Over land, such an approach is impossible, therefore, on a sparse network, a direct measurement of evaporation is carried out, however, spatial climatic generalization of these data is difficult (Kislov A.V., 2011).

On fig. 3.5 and in table. Table 3.3 shows the calculated annual amounts of evaporation from the underlying surface, from which it follows that evaporation from the oceans significantly exceeds evaporation from the land. In most of the World Ocean in middle and low latitudes, evaporation varies from 600 to 2500 mm, and the maxima reach 3000 mm. In polar waters, in the presence of ice, evaporation is relatively small. On land, annual evaporation amounts range from 100–200 mm in polar and desert regions (even less in Antarctica) to 800–1000 mm in humid tropical and subtropical regions (southern Asia, the Congo Basin, southeast USA, east coast of Australia , islands of Indonesia, Madagascar). The maximum values on land are slightly more than 1000 mm (Khromov S.P., Petrosyants M.A., 2001).

Rice. 3.5. Distribution of average annual values (mm/year) of evaporation from the underlying surface (Atlas of the heat balance of the globe, 1963)

Table 3.3. Annual evaporation values (mm) for different zones of the Northern Hemisphere (according to Budyko M.I., 1980)

Thus, on average over the latitudinal zones in the Northern Hemisphere, the highest annual evaporation values are observed in the tropics. As we move from the tropics to the poles, evaporation decreases. In the equatorial zone and at high latitudes, the average annual values of evaporation over land and sea are approximately the same, but in the tropics and temperate latitudes, evaporation from the sea surface is greater than from the land surface. The distribution of evaporation is similar in the Southern Hemisphere, but in the whole hemisphere, evaporation is higher and is approximately 1250 mm, so the area occupied by the ocean is larger in that hemisphere (for the Northern Hemisphere, the average annual evaporation is about 770 mm) (Climatology, 1989).

To obtain physically substantiated ideas about the features of the spatial pattern of evaporation, it can be taken into account that the turbulent flow of water vapor is determined by the vertical moisture gradient in the near-water layer and the development of the turbulent regime, which can be parametrically characterized by the modulus of the wind velocity vector and the criterion of atmospheric stratification stability. From this point of view, it becomes clear, for example, why evaporation is high along the cores of warm currents (Gulf Stream, Kuroshio, Brazilian, East Australian). It especially increases in winter, when dry cold air, formed in extratropical continental centers of high pressure, enters the sea areas (due to the predominance of western transport). At the same time, the specific humidity gradient increases and turbulence sharply increases due to the emerging unstable temperature stratification.

The provisions considered allow us to explain the existence of large precipitation of the WTC from the point of view of the balance of the amount of precipitation. (r) and evaporation rates (E)(Fig. 3.6). Over vast parts of the oceans, the air masses of the trade winds accumulate moisture (here E– r> 0) and “pour” this water into the VZK (where E– r< 0). Cloud systems of polar frontal cyclones form in tropical humid air, so that the water vapor they carry to high latitudes and continents (where E– r< 0) was also collected from tropical and subtropical areas of the World Ocean.

The moisture balance "evaporation minus precipitation" makes it possible to understand the main geographical patterns of river runoff formation - the most full-flowing rivers are those whose basins are located in areas where E -r< 0. Typical examples are the rivers Amazon, Congo, Ganges, Brahmaputra, etc. Moreover, not only the named great rivers, which stretch for thousands of kilometers, are full-flowing, but also relatively small rivers of large islands, for example, Indonesia, fed year-round by heavy rainfall, the amount of which is significant exceeds evaporation.

For the ocean, the atmospheric moisture balance "evaporation minus precipitation" is a vertical flow of "fresh water". It determines in the main features the spatial heterogeneity of the water salinity field. In the Pacific Ocean, precipitation exceeds evaporation, while in the Atlantic (and Indian Ocean) evaporation is greater than precipitation and the salinity of the near-surface layers is greater, and its spatial distribution follows the distribution of the "precipitation minus evaporation" balance. However, not all features of the salinity field are determined exclusively by this balance. Thus, water freshening locally increases near the mouths of large rivers (Amazon, Congo, Ganges). In the polar latitudes, in addition to the above factors, fresh waters formed during the melting of snow and ice cover play an active role in the formation of the salinity field (Kislov A.V., 2011).

Rice. 3.6. Atmospheric balance of moisture "evaporation minus precipitation" over the oceans (cm/year): 1 - isolines >0 ; 2 - isolines <0 (Kislov A.V., 2011)

Water, which is part of the air, is in it in a gaseous, liquid and solid state. It enters the air due to evaporation from the surface of water bodies and land (physical evaporation), as well as due to transpiration (evaporation by plants), which is a physical and biological process. Surface layers of air enriched with water vapor become lighter and rise upwards. As a result of the adiabatic decrease in the temperature of the rising air, the content of water vapor in it, in the end, becomes the maximum possible. Condensation, or sublimation, of water vapor occurs, clouds form, and from them - precipitation that falls to the ground. This is how the water cycle works. Water vapor in the atmosphere is renewed on average about every eight days. An important link in the water cycle is evaporation, which consists in the transition of water from a liquid or solid state of aggregation (sublimation) to a gaseous state and the entry of invisible water vapor into the air.

Rice. 37. Average annual values of evaporation from the underlying surface (mm/year)

Moist air is slightly lighter than dry air because it is less dense. For example, air saturated with water vapor at a temperature of 0 ° and a pressure of 1000 mb is less dense than dry air - by 3 g / m (0.25%). At higher temperatures and correspondingly higher moisture content, this difference increases.

Evaporation shows the actual amount of evaporating water, as opposed to evaporability - the maximum possible evaporation, not limited by moisture reserves. Therefore, evaporation over the oceans is almost equal to evaporation. The intensity or rate of evaporation is the amount of water in grams that evaporates from 1 cm 2 of the surface per second (V \u003d g / cm 2 in s). Measuring and calculating evaporation is a difficult task. Therefore, in practice, evaporation is taken into account in an indirect way - by the size of the water layer (in mm), evaporated over longer periods of time (a day a month). A layer of water of 1 mm from an area of 1 m is equal to a mass of water of 1 kg. The intensity of evaporation from the water surface depends on a number of factors: 1) on the temperature of the evaporating surface: the higher it is, the greater the speed of movement of molecules and more of them come off the surface and enter the air; 2) from the wind: the greater its speed, the more intense the evaporation, since the wind carries moisture-saturated air and brings drier air; 3) from the lack of humidity: the more it is, the more intense the evaporation; 4) on pressure: the larger it is, the less evaporation, since it is more difficult for water molecules to break away from the evaporating surface.

When considering evaporation from the soil surface, it is necessary to take into account such physical properties as color (dark soils evaporate more water due to high heating), mechanical composition (loamy soils have higher water-lifting capacity and evaporation rate than sandy soils), humidity (than the drier the soil, the weaker the evaporation). Also important are such indicators as the level of groundwater (the higher it is, the greater the evaporation), the relief (on elevated places the air is more mobile than in the lowlands), the nature of the surface (rough compared to smooth has a larger evaporating area), vegetation, which reduces evaporation from the soil. However, plants themselves evaporate a lot of water, taking it from the soil with the help of the root system. Therefore, in general, the influence of vegetation is diverse and complex.

Heat is expended on evaporation, as a result of which the temperature of the evaporating surface decreases. This is of great importance for plants, especially in equatorial-tropical latitudes, where evaporation reduces their overheating. The southern oceanic hemisphere is colder than the northern partly for the same reason.

The daily and annual course of evaporation is closely related to air temperature. Therefore, the maximum evaporation during the day is observed around noon and is well expressed only in the warm season. In the annual course of evaporation, the maximum falls on the warmest month, the minimum - on the coldest. In the geographic distribution of evaporation and evaporation, which depend primarily on temperature and water reserves, zoning is observed (Fig. 37).

In the equatorial zone, evaporation and evaporation over the ocean and land are almost the same and amount to about 1000 mm per year.

In tropical latitudes, their average annual values are maximum. But the highest values of evaporation - up to 3000 mm are noted over warm currents, and the evaporation of 3000 mm - in the tropical deserts of the Sahara, Arabia, Australia, with actual evaporation of about 100 mm.

In temperate latitudes over the continents of Eurasia and North America, evaporation is less and gradually decreases from south to north due to lower temperatures and deeper into the continents due to a decrease in moisture reserves in the soil (in deserts up to 100 mm). Evaporation in deserts, on the contrary, is maximum - up to 1500 mm / year.

In the polar latitudes, evaporation and evaporation are low, 100–200 mm, and are the same over Arctic sea ice and land glaciers.

Condensation and sublimation

Water vapor has only its inherent property, which sharply distinguishes it from other atmospheric gases: its quantitative content, or air humidity, depends on the temperature of the air mass. Air humidity is characterized by several indicators.

Absolute humidity - the amount of water vapor in grams contained in 1 m 3 of air. Absolute humidity rises with increasing air temperature, because the warmer the air mass, the more vapor it can hold.

Relative Humidity - ratio in percentage of actual saturation to maximum possible at a given temperature. As the air cools, the absolute humidity decreases as its moisture capacity decreases. The temperature at which air becomes saturated is called dew point . Further cooling of the air leads to moisture condensation. Relative humidity also depends on absolute humidity.

Evaporation It consists in the transition of water from a liquid or solid phase to a gaseous one and in the entry of water vapor into the atmosphere.

Evaporation - this is the maximum possible evaporation under given meteorological conditions, not limited by moisture reserves. The same applies to the term "potential evaporation".

The climatic and, especially, biophysical significance of evaporation lies in the fact that it shows the drying ability of air: the more it can evaporate with limited moisture reserves in the soil, the more pronounced aridity. In some places, this leads to the appearance of deserts, in others it causes temporary droughts, and thirdly, where evaporation is negligible, waterlogged conditions are created.

Evaporation and evaporation reflect both the precipitation regime and the heat regime. The ratio of the input and output of atmospheric moisture is called atmospheric humidification.

Condensation - the transition of vapor to a drop-liquid state.

Sublimation – the transition of moisture to a solid (snow, ice) state.

Condensation requires the following two conditions:

Lowering the air temperature to the dew point;

The presence of condensation nuclei - microscopic bodies on which vapor can settle.

Condensation and sublimation occur both on the surface of the Earth and local objects and in the free atmosphere. In the first case, there are dew or frost. On ice, snow or in the sands of deserts, a layer of moisture settles, which participates in their water balance. During the advection of warm air onto a chilled area, a liquid deposit settles on objects (walls, trunks, etc.), and if the temperature is below 0 °, a solid one.

Clouds. Cloud classification.

Condensation and sublimation of moisture in the free atmosphere gives rise to clouds. Primary very small cloud drops appear on the condensation nuclei. Usually they freeze immediately and become nuclei for further growth of droplets both by condensation and coagulation-mutual fusion. This occurs at temperatures 10-15° below 0°C.

In modern meteorology, the following types of clouds are distinguished:

1. Cirrus clouds are at an altitude above 6 km and consist of ice crystals and needles: white, thin clouds of a fibrous structure, transparent, without their own shadows. Main types: filiform and dense; many varieties. They don't give drops.

2. Cirrocumulus clouds are located at an altitude above 6 km and consist of ice crystals and needles: white thin layers or ridges in the form of small waves and flakes, without their own shadows. They are divided into two types: 1) wavy and 2) cumulus. They don't give drops.

3. Cirrostratus clouds are located at an altitude above 6 km and consist of ice crystals. They look like a white homogeneous thin veil, sometimes slightly wavy; do not blur the solar or lunar disk. Precipitation does not reach the ground.

4. Altocumulus are located at an altitude of 2-6 km and consist of tiny droplets, often supercooled: white, sometimes grayish or bluish in the form of waves, heaps, ridges, flakes, between which gaps of the blue sky are visible. Sometimes they can merge. Types of altocumulus clouds: 1) wavy and 2) cumulus. Precipitation does not fall.

5. Altostratus clouds concentrated at a height of 2-6 km and consist of a mixture of snowflakes and tiny droplets: a gray or bluish uniform veil is slightly wavy. The sun and the moon shine through as if through frosted glass. Usually they cover the whole sky. In summer, precipitation does not reach the ground, in winter they give snowfall. Types: 1) foggy and 2) wavy.

6. Stratocumulus clouds located at an altitude of 2-6 km and consist of droplets of uniform size: gray large ridges, waves, heaps or plates; can be separated by gaps or merge into a continuous cover. They differ from Altocumulus by a somewhat smaller height, larger heaps and greater density. Light, short-lived rains rarely fall. Usually there is no precipitation. Types of stratocumulus clouds: 1) wavy and 2) cumulus.

7. Layered clouds located below 2 km, below they can merge with fogs: a monotonous gray layer, similar to fog, is sometimes torn to shreds below. Usually they cover the entire sky, they can also be in the form of broken masses. Types of stratus clouds: 1) foggy, 2) wavy, 3) broken-layered. There may be drizzle or occasional snow.

8. Nimbostratus clouds located at an altitude below 2 km, below they can merge with fog; consist of large drops at the bottom and small ones at the top: a dark gray cloudy layer, as it were, dimly lit from the inside. Heavy rains or snows fall, sometimes intermittently. There are no views.

9. Cumulus clouds are clouds of vertical development and are within the lower and middle tiers up to 2-3 km; consist of droplets, the system is stable, without precipitation. Dense high clouds with white cumulus and domed tops and flat bases of gray or blue. May be in the form of individual clouds or large clusters. Precipitation usually does not fall. Types of cumulus clouds: 1) flat, 2) medium, 3) powerful. Many varieties - fractocumulus, tower-shaped, orographic, etc.

10. Cumulonimbus, or thunderclouds located at an altitude of up to 2 km and consist of drops at the bottom and crystals at the top: white dense clouds with a dark base, look like huge anvils, mountains, etc. Types of cumulonimbus (thunderstorm) clouds: 1) bald, 2) hairy. Showers, hail, accompanied by thunderstorms

The average annual cloudiness for the whole Earth is estimated at 5.4 points, over land - 4.8 points, over the oceans - 5.8 points. The cloudiest places are the northern parts of the Atlantic and Pacific oceans, where the cloudiness exceeds 8 points, the most cloudless are deserts, no more than 1 - 2 points.

The geographic significance of clouds is that precipitation falls from them; they trap part of the solar radiation and thereby affect the light and thermal regimes of the earth's surface, prevent the thermal radiation of the earth, creating a "greenhouse effect". Finally, clouds complicate the work of aviation, aerial photography, etc.

Precipitation

Water in a liquid or solid state that falls from clouds or is deposited from the air on the surface of the earth is called precipitation.

Precipitation is classified according to its physical state. liquid(drizzle, rain) and solid(snow, groats, hail) and by the nature of the fallout - drizzling, obligatory and storm. Atmospheric precipitation is divided into the following two groups: a) terrestrial precipitation formed directly on the ground ( frost, frost); b) precipitation falling from clouds ( rain, snow, hail, grits, freezing rain).

The nature of precipitation also varies significantly.

Drizzling precipitation is precipitation that falls in the form of drizzle or its solid counterparts (snow grains, fine snow). Most often they are of intramass origin.

Complimentary Precipitation - prolonged, sufficiently uniform intensity of precipitation in the form of rain, snow or drizzle, falling simultaneously over a large area.

Stormwater Precipitation is precipitation of great intensity but of short duration. They fall out of cumulonimbus clouds in both liquid and solid form (rain showers, snow showers, etc.).

Distribution rainfall on the surface of the globe is very uneven and wears zonal character. Their number decreases from the equator to the poles, which is mainly due to air temperature and atmospheric circulation. In addition, relief and sea currents also play a large role in the distribution of precipitation. Warm and humid air masses, meeting with the mountains, rise along their slopes, cool down and give abundant precipitation in the foothill areas. It is on the windward slopes of the mountains that the wettest regions of the Earth are located.

A rain gauge and a precipitation gauge are used to measure the amount of precipitation.

rain gauge- this is a cylindrical metal bucket with a cross-sectional area of \u200b\u200b500 cm 2, 40 cm high, which is installed on a wooden pole at a height of 2 m. A diaphragm is inserted into the bucket from above, which does not retain precipitation and prevents their evaporation. The bucket is closed with a special cone-shaped protection (Nifer protection). The precipitates collected over 12 hours are poured into a measuring glass with divisions.

rain gauge The Tretyakov system is designed in the same way as the rain gauge, but with the difference that its protection consists of 16 separate plates, and the cross-sectional area of \u200b\u200bthe bucket is 200 cm 2.

Atmosphere pressure

The weight of the air determines the atmospheric pressure. Behind normal atmospheric pressure is the air pressure at sea level at a latitude of 45° and at a temperature of 0°C. In this case, the atmosphere presses on every 1 cm2 of the earth's surface with a force of 1.033 kg, and the mass of this air is balanced by a column of mercury 760 mm high. The principle of pressure measurement is based on this dependence. It is measured in millimeters (mm) of mercury (or millibars (mb): 1 mb = 0.75 mm of mercury) and in hectopascals (hPa) when 1 mm = 1 hPa.

Atmospheric pressure is measured using barometers. There are two types of barometers: mercury and metal (or aneroid).

Mercury - p When the pressure changes, the height of the mercury column also changes. These changes are recorded by the observer on a scale attached next to the barometer's glass tube.

Metal barometer, or aneroid, When the pressure changes, the walls of the box oscillate and push in or out. These vibrations are transmitted by a system of levers to the arrow, which moves along a scale with divisions.

Atmospheric pressure is constantly changing due to temperature changes and air movement. During the day, it rises twice (in the morning and in the evening), twice decreases (in the afternoon and after midnight). During the year on the continents, the maximum pressure is observed in winter, when the air is supercooled and compacted, and the minimum pressure is observed in summer.

The distribution of atmospheric pressure over the earth's surface has a well-defined zonal character, which is due to uneven heating of the earth's surface, and, consequently, a change in pressure. The change in pressure is explained by the movement of air. It is high where there is more air, low where the air is leaving. Heating up from the surface, the air rushes up and the pressure on the warm surface decreases. But at altitude, the air cools, condenses, and begins to descend to neighboring cold areas, where the pressure increases. Thus, heating and cooling of air from the Earth's surface is accompanied by its redistribution and pressure change.

Winds and their origin

The air is constantly moving: it rises - ascending movement, falling descending motion. Air movement in horizontal direction is called by the wind. The reason for the occurrence of wind is the uneven distribution of air pressure on the surface of the Earth, which is caused by an uneven distribution of temperature. In this case, the air flow moves from places with high pressure to the side where the pressure is less.

The wind is characterized speed, direction and strength.

Speed wind is measured in meters per second (m/s), kilometers per hour (km/h), points (on the Beaufort scale from 0 to 12, currently up to 13 points). The wind speed depends on the pressure difference and is directly proportional to it: the greater the pressure difference (horizontal baric gradient), the greater the wind speed.

Direction wind is determined by the side of the horizon from which the wind is blowing. For its designation, eight main directions (rhumbs) are used: N, NW, W, SW, S, SE, B, NE. The direction depends on the pressure distribution and on the deflecting effect of the Earth's rotation.

Force wind depends on its speed and shows what dynamic pressure the air flow exerts on any surface. Wind strength is measured in kilograms per square meter (kg/m2).

Winds are extremely diverse in origin, nature and significance. So, in temperate latitudes, where western transport dominates, winds prevail Western directions (NW, W, SW). In the polar regions, winds blow from the poles to low pressure zones of temperate latitudes. The most extensive wind zone of the globe is located in tropical latitudes, where the trade winds blow.

trade winds- permanent winds of tropical latitudes. They are formed because in the equatorial zone, heated air rises, and tropical air comes in its place from the north and south.

breezes- local winds that blow from the sea to the land during the day, and from land to the sea at night. In this regard, distinguish day and night breezes. Day A (sea) breeze is produced when the land heats up faster than the sea during the day, and a lower pressure is established over it. At this time, over the sea (more chilled), the pressure is higher and the air begins to move from the sea to the land. Night(coastal) breeze blows from land to sea, since at this time the land cools faster than the sea, and reduced pressure is above the water surface - air moves from the coast to the sea.

Monsoons- these are winds similar to breezes, but changing their direction depending on the season and covering vast areas. In winter they blow from land to sea, in summer - from sea to land. In winter, the mainland is colder and, therefore, the pressure over it is higher. In summer, on the contrary, the land is warm and the pressure over it is lower. With the change of monsoons, dry, cloudy winter weather changes to rainy summer weather. extratropical monsoons - monsoons of temperate and polar latitudes. tropical monsoons - monsoons of tropical latitudes.

Föhn is a warm, sometimes hot, dry wind blowing into the mountains with considerable force. Usually it lasts less than a day, less often up to a week. The most typical foehn occurs when the air current of the general circulation of the atmosphere crosses a mountain range. Foehns are frequent in the mountains of Central Asia, in the Rocky Mountains, etc. In each country, this wind has its own name. In early spring, the foehn can cause rapid snowmelt in the mountains and catastrophic flooding of rivers. Summer hair dryers sometimes lead to the death of orchards and vineyards.

Bora- a stormy and very cold wind blowing through low mountain passes mainly in the cold part of the year. In Novorossiysk, it is called the north-east, on the Apsheron Peninsula - nordom , on Baikal - sarma , in the Rhone Valley - mistral. Boron blows from one day to a week. Bora is formed at large thermodynamic contrasts on both sides of low mountain ranges. Bora causes great destruction to cities and ports.

air masses

air masses- separate large volumes of air that have certain common properties (temperature, humidity, transparency, etc.) and move as a whole. There are main (zonal) types of air masses that form in belts with different atmospheric pressure: arctic (antarctic), temperate (polar), tropical and equatorial. Zonal air masses are divided into maritime and continental - depending on the nature of the underlying surface in the area of their formation.

Arctic air is formed over the Arctic Ocean, and in winter also over the north of Eurasia and North America. The air is characterized by low temperature, low moisture content, good visibility and stability. Its intrusions into temperate latitudes cause significant and sharp cooling and determine predominantly clear and slightly cloudy weather.

Moderate(polar) air. This is the air of temperate latitudes. It also has two subtypes. In winter it is very chilled and stable, the weather is usually clear with hard frosts. In summer, it gets very warm, ascending currents arise in it, clouds form, it often rains, thunderstorms are observed. Temperate air penetrates into the polar, as well as subtropical and tropical latitudes.

Tropical air is formed in tropical and subtropical latitudes, and in summer - in continental regions in the south of temperate latitudes. There are two subtypes of tropical air. It forms over tropical water areas (tropical zones of the ocean), is characterized by high temperature and humidity. Tropical air penetrates into temperate and equatorial latitudes.

Equatorial air is formed in the equatorial zone from tropical air brought by the trade winds. It is characterized by high temperatures and high humidity throughout the year. In addition, these qualities are preserved both over land and over the sea, therefore, equatorial air is not divided into marine and continental subtypes.

Air masses are in constant motion. Moreover, if air masses move to higher latitudes or to a colder surface, they are called warm because they bring warmth. Air masses moving to lower latitudes or warmer surfaces are called cold. They bring coldness.

atmospheric fronts

atmospheric front called the division between air masses with different physical properties. The intersection of the front with the earth's surface is called front line. At the front, all the properties of air masses - temperature, wind direction and speed, humidity, cloudiness, precipitation - change dramatically. The passage of the front through the place of observation is accompanied by more or less abrupt changes in the weather.

There are fronts associated with cyclones, and climatic fronts. In cyclones, fronts are formed when warm and cold air meet, and the top of the frontal system, as a rule, is located in the center of the cyclone. Cold air meeting warm air always ends up at the bottom. It leaks under the warm, trying to push it up. Warm air, on the contrary, flows onto cold air and if it pushes it, then it itself rises along the interface plane. Depending on which air is more active, in which direction the front is moving, it is called warm or cold.

Warm The front moves in the direction of cold air and means the onset of warm air. It slowly pushes cold air out. Being lighter, it flows onto the wedge of cold air, gently rising up along the interface. In this case, an extensive zone of clouds forms in front of the front, from which heavy precipitation falls. The gradual replacement of cold air with warm air leads to a decrease in pressure and an increase in wind. After the passage of the front, a sharp change in the weather is observed: the air temperature rises, the wind changes direction by about 90 ° and weakens, visibility worsens, fogs form, and drizzling precipitation may fall.

Cold The front moves towards warmer air. In this case, cold air - as denser and heavier - moves along the earth's surface in the form of a wedge, moves faster than warm air and, as it were, lifts warm air in front of it, vigorously pushing it up. Large cumulonimbus clouds form above the front line and in front of it, from which heavy rains fall, thunderstorms arise, and strong winds are observed. After the passage of the front, precipitation and cloudiness significantly decrease, the wind changes direction by about 90 ° and weakens somewhat, the temperature drops, air humidity decreases, its transparency and visibility increase; the pressure is rising.

climatic fronts - fronts of a global scale, which are sections between the main (zonal) types of air masses. There are five fronts: arctic, Antarctic, two moderate(polar) and tropical.

Arctic(Antarctic) front separates the Arctic (Antarctic) air from the air of temperate latitudes, two moderate(polar) fronts separate temperate air from tropical air. Tropical A front forms where tropical and equatorial air meet, differing in humidity rather than temperature. All fronts, together with the boundaries of the belts, shift towards the poles in summer and towards the equator in winter. Often they form separate branches, spreading over long distances from climatic zones. The tropical front is always in the hemisphere where it is summer.

Cyclones and anticyclones

In the troposphere, eddies of various sizes constantly arise, develop and disappear - from small to giant cyclones and anticyclones.

Cyclone is an area of low pressure in the center. Therefore, the air in the cyclone moves in a spiral from the periphery (from areas of high pressure) to the center (to the area of low pressure) and then rises up, forming ascending flows. In a cyclone, the air moves along a curved path and is directed counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Cyclones are associated with vast areas of clouds and precipitation, significant temperature changes, and strong winds. However, cyclones are also known that exist throughout the year in constant areas of low pressure: Icelandic cyclone (minimum), located in the North Atlantic in the area of about. Iceland, and Aleutian cyclone (minimum) in the Aleutian Islands in the North Pacific.

In addition to temperate latitudes, cyclones are observed in the tropical zone. tropical cyclones occur only over the sea, between 10-15°N. and y.sh. When moving to land, they quickly fade. These are, as a rule, small cyclones, their diameter is about 250 km, but with very low pressure in the center. On the globe, on average, more than 70 cases of tropical cyclones are recorded per year. They are best known in the Antilles, off the southeast coast of Asia, in the Arabian Sea, the Bay of Bengal, east of about. Madagascar. In different areas they have local names ( cyclone- in the Indian Ocean; Hurricane- in North and Central America; typhoon in East Asia). Cyclones are especially typical for the territory of Europe, where they move from the Atlantic to the east and exist up to 5-7 days, i.e. until the atmosphere levels out

Anticyclone is an area with increased pressure in the center. Due to this, the movement of air in the anticyclone is directed from the center (from the region of higher pressure) to the periphery (in the region of lower pressure). In the center of the anticyclone, the air descends, forming descending flows, and spreads in all directions, i.e. from the center to the periphery. At the same time, it also rotates, but the direction of rotation is opposite to the cyclonic one - it occurs clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. Anticyclones in temperate latitudes most often follow cyclones, often they take a sedentary (stationary) state and also exist until the pressure equalizes (6-9 days). Due to downward movements in the anticyclone, the air is not saturated with moisture, cloud formation does not occur, and cloudy and dry weather prevails with light winds and calm. In addition to temperate latitudes, anticyclones are most common in subtropical latitudes - in high pressure zones. Here, these are constant atmospheric vortices existing throughout the year (high-pressure areas): North Atlantic(Azores) anticyclone (maximum) in the area of the Azores and South Atlantic anticyclone; North Pacific(Canarian) anticyclone in the area of the Canary Islands in the Pacific Ocean and South Pacific; Indian anticyclone (maximum) in the Indian Ocean. As you can see, they are all located above the oceans. The only powerful anticyclone over land occurs in winter in Asia with a center over Mongolia - Asiatic(Siberian) anticyclone. The sizes of cyclones and anticyclones are comparable: their diameter can reach 3-4 thousand km, and their height can reach a maximum of 18-20 km, i.e. they are flat vortices with a strongly inclined axis of rotation. They usually move from west to east at a speed of 20-40 km / h (except for stationary ones).

Weather

The state of the atmosphere in a given area at a given time is called weather. Weather is characterized by elements and phenomena. Elements weather: air temperature, humidity, pressure. To phenomena include: wind, clouds, precipitation. Sometimes weather phenomena are extraordinary, even catastrophic, for example, hurricanes, thunderstorms, downpours, droughts.

The weather is changeable. The main reasons are the change in the amount of solar heat received during the day and throughout the year, the movement of air masses, atmospheric fronts, cyclones and anticyclones. More clearly and steadily change in the weather during the day is expressed in the equatorial latitudes. In the morning - clear, sunny weather, and in the afternoon showers fall. In the evening and at night again clear and quiet. In temperate latitudes, regular changes in the weather during the day, due to the influx of solar heat, are often disturbed by the change of air masses, the passage of atmospheric vortices and fronts.

weather observations. There is a World Weather Watch (WWW) that brings together the National Weather Services. It has three world centers: Moscow, Washington and Melbourne. On the territory of the state, systematic observations of the weather in the weather service system are carried out meteorological stations. A meteorological station is a site on which various installations and instruments are located in a certain order, there are

premises for employees. Meteorological stations conduct weather observations eight times a day at 00, 03, 06. . . . . .21 hours for all instruments and according to a single program for all stations in the world. The results of observations are encrypted using a special international synoptic code and transmitted to the central offices of the weather service. At the same time, all the results of weather observations are stored at the station itself and in the given area. Studying them by specialists allows not only to fully and accurately characterize the weather at the observation point, but also to warn the population about dangerous phenomena - floods, hurricanes, etc.

According to the results of observations in hydrometeorological centers, synoptic maps are compiled every 3 or 6 hours. synoptic map- a geographical map on which the results of meteorological observations at a network of stations at a certain time are plotted with numbers and symbols. Analysis of the situation of current maps allows you to make a weather forecast. Weather forecast- drawing up scientifically based assumptions about the future state of the weather. It also allows you to determine the possibility of any dangerous natural phenomenon. Weather forecasts can be short-term (12-24 hours) and long-term (for a decade, a month, a season).

Weather plays an important role in human life. In economic activity, it acts as a real component of the production cycle of air, water, rail and road transport. Employees of the river and sea fleets, ports, and airfields cannot ignore the weather and the weather forecast. A person's rest, effective and interesting use of free time, and finally, the state of his health directly depend on the weather, and the weather forecast helps to take appropriate measures in advance, to use free time more efficiently. The weather predetermines the expenditure of energy resources, the nature and range of output of consumer goods, and much more.

Climate

Climate- long-term weather regime, characteristic of any area, which has been maintained with slight fluctuations for centuries. It manifests itself in the natural change of all the weather observed in the area. Like weather, climate depends on the amount of solar radiation (on latitude), on the movement of air masses, atmospheric fronts, cyclones and anticyclones (on atmospheric circulation), on the properties and forms of the earth's surface. Key climate indicators: temperature air (average annual, January and July), prevailing wind direction, annual amount and pattern of precipitation. Geographical maps on which climate indicators are plotted are called climatic.

climate-forming factors. There are three main climate-forming factors and factors influencing the climate. Main factors are the factors that determine the climate anywhere in the world. These include: solar radiation, atmospheric circulation and terrain.

Solar radiation is a factor that determines the flow of solar energy to certain parts of the earth's surface.

Atmospheric circulation is a factor that determines the movement of air masses both vertically and along the earth's surface.

Relief is a factor that qualitatively changes the influence of the first two climate-forming factors.

In addition to the main ones, there are factors that have a significant impact on the climate in certain (often extensive) areas. In particular, the distribution of land and sea and the remoteness of the territory from the seas and oceans. Land and sea heat up and cool down differently. Marine air masses differ significantly from continental ones, but as they move deeper into the continents, they change their properties. Therefore, at the same latitude, there are significant differences in temperature and precipitation distribution.

Nautical, or oceanic, climate is the climate of the ocean, islands and western or eastern coastal parts of the continents. It is formed at a high frequency of marine air masses and is characterized by small annual (≈10°C over oceans) and daily (1-2°C) air temperature amplitudes and a large amount of precipitation.

Continental- the climate of the mainland, with a small amount of precipitation, high summer and low winter air temperatures, large annual and daily amplitudes.

The climate is greatly influenced sea currents. They carry heat (or cold) from one latitude to another, heating or cooling the air masses located above them. Air masses, acquiring new properties under the influence of currents, come to the mainland already changed and cause on the coast a different weather that is not characteristic of these latitudes. Therefore, the climate of the coasts washed by warm currents is usually warmer and milder than on the continents. Cold currents, in addition, increase the dryness of the climate, they cool the lower layers of air in the coastal part, which prevents the formation of clouds and precipitation.

Climate, like all meteorological quantities, zoned. There are 7 main and 6 transitional climatic zones. The main ones are: equatorial, two subequatorial (in the northern and southern hemispheres), two tropical, two temperate and two polar. The names of the transitional zones are closely linked with the names of the main climatic zones and characterize their location on Earth: two subequatorial, subtropical and subpolar (subarctic and subantarctic). The identification of climatic zones is based on thermal zones and the prevailing types of air masses and their movement. In the main belts, one type of air mass dominates during the year, and in transitional types of air masses in winter and summer they change due to the change of seasons and the displacement of atmospheric pressure zones.

Cyclones and anticyclones

The lower layers of the atmosphere are extremely mobile. They constantly move individual masses of air. The form of their movement is often vortex: from small whirlwinds, observed before a thunderstorm, to huge, exciting spaces in the hundreds 11p thousand, and sometimes millions of square kilometers. These rnkhri are called cyclones and anticyclones.

A cyclone is understood as a huge whirlwind in the lower layer of at-

spheres with low atmospheric pressure at the center.

whirlwind is a constant change in wind direction:

in the northern hemisphere - counterclockwise, in the southern - but

"owl. -

Such vortices are formed at the meeting points of warm and cold air, on the so-called climatological fronts. for the temperate zone - on the arctic front and the front of temperate latitudes; for the tropical - on the tropical front. Cyclones of extratropical latitudes. The study of Cyclopocs po.sholp reveals a number of their features.

1. A cyclone is a huge air vortex with a small axis of inclination (1-2°), occupying a space 8-9 km high with a diameter of 1 to 3 thousand km. A slight inclination of the vortex axis distinguishes the cyclone from small eddies, which have a larger angle of inclination and are formed as a result of uneven heating of the Earth's surface.

2. A whirlwind is formed as a result of the meeting of two air masses with different temperatures and the effect of a deflecting force: the rotation of the Earth on their direction during movement.

3. In the vortex, air rises and spreads to the sides, therefore, a region of low atmospheric pressure is formed in the center of the vortex.

4. The rise and spread of air from the cyclone is facilitated by jet streams, which carry air far beyond the ground cyclone.

5. Updrafts in a cyclone provide cloud formation and precipitation.

6. Two fronts are well expressed in the cyclone: warm and cold, during the passage of which a sharp change in weather is observed. Usually cyclones bring inclement weather: in winter - snowfalls and blizzards, in summer - rains and thunderstorms.

The emergence and development of cyclones. There are many theories explaining the formation of cyclones. Let's get acquainted with the wave theory, as the most common. Warm and cold air, having different densities, move in opposite directions along the Earth's surface and form waves on the interface.

With wave curvature of the frontal surface and the front line, the air flows on both sides of the front are correspondingly curved. The deviation of the flows from their original direction leads to the compaction and rarefaction of the air near different sections of the front. Where warm air invades cold air (wave crest), a decrease in pressure is observed, which leads to the formation of cyclonic centers. In the TS parts of the waves, where the cold air deviates towards the teplins (the wave base), air compaction and pressure increases are observed, as a result of which high pressure spurs and sometimes even independent anticyclones are formed in the intervals between cyclins. Reducing the pressure on the ridges bo.hi contribute to the invasion of warm air into the area of cold air, and, conversely, to an increase in pressure at the base in<ип способствуют холодные вторжения в "область теплой воздушно массы.

Rice. 37. Average annual values of evaporation from the underlying surface (mm/year)

In the equatorial zone, evaporation and evaporation over the ocean and land are almost the same and amount to about 1000 mm per year.

In the polar latitudes, evaporation and evaporation are low, 100–200 mm, and are the same over Arctic sea ice and land glaciers.