Cloudy in spring. Cloudiness, its daily and annual variation. So clouds can be

Humidity

Humidity is the content of water vapor in it. Its characteristics are:

absolute humidity A - the amount of water vapor (in g) in 1 m 3 of air;

saturating (saturated) steam A - the amount of steam (in g) required to completely saturate a unit volume (its elasticity is denoted by the letter E);

relative humidity R is the ratio of absolute humidity to saturating steam, expressed as a percentage ( R=100% × a/A);

Dew point is the temperature at which air would reach saturation at a given moisture content and constant pressure.

In the equatorial zone and subtropics, the absolute humidity near the ground reaches 15-20 g/m 3 . In temperate latitudes in summer - 5 - 7 g / m 3, in winter (as well as in the Arctic basin) it decreases to 1 g / m 3 and below. The amount of water vapor in the air drops rapidly with altitude. Humidity affects the change in air temperature, as well as the formation of clouds, fogs, precipitation.

Along with the process of evaporation of water in the atmosphere, the reverse process also occurs - the transition of water vapor with a decrease in temperature into a liquid or directly into a solid state. The first process is called condensation, second - sublimation.

The decrease in temperature occurs adiabatically in the rising moist air and leads to condensation or sublimation of water vapor, which is the main reason for the formation of clouds. The reasons for the rise of air in this case may be: 1) convection, 2) upward sliding along an inclined frontal surface, 3) undulating movements, 4) turbulence.

In addition to the above, a decrease in temperature can also occur due to radiative cooling (from radiation) of the upper layers of inversions or the upper boundary of clouds.

Condensation occurs only if the air is saturated with water vapor and there are condensation nuclei in the atmosphere. Condensation nuclei are the smallest solid, liquid and gaseous particles that are constantly present in the atmosphere. The most common are the nuclei containing compounds of chlorine, sulfur, nitrogen, carbon, sodium, calcium, and the most common nuclei are compounds of sodium and chlorine, which have hygroscopic properties.

Condensation nuclei enter the atmosphere mainly from the seas and oceans (about 80%) by evaporation and spraying them from the water surface. In addition, the sources of condensation nuclei are products of combustion, soil weathering, volcanic activity, etc.

As a result of condensation and sublimation, tiny water droplets (with a radius of about 50 mk) and ice crystals that look like a hexagonal prism. Their accumulation in the surface layer of air gives a haze or fog in the overlying layers of the cloud. The merging of small cloud drops or the growth of ice crystals leads to the formation of various kinds of precipitation: rain, snow.

Clouds can consist only of drops, only of crystals, and be mixed, i.e., consist of drops and crystals. Water droplets in clouds at negative temperatures are in a supercooled state. In most cases, liquid drop clouds are observed down to a temperature of -12 ° C, purely icy (crystalline) clouds - at temperatures below -40 ° C, mixed clouds - from -12 to -40 ° C.

Clouds are watery. Water content is the amount of water in grams contained in one cubic meter of a cloud. (g / m 3). Water content in liquid drop clouds ranges from 0.01 to 4 g per cubic meter of cloud mass (in some cases, more than 10 g/m 3). In ice clouds, water content is less than 0.02 g / m 3, and in mixed clouds up to 0.2-0.3 g/m 3 . Moisture should not be confused with moisture.

Clouds are classified:

By the height of the lower border by 3 (sometimes 4) tiers,

By origin (genetic classification) into 3 groups,

In appearance (morphological classification) are divided into several forms:

The main forms are distinguished:

Cumulus clouds are white, gray, dark gray separate formations in the form of heaps of various shapes.

Cirrus- separate thin light clouds of white color, transparent, fibrous or filamentous structure have the form of hooks, threads, feathers or stripes.

stratus clouds- are a uniform gray cover, of varying transparency.

cirrocumulus clouds, which are small white flakes or small balls (lambs), resembling lumps of snow,

Cirrostratus clouds that look like a white veil, often covering the entire sky, and giving it a milky white hue.

Stratocumulus gray clouds with dark stripes - cloudy shafts.

Other features of the appearance (presence of waviness, specific cloud shapes) and association with precipitation are also noted. In total, there are 10 main forms of clouds and 70 of their varieties.

The shape of clouds is determined by observing them in accordance with the accepted classification using a specially published Cloud Atlas.

Clouds that form within air masses are called intramass, formed on atmospheric fronts - frontal arising above the mountains when air flows over obstacles (mountains) - orographic.

When specifying the height of the upper and lower boundaries of the clouds, one must keep in mind that they can be both quite clear and extremely blurry. Especially dangerous is the transitional pre-cloud layer, reaching 200 m under the sub-inversion clouds.

Artificial cirrus clouds that arise behind a flying aircraft in the upper troposphere should be singled out as a separate group. They are called contrails (sometimes contrails). They arise as a result of the sublimation of water vapor contained in the exhaust gases of the engine.

The concept of "cloudiness" refers to the number of clouds observed in one place. Clouds, in turn, are called atmospheric phenomena formed by a suspension of water vapor. The classification of clouds includes many of their types, divided by size, shape, nature of formation and altitude.

In everyday life, special terms are used to measure cloudiness. Expanded scales for measuring this indicator are used in meteorology, maritime affairs and aviation.

Meteorologists use a ten-point cloud scale, which is sometimes expressed as a percentage of coverage of the observable sky (1 point - 10% coverage). In addition, the height of cloud formation is divided into upper and lower tiers. The same system is used in maritime affairs. Aeronautical meteorologists use a system of eight octants (parts of the visible sky) with a more detailed indication of the height of the clouds.

A special device is used to determine the lower boundary of the clouds. But only aviation weather stations are in dire need of it. In other cases, a visual assessment of the height is made.

Cloud types

Cloudiness plays an important role in the formation of weather conditions. Cloud cover prevents the Earth's surface from heating and prolongs the process of its cooling. Cloud cover significantly reduces daily temperature fluctuations. Depending on the amount of clouds at a certain time, several types of cloudiness are distinguished:

1. "Clear or partly cloudy" corresponds to cloudiness of 3 points in the lower (up to 2 km) and middle tiers (2 - 6 km) or any amount of clouds in the upper (above 6 km).
2. "Changing or variable" - 1-3/4-7 points in the lower or middle tier.
3. "With clearings" - up to 7 points of total cloudiness of the lower and middle tiers.
4. "Cloudy, cloudy" - 8-10 points in the lower tier or not translucent clouds on average, as well as with precipitation in the form of rain or snow.

Types of clouds

The world classification of clouds distinguishes many types, each of which has its own Latin name. It takes into account the shape, origin, height of education and a number of other factors. The classification is based on several types of clouds:

• Cirrus clouds are thin filaments of white. They are located at an altitude of 3 to 18 km, depending on the latitude. They consist of falling ice crystals, to which they owe their appearance. Among the cirrus at a height of over 7 km, clouds are divided into cirrocumulus, altostratus, which have a low density. Below, at an altitude of about 5 km, there are altocumulus clouds.
• Cumulus clouds are dense formations of white color and a considerable height (sometimes more than 5 km). They are located most often in the lower tier with vertical development in the middle. Cumulus clouds at the upper boundary of the middle tier are called altocumulus.
• Cumulonimbus, shower and thunderclouds, as a rule, are located low above the Earth's surface 500-2000 meters, are characterized by precipitation in the form of rain, snow.
• Stratus clouds are a layer of low-density suspended matter. They let in the light of the sun and moon and are at an altitude of between 30 and 400 meters.

Cirrus, cumulus and stratus types, mixing, form other types: cirrocumulus, stratocumulus, cirrostratus. In addition to the main types of clouds, there are other, less common ones: silvery and mother-of-pearl, lenticular and vymeform. And clouds formed by fires or volcanoes are called pyrocumulative.

The degree of coverage of the firmament by clouds is called the amount of clouds or cloudiness. Cloudiness is expressed in tenths of sky coverage (0–10 points). With clouds that completely cover the sky, cloudiness is indicated by the number 10, with a completely clear sky - by the number 0. When deriving average values, tenths of a unit can also be given. So, for example, the number 5.7 means that clouds cover 57% of the sky.

Cloudiness is usually determined by the observer by eye. But there are also devices in the form of a convex hemispherical mirror that reflects the entire sky, photographed from above, or in the form of a camera with a wide-angle lens.

It is customary to estimate separately the total amount of clouds (total cloudiness) and the amount of lower clouds (lower cloudiness). This is significant because high and, to some extent, medium clouds obscure the sunlight less and are less important in practical terms (for example, for aviation). Further, we will only talk about general cloudiness.

Cloudiness is of great climate-forming importance. It affects the circulation of heat on the Earth: it reflects direct solar radiation and, consequently, reduces its inflow to the earth's surface; it also increases the scattering of radiation, reduces the effective radiation, changes the illumination conditions. Although modern aircraft fly above the middle layer of clouds and even above the upper layer, cloud cover can make it difficult for an aircraft to take off and travel, interfere with orientation without instruments, can cause aircraft icing, etc.

The daily course of cloudiness is complex and depends to a greater extent on the types of clouds. Stratocumulus and stratocumulus clouds associated with the cooling of air from the earth's surface and with a relatively weak turbulent upward transport of water vapor have a maximum at night and in the morning. Cumulus clouds, associated with stratification instability and well-defined convection, appear mainly in the daytime and disappear by night. True, over the sea, where the temperature of the underlying surface has almost no diurnal variation, convection clouds also have almost no variation, or a weak maximum occurs in the morning. Clouds of an ordered ascending movement associated with fronts do not have a clear diurnal course.

As a result, in the daily course of cloudiness over land at temperate latitudes, two maxima are outlined in summer: in the morning and a more significant one in the afternoon. In the cold season, when convection is weak or absent, the morning maximum prevails, which may become the only one. In the tropics on land, the afternoon maximum prevails throughout the year, since convection is the most important cloud-forming process there.

In the annual course, the cloudiness in different climatic regions varies in different ways. Over the oceans of high and middle latitudes, the annual variation is generally small, with a maximum in summer or autumn and a minimum in spring. Novaya Zemlya cloudiness values ​​in September and October - 8.5, in April - 7.0 b points.

In Europe, the maximum occurs in winter, when cyclonic activity with its frontal cloudiness is most developed, and the minimum occurs in spring or summer, when convection clouds predominate. So, in Moscow, the values ​​of cloudiness in December are 8.5, in May - 6.4; in Vienna in December - 7.8, in August - 5.0 points.

In Eastern Siberia and Transbaikalia, where anticyclones dominate in winter, the maximum is in summer or autumn, and the minimum is in winter. So, in Krasnoyarsk, the cloudiness values ​​are 7.3 in October and 5.3 in February.

In the subtropics, where anticyclones predominate in summer and cyclonic activity in winter, the maximum occurs in winter, the minimum in summer, as in the temperate latitudes of Europe, but the amplitude is greater. So, in Athens in December 5.9, in June 1.1 points. The annual course is the same in Central Asia, where in summer the air is very far from saturation due to high temperatures, and in winter there is quite intense cyclonic activity: in Tashkent in January 6.4, in July 0.9 points.

In the tropics, in the areas of the trade winds, the maximum cloudiness occurs in the summer, and the minimum in the winter; in Cameroon in July - 8.9, in January - 5.4 points. In the monsoonal climate of the tropics, the annual variation is the same, but more pronounced: in Delhi in July 6.0, in November 0.7 points.

At high-mountain stations in Europe, the minimum of cloudiness is observed mainly in winter, when the stratus clouds covering the valleys lie below the mountains (if we do not talk about windward slopes), the maximum is observed in summer with the development of convection clouds (S.P. Khromov, M.A. Petrosyants , 2004).

Purpose of the lesson: learn the classification of clouds and master the skills of determining the type of clouds using the "Cloud Atlas"

General provisions

The processes of formation of a separate cloud proceed under the influence of many factors. Clouds and their precipitation play an important role in the formation of various types of weather. Therefore, cloud classification provides specialists with the ability to track the spatial and temporal variability of cloud formations, which is a powerful tool for studying and predicting processes occurring in the atmosphere.

For the first time, an attempt to separate clouds according to their appearance into different groups was made in 1776 by J. B. Lamarck. However, the classification proposed by him, due to its imperfection, did not find wide application.

changes. The first classification of clouds that entered science was developed by the English amateur meteorologist L. Howard in 1803. In 1887, the scientists Hildebrandson in Sweden and Abercrombie in England, having revised the classification of L. Howard, proposed a draft of a new classification, which formed the basis of all subsequent classifications . The idea of ​​creating the first unified cloud atlas was supported at the International Conference of Directors of Meteorological Services in Munich in 1891. The committee created by it prepared and published in 1896 the first International Cloud Atlas with 30 color lithographs. The first Russian edition of this Atlas was published in 1898. The further development of meteorology and the introduction of the concepts of atmospheric fronts and air masses into the practice of synoptic analysis required a much more detailed study of clouds and their systems. This predetermined the need for a significant revision of the classification used at that time, which resulted in the publication in 1930 of a new International Cloud Atlas. This Atlas was published in Russian in 1933 in a somewhat abridged version.

Clouds and precipitation falling from them are among the most important meteorological (atmospheric) phenomena and play a decisive role in the formation of weather and climate, in the distribution of flora and fauna on Earth. By changing the radiation regime of the atmosphere and the earth's surface, clouds have a noticeable effect on the temperature and humidity regime of the troposphere and the surface layer of air, where human life and activity take place.

A cloud is a visible set of droplets and/or crystals suspended in the atmosphere and in the process of continuous evolution, which are products of condensation and/or sublimation of water vapor at altitudes from several tens of meters to several kilometers.

The change in the phase structure of the cloud - the ratio of drops and crystals by mass, number of particles and other parameters per unit volume of air - occurs under the influence of temperature, humidity and vertical movements both inside and outside the cloud. In turn, the release and absorption of heat as a result of phase transitions of water and the presence of the particles themselves in the air flow have an inverse effect on the parameters of the cloudy environment.

According to the phase structure, clouds are divided into three groups.

1. Water, consisting only of drops with a radius of 1-2 microns or more. Drops can exist not only at positive, but also at negative temperatures. The purely drop structure of the cloud is preserved, as a rule, up to temperatures of the order of –10...–15 °C (sometimes even lower).

2. Mixed, consisting of a mixture of supercooled drops and ice crystals at temperatures of –20...–30 °C.

3. Ice, consisting only of ice crystals at sufficiently low temperatures (about -30 ... -40 ° C).

Cloud cover during the day reduces the influx of solar radiation to the earth's surface, and at night noticeably weakens its radiation and, consequently, cooling, very significantly reduces the daily amplitude of air and soil temperatures, which entails a corresponding change in other meteorological quantities and atmospheric phenomena.

Regular and reliable observations of cloud forms and their transformation contribute to the timely detection of dangerous and adverse hydrometeorological phenomena associated with one or another type of cloud.

The program of meteorological observations includes tracking the dynamics of cloud development and determining the following cloud characteristics:

a) the total amount of clouds,

b) the amount of lower clouds,

c) the shape of the clouds,

d) the height of the lower boundary of the clouds of the lower or middle tier (in the absence of clouds of the lower tier).

The results of observations of clouds from meteorological observation units in real time using the code KN-01 (the national version of the international code FM 12-IX SYNOP) are regularly transmitted to local forecasting authorities (organizations and divisions of the UGMS) and the Hydrometeorological Research Center of the Russian Federation (Hydrometeorological Center Russia) for synoptic analysis and compilation of weather forecasts of various lead times. In addition, these data are calculated for various time intervals and used for climate assessments and generalizations.

The number of clouds is defined as the total proportion of the sky covered by clouds from the entire visible surface of the sky and is estimated in points: 1 point is 0.1 share (part) of the entire sky, 6 points - 0.6 of the sky, 10 points - the entire sky is covered by clouds .

Long-term observations of clouds have shown that they can be located at different heights, both in the troposphere and in the stratosphere and even in the mesosphere. Tropospheric clouds are usually observed as individual, isolated cloud masses or as a continuous cloud cover. Depending on the structure, clouds are divided in appearance into forms, types and varieties. Noctilucent and mother-of-pearl clouds, in contrast to tropospheric clouds, are observed quite rarely and are characterized by relatively little diversity. The classification of tropospheric clouds by appearance currently used is called the international morphological classification.

Along with the morphological classification of clouds, genetic classification is also used, i.e., classification according to the conditions (reasons) for the formation of clouds. In addition, clouds are classified according to their microphysical structure, i.e., according to the state of aggregation, the type and size of cloud particles, and also according to their distribution within the cloud. In accordance with the genetic classification, clouds are divided into three groups: stratus, undulating and cumulus (convective).

The main distinguishing features in determining the shape of clouds are their appearance and structure. Clouds can be located at different heights in the form of separate isolated masses or a continuous cover, their structure can be different (homogeneous, fibrous, etc.), and the lower surface can be even or dissected (and even torn). In addition, clouds can be dense and opaque or thin - a blue sky, moon or sun shines through them.

The height of clouds of the same shape is not constant and may vary somewhat depending on the nature of the process and local conditions. On average, cloud heights are higher in the south than in the north, and higher in summer than in winter. Above the mountainous regions, clouds are located lower than above the plains.

Precipitation is an important characteristic of clouds. Clouds of some forms almost always give precipitation, while others either do not give precipitation at all, or precipitation from them does not reach the surface of the earth. The fact of precipitation, as well as their type and nature of precipitation, serve as additional signs for determining the forms, types and varieties of clouds. The following types of precipitation fall from clouds of certain shapes:

– showers – from cumulonimbus clouds (Cb);

- oblique - from stratocumulus (Ns) in all seasons, from altostratus (As) - in winter and sometimes weak - from stratocumulus (Sc);

– drizzling – from stratus clouds (St).

In the process of development and decay of the cloud, its appearance and structure change, and it can transform from one form to another.

When determining the amount and shape of clouds, only clouds visible from the surface of the earth are taken into account. If the whole sky or part of it is covered with clouds of the lower (middle) tier, and clouds of the middle (upper) tier are not visible, this does not mean that they are absent. They may be above the underlying cloud layers, but this is not taken into account in cloud observations.

Cloudiness is determined visually using a 10-point system. If the sky is cloudless or there are one or more small clouds occupying less than one tenth of the entire sky, then the cloudiness is considered to be 0 points. With cloudiness equal to 10 points, the entire sky is covered with clouds. If 1/10, 2/10, or 3/10 parts of the sky are covered by clouds, then the cloudiness is considered to be equal to 1, 2, or 3 points, respectively.

Determination of light intensity and background radiation*

Photometers are used to measure illumination. The deviation of the galvanometer pointer determines the illumination in lux. Photometers can be used.

To measure the level of radiation background and radioactive contamination, dosimeters-radiometers ("Bella", "ECO", IRD-02B1, etc.) are used. Typically, these devices have two modes of operation:

1) assessment of the radiation background in terms of the equivalent dose rate of gamma radiation (μSv/h), as well as contamination in terms of gamma radiation of samples of water, soil, food, crop products, animal husbandry, etc.;

* Units of measurement of radioactivity

Radionuclide activity (А)- decrease in the number of radionuclide nuclei for a certain

fixed time interval:

[A] \u003d 1 Ci \u003d 3.7 1010 dispersal / s \u003d 3.7 1010 Bq.

Absorbed radiation dose (D) is the energy of ionizing radiation transferred to a certain mass of the irradiated substance:

[D] = 1 Gy = 1 J/kg = 100 rad.

Equivalent radiation dose (N) is equal to the product of the absorbed dose by

average quality factor of ionizing radiation (K), taking into account biological

logical effect of various radiations on biological tissue:

[N] = 1 Sv = 100 rem.

Exposure dose (X) is a measure of the ionizing effect of radiation, a single

which is equal to 1 Ku/kg or 1 P:

1 P \u003d 2.58 10-4 Ku / kg \u003d 0.88 rad.

Dose rate (exposure, absorbed or equivalent) is the ratio of the dose increment for a certain time interval to the value of this time interval:

1 Sv/s = 100 R/s = 100 rem/s.

2) assessment of the degree of contamination with beta-, gamma-radiating radionuclides of surfaces and samples of soil, food, etc. (particles / min. cm2 or kBq / kg).

The maximum allowable exposure dose is 5 mSv/year.

Determining the level of radiation safety

The level of radiation safety is determined using the example of using a household dosimeter-radiometer (IRD-02B1):

1. Set the operation mode switch to the "µSv/h" position.

2. Turn on the device, for which set the switch "off - on."

V "on" position. Approximately 60 seconds after switching on, the device is ready

to work.

3. Place the device in the place where the equivalent dose rate is determined gamma radiation. After 25-30 seconds, the digital display will display a value that corresponds to the dose rate of gamma radiation in a given place, expressed in microsieverts per hour (µSv/h).

4. For a more accurate estimate, it is necessary to take the average of 3-5 consecutive readings.

The indication on the digital display of the device 0.14 means that the dose rate is 0.14 µSv/h or 14 µR/h (1 Sv = 100 R).

After 25-30 seconds after the start of operation of the device, it is necessary to take three consecutive readings and find the average value. The results are presented in the form of a table. 2.

Table 2. Determining the level of radiation

Registration of the results of microclimatic observations

The data of all microclimatic observations are recorded in a notebook, and then processed and presented in the form of a table. 3.

Table 3. Results of processing microclimatic

observations