Types of precipitation that fall from the atmosphere. What types of precipitation are there? Physical characteristics of precipitation

The atmosphere of our planet is constantly in motion - it is not for nothing that it is called the fifth ocean. In its thickness, movements of warm and cold air masses are observed - winds blow at different speeds and directions.


Sometimes the moisture contained in the atmosphere condenses and falls to the surface of the earth in the form of rain or snow. Forecasters call this precipitation.

Scientific definition of precipitation

Atmospheric precipitation in the scientific community is usually called ordinary water, which in liquid (rain) or solid (snow, frost, hail) form falls from the atmosphere onto the surface of the Earth.

Precipitation can fall from clouds, which themselves are water condensed into tiny droplets, or form directly in air masses when two atmospheric flows collide with different temperatures.

The amount of precipitation determines climatic features terrain, and also serves as the basis for agricultural productivity. Therefore, meteorologists constantly measure how much precipitation fell in a particular area over a certain period. This information forms the basis of productivity, etc.

Precipitation is measured in millimeters of the layer of water that would cover the surface of the earth if the water were not absorbed or evaporated. On average, 1000 millimeters of precipitation falls per year, but some areas receive more, while others receive less.

Thus, in the Atacama Desert only 3 mm of precipitation falls in a whole year, and in Tutunendo (Colombia) a layer of more than 11.3 meters of rainwater accumulates per year.

Types of precipitation

Meteorologists distinguish between three main types of precipitation: rain, snow and hail. Rain consists of drops of water in a liquid state, hail and in a solid state. However, there are also transitional forms of precipitation:

— rain and snow are a common occurrence in autumn, when snowflakes and drops of water alternately fall from the sky;

- freezing rain - enough rare view precipitation, which is ice balls filled with water. Falling to the ground, they break, water flows out and immediately freezes, covering asphalt, trees, roofs of houses, wires, etc. with a layer of ice;

- snow pellets - small white balls, reminiscent of cereals, falling from the sky at air temperatures close to zero. The balls consist of ice crystals weakly frozen together and are easily crushed in the fingers.

Precipitation can be torrential, continuous and drizzling.

— Heavy precipitation usually occurs suddenly and is characterized by high intensity. They can last from a few minutes to several days (in tropical climate), often accompanied by thunderstorms and sharp gusts of wind.

— Heavy precipitation occurs over a long period of time, several hours or even days in a row. They begin with low intensity, gradually increase and then continue, without changing intensity, all the time until the end.

— Drizzle precipitation differs from regular precipitation in the very small size of the droplets and in that it falls not only from clouds, but also from fog. Drizzling precipitation is often observed at the beginning and end of rainfall, but can last for several hours or days as an independent phenomenon.

Precipitation formed on the surface of the earth

Some types of precipitation do not fall from above, but are formed directly in the lowest layer of the atmosphere in contact with the earth's surface. They occupy a small percentage of the total precipitation, but are also taken into account by meteorologists.

— Frost is ice crystals that freeze in the early morning on protruding objects and the surface of the ground if the night temperature drops below zero.

— Dew is drops of water that condense in the warm season as a result of night cooling of the air. Dew falls on plants, protruding objects, stones, walls of houses, etc.

— Frost is ice crystals that form in winter at temperatures from – 10 to – 15 degrees on tree branches and wires in the form of a fluffy fringe. Appears at night and disappears during the day.

— Ice and glaze - freezing of an ice layer on the surface of the earth, trees, walls of buildings, etc. as a result of rapid cooling of the air during or after rain and snow and freezing rain.


All types atmospheric precipitation are formed as a result of condensation of water evaporated from the surface of the planet. The most powerful “source” of precipitation is the surface of the seas and oceans; land provides no more than 14% of all atmospheric moisture.

Precipitation- water in a liquid or solid state that falls from clouds or precipitates directly from the air onto the surface of the Earth. These include:

Rain. The smallest droplets of water, with a diameter of 0.05 to 0.1 mm, that make up the clouds, merging with each other, gradually increase in size, become heavy and fall to the ground in the form of rain. The stronger the ascending jets of air from the sun-heated surface, the larger the falling drops should be. Therefore, in the summer, when the surface air is heated by the earth and rapidly rises, rain usually falls in the form of large drops, and in the spring and autumn - drizzle. If rain falls from stratus clouds, then such rain is blanket rain, and if it falls from stratus clouds, it is torrential. It is necessary to distinguish drizzle from rain. This type of precipitation usually falls from stratus clouds. The droplets are much smaller in size than raindrops. The speed of their fall is so slow that they appear suspended in the air.

Snow. It is formed when the cloud is in air with a temperature below 0°. Snow is made up of crystals various forms. The most snow falls on the slopes of Rainier (state) - an average of 14.6 m annually. This is enough to fill a 6-story house.

hail. It occurs with strong upward air currents in the warm season. Droplets of water falling on greater height with air currents, freeze, and ice crystals begin to grow on them in layers. The drops become heavier and begin to fall down. When falling, they increase in size from merging with drops of supercooled water. Sometimes hail reaches the size of a chicken egg, usually with varying layers of density. Typically, hail falls from powerful cumulonimbus clouds during rainfall. The frequency of hail varies: in it it happens 10-15 times a year, on land, where there are much more powerful updrafts - 80-160 times a year. Hail falls less frequently over the oceans. Hail causes great material damage: it destroys crops, vineyards, and if the hailstones are large in size, then it can cause the destruction of houses and the death of people. In our country, methods for identifying hail clouds have been developed and hail control services have been created. Dangerous clouds are “shot” with special chemicals.

Rain, snow, and hail are called hydrometeorites. In addition to them, precipitation also includes those that are deposited directly from the air. These include dew, fog, frost, etc.

Dew(Latin ros - moisture, liquid) - precipitation in the form of water droplets deposited on the surface of the earth and ground objects when the air cools. In this case, water vapor, cooling, changes from a state to liquid and settles. Most often, dew is observed at night, in the evening or early in the morning.

Fog(turk, darkness) is an accumulation of small water drops or ice crystals in the lower part of the troposphere, usually near the surface of the earth. visibility is sometimes reduced to several meters. Fogs are distinguished by their origin into advective fogs (due to the cooling of warm moist air over a colder surface of land or water) and radiation fogs (formed as a result of cooling earth's surface). In a number of regions of the Earth there are often fogs on the coasts in places where cold currents pass. For example, Atacama is located on the coast. It's cold along the coast. Its cold deep waters contribute to the formation of fogs, from which drizzle settles on the coast - the only source of moisture in the Atacama Desert.

Water molecules continuously evaporate from the surface of lakes, seas, rivers and oceans - enter the atmosphere, where they are converted into water vapor, and then into various types of precipitation. There is always water vapor in the air, which is usually impossible to see, but the humidity of the air depends on the amount of it.

Air humidity varies in all areas globe, in hot weather it increases when evaporation from the surface of reservoirs into the atmosphere increases. Low humidity is usually found over desert areas because there is little water vapor, so the air in deserts is very dry.

Water vapor goes through many tests before falling to the ground in the form of rain, snow or frost.

The surface of the earth is heating up sun rays, and transfers the resulting heat to the air. Since heated air masses much lighter than cold ones, they rise. Tiny water droplets that formed in the air continue to travel with it into in the form of precipitation.

Types of precipitation, fog and clouds.

To imagine how further transformation of water vapor occurs in the atmosphere, you can conduct a fairly simple experiment. You need to take a mirror and bring it closer to the spout of a boiling kettle. After a few seconds, the cool surface of the mirror will fog up, then large water drops will form on it. The released steam turned into water, which means that a phenomenon called condensation occurred.

A similar phenomenon occurs with water vapor at a distance of 2-3 km from the earth. Since the air at this distance is colder than near the surface of the earth, steam condenses in it and water droplets are formed, which can be observed from the ground in the form of clouds.

When flying on an airplane, you can see how clouds sometimes appear below the aircraft. Or you can even find yourself among the clouds if you climb a high mountain in low clouds. At this moment, surrounding objects and people will turn into invisible beings, swallowed up by a thick veil of fog. Fog is the same clouds, but only located near the earth's surface.

If the drops in the clouds begin to grow and become heavier, then the snow-white clouds gradually darken and turn into clouds. When heavy drops are no longer able to stay in the air, then rain pours from thunderclouds onto the ground. in the form of precipitation.

Dew and frost as types of precipitation.

Near bodies of water in summer, a lot of steam forms in the air and it becomes highly saturated with water pores. With the onset of night, coolness comes and at this time less steam is required to saturate the air. Excess moisture condenses on the ground, leaves, grass and other objects, and such type of precipitation called dew. Dew can be observed in the early morning, when transparent small drops are visible covering various objects.

With the arrival of late autumn, the temperature overnight can drop below 0°C, then dew drops freeze and turn into amazing transparent crystals called frost.

In winter, ice crystals freeze and settle on window glass in the form of extraordinary beauty. frosty patterns. Sometimes frost simply covers the surface of the earth, like a thin layer of snow. The fantastic patterns formed by frost are best seen on rough surfaces, such as:

• tree branches;
• loose ground surface;
• wooden benches.

Snow and hail as types of precipitation.

Hail is the name given to irregularly shaped pieces of ice that fall to the ground with rain in the summer. There is also “dry” hail, which falls without rain. If you carefully cut a hailstone, you will see on the cut that it consists of alternating opaque and transparent layers.

When air currents carry water vapor to a height of about 5 km, then water droplets begin to settle on the dust particles, and they instantly freeze. The resulting ice crystals begin to increase in size, and when they reach heavy weight I'm starting to fall. But a new stream comes from the earth warm air and he returns them back to the cold cloud. The hailstones begin to grow again and try to fall, this process is repeated several times, and as soon as they gain a sufficiently heavy weight they fall to the ground.

The size of these types of precipitation(hailstones) usually range from 1 to 5 mm in diameter. Although there have been cases when the size of hailstones exceeded a chicken egg, and the weight reached approximately 400-800 g.

Very big damage hail can cause agriculture, it damages vegetable gardens and crops, and also leads to the death of small animals. Large hailstones can damage cars and even pierce aircraft skins.

To reduce the likelihood of hail falling on the ground, scientists are constantly developing new substances that are thrown into the ground using special rockets. thunderclouds and thus they are dispersed.

With the arrival of winter, the earth is enveloped in a snow-white blanket consisting of tiny ice crystals called snow. Because of low temperatures droplets of water freeze and ice crystals form in the clouds, then new water molecules attach to them and as a result the birth individual snowflake. All snowflakes have six corners, but the patterns woven on them by frost differ from each other. When snowflakes are exposed to wind flow, they stick together and form snow flakes. Walking through the snow in frosty weather, we often hear crunching noises under our feet, as ice crystals break in the snowflakes.

Such types of precipitation, as snow brings many problems, traffic on roads becomes difficult due to snow, power lines break under its weight, and melting snow leads to floods. But due to the fact that the plants are covered with a blanket of snow, they are able to withstand even severe frosts.

Anyone who has children knows very well How many different “whys” do you have to answer every day?. Just recently I had to teach a whole lesson with my son on this topic.

How clouds and precipitation form

One of the most important and unique atmospheric properties our planet - enough steam for cloud formations. The weather is largely characterized by whether there are clouds in the sky, whether the weather is dry or it's raining. But where does all the water that becomes rain come from?, and how does it stay in the air? Everyone knows that precipitation falls from clouds, and if you fly above them in a plane, you can see bright sun. How do clouds form?

The vapor in the air is invisible, but as the temperature drops environment its condensation occurs, and then we see clouds. In fact, precipitation is water in a solid or liquid state that falls from clouds or settling on the surface of objects or the ground. This is the result of condensation of water vapor in the air. The evaporation process is ongoing, no matter what temperature the thermometer outside the window shows. The only difference is that the higher the temperature, the more intense this process occurs.

What types of clouds are there?

Regarding the height, the following clouds are distinguished:

• lower tier- their height is low, about 2000 meters;
• middle tier- the altitude of their “flight” is from 2000 to 7000 meters;
• upper tier occupied by clouds whose height is at least 7000 meters;
• vertical development cloud observed at altitudes less than 2000 meters.

Classification of precipitation

There is quite extensive classification this natural phenomenon, and therefore I will briefly describe main types. When the nature of origin is implied, a distinction is made between:

• orographic- observed on mountain slopes and characterized by abundance;
• frontal- become the result of the meeting of air masses of different temperatures;
• convective- occur due to intense heating of the earth's surface and, consequently, abundant evaporation.

Concerning nature of the loss, the following types are distinguished:

• drizzling- small droplets in a small area;
• cover- quite long and cover impressive territories;
• stormwater- characterized by short duration, but covering a small area they fall most intensely.

Absolute maximum and minimum

The record holder for the amount of precipitation is Hawaii Islands - 11748 mm/year. The opposite value is the minimum, fixed in the Libyan Desert - less than 40 mm/year. However, there may be no precipitation there for many years.

Classification of precipitation. By appearance precipitation are divided into liquid, solid and terrestrial.

Liquid precipitation includes:

rain – precipitation in the form of drops of various sizes with a diameter of 0.5–7 mm;

drizzle - small droplets with a diameter of 0.05–0.5 mm, seemingly in suspension.

Solid sediments include:

snow – ice crystals that form various kinds of snowflakes (plates, needles, stars, columns) 4–5 mm in size. Sometimes snowflakes are combined into snow flakes, the size of which can reach 5 cm or more;

snow pellets - precipitation in the form of opaque spherical grains of white or matte white (milky) color with a diameter of 2 to 5 mm;

ice pellets are solid particles that are transparent on the surface and have an opaque, matte core in the center. The diameter of the grains is from 2 to 5 mm;

hail – more or less large pieces of ice (hailstones), having a spherical or irregular shape and a complex internal structure. The diameter of hailstones varies within a very wide range: from 5 mm to 5–8 cm. There are cases when hailstones weighing 500 g or more fell.

If precipitation does not fall from clouds, but is deposited from atmospheric air on the surface of the earth or on objects, then such precipitation is called ground precipitation. These include:

dew - tiny drops of water that condense on the horizontal surfaces of objects (decks, boat covers, etc.) due to radiation cooling them on clear cloudless nights. A slight wind (0.5–10 m/s) promotes the formation of dew. If the temperature of horizontal surfaces is below zero, then under similar conditions water vapor sublimates on them and frost forms - a thin layer of ice crystals;

liquid deposit – tiny drops of water or a continuous film of water, formed in cloudy and windy weather on the windward predominantly vertical surfaces of cold objects (walls of superstructures, protective devices of winches, cranes, etc.).

glaze is an ice crust that forms when the temperature of these surfaces is below 0 °C. In addition, a hard coating may form on the surfaces of the vessel - a layer of crystals densely or densely sitting on the surface or a thin continuous layer of smooth transparent ice.

In foggy frosty weather with low winds, granular or crystalline frost may form on the vessel's equipment, ledges, cornices, wires, etc. Unlike frost, rime does not form on horizontal surfaces. The loose structure of frost distinguishes it from solid plaque. Granular rime is formed at air temperatures from -2 to -7 ° C due to freezing on the subject of supercooled fog droplets, and crystalline rime, which is a white precipitate of crystals of a fine structure, is formed at night with a cloudless sky or thin clouds from particles of fog or haze at a temperature from –11 to –2 °C and above.

According to the nature of precipitation, precipitation is divided into shower, heavy and drizzling.

Rainfall falls from cumulonimbus (thunderstorm) clouds. In summer it is large drops of rain (sometimes with hail), and in winter it is heavy snowfall with frequent changes in the shape of snowflakes, snow or ice grains. Precipitation occurs from nimbostratus (summer) and altostratus (winter) clouds. They are characterized by small fluctuations in intensity and long duration of fallout.

Drizzle falls from stratus and stratocumulus clouds in the form of small drops with a diameter of no more than 0.5 mm, descending at very low speeds.

Based on intensity, precipitation is divided into strong, moderate and light.

Clouds and precipitation.

Upper level clouds.

Cirrus (Ci)- Russian name feathery, individual tall, thin, fibrous, white, often silky clouds. Their fibrous and feathery appearance is due to the fact that they are composed of ice crystals.

Cirrus appear in the form of isolated bunches; long, thin lines; feathers like smoke torches, curved stripes. Cirrus clouds can appear in parallel bands that cross the sky and appear to converge on a single point on the horizon. This will be the direction to the area low pressure. Because of their height, they become illuminated earlier than other clouds in the morning and remain illuminated after the Sun has set. Cirrus are generally associated with clear weather, but if they are followed by lower and denser clouds, then there may be rain or snow in the future.

Cirrocumulus (Cc) , the Russian name for cirrocumulus, are tall clouds made up of small white flakes. Usually they do not reduce illumination. They are placed in the sky in separate groups of parallel lines, often like ripples, similar to sand on the coast or waves on the sea. Cirrocumulus are composed of ice crystals and are associated with clear weather.

Cirrostratus (Cs), The Russian name is cirrostratus - thin, white, high clouds, sometimes covering the sky completely and giving it a milky tint, more or less distinct, reminiscent of a thin tangled network. The ice crystals they are made of refract light to form a halo with the Sun or Moon at the center. If the clouds subsequently thicken and lower, precipitation can be expected in about 24 hours. These are the clouds of a warm front system.

Upper level clouds do not produce precipitation.

Mid-level clouds. Precipitation.

Altocumulus (Ac), Russian name altocumulus,- middle-tier clouds, consisting of a layer of large individual spherical masses. Altocumulus (Ac) are similar to the upper level clouds of sirrocumulus. Since they lie lower, their density, water content and the size of individual structural elements are greater than those of sirrocumulus. Altocumulus (Ac) can vary in thickness. They can range from blinding white if they are illuminated by the Sun to dark gray if they cover the entire sky. They are often mistaken for stratocumulus. Sometimes individual structural elements merge and form a series of large swells, like ocean waves, with stripes of blue sky between them. These parallel stripes differ from cirrocumulus in that they appear on the palate in large dense masses. Sometimes altocumulus appear before a thunderstorm. As a rule, they do not produce precipitation.

Altostratus (As) , Russian name altostratified, - middle-tier clouds that look like a gray fibrous layer. The Sun or Moon, if visible, appears as if through frosted glass, often with crowns around the star. Halos do not form in these clouds. If these clouds thicken, lower, or turn into low ragged Nimbostratus, then precipitation begins to fall from them. Then you should expect prolonged rain or snow (for several hours). In the warm season, drops from altostratus, evaporating, do not reach the surface of the earth. IN winter time they can produce significant snowfalls.

Low level clouds. Precipitation.

Stratocumulus (Sc) Russian name stratocumulus– low clouds that look like soft, gray masses, like waves. They can be formed into long, parallel shafts similar to altocumulus. Sometimes precipitation falls from them.

Stratus (St), The Russian name is stratified - low, homogeneous clouds resembling fog. Often their lower boundary is at an altitude of no more than 300 m. The curtain of dense stratus gives the sky a hazy appearance. They can lie on the very surface of the earth and are then called fog. Stratus can be dense and transmit sunlight so poorly that the Sun is not visible at all. They cover the Earth like a blanket. If you look from above (having broken through the thickness of the clouds on an airplane), they are dazzlingly white illuminated by the sun. Strong wind sometimes tears the stratus into shreds, called stratus fractus.

Lungs can fall out of these clouds in winter ice needles, and in the summer - drizzle– very small droplets suspended in the air and gradually settling. Drizzle comes from continuous low stratus or from those lying on the surface of the Earth, that is, from fog. Fog is very dangerous in navigation. Freezing drizzle can cause icing on the boat.

Nimbostratus (Ns) , Russian name for stratostratus, - low, dark. Stratus, shapeless clouds, almost uniform, but sometimes with damp patches at the base. Nimbostratus usually cover vast territories measured in hundreds of kilometers. Throughout this vast territory there is simultaneously snow or rain. Precipitation falls for long hours (up to 10 hours or more), drops or snowflakes are small in size, the intensity is low, but during this time a significant amount of precipitation can fall. They are called cover. Similar precipitation may also fall from Altostratus, and sometimes from Stratocumulus.

Clouds of vertical development. Precipitation.

Cumulus (Cu) . Russian name cumulus, - dense clouds formed in vertically rising air. As the air rises, it cools adiabatically. When its temperature reaches the dew point, condensation begins and a cloud appears. Cumulus have a horizontal base, convex upper and lateral surfaces. Cumulus appear as separate flakes, and never cover the palate. When the vertical development is small, the clouds look like tufts of cotton wool or cauliflower. Cumulus are called "fair weather" clouds. They usually appear by midday and disappear by evening. However, Cu can merge with altocumulus, or grow and turn into thunderous cumulonimbus. Cumulus are distinguished by high contrast: the white, illuminated by the Sun, and the shadow side.

Cumulonimbus (Cb), Russian name cumulonimbus, - massive clouds of vertical development, rising in huge columns to great heights. These clouds begin in the lowest tier and extend to the tropopause, and sometimes extend into the lower stratosphere. They are taller than the highest mountains on Earth. Their vertical thickness is especially great in equatorial and tropical latitudes. The upper part of Cumulonimbus is composed of ice crystals, often stretched by the wind in an anvil shape. At sea, the top of the cumulonimbus can be visible at a great distance, when the base of the cloud is still below the horizon.

Cumulus and cumulonimbus are called clouds of vertical development. They are formed as a result of thermal and dynamic convection. On cold fronts, cumulonimbus arise as a result of dynamic convection.

These clouds can appear in the cold air at the rear of the cyclone and at the front of the anticyclone. Here they are formed as a result of thermal convection and give, accordingly, intramass, local rainfall. Cumulonimbus and associated showers over the oceans occur more often at night, when the air above the water surface is thermally unstable.

Particularly powerful cumulonimbus develop in the intertropical convergence zone (near the equator) and in tropical cyclones. Associated with cumulonimbus are: atmospheric phenomena like rain showers, snow showers, snow pellets, thunderstorms, hail, rainbows. It is with cumulonimbus that tornadoes (tornadoes), the most intense and most often observed in tropical latitudes, are associated.

Shower rain (snow) characterized by large drops (snow flakes), sudden onset, sudden end, significant intensity and short duration (from 1-2 minutes to 2 hours). Rain showers in summer are often accompanied by thunderstorms.

Ice grains It is a hard, opaque piece of ice up to 3 mm in size, moist on top. Ice pellets fall with heavy rain in spring and autumn.

Snow pellets has the appearance of opaque soft grains of white branches from 2 to 5 mm in diameter. Snow pellets are observed when the wind is squally. Snow pellets are often observed simultaneously with heavy snow.

hail falls only in the warm season exclusively during showers and thunderstorms of their most powerful cumulonimbus and usually lasts no more than 5-10 minutes. These are pieces of ice with a layered structure, about the size of a pea, but there are also many larger sizes.

Other precipitation.

Precipitation in the form of drops, crystals or ice on the surface of the Earth or objects is often observed, not falling from clouds, but precipitating from the air under a cloudless sky. This is dew, frost, frost.

Dew drops that appear on the deck at night in summer. At negative temperatures it forms frost. Frost - ice crystals on wires, ship equipment, racks, yards, masts. Frost forms at night, more often when there is fog or haze, at air temperatures below -11°C.

Ice an extremely dangerous phenomenon. It is an ice crust that results from the freezing of supercooled fog, drizzle, raindrops or droplets on supercooled objects, especially on windward surfaces. A similar phenomenon occurs from splashing or flooding of the deck. sea ​​water at negative air temperatures.

Determining cloud height.

At sea, cloud heights are often determined approximately. This is a difficult task, especially at night. The height of the lower base of vertical clouds (any variety of cumulus), if they were formed as a result of thermal convection, can be determined from psychrometer readings. The height to which the air must rise before condensation begins is proportional to the difference between the air temperature t and the dew point td. At sea, this difference is multiplied by 126.3 to obtain the height of the lower boundary of the cumulus clouds N in meters. This empirical formula looks like:

H = 126.3 ( t – t d ). (4)

The height of the base of lower layer stratus clouds ( St, Sc, Ns) can be determined using empirical formulas:

H = 215 (t – t d ) (5)

H = 25 (102 - f); (6)

Where f – relative humidity.

Visibility. Fogs.

Visibility This is the maximum horizontal distance at which an object can be clearly visible and recognized in daylight. In the absence of any impurities in the air, it is up to 50 km (27 nautical miles).

Visibility is reduced due to the presence of liquid and solid particles in the air. Visibility is impaired by smoke, dust, sand, and volcanic ash. This occurs when there is fog, smog, haze, or precipitation. The visibility range decreases due to splashes in the sea in stormy weather with a wind force of 9 or more (40 knots, about 20 m/s). Visibility becomes worse during low, continuous clouds and at dusk.

Haze

Haze is a clouding of the atmosphere due to solid particles suspended in it, such as dust, as well as smoke, burning, etc. With severe haze, visibility decreases to hundreds, and sometimes to tens of meters, as in dense fog. Haze is usually a consequence of dust (sand) storms. Even relatively large particles are lifted into the air by strong winds. This is a typical phenomenon of deserts and plowed steppes. Large particles spread in the lowest layer and settle near their source. Small particles are carried over long distances by air currents, and due to air turbulence they penetrate upward to a considerable height. Fine dust remains in the air for a long time, often in the complete absence of wind. The color of the Sun becomes brownish. The relative humidity during these events is low.

Dust can be transported over long distances. It was celebrated in the Greater and Lesser Antilles. Dust from the Arabian deserts is carried by air currents into the Red Sea and the Persian Gulf.

However, during haze, visibility is never as bad as during fog.

Fogs. General characteristics.

Fogs pose one of the greatest dangers to navigation. They are responsible for many accidents, human lives, and sunken ships.

Fog is said to occur when horizontal visibility, due to the presence of droplets or water crystals in the air, becomes less than 1 km. If visibility is more than 1 km, but not more than 10 km, then such a decrease in visibility is called haze. Relative humidity during fog is usually more than 90%. Water vapor itself does not reduce visibility. Visibility is reduced by water droplets and crystals, i.e. water vapor condensation products.

Condensation occurs when the air is oversaturated with water vapor and the presence of condensation nuclei. Above the sea it is mainly small particles of sea salt. Supersaturation of air with water vapor occurs when the air is cooled or in cases of additional supply of water vapor, and sometimes as a result of mixing of two air masses. In accordance with this, fogs are distinguished cooling, evaporation and mixing.

Based on intensity (based on the visual range D n), fogs are divided into:

strong D n 50 m;

moderate 50 m<Д n <500 м;

weak 500 m<Д n < 1000 м;

heavy haze 1000 m<Д n <2000 м;

light haze 2000 m<Д n <10 000 м.

Based on their state of aggregation, fogs are divided into droplet-liquid, icy (crystalline) and mixed. Visibility conditions are worst in icy fogs.

Cooling mists

Water vapor condenses as the air cools to its dew point. This is how cooling fogs are formed - the largest group of fogs. They can be radiative, advective and orographic.

Radiation mists. The Earth's surface emits long-wave radiation. During the day, energy losses are offset by the arrival of solar radiation. At night, radiation causes the Earth's surface temperature to drop. On clear nights, the cooling of the underlying surface occurs more intensely than in cloudy weather. The air adjacent to the surface also cools. If the cooling is to the dew point and below, then dew will form in calm weather. A weak wind is required for fog to form. In this case, as a result of turbulent mixing, a certain volume (layer) of air is cooled and condensation forms in this layer, i.e. fog. Strong wind leads to mixing of large volumes of air, dispersion of condensate and its evaporation, i.e. to the disappearance of the fog.

Radiation fog can extend up to a height of 150 m. It reaches its maximum intensity before or shortly after sunrise, when the minimum air temperature occurs. Conditions necessary for the formation of radiation fog:

High air humidity in the lower layers of the atmosphere;

Stable stratification of the atmosphere;

Partly cloudy or clear weather;

Light wind.

The fog disappears as the earth's surface warms up after sunrise. The air temperature rises and the droplets evaporate.

Radiation mists above the water surface are not formed. Daily fluctuations in the temperature of the water surface, and therefore the air, are very small. The temperature at night is almost the same as during the day. Radiative cooling does not occur, and there is no condensation of water vapor. However, radiation fogs can cause problems in navigation. In coastal areas, fog, as a single whole, flows with cold, and therefore heavy, air onto the water surface. This can also be amplified by the night breeze from land. Even clouds formed at night over elevated coasts can be carried by the night breeze to the surface of the water, as is observed on many coasts of temperate latitudes. The cloud cap from the hill often flows down, covering the approaches to the shore. More than once this led to a collision between ships (port of Gibraltar).

Advection fogs. Advective fogs result from the advection (horizontal transfer) of warm, moist air onto a cold underlying surface.

Advective fogs can simultaneously cover vast horizontal spaces (many hundreds of kilometers), and vertically extend up to 2 kilometers. They do not have a daily cycle and can exist for a long time. Over land at night they intensify due to radiation factors. In this case, they are called advective-radiative. Advective fogs also occur with significant winds, provided that the air stratification is stable.

These fogs are observed over land in the cold season when relatively warm and humid air enters it from the water surface. This phenomenon occurs in Foggy Albion, Western Europe, and coastal areas. In the latter case, if fogs cover relatively small areas, they are called coastal.

Advective fogs are the most common fogs in the ocean, occurring near the coasts and in the depths of the oceans. They always stand above cold currents. In the open sea, they can also be found in warm sectors of cyclones, in which air is transported from warmer areas of the ocean.

They can be found off the coast at any time of the year. In winter, they form over land and can partially slide to the water surface. In summer, advective fogs occur off the coast in cases where warm, moist air from the continent, in the process of circulation, passes to a relatively cold water surface.

Signs of the imminent disappearance of advective fog:

- change in wind direction;

- disappearance of the warm sector of the cyclone;

- it started to rain.

Orographic fogs. Orographic fogs or slope fogs are formed in mountainous areas with a low-gradient baric field. They are associated with the valley wind and are observed only during the day. The air rises up the slope with the valley wind and is cooled adiabatically. Once the temperature reaches the dew point, condensation begins and a cloud forms. For residents of the slope it will be fog. Sailors can encounter such fogs off the mountainous coasts of islands and continents. Fogs can obscure important landmarks on the slopes.

Mists of evaporation

Condensation of water vapor can occur not only as a result of cooling, but also when the air is oversaturated with water vapor due to evaporation of water. The evaporating water should be warm and the air cold, the temperature difference should be at least 10 °C. Cold air stratification is stable. In this case, an unstable stratification is established in the lowest driving layer. This causes a large amount of water vapor to flow into the atmosphere. It will immediately condense in the cold air. A fog of evaporation appears. Often it is small vertically, but its density is very high and, accordingly, visibility is very poor. Sometimes only the masts of the ship stick out from the fog. Such fogs are observed over warm currents. They are characteristic of the Newfoundland region, at the junction of the warm Gulf Stream and the cold Labrador Current. This is an area of ​​heavy shipping.

In the Gulf of St. Lawrence, fog sometimes extends vertically up to 1500m. At the same time, the air temperature can be below 9°C below zero and the wind is almost gale force. The fog in such conditions consists of ice crystals and is dense with very poor visibility. Such dense sea fogs are called frost smoke or arctic frost smoke and pose a serious danger.

At the same time, with unstable air stratification, there is a slight local hovering of the sea, which does not pose a danger to navigation. The water seems to be boiling, streams of “steam” rise above it and immediately dissipate. Such phenomena occur in the Mediterranean Sea, off Hong Kong, in the Gulf of Mexico (with the relatively cold north wind “Norther”) and in other places.

Mixing mists

Fog can also form when two air masses mix, each of which has high relative humidity. The reservoir may be oversaturated with water vapor. For example, if cold air meets warm and humid air, the latter will cool at the mixing boundary and fog may appear there. Fog ahead of a warm front or occluded front is common in temperate and high latitudes. This mixing fog is known as frontal fog. However, it can also be considered as evaporation fog, since it occurs when warm droplets evaporate in cold air.

Mixing fogs form at the edge of ice and above cold currents. An iceberg in the ocean can be surrounded by fog if there is enough water vapor in the air.

Geography of fogs

The type and shape of clouds depend on the nature of the prevailing processes in the atmosphere, the season of the year and the time of day. Therefore, much attention is paid to observations of the development of clouds over the sea when sailing.

There are no fogs in the equatorial and tropical regions of the oceans. It’s warm there, there are no differences in temperature and air humidity day and night, i.e. There is almost no daily variation of these meteorological quantities.

There are a few exceptions. These are vast areas off the coast of Peru (South America), Namibia (South Africa) and off Cape Guardafui in Somalia. In all these places it is observed upwelling(rising of cold deep waters). Warm, moist air from the tropics flows over cold water and forms advective fog.

Fogs in the tropics can occur near continents. Thus, the port of Gibraltar has already been mentioned; fog is possible in the port of Singapore (8 days a year); in Abidjan there are up to 48 days of fog. Their greatest number is in the Bay of Rio de Janeiro - 164 days a year.

In temperate latitudes, fogs are a very common phenomenon. Here they are observed off the coast and in the depths of the oceans. They occupy vast territories and occur in all seasons of the year, but are especially frequent in winter.

They are also typical for polar regions near the boundaries of ice fields. In the North Atlantic and the Arctic Ocean, where the warm waters of the Gulf Stream penetrate, there is constant fog during the cold season. They are often found at the ice edge in summer.

Fogs most often occur at the junction of warm and cold currents and in places where deep water rises. The frequency of fogs is also high along the coasts. In winter, they occur when warm, moist air advects from the ocean onto land, or when cold continental air flows down onto relatively warm water. In the summer, air from the continent hitting the relatively cold water surface also produces fog.