Fogging conditions
1. Fog occurs when near the earth's surface are created favorable conditions for condensation of water vapor. The condensation nuclei necessary for this always exist in the air.
Due to the hygroscopicity of condensation nuclei, the formation of fog begins at a relative humidity of less than 100% (about 90-95%), that is, even before the dew point is reached. It is known that at temperatures of about -10 ° С the fog can be mixed, and at lower temperatures it can even be purely crystalline. The existence of fog at such temperatures is possible with values of relative humidity less than 100%. This moisture indicates a lack of saturation in relation to liquid water, but for ice crystals it will correspond to saturation.
The approach to saturation occurs mainly as a result of air cooling. An increase in air humidity due to evaporation from a warm surface into cold air plays a secondary role.
Depending on these reasons for the formation of mists, they are divided into two main classes: cooling mists and evaporation mists. The first of these classes is absolutely dominant.
2. Air cooling at the earth's surface occurs under different conditions. First, when air moves from a warmer underlying surface to a colder one. The fogs that arise in this case are called advective. Secondly, with radiation cooling of the underlying surface. In this case, the air is cooled mainly from the earth's surface. The resulting fogs are called radiation fogs. Thirdly, with the influence of both factors. The fogs that arise in this case are called advective-radiation.
3. Advective fogs occur in warm air masses ah moving over a colder surface, i.e., when air masses move from low latitudes in high or in winter with warm sea to cold land, in summer from warm land to cold sea, as well as from warm areas of the sea surface to cold ones (for example, near Newfoundland when air is transferred from the Gulf Stream to the Labrador Current).
On land, advective fog occurs most often in autumn and winter, when there are particularly significant differences in temperature between low and high latitudes, and between land and sea. At sea, they are observed more often in spring and summer.
Advective fogs extend hundreds of meters in height. They arise at significant wind speeds, therefore, droplets can coagulate in them, and they take on a drizzling character: the largest droplets fall out of them.
4. Radiation fogs are of two types: ground and high. Ground fogs are observed only over land on clear and quiet nights. They are associated with nighttime radiation cooling of the soil or snow cover. Upward, they extend only tens of meters. Their distribution is local in nature: they appear in spots, especially in lowlands, near swamps, in forest glades. They do not arise over large rivers due to convection over warm (at night) water.
Ground fogs are formed in calm weather, but not during calm weather - a low wind speed is necessary for the occurrence of turbulence, which causes the spread of cooling and fog formation upward. These fogs appear in the surface inversion layer and disappear with it after sunrise.
High radiation fogs can be observed on land and at sea up to a height of several hundred meters in stable anticyclones during the cold season. This is the result of a gradual, day after day, cooling of the air in lower layers anticyclone. Such fog can persist for weeks over large areas, completely capturing them.
5. Evaporation fogs occur most often in autumn and winter in cold air above warmer open water. Over rivers and lakes in the interior of the continent, they appear in the evening or at night, where air flows down, cooled over neighboring soil areas. Evaporation fogs can also occur in the evening during or after rain, when the soil is moist and highly evaporated and the air temperature drops. Over the Arctic seas, evaporation fogs arise over open water holes or open water at the edge of the ice, where colder air from the ice sheet or mainland is transported. Above inland seas such as Baltic and Black, they are observed in winter when cold air masses are transferred to them from land. Evaporation fog usually swirls and dissipates quickly, as it heats up from below warm water... But if the cause of fogging persists for a long time, then the fog can be observed for a long time.
Fogs of the listed types are intramass, that is, they arise inside air masses, regardless of the fronts. However, there are also fogs associated with fronts. These include one of the types of evaporation fog - prefrontal fog. Falling out frontal precipitation moisten the soil. As a result of increased evaporation from both the soil and falling raindrops, the air near the earth's surface reaches saturation and fog forms in it. Such fog is observed as a continuous strip ahead of the front along with rain.
6. It is possible to "predict the appearance of ground radiation fog on the next night, based on the state of the weather in the evening. If the weather is calm and clear and in the evening observation period the temperature is close to the dew point, then with more or less confidence it is possible to predict the appearance of ground fog at night. For For this purpose, on the basis of long-term observations, graphs are plotted or empirical formulas are derived that make it possible to determine the nighttime temperature decrease in a given area by the values of meteorological values for the evening. If the nighttime minimum temperature is significantly lower than the dew point determined from the evening observations, only then will sufficient amount of water vapor condense.
7.In daily course fogs on the plain have a maximum intensity and recurrence in the morning. On the high levels in the mountains, fogs are distributed evenly throughout the day or have a weak maximum in the afternoon. The reason lies in the special fogging conditions in the mountains.
Mountain fog is essentially a cloud that occurs due to the upward movement of air along mountain slopes. This fog, associated with adiabatic air cooling, can be distinguished into a special type of slope fog.
Having plunged into a frosty tale, there is a desire to understand how long the fog will last, how the fog is formed and why it dissipates. From general concept it is known about phenomena that a cloud is a concentration of drops in intermediate layer atmosphere, or crystals (snowflakes), making it richer and thicker. What exactly thickens depends on the temperature. If the thermometer drops to -15 degrees, then the drops crystallize and give a shine from artificial lighting at night.
Summer fog in the lower atmosphere
The cycle of water movement between the middle layers of the atmosphere and the earth gives us the opportunity to enjoy beautiful clouds... Why does fog form in the lower atmosphere in summer?
- intramass - fogs formed in homogeneous air masses. Their occurrence is more obvious, so they are more common than others;
- frontal - fogs formed at the boundaries of atmospheric fronts.
A sharp temperature drop makes it possible to stop the movement of water and freeze directly above the ground. It happens on a cool morning after a hot one. sultry day... Vapors do not have time to rise higher during the night and freeze at eye level.
In addition to the fact of evaporation for the occurrence of a sufficiently sharp cooling atmospheric air... In the first case, steam condensation occurs due to a decrease in air temperature, lower than it was for dew. In the second case, warm water vapor is blown into the layer of cold air or otherwise penetrates, saturating it with wet drops. It is interesting that in nature it is the fogs of the second case that are much more common.
Suddenly, ice cracks on the river and a reservoir opens up. Vapors from warm water burst out from under the ice and freeze in the air, not having time to rise high. In places like this winter's tale fascinates with openwork patterns.
Permanent crevices in reservoirs form a settled fog. The difference in air and water temperatures keeps the fog of fogs throughout the winter.
Watch the video on what fog is and how it appears.
Fogs formed due to the collision of humid heavy air with a cold stream seem to materialize from the air in the form of frozen drops. If, at the same time, the area is dusty, then the dust particles attract wet drizzle, concentrating more and more moisture in one place. The droplets in the air are increasing. This explains the persistent smog in the industrial areas of cities.
In summer, such fogs are a little thicker, since the size of one drop is summer time reaches 15 microns, in winter a maximum of 5 microns. Light is refracted and reflected from suspended droplets, making the view impossible even at arm's length. The size of the drops directly affects the color of the clot. A small drop scatters blue rays, a large one scatters everything. Therefore, the color of the haze ranges from blue to pale white.
The time of the creeping phenomenon depends on the time the air warms up on the ground. It takes the sun's rays from half an hour to a couple of days to break through to the surface of the earth and warm it up. The drops evaporate and the veil disappears.
It is believed that if the steam has gone to the side, then there will be a clear and sunny weather... If up - it will be rain. In fact, the temperature is lower in the atmosphere higher. Evaporation stops, the drops freeze again, redistributing from fog to clouds.
Fog can be classified into:
- A rather rare fog is called haze. At eye level, through such a haze, you can see into the distance up to 9 km. It is presented in the form of a gray or pale blue shade of a piece of land, which can be easily confused with smoke during fires or dustiness during gusts of wind. High humidity distinguishes haze from the indicated phenomena.
It tightens and evaporates as an independent phenomenon. Sometimes it thickens strongly, turning into fog. It occurs during precipitation (rain, drizzle or rain and snow), after sultry clear days, accompanied by strong heating of the earth. Heat soil contributes to the evaporation of falling moisture, the accumulation of small droplets in the lower atmosphere.
- A layer of clot creeping along the ground, extending from the reservoir. This phenomenon is called drift. It can spread in a continuous thick veil, washes intermittently in areas. The visibility ranges from a few meters to a kilometer. Snow can be observed in late night hours or in the morning.
- Fog with gaps provides poor visibility from 10 to 1000 km around it, but allows you to see the sky well and distinguish clouds. Its appearance is also due to a decrease in temperature at night. It is possible to get into such darkness on a cold winter day, when the rays of the clear sun warm the air more than usual.
- When visibility is difficult for hundreds of meters, not only around, but also upwards, the fog is solid. It occurs under the same conditions as fog with gaps, also in the predawn hours, at night and at dusk.
"A sad time, the charm of the eyes ...". Foggy Albion, gray London or Petersburg in smoke. A mesmerizing phenomenon always attracts the inspiration of authors in literature and painting. Fog in life is able to turn a clear silhouette of nature, buildings, people into weightless, intangible silhouettes, mysterious characters.
Meanwhile, people forced to live in fog are unable to defend themselves or free themselves from the importunity of this gray pore. You have to exist with it, getting used to it. It is not recognized as a threat, it does not count natural disaster, but has an impact on the uninterrupted operation of production, on road accidents, on the general health of the population.
Because of the mists, massive disasters, they are able to influence the pricing of real estate in the districts, completely negating their belonging to the elite or resort areas. The competent use of this phenomenon can positively affect the development of the future harvest, increasing it. This is possible due to the additional saturation of the lower atmosphere with moisture.
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Continuing the conversation about the weather, the heading is led by Candidate of Geographical Sciences M. SOFER
WHAT WE KNOW THE MIST
The period of autumn is approaching when bright and beautiful colors will be replaced by faded and dull ones. Increasingly, the objects around us will seem to dissolve in a weightless and intangible environment - the time of fog will come.
Fog is a phenomenon that cannot be protected and cannot be eliminated, it must be reckoned with. Compared to other meteorological phenomena such as a hurricane, thunderstorm, snowfall, fog cannot be called a formidable force of nature. However, it has a noticeable effect on human living conditions, affects production processes, and the work and safety of movement of all types of transport, and even the well-being of people.
In fog, visibility deteriorates sharply, therefore, for safety reasons, they restrict the movement of ships and aircraft, and suspend work on construction sites. Transport accidents are also frequent, for example, in 1989 in Italy, when more than 80 cars collided and caught fire due to fog near Milan.
The number of foggy days per year determines the suitability or unsuitability of territories for health purposes, tourism and simply for comfortable living conditions. At the same time, mists can be beneficial to Agriculture- in arid regions, they supply soil with additional moisture, which increases productivity.
Who has not heard of the famous London or St. Petersburg fogs?
Their descriptions entered classical literature, became business card These cities. The London fogs from a phenomenon common for coastal cities have turned into its symbol, a kind of myth. Oddly enough, foggy London gained its own popularity after it was presented on the paintings of the Impressionists.
And what does the fog consist of and how does it form?
The composition of the fog is obvious - water. Wait for the kettle to boil, or exhale strongly in the cold, and you will see the process of fog formation. At different temperatures, the air can contain different amount water vapor. The warmer, the more. From the warmth of closeness of air to the state of saturation with moisture determines our feeling of "dryness" or "dampness". If the temperature drops, then part of the moisture condenses. In everyday life, these are "clouds of steam", in nature, they are clouds, rain, dew, fog.
An ordinary fog is a "cocktail" of droplets of different sizes. It can simultaneously contain both very small and very large droplets. Some are more, others are less, depending on ... the temperature. The higher it is, the more large droplets This means that "warm" fogs consist of "thicker" droplets, and "cold" ones - of more "thin" ones. Accordingly, their water content is different. In the first, you can get wet, in the second - dampen.
However, more often we distinguish fogs not by temperature, but by another sign - a simple and practically important one. We estimate the most dangerous and unpleasant as “strong”, “thick”, “dense.” But what is behind these estimates? It turned out that in 1 cm3 of weak fog there are 50-100 drops, and strong - 500-600, that is ... almost ten times more T em who plunged into the dank dampness of the fog, it seems that everything around is as if saturated with water. This belief is based on the traditional concept of 100% moisture in fog. However, measurements show that relative humidity maybe less, sometimes 80-90%, and in individual cases and below. About the same humidity in the clouds. So the expression "fog moisture" is not at all a tautology of the "wet water" type.
After all, it only seems that in heavy fog clothes get wet quickly. But in fact, if you try to "squeeze out" a few cubic meters of fog, then ... there will not be enough moisture even for one sip. Apparently, we most likely overestimate the water content of the fogs. 1 m3 of fog contains 0.2-0.5 g of water. This means that by "squeezing out" all the moisture from 1000 m3 of fog, we will barely quench our thirst.
At the same time, a simple calculation shows that 1 km3 of fog can contain up to half a million liters of water. And this amount of moisture is already enough to irrigate tens of hectares of fields. In many places, fog and dew are a significant source of moisture for plants.
What fogs are there?
At first glance, all fogs are the same. Most often, we are not interested in the reasons for the appearance of fog, we wait for it to dissipate, and forget about it until the next appearance. However, meteorologists treat fogs differently. They know that there is no fog "in general", there are certain processes that each time lead to the formation of this or that type of fog.
It is easy to say that fog is "excess" moisture released in the form of tiny droplets. It is more difficult to explain where these "surpluses" came from. In any case, they boil down to the frightening word "heat and moisture exchange", or, more simply, to two reasons: evaporation from a warm surface into cold air and cooling of a warm air mass.
Almost everyone has witnessed these processes .. Some have watched the ice-free ice-hole soaring. Others saw a damp haze approaching from the sea to land in winter, and in summer the fog stubbornly stayed away from the coast. Still others cursed the road crossing lowlands, ravines, ravines, where cold air flows and where fogs are regularly born. The fourth - remember the beautiful in form and accurate in observation verses of Russian poets, who did not disregard this seemingly nondescript weather phenomenon.
Let us recall only some textbook-known lines. Pushkinskys: "The sky was breathing in autumn ... The fog lay on the fields ...", or: "The daylight went out, the blue evening fog fell on the sea ...". Compare them with Yesenin's: "The fields are squeezed, the groves are bare, the water is foggy and damp ...", or: "A spicy evening. The dawns are dying out. Fog is creeping across the grass ... "
It's amazing how dynamic the fogs are in the eyes of poets, they “blow”, “fall”, “lie down”, “rise”, “creep” ... Do many people notice this?
Where are the fogs spelled out? It is quite simple to determine this - wherever there is a collision of air masses with different temperatures and humidity. These are the so-called border areas: land - sea, warm - cold current, border sea ice, the border snow cover. Such conditions are developing in the northern hemisphere, so there are areas that can be safely considered "fog poles".
So, at the junction of the warm Gulf Stream and the cold Labrador Current in the area of Newfoundland Island, there are 120 foggy days per year, especially a lot of them in summer: on average, there are 22 foggy days per month. That is why this area is considered one of the most dangerous for sailors. Its notoriety is transmitted (is it not by fogs?) To the fatal "Bermuda Triangle" located in the neighborhood
Fogs often visit in the Kola Peninsula region (50-100 foggy days a year), a little less often they are on the coasts of the Barents, Severny and Baltic seas, in Okhotsk and Japanese seas, they are typical for Florida and California. The famous red pillars of the San Francisco Strait Bridge are often obscured by a whitish veil. New Yorkers are well aware that in winter, warm winds from the ocean almost always bring fog.
The greater the temperature difference, the more intense the fog. Any of us can become a forecaster. If the temperature difference between water and air reaches 15 C, then the probability of fog formation is 85-90%. Such conditions develop on the shores southern seas and in the foothill areas.
The “urban” fogs have a completely different pedigree. At unfavorable conditions and polluted air, fog in the city can easily arise and persist for several days. A classic example is London and Petersburg of the past centuries. Remember the feeling of Dostoevsky's "Poor People": "There was no rain, but there was fog, no worse than good rain ... There is fog under your feet, fog over your head too ..."
However, real observations do not always correspond to the prevailing fiction representations. City fogs depend on dozens of factors (winds, relief, proximity to water bodies, type of industry, type of transport, etc.), which can be combined in the most bizarre way. Therefore, do not be surprised that, according to climatologists, one of the most foggy cities in the world is ... Rio de Janeiro. There, during the shadow of the year, an average of 164 days with fogs are observed. The second place is firmly occupied by the capital of Ecuador, Quito - 92 foggy days a year. Then Helsinki - 60 days, Bucharest - 55 days and London - 46 days follow by a wide margin.
Many northern European cities are not at all as "foggy" as they sometimes seem. In Stockholm, for example, fog can be observed only 13 days a year, while in Dublin and Reykjavik only 5-7 days. Paradoxically, fog is almost as rare in another climatic zone- in Mongolia.
The "Brief Climate Guide to the Countries of the World" (1984) dispassionately testifies that in St. Petersburg and Moscow the number of foggy days a year is almost the same: about 30. This is 7 days more than in Rome, but 14 days less than in Berlin.
There are cities on the planet whose inhabitants cannot even remember when they saw fog in last time... For example, in Beirut there is one foggy day a year. For a resident of Khartoum and Bombay, this weather phenomenon does not exist at all.
Fog visibility.
None of the characteristics of the fog are as important to us as the visibility in it. No wonder, when they want to emphasize the density of the fog, they say: nothing is visible at arm's length. Or: not to be seen two steps away! Messages about possible fogs must be included in weather reports. And information about a sharp decrease in visibility is spread as an emergency message or a storm warning.
It is obvious to everyone that the strength, density, density of the fog are manifested through the range of visibility in it. If objects are visible at a distance of 500-1000 m, the fog is considered weak, with visibility within 50-500 m - moderate, less than 50 m - strong. It is the limited visibility that makes heavy fog the most dangerous. weather phenomenon... A dense fog can completely paralyze the life of a large city, restrict aviation operations, and block roads.
But what determines density? Just the number and size of moisture droplets per unit volume, i.e. the water content of the fog, which in turn depends on the temperature. Therefore, the "warm" fog is almost always thick and dense, and the "cold" one is more liquid and transparent. If you notice how the fog "swirls", i.e. air masses alternate in it, which means you observe temperature pulsations, and with them the dynamics of water content and droplet sizes.
Be careful! You may also notice a change in the color of the fog. The smallest droplets scatter short wavelengths of light (blue rays) best, so faint fogs and haze are bluish in color. In denser fogs, the droplets are larger and scatter light waves of all wavelengths almost equally. Therefore, the color of such fogs is closer to white. However, poets see a much more varied palette. So, Dostoevsky's fogs are "milky", Blok's are "gray-haired", Bunin's are "silvery", Gumilyov's are "fair-haired", and Tsvetaeva's are "blond." What are yours?
Fog audibility
Have you tried talking in the fog? An observant person will confirm: even in the densest fog, sounds are heard perfectly. But how far do car or ship signals travel through thick fog? Do their bass sounds go out as if in a layer of cotton wool?
Knowledge of this issue was vital for sailors, since in heavy fog, light signals do not pass and the risk of collision of ships increases dramatically. According to British statistics a century ago, over ten years, 273 shipwrecks were recorded off the coast of England due to thick fog. The problem came out on state level, long-term studies began. They were accompanied by great noise - cannon shots, whistles and powerful sirens sounded the coast day and night, in any weather, in fog, rain, snow. The mind was not in vain ...
It was found that sounds spread well over a long distance only when air environment continuous and homogeneous. If the atmosphere consists of layers of air of different density and temperature, then at the junction of each layer, sound energy is lost and the sound “does not go” - it quickly goes out. In the same time overcast weather transparent to sounds, and in the thickest fog, sounds can spread over a distance almost twice as much as in clear weather... How, then, can one explain the "dips" of the sound, the impression of its "viscous" passage through the shaggy, stirring clots of water vapor? The answer lies in the very structure of the fog. If the fog swirls, pulsates, then it is heterogeneous, the drops are different not only in temperature and size, but also in sound permeability. It often happens in the mountains.
Normal plain fog consists of huge number extremely small water droplets - less than a thousandth of a millimeter in diameter. They create a relatively dense, but homogeneous environment, so the scattering sound waves almost never happens. This is why ships, trains and vehicles trapped in the fog give sound signals. Horns and sirens are reliable sources of information in the thickest fog.
But it is one thing to warn neighbors about your whereabouts, and another to create conditions for safe movement. The most radical way is the elimination of fogs. Humanity has come close to the practical possibility of fighting fogs. This problem is not so much a technological problem as an economic and environmental one. What is the cost of weather control and what are its implications? While this question remains open ...
Finding yourself in the middle of a solid white cloud, so dense that at arm's length it is practically impossible to discern anything, you often ask yourself the question: why such a thick fog has formed, why is it white and you start to wonder how long this phenomenon usually lasts, and also why any fog dissipates.
Fogs form when droplets or ice crystals accumulate in the air in the lower layers of the atmosphere, due to which a cloud-like veil forms along the earth's surface, limiting visibility so much that space is not visible beyond one kilometer, and in some cases objects become difficult to distinguish even at a distance several meters.
If the temperature environment exceeds -10 ° С, the vapor veil consists only of drops. If the temperature indicators fluctuate from -10 to -15 ° С - from water droplets and ice crystals, and when it is -15 ° С outside - the fog consists of small ice crystals, shimmering in the light of night lights.
Why this phenomenon is formed is easy to answer: it owes its appearance either to the evaporation of water from warm surface into cold air, or cooling of warm air currents saturated with moisture. For example, the appearance of terrestrial clouds can often be observed in the evening or in the morning after the temperature of the soil and vegetation (grass) decreases, the lower layers of the atmosphere cool so much that they begin to release excess moisture in the form of water droplets.
Another example, this time in winter, is fog over a river, lake or other body of water, on the ice of which an ice-hole has formed: in cold weather, there is always a shroud above it, spreading over the water surface. This happens because the water temperature during frosts is warmer than the surrounding ice and the air in contact with it (because of this, the air above the water is always warmer than the rest and the fog over the river in the area of the ice hole is almost always there).
After warm air mixes with cold air currents, it begins to cool, emitting steam and forming a cloud at the very surface of the Earth. Therefore, the fog over the river and other bodies of water is usually stable and long-term: cold and warm air currents and currents constantly mix here.
A striking example of this phenomenon is located in Atlantic Ocean Canadian island Newfoundland. Due to the fact that here two currents collide with each other - warm Gulf Stream and cold Labrador, locals forced to spend in the midst of the haze about one hundred and twenty foggy days a year.
Ground cloud formation
When water-saturated air cools or mixes with colder air currents, droplets begin to form in the atmosphere. After that, if there is over ground surface the smallest dust particles, they begin to adhere to them, layering on each other and forming droplets of larger sizes (the more dust in the air, the faster a cloud forms, therefore big cities almost always shrouded in a faint, almost imperceptible veil).
In the warm season, the size of such a drop ranges from 5 to 15 microns, during frosts - from 2 to 5 microns, so the winter cold fog is not as thick as the summer one. As soon as the droplets reach the required volumes, the objects turn out to be vague and difficult to distinguish: with a strong fog, the air acquires a whitish tint and bluish - with a weak one.
The answer to the question why this phenomenon happens different colors, is simple: smaller droplets scatter short blue rays better, while in thick ground clouds, larger droplets and light waves scatter all rays equally, regardless of their length.
The water content of such clouds usually does not exceed 0.5 g / m3, but sometimes thick fog can contain up to 1.5 g / m3 (this water is enough for the plants to receive the necessary moisture, this is especially important for the vegetation of the arid regions of the planet). How impenetrable the veil turns out to be depends largely on the humidity of the air, which during the appearance of ground clouds usually ranges from 85 to 100%:
- if the visibility does not exceed 50 meters, there is a thick fog, and the number of drops is 1200 per cubic centimeter;
- if the space is viewed at a distance of 50 to 500 meters - moderate (water drops in this case from 100 to 600);
- if the visibility is a kilometer - weak (drops - from 50 to 100).
Fogs are not uncommon during frosts, and the phenomenon can be seen even when the humidity does not exceed fifty percent. They can usually be seen in cities, especially at train and bus stations, where the veil is formed by the steam that appears during the combustion of fuel and is released into the air through chimneys and exhaust pipes.
Kinds
Terrestrial clouds do not always owe their origin only to nature: big number fogs arise in cities, and therefore they consist not only of drops and dust, but also smoke, soot that are emitted by factory or chimneys, or arise after or during fires when a forest, peat or steppe is burning. By origin, meteorologists divide fogs into dry (smoke, soot, etc. are to blame for their formation) and wet (only water and dust are involved), while often the second form flows into the first.
In turn, humid fogs, the formation of which was directly influenced by nature - this is evening, night or morning fog (it is this period that is optimal for the appearance of clouds creeping on the ground), meteorologists are also divided into groups:
- Underground. Evening or morning fog that spreads low over the earth's surface or body of water (for example, fog over a river). The shroud can be continuous, or it can go in separate shreds, and the visibility will not exceed a kilometer.
- Translucent. Despite the fact that visibility along the surface is low and in some cases does not exceed several meters, clouds can be clearly distinguished in the sky. This type includes night, evening, and morning fog.
- Solid. Visibility of dense fog is very limited and often does not exceed fifty meters. The sky is almost invisible, so the clouds are almost impossible to distinguish. This is mainly evening, night and morning fog, and during cold weather with an increase in temperature, cold fog can be seen during the day.
Why do fogs disappear
The duration of this phenomenon is different and can range from half an hour to several days (especially during cold weather or in the collision of warm and cold air and water flows e.g. fog over a river). The main reason why any fog dissipates is the heating of the air. Since a shroud forms near the surface, after Sun rays it is heated, the air is also heated, as a result of which the drops evaporate and turn into steam.
The higher above the earth's surface, the weaker the fog dissipates, since in the upper atmosphere the air temperature begins to drop again, the vapor transforms into water droplets and forms clouds.
Fog is a natural phenomenon when a large content of water vapor is formed in the atmosphere. It mainly arises from the contact of cold and warm air... Fogs occur at any time of the year, but most often they occur in late summer or autumn, when the air cools faster than the ground cools. As a result, cool air sinks to the ground or water, which still retains heat, condensation occurs, and many water droplets hang in the air. It turns out that a huge cloud hangs directly above the ground or a body of water. In the place where the fog has formed, the air humidity is 100%. Fogs are different in structure. If the air temperature is not very cold, above 10 degrees of frost, then the foggy cloud also consists of water droplets. At a temperature of 10-15 degrees below zero, the cloud consists of a mixture of water droplets with ice crystals. If the temperature drops below 15 degrees below zero, then an ice fog is formed, when the entire cloud consists of ice crystals. In cities and settlements fogs are denser because condensate mixes with exhaust gases and dust.
What fogs are there
Fogs are different. It depends on how good the visibility is in the foggy location.
Haze is the weakest type of fog.
Ground fog - fog spreading over the ground or a body of water in a thin layer. This fog has no great influence for visibility.
Translucent fog with visibility ranging from several tens to several hundred meters. Through such a fog, the sun and clouds are visible.
Solid fog, when a whitish cloud envelops the earth, through which it is impossible to see literally nothing at a distance of several meters, and sometimes even over an outstretched arm. With such fog, traffic becomes impossible. If the driver is caught in a cloud of solid fog, it is better for him to wait until the fog clears. 
There are not only natural fogs, but also artificial ones. Artificial fogs arise from industrial human activities. Artificial fog consists of dust, smoke, exhaust gases, chemical substances, other combustion products. Otherwise, it is called smog. Smog- one of the most important problems of modern cities, as it causes irreparable harm to human health and pollutes the environment.
Dry fog may occur, consisting of dust, smoke and soot instead of water droplets. This can happen due to burning peat bogs or due to a volcanic eruption.
Also referred to as artificial fog is radiation fog, when the air is cooled due to the presence of radiation in it.
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