Finding yourself in the middle of a continuous white cloud, so dense that it is practically impossible to distinguish anything at arm's length, you often ask yourself the question: why such a thick fog formed, why did it white and you begin to wonder how long this phenomenon usually lasts, and also why any fog dissipates.

Fogs form when they accumulate in the air in lower layers atmosphere of drops or ice crystals, due to which along earth's surface a cloud-like veil is formed, limiting visibility so much that space beyond one kilometer is not visible, and in some cases objects become difficult to distinguish even at a distance of several meters.

If the ambient temperature exceeds -10°C, the vapor blanket consists only of droplets. If the temperature fluctuates from -10 to -15°C, it is made up of water droplets and ice crystals, and when it is -15°C outside, the fog consists of small ice crystals, shimmering in the light of night lamps.

Why this phenomenon is formed is not difficult to answer: its appearance is due either to the evaporation of water from warm surface into cold air, or cooling of moisture-saturated warm air currents. For example, the appearance of ground clouds can often be observed in the evening or in the morning after the temperature of the soil and vegetation (grass) drops; 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 veil over it, spreading over the water surface. This happens because the temperature of the water during frost is warmer than the ice surrounding it and the air in contact with it (because of this, the air above the water is always warmer than the rest and there is almost always fog over the river in the area of ​​the ice hole).

After warm air mixes with cold air air currents, it begins to cool, releasing 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-lasting: cold and warm air currents and currents constantly mix here.

A striking example of this phenomenon is considered to be located in Atlantic Ocean Canadian island of Newfoundland. Due to the fact that two currents collide with each other here - warm Gulf Stream and cold Labrador, local residents forced to spend about one hundred and twenty foggy days a year among the haze.

Formation of terrestrial clouds

When air saturated with water vapor cools or mixes with colder air currents, droplets begin to be released into the atmosphere. After this, if there are tiny particles of dust above the earth’s surface, they begin to stick to them, layering on top of each other and forming drops of larger sizes (the more dust in the air, the faster a cloud forms, so large cities are almost always shrouded in a weak, 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 winter cold fog is not as thick as summer fog. As soon as the drops reach the required volumes, objects turn out to be blurry and difficult to distinguish: the air acquires a whitish tint in case of strong fog and bluish in light fog.

The answer to the question why this phenomenon happens different colors, is simple: smaller droplets are better at scattering short blue rays, while in dense terrestrial 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 dense fog can contain up to 1.5 g/m3 (this water is enough for plants to receive the necessary moisture, this is especially important for vegetation in the arid regions of the planet). How impenetrable the shroud will be depends largely on the humidity of the air, which is usually between 85 and 100% during the occurrence of ground clouds:

• if visibility does not exceed 50 meters, thick fog is observed, and the number of drops is 1200 per cubic centimeter;
• if the space is visible at a distance of 50 to 500 meters - moderate (water drops in this case from 100 to 600);
• if visibility is a kilometer - weak (drops - from 50 to 100).

Fogs are also common during frosts, and the phenomenon can be seen even when the humidity does not exceed fifty percent. They can usually be observed in cities, especially at railway and bus stations, where the haze is formed by 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: a large number of fogs occur in cities, and therefore they consist not only of drops and dust, but also smoke, soot, which are emitted by factory or chimneys, or arise after or during fires, when a forest, peat or steppe burns. Based on their origin, meteorologists divide fogs into dry (smoke, soot, etc. are to blame for their formation) and wet (only water and dust are involved), and often the second form flows into the first.

In turn, wet fogs, the formation of which is directly influenced by nature - this is evening, night or morning fog (this period is optimal for the formation of clouds creeping along the ground), meteorologists are also divided into groups:

1. 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 may be continuous, or it may be in separate wisps, and visibility will not exceed a kilometer.
2. 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.
3. Solid. Visibility of dense fog is very limited and often does not exceed fifty meters. The sky is almost invisible, so it is almost impossible to distinguish clouds. This is mainly evening, night and morning fog, and during cold weather when temperatures rise, cold fog can be seen during the day.

Why do fogs disappear?

The duration of this phenomenon varies and can range from half an hour to several days (especially during cold weather or when warm and cold air and water flows, for example, fog over a river). The main reason why any fog dissipates is the air warming up. Since a veil forms near the surface, after Sun rays it is heated, the air also heats up, 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 layers of the atmosphere the air temperature begins to drop again, the steam transforms into water droplets and forms clouds.

Fogs. Types of fogs. Impact on flights.

When water vapor saturates and then condenses or sublimates, tiny droplets of water and ice crystals form in the surface layer of the atmosphere. The accumulation of such particles causes deterioration in horizontal visibility. Air turbidity caused by the accumulation of condensation or sublimation products in the ground layer, with visibility less than 1000 m, is called fog. If, under the same conditions, visibility is more than 1000m, but less than 10 km, then the phenomenon is called haze. In international aviation codes, haze is a phenomenon with visibility from 1000m to 5 km.

To form fog you need following conditions:

Air saturation with water vapor at the surface of the earth is up to 100%;

Presence of condensation nuclei.

By synoptic conditions Fog formations are divided into

Intra-mass;

Frontal.

Intramass fogs, depending on the process leading to saturation of air with water vapor, are divided into:

Cooling mists;

Mists of evaporation.

Cooling fogs arise due to cooling of the earth's surface (radiative), or when relatively warm air moves over a cold underlying surface (advective). This group also includes fogs associated with atmospheric fronts (frontal).

Radiation fogs are formed due to radiation cooling of the earth's surface and due to this cooling of the ground layer of air. In the warm half of the year, radiation fogs are formed at night in clear or partly cloudy weather with a weak wind not exceeding 3 m/s. They occur mainly over lowlands and wetlands. The vertical thickness (thickness) of such fogs can range from several meters to several tens of meters. They are especially dense in the lowest ground layer, where the greatest air cooling occurs; with height, their density quickly decreases. While flying through the fog, you can clearly see rivers, large landmarks and lights, and the airfield. And horizontal visibility near the ground can be up to 100m or less. Oblique visibility sharply deteriorates when an aircraft enters a layer of fog on landing.

Flight above the radiation fog does not present any particular difficulties, because... This fog is usually located in patches and allows for visual orientation. The indicated visibility conditions during radiation fogs sometimes lead to an incorrect assessment of the meteorological situation.

Radiation fogs of the warm half of the year usually dissipate with sunrise, and sometimes rise above the ground, forming a thin layer of scattered stratus (St fr) clouds, the height of which does not exceed 100-200 m. Fog dissipation can occur when the wind increases to 4-5 m/s or more.

In the cold half of the year, radiation fog can be more dangerous than in the warm half. During this period, at steady state clear weather cooling of the air can spread to high altitudes. The resulting radiation fog has a vertical thickness from several hundred meters to 1.5-2 km and persists for a long time (sometimes up to several days).

Advective fogs arise during the movement (advection) of relatively warm, moist air masses along a cold underlying surface. Through turbulent mixing, cooling extends to a height of several hundred meters, where an inversion layer is usually observed. Fog appears in the cooled ground layer, which is often accompanied by drizzling precipitation. Under the influence of the retarding inversion layer underneath, the greatest accumulation of water vapor is observed. As a result, the density of advective fog increases as it rises. With this fog, horizontal visibility is somewhat better near the ground, but at a height (above several tens of meters) it deteriorates sharply.

Unlike radiation fogs, advective fogs can be observed with wind speeds of 5-10 m/s or more. These fogs can occur at any time of the day and persist for a long time and spread over a large area.

Advective fogs represent great danger for aviation, especially at low altitudes. Moving at significant speeds (20-40 km/h), they can close the large territory operating and reserve airfields and hold for a long time. Flight above advective fog is only possible using instruments and favorable conditions weather at the landing airfield. Advective fogs can cause icing, sleet, and drizzle.

Frontal fogs are associated with atmospheric fronts that separate warm and cold air masses. Most often, frontal fog occurs on warm front in a wedge of cold air located in the front part, in the zone of precipitation.

The reason for the formation of this type of fog is the decrease in pressure ahead of the front. It leads to adiabatic expansion of surface air and its cooling. Water vapor, which is in the air in a state close to saturation (due to the evaporation of precipitation), condenses when the air is cooled to the dew point and below. The result of condensation is frontal fog. This fog occupies a strip up to 200 km wide. Sometimes it can merge with overlying clouds or join advective fog that has arisen in the post-frontal air. Frontal fog is especially dangerous for flights when it merges with frontal clouds. If the frontal fog merges with the advective fog of the transfrontal warm sector, then the weather conditions are extremely unfavorable and dangerous for flights over large areas.

Evaporation fogs arise due to the influx of water vapor from a warm water surface into cooled air. For the formation of such fogs, a difference between air and water surface temperatures of more than 10°C is required.

Evaporation fogs occur at sea over ice-free bays in winter time and autumn - over rivers and lakes in autumn months when the surface of the water in rivers and lakes turns out to be significantly warmer than the air. These fogs can reach great intensity and heights of several meters, sometimes tens of meters.

Frosty fogs are formed due to the entry of water vapor into the surface layers of air with combustion products. IN populated areas and at airfields in Siberia, such fogs occur during the firing of furnaces and during work aircraft engines at air temperatures below -40°C. IN big cities, where a large amount of water vapor generated during fuel combustion enters the air around the clock, such fogs can also occur at more high temperature, about -16°C and below.

In the presence of a weak wind and its slight increase with height, such fogs form above the ground at an altitude of 50-200 m, significantly worsening oblique visibility from an airplane.

Natural phenomena are often more admired than man-made ones. No matter what a person does, everyone will look at mountains, hurricanes and tsunamis with admiration. Admiration, horror and awe. All this is natural in relation to such majestic and hazardous phenomena. Interest can also be aroused by more mundane moments; many would not mind learning how fog is formed and whether it is something to be wary of. natural phenomenon.

Fight against nature

Man fights with nature throughout his entire existence. Civilization opposes itself to chaotic primordial power:

• People tend to love orderliness and consistency.
• Since primitive times, it was nature, in all its manifestations, that most “spoiled life” for man.
• Fighting with environment, the first settlers colonized new lands and asserted their power.
• Every year farmers entered into a deadly race with nature. Its meaning was to get as much harvest as possible in a short time and feed everyone who needs it.
• Even in ancient times, doctors were faced with the problems of mass epidemics. Their sources were microorganisms, the same elements of living nature.

Today, although people have become quite distant from nature, having conquered it in many areas through their activities, humanity still largely depends on it. And it cannot be said that no “sudden turn” performed by Mother Nature will be able to erase our civilization and any memories of it.

Where does the fog come from?

The fog, oddly enough, fog comes from the air. To do this, depending on the area, you will need:

• Availability large quantity industrial enterprises and road transport.
• Special weather conditions.
• Reservoirs, preferably rivers and lakes.

Fog caused by the influence of exhaust gases and emissions from factories is usually called smog, and it is typical for industrial centers. If about 150 years ago it was most often found in England, today the “palm” has moved to South America and China. It just so happens that Europe and the USA are trying to move their production as far as possible so as not to “enjoy” the smog and other possible consequences.

Weather changes and the presence of bodies of water affect the amount of evaporated moisture, which leads to the formation of fog. This variety is less dangerous for people, it practically does not cause exacerbation chronic bronchitis and new attacks of bronchial asthma. But visibility is still reduced.

Such fog spreads over the surface and disappears within a few hours. But exceptions are possible, strict rules nature doesn't have much.

How does fog appear?

To understand the formation of fog, you need to remember movement of air masses:

1. Air moves not only horizontally, but also vertically.
2. There are two types of masses - cold and heated air.
3. Obeying the laws of physics, warm air rises higher, and cold air, on the contrary, descends closer to the surface.
4. During such movement, condensation occurs - evaporation and fixation of microscopic droplets of water in the air.
5. They are best fixed on dust particles, so in industrial areas even ordinary fog occurs earlier. What can we say about smog?

Enormous volumes of air are constantly moving, the laws of physics also apply without change. But fog is a rare phenomenon, sometimes forgotten about for months. And the secret is simple, For maximum effect the maximum level of humidity will be required. In dry climates, such phenomena occur only under very low temperatures, extremely low.

So Any fog is based on the movement of warm and cold air , contact and a kind of “conflict” of these two environments, ending with the evaporation of moisture into the environment.

How to make fog at home?

Fog can also be created artificially. The only question is the scale and goals:

At home you will need:

• An empty bottle, preferably a liter bottle. One third filled with hot water.
• A drop of vodka to add to the water.
• Ice tongs and, in fact, a piece of ice. It will need to be kept close to the neck.

That's the whole simple scheme. Of course, you won’t be able to achieve a thick and long fog, but even this result will surprise your guests. For the same purposes, you can acquire a special machine that, based on the same principles, will produce fog in industrial scale. But this is an expensive option and bulky equipment. For those who are not looking for easy ways.

Formation of fog in stages

There is nothing secret about the formation of fog; physicists revealed the secret of this natural phenomenon centuries ago. This is how fog forms in the atmosphere:

1. There is constant air circulation in the atmosphere.
2. Warm and cold masses move, replacing each other.
3. During movement, condensation and evaporation of moisture occurs.
4. Water can also evaporate from the surface of water sources if ambient temperature slightly lower than water temperature.
5. Droplets are fixed on any surface and linger in the air for some time.
6. The delay is observed for several hours, as a rule. At this time, the surface is covered with a light haze and visibility is significantly reduced.

Fog can be a challenge for those suffering from chronic lung disease. Most often, problems arise with smog. Reduced visibility increases the risk of accidents, so motorists need to either be extremely careful or limit their time behind the wheel of a vehicle for a couple of hours.

Fog - atmospheric phenomenon, the accumulation of water in the air when tiny condensation products of water vapor are formed (at air temperatures above −10° these are tiny droplets of water, at −10…-15° they are a mixture of water droplets and ice crystals, at temperatures below −15° they are ice crystals sparkling in the sun or in the light of the moon and lanterns).

Relative air humidity during fogs is usually close to 100% (at least exceeds 85-90%). However, in very coldy(-30° and below) in populated areas, at railway stations and airfields, fogs can be observed at any time relative humidity air (even less than 50%) - due to the condensation of water vapor formed during the combustion of fuel (in engines, stoves, etc.) and released into the atmosphere through exhaust pipes and chimneys.

The continuous duration of fogs usually ranges from several hours (and sometimes half an hour to an hour) to several days, especially in cold period of the year.

At weather stations it is noted the following types fog:

• Ground fog is fog that spreads low over the earth's surface (or body of water) in a continuous thin layer or in the form of separate wisps, so that in the fog layer the horizontal visibility is less than 1000 m, and at a level of 2 m it exceeds 1000 m (usually the same as for haze, from 1 to 9 km, and sometimes 10 km or more). It is observed, as a rule, in the evening, night and morning hours. Separately, ground ice fog is noted - observed at air temperatures below −10 ... -15 ° and consisting of ice crystals sparkling in the sun's rays or in the light of the moon and lanterns.

• Translucent fog - fog with horizontal visibility at a level of 2 m less than 1000 m (usually it is several hundred meters, and in some cases it drops even to several tens of meters), poorly developed vertically, so that it is possible to determine the state of the sky (the number and shape of clouds ). It is most often observed in the evening, at night and in the morning, but can also be observed during the day, especially in the cold half of the year when the air temperature rises. Separately, translucent ice fog is noted - observed at air temperatures below −10 ... -15 ° and consisting of ice crystals sparkling in the sun's rays or in the light of the moon and lanterns.

• Fog is a continuous fog with horizontal visibility at a level of 2 m less than 1000 m (usually it is several hundred meters, and in some cases it drops even to several tens of meters), sufficiently developed vertically so that it is impossible to determine the state of the sky (the number and shape of clouds ). It is most often observed in the evening, at night and in the morning, but can also be observed during the day, especially in the cold half of the year when the air temperature rises. Separately, ice fog is noted - observed at air temperatures below −10 ... -15 ° and consisting of ice crystals sparkling in the sun's rays or in the light of the moon and lanterns.

The highest number of foggy days at sea level - an average of more than 120 per year - is observed on the Canadian island of Newfoundland in the Atlantic Ocean.

Average annual number of days with fog in some Russian cities:

Arkhangelsk	31	Astrakhan	36	Vladivostok	116	Voronezh	32	Ekaterinburg	12
Murmansk	24	Naryan-Mar	40	Omsk	27	Orenburg	22	Petropavlovsk-Kamchatsky	94
Syktyvkar	21	Tomsk	19	Khabarovsk	16	Khanty-Mansiysk	15	Yuzhno-Kurilsk	118
Irkutsk	52	Kazan	16	Moscow	9	Saint Petersburg	13
Rostov-on-Don	36	Samara	41

Pier in the fog. Vancouver Island, Sydney

Mountain road in fog (D81 highway in Corsica)

Fogs prevent the normal operation of all types of transport (especially aviation), so fog forecasts are of great economic importance.

Artificial fog creation is used for scientific research, V chemical industry, heating engineering and other areas.

Classification

Sea fog in the Oresund Strait

Country road in the fog (Moscow region, Naro-Fominsk)

Fog in San Francisco (Golden Gate)

Fog on the Volga near Nizhny Novgorod

According to the method of occurrence, fogs are divided into two types:

• Cooling fogs are formed due to the condensation of water vapor when the air is cooled below the dew point.
• Evaporation fogs are evaporation from a warmer evaporating surface into cold air over bodies of water and wet land areas.

In addition, fogs differ in the synoptic conditions of formation:

• Intramass - formed in homogeneous air masses.
• Frontal - formed at the boundaries atmospheric fronts.

Haze is a very faint fog. In haze, the visibility range is several kilometers. In the practice of meteorological forecasting, the following are considered: haze - visibility more/equal to 1000 m, but less than 10 km, and fog - visibility less than 1000 m. Heavy fog is considered when visibility is less than or equal to 500 m.

Intramass fogs

Intramass fogs predominate in nature; as a rule, they are cooling fogs. They are also usually divided into several types:

• Radiation fogs are fogs that appear as a result of radiation cooling of the earth's surface and the mass of moist surface air to the dew point. Typically, radiation fog occurs at night in anticyclone conditions with cloudless weather and a light breeze. Radiation fog often occurs in conditions temperature inversion, preventing the rise air mass. After sunrise, radiation fogs usually dissipate quickly. However, in the cold season, in stable anticyclones they can persist during the day, sometimes for many days in a row. An extreme form of radiation fog, smog, can occur in industrial areas.

• Advective fogs are formed due to the cooling of warm, moist air as it moves over a colder surface of land or water. Their intensity depends on the temperature difference between the air and the underlying surface and on the moisture content of the air. These fogs can develop both over the sea and over land and cover vast areas, including in some cases up to hundreds of thousands of km². Advection fogs usually occur when cloudy weather and most often in the warm sectors of cyclones. Advection fogs are more persistent than radiation fogs and often do not dissipate during the day.

Sea fog is advective fog that arises over the sea during the transfer of cold air to warm water. This fog is evaporation fog. Fogs of this type are frequent, for example, in the Arctic, when air flows from the ice cover to the open surface of the sea.

Frontal fogs

Frontal fogs form near atmospheric fronts and move with them. Air saturation with water vapor occurs due to the evaporation of precipitation falling in the front zone. The decline observed here plays some role in the intensification of fogs ahead of fronts. atmospheric pressure, which creates a slight pdiabatic decrease in air temperature.

Dry fogs

To the fogs in colloquial speech and in fiction sometimes referred to as so-called dry fogs (haze, haze) - a significant deterioration in visibility due to smoke from forest, peat or steppe fires, or due to loess dust or part of the sand, raised and carried by the wind sometimes over considerable distances, as well as due to emissions from industrial enterprises .

The transitional stage between dry and wet fogs is not uncommon - such fogs consist of water particles along with fairly large masses of dust, smoke and soot. These are the so-called dirty urban fogs, which are a consequence of the presence in the air of large cities of a mass of solid particles emitted during combustion by chimneys, and even more so by factory chimneys.

Characteristics of fogs

View of Bragino (Yaroslavl)

Fog in the Izborskaya Valley (Pskov region)

The fog water content indicator is used to characterize fogs; it denotes the total mass of water droplets per unit volume of fog. The water content of fogs usually does not exceed 0.05-0.1 g/m³, but in some dense fogs it can reach 1-1.5 g/m³.

In addition to water content, the transparency of fog is affected by the size of the particles that form it. The radius of fog droplets typically ranges from 1 to 60 µm. Most drops have a radius of 5-15 microns at positive air temperatures and 2-5 microns at negative temperatures.

Fog is an accumulation of water droplets or ice crystals suspended in the ground layer of air, impairing horizontal visibility to 1000 m or less. In essence, it is a cloud lying on the surface of the earth or water.

Based on the main physical reasons that cause the formation of fogs, they can be divided into two main classes: cooling fogs and evaporation fogs. The first of these classes absolutely predominates.

Cooling fogs are formed by condensation or water vapor when air cools from the earth's or water's surface. They are divided into two types: radiative and advective.

Radiation fogs appear in conditions of stagnant air due to its nighttime cooling from the cooling underlying surface. Observed on clear, quiet nights and in the morning before sunrise. As soon as the sun's rays begin to warm up, these fogs quickly disappear.

Advection fogs are associated with cooling warm air when moving it to a cold surface (the same process is associated with the formation of low stratus clouds, which can turn into fog when descending). These are the most powerful and lasting fogs. They are observed at any time of the day and can be transported over long distances.

Evaporation fogs (vapor) are formed due to the evaporation of water vapor from an underlying surface warmer than the air. Such fogs are most intense in winter over non-freezing bays and polynyas; over rivers and lakes they appear more often in autumn, and on land - after heavy rains in the evening and at night in the summer - autumn period.

Most common feature The distribution of fogs over the earth's surface is an increase in their frequency at high latitudes. Depending on the conditions of formation, fogs in Russia have different continuous durations. In continental areas, short-term fogs prevail, lasting no more than 2–4 hours, and on the coasts northern seas they may not stop for several days.

In the European part of Russia greatest number days with fog are observed on the coast of the Arctic seas, in high mountain areas, on the slopes of hills facing moisture-carrying streams. Particular attention should be paid to (), where the frequency of fogs is extremely high throughout the year. In some places, the average annual number of days with fog can reach 230–280, and their duration per year is 2050 hours. One fog lasts on average 9 hours.

Under monsoon circulation conditions Far East A large number of fogs are observed during the warm period of the year. On , and the Kuril Islands in some years, the number of days with fog can exceed 160–180 per year with a duration of 1000–1400 hours.

The annual cycle depends on geographical conditions: over continents, fogs most often form in autumn, over seas and oceans - in spring, when the water surface is coldest.

Fogs with visibility of 500–200 meters are already seriously impeding traffic. Fogs with visibility less than 50 m and lasting 12 hours or more are considered particularly dangerous weather phenomena and can completely paralyze the work of air and sea ports and ground transport. The average continuous duration of fog with visibility of 500 m or less is usually 2–4 hours, but in some cases they can persist for more than a day.

In large industrial centers, due to the large number of active condensation nuclei emitted industrial enterprises, fogs can form even in unsaturated air and are observed 1.5–2 times more often than in the surrounding area. In Yakutsk, for example, the duration of fogs in the city center is 1300 hours, and on the outskirts (near the airport) - 475 hours.

IN major cities In the North-West, the number of days with visibility less than 500 m can range from 6 to 65. The longest fogs with such visibility are observed here in the autumn months. Their continuous duration is on average 3 hours. The maximum duration of fogs per year in some cities is close to 200–300 hours.