Fog at what time of day. Why is there fog in severe frosts? Dew weather prediction

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

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

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

The following types of fog are noted at weather stations:

• Ground fog - fog that creeps low over earth's surface(or a body of water) in a continuous thin layer or in the form of separate tufts, so that in a layer of fog the horizontal visibility is less than 1000 m, and at a level of 2 m it exceeds 1000 m (usually, as in 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 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 even drops 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 more often observed in the evening, at night and in the morning, but it can also be observed during the day, especially in the cold half of the year when the air temperature rises. A translucent ice fog is noted separately - observed at air temperatures below -10 ... -15 ° and consisting of ice crystals sparkling in the sun or in the light of the moon and lanterns.

• Fog - 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 even drops to several tens of meters), developed vertically enough so that it is impossible to determine the state of the sky (the number and shape of clouds ). It is more often observed in the evening, at night and in the morning, but it 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 or in the light of the moon and lanterns.

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

The average annual number of days with fog in some Russian cities:

Pier in the fog. Vancouver Island, City of Sydney

Mountain road in fog (highway D81 in Corsica)

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

Artificial fogging is used in scientific research, in the chemical industry, heat engineering and other areas.

Classification

Sea fog in the Øresund 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 - formed due to the condensation of water vapor when the air is cooled below the dew point.
• Evaporation fogs are vapors from a warmer evaporating surface in cold air over water bodies and wet land areas.

In addition, fogs differ in synoptic conditions education:

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

Haze is a very faint mist. With haze, the visibility range is several kilometers. In the practice of meteorological forecasting, it is considered: haze - visibility is more than / equal to 1000 m, but less than 10 km, and fog - visibility is 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 - fogs that appear as a result of radiative cooling of the earth's surface and a mass of moist surface air to the dew point. Radiation fog usually occurs at night in anticyclone conditions with cloudless weather and a light breeze. Radiation fog often occurs under conditions temperature inversion, preventing the rise air mass. Radiation fogs usually dissipate quickly after sunrise. However, in the cold season, in stable anticyclones, they can persist during the day, sometimes for many days in a row. In industrial areas, an extreme form of radiation fog, smog, can occur.

• Advective fog - 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, in some cases up to hundreds of thousands of km². Advective fogs are usually cloudy weather and most often in the warm sectors of cyclones. Advective fogs are more stable than radiative fogs and often do not dissipate during the day.

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

Frontal fogs

Frontal fogs form near atmospheric fronts and move with them. Saturation of air with water vapor occurs due to the evaporation of precipitation falling in the front zone. A certain role in the intensification of fogs ahead of the fronts is played by the drop in atmospheric pressure observed here, which creates a slight pdiabatic decrease in air temperature.

Dry fogs

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

A transitional step between dry and wet fogs is also not uncommon - such fogs consist of water particles together with rather large masses of dust, smoke and soot. These are the so-called dirty, urban fogs, which are the result of the presence in the air of large cities of a mass of solid particles emitted during combustion by smoke, and to an even greater extent - factory pipes.

Mist Characteristics

View of Bragino (Yaroslavl)

Fog in the Izborsk Valley (Pskov region)

The indicator of fog water content is used to characterize fogs, it denotes total mass water droplets per unit volume of mist. 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 the fog is affected by the size of the particles forming it. The radius of fog droplets usually ranges from 1 to 60 µm. Most of the drops have a radius of 5-15 microns at a positive air temperature and 2-5 microns at a negative temperature.

Of course, a barometer is an irreplaceable thing, but what if it is not there? To determine the weather, you can use the simplest devices. One of them has already been prepared by nature itself - this is dried feather grass. It is sensitive to all changes in the atmosphere. In clear weather, its panicle twists into a spiral, and with an increase in air humidity, it straightens.

Can be made if needed homemade barometer. Cut off a part of the trunk (10-15 cm) of a young spruce along with a branch. Remove bark. The trunk is fixed motionless, and the branch remains free. Branch and will respond to weather changes. Go down before rain, go up in clear weather. The longer the branch, the greater the amplitude of its movement.

Rain weather forecast

Signs of bad weather If it gets warm after the rain, earth is coming steam, and light rain with the sun still continues - inclement weather will continue. If after heavy rain clearing up quickly, which means that the rainy weather will continue. If bubbles form on the water from raindrops, - to a long bad weather. Rain falling against the wind is usually very heavy.
Signs of better weather If the rain stops or comes intermittently, and in the evening a creeping fog appears and dew falls, the weather promises to improve. If a little rain falls on a summer morning, the day promises to be sunny and fine.

Dew weather prediction

Signs of bad weather If after sunset there is no dew at all or it is very weak, one should expect worsening weather. If the evening and / or morning dew does not dry for a long time, a thunderstorm is possible. Before a night thunderstorm, fog does not appear in the evening, and dew does not fall.
Signs of better weather If there is heavy dew and fog in the morning, this is for good weather and a clear day. Signs that good weather continues If dew forms on the ground and grass shortly after sunset, which intensifies before sunrise, and disappears two hours after sunrise, it is a sign that good weather continues. If dew falls in the morning, it will not rain until noon.

Frost weather prediction

Signs of bad weather Hoarfrost on trees - to frost.
Abundant frost on the grass and / or tree branches - promises good weather for the next couple of days. Fluffy frost on trees and bushes indicates that the day will be sunny and fine. In autumn time. If frost falls at night, dry weather should be expected. sunny weather. AT winter time. If frost falls at night, there will be no snow during the day.

Fog weather prediction

Signs of bad weather If continuous fog does not disappear after sunrise, this portends worsening weather. If the fog formed in the evening melts before sunrise, but does not spread along the water, but rises, this portends a deterioration in the weather. If fog does not form at all at night (or it forms, but quickly dissipates), rain should be expected, possibly accompanied by a thunderstorm. If the sun sets in fog, it portends rain. Fog over the forest stands - to the rain.
Signs of better weather If fog spreads over the water early in the morning, the weather will be sunny, without precipitation. The appearance of fog in the early evening promises better weather.

Signs that good weather continues If, after sunset, a light fog forms in hollows and low places (swamps, hollows, rivers), or throughout the entire area, which accumulates in the lowlands at night, but quickly dissipates (does not rise!) After sunrise, this is a sign of the preservation of a clear warm good weather for the next couple of days. If fog spreads over the water, this is for good weather. In winter: If fog appears, a thaw should be expected. Predicting the approach of fog If an increase in relative humidity is accompanied by a drop in temperature, fog should be expected. If there is no sign of temperature rise at high relative humidity, then thickening of the fog is to be expected. If in the fog Atmosphere pressure lowered and practically does not change during the day, the fog will continue its thickening. If there is a decrease in temperature during fog, the fog will intensify.

Sky weather prediction

Signs of bad weather If during the day the sky is whitish, cloudy, the evening dawn is not golden, but reddish, and the sun itself also has a red color, this indicates the approach of a warm front, which means rain. In winter time. If the sky is whitish and there is no fog, and the evening dawn and the setting sun are red or crimson, you should expect unstable weather without severe frosts, but with snowfalls. In winter time. A yellowish-brown dawn in winter indicates that frosts will continue and possibly intensify. If the morning and evening dawns turn bright red, dark red or crimson, and the Sun also turns crimson, this indicates a further deterioration in the weather. The golden-bronze color of the sun at sunrise, sunset, as well as the light yellow colors of dawn, portend bad weather. The dark blue color of the sky early in the morning and thick ragged clouds that appeared after sunrise indicate that the day will be windy. The sky is blue - to heat, light - to frost, dark - to a snowstorm. In passing: for the maritime Arctic air, the characteristic bright blue of the sky, its arrival in the summer brings cool, unstable weather. Upon admission to temperate latitudes from the south of the warm masses of continental tropical air, which in addition to high temperatures and humidity is also very dusty, the sky acquires a characteristic whitish tint with a barely noticeable pale blue at the zenith and yellowish-red tones near the horizon. In general, a change in the shades of the sky is a clear sign of the movement of air masses.

Signs of better weather If after rainy weather the sun appears in the evening, and at sunset there are no clouds in the western half of the sky, then the bad weather should end.
Signs that good weather continues Pure sunset rolling from yellow color(near the horizon) to golden pink and then green, a sign of persistent clear weather. Its greenish color indicates a long-term preservation of the nature of the weather (warm in summer, frosty in winter). If after sunset a silvery glow lasts for a long time, and twilight is short, it is a sign of good weather. If the sky has a rich dark blue hue and at the same time seems high, and the horizon is close, or drawn in by a hot haze, - good weather will continue. AT highlands. A noticeable grayish or bluish haze in the air during the day in relatively hot and slightly cloudy weather predicts its stability. In winter time. The pure blue color of the sky, - to clear, stable weather.

Download all signs with illustrations and explanations in the format pdf

Add to blog:

Based on materials by Chris Kaspersky "Encyclopedia of Weather Signs. Weather Prediction Based on Local Signs"

Finding yourself in the middle of a white continuous cloud, so dense that it is almost impossible to distinguish anything at arm's length, you often ask yourself the question: why did such a thick fog form, why did it white color and you start thinking about how long this phenomenon usually lasts, and also why any fog clears.

Fogs are formed 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 ambient temperature exceeds -10°C, the vapor veil consists only of droplets. If the temperature fluctuates from -10 to -15 ° C - from 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 lights.

Why this phenomenon is formed is not difficult to answer: it owes its appearance either to the evaporation of water from a warm surface into cold air, or to the cooling of warm air streams saturated with moisture. For example, the formation of terrestrial 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 frosts, there is always a veil over it, spreading over the water surface. This happens because the temperature of the water 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 there is almost always fog over the river in the area of ​​the hole).

After the warm air mixes with cold 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 are constantly mixed here.

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

Formation of terrestrial clouds

When water-saturated air cools or mixes with colder air currents, droplets begin to form in the atmosphere. After that, if there are tiny particles of dust above the earth's surface, they begin to stick to them, layering on each other and forming drops more large sizes(the more dust in the air, the faster the cloud forms, so big cities almost always shrouded in a faint, almost imperceptible veil).

AT warm time During the year, the size of such a drop varies 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 drops reach the required volumes, the objects turn out to be vague and difficult to distinguish: air at heavy fog acquires a whitish tint and bluish - with a weak one.

The answer to the question why this phenomenon occurs different colors, is simple: smaller drops scatter short blue rays better, while in dense terrestrial clouds, larger drops 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 plants to receive the necessary moisture, this is especially important for the vegetation of arid regions of the planet). How impenetrable the shroud will be depends largely on the humidity of the air, which during the formation of terrestrial clouds is usually from 85 to 100%:

• if visibility does not exceed 50 meters, dense fog is observed, 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 visibility is a kilometer - weak (drops - from 50 to 100).

Fogs are also frequent during frosts, and the phenomenon can be seen even when the humidity does not exceed fifty percent. They are commonly seen in cities, especially at train and bus stations, where the veil is formed by the steam generated during fuel combustion and 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 of smoke, soot, which are emitted by factory or chimneys, or occur after or during fires, when a forest, peat or steppe burns. 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, wet fogs, the formation of which was directly influenced by nature, are evening, night or morning fog (this is the period that is optimal for the appearance of clouds creeping along the ground), meteorologists are also divided into groups:

1. Underground. Evening or morning fog, which spreads low over the earth's surface or a body of water (for example, fog over a river). The veil can be continuous, or it can go in separate shreds, 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 a few meters, it is quite possible to distinguish clouds in the sky. This type includes night, evening, and morning fog.
3. Solid. The visibility of the 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 when warm and cold air and water flows collide, for example, fog over a river). The main reason why any fog dissipates is the heating of the air. Since the veil is formed 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, as in the upper atmosphere the air temperature begins to drop again, the steam is converted into water droplets and forms clouds.

Any person has ever fallen into the fog, even if it is very weak. Sometimes in this "whitish haze" it is impossible to see anything even at a distance of one meter. So what is fog?

What is fog

Fog is a cloud that has descended to the surface of the earth, that is, tiny droplets of water suspended in the air. These droplets are formed either during the evaporation of water bodies that are warmer than the surrounding air (and then this is an evaporation fog), or during the condensation of cold air near the warm surface of the earth (and then this is a cooling fog).

How fogs are formed

Most often, fogs form in autumn, at night or in the morning, when the surface of water bodies cools more slowly than the air above it. warm water evaporates, and the smallest droplets of evaporated moisture form a fog.

The surface of the earth and the layers of air immediately above it autumn nights and in the mornings, on the contrary, quickly cool down. When such cold layers of air come into contact with warm ones, fog is also formed.

In addition, fog is formed more strongly if there are many microscopic dust particles in the air, on which moisture condenses. So the city of fogs is called London, the capital of Great Britain surrounded by water, the air of which is very polluted (the famous London "smog").

Natural phenomena are often more admired than man-made ones. No matter what a person does, everyone will look with admiration at the mountains, hurricanes and tsunamis. Admiration, horror and awe. All this is natural, in relation to such majestic and hazards. Interest can also be caused by more ordinary moments, many would not refuse to know how fog is formed and whether it is worth fearing this. natural phenomenon.

Fight with nature

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

• People tend to love orderliness and constancy.
• Since primitive times, it was nature, in all its manifestations, that most of all “spoiled life” for a person.
• 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.
• Physicians in ancient times faced the problems of mass epidemics. Their sources were microorganisms, the same elements of wildlife.

Today, although people have moved far enough away from nature, having conquered it in many areas of their activity, humanity still depends on it in many ways. And yet it cannot be said that no “sudden turn” in the performance of Mother Nature will be able to erase our civilization and any memories of it.

Where does fog come from?

Fog, oddly enough, mist is taken from the air. To do this, depending on the area, you will need:

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

Fog caused by exposure to exhaust gases and emissions from factories is called smog, and it is typical for industrial centers. If 150 years ago he most often met in England, today the "palm tree" has moved to South America and China. It just so happened that Europe and the United States 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 water bodies 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 of chronic bronchitis and new attacks. bronchial asthma. But the visibility is still reduced.

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

How does fog appear?

To deal with the formation of fog, it is necessary to remember about 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, while cold air, on the contrary, descends closer to the surface.
4. During such a movement, condensation occurs - evaporation and fixation of microscopic water droplets in the air.
5. Best of all, they are fixed on dust particles, so even ordinary fog occurs earlier in industrial areas. What can we say about the smog.

Colossal volumes of air are constantly moving, the laws of physics also operate without change. But fog is a rare phenomenon, sometimes people forget about it for months. And the secret is simple for maximum effect maximum humidity level is also required. In a dry climate, such phenomena occur only at very low temperatures, extremely low.

So that 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 purpose:

At home you will need:

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

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

Fog formation by stages

There is nothing secret about the formation of fog; physicists uncovered the secret of this natural phenomenon centuries ago. How does fog form in the atmosphere?:

1. There is a constant circulation of air 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 the ambient temperature is slightly lower than the water temperature.
5. Droplets are fixed on any surface and linger in the air for a while.
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.

The fog can be a challenge for those suffering from chronic lung diseases. Most often, problems arise with smog. Reduced visibility increases the risk of accidents, so motorists need to either be extremely careful or limit their driving for a couple of hours.