The summer fog by the river is incredibly beautiful. Only in such moments do you understand how good it is to live! And the distant shores, hidden by a foggy haze, evoke lyrical memories and dreams.

However, even the most inveterate esthete will not always have an answer to the question of what fog is and what is the mechanism of its formation. If you don’t know this either, we invite you to read our article.

We should start with the fact that this natural phenomenon occurs when air heated during the day comes into contact with the cold surface of water or soil.

So what is fog? This is condensation in the form of tiny droplets (aerosol), which, having collected in one place, sometimes reduce visibility to zero.

Note that the formation of fogs is impossible without solid or liquid particles called condensation nuclei. It is on them that water begins to precipitate, forming drops. It goes without saying that classic water fogs are formed only when the ambient temperature is not lower than -20 degrees Celsius. Otherwise, their ice form will form.

By the way, what is ice fog? In fact, their formation begins with the condensation of the same water on particles in the air, but due to the low temperature, these droplets instantly turn into the solid fraction. Considering that the refractive index of ice is higher, visibility in this case drops even more.

This will be confirmed to you by all drivers who have at least once worked in the Far North. In such conditions it is extremely difficult to drive a car, since there is almost no help. And the glass freezes over in a couple of minutes, so it’s simply impossible to see the road.

Most often, fog (the nature of which we have discussed) is formed in autumn time, since the air during this period cools more slowly than water or earth's surface. At the location where this natural phenomenon occurs, the atmospheric humidity tends to 100%.

As we have already said, the structure of the fog can be very different. The formation can be represented only by water droplets, water and ice, and also exclusively by ice crystals.

As you can see, fog is a multifaceted natural phenomenon, and therefore it is not surprising that there are several types of it:

• Solid type. Visibility is limited to almost zero, road traffic and aircraft flights are suspended.
• Smoky variety. Visibility is moderate, and the danger at low speeds is low.
• “Underground” - fog spreads at ground level.

On the shores of Canadian Newfoundland, all local residents are familiar with this natural phenomenon. The fact is that in these parts the Gulf Stream connects with the Labrador Current, which causes big difference temperatures For six months everything here is shrouded in a gloomy haze, and therefore pilots and sailors really do not like this area.

But there are places on our planet where fogs have never been seen. For example, this is the Indian city of Bombay. Well, Chile hasn’t even seen rain in the last few hundred (or even thousands) of years, so this natural phenomenon definitely has nowhere to come from there.

So you have learned what fog is and where it comes from.

Fog is an accumulation of small water droplets or ice crystals, or both, in the surface layer of the atmosphere, up to a height of several hundred meters, reducing horizontal visibility to 1 km or less.
Fog is formed as a result of condensation or sublimation of water vapor on aerosol (liquid or solid) particles contained in the air. Fog of water droplets is observed at air temperatures above -20 °C, but can occur even at temperatures below -40 °C. At temperatures below -20 °C, ice fogs predominate.
Visibility in fog depends on the size of the particles that form the fog and on its water content (the amount of condensed water per unit volume.). The radius of fog droplets ranges from 1 to 60 microns. Most drops have a radius of 5-15 microns at positive air temperatures and 2-5 microns at negative temperatures. The water content of fog usually does not exceed 0.05-0.1 g/m3, but in some dense fogs it can reach 1-1.5 g/m3. The number of drops per 1 cm3 ranges from 50-100 in light fogs to 500-600 in dense fogs. In very dense fogs, visibility can be reduced to a few meters.

Based on visibility range they distinguish the following types fogs:
1) Haze is a very thin fog, a continuous more or less uniform gray or bluish clouding of the atmosphere with a horizontal visibility range (at the eye level of an observer standing on the ground, i.e. about 2 m above the earth’s surface) from 1 to 9 km. It can be observed before or after fog, and more often as an independent phenomenon. Often observed during precipitation, especially liquid and mixed (rain, drizzle, rain with snow, etc.) due to humidification of air in the surface layer of the atmosphere due to partial evaporation of precipitation.
Haze should not be confused with deterioration in horizontal visibility due to dust, smoke, etc. In contrast to these phenomena, relative humidity air during haze exceeds 85-90%.
2) Ground fog - 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. It is observed how usually in the evening, night and morning hours.
3) 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 (amount and cloud shape). 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.
4) 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 it drops even to several tens of meters), sufficiently developed vertically, so that it is impossible to determine the state of the sky (amount and cloud shape). 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.
According to the method of occurrence, cooling fogs are divided into evaporation fogs. The first ones occur when the air is cooled below the dew point temperature, the water vapor contained in it reaches saturation and partially condenses; the second - with additional supply of water vapor from a warmer evaporating surface into cold air, as a result of which saturation is also achieved. Cooling fogs are the most common.

According to the synoptic conditions of formation, they are distinguished:
1) intra-mass fogs, formed in homogeneous air masses,
2) frontal fogs, the appearance of which is associated with atmospheric fronts.
Intramass fogs predominate, in most cases these are cooling fogs. Intramass fogs are divided into radiation and advection.
Radiation ones are formed over land when the temperature decreases due to radiative cooling of the earth's surface, and from it the air. They most often occur on clear nights with light winds, mainly in anticyclones. 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.
Advection fogs are formed due to the cooling of warm humid air when it moves over a colder surface of land or water. The intensity of advective fogs depends on the temperature difference between the air and the underlying surface and on the moisture content of the air. They can develop both over land and over the sea and cover a huge area, sometimes on the order of several tens or even hundreds of thousands of km2. Advective fogs usually occur in 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. Some advective fogs are evaporative fogs and occur when cold air is transferred to warm water. Fogs of this type are common, for example, in the Arctic, when air flows from the ice cover to the open surface of the sea.
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. Fall plays some role in increasing fog ahead of fronts atmospheric pressure, which creates a slight adiabatic decrease in air temperature. Fogs occur more often in populated areas than far away from them. This is facilitated by the increased content of hygroscopic condensation nuclei (for example, combustion products) in the air.
Fog significantly affects visibility, which is one of the most important factors of safe navigation for a navigator. Visibility is the distance at which during the day the last signs of the observed object disappear (its outlines become indistinguishable), and at night an unfocused light source of a certain intensity becomes indistinguishable. Visibility is assessed in points, measured by eye for a number of objects located at different distances from the observer, according to the international visibility scale (Table 1):
Table 1. International visibility scale.
Score Visibility range Score Visibility range
0
1
2
3
4 0-50 m
50-200 m
200-500 m
500-1000 m
1-2 km 5
6
7
8
9 2-4 km
4-10 km
10-20 km
20-50 km
50 km

Table 2. Designation of fog when plotting data on weather maps.

Any person has ever been caught in a fog, even a very weak one. 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 by the evaporation of bodies of water that are warmer than the air surrounding them (and then this is evaporation fog), or by the condensation of cold air near the warm surface of the earth (and then this is cooling fog).

How fogs are formed

Most often, fogs form in the fall, at night or in the morning, when the surface of reservoirs cools more slowly than the air above it. Warm water evaporates, and tiny droplets of evaporated moisture form fog.

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

In addition, fog forms more strongly if there are many microscopic dust particles in the air, on which moisture condenses. This is how London is called the city of fog, the capital of Great Britain surrounded by water, whose air 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 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 of 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; nature does not have many strict rules.

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, 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, a maximum level of humidity is 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 on an 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 the ambient temperature is slightly lower than the 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.

Nature gives us many various phenomena, most of which we have long been accustomed to. However, despite this, the nature of the origin of many phenomena is not clear to everyone. One of these phenomena is fog - everyone is used to it, but not everyone can give an accurate explanation of its origin.

Fog formation

The fog is the same cloud that we are used to seeing in the sky. The only difference is that the fog extends near the surface of the earth.

Fog usually forms early in the morning or at night over water bodies and in lowlands. The formation of fog is associated with a cold flow of air descending onto the warm surfaces of water or land. Most often, fogs form in the fall - at this time the air cools much faster than water or land. With the onset of darkness and in calm weather, thin layers of fog begin to form above the ground in low places. At night, the earth gradually cools, which leads to cooling of the lower layers of air. When cool air comes into contact with warm air, fog is formed.

Despite the fact that such a natural phenomenon, fog is quite common and understandable, this phenomenon itself is of interest for its beautiful and unique appearance.