Scattering in dense fog can be considered. What is fog and how is fog formed?
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 falls onto the ground or water, which still retains heat, condensation occurs, and many water droplets hang in the air. It looks like a huge cloud is hanging right above the ground or a body of water. In the place where the fog formed, the air humidity is 100%. Fogs have different structures. If the air temperature is not very cold, above 10 degrees below zero, then the foggy cloud 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 ice fog forms when the entire cloud consists of ice crystals. In cities and towns, fogs are denser due to the fact that condensation mixes with exhaust gases and dust.
What kind of fogs are there?
Fogs are different. It depends on how good the visibility is in the foggy area.
Haze is the weakest type of fog.
Ground fog is fog that spreads over the ground or body of water in a thin layer. This fog does not have much effect on visibility.
Translucent fog, visibility in which ranges from several tens to several hundred meters. Through such fog the sun and clouds are visible.
Continuous fog, when a whitish cloud envelops the earth, through which it is impossible to see literally anything at a distance of several meters, and sometimes even at arm's length. With such fog, traffic becomes impossible. If a driver finds himself in a cloud of continuous 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 human industrial activities. Artificial fog consists of dust, smoke, exhaust gases, chemicals, and 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.
Fog is a natural phenomenon when a high content of water vapor is formed in the atmosphere. It mainly occurs 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 falls onto the ground or water, which still retains heat, condensation occurs, and many water droplets hang in the air. It looks like a huge cloud is hanging right above the ground or a body of water. In the place where the fog formed, the air humidity is 100%. Fogs have different structures. If the air temperature is not very cold, above 10 degrees below zero, then the foggy cloud 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 ice fog forms when the entire cloud consists of ice crystals. In cities and towns, fogs are denser due to the fact that condensation mixes with exhaust gases and dust.
What kinds of fogs are there?
Fogs are different. It depends on how good the visibility is in the foggy area.
Haze is the weakest type of fog.
Ground fog is fog that spreads over the ground or body of water in a thin layer. This fog does not have much effect on visibility.
Translucent fog, visibility in which ranges from several tens to several hundred meters. Through such fog the sun and clouds are visible.
Continuous fog, when a whitish cloud envelops the earth, through which it is impossible to see literally anything at a distance of several meters, and sometimes even at arm's length. With such fog, traffic becomes impossible. If a driver finds himself in a cloud of continuous 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 human industrial activities. Artificial fog consists of dust, smoke, exhaust gases, chemicals, and 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 peatlands or due to a volcanic eruption.
Artificial fog also includes radiation fog, when the air cools due to the presence of radiation in it.
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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, the following types of fog are distinguished:
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, the relative air humidity 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, moist air as 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 frequent, 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. Some role in the increase in fog ahead of fronts is played by the drop in 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.
Fog. Haze
Fog and haze are the result of condensation of water vapor (i.e., the transition of water vapor contained in the air into a liquid state) in close proximity to the earth's surface. Fog are a collection of water droplets or ice crystals suspended in the air that degrade the meteorological visibility range to less than 1 km. With visibility from 1 to 10 km, this set is called haze.
At positive temperatures, fog consists of water droplets with a radius of 2 ... 5 microns, and at negative temperatures it consists of supercooled water droplets, ice crystals or frozen droplets. The water droplets that form the haze have a radius of less than 1 micron. When the droplets become larger, the haze can turn into fog, and when evaporation occurs, the fog can turn into haze.
Visibility in fog depends on the size of the droplets or crystals that form it and on the water content of the fog. The water content of the fog is the amount of liquid or solid water contained in 1m³. Observations show that the water content of fog is 0.02-1.0 g/m³. The water content of fog is influenced by temperature - at positive temperatures it is significantly greater than at negative temperatures.
The number of drops per unit volume in a weak fog is 1-10 pcs/cm³, in a strong fog – 400... 600 pcs/cm³.
Fogs usually form when the partial pressure of water vapor in the layer of the atmosphere adjacent to the earth's surface exceeds the saturated vapor pressure, and the relative air humidity is 100% or slightly less.
According to the physical conditions of formation, fogs can be divided into three groups:
1. cooling mists;
2. fogs not associated with cooling;
3. fogs caused by human activity.
Cooling mists are formed as a result of a decrease in the temperature of the air adjacent to the earth's surface below the dew point (dew point is the temperature at which relative humidity reaches 100%). Cooling fogs, in turn, are divided into radiative and advective.
Radiation mists are formed as a result of radiative cooling of the soil, which then cools the air adjacent to it. The following conditions favor the formation of such fogs: sufficient relative humidity; clear or partly cloudy weather and light wind.
Advective fogs are formed when warm air moves over a cold active surface. The following reasons for their occurrence are possible:
1. Movement of tropical air to higher latitudes;
2. The movement of warm continental air to the colder surface of the sea; such fogs are observed over the seas in summer. When the wind direction changes, they can move to the coast;
3. Movement of warm sea air to the colder surface of the continent. These fogs are called coastal fogs;
4. Movement of air from a warm surface to a cold one. Such fogs form where cold and warm sea currents meet. They are called marine;
Marine fogs also include fogs that form over the ice of the Arctic basin. Such fogs form at any time of the day and can exist at significant wind speeds.
To fogs not associated with cooling , include evaporation fogs and displacement fogs.
Mists of evaporation observed in cases where the temperature of the water surface is higher than the temperature of the adjacent air. Their formation is due to the cooling and condensation of steam coming from the water surface into the air. Such fogs often form in autumn over rivers and lakes. In cold times, they appear over ice-free bays of the seas, as well as over polynyas among the ice.
Displacement fogs are formed by mixing two air masses that have different temperatures and contain water vapor close to the saturation state. Most often, such fogs form on the shores of seas and lakes when there is a large contrast in air temperature over land and over the water surface.
To fogs caused by human activity, These include urban and frosty (furnace) fogs, as well as specially created artificial fogs, for example, to combat frost.
City fogs are formed in large cities, where large quantities of industrial waste are emitted into the air; they are also condensation nuclei, and in this case, condensation (fog formation) begins already at a relative humidity of 75%. Urban fogs sometimes have a dark color due to the presence of smoke particles, soot and other impurities in the droplets.
Frosty (furnace) mists are formed in winter at low air temperatures and in the presence of a ground inversion (a retaining layer that prevents the transfer of heat, water vapor and various impurities. The temperature in this layer increases with height). They usually occur in the morning over small populated areas, when a large number of condensation nuclei begin to enter the air along with smoke from the furnace fires, which is where the name fogs comes from.
In Magadan, advective fogs are mainly observed.
Below we present the average number of days with fog, the largest number of days and the average duration of fog in hours according to the Magadan station.
VIII |
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Average number of days with fog |
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0.03 |
0.03 |
0.05 |
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Most days with fog |
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Average duration of fogs (hours) |
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0.03 |
0.03 |
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