How is the fog formed? thank you

When the visibility in the atmosphere is lower than 1 km due to the condensation of suspended water vapor, meteorology calls this weather phenomenon fog.

Conditions for fog formation:

One is cooling, and the other is humidifying to increase the water vapor content.

Types of fog:

1. Radiation fog: It mostly appears at night and early morning when the sun is shining, the breeze is blowing gently, and the water vapor near the ground is rich and stable or the temperature is reversed.

2. advection fog: Warm and humid air moves horizontally, passes through the cold ground or water surface, and gradually cools to form fog, which is called advection fog in meteorology.

3. Mixed fog: Sometimes the fog formed by two reasons is called mixed fog.

4. Evaporation fog: that is, cold air flows through warm water. If there is a big difference between the air temperature and the water temperature, a large amount of water vapor will evaporate on the water surface, and the cold air near the water surface will condense into fog. At this time, there is often an inversion layer on the fog layer, otherwise convection will make the fog dissipate. Therefore, the evaporation fog has a small range and weak intensity, and generally appears around the pond in the second half of the year.

5. Smog: The smog in the city is caused by another reason, and that is human activities. Morning and evening are the peak hours of heating boilers. Under the condition of low air pressure and low wind speed, a large number of pollutants, such as smoke, suspended solids and automobile exhaust, are difficult to diffuse, and it is easier to form smoke (fog) when combined with water vapor in the lower air, and this smoke (fog) often lasts for a long time.

Generally speaking, there is a lot of fog in autumn and winter mornings. Why? We know that when the water vapor contained in the air reaches the maximum, it reaches saturation. The higher the temperature, the more water vapor is contained in the air. 1 m3 air, the maximum water vapor capacity is 6.36g at 4℃; When the temperature is 20℃, the maximum water vapor content in 1 m3 air is17.30g. If there is more water vapor in the air than saturated water vapor at a certain temperature, the excess water vapor will condense out. When there is enough water, it will combine with tiny dust particles in the air, and at the same time, water molecules themselves will combine with each other and become small water droplets or ice crystals. The water vapor in the air exceeds saturation and condenses into water droplets, which is mainly caused by the temperature drop.

If the ground heat is lost, the temperature drops, and the air is quite humid, then when it cools to a certain extent, part of the water vapor in the air will condense out and become many small water droplets suspended in the air layer near the ground. This is fog. Both it and clouds are caused by temperature drop, and fog can actually be said to be a cloud near the ground.

So the fog didn't fall from the sky, nor did it come out of the ground? It's condensed water vapor in the air. However, it is closely related to the temperature and humidity of the sky and the ground.

In the atmosphere near the ground, there are countless small water droplets floating in the air with a diameter of about a few thousandths of a millimeter, which makes the sky and the earth white and the visible distance is very small. This weather phenomenon is called fog.

So, how did the fog form? We know that there is a limit to the amount of water vapor that can be contained in the air. When it reaches the maximum limit, it is called water vapor saturation. The higher the temperature, the more water vapor is contained in the air.

For example, when the temperature is 4℃, the maximum amount of water vapor per cubic meter of air can be 6.36 grams; When the temperature is 20℃, the water vapor saturation per cubic meter of air is 17.30 g.

If the air contains more water vapor than saturated water vapor at a certain temperature, the excess water vapor will condense out and become small water droplets or ice crystals. So if the water vapor in the air exceeds the saturation, it will condense into water droplets, which is mainly caused by the temperature drop.

The loss of ground heat will reduce the ground temperature, at the same time, it will affect the air near the ground, and it will also reduce the air temperature. If the air near the ground is quite humid, when the temperature drops to a certain extent, some water vapor in the air will condense out and become many small water droplets suspended in the space near the ground. If there are more water droplets in the air layer near the ground and the visibility is low, fog is formed.

Fog and clouds are water vapor condensates composed of small water droplets or ice crystals floating in the air, but fog is generated in the near layer of the atmosphere, while clouds are generated in the higher layer of the atmosphere. Since fog is water vapor condensation, we should look for its reason from the conditions that cause water vapor condensation. There are two reasons for water vapor saturation in the atmosphere: first, evaporation increases water vapor in the atmosphere; The other is the cooling of the air itself. Cooling is more important for fog. When there are condensation nuclei in the air, if water vapor continues to increase or melt, condensation will occur in saturated air. Fog is formed when condensed water drops reduce the horizontal visibility to less than 1 km.

In addition, excessive wind speed and strong disturbance are not conducive to the formation of fog.

Therefore, in the area that is conducive to the cooling of the lower air layer, if the water vapor is sufficient, the wind is mild, the atmospheric stratification is stable, and there are a large number of condensation nuclei, it is most likely to produce fog. Generally speaking, there are more opportunities to form fog in industrial areas and urban centers, because there are abundant condensation nuclei there.

Going out early in the morning, the misty smoke always gives people a little reverie. So how did the fog form? We know that there is a certain amount of water vapor in the air, with more water vapor at high temperature and less water vapor at low temperature. According to this truth, there is water vapor in the air during the day when the temperature is high. When the temperature drops at night, the air cools and condenses into water droplets or ice crystals, which float in the atmosphere near the ground and form fog. The temperature is the lowest in the early morning, so fog often appears in the morning. When the sun rises, water droplets or ice crystals turn into water vapor again, and the fog gradually dissipates.

Regarding the types of fog, we mentioned the most common radiation fog on land, which mainly occurs at night or in the morning when the sun is shining, the breeze is blowing gently and it is full of water vapor. There is also the sea fog that often appears in coastal areas in spring and summer in China. We also call it advection fog. And steam fog that mostly appears in the high latitude Arctic region; And uphill fog and frontal fog. Their formation principle is similar to other kinds, and they are all formed by the interaction of cold and warm air currents.

Of course, fog does a lot of harm. In addition to the serious impact on traffic that we all know, because it has strong adsorption and contains a lot of pollutants, it will also increase the risk of people suffering from rhinitis, pharyngitis, bronchitis and lung cancer. Here, we also suggest that you suspend outdoor sports in foggy days. In addition, the chemical components in the droplets will also have a strong corrosive effect on metals; Drops of fog on crops will also reduce crop production.

What should we do with it? Usually, we divide fog into warm fog and cold fog. Above 0 degrees is warm fog, below 0 degrees is cold fog.

There are three methods to eliminate warm fog. One is heating method, which is used in small areas such as airport runways, that is, heating air to make fog droplets evaporate and disappear; The second method is hygroscopic method, that is, sprinkling some hygroscopic substances such as salt or urea as a catalyst to evaporate the fog; The third method, called artificial disturbance synthesis method, is to use a helicopter to fly slowly over the fog area to drive down the dry air at the top of the fog and mix it with the air in the fog to make the fog evaporate and disappear.

The method of eliminating cold fog artificially is to sprinkle silver iodide, dry ice, liquefied propane and other catalysts into the fog to produce a large number of ice crystals, which will absorb the water vapor in the fog and grow up, and then fall to the ground, and the fog will disappear. This method has a remarkable effect.

Humans have thought so many ways to eliminate fog, but we can't just deny it, because many times, fog also has its loveliness. For example, the water contained in fog can moisten the land and nourish crops. In some arid areas, people often collect fog water to irrigate crops, and people living by the sea also collect fog water to drink. Not only that, winter fog can also play a role in heat preservation, reducing ground heat dissipation and preventing crops from freezing, which is especially beneficial to winter crops. And those plants that like warm water, such as tea, coffee and medicinal materials, thrive in foggy places. In many tourist attractions, it is also because of the fog that they have unique scenery. For example, Shennongjia in Hubei Province is a misty fairyland on earth, which is not only mysterious, but also rich in many precious Chinese herbal medicines. Another example is Lushan Mountain, which is surrounded by the vast Poyang Lake. It is also looming because of countless fog drops, making it difficult for us to see its true colors.

This is a pleasant and worrying fog, but it was a good "scenery" last week. However, the annoying haze also slipped out and walked away. The changeable smog and sandstorm have different environments. Sandstorms are mostly formed in extremely dry areas, and smog is often formed in humid air. Haze is an atmospheric optical phenomenon, usually due to dust blown from the ground, or a large number of dry particulate pollutants such as smoke particles discharged into the atmosphere, making aerosol particles float in the atmosphere, scattering sunlight and producing atmospheric turbidity. The scattering law of aerosol particles to solar light is still unclear. Because of this complex scattering, people feel that the atmosphere is not very transparent. When looking at the distance through the smog layer, if the background is bright, the originally bright objects in the distance will appear yellow or red, and if the background is dark, the originally dark objects in the distance will appear light blue.

Haze, like haze, is a common weather phenomenon in winter. It is mainly formed by the diffusion of a large number of smoke particles discharged from urban, industrial and mining areas or forest fires in the air. In the presence of inversion layer, it will be more obvious and serious. This inversion layer refers to the atmosphere where air inversion occurs and cannot be automatically purified. When smoke appears, the sky will turn black, gray or brown. If there is smoke at sunrise or dusk, the sun we see will turn red. Unlike smog, smog is rare during the day and often appears in the morning and evening.

You see, it's dark and gray now. Let's go and see the beautiful aurora in Hokkaido, Japan. Aurora is like a girl with thousands of faces, not only colorful, but also unpredictable. Some auroras will disappear soon after they appear, while others can stay in the sky for hours; Some are very bright, even masking the brilliance of the stars and the moon, while others are very light, just like a faint cloud. How are these beautiful auroras formed? As we know, the earth is a big magnetic field, and the powerful charged particle stream of the solar wind will rush towards it violently. When passing through the earth's atmosphere, the particle flow collides with different gas molecules in the atmosphere, thus exciting these colorful auroras.