What does fog mean?

Fog is a common weather phenomenon, which refers to water vapor condensate composed of water droplets or ice crystals suspended in the near-surface atmosphere.

Fog is caused by the following reasons:

1, water vapor condensation:

When the water vapor in the air is cold, it condenses into nuclei and forms small water droplets. When the water vapor saturation in the air is high, these small water droplets will gather to form fog.

2, radiation cooling:

At night or early in the morning, the surface will lose heat, which will lead to the drop of air temperature near the surface and the condensation of water vapor into fog.

3, humidity increase:

When the water vapor content in the air increases, once it reaches saturation, it will form fog. After lakes, rivers and water surfaces evaporate or rain, the water vapor content in the air increases and it is easy to form fog.

4, smoke condensation:

Combustion will release a lot of smoke and gas, in which suspended particles can become the core of water vapor condensation and form smoke.

5. Topography and landform conditions:

Mountains, lakes and other terrain will hinder air flow, increase humidity and easily form fog.

The types of fog are as follows:

1, radiation fog:

After sunset, the hot air on the ground radiates into the sky, and the cooled ground condenses the air nearby. Wet air will drop below the dew point, forming countless small water droplets suspended in the air, which is radiation fog.

It mainly appears in the early morning of autumn or winter, with clear weather and weak wind, and will naturally dissipate shortly after sunrise or after the wind speed increases. Most of them appear at night and early morning when the sun is shining, the breeze is blowing gently, and the water vapor near the ground is abundant and stable or there is inversion.

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. In Mao Mao, this fog is often accompanied by rainy weather.

3, evaporation fog:

That is, cold air flows through warm water. If there is a big difference between air temperature and water temperature, a large amount of water vapor will condense into fog due to the evaporation of cold air near the water surface. 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.