The relationship between fog and weather

Fog is ever-changing and complicated, but it is nothing more than radiation fog and advection fog. Although there are various phenomena, the essence is the same: water vapor condenses when it meets cold. Sometimes fog indicates sunny days, sometimes fog indicates rainy days, and it looks chaotic. However, as long as the characteristics of radiation fog and advection fog are mastered, observed in many aspects and carefully analyzed, the laws of fog, sunny and rainy weather can be accurately grasped, and the weather can be predicted. This is very useful for agriculture, transportation, aerospace and navigation.

Fog is closely related to future weather changes. The working people in China have known this truth since ancient times, and it is reflected in many folk proverbs. For example, "Huangmei is foggy, rocking the boat doesn't ask for directions." This means that the fog at the turn of spring and summer is a harbinger of rain, so people also have the saying of "summer fog and rain". Another example is: "I can't see anyone in the fog, so I dare to wash my clothes." This means that winter fog is sunny, and so is autumn fog.

To accurately understand the sky through fog, we must also look at the duration of fog. Radiation fog is caused by cold weather and water vapor condensation, so it disappears when the temperature rises during the day, and the weather is fine; On the other hand, "fog is rain." If the fog doesn't disperse during the day, it may rain the next day, so the folk proverb says, "The fog doesn't reach noon, and the rain will ring after noon." The fog shows signs of rain and sunshine.

It can be explained from the knowledge of meteorology. As long as there is a lot of water vapor in the lower air, when the temperature drops suddenly at night, the water vapor will condense into fog. Fog has radiation fog, that is, fog formed under relatively clear and stable conditions. As long as the sun comes out and the temperature rises, the fog will naturally disappear. In this regard, the folk saying is: "The fog is heavy in the morning, and it will be fine for a long time." "The sun is shining in the fog and the stone is broken." "It's foggy in the morning, even though you are drying rice." People see radiation fog, which is often "ten fogs and nine sunny days", so they come to these sayings.

In autumn and winter, after the cold air in the north goes south, as the weather turns fine and sunny, the moisture content in the air gradually increases, which is easy to form radiation fog, so the fog in autumn and winter can often predict the good weather tomorrow.

The fog in spring and summer is different. Most of it comes from the warm and humid air flow at sea. When it hits the cold ground, the air in the lower layer becomes cold and the water vapor condenses into fog. This fog is called advection fog. It is formed when warm and humid air from the ocean invades the mainland and suddenly encounters cold. When these warm and humid air currents meet the dry and cold air currents in the mainland, it will naturally be rainy. So the fog in spring and summer indicates rainy weather.

Fog is closely related to the weather, so we can know the change of the weather through fog. However, the above explanation of radiation fog and advection fog is only for the general situation. The relationship between fog and weather is not so simple, there are many complicated contents, which cannot be copied mechanically, but should be analyzed in detail. In other words, if we want to know fog accurately, we need observation, analysis and comprehensive judgment in many aspects.