How do thunderstorms come about?

Thundershower is produced under the condition of strong convective movement of wet air, and its occurrence is closely related to the stability of the atmosphere. Stability is the degree of atmospheric stability. The atmosphere is unstable and top-heavy. As long as it is slightly subjected to external force, it will explode and fly up and down, forming a strong convection; A stable atmosphere is top-heavy. Even if it is touched by an external force and forced to rise or fall, as long as the external force disappears, it will immediately return to its original position, and it is difficult to form a strong convection. Meteorology tells us that top-heavy or top-heavy atmospheric changes mainly depend on the temperature of the upper and lower atmosphere. If the upper temperature of the gas layer drops or the lower temperature rises, it will cause top-heavy phenomenon and the atmosphere will become unstable; However, if the upper part of the gas layer heats up or the lower part cools down, the atmosphere will be top-heavy and its stability will increase. The temperature is constantly changing throughout the day, so the atmospheric stability is also changing.

In summer, the weather is clear and the wind is light, and the ground is exposed to strong sunlight, which heats the air near the ground. The closer to the ground, the higher the temperature rises. Afternoon is the time when the ground temperature rises the highest, and it is also the most unstable period of the day. So at this time, the strong convection movement develops fastest. If the air is very humid and rich in water vapor at this time, then the thunderstorm from afternoon to night will be decided. This kind of thunderstorm formed by intense ground heating is called thermal thunderstorm. From midnight to early morning in summer, the ground temperature drops to the lowest, the atmosphere tends to be stable, and it is not easy to form thermal thunderstorms.

The occurrence of thunderstorms in spring is different from that in summer. In summer, thermal thunderstorms often occur under the same heating air mass. It's sunny before a thunderstorm, but thunderstorms usually occur in areas where cold and warm air masses meet in spring. When two cold and warm air masses meet, warm and humid air climbs on the back of cold air, and a large amount of water vapor condenses out, which makes the sky gloomy. It has rained for several days, and there is no sunshine on the ground all day. It is impossible for the temperature to rise very high during the day and fall very low at night, and the daily change of the temperature is very small. But at the top of the high-altitude clouds, the sun is still shining during the day, and the temperature there changes greatly every day. During the day, the clouds are heated by the sun, so the temperature tends to rise, the atmospheric head becomes lighter, the stability increases, and the possibility of thunderstorm formation decreases; At night, the cloud top radiates heat into space, and the temperature in the upper part of the cloud drops, especially from midnight to morning, the temperature drops to the lowest in a day, and the atmospheric head becomes heavier and tends to be unstable, which makes the convective movement in the cloud develop and forms the Lei Yun with thunder and lightning and torrential rain. This is why spring thunder appears from midnight to morning.