Why is autumn "crisp in autumn"?

Caption: Describe the crisp autumn in Wan Li. From: Tang Du Fu's poem "Cui Shi Dongshan Caotang": "Love you, Yushan Caotang is quiet and fresh in autumn." Example: Fang plans to recover lost territory and send troops to the west. ◎ Liang Qing and Zhu Xi's "Two Kinds of Autumn Essays and Poems" are synonymous: autumn is crisp, antonym: spring rain is continuous, grammar: couplet; As a predicate; Why is autumn "crisp in autumn"? In most parts of China, there are few rainy days and clouds in autumn, which makes people feel very comfortable. This is because after the autumn, the cool and dry cold wind drove away the warm and humid hot air, and the water in the air decreased, the temperature dropped, and the cloud amount also decreased, resulting in the "clear autumn" weather in Wan Li during the day and the stars at night. The temperature drops. People feel much cooler. Therefore, people call autumn a "crisp autumn" season. Excerpted from China Drama Publishing House's "100,000 Reasons for Popularizing Science in 2 1 Century-Atmospheric Meteorology", when autumn comes, warm and humid air has moved from the mainland to the Pacific Ocean, and dry and cold air in the north has begun to move south. This dry and cold air is so dry that it is difficult to condense into clouds. At the same time, dry cold air is heavy, so it will sink, and when it sinks to the ground, it will become hot, and the original clouds in the sky in this area will be reduced because of heat evaporation. Therefore, in these areas controlled by cold air, the weather is always sunny. In autumn, the ground absorbs the heat of the sun during the day, because there is no cloud cover in the sky at night, and the heat can be freely emitted. After the autumnal equinox, the nights are long and the days are short, the heat absorbed during the day is less than the heat emitted at night, and the ground temperature gradually decreases. At the same time, the moisture in the air decreases in autumn, dry cold air fills people's surroundings, and the moisture secreted by people's skin is easy to evaporate. For these reasons, people think it's cool.